Software Technology for “Methods and apparatus for adjusting the blanking period in transition between operating states in a device medical”

Medical Device – Saul E. Greenhut, Robert W. Stadler, Xusheng Zhang, Medtronic Inc

Abstract for “Methods and apparatus for adjusting the blanking period in transition between operating states in a device medical”

“A medical device and method for adjusting a blanking time that includes sensing cardiac signals from a plurality electrodes. The plurality electrodes form a plurality if sensing vectors. This determines whether to adjust the blanking periods during a first operational state. It also allows you to advance from the first state to a new operating status in response to the sensed heart signals.

Background for “Methods and apparatus for adjusting the blanking period in transition between operating states in a device medical”

Implantable medical devices can be used to prevent or treat cardiac arrhythmias. They deliver anti-tachycardia pace therapies and electric shock therapies to defibrillate the heart. This device is commonly called an implantable cardioverter-defibrillator (?ICD?)). It senses the heart rhythm of a patient and classifies it according to various rate zones to detect fibrillation or tachycardia.

The ICD will deliver the appropriate therapy if it detects an abnormal rhythm. Anti-tachycardia pace therapy can often stop ventricular tachycardia. When necessary, anti-tachycardia pace therapies are followed up by high-energy shocked therapy. A shock therapy can be used to stop tachycardia. This is known as “cardioversion”. Ventricular fibrillation is a severe form of tachycardia and can be treated with high-energy shock therapy. Defibrillation is commonly used to refer to the termination of VF. Accurate arrhythmia detection and discrimination are important in selecting the appropriate therapy for effectively treating an arrhythmia and avoiding the delivery of unnecessary cardioversion/defibrillation (CV/DF) shocks, which are painful to the patient.”

In the past, ICD systems used intra-cardiac electrodes that were connected to transvenous leads to sense cardiac electrical signals and deliver electrical therapies. The new ICD systems can be subcutaneously or submuscularly implanted and use electrodes that are embedded on the ICD housing or carried by subcutaneous leads. These systems are referred to as “subcutaneous ICD” These systems are also known as?subcutaneous ICD? These systems do not require electrodes to be in direct contact with your heart. The SubQ ICD system is less invasive than ICDs that use intra-cardiac electrodes. They can be implanted quicker and more easily than ICD systems using intra-cardiac ones. Subcutaneous systems are more difficult to detect cardiac arrhythmias. A SubQ ECG signal might have a R-wave amplitude that is one-tenth to one hundredth as large as intra-ventricular R-waves. Subcutaneously sensed ECG signals may have a lower signal quality than intra-cardiac ECG signals.

The ECG signal characteristics of subcutaneous ICDs will determine their ability to detect tachyarrhythmias or reject noise. ECG vectors that have higher amplitude R wave waves, higher frequency (higher slewrate) R-waves and higher R/T waves ratios, lower frequency signals (e.g. P and T waves), around R-waves and lower susceptibility for skeletal myopotentials and greater Rwave consistency from cycle-to-cycle are preferable to those without these attributes. These physical vectors can be used by a subcutaneous ICD to generate virtual ECGs. The changing environment in a subcutaneous system can make it difficult to choose the best vector. It is therefore necessary to develop systems and methods for reliable and accurate detection of arrhythmias via optimal sensing vectors that can sense ECG signals using subcutaneous electrodes.

“FIG. “FIG. FIG. FIG. 1 shows an extravascular cardiac defibrillation device 10. It is an implanted, subcutaneous ICD. The techniques described in this disclosure can also be used with extravascular implanted cardio defibrillation devices, such as cardiac defibrillation units that have a lead placed at least partially in the substernal or submuscular locations. The techniques described in this disclosure can also be used with implantable systems such as implantable pacing and implantable neurostimulation system, drug delivery systems, or any other system that has leads, catheters, or other components implanted at extravascular locations. For illustration purposes, this disclosure is made in the context an implantable extravascular heart defibrillation device.

“Extravascular cardiac Defibrillation System 10 includes an implantable cardioverter (ICD), 14 that is connected to at most one implantable cardiac lead 16. FIG. 14 shows the ICD 14. Subcutaneously, 1 is placed on the left side patient 12. The medially connected defibrillation leads 16 and ICD 14 extend medially toward the sternum 28 of the patient. Near xiphoid Process 24, the defibrillation leads 16 bends or curves and extends substantially parallel to sternum 28, at a site near ICD 14. FIG. FIG.

The therapy vector is a line that runs from the defibrillation electrode 16 to a second electrode, such as a housing or ICD 25 of ICD 14, or an electrode on a second lead. It is approximately across the ventricle 26. One example of the therapy vector is a line that runs from the point on the defibrillation device 18 to the point on the housing, or can 25, ICD 14. Another example is that defibrillation leads 16 can be placed along the sternum 28 so that a therapy line between the defibrillation electrode 18, housing, or can 25 (or any other electrode) extends substantially across the atrium of the heart 26. Extravascular ICD 10 can be used in this instance to provide atrial therapies such as treatments for atrial fibrillation.

FIG. 1 illustrates the embodiment. FIG. 1 illustrates an example configuration for an extravascular ICD 10 and should not be taken as a limitation of the techniques described. FIG. 1 illustrates an example. However, it is shown as being offset laterally from sternum 28’s midline in FIG. Defibrillation leads 16 can be placed so that they are located more centrally over sternum 28, or to the right of Sternum 28. Defibrillation leads 16 can be placed so that they are not parallel to sternum 28. Instead, they may be offset at an angle from sternum28 (e.g., angled from sternum at either the distal or proximal ends). Another example is that the distal end defibrillation leads 16 could be placed near the patient’s second or third rib. The distal end defibrillation leads 16 can be placed near the second or third rib of the patient depending on where ICD 14 is located, location of electrodes 18, 20 and 22, or any other factors.

ICD 14 was shown as being placed near the midaxillary lines of patient 12 but it could also be implanted in other subcutaneous locations, such as farther posterior on the body toward the posterior axillary, further anterior on your torso towards the anterior axillary, in the pectoral region or other locations. Lead 16 will follow a different route if ICD 14 is placed pectorally. This would be, for example, along the inferior side of the sternum 28. The extravascular ICD 14 may also include a second lead with a defibrillation device that runs along the left side. This allows the second lead to be used as an anode/cathode in the therapy vector.

ICD 14 contains a housing (or can) 25 that acts as a hermetic seal to protect components. ICD 14’s housing 25 may be made of conductive material such as titanium, or any other biocompatible conductive material, or a combination conductive and nonconductive materials. The housing 25 of ICD 14 can be used as an electrode in some cases. This is known as a housing electrode, or can electrode. It may also be used with electrodes 20, 22, or 22 to deliver therapy to the heart 26 or sense electrical activity. ICD 14 may also contain a connector assembly (sometimes called a connector block, header), which includes electrical feedthroughs that allow for electrical connections between conductors in the defibrillation leads 16 and electronic components within the housing. One or more components may be enclosed in housing, such as processors, memories and transmitters, receivers and sensors, as well as sensing circuitry, therapy circuitry, and other appropriate components (often referred herein to simply “modules”).

“Defibrillation leads 16 include a lead body with a proximal and distal ends that connect to ICD 14 and one or more electrodes 18, 20 and 22. The defibrillation leads 16 can be made from non-conductive materials such as silicone, fluoropolymers and mixtures thereof. They are shaped to create one or more lumens that the conductors extend within. These techniques are not the only ones. Defibrillation leads 16 are shown as having three electrodes 18, 20, and 22, but there may be more or less electrodes.

“Defibrillation leads 16 include one or more elongated electric conductors (not shown) that extend from the connector at the proximal end to the electrodes 18, 20, and 22. The one or more elongated electric conductors within the lead body 16 of defibrillation leads 16 can be contacted with the respective electrodes 18, 20, and 22. The connector at the proximal tip of defibrillation leads 16 can be connected to ICD 14. When this connector is connected, the respective conductors could electrically couple with circuitry such as a therapy or sensing module of ICD 14 through connections in the connector assembly. The therapy module of ICD 14 transmits therapy to one or several electrodes 18-20 and 22. Sensing modules within ICD 14 receive electrical signals from one of the electrodes 18-20 and 22.

ICD 14 can sense electrical activity of the heart 26 using one or more sensing channels that include combinations between electrodes 20 and 22, and the housing, or can 25 of ICD 14 ICD 14 can sense electrical activity of the heart 26 using one or more sensing vectors that include combinations of electrodes 20-22 and the housing, or can 25 ICD 14. ICD 14 can sense electrical signals using a sensor vector between electrodes 20-22 or can 25 ICD 14. ICD 14 can sense electrical signals using a sense vector between electrodes 22 and the housing, or can 25 ICD 14; or electrical signals using a sense vector between the electrode 22 and the housing, or can 25 ICD 14 or any combination thereof ICD 14 can sense cardiac electrical signals in certain instances. This could be done using a sensing channel that includes defibrillation electro 18, such as between electrode 18 (or 20) and an electrode 22 (or can 25 of ICD 14).

“ICD can analyze the electrical signals that are being sent to it to detect tachycardia. In response, ICD may produce and deliver electrical therapy to the heart 26. ICD 14 could deliver one or more defibrillation shocked via a therapy vector which includes the defibrillation electrode 18, defibrillation leads 16 and can 25, for example. For example, a defibrillation electrode 18 could be an extended coil electrode or another type of electrode. ICD 14 may deliver one of several pacing therapies before or after the delivery of defibrillation shock. These include anti-tachycardia pacing or post shock pacing. ICD 14 can generate and deliver pacing pulses using therapy vectors that include either one or both electrodes 20 or 22 and/or the housing/can 25. The electrodes 20 and 22 can include ring electrodes or hemispherical or coil electrodes. They may also contain segmented or directional electrodes. Although electrodes 20 and 22 can be of the same type or different types, the FIG. Both electrodes 20 and 22, are shown as ring electrodes.

An attachment feature 29 may be included in “Defibrillation Lead 16” at the distal end. Attachment feature 29 could be a loop or link, or any other attachment feature. Attachment feature 29 could be, for example, a loop made by a suture. Attachment feature 29 could also be a link, loop, ring, ring of metal, covered metal or polymer. Attachment feature 29 can be made into any number of shapes, with uniform thickness or varying dimensions. Attachment 29 can be integrated into the lead or added by the user before implantation. Attachment feature 29 can be used to assist in the implantation of lead 16 or to secure lead 16 at a desired location. Sometimes, the attachment mechanism may be used in conjunction with or instead of the attachment function. Defibrillation leads 16 are illustrated with attachment features 29. However, other examples may not show an attachment feature 29.

“Lead 16 could also contain a connector at its proximal end, such as a DF4 or bifurcated connector (e.g. DF-1/IS-1 connector) or any other type of connector. A terminal pin may be attached to the connector assembly of ICD 14 at the connector’s proximal end. Lead 16 may have an attachment feature at its proximal end that can be used to attach an implant tool. The connector may seperate from the attachment feature at the lead’s proximal end. It may be integral to the lead, or may be added by the user before implantation.”

“Defibrillation leads 16 may include a suture-sleeve, or other fixation mechanism (not illustrated), located near electrode 22. This is designed to fixate lead 16 close to the xiphoid process and lower sternum locations. The user may add or modify the fixation mechanism, such as a suture sleeve.

FIG. 1 illustrates an example. “The example illustrated in FIG. 1 is an example and should not be taken to limit the techniques described herein. Extravascular cardiac defibrillation systems 10 could include multiple leads. Extravascular cardiac defibrillation systems 10 could include a pacing and defibrillation leads 16.

FIG. “In the example illustrated in FIG. 1, the defibrillation leads 16 are placed subcutaneously. Other times, optional pacing leads and defibrillation led 16 may be placed at extravascular locations. One example is that defibrillation leads 16 can be placed at least partially in the substernal area. This configuration allows at least part of the defibrillation device 16 to be placed below or above the mediastinum, and more specifically, the anterior mediastinum. Anterior mediastinum is bordered laterally by the pleurae, posteriorly and anteriorly, respectively, by the pericardium and sternum 28. The defibrillation leads 16 can be implanted at least partially in extra-pericardial areas, i.e. locations that are not directly in contact with the outer surface 26 of the heart. Other extra-pericardial locations include the mediastinum and the area offset from the sternum 28, the superior mediastinum and the middle mediastinum. Also, the sub-xiphoid/inferior xiphoid region, near the apex, may be used. The lead can also be placed at an epicardial or pericardial location other than the heart 26.

“FIG. “FIG. FIG. FIG. 2 shows the subcutaneous device 14. It includes a low voltage battery (153) and a power supply. This supply supplies power to both the circuitry of subcutaneous device 14, as well as the pacing output caps to provide pacing energy. For example, the low voltage battery 153 could be made of one or more conventional LiCFx, LiMnO2 and LiI2 cells. Subcutaneous device 14 also contains a high-voltage battery 112, which may be made of one or more conventional LiSVO cells or LiMnO2 cell. FIG. 2 shows a low voltage battery as well as a high-voltage battery. 2. According to one embodiment of the invention, the device 14 could use a single battery for high and low voltage purposes.

Refer to FIG. 2, subcutaneous device 14 functions are controlled by means of software, firmware and hardware that cooperatively monitor the ECG signal, determine when a cardioversion-defibrillation shock or pacing is necessary, and deliver prescribed cardioversion-defibrillation and pacing therapies. Circuitry described in U.S. Pat. 14 may be included in the subcutaneous device 14. No. No. U.S. Pat. No. No. 5,188,105?Apparatus & Method for Treating Tachyarrhythmias? to Keimel for selectively delivering single phase, simultaneous biphasic and sequential biphasic cardioversion-defibrillation shocks typically employing ICD IPG housing electrodes 28 coupled to the COMMON output 123 of high voltage output circuit 140 and cardioversion-defibrillation electrode 24 disposed posterially and subcutaneously and coupled to the HVI output 113 of the high voltage output circuit 140.”

“The cardioversion-defibrillation shock energy and capacitor charge voltages can be intermediate to those supplied by ICDs having at least one cardioversion-defibrillation electrode in contact with the heart and most AEDs having cardioversion-defibrillation electrodes in contact with the skin. ICDs that use most biphasic waveforms have a maximum voltage of approximately 750 Volts and an associated maximum energy around 40 Joules. The average maximum voltage required for AEDs is between 2000 and 5000 Volts. This can vary depending on the model and waveform. Subcutaneous device 14 according to the present invention can use maximum voltages between 300 and approximately 1500 Volts. It also has energies between 25 and 150 joules. The total high voltage capacitance may range from 50 to 300 microfarads. Such cardioversion-defibrillation shocks are only delivered when a malignant tachyarrhythmia, e.g., ventricular fibrillation is detected through processing of the far field cardiac ECG employing the detection algorithms as described herein below.”

“In FIG. 2. The sense amp 190 is used in conjunction with pacer/device circuit 178 to process the far field ECG sensor signal. This sense signal is generated across a specific ECG sense vector that is defined by one pair of subcutaneous electrodes 18, 22, and the can or housing 25. Or, an optional virtual signal (i.e. a mathematical combination between two vectors), if chosen. The device can generate a virtual vector signal, as described in U.S. Pat. No. No. Lee, et. al. incorporated herein as a reference in its entirety. A physician may also select vector selection and program it via a telemetry connection to a programmer.

“The switch matrix/MUX 191 selects the sensing electrode pair to detect the ECG signal of concern. This is the R wave for patients at high risk of sudden death from ventricular fibrillation. The far-field ECG signals are transmitted through the switch matrix/MUX 191 into the input of sense amplifier 190. This, along with pacer/device Timing Circuit 178, evaluates the detected ECG. The escape interval timer in the pacer timing circuit (178) and/or control circuit (144) are used to determine Bradycardia or asystole. When the interval between successive R waves exceeds the escape interval, Pace Trigger signals are applied on the pacing pulse generator 192. This generates pacing stimulation. Bradycardia pacing is often temporarily provided to maintain cardiac output after delivery of a cardioversion-defibrillation shock that may cause the heart to slowly beat as it recovers back to normal function. The use of U.S. Pat. 103-106 may help in the detection of subcutaneous far field signals when there is noise. No. No. Lee, et. and incorporated herein as reference in its entirety.”

“Detection and treatment of malignant tachyarrhythmias is done in the Control circuit. This is determined by the intervals between R wave sense event signals, which are output from the pacer/device timer timing 178 and the sense amplifier circuit circuit 190 to control and timing circuit 144. The present invention does not only use interval-based signal analysis, but also uses supplemental sensors and morphology processing methods and apparatus.

“Supplemental sensors, such as tissue color, oxygenation, respiration, and patient activity, may be used to help make the decision whether to apply or withhold defibrillation therapy, as described in U.S. Pat. No. No. Alt, and are incorporated by reference in their entirety. Sensor processing block 194 transmits sensor data via data bus 140 to microprocessor 142. The apparatus and method described in U.S. Pat. may be used to determine patient activity and/or position. No. No. Sheldon, and is incorporated by reference in its entirety. The apparatus and method described in U.S. Pat. may be used to determine patient respiration. No. 4,567,892 ?Implantable Cardiac Pacemaker? Plicchi, et. al. are incorporated by reference in their entirety. The sensor apparatus and method described in U.S. Pat. may be used to determine patient tissue oxygenation or tissue colour. No. No. 5,176,137 to Erickson et al. and incorporated by reference in its entirety herein. The oxygen sensor in the ‘137 patent could be found in the subcutaneous device pouch or on the lead 18. This allows for the detection of oxygenation or color of tissue contact or near-contact.

“Certain steps are performed cooperatively in microcomputer142. This includes microprocessor RAM and ROM. As well as associated circuitry and stored detection criteria. These may be programmed into RAM using a telemetry interface (not illustrated) that is standard in the art. Microcomputer 142, timing and control circuits 144, 178, pacer timing/amplifier and circuit 140 are able to exchange data and commands via a bidirectional data/control bus. The control circuit 144 and pacer timing/amplifier circuits 178 are both clocked at a slower clock rate. The microcomputer 142 sleeps normally, but it is awakened by interrupts from each R-wave event. These interrupts are received upon receipt of downlink telemetry programming instructions or cardiac pacing pulses. This allows the microcomputer to perform any mathematical calculations, update the time intervals controlled and monitored by pacer/device timing circuitry (178).

“When malignant tachycardia occurs, high voltage capacitors 156-158, 160- and 162 are charged to a preset voltage level using a high-voltage charger 164. It is considered inefficient to keep a constant charge on high voltage output capacitors 160, 156 and 162. Instead, the charging process is initiated by control circuit 144 issuing a high voltage charge order HVCHG on line 145 to high-voltage charge circuit 162. Charging is controlled using bi-directional control/databus 166 and a feedback sign VCAP from HV output circuit 140. The high voltage output capacitors 156 to 158, 160, 162 can be made of aluminum electrolytic, film or wet tantalum.

“The negative terminal on high voltage battery 112 can be directly connected to system ground. The switch circuit 114 is usually open so that high voltage battery 112’s positive terminal is not connected to the positive power input of high voltage charger circuit 164. Conductor 149 connects to switch circuit circuit 114. The high voltage command HVCHG is also carried via switch circuit. Switch circuit 114 closes when positive high voltage battery voltage EXTB+ is connected to the positive power input to high voltage charger circuit 164. For example, switch circuit 114 could be a field effect transistor. Its source-to-drain path may interrupt the EXT-B+ conductor 118, and its gate receives the HVCHG signal from conductor 145. The high voltage charge circuit (164) is now ready to start charging the high-voltage output capacitors 156 and 158 with high voltage battery 112.

“High voltage output capacitors 156, 158, 160, and 162 may be charged to very high voltages, e.g., 300-1500V, to be discharged through the body and heart between the electrode pair of subcutaneous cardioversion-defibrillation electrodes 113 and 123. It is not necessary to know the details of the voltage charging circuitry in order to practice the invention. One high voltage charging circuit that is believed to be suitable for the purpose of the invention has been disclosed. The high voltage capacitors 156 to 160, 160, 162 and 160 can be charged by, for example, the high voltage charge circuit (164) and a high frequency high-voltage transformer (168), as detailed in U.S. Patent. No. 4,548,209 ?Energy Converter for Implantable Cardioverter? to Wielders, et al. Diodes 170 to 172, 174, 174, and 176 are used to maintain proper charging polarities. They connect the high-voltage transformer’s output windings 168 and the capacitors 156. The high voltage output circuit 140 provides a VCAP feedback signal that indicates the voltage to the timing control circuit 144. Timing and control circuit 144 terminates the high voltage charge command HVCHG when the VCAP signal matches the programmed capacitor output voltage, i.e., the cardioversion-defibrillation peak shock voltage.”

“Control circuit 144 then generates the first and second control signals, NPULSE 1, and NPULSE 2. These signals are applied to high voltage output circuit 140 in order to trigger the delivery of defibrillating or cardioverting shocks. The NPULSE1 signal triggers the discharge of the first capacitor bank (comprising capacitors 156 and 158). The NPULSE2 signal causes the discharge of the first and second capacitor banks, which are comprised of capacitors 160 and 162. You can choose from a variety of output pulse modes by changing the time order and number of assertions of the NPULSE1 and NPULSE2 signals. The NPULSE 1 and NPULSE2 signals can be delivered sequentially, simultaneously, or individually. In this way, control circuitry 144 serves to control operation of the high voltage output stage 140, which delivers high energy cardioversion-defibrillation shocks between the pair of the cardioversion-defibrillation electrodes 18 and 25 coupled to the HV-1 and COMMON output as shown in FIG. 2.”

“Thus, subcutaneous device 14 monitors the patient’s cardiac status and initiates the delivery of a cardioversion-defibrillation shock through the cardioversion-defibrillation electrodes 18 and 25 in response to detection of a tachyarrhythmia requiring cardioversion-defibrillation. The high HVCHG signal causes high voltage battery 112 and high voltage charge circuit 164 to be connected. This allows for the charging of output capacitors 160, 156, 160 and 162 to begin. The charging continues until the programed charge voltage has been reflected by VCAP signal. At that point control and timing circuits 144 lower the HVCHG signal to terminate charging and open switch circuit 114. Subcutaneous device 14 can either be programmed to deliver cardioversion shocks directly to the heart using the timed synchrony described above. Episode data related to the detection of the tachyarrhythmia and delivery of the cardioversion-defibrillation shock can be stored in RAM for uplink telemetry transmission to an external programmer as is well known in the art to facilitate in diagnosis of the patient’s cardiac state. The patient who receives the device 14 prophylactically would be asked to report any such episodes to their physician. This will allow them to further evaluate the patient’s condition, and determine if an ICD is needed.

“There are many telemetry systems that provide the required communications channels between an external program unit and an implanted gadget. These systems are well-known in the art. The following U.S. Patent discloses telemetry systems that are believed to be suitable for practicing the invention. No. Wyborny and al. 5,127,404 entitled “Telemetry Format for Implanted Medical Equipment?” ; U.S. Pat. No. No. ; and U.S. Pat. No. Thompson et.al. entitled “Telemetry System to a Medical Device?”. Wyborny et al. Thompson et.al. The ‘063 patents are often assigned to the assignees of the present invention and are hereby incorporated in their entirety.

“According to an embodiment, the invention requires an index of merit to evaluate the quality of the signal in order to select the preferred ECG vector sets automatically. ?Quality? Quality is the ability of the signal to accurately estimate heart rate and distinguish between patient’s normal sinus rhythm and patient’s ventricular tapyarrhythmia.

“R-wave amplitude, Rwave peak amplitude to waveform ampltude between Rwaves (i.e. signal to noise ratio), low-slope content, relative high frequency power versus low frequency, mean frequency estimation and probability density function are some examples of appropriate indices.”

“Automatic vector selection can be performed at implantation, or periodically (daily/weekly/monthly), or both. Automatic vector selection can be performed at implant as part of the automatic device turn-on procedure. This performs activities such as measuring lead impedances or battery voltages. The implanting physician can initiate the device turn-on procedure by pressing a button or alternatively it may be initiated automatically upon detection of device/lead placement. In order to ensure that the ECG vector quality of the patient and the device/lead position are adequate, the turn-on procedure can also be used the automatic vector selection criteria. This ECG quality indicator allows the implanting physician the ability to move the device to a different orientation or location to increase the quality of ECG signals. The device turn-on procedure may include the selection of the preferred ECG vector or vectors. These vectors may be the ones that provide maximum rate estimation and detection accuracy. The physician may choose to use an apriori set of vectors. As long as they are not less than a certain threshold or are slightly better than other vectors, those vectors will be chosen. Some vectors might be almost identical, so they are not tested unless their a priori chosen vector index falls below a predetermined threshold.

“Depending on the metric power consumption and the power requirements of your device, the ECG signal metric quality may be measured using a range of vectors or a subset as often as you wish. Data can be collected on a daily, weekly, monthly, hourly or daily basis. You may also be able to take more frequent measurements, such as every minute, and use them to determine the susceptibility of vectors for occasional noise, motion noise or EMI.

“Alternatively, the 14-inch subcutaneous device may include an indicator/sensor for patient activity (piezoresistive or accelerometer, or the similar) that delays automatic vector measurement between periods of high or low patient activity and periods of minimal or no activity. A typical scenario would be to test/evaluate ECG vectors daily or weekly, while the patient is asleep. This could be done using an internal clock (e.g. 2:00 AM) or by inferring sleep via a 2-axis accelerometer and a lack or activity. Another scenario is to test/evaluate ECG vectors once a week or every other day while the patient exercises.

“If periodic, infrequent, automatic measurements are taken, it might also be worthwhile to measure noise (e.g. muscle, motion, EMI etc.). You can then delay the vector selection measurement until the noise has subsided.

Subcutaneous device 14 may optionally include a sensor that measures the patient’s position (via a 2-axis accelerometer). This sensor can be used to verify that differences in ECG quality do not just result from changing posture/position. The sensor can be used to collect data in several postures. ECG quality may then be averaged, combined or selected for a preferred position.

“One embodiment allows for vector quality metric calculations to be done by the clinician either at the time the implant is placed, during a follow-up visit in a clinic setting or remotely using a remote link between the programmer and the device. Another embodiment allows the device to automatically calculate the vector quality metrics for each sensing vector. This could be done multiple times per day, once per week, or monthly. The values can also be averaged over the course of a week for each vector, for example. Averaging can be either a moving average, or a recursive average, depending on memory and time weighting.

“FIG. “FIG. FIG. FIG. 3 shows how the device senses the cardiac signal for each vector available. It does this using sensing techniques that are known in the art. No. No. FIG. FIG. 3 shows an example of how the device can sense an ECG signal 100. It includes a horizontal sensing channel 102 that extends between the housing, can 25, and electrode 22, and a diagonal sensing track 104 that extends between the electrode 20 and 25. A vertical sensing track 106 runs between electrodes 20 through 22. When the detected signal exceeds a time dependent self-adjusting threshold 110, the device detects an R-wave 108.

“Once R-wave108 has been sensed, the device creates a vector quality measurement detection window 112 using the sensed Rwave108 for each sensing vector 102-106. This is used to determine a vector quality measure associated with the sensing Vectors 102-106. A device, according to one embodiment, sets a quality measurement detection window 112 at a predetermined distance of 116 from R-wave108. It also has a detection window width of 118 to allow analysis of signal 100 in the expected range of signal 100. This allows for a determination of a vector quality metric associated with sensing vectors 102-106. The device defines the quality-metric detection windows 112 to have a width of 200 ms. It also places a start point at 114 of the quality-metric detection windows 112 between 150-180 milliseconds and the sensed R?wave 108. The width 118 extends 200 ms from the detection point 114 to the detection end point 120. This is approximately 350-380ms from R-wave108. Another embodiment states that the width 118 extends approximately 270ms from the detection windows start point 114 and end point 120. This is roughly a distance of about 420-450ms from the R-wave 108. After the quality-metric detection window 112 has been set, the device determines the minimum signal difference (122) between the sensed signals 100 and 110 within the quality-metric detection window 112. This is the distance between the sensor 100 and 110 as described below.

“FIG. “FIG. FIGS. FIGS. 3 and 4. For each cardiac signal 100 derived from the respective sensing channels 102-106 the device determines the sensedR-wave108 of the cardiac signals 100, Block 200 and then sets the quality-metric detection window 112, Block 222. This is based on the sensedR-wave108 for the sensing vector 102-106. The quality metric window 112 has been located. Once that window is set, the device calculates the minimum signal deviation 122 between the detected cardiac signal 100, and the sensing threshold 110 for each sensing vector. Block 204. The stored minimum signal difference 122 is used to determine whether the minimum signal difference 122 has been established for the predetermined threshold number for each sensing vector 102-106. Block 206. If the minimum signal differ has not been determined for the threshold number of cardiac cycles each sensing Vector 102-106 No in Block 206 then the device receives the next R-wave 108 and repeats the process for the next sensed cardiac cycle each sensing Vector 102-106. One embodiment states that the minimum signal difference of 122 is calculated for 15 cardiac cycles.

“Once the minimum sign difference 122 has been established for all predetermined threshold numbers of cardiac cycles, Yes, in Block 206 the device determines a vector selection metric (102-106) based on the 15 minimum signals differences 122 for each vector. Block 208 In one embodiment, the device determines a median of 15 minimum signal difference 122 for each sensing channel and sets the vector selection metrics for that sensing vector equal the determined median of associated minimum signal differences. The device then ranks the vector selection metrics of the sensing channels 102-106 in Block 220. In the example shown in FIG. 3, the device ranks the selected vector selection metrics from highest-to-lowest. 3. The diagonal sensing 104 would rank highest, as the median signal difference for this vector was 0.84 milivolts. The horizontal sensing 102 would rank second, because the median signal difference is 0.82 milivolts. And the vertical sensing 106 would rank third, as the median signal difference is 0.55 milivolts.

“Once Block 210 has been ranked, the device chooses which sensing vector(s), to use during the subsequent sensing and arrhythmia detection. Block 212 follows. Depending on how long it takes between updating the sensing vectors 102?106, the device will wait until Block 214 to determine the next vector selection determination.

“FIG. “FIG. FIGS. FIGS. 3 and 5 illustrate another embodiment. The device determines the sensing vector 102 to 106 for each cardiac signal 100 and then sets the quality-metric detection window 112, Block 300. This is based on the sensing vector 102 to 106’s sensed R wave 108. The quality metric window 112 has been located. Once this window is set, the device determines what the minimum signal difference is between the sensed heart signal 100 and the threshold 110 in the quality measurement detection window 112. This window covers the sensing vectors 101-106. Block 304. The device stores the determined minimum signal differential 122 and determines whether the minimum sign difference 122 has been calculated for a predetermined threshold amount of cardiac cycles for each sensing channel 102-106 (Block 306).

“If the minimum signal differ 122 is not determined for the threshold number 102-106 of cardiac cycles, No in Block 306, then the device determines if a predetermined timer has expired. Block 308. The device receives the next R-wave108 for each sensing channel 102-106 if the timer hasn’t expired. If it has, Block 308 determines whether the predetermined timer has expired. This is then repeated for the next cardiac cycle for each sensing vector 102-106. One embodiment states that the Block 308 timer is set at 40 seconds.

“In some cases, the device might not have been able to obtain minimum signal differences 122 for one of the sensing Vectors. Therefore, if Block 308 has expired, the device determines whether at least two of the sensing Vectors 102-106 were obtained. Block 314. If the minimum signal differences were not achieved for at least two of the sensing channels, i.e. for one or none of the sensing Vectors 102 to106, then Block 308 is used. Block 310 determines whether no sensing can be made. Block 310 waits for the next scheduled vector selection determination. Block 312 will repeat the process.

“If at least two of the sensing channels 102-106 had the minimum signal differences, then Block 314, the device selects the Block 320 sensing vectors to be used during the subsequent arrhythmia detection and sensing. The device waits for Block 312, which is the next scheduled vector selection determination. This time, it depends on how long the updating of the sensing Vectors 102-106 takes.

“If the minimum signal differential 122 has been calculated for the predetermined number 102-106 of cardiac cycles, then yes, in Block 306, the device calculates a vector selection metric based on the 15 minimum signals differences 122 for each vector, Block 316. In one embodiment, the device determines a median of 15 minimum signal difference 122 for each sensing channel and sets the vector selection metrics for that sensing file equal to the determined median value of the minimum signal differences. The device then ranks the vector selection metrics of the sensing channels 102-106 in Block 316. In the example shown in FIG. 3, the device ranks the selected vector selection metrics from highest-to-lowest. 3. The diagonal sensing 104 would rank highest, as the median signal difference for this vector was 0.84 milivolts. The horizontal sensing 102 would rank second, because the median signal difference is 0.82 milivolts. And the vertical sensing 106 would rank third, as the median signal difference is 0.55 millivolts.

“Once the Block 318 sensing vectors are ranked, the device selects which sensing vector(s), to be used during the subsequent sensing and arrhythmia detection. Block 320. Another embodiment allows the user to choose the sensing vectors by displaying the ranking results, such as on a programmer. The device waits for Block 312, which is the next scheduled vector selection determination. This time, it depends on how long the updating of the sensing Vectors 102-106 takes. Another embodiment allows the user to manually initiate the vector selection procedure. The device will wait for input from the user before proceeding with the next scheduled vector selection.

“FIG. “FIG. 6” is a flowchart showing a method of selecting one or more sensing channels according to another exemplary embodiment. In some cases, the device might not have been able obtain the minimum signal difference 122 required for one or more sensing vectors. There may also be cases where the minimum signal differences 122 for one or several cardiac cycles in the sensing vectors 101-106 are equal to zero if the ECG signal is greater or equal to the threshold in one or multiple cardiac cycles, or during the quality metric sensoring window 112. These instances of zero minimum signals differences could be due to T-wave oversensing or frequent premature ventricular contractions.

According to FIGS. 3. and 6. For each cardiac signal 100 derived from the respective sensing channels 102-106 the device determines the sensedR-wave108 of the cardiac signals 100, Block 400 and sets the quality-metric detection window 112, block 402, based upon the sensedR-wave108 for the sensing vector 102?106 as described above. The quality metric window 112 has been located. Once that window is set, the device calculates the minimum signal deviation 122 between the detected cardiac signal 100, and the sensing threshold 110 in the quality-metric detection window 112. This is for each of the sensing channels 102-106. Block 404 The device also determines whether there was a zero minimum signal differential during Block 416 for each of the sensing vectors 102-106. If there is no minimum signal difference, the block 416 Block is cleared. The R-wave associated to that vector is then discarded. Block 418 Block is used to determine if a timer is expired.

“If there was no zero minimum signal deviation during the detection window 112 No in Block 416 the device determines if the minimum signal differ 122 has been determined for a threshold number of cardiac cycle, Block 406, i.e. such 15 cardiac cycles. The device will determine whether the timer has expired if the minimum signal difference (122) has not been established for each sensing vector from 102 to106. If the timer hasn’t expired, No. in Block 408 the device receives the next R-wave108 for each sensing Vector 102-106. The process is repeated for the next sensed cardiac cycle 102-106. One embodiment states that the Block 408 timer is set at 40 seconds.

“If the timer is over, yes in Block 408, the device checks to see if the minimum signal difference was achieved for at least two of the sensing vectors (102-106, Block 414). If the minimum signal differences were not achieved for at least 2 sensing channels, i.e. for one or none the sensing Vectors 102-106 Block 414, then the device determines that no sensing can be made. Block 410. Depending on how long it takes between the updating of the sensing vecs 102 to 106, the device waits for the next vector selection determination Block 412. At which point the vector selection process will be repeated.

“If at least two of the sensing channels 102-106 had the minimum signal differences, then Block 414 says that the device will select those sensing vectors from Block 320 for use in subsequent arrhythmia detection and sensing. The device waits for Block 412 to determine the next vector selection determination. This is depending on how long it takes between the updating of the sensing Vectors 102-106.

“If the minimum signal differential 122 has been calculated for the threshold number 102-106 of cardiac cycles, then yes in Block 406, the device calculates a vector selectionmetric for each vector from 102 to 106 based upon the 15 minimum signal differences for that vector (Block 420). In one embodiment, the device determines a median of 15 minimum signal difference 122 for each sensing channel and sets the vector selection metrics for that sensing vector equal the determined median of associated minimum signal differences. The device then ranks the vector selection metrics of the sensing channels 102-106 in Block 422, once a single vector selectionmetric has been determined. The device will rank the selected vector selection metrics in Block 420 from highest to least. In the example shown in FIG. 3. The diagonal sensing 104 would rank highest, as the median signal difference for this vector was 0.84 milivolts. The horizontal sensing 102 would rank second, because the median signal difference is 0.82 milivolts. And the vertical sensing 106 would rank third, as the median signal difference is 0.55 milivolts.

“FIG. “FIG.7 is a graphic representation of cardiac signals sensed along multiple sensor vectors during selections of a sensing channel in a medical device following another embodiment. FIG. FIG. 7 shows how the device detects a cardiac signal 500 during the vector selection process. This is for one or more available sensing vectors, as described above. An R-wave 508 signal is detected when the signal 500 exceeds a self-adjusting, time-dependent sensing threshold 510. The device senses an R-wave 508. It then sets a predetermined blanking time 509 and a quality window 512. These are based on the R-wave 508 sensed for each sensing vector 102-106. This is used to determine a vector quality measure associated with sensing vectors 102-106. One embodiment sets the blanking time 509 to extend a predetermined time period that starts at the R-wave 508 and ends at the blanking endpoint 511. The blanking time 509 could be set at 150 ms. However, any initial setting can be used. The current blanking period setting will determine the width of the blanking adjustment window 513. According to one embodiment, the blanking time is usually set between 150-180 ms. Therefore, 30 ms would be the blanking adjustment window 513 if the blanking duration was 150 ms. The blanking period adjustment window 513’s width (517) is determined by the chosen blanking period range.

The device also sets the quality-metric detection window 512 at the blanking time adjustment endpoint 514 with a detection window width of 518 to allow analysis of the signal 500 in the expected range of 500 where a T wave of the QRS signal is associated with the sensedR-wave 508 to occur. The device defines the quality-metric detection windows 512 to have a width of 200 ms. It also places the blanking time adjustment endpoint 514 at the start of the quality measurement window 512. The detection window width 518 extends 200 ms beyond the detection window stop point 515. This allows for analysis of the signal 500 within an expected range of the signal 500.

“FIG. 8 shows a flowchart showing a method of selecting one or more sensing channels according to an exemplary embodiment. FIGS. FIGS. 7 and 8 show that the device acquires a sensing vector 102-106 for each cardiac signal 500. Then, it sets the blanking adjustment window 513 for each sensing vector 102-106 and the quality measurement detection window 512 for Block 602. These are based on the sensing vector 102-106. The blanking adjustment window 513 is opened and the quality measurement detection window512 is closed. Once these windows are open, the device determines the minimum signal differences 519 between the detected cardiac signal 500, the sensing threshold510, and the sensing threshold510 within the blanking adjustment window 513, and the minimum signal differences 522 between each sensed vector’s sensed R-wave 508, Block 602. The stored minimum signal differences 519 & 522 are used to determine whether the minimum signal difference 519 & 522 have been established for a predetermined threshold amount of cardiac cycles, Block 606.

“If the minimum signal difference 519 or 522 has not been determined for the predetermined threshold amount of cardiac cycles for each sense vector 102 to106, No in Block 606 the device receives the next R-wave 508 for each sensing Vector 102-106 and this process is repeated for the next sensed cardiac cycle of each of the sensing channels 102-106. One embodiment states that the minimum signal differences 519 or 522 can be determined for 15 cardiac cycles.

“Once the minimum signals differences 519 and 522, have been determined for all predetermined threshold numbers of cardiac cycles, yes in Block 606, device determines a vector selectionmetric for each vector from 102 to 106 based upon the 15 minimum signal difference 522 for that vector (Block 608). In one embodiment, the device determines the median value of 15 minimum signal difference 522 for each sensing metric and sets the vector selection metrics for that sensing metric equal to the determined median value of the associated minimum signals differences 522. Once one vector selection metric has been determined for each sensing vector 102-106 in Block 608, it is used to rank the vector selection metrics for sensing vectors 101-106, Block 608. In the example shown in FIG. 7, the device ranks the selected vector selection metrics from highest-to-lowest. 7 would rank the diagonal sensing 104 highest, as the median signal difference was 0.86 millivolts. The horizontal sensing 102 would rank second, at 0.63 millivolts. Vertical sensing 106 would rank third, because the median signal difference is 0.32 millivolts.

“Once Block 610 has been ranked, the device will select the sensing vector(s), which will be used during the subsequent arrhythmia detection and sensing by the device, Block 612. The device can also determine whether the current blanking period exceeds a predetermined threshold that corresponds to a desired maximum period of time, i.e. 180 ms, as described above in Block 614. The amount of time between the updating of the sensing Vectors 102-106 will determine the time required. If the current blanking exceeds the threshold No in Block 614 then the device waits for the next scheduled vector selection determination. At that time, the vector selection process is repeated.

“If the current blanking exceeds the blanking threshold, yes in Block 614. The device calculates a blanking adjustment metric for each vector from 102 to 106 based upon the 15 minimum signal difference 519, Block 616. In one embodiment, the device determines a median of 15 minimum signal difference 519 for each sensing channel and adjusts the blanking period metric equal to the determined median value of the minimum signal differences 519. After determining a single blanking adjustment metric for each sensing vector 102-106 in Block 606, the device determines if an adjustment is needed for the sensing channels 102-106, Block 618. To avoid double counting R-waves, it is possible to increase the blanking period. One embodiment determines whether the blanking time should be adjusted from the current setting by determining, for each one of the highest ranked vectors in Block 610, if the determined blanking adjustment metric is less that a percentage of the corresponding determined vector select metric and less then a predetermined minimum blanking threshold.

FIG. 7 would rank the diagonal sensing vector 104 highest, as the median minimum sign difference for that vector was 0.86 milivolts. The horizontal sensing vektor 102 would rank second, since that vector’s median minimum signal differ is 0.63 milivolts. 7. The device determines if the blanking time adjustment metric calculated for the diagonal sensing vector 104 is less than half the vector selection metrics for that sensing vector, i.e. 0.63 millivolts and less that of 0.05 millivolts and less than half of that for that vector selection metric, metrics.

“If the blanking time adjustment metric is less than the predetermined percentage of one of two highest-ranked vectors, or is not lower than the predetermined minimal blanking threshold, No in Block 608, the device waits for the next scheduled vector selection determination. Block 622 is then used to repeat the vector selection process. The time between the updating of sensing vectors 101-106 will determine how long it takes for the next scheduled update to take place. It may be an hour, a weekend, or a month depending on what you have programmed.

“If the blanking time adjustment metric is lower than the predetermined percentage of one of two highest-ranked vectors or less than a threshold for the minimum blanking periods, Block 618 will update the blanking duration to Block 620. The blanking period can be extended to 180 ms or increased by a predetermined amount such as 10ms. Another embodiment states that instead of automatically increasing the blanking time, the device can generate an alarm or other stored indication that informs the attending physician that the blanking should be increased. This allows the user to adjust the blanking periods manually using a program or other input device.

“FIG. “FIG. FIG. FIG. 9 illustrates how the device can transition between a Not Concerned State 702, an Armed State 704, and an Armed State 704, according to one embodiment. U.S. Pat. No. No. 7,894,894 to Stadler and al., incorporated by reference in its entirety. During normal operation, the device is placed in the Not Concerned State 702. R-wave intervals are being evaluated for periods of rapid rate and/or asystole. The device moves from the Not Concerned state 702 to the Concerned state 704. If there are short R-wave intervals in two different ECG sensing vectors, it is indicative that an event may need therapy. The Concerned State 704 is where the device examines a predetermined range of ECG signals in order to detect if the signal has been corrupted by noise. This allows the device to distinguish rhythms that require shock therapy from others that don’t. It uses a combination R-wave intervals as well as ECG signal morphology information. No. No. No. No.

“If shock therapy is required, the device will transition from the Concerned State 700 to the Armed State 706. The device will return to the Not Concerned State 722, if a rhythm that requires shock therapy is not detected while it is in the Concerned State 7004 and the Rwave intervals are found to be no longer short. If a rhythm that requires shock therapy is not detected while the device remains in the Concerned State 704, and the R-wave intervals are determined to be short, the device returns to the Not Concerned State 702.

“In the Armed State 706 the device charges high voltage shocking capacitors. It continues to monitor R wave intervals and ECG signal structure for spontaneous termination. The device will return to the Not Concerned Status 702 if shock therapy is required for spontaneous termination. The device switches from the Armed State 706 to the Shock State 708. If shock therapy is required, but the rhythm is not stopped by the capacitors being charged, the device will return to the Not Concerned State 702. The shock state 708 is where the device delivers a shock, and then returns to the Armed State 706 for evaluation of the effectiveness of the therapy.

“FIG. “FIG. FIG. FIG. 10 illustrates how, according to one embodiment of the present disclosure. Block 802 uses the method described in U.S. Patent Application Ser. No. No. No. No. 7,894,894 to Stadler and al., both incorporated by reference in their entirety herein. According to one embodiment, the Concerned State 704 uses the most recent ECG data from both channels ECG1 or ECG2 while the device is there. This allows processing to be triggered in the Concerned State 704. The timeout is three seconds. While the processing is described as occurring over a period of three seconds, it is possible to choose other times for processing time when the Concerned States 304 is active. However, the preferred range should be between 0.5 and 10 seconds. The three-second timer ends after which individual R-waves can be sensed in channels ECG1 or ECG2 in the Concerned State 704. However, the possibility of changing to the Concerned State 704 to another state is limited. It is beneficial to process the latest three-seconds ECG data upon initial entry into the Concerned State 7004, i.e. ECG data for three seconds prior to the transition to Concerned State 704. This requires continuous circular buffering for the last three seconds of ECG data, even if you are in the Not Concerned States 702

“While in the Concerned Status 704, the device determines the sinusoidality and noise of the signals in the two sensing channel to determine whether a ventricular fibrillation or fast ventricular tapycardia (VT), event is likely. The signal’s sinusoidality and low noise indicate that there is a greater likelihood of VT/VF occurring. The device then classifies the sensing channel as either shockable, or not shockable based on the analysis. One embodiment of the invention may classify both ECG1 or ECG2 as either shockable, not shockable according to commonly assigned U.S. patent Ser. No. No. The device’s transition status from the Concerned State 704 to Block 804 is determined based on the classification of the current vectors as shockable or non-shockable.

“Example: According to an embodiment, the transition from ECG1 to ECG2 is confirmed if there are a predetermined number of segments of three seconds in each channel ECG1 or ECG2. This could be two out of three, for example. The device will transition from the Armed State 704 to ECG1 and ECG2 if the predetermined number three-second segments on both channels ECG1 or ECG2 has been classified as being shockable. If the predetermined number three-second segments on both channels ECG1 or ECG2 has not been classified shockable, then No in Block 804 the device transitions from the Concerned State 704 to the Armed State 706. A decision is made as to whether the device should transition back to the Not Concerned State 7002 in Block 806.

“Determining whether to transition from the Concerned State 704 back to the Not Concerned State 702 is done, for example, by determining if a heart beat estimate is less than the threshold level in at most one of the channels ECG1 or ECG2, as described on U.S. patent application S. No. No. No. 7.894,894 to Stadler and al., both incorporated by reference in their entirety. If the device is not to transition to the Not Concerned States 702, that is, if both the heart rate estimates exceed the threshold, No in Block806 is used. The process is then repeated with the signal generated in the next three-second window, which is Block 808. If the device is to be moved to the Not Concerned State 702 (i.e. both heart rate estimates exceed the threshold), Block 806 will determine if a Blanking Period adjustment was made in the Concerned State. Block 809 If the blanking time was adjusted, Block 809 states that the device adjusts it. Block 811. One embodiment may reduce the blanking time by a predetermined amount. Another example is that the device may reset the blanking to the original or nominal period used before the adjustment occurred while the device was in the Not Concerned State 702. If the blanking period was changed from 150 ms or 180 ms during operation of the device in the Concerned State 704 to Not Concerned State 702 (Yes in Block 809), the device will adjust the blanking period to the initial 150ms setting in Block 811. If the blanking time was not adjusted, No in Block 809, or once the blanking period is returned to its initial or nominal setting, Block 811, the device will be in the Not Concerned State.

“When the device switches from the Concerned State 704 to the Armed State 706 Yes in Block 804, processing is continued by a three second timeout as it was during the Concerned State. Once the device is in the Armed State 706 it can be determined if a blanking adjustment was made during the Concerned State 704. Block 810. If the blanking was adjusted, Block 810 will confirm that the blanking is being adjusted. Block 812. One embodiment states that the device can reduce the blanking time by a predetermined amount. Another example is that the device may reset the blanking to the original or nominal blanking periods used prior to the adjustment taking place in the Concerned State 704. If the blanking period was increased from 150 ms or 180 ms during operation in the Concerned State 704 to the Armed State 706 Yes in Block 804, the blanking period is adjusted to the initial 150ms setting. Block 812. Block 810 does not allow for the adjustment of the blanking time. Block 812 allows the device to adjust the blanking to period to the initial 150 ms setting.

“During the charging, the classifications of segments for each channel ECG1 or ECG2 as either shockable (or not) continues. After the next three seconds have been acquired using the adjusted Blanking Period, Block 802, a determination is made whether the event continues be a shockable. This is done by determining whether a predetermined amount of segments, such the last two segments, have been classified in both channels ECG1/ECG2 as not-shockable, Block 816. The event may not be shockable if the three second segments are classified as not shocking. Block 816 says “Yes.” and then the charging of capacitors is stopped. Block 818 states that a decision is made about whether or not to move to the Not Concerned States 702 and Block 820.

“Accordingly to an embodiment, the device will transition between the Armed State 706 and the Not Concerned State 7002, Yes in Block 820, provided certain termination requirements have been met. If, for both channels ECG1 or ECG2, less than two of the three-second segments that were in shock are available, less than three of the eight last three-second segments and less than three of the last eight are considered shockable, the latest three-second segment is not considered shockable. A fourth consecutive not-shockable classification in either channel ECG1 or ECG2 could be another possible criteria to return to the Not Concerned States 702.

“In addition the two criteria above, at least one current heart rate estimate must be slower that the programmed threshold and capacitor charging cannot be in progress.” If all of these conditions are met, Block 820 will allow the device to transition from the Armed State 706 to the Not Concerned State 7002.

“If any of these requirements is not met, a return to the Not Concerned state is not indicated. Block 820 then determines whether the shockable rhythm has been redetected. Block 822 does this by determining if predetermined redetection criteria have been fulfilled. A determination is made about whether there are a certain number of three-second segments in each of the channels ECG1 or ECG2, for example, two of the three most recent ones, that have been considered to be shockable. If the predetermined redetection criteria are not met, Block 802 will continue to determine whether therapy should be terminated. This is done so that processing switches from Block 820 to Block 822 to determine whether therapy should be terminated. Then, the decision as to whether shockable events can still be detected, Block 822. Until the event terminates, the device is switched from the Armed State 706 into the Not Concerned State 700 or the event is re-evaluated. If the predetermined redetection criteria are met, Block 822 will allow charging to be re-initiated (Block 814), and the process is then repeated.

“If the three predetermined segments of capacitor charging are not classified as not-shockable, No in Block 806, a determination is made about whether the capacitors have been charged. Block 824. The capacitor charging process continues as long as No in Block816 is being used. Next, a signal is generated in Block 828. Finally, once the capacitors have been charged, Yes in Block824, it is determined whether the delivery of therapy is appropriate. This is done by checking whether the predetermined delivery confirmation requirements are met. According to the embodiment of the invention, predetermined therapy delivery confirmations include determining whether at least five of the eight last three-second segments have been classified as shockable for either channel ECG1 or ECG2. At least two of the three last three-second segments have been classified as shockable. A determination is also made about whether the latest three-second segment was classified as being shockable by at least one channel ECG1 or ECG2.

“If the predetermined delivery requirements for therapy are not met, and the delivery of the therapy cannot be confirmed, No in Block826. The determination of whether the treatment should transition from the Armed State 702 to the Not Concerned State 7002, Block 820 is repeated. If the therapy delivery requirements have been met, then the delivery of the therapy can be confirmed in Block 826. The device will transition from the Armed State 702 to the Shock State 708.

“It is understood, in addition the three sensing signals 102-16, that may optionally be used, a virtual signal (i.e. a mathematical combination between two vectors) can also be used in place or in addition to the sensing vectors. The device could generate a virtual signal, as described in U.S. Pat. No. No. Lee, et. al. Both patents are incorporated by reference in their entirety. A physician may also select vector selection and program it via telemetry from a programmer.

“In addition to the minimum signal difference being described, the device could use other criteria for ranking vectors. One embodiment may calculate a maximum signal strength for each vector within the detection window. It will then determine the difference between each maximum amplitude, the sensing threshold, and determine a median maximum difference for each sensing channel over 15 cardiac cycles. The device will then choose the vector with the highest median maximum amplitude difference to use in subsequent arrhythmia detection and sensing. Another embodiment states that the maximum quality metric window amplitude may be subtracted or the maximum quality metric windows amplitude subtracted from a sense threshold at the time the maximum magnitude.

“The foregoing description contains specific embodiments and a method and apparatus to select a sensing configuration in a medical device. You are welcome to modify the embodiments mentioned without departing from what is disclosed in the claims.

Summary for “Methods and apparatus for adjusting the blanking period in transition between operating states in a device medical”

Implantable medical devices can be used to prevent or treat cardiac arrhythmias. They deliver anti-tachycardia pace therapies and electric shock therapies to defibrillate the heart. This device is commonly called an implantable cardioverter-defibrillator (?ICD?)). It senses the heart rhythm of a patient and classifies it according to various rate zones to detect fibrillation or tachycardia.

The ICD will deliver the appropriate therapy if it detects an abnormal rhythm. Anti-tachycardia pace therapy can often stop ventricular tachycardia. When necessary, anti-tachycardia pace therapies are followed up by high-energy shocked therapy. A shock therapy can be used to stop tachycardia. This is known as “cardioversion”. Ventricular fibrillation is a severe form of tachycardia and can be treated with high-energy shock therapy. Defibrillation is commonly used to refer to the termination of VF. Accurate arrhythmia detection and discrimination are important in selecting the appropriate therapy for effectively treating an arrhythmia and avoiding the delivery of unnecessary cardioversion/defibrillation (CV/DF) shocks, which are painful to the patient.”

In the past, ICD systems used intra-cardiac electrodes that were connected to transvenous leads to sense cardiac electrical signals and deliver electrical therapies. The new ICD systems can be subcutaneously or submuscularly implanted and use electrodes that are embedded on the ICD housing or carried by subcutaneous leads. These systems are referred to as “subcutaneous ICD” These systems are also known as?subcutaneous ICD? These systems do not require electrodes to be in direct contact with your heart. The SubQ ICD system is less invasive than ICDs that use intra-cardiac electrodes. They can be implanted quicker and more easily than ICD systems using intra-cardiac ones. Subcutaneous systems are more difficult to detect cardiac arrhythmias. A SubQ ECG signal might have a R-wave amplitude that is one-tenth to one hundredth as large as intra-ventricular R-waves. Subcutaneously sensed ECG signals may have a lower signal quality than intra-cardiac ECG signals.

The ECG signal characteristics of subcutaneous ICDs will determine their ability to detect tachyarrhythmias or reject noise. ECG vectors that have higher amplitude R wave waves, higher frequency (higher slewrate) R-waves and higher R/T waves ratios, lower frequency signals (e.g. P and T waves), around R-waves and lower susceptibility for skeletal myopotentials and greater Rwave consistency from cycle-to-cycle are preferable to those without these attributes. These physical vectors can be used by a subcutaneous ICD to generate virtual ECGs. The changing environment in a subcutaneous system can make it difficult to choose the best vector. It is therefore necessary to develop systems and methods for reliable and accurate detection of arrhythmias via optimal sensing vectors that can sense ECG signals using subcutaneous electrodes.

“FIG. “FIG. FIG. FIG. 1 shows an extravascular cardiac defibrillation device 10. It is an implanted, subcutaneous ICD. The techniques described in this disclosure can also be used with extravascular implanted cardio defibrillation devices, such as cardiac defibrillation units that have a lead placed at least partially in the substernal or submuscular locations. The techniques described in this disclosure can also be used with implantable systems such as implantable pacing and implantable neurostimulation system, drug delivery systems, or any other system that has leads, catheters, or other components implanted at extravascular locations. For illustration purposes, this disclosure is made in the context an implantable extravascular heart defibrillation device.

“Extravascular cardiac Defibrillation System 10 includes an implantable cardioverter (ICD), 14 that is connected to at most one implantable cardiac lead 16. FIG. 14 shows the ICD 14. Subcutaneously, 1 is placed on the left side patient 12. The medially connected defibrillation leads 16 and ICD 14 extend medially toward the sternum 28 of the patient. Near xiphoid Process 24, the defibrillation leads 16 bends or curves and extends substantially parallel to sternum 28, at a site near ICD 14. FIG. FIG.

The therapy vector is a line that runs from the defibrillation electrode 16 to a second electrode, such as a housing or ICD 25 of ICD 14, or an electrode on a second lead. It is approximately across the ventricle 26. One example of the therapy vector is a line that runs from the point on the defibrillation device 18 to the point on the housing, or can 25, ICD 14. Another example is that defibrillation leads 16 can be placed along the sternum 28 so that a therapy line between the defibrillation electrode 18, housing, or can 25 (or any other electrode) extends substantially across the atrium of the heart 26. Extravascular ICD 10 can be used in this instance to provide atrial therapies such as treatments for atrial fibrillation.

FIG. 1 illustrates the embodiment. FIG. 1 illustrates an example configuration for an extravascular ICD 10 and should not be taken as a limitation of the techniques described. FIG. 1 illustrates an example. However, it is shown as being offset laterally from sternum 28’s midline in FIG. Defibrillation leads 16 can be placed so that they are located more centrally over sternum 28, or to the right of Sternum 28. Defibrillation leads 16 can be placed so that they are not parallel to sternum 28. Instead, they may be offset at an angle from sternum28 (e.g., angled from sternum at either the distal or proximal ends). Another example is that the distal end defibrillation leads 16 could be placed near the patient’s second or third rib. The distal end defibrillation leads 16 can be placed near the second or third rib of the patient depending on where ICD 14 is located, location of electrodes 18, 20 and 22, or any other factors.

ICD 14 was shown as being placed near the midaxillary lines of patient 12 but it could also be implanted in other subcutaneous locations, such as farther posterior on the body toward the posterior axillary, further anterior on your torso towards the anterior axillary, in the pectoral region or other locations. Lead 16 will follow a different route if ICD 14 is placed pectorally. This would be, for example, along the inferior side of the sternum 28. The extravascular ICD 14 may also include a second lead with a defibrillation device that runs along the left side. This allows the second lead to be used as an anode/cathode in the therapy vector.

ICD 14 contains a housing (or can) 25 that acts as a hermetic seal to protect components. ICD 14’s housing 25 may be made of conductive material such as titanium, or any other biocompatible conductive material, or a combination conductive and nonconductive materials. The housing 25 of ICD 14 can be used as an electrode in some cases. This is known as a housing electrode, or can electrode. It may also be used with electrodes 20, 22, or 22 to deliver therapy to the heart 26 or sense electrical activity. ICD 14 may also contain a connector assembly (sometimes called a connector block, header), which includes electrical feedthroughs that allow for electrical connections between conductors in the defibrillation leads 16 and electronic components within the housing. One or more components may be enclosed in housing, such as processors, memories and transmitters, receivers and sensors, as well as sensing circuitry, therapy circuitry, and other appropriate components (often referred herein to simply “modules”).

“Defibrillation leads 16 include a lead body with a proximal and distal ends that connect to ICD 14 and one or more electrodes 18, 20 and 22. The defibrillation leads 16 can be made from non-conductive materials such as silicone, fluoropolymers and mixtures thereof. They are shaped to create one or more lumens that the conductors extend within. These techniques are not the only ones. Defibrillation leads 16 are shown as having three electrodes 18, 20, and 22, but there may be more or less electrodes.

“Defibrillation leads 16 include one or more elongated electric conductors (not shown) that extend from the connector at the proximal end to the electrodes 18, 20, and 22. The one or more elongated electric conductors within the lead body 16 of defibrillation leads 16 can be contacted with the respective electrodes 18, 20, and 22. The connector at the proximal tip of defibrillation leads 16 can be connected to ICD 14. When this connector is connected, the respective conductors could electrically couple with circuitry such as a therapy or sensing module of ICD 14 through connections in the connector assembly. The therapy module of ICD 14 transmits therapy to one or several electrodes 18-20 and 22. Sensing modules within ICD 14 receive electrical signals from one of the electrodes 18-20 and 22.

ICD 14 can sense electrical activity of the heart 26 using one or more sensing channels that include combinations between electrodes 20 and 22, and the housing, or can 25 of ICD 14 ICD 14 can sense electrical activity of the heart 26 using one or more sensing vectors that include combinations of electrodes 20-22 and the housing, or can 25 ICD 14. ICD 14 can sense electrical signals using a sensor vector between electrodes 20-22 or can 25 ICD 14. ICD 14 can sense electrical signals using a sense vector between electrodes 22 and the housing, or can 25 ICD 14; or electrical signals using a sense vector between the electrode 22 and the housing, or can 25 ICD 14 or any combination thereof ICD 14 can sense cardiac electrical signals in certain instances. This could be done using a sensing channel that includes defibrillation electro 18, such as between electrode 18 (or 20) and an electrode 22 (or can 25 of ICD 14).

“ICD can analyze the electrical signals that are being sent to it to detect tachycardia. In response, ICD may produce and deliver electrical therapy to the heart 26. ICD 14 could deliver one or more defibrillation shocked via a therapy vector which includes the defibrillation electrode 18, defibrillation leads 16 and can 25, for example. For example, a defibrillation electrode 18 could be an extended coil electrode or another type of electrode. ICD 14 may deliver one of several pacing therapies before or after the delivery of defibrillation shock. These include anti-tachycardia pacing or post shock pacing. ICD 14 can generate and deliver pacing pulses using therapy vectors that include either one or both electrodes 20 or 22 and/or the housing/can 25. The electrodes 20 and 22 can include ring electrodes or hemispherical or coil electrodes. They may also contain segmented or directional electrodes. Although electrodes 20 and 22 can be of the same type or different types, the FIG. Both electrodes 20 and 22, are shown as ring electrodes.

An attachment feature 29 may be included in “Defibrillation Lead 16” at the distal end. Attachment feature 29 could be a loop or link, or any other attachment feature. Attachment feature 29 could be, for example, a loop made by a suture. Attachment feature 29 could also be a link, loop, ring, ring of metal, covered metal or polymer. Attachment feature 29 can be made into any number of shapes, with uniform thickness or varying dimensions. Attachment 29 can be integrated into the lead or added by the user before implantation. Attachment feature 29 can be used to assist in the implantation of lead 16 or to secure lead 16 at a desired location. Sometimes, the attachment mechanism may be used in conjunction with or instead of the attachment function. Defibrillation leads 16 are illustrated with attachment features 29. However, other examples may not show an attachment feature 29.

“Lead 16 could also contain a connector at its proximal end, such as a DF4 or bifurcated connector (e.g. DF-1/IS-1 connector) or any other type of connector. A terminal pin may be attached to the connector assembly of ICD 14 at the connector’s proximal end. Lead 16 may have an attachment feature at its proximal end that can be used to attach an implant tool. The connector may seperate from the attachment feature at the lead’s proximal end. It may be integral to the lead, or may be added by the user before implantation.”

“Defibrillation leads 16 may include a suture-sleeve, or other fixation mechanism (not illustrated), located near electrode 22. This is designed to fixate lead 16 close to the xiphoid process and lower sternum locations. The user may add or modify the fixation mechanism, such as a suture sleeve.

FIG. 1 illustrates an example. “The example illustrated in FIG. 1 is an example and should not be taken to limit the techniques described herein. Extravascular cardiac defibrillation systems 10 could include multiple leads. Extravascular cardiac defibrillation systems 10 could include a pacing and defibrillation leads 16.

FIG. “In the example illustrated in FIG. 1, the defibrillation leads 16 are placed subcutaneously. Other times, optional pacing leads and defibrillation led 16 may be placed at extravascular locations. One example is that defibrillation leads 16 can be placed at least partially in the substernal area. This configuration allows at least part of the defibrillation device 16 to be placed below or above the mediastinum, and more specifically, the anterior mediastinum. Anterior mediastinum is bordered laterally by the pleurae, posteriorly and anteriorly, respectively, by the pericardium and sternum 28. The defibrillation leads 16 can be implanted at least partially in extra-pericardial areas, i.e. locations that are not directly in contact with the outer surface 26 of the heart. Other extra-pericardial locations include the mediastinum and the area offset from the sternum 28, the superior mediastinum and the middle mediastinum. Also, the sub-xiphoid/inferior xiphoid region, near the apex, may be used. The lead can also be placed at an epicardial or pericardial location other than the heart 26.

“FIG. “FIG. FIG. FIG. 2 shows the subcutaneous device 14. It includes a low voltage battery (153) and a power supply. This supply supplies power to both the circuitry of subcutaneous device 14, as well as the pacing output caps to provide pacing energy. For example, the low voltage battery 153 could be made of one or more conventional LiCFx, LiMnO2 and LiI2 cells. Subcutaneous device 14 also contains a high-voltage battery 112, which may be made of one or more conventional LiSVO cells or LiMnO2 cell. FIG. 2 shows a low voltage battery as well as a high-voltage battery. 2. According to one embodiment of the invention, the device 14 could use a single battery for high and low voltage purposes.

Refer to FIG. 2, subcutaneous device 14 functions are controlled by means of software, firmware and hardware that cooperatively monitor the ECG signal, determine when a cardioversion-defibrillation shock or pacing is necessary, and deliver prescribed cardioversion-defibrillation and pacing therapies. Circuitry described in U.S. Pat. 14 may be included in the subcutaneous device 14. No. No. U.S. Pat. No. No. 5,188,105?Apparatus & Method for Treating Tachyarrhythmias? to Keimel for selectively delivering single phase, simultaneous biphasic and sequential biphasic cardioversion-defibrillation shocks typically employing ICD IPG housing electrodes 28 coupled to the COMMON output 123 of high voltage output circuit 140 and cardioversion-defibrillation electrode 24 disposed posterially and subcutaneously and coupled to the HVI output 113 of the high voltage output circuit 140.”

“The cardioversion-defibrillation shock energy and capacitor charge voltages can be intermediate to those supplied by ICDs having at least one cardioversion-defibrillation electrode in contact with the heart and most AEDs having cardioversion-defibrillation electrodes in contact with the skin. ICDs that use most biphasic waveforms have a maximum voltage of approximately 750 Volts and an associated maximum energy around 40 Joules. The average maximum voltage required for AEDs is between 2000 and 5000 Volts. This can vary depending on the model and waveform. Subcutaneous device 14 according to the present invention can use maximum voltages between 300 and approximately 1500 Volts. It also has energies between 25 and 150 joules. The total high voltage capacitance may range from 50 to 300 microfarads. Such cardioversion-defibrillation shocks are only delivered when a malignant tachyarrhythmia, e.g., ventricular fibrillation is detected through processing of the far field cardiac ECG employing the detection algorithms as described herein below.”

“In FIG. 2. The sense amp 190 is used in conjunction with pacer/device circuit 178 to process the far field ECG sensor signal. This sense signal is generated across a specific ECG sense vector that is defined by one pair of subcutaneous electrodes 18, 22, and the can or housing 25. Or, an optional virtual signal (i.e. a mathematical combination between two vectors), if chosen. The device can generate a virtual vector signal, as described in U.S. Pat. No. No. Lee, et. al. incorporated herein as a reference in its entirety. A physician may also select vector selection and program it via a telemetry connection to a programmer.

“The switch matrix/MUX 191 selects the sensing electrode pair to detect the ECG signal of concern. This is the R wave for patients at high risk of sudden death from ventricular fibrillation. The far-field ECG signals are transmitted through the switch matrix/MUX 191 into the input of sense amplifier 190. This, along with pacer/device Timing Circuit 178, evaluates the detected ECG. The escape interval timer in the pacer timing circuit (178) and/or control circuit (144) are used to determine Bradycardia or asystole. When the interval between successive R waves exceeds the escape interval, Pace Trigger signals are applied on the pacing pulse generator 192. This generates pacing stimulation. Bradycardia pacing is often temporarily provided to maintain cardiac output after delivery of a cardioversion-defibrillation shock that may cause the heart to slowly beat as it recovers back to normal function. The use of U.S. Pat. 103-106 may help in the detection of subcutaneous far field signals when there is noise. No. No. Lee, et. and incorporated herein as reference in its entirety.”

“Detection and treatment of malignant tachyarrhythmias is done in the Control circuit. This is determined by the intervals between R wave sense event signals, which are output from the pacer/device timer timing 178 and the sense amplifier circuit circuit 190 to control and timing circuit 144. The present invention does not only use interval-based signal analysis, but also uses supplemental sensors and morphology processing methods and apparatus.

“Supplemental sensors, such as tissue color, oxygenation, respiration, and patient activity, may be used to help make the decision whether to apply or withhold defibrillation therapy, as described in U.S. Pat. No. No. Alt, and are incorporated by reference in their entirety. Sensor processing block 194 transmits sensor data via data bus 140 to microprocessor 142. The apparatus and method described in U.S. Pat. may be used to determine patient activity and/or position. No. No. Sheldon, and is incorporated by reference in its entirety. The apparatus and method described in U.S. Pat. may be used to determine patient respiration. No. 4,567,892 ?Implantable Cardiac Pacemaker? Plicchi, et. al. are incorporated by reference in their entirety. The sensor apparatus and method described in U.S. Pat. may be used to determine patient tissue oxygenation or tissue colour. No. No. 5,176,137 to Erickson et al. and incorporated by reference in its entirety herein. The oxygen sensor in the ‘137 patent could be found in the subcutaneous device pouch or on the lead 18. This allows for the detection of oxygenation or color of tissue contact or near-contact.

“Certain steps are performed cooperatively in microcomputer142. This includes microprocessor RAM and ROM. As well as associated circuitry and stored detection criteria. These may be programmed into RAM using a telemetry interface (not illustrated) that is standard in the art. Microcomputer 142, timing and control circuits 144, 178, pacer timing/amplifier and circuit 140 are able to exchange data and commands via a bidirectional data/control bus. The control circuit 144 and pacer timing/amplifier circuits 178 are both clocked at a slower clock rate. The microcomputer 142 sleeps normally, but it is awakened by interrupts from each R-wave event. These interrupts are received upon receipt of downlink telemetry programming instructions or cardiac pacing pulses. This allows the microcomputer to perform any mathematical calculations, update the time intervals controlled and monitored by pacer/device timing circuitry (178).

“When malignant tachycardia occurs, high voltage capacitors 156-158, 160- and 162 are charged to a preset voltage level using a high-voltage charger 164. It is considered inefficient to keep a constant charge on high voltage output capacitors 160, 156 and 162. Instead, the charging process is initiated by control circuit 144 issuing a high voltage charge order HVCHG on line 145 to high-voltage charge circuit 162. Charging is controlled using bi-directional control/databus 166 and a feedback sign VCAP from HV output circuit 140. The high voltage output capacitors 156 to 158, 160, 162 can be made of aluminum electrolytic, film or wet tantalum.

“The negative terminal on high voltage battery 112 can be directly connected to system ground. The switch circuit 114 is usually open so that high voltage battery 112’s positive terminal is not connected to the positive power input of high voltage charger circuit 164. Conductor 149 connects to switch circuit circuit 114. The high voltage command HVCHG is also carried via switch circuit. Switch circuit 114 closes when positive high voltage battery voltage EXTB+ is connected to the positive power input to high voltage charger circuit 164. For example, switch circuit 114 could be a field effect transistor. Its source-to-drain path may interrupt the EXT-B+ conductor 118, and its gate receives the HVCHG signal from conductor 145. The high voltage charge circuit (164) is now ready to start charging the high-voltage output capacitors 156 and 158 with high voltage battery 112.

“High voltage output capacitors 156, 158, 160, and 162 may be charged to very high voltages, e.g., 300-1500V, to be discharged through the body and heart between the electrode pair of subcutaneous cardioversion-defibrillation electrodes 113 and 123. It is not necessary to know the details of the voltage charging circuitry in order to practice the invention. One high voltage charging circuit that is believed to be suitable for the purpose of the invention has been disclosed. The high voltage capacitors 156 to 160, 160, 162 and 160 can be charged by, for example, the high voltage charge circuit (164) and a high frequency high-voltage transformer (168), as detailed in U.S. Patent. No. 4,548,209 ?Energy Converter for Implantable Cardioverter? to Wielders, et al. Diodes 170 to 172, 174, 174, and 176 are used to maintain proper charging polarities. They connect the high-voltage transformer’s output windings 168 and the capacitors 156. The high voltage output circuit 140 provides a VCAP feedback signal that indicates the voltage to the timing control circuit 144. Timing and control circuit 144 terminates the high voltage charge command HVCHG when the VCAP signal matches the programmed capacitor output voltage, i.e., the cardioversion-defibrillation peak shock voltage.”

“Control circuit 144 then generates the first and second control signals, NPULSE 1, and NPULSE 2. These signals are applied to high voltage output circuit 140 in order to trigger the delivery of defibrillating or cardioverting shocks. The NPULSE1 signal triggers the discharge of the first capacitor bank (comprising capacitors 156 and 158). The NPULSE2 signal causes the discharge of the first and second capacitor banks, which are comprised of capacitors 160 and 162. You can choose from a variety of output pulse modes by changing the time order and number of assertions of the NPULSE1 and NPULSE2 signals. The NPULSE 1 and NPULSE2 signals can be delivered sequentially, simultaneously, or individually. In this way, control circuitry 144 serves to control operation of the high voltage output stage 140, which delivers high energy cardioversion-defibrillation shocks between the pair of the cardioversion-defibrillation electrodes 18 and 25 coupled to the HV-1 and COMMON output as shown in FIG. 2.”

“Thus, subcutaneous device 14 monitors the patient’s cardiac status and initiates the delivery of a cardioversion-defibrillation shock through the cardioversion-defibrillation electrodes 18 and 25 in response to detection of a tachyarrhythmia requiring cardioversion-defibrillation. The high HVCHG signal causes high voltage battery 112 and high voltage charge circuit 164 to be connected. This allows for the charging of output capacitors 160, 156, 160 and 162 to begin. The charging continues until the programed charge voltage has been reflected by VCAP signal. At that point control and timing circuits 144 lower the HVCHG signal to terminate charging and open switch circuit 114. Subcutaneous device 14 can either be programmed to deliver cardioversion shocks directly to the heart using the timed synchrony described above. Episode data related to the detection of the tachyarrhythmia and delivery of the cardioversion-defibrillation shock can be stored in RAM for uplink telemetry transmission to an external programmer as is well known in the art to facilitate in diagnosis of the patient’s cardiac state. The patient who receives the device 14 prophylactically would be asked to report any such episodes to their physician. This will allow them to further evaluate the patient’s condition, and determine if an ICD is needed.

“There are many telemetry systems that provide the required communications channels between an external program unit and an implanted gadget. These systems are well-known in the art. The following U.S. Patent discloses telemetry systems that are believed to be suitable for practicing the invention. No. Wyborny and al. 5,127,404 entitled “Telemetry Format for Implanted Medical Equipment?” ; U.S. Pat. No. No. ; and U.S. Pat. No. Thompson et.al. entitled “Telemetry System to a Medical Device?”. Wyborny et al. Thompson et.al. The ‘063 patents are often assigned to the assignees of the present invention and are hereby incorporated in their entirety.

“According to an embodiment, the invention requires an index of merit to evaluate the quality of the signal in order to select the preferred ECG vector sets automatically. ?Quality? Quality is the ability of the signal to accurately estimate heart rate and distinguish between patient’s normal sinus rhythm and patient’s ventricular tapyarrhythmia.

“R-wave amplitude, Rwave peak amplitude to waveform ampltude between Rwaves (i.e. signal to noise ratio), low-slope content, relative high frequency power versus low frequency, mean frequency estimation and probability density function are some examples of appropriate indices.”

“Automatic vector selection can be performed at implantation, or periodically (daily/weekly/monthly), or both. Automatic vector selection can be performed at implant as part of the automatic device turn-on procedure. This performs activities such as measuring lead impedances or battery voltages. The implanting physician can initiate the device turn-on procedure by pressing a button or alternatively it may be initiated automatically upon detection of device/lead placement. In order to ensure that the ECG vector quality of the patient and the device/lead position are adequate, the turn-on procedure can also be used the automatic vector selection criteria. This ECG quality indicator allows the implanting physician the ability to move the device to a different orientation or location to increase the quality of ECG signals. The device turn-on procedure may include the selection of the preferred ECG vector or vectors. These vectors may be the ones that provide maximum rate estimation and detection accuracy. The physician may choose to use an apriori set of vectors. As long as they are not less than a certain threshold or are slightly better than other vectors, those vectors will be chosen. Some vectors might be almost identical, so they are not tested unless their a priori chosen vector index falls below a predetermined threshold.

“Depending on the metric power consumption and the power requirements of your device, the ECG signal metric quality may be measured using a range of vectors or a subset as often as you wish. Data can be collected on a daily, weekly, monthly, hourly or daily basis. You may also be able to take more frequent measurements, such as every minute, and use them to determine the susceptibility of vectors for occasional noise, motion noise or EMI.

“Alternatively, the 14-inch subcutaneous device may include an indicator/sensor for patient activity (piezoresistive or accelerometer, or the similar) that delays automatic vector measurement between periods of high or low patient activity and periods of minimal or no activity. A typical scenario would be to test/evaluate ECG vectors daily or weekly, while the patient is asleep. This could be done using an internal clock (e.g. 2:00 AM) or by inferring sleep via a 2-axis accelerometer and a lack or activity. Another scenario is to test/evaluate ECG vectors once a week or every other day while the patient exercises.

“If periodic, infrequent, automatic measurements are taken, it might also be worthwhile to measure noise (e.g. muscle, motion, EMI etc.). You can then delay the vector selection measurement until the noise has subsided.

Subcutaneous device 14 may optionally include a sensor that measures the patient’s position (via a 2-axis accelerometer). This sensor can be used to verify that differences in ECG quality do not just result from changing posture/position. The sensor can be used to collect data in several postures. ECG quality may then be averaged, combined or selected for a preferred position.

“One embodiment allows for vector quality metric calculations to be done by the clinician either at the time the implant is placed, during a follow-up visit in a clinic setting or remotely using a remote link between the programmer and the device. Another embodiment allows the device to automatically calculate the vector quality metrics for each sensing vector. This could be done multiple times per day, once per week, or monthly. The values can also be averaged over the course of a week for each vector, for example. Averaging can be either a moving average, or a recursive average, depending on memory and time weighting.

“FIG. “FIG. FIG. FIG. 3 shows how the device senses the cardiac signal for each vector available. It does this using sensing techniques that are known in the art. No. No. FIG. FIG. 3 shows an example of how the device can sense an ECG signal 100. It includes a horizontal sensing channel 102 that extends between the housing, can 25, and electrode 22, and a diagonal sensing track 104 that extends between the electrode 20 and 25. A vertical sensing track 106 runs between electrodes 20 through 22. When the detected signal exceeds a time dependent self-adjusting threshold 110, the device detects an R-wave 108.

“Once R-wave108 has been sensed, the device creates a vector quality measurement detection window 112 using the sensed Rwave108 for each sensing vector 102-106. This is used to determine a vector quality measure associated with the sensing Vectors 102-106. A device, according to one embodiment, sets a quality measurement detection window 112 at a predetermined distance of 116 from R-wave108. It also has a detection window width of 118 to allow analysis of signal 100 in the expected range of signal 100. This allows for a determination of a vector quality metric associated with sensing vectors 102-106. The device defines the quality-metric detection windows 112 to have a width of 200 ms. It also places a start point at 114 of the quality-metric detection windows 112 between 150-180 milliseconds and the sensed R?wave 108. The width 118 extends 200 ms from the detection point 114 to the detection end point 120. This is approximately 350-380ms from R-wave108. Another embodiment states that the width 118 extends approximately 270ms from the detection windows start point 114 and end point 120. This is roughly a distance of about 420-450ms from the R-wave 108. After the quality-metric detection window 112 has been set, the device determines the minimum signal difference (122) between the sensed signals 100 and 110 within the quality-metric detection window 112. This is the distance between the sensor 100 and 110 as described below.

“FIG. “FIG. FIGS. FIGS. 3 and 4. For each cardiac signal 100 derived from the respective sensing channels 102-106 the device determines the sensedR-wave108 of the cardiac signals 100, Block 200 and then sets the quality-metric detection window 112, Block 222. This is based on the sensedR-wave108 for the sensing vector 102-106. The quality metric window 112 has been located. Once that window is set, the device calculates the minimum signal deviation 122 between the detected cardiac signal 100, and the sensing threshold 110 for each sensing vector. Block 204. The stored minimum signal difference 122 is used to determine whether the minimum signal difference 122 has been established for the predetermined threshold number for each sensing vector 102-106. Block 206. If the minimum signal differ has not been determined for the threshold number of cardiac cycles each sensing Vector 102-106 No in Block 206 then the device receives the next R-wave 108 and repeats the process for the next sensed cardiac cycle each sensing Vector 102-106. One embodiment states that the minimum signal difference of 122 is calculated for 15 cardiac cycles.

“Once the minimum sign difference 122 has been established for all predetermined threshold numbers of cardiac cycles, Yes, in Block 206 the device determines a vector selection metric (102-106) based on the 15 minimum signals differences 122 for each vector. Block 208 In one embodiment, the device determines a median of 15 minimum signal difference 122 for each sensing channel and sets the vector selection metrics for that sensing vector equal the determined median of associated minimum signal differences. The device then ranks the vector selection metrics of the sensing channels 102-106 in Block 220. In the example shown in FIG. 3, the device ranks the selected vector selection metrics from highest-to-lowest. 3. The diagonal sensing 104 would rank highest, as the median signal difference for this vector was 0.84 milivolts. The horizontal sensing 102 would rank second, because the median signal difference is 0.82 milivolts. And the vertical sensing 106 would rank third, as the median signal difference is 0.55 milivolts.

“Once Block 210 has been ranked, the device chooses which sensing vector(s), to use during the subsequent sensing and arrhythmia detection. Block 212 follows. Depending on how long it takes between updating the sensing vectors 102?106, the device will wait until Block 214 to determine the next vector selection determination.

“FIG. “FIG. FIGS. FIGS. 3 and 5 illustrate another embodiment. The device determines the sensing vector 102 to 106 for each cardiac signal 100 and then sets the quality-metric detection window 112, Block 300. This is based on the sensing vector 102 to 106’s sensed R wave 108. The quality metric window 112 has been located. Once this window is set, the device determines what the minimum signal difference is between the sensed heart signal 100 and the threshold 110 in the quality measurement detection window 112. This window covers the sensing vectors 101-106. Block 304. The device stores the determined minimum signal differential 122 and determines whether the minimum sign difference 122 has been calculated for a predetermined threshold amount of cardiac cycles for each sensing channel 102-106 (Block 306).

“If the minimum signal differ 122 is not determined for the threshold number 102-106 of cardiac cycles, No in Block 306, then the device determines if a predetermined timer has expired. Block 308. The device receives the next R-wave108 for each sensing channel 102-106 if the timer hasn’t expired. If it has, Block 308 determines whether the predetermined timer has expired. This is then repeated for the next cardiac cycle for each sensing vector 102-106. One embodiment states that the Block 308 timer is set at 40 seconds.

“In some cases, the device might not have been able to obtain minimum signal differences 122 for one of the sensing Vectors. Therefore, if Block 308 has expired, the device determines whether at least two of the sensing Vectors 102-106 were obtained. Block 314. If the minimum signal differences were not achieved for at least two of the sensing channels, i.e. for one or none of the sensing Vectors 102 to106, then Block 308 is used. Block 310 determines whether no sensing can be made. Block 310 waits for the next scheduled vector selection determination. Block 312 will repeat the process.

“If at least two of the sensing channels 102-106 had the minimum signal differences, then Block 314, the device selects the Block 320 sensing vectors to be used during the subsequent arrhythmia detection and sensing. The device waits for Block 312, which is the next scheduled vector selection determination. This time, it depends on how long the updating of the sensing Vectors 102-106 takes.

“If the minimum signal differential 122 has been calculated for the predetermined number 102-106 of cardiac cycles, then yes, in Block 306, the device calculates a vector selection metric based on the 15 minimum signals differences 122 for each vector, Block 316. In one embodiment, the device determines a median of 15 minimum signal difference 122 for each sensing channel and sets the vector selection metrics for that sensing file equal to the determined median value of the minimum signal differences. The device then ranks the vector selection metrics of the sensing channels 102-106 in Block 316. In the example shown in FIG. 3, the device ranks the selected vector selection metrics from highest-to-lowest. 3. The diagonal sensing 104 would rank highest, as the median signal difference for this vector was 0.84 milivolts. The horizontal sensing 102 would rank second, because the median signal difference is 0.82 milivolts. And the vertical sensing 106 would rank third, as the median signal difference is 0.55 millivolts.

“Once the Block 318 sensing vectors are ranked, the device selects which sensing vector(s), to be used during the subsequent sensing and arrhythmia detection. Block 320. Another embodiment allows the user to choose the sensing vectors by displaying the ranking results, such as on a programmer. The device waits for Block 312, which is the next scheduled vector selection determination. This time, it depends on how long the updating of the sensing Vectors 102-106 takes. Another embodiment allows the user to manually initiate the vector selection procedure. The device will wait for input from the user before proceeding with the next scheduled vector selection.

“FIG. “FIG. 6” is a flowchart showing a method of selecting one or more sensing channels according to another exemplary embodiment. In some cases, the device might not have been able obtain the minimum signal difference 122 required for one or more sensing vectors. There may also be cases where the minimum signal differences 122 for one or several cardiac cycles in the sensing vectors 101-106 are equal to zero if the ECG signal is greater or equal to the threshold in one or multiple cardiac cycles, or during the quality metric sensoring window 112. These instances of zero minimum signals differences could be due to T-wave oversensing or frequent premature ventricular contractions.

According to FIGS. 3. and 6. For each cardiac signal 100 derived from the respective sensing channels 102-106 the device determines the sensedR-wave108 of the cardiac signals 100, Block 400 and sets the quality-metric detection window 112, block 402, based upon the sensedR-wave108 for the sensing vector 102?106 as described above. The quality metric window 112 has been located. Once that window is set, the device calculates the minimum signal deviation 122 between the detected cardiac signal 100, and the sensing threshold 110 in the quality-metric detection window 112. This is for each of the sensing channels 102-106. Block 404 The device also determines whether there was a zero minimum signal differential during Block 416 for each of the sensing vectors 102-106. If there is no minimum signal difference, the block 416 Block is cleared. The R-wave associated to that vector is then discarded. Block 418 Block is used to determine if a timer is expired.

“If there was no zero minimum signal deviation during the detection window 112 No in Block 416 the device determines if the minimum signal differ 122 has been determined for a threshold number of cardiac cycle, Block 406, i.e. such 15 cardiac cycles. The device will determine whether the timer has expired if the minimum signal difference (122) has not been established for each sensing vector from 102 to106. If the timer hasn’t expired, No. in Block 408 the device receives the next R-wave108 for each sensing Vector 102-106. The process is repeated for the next sensed cardiac cycle 102-106. One embodiment states that the Block 408 timer is set at 40 seconds.

“If the timer is over, yes in Block 408, the device checks to see if the minimum signal difference was achieved for at least two of the sensing vectors (102-106, Block 414). If the minimum signal differences were not achieved for at least 2 sensing channels, i.e. for one or none the sensing Vectors 102-106 Block 414, then the device determines that no sensing can be made. Block 410. Depending on how long it takes between the updating of the sensing vecs 102 to 106, the device waits for the next vector selection determination Block 412. At which point the vector selection process will be repeated.

“If at least two of the sensing channels 102-106 had the minimum signal differences, then Block 414 says that the device will select those sensing vectors from Block 320 for use in subsequent arrhythmia detection and sensing. The device waits for Block 412 to determine the next vector selection determination. This is depending on how long it takes between the updating of the sensing Vectors 102-106.

“If the minimum signal differential 122 has been calculated for the threshold number 102-106 of cardiac cycles, then yes in Block 406, the device calculates a vector selectionmetric for each vector from 102 to 106 based upon the 15 minimum signal differences for that vector (Block 420). In one embodiment, the device determines a median of 15 minimum signal difference 122 for each sensing channel and sets the vector selection metrics for that sensing vector equal the determined median of associated minimum signal differences. The device then ranks the vector selection metrics of the sensing channels 102-106 in Block 422, once a single vector selectionmetric has been determined. The device will rank the selected vector selection metrics in Block 420 from highest to least. In the example shown in FIG. 3. The diagonal sensing 104 would rank highest, as the median signal difference for this vector was 0.84 milivolts. The horizontal sensing 102 would rank second, because the median signal difference is 0.82 milivolts. And the vertical sensing 106 would rank third, as the median signal difference is 0.55 milivolts.

“FIG. “FIG.7 is a graphic representation of cardiac signals sensed along multiple sensor vectors during selections of a sensing channel in a medical device following another embodiment. FIG. FIG. 7 shows how the device detects a cardiac signal 500 during the vector selection process. This is for one or more available sensing vectors, as described above. An R-wave 508 signal is detected when the signal 500 exceeds a self-adjusting, time-dependent sensing threshold 510. The device senses an R-wave 508. It then sets a predetermined blanking time 509 and a quality window 512. These are based on the R-wave 508 sensed for each sensing vector 102-106. This is used to determine a vector quality measure associated with sensing vectors 102-106. One embodiment sets the blanking time 509 to extend a predetermined time period that starts at the R-wave 508 and ends at the blanking endpoint 511. The blanking time 509 could be set at 150 ms. However, any initial setting can be used. The current blanking period setting will determine the width of the blanking adjustment window 513. According to one embodiment, the blanking time is usually set between 150-180 ms. Therefore, 30 ms would be the blanking adjustment window 513 if the blanking duration was 150 ms. The blanking period adjustment window 513’s width (517) is determined by the chosen blanking period range.

The device also sets the quality-metric detection window 512 at the blanking time adjustment endpoint 514 with a detection window width of 518 to allow analysis of the signal 500 in the expected range of 500 where a T wave of the QRS signal is associated with the sensedR-wave 508 to occur. The device defines the quality-metric detection windows 512 to have a width of 200 ms. It also places the blanking time adjustment endpoint 514 at the start of the quality measurement window 512. The detection window width 518 extends 200 ms beyond the detection window stop point 515. This allows for analysis of the signal 500 within an expected range of the signal 500.

“FIG. 8 shows a flowchart showing a method of selecting one or more sensing channels according to an exemplary embodiment. FIGS. FIGS. 7 and 8 show that the device acquires a sensing vector 102-106 for each cardiac signal 500. Then, it sets the blanking adjustment window 513 for each sensing vector 102-106 and the quality measurement detection window 512 for Block 602. These are based on the sensing vector 102-106. The blanking adjustment window 513 is opened and the quality measurement detection window512 is closed. Once these windows are open, the device determines the minimum signal differences 519 between the detected cardiac signal 500, the sensing threshold510, and the sensing threshold510 within the blanking adjustment window 513, and the minimum signal differences 522 between each sensed vector’s sensed R-wave 508, Block 602. The stored minimum signal differences 519 & 522 are used to determine whether the minimum signal difference 519 & 522 have been established for a predetermined threshold amount of cardiac cycles, Block 606.

“If the minimum signal difference 519 or 522 has not been determined for the predetermined threshold amount of cardiac cycles for each sense vector 102 to106, No in Block 606 the device receives the next R-wave 508 for each sensing Vector 102-106 and this process is repeated for the next sensed cardiac cycle of each of the sensing channels 102-106. One embodiment states that the minimum signal differences 519 or 522 can be determined for 15 cardiac cycles.

“Once the minimum signals differences 519 and 522, have been determined for all predetermined threshold numbers of cardiac cycles, yes in Block 606, device determines a vector selectionmetric for each vector from 102 to 106 based upon the 15 minimum signal difference 522 for that vector (Block 608). In one embodiment, the device determines the median value of 15 minimum signal difference 522 for each sensing metric and sets the vector selection metrics for that sensing metric equal to the determined median value of the associated minimum signals differences 522. Once one vector selection metric has been determined for each sensing vector 102-106 in Block 608, it is used to rank the vector selection metrics for sensing vectors 101-106, Block 608. In the example shown in FIG. 7, the device ranks the selected vector selection metrics from highest-to-lowest. 7 would rank the diagonal sensing 104 highest, as the median signal difference was 0.86 millivolts. The horizontal sensing 102 would rank second, at 0.63 millivolts. Vertical sensing 106 would rank third, because the median signal difference is 0.32 millivolts.

“Once Block 610 has been ranked, the device will select the sensing vector(s), which will be used during the subsequent arrhythmia detection and sensing by the device, Block 612. The device can also determine whether the current blanking period exceeds a predetermined threshold that corresponds to a desired maximum period of time, i.e. 180 ms, as described above in Block 614. The amount of time between the updating of the sensing Vectors 102-106 will determine the time required. If the current blanking exceeds the threshold No in Block 614 then the device waits for the next scheduled vector selection determination. At that time, the vector selection process is repeated.

“If the current blanking exceeds the blanking threshold, yes in Block 614. The device calculates a blanking adjustment metric for each vector from 102 to 106 based upon the 15 minimum signal difference 519, Block 616. In one embodiment, the device determines a median of 15 minimum signal difference 519 for each sensing channel and adjusts the blanking period metric equal to the determined median value of the minimum signal differences 519. After determining a single blanking adjustment metric for each sensing vector 102-106 in Block 606, the device determines if an adjustment is needed for the sensing channels 102-106, Block 618. To avoid double counting R-waves, it is possible to increase the blanking period. One embodiment determines whether the blanking time should be adjusted from the current setting by determining, for each one of the highest ranked vectors in Block 610, if the determined blanking adjustment metric is less that a percentage of the corresponding determined vector select metric and less then a predetermined minimum blanking threshold.

FIG. 7 would rank the diagonal sensing vector 104 highest, as the median minimum sign difference for that vector was 0.86 milivolts. The horizontal sensing vektor 102 would rank second, since that vector’s median minimum signal differ is 0.63 milivolts. 7. The device determines if the blanking time adjustment metric calculated for the diagonal sensing vector 104 is less than half the vector selection metrics for that sensing vector, i.e. 0.63 millivolts and less that of 0.05 millivolts and less than half of that for that vector selection metric, metrics.

“If the blanking time adjustment metric is less than the predetermined percentage of one of two highest-ranked vectors, or is not lower than the predetermined minimal blanking threshold, No in Block 608, the device waits for the next scheduled vector selection determination. Block 622 is then used to repeat the vector selection process. The time between the updating of sensing vectors 101-106 will determine how long it takes for the next scheduled update to take place. It may be an hour, a weekend, or a month depending on what you have programmed.

“If the blanking time adjustment metric is lower than the predetermined percentage of one of two highest-ranked vectors or less than a threshold for the minimum blanking periods, Block 618 will update the blanking duration to Block 620. The blanking period can be extended to 180 ms or increased by a predetermined amount such as 10ms. Another embodiment states that instead of automatically increasing the blanking time, the device can generate an alarm or other stored indication that informs the attending physician that the blanking should be increased. This allows the user to adjust the blanking periods manually using a program or other input device.

“FIG. “FIG. FIG. FIG. 9 illustrates how the device can transition between a Not Concerned State 702, an Armed State 704, and an Armed State 704, according to one embodiment. U.S. Pat. No. No. 7,894,894 to Stadler and al., incorporated by reference in its entirety. During normal operation, the device is placed in the Not Concerned State 702. R-wave intervals are being evaluated for periods of rapid rate and/or asystole. The device moves from the Not Concerned state 702 to the Concerned state 704. If there are short R-wave intervals in two different ECG sensing vectors, it is indicative that an event may need therapy. The Concerned State 704 is where the device examines a predetermined range of ECG signals in order to detect if the signal has been corrupted by noise. This allows the device to distinguish rhythms that require shock therapy from others that don’t. It uses a combination R-wave intervals as well as ECG signal morphology information. No. No. No. No.

“If shock therapy is required, the device will transition from the Concerned State 700 to the Armed State 706. The device will return to the Not Concerned State 722, if a rhythm that requires shock therapy is not detected while it is in the Concerned State 7004 and the Rwave intervals are found to be no longer short. If a rhythm that requires shock therapy is not detected while the device remains in the Concerned State 704, and the R-wave intervals are determined to be short, the device returns to the Not Concerned State 702.

“In the Armed State 706 the device charges high voltage shocking capacitors. It continues to monitor R wave intervals and ECG signal structure for spontaneous termination. The device will return to the Not Concerned Status 702 if shock therapy is required for spontaneous termination. The device switches from the Armed State 706 to the Shock State 708. If shock therapy is required, but the rhythm is not stopped by the capacitors being charged, the device will return to the Not Concerned State 702. The shock state 708 is where the device delivers a shock, and then returns to the Armed State 706 for evaluation of the effectiveness of the therapy.

“FIG. “FIG. FIG. FIG. 10 illustrates how, according to one embodiment of the present disclosure. Block 802 uses the method described in U.S. Patent Application Ser. No. No. No. No. 7,894,894 to Stadler and al., both incorporated by reference in their entirety herein. According to one embodiment, the Concerned State 704 uses the most recent ECG data from both channels ECG1 or ECG2 while the device is there. This allows processing to be triggered in the Concerned State 704. The timeout is three seconds. While the processing is described as occurring over a period of three seconds, it is possible to choose other times for processing time when the Concerned States 304 is active. However, the preferred range should be between 0.5 and 10 seconds. The three-second timer ends after which individual R-waves can be sensed in channels ECG1 or ECG2 in the Concerned State 704. However, the possibility of changing to the Concerned State 704 to another state is limited. It is beneficial to process the latest three-seconds ECG data upon initial entry into the Concerned State 7004, i.e. ECG data for three seconds prior to the transition to Concerned State 704. This requires continuous circular buffering for the last three seconds of ECG data, even if you are in the Not Concerned States 702

“While in the Concerned Status 704, the device determines the sinusoidality and noise of the signals in the two sensing channel to determine whether a ventricular fibrillation or fast ventricular tapycardia (VT), event is likely. The signal’s sinusoidality and low noise indicate that there is a greater likelihood of VT/VF occurring. The device then classifies the sensing channel as either shockable, or not shockable based on the analysis. One embodiment of the invention may classify both ECG1 or ECG2 as either shockable, not shockable according to commonly assigned U.S. patent Ser. No. No. The device’s transition status from the Concerned State 704 to Block 804 is determined based on the classification of the current vectors as shockable or non-shockable.

“Example: According to an embodiment, the transition from ECG1 to ECG2 is confirmed if there are a predetermined number of segments of three seconds in each channel ECG1 or ECG2. This could be two out of three, for example. The device will transition from the Armed State 704 to ECG1 and ECG2 if the predetermined number three-second segments on both channels ECG1 or ECG2 has been classified as being shockable. If the predetermined number three-second segments on both channels ECG1 or ECG2 has not been classified shockable, then No in Block 804 the device transitions from the Concerned State 704 to the Armed State 706. A decision is made as to whether the device should transition back to the Not Concerned State 7002 in Block 806.

“Determining whether to transition from the Concerned State 704 back to the Not Concerned State 702 is done, for example, by determining if a heart beat estimate is less than the threshold level in at most one of the channels ECG1 or ECG2, as described on U.S. patent application S. No. No. No. 7.894,894 to Stadler and al., both incorporated by reference in their entirety. If the device is not to transition to the Not Concerned States 702, that is, if both the heart rate estimates exceed the threshold, No in Block806 is used. The process is then repeated with the signal generated in the next three-second window, which is Block 808. If the device is to be moved to the Not Concerned State 702 (i.e. both heart rate estimates exceed the threshold), Block 806 will determine if a Blanking Period adjustment was made in the Concerned State. Block 809 If the blanking time was adjusted, Block 809 states that the device adjusts it. Block 811. One embodiment may reduce the blanking time by a predetermined amount. Another example is that the device may reset the blanking to the original or nominal period used before the adjustment occurred while the device was in the Not Concerned State 702. If the blanking period was changed from 150 ms or 180 ms during operation of the device in the Concerned State 704 to Not Concerned State 702 (Yes in Block 809), the device will adjust the blanking period to the initial 150ms setting in Block 811. If the blanking time was not adjusted, No in Block 809, or once the blanking period is returned to its initial or nominal setting, Block 811, the device will be in the Not Concerned State.

“When the device switches from the Concerned State 704 to the Armed State 706 Yes in Block 804, processing is continued by a three second timeout as it was during the Concerned State. Once the device is in the Armed State 706 it can be determined if a blanking adjustment was made during the Concerned State 704. Block 810. If the blanking was adjusted, Block 810 will confirm that the blanking is being adjusted. Block 812. One embodiment states that the device can reduce the blanking time by a predetermined amount. Another example is that the device may reset the blanking to the original or nominal blanking periods used prior to the adjustment taking place in the Concerned State 704. If the blanking period was increased from 150 ms or 180 ms during operation in the Concerned State 704 to the Armed State 706 Yes in Block 804, the blanking period is adjusted to the initial 150ms setting. Block 812. Block 810 does not allow for the adjustment of the blanking time. Block 812 allows the device to adjust the blanking to period to the initial 150 ms setting.

“During the charging, the classifications of segments for each channel ECG1 or ECG2 as either shockable (or not) continues. After the next three seconds have been acquired using the adjusted Blanking Period, Block 802, a determination is made whether the event continues be a shockable. This is done by determining whether a predetermined amount of segments, such the last two segments, have been classified in both channels ECG1/ECG2 as not-shockable, Block 816. The event may not be shockable if the three second segments are classified as not shocking. Block 816 says “Yes.” and then the charging of capacitors is stopped. Block 818 states that a decision is made about whether or not to move to the Not Concerned States 702 and Block 820.

“Accordingly to an embodiment, the device will transition between the Armed State 706 and the Not Concerned State 7002, Yes in Block 820, provided certain termination requirements have been met. If, for both channels ECG1 or ECG2, less than two of the three-second segments that were in shock are available, less than three of the eight last three-second segments and less than three of the last eight are considered shockable, the latest three-second segment is not considered shockable. A fourth consecutive not-shockable classification in either channel ECG1 or ECG2 could be another possible criteria to return to the Not Concerned States 702.

“In addition the two criteria above, at least one current heart rate estimate must be slower that the programmed threshold and capacitor charging cannot be in progress.” If all of these conditions are met, Block 820 will allow the device to transition from the Armed State 706 to the Not Concerned State 7002.

“If any of these requirements is not met, a return to the Not Concerned state is not indicated. Block 820 then determines whether the shockable rhythm has been redetected. Block 822 does this by determining if predetermined redetection criteria have been fulfilled. A determination is made about whether there are a certain number of three-second segments in each of the channels ECG1 or ECG2, for example, two of the three most recent ones, that have been considered to be shockable. If the predetermined redetection criteria are not met, Block 802 will continue to determine whether therapy should be terminated. This is done so that processing switches from Block 820 to Block 822 to determine whether therapy should be terminated. Then, the decision as to whether shockable events can still be detected, Block 822. Until the event terminates, the device is switched from the Armed State 706 into the Not Concerned State 700 or the event is re-evaluated. If the predetermined redetection criteria are met, Block 822 will allow charging to be re-initiated (Block 814), and the process is then repeated.

“If the three predetermined segments of capacitor charging are not classified as not-shockable, No in Block 806, a determination is made about whether the capacitors have been charged. Block 824. The capacitor charging process continues as long as No in Block816 is being used. Next, a signal is generated in Block 828. Finally, once the capacitors have been charged, Yes in Block824, it is determined whether the delivery of therapy is appropriate. This is done by checking whether the predetermined delivery confirmation requirements are met. According to the embodiment of the invention, predetermined therapy delivery confirmations include determining whether at least five of the eight last three-second segments have been classified as shockable for either channel ECG1 or ECG2. At least two of the three last three-second segments have been classified as shockable. A determination is also made about whether the latest three-second segment was classified as being shockable by at least one channel ECG1 or ECG2.

“If the predetermined delivery requirements for therapy are not met, and the delivery of the therapy cannot be confirmed, No in Block826. The determination of whether the treatment should transition from the Armed State 702 to the Not Concerned State 7002, Block 820 is repeated. If the therapy delivery requirements have been met, then the delivery of the therapy can be confirmed in Block 826. The device will transition from the Armed State 702 to the Shock State 708.

“It is understood, in addition the three sensing signals 102-16, that may optionally be used, a virtual signal (i.e. a mathematical combination between two vectors) can also be used in place or in addition to the sensing vectors. The device could generate a virtual signal, as described in U.S. Pat. No. No. Lee, et. al. Both patents are incorporated by reference in their entirety. A physician may also select vector selection and program it via telemetry from a programmer.

“In addition to the minimum signal difference being described, the device could use other criteria for ranking vectors. One embodiment may calculate a maximum signal strength for each vector within the detection window. It will then determine the difference between each maximum amplitude, the sensing threshold, and determine a median maximum difference for each sensing channel over 15 cardiac cycles. The device will then choose the vector with the highest median maximum amplitude difference to use in subsequent arrhythmia detection and sensing. Another embodiment states that the maximum quality metric window amplitude may be subtracted or the maximum quality metric windows amplitude subtracted from a sense threshold at the time the maximum magnitude.

“The foregoing description contains specific embodiments and a method and apparatus to select a sensing configuration in a medical device. You are welcome to modify the embodiments mentioned without departing from what is disclosed in the claims.

Click here to view the patent on Google Patents.

What is a software medical device?

The FDA can refer to software functions that include ” Software As a Medical Device” and “Software in a Medical Device(SiMD)”, which are software functions that are integral to (embedded in a) a medical device.

Section 201(h),?21 U.S.C. 321(h),(1) defines a medical device to be?an apparatus, implements, machine, contrivances, implant, in vitro regulator, or other similar or related articles, as well as a component or accessory. . . (b) is intended for diagnosis or treatment of disease or other conditions in humans or animals. (c) Is intended to alter the structure or function of human bodies or animals. To be considered a medical device, and thus subject to FDA regulation, the software must meet at least one of these criteria:

• It must be used in diagnosing and treating patients.
• It must not be designed to alter the structure or function of the body.

If your software is designed to be used by healthcare professionals to diagnose, treat, or manage patient information in hospitals, the FDA will likely consider such software to be medical devices that are subject to regulatory review.

Is Your Software a Medical Device?

FDA’s current oversight, which puts more emphasis on the functionality of the software than the platform, will ensure that FDA does not regulate medical devices with functionality that could be dangerous to patient safety. Examples of Device Software and Mobile Medical Apps FDA is focused on

• Software functions that aid patients with diagnosed mental disorders (e.g., depression, anxiety, and post-traumatic stress disorder (PTSD), etc.) by providing “Skill of the Day”, a behavioral technique, or audio messages, that the user can access when they are experiencing anxiety.
• Software functions that offer periodic reminders, motivational guidance, and educational information to patients who are recovering from addiction or smokers trying to quit;
• Software functions that use GPS location data to alert asthmatics when they are near high-risk locations (substance abusers), or to alert them of potential environmental conditions that could cause symptoms.
• Software that uses video and games to encourage patients to exercise at home.
• Software functions that prompt users to choose which herb or drug they wish to take simultaneously. They also provide information about interactions and give a summary of the type of interaction reported.
• Software functions that take into account patient characteristics, such as gender, age, and risk factors, to offer patient-specific counseling, screening, and prevention recommendations from established and well-respected authorities.
• Software functions that use a list of common symptoms and signs to give advice about when to see a doctor and what to do next.
• Software functions that help users to navigate through a questionnaire about symptoms and to make a recommendation on the best type of healthcare facility for them.
• These mobile apps allow users to make pre-specified nurse calls or emergency calls using broadband or cell phone technology.
• Apps that allow patients or caregivers to send emergency notifications to first responders via mobile phones
• Software that tracks medications and provides user-configured reminders to improve medication adherence.
• Software functions that give patients access to their health information. This includes historical trending and comparisons of vital signs (e.g. body temperature, heart rate or blood pressure).
• Software functions that display trends in personal healthcare incidents (e.g. hospitalization rates or alert notification rate)
• Software functions allow users to electronically or manually enter blood pressure data, and to share it via e-mail, track it and trend it, and upload it to an electronic or personal health record.
• Apps that offer mobile apps for tracking and reminders about oral health or tools to track users suffering from gum disease.
• Apps that offer mobile guidance and tools for prediabetes patients;
• Apps that allow users to display images and other messages on their mobile devices, which can be used by substance abusers who want to quit addictive behaviors.
• Software functions that provide drug interaction and safety information (side effects and drug interactions, active ingredient, active ingredient) in a report based upon demographic data (age and gender), current diagnosis (current medications), and clinical information (current treatment).
• Software functions that allow the surgeon to determine the best intraocular lens powers for the patient and the axis of implantation. This information is based on the surgeon’s inputs (e.g., expected surgically induced astigmatism and patient’s axial length, preoperative corneal astigmatism etc.).
• Software, usually mobile apps, converts a mobile platform into a regulated medical device.
• Software that connects with a mobile platform via a sensor or lead to measure and display electrical signals from the heart (electrocardiograph; ECG).
• Software that attaches a sensor or other tools to the mobile platform to view, record and analyze eye movements to diagnose balance disorders
• Software that collects information about potential donors and transmits it to a blood collection facility. This software determines if a donor is eligible to collect blood or other components.
• Software that connects to an existing device type in order to control its operation, function, or energy source.
• Software that alters or disables the functions of an infusion pump
• Software that controls the inflation or deflation of a blood pressure cuff
• Software that calibrates hearing aids and assesses sound intensity characteristics and electroacoustic frequency of hearing aids.

What does it mean if your software/SaaS is classified as a medical device?

SaaS founders need to be aware of the compliance risks that medical devices pose. Data breaches are one of the biggest risks. Medical devices often contain sensitive patient data, which is why they are subject to strict regulations. This data could lead to devastating consequences if it were to become unprotected. SaaS companies who develop medical devices need to take extra precautions to ensure their products are safe.

So who needs to apply for FDA clearance? The FDA defines a ?mobile medical app manufacturer? is any person or entity who initiates specifications, designs, labels, or creates a software system or application for a regulated medical device in whole or from multiple software components. This term does not include persons who exclusively distribute mobile medical apps without engaging in manufacturing functions; examples of such distributors may include the app stores.

Software As Medical Device Patenting Considerations

The good news is that investors like medical device companies which have double exclusivity obtained through FDA and US Patent and Trademark Office (USPTO) approvals. As such, the exit point for many medical device companies is an acquisition by cash rich medical public companies. This approach enables medical devices to skip the large and risky go-to-market (GTM) spend and work required to put products in the hands of consumers.

Now that we have discussed the FDA review process, we will discuss IP issues for software medical device companies. Typically, IP includes Patents, Trademarks, Copyrights, and Trade secrets. All of these topics matter and should be considered carefully. However, we will concentrate on patents to demonstrate how careless drafting and lack of planning can lead to problems, namely unplanned disclosures of your design that can then be used as prior art against your patent application.

In general, you should file patent application(s) as soon as practicable to get the earliest priority dates. This will help you when you talk to investors, FDA consultants, prototyping firms, and government agencies, among others. Compliance or other documents filed with any government agency may be considered disclosure to third parties and could make the document public. In general, disclosures to third parties or public availability of an invention trigger a one year statutory bar during which you must file your patent application. Failure to file your application within the required time frame could result in you losing your right to protect your invention.

The information from your FDA application may find its way into FDA databases, including DeNovo, PMA and 510k databases and FDA summaries of orders, decisions, and other documents on products and devices currently being evaluated by the FDA. Your detailed information may be gleaned from Freedom of Information Act requests on your application. This risk mandates that you patent your invention quickly.

When you patent your medical device invention, have a global picture of FDA regulatory framework when you draft your patent application. Be mindful of whether your software/SaaS application discusses the diagnosing and treating patients or affecting the structure or function of the body and add language to indicate that such description in the patent application relates to only one embodiment and not to other embodiments. That way you have flexibility in subsequent discussions with the FDA if you want to avoid classification of your software/SaaS/software as a medical device. In this way, if you wish to avoid FDA registration and oversight, you have the flexibility to do so.

An experienced attorney can assist you in navigating the regulatory landscape and ensure that you comply with all applicable laws. This area of law is complex and constantly changing. It is important that you seek legal advice if you have any questions about whether or not your software should be registered with FDA.

Patent PC is an intellectual property and business law firm that was built to speed startups. We have internally developed AI tools to assist our patent workflow and to guide us in navigating through government agencies. Our business and patent lawyers are experienced in software, SaaS, and medical device technology. For a flat fee, we offer legal services to startups, businesses, and intellectual property. Our lawyers do not have to track time as there is no hourly billing and no charges for calls or emails. We just focus on getting you the best legal work for your needs.

Our expertise ranges from advising established businesses on regulatory and intellectual property issues to helping startups in their early years. Our lawyers are familiar with helping entrepreneurs and fast-moving companies in need of legal advice regarding company formation, liability, equity issuing, venture financing, IP asset security, infringement resolution, litigation, and equity issuance. For a confidential consultation, contact us at 800-234-3032 or make an appointment here.