Beat classification to avoid delivering a shock during ventricular repolarization

Abstract

Wearable, automatic external and implantable defibrillators and methods of operation in such systems are disclosed that have shock delivery mitigation measures to avoid delivering a defibrillation shock on a T-wave. One or more detected cardiac events are analyzed prior to the issuance of a defibrillation shock to characterize the detected event as sensed for the purpose of synchronizing a defibrillation shock. The detected event can be characterized as an R-wave or a T-wave and then a shock delivery protocol is selected based on the characterization of the detected event to avoid shocking T and potentially proarrhythmic.

Description

TECHNICAL FIELD

[0001] This application claims the benefit of and priority to U.S. Provisional Patent Application No. 63 / 089,152, filed October 8, 2020, and titled “CARDIAC BEAT CLASSIFICATION TO AVOID DELIVERING SHOCK DURING VENTRICULAR REPOLARIZATION,” the disclosure of which is incorporated herein by reference. BACKGROUND

[0002] External, wearable, and implantable defibrillators are used to correct a rapid heart rhythm, such as polymorphic ventricular tachycardia or ventricular fibrillation. In operation, the defibrillator senses the heart rhythm and determines if a defibrillation shock therapy is needed. Typically, if the defibrillator determines that a defibrillation shock is needed, a high power capacitor is charged to an appropriate energy or voltage level to effect defibrillation. Once the capacitor is ready to deliver therapy, the device senses the heart rhythm to detect a new cardiac cycle. If a cardiac cycle is detected, the defibrillator delivers a “synchronized” therapy after a short detection post-time interval expires. If a “beat” is not detected, a defibrillation therapy is delivered in an asynchronous manner after an override interval expires.

[0003] Despite decades of effort to ensure that fast, reliable, and accurate decisions are made, inappropriate shocks remain one of the most common adverse events associated with cardiac defibrillators. Inappropriate shocks cause patient distress, reduce the available battery capacity of the device, and can lead to deleterious psychological consequences. Moreover, in certain limited circumstances, an inappropriate therapy can be pro-arrhythmic, leading to the onset of ventricular fibrillation. For example, a pro-arrhythmic inappropriate shock occurs if a defibrillation shock occurs during a vulnerable time of a cardiac cycle, such as during a T-wave.

[0004] Mitigation measures are needed to reduce the likelihood of pro-arrhythmic defibrillation shocks. SUMMARY

[0005] The present inventors have recognized that, among other things, one cause of potential inappropriate shocks is sensing maladies, such as can occur if a defibrillator simultaneously senses an R-wave (ventricular depolarization) and a T-wave (ventricular repolarization) of the heart, which can cause the defibrillator to count a heart rate that is twice the actual heart rate. This overcounting can cause the defibrillator to falsely identify a need for therapy delivery, and subsequently prepare for and deliver a defibrillation shock. If overcounting of T-waves occurs, there is a risk that the shock therapy will be synchronized to the T-wave, thereby increasing the risk of inducing proarrhythmia. The present inventors have identified a need for mitigation strategies applicable to defibrillation shock synchronization that reduce the likelihood of proarrhythmia inappropriate shocks, and have developed such mitigation as described below.

[0006] A first illustrative and non-limiting example takes the form of a method of delivering a defibrillation shock in a defibrillator having electrodes for sensing a cardiac signal, analysis circuitry for analyzing the sensed cardiac signal, a therapy delivery capacitor for storing energy for a defibrillation shock, a charger for charging the therapy delivery capacitor, and a therapy output circuit for delivering a defibrillation shock using the energy stored on the therapy delivery capacitor; the method comprising: determining a need for a defibrillation shock, and charging the therapy delivery capacitor for defibrillation shock delivery to a predetermined shock threshold; after completing charging the therapy delivery capacitor to the predetermined shock threshold: sensing an Nth cardiac event; characterizing the Nth cardiac event as an R-wave or a T-wave; and: delivering the defibrillation shock according to a first shock protocol if the Nth cardiac event is an R-wave; or delivering the defibrillation shock according to a second shock protocol if the Nth cardiac event is a T-wave.

[0007] Additionally or alternatively, the step of characterizing the Nth cardiac event as an R-wave or a T-wave includes detecting at least one prior cardiac event, and determining one or more of an interval or an amplitude associated with the prior cardiac event that indicates whether the Nth cardiac event is to be characterized as an R-wave or a T-wave.

[0008] Additionally or alternatively, the step of characterizing the Nth cardiac event as an R-wave or a T-wave includes detecting at least one prior cardiac event, and analyzing a morphology of the at least one prior cardiac event to characterize the Nth cardiac event as an R-wave or a T-wave.

[0009] Additionally or alternatively, delivering the defibrillation shock according to the first shock protocol includes delivering the defibrillation shock after expiration of a first shock delay following the Nth cardiac event; and delivering the defibrillation shock according to the second shock protocol includes delivering the defibrillation shock after expiration of a second shock delay following the Nth cardiac event.

[0010] Additionally or alternatively, the method further includes calculating the second shock delay by: sensing each of N-1, N-2, and N-3 cardiac electrical events, where the N-1 cardiac electrical event precedes the Nth cardiac electrical event, the N-2 cardiac electrical event precedes the N-1 cardiac electrical event, and the N-3 cardiac electrical event precedes the N-2 cardiac electrical event, each of the Nth, N-1, N-2, and N-3 cardiac electrical events representing a consecutive detection of a cardiac event; determining an interval Ii, the interval Ii representing an interval from the N-1 cardiac electrical event to the Nth cardiac electrical event; determining an interval I2, the interval I2 representing an interval from the N-2 cardiac electrical event to the N-1 cardiac electrical event; determining an interval I3, the interval I3 representing an interval from the N-3 cardiac electrical event to the N-2 cardiac electrical event; and setting the second shock delay equal to {I2+I3-Ii}. Additionally or alternatively, the method can include calculating the first shock delay equal to an average of I2 and I3 minus Ii.

[0011] Additionally or alternatively, delivering the defibrillation shock according to the second shock protocol includes sensing a next cardiac electrical event, and: delivering the defibrillation shock after detecting the next cardiac electrical event, or delivering the defibrillation shock after expiration of a predetermined timeout interval without sensing another cardiac electrical event.

[0012] Additionally or alternatively, delivering the defibrillation shock according to the second shock protocol includes sensing a next cardiac electrical event and characterizing the next cardiac electrical event as an R-wave or a T-wave, and: if the next cardiac electrical event is an R-wave, delivering the defibrillation shock after the next cardiac electrical event using the first shock protocol; or if the next cardiac electrical event is a T-wave, then: sensing a subsequent cardiac electrical event after the next cardiac electrical event and delivering the defibrillation shock after detecting the subsequent cardiac electrical event, or delivering the defibrillation shock after expiration of a predetermined timeout interval without sensing another cardiac electrical event after the next cardiac electrical event.

[0013] Additionally or alternatively, the step of characterizing the Nth cardiac electrical event as an R-wave or a T-wave includes: sensing each of an N-1th and an N-2th cardiac electrical event, where the N-1th cardiac electrical event precedes the Nth cardiac electrical event and the N-2th cardiac electrical event precedes the N-1th cardiac electrical event, each of the Nth, N-1th and N-2th cardiac electrical events representing a consecutive detection of a cardiac event; observing an interval between the Nth and N-1th cardiac electrical events; determining an amplitude of each of the N-1th and N-2th cardiac electrical events; calculating a peak ratio as a ratio of the amplitude of the N-1th cardiac electrical event to the amplitude of the N-2th cardiac electrical event; determining whether the peak ratio falls within a similarity range, and: characterizing the Nth cardiac electrical event as a T-wave if the peak ratio falls within the similarity range, if the interval is within an R-T interval range, otherwise characterizing the Nth cardiac electrical event as an R-wave; characterizing the Nth cardiac electrical event as a T-wave if the peak ratio is above the similarity range, if the interval is within the R-T interval range, otherwise characterizing the Nth cardiac electrical event as an R-wave; or characterizing the Nth cardiac electrical event as an R-wave if the peak ratio is below the similarity range.

[0014] Additionally or alternatively, the method can further include calculating the R-T interval range by: sensing a reference cardiac electrical event; defining a refractory period and a T-wave period for identifying first and second peaks associated with the reference cardiac event; identifying a maximum peak during the refractory period as the first peak; identifying a maximum value during the T-wave period as the second peak; determining an R-T interval for the reference cardiac event as an interval between the first and second peaks; and setting the R-T interval range around the R-T interval.

[0015] Additionally or alternatively, the method can further include calculating the R-T interval range by: sensing a reference cardiac electrical event by observing a crossing of a cardiac event detection threshold by a cardiac electrical signal, and identifying a first time point at the crossing; defining a T-wave period for identifying a T-wave peak; identifying a maximum peak during the T-wave period, and identifying a second time point at the maximum peak during the T-wave period; determining an R-T interval for the reference cardiac event as an interval between the first and second time points; setting the R-T interval range around the R-T interval.

[0016] Additionally or alternatively, the method can include sensing at least an N-1th and an N-2th cardiac electrical event, where the N-1th cardiac electrical event occurs after the N-2th cardiac electrical event and before an Nth cardiac electrical event.

[0017] Additionally or alternatively, the step of characterizing the Nth ECG event as an R wave or T wave includes: calculating the rectified peak ratio of the N-1 and N-2 ECG events as the ratio of the maximum rectified peak value of the N-1 ECG event to the maximum rectified peak value of the N-2 ECG event; calculating the peak-to-peak ratio of the N-1 and N-2 ECG events as the ratio of the sum of the amplitudes of the maximum positive and negative peaks associated with the N-1 sensed ECG event and the sum of the amplitudes of the maximum positive and negative peaks associated with the N-2 ECG event; and observing the Nth and N-1 ECG events... The interval between electrical events; and: if the rectified peak ratio is within a first range, if the interval is within the RT interval range and the peak-to-peak ratio is above a second threshold, then the Nth ECG event is characterized as a T wave, or otherwise the Nth ECG event is characterized as an R wave; if the rectified peak ratio is below the first range, then the Nth ECG event is characterized as an R wave; if the rectified peak ratio is above the first range, if the interval is less than the RT interval estimate and the peak-to-peak ratio is above the second threshold, then the Nth ECG event is characterized as a T wave, or otherwise the Nth ECG event is characterized as an R wave.

[0018] Additionally or alternatively, the step of characterizing the Nth ECG event as an R wave or a T wave includes: observing the interval between the Nth and N-1th ECG events; determining the amplitude of each of the N-1th and N-2th ECG events; calculating the peak-to-peak ratio as the ratio of the amplitude of the N-1th ECG event to the amplitude of the N-2th ECG event; determining whether the peak-to-peak ratio falls within a similarity range, and: if the peak-to-peak ratio falls within a similarity range, and if the interval is within the RT interval range, then the Nth ECG event is characterized as a T wave, otherwise the Nth ECG event is characterized as an R wave; if the peak-to-peak ratio is above a similarity range, and if the interval is within the RT interval range, then the Nth ECG event is characterized as a T wave, otherwise the Nth ECG event is characterized as an R wave; or if the peak-to-peak ratio is below a similarity range, then the Nth ECG event is characterized as an R wave.

[0019] Additionally or alternatively, the method may further include sensing N-1 ECG events prior to the Nth ECG event, wherein the step of characterizing the Nth ECG event as an R wave or a T wave includes: determining the interval from the N-1 ECG event to the Nth ECG event; comparing the interval with a range of RT intervals; and if the interval is within the range of RT intervals, characterizing the Nth sensed ECG event as a T wave; otherwise, characterizing the Nth ECG event as an R wave.

[0020] Alternatively or additionally, the range and estimate of the RT interval can be calculated by analyzing one or more cardiac cycles.

[0021] Additional or alternative locations, RT interval range and RT interval estimation are preset.

[0022] Another illustrative, non-limiting example takes the form of an implantable defibrillator comprising: a plurality of electrodes adapted for implantation in a patient and configured to receive cardiac electrical signals and / or deliver a defibrillation shock; a hermetically sealed housing; operating circuitry disposed within the housing and coupled to the plurality of electrodes, the operating circuitry including a battery, analysis circuitry for analyzing cardiac signals from the electrodes, a therapeutic delivery capacitor for storing energy for the defibrillation shock, a charger configured to charge the therapeutic delivery capacitor using power from the battery, and a therapeutic output circuitry for delivering a defibrillation shock to the electrodes using the energy stored in the therapeutic delivery capacitor; wherein the operating circuitry is configured to perform the method described in any of the foregoing examples.

[0023] Additionally or alternatively, the implantable defibrillator may also include a lead coupled to the canister, wherein at least one of a plurality of electrodes is disposed on or on a portion thereof, and at least one of the plurality of electrodes is disposed on the lead, wherein the lead is adapted for subcutaneous placement, and the implantable defibrillator is a subcutaneous implantable defibrillator.

[0024] Additionally or alternatively, the implantable defibrillator may also include a lead coupled to the canister, wherein at least one of a plurality of electrodes is disposed on or on a portion of the housing, and at least one of the plurality of electrodes is disposed on the lead, wherein the lead is adapted for transvenous placement, with a portion of it located in the patient’s heart, and the implantable defibrillator is a transvenous implantable defibrillator.

[0025] Another illustrative, non-limiting example takes the form of a wearable defibrillator comprising: a vest carrying a plurality of electrodes and adapted to be worn by a patient such that at least two electrodes are in contact with the patient when worn; operating circuitry coupled to the plurality of electrodes, the operating circuitry including a battery, analysis circuitry for analyzing cardiac signals from the electrodes, a therapeutic delivery capacitor for storing energy for a defibrillation shock, a charger configured to charge the therapeutic delivery capacitor using power from the battery, and therapeutic output circuitry for delivering a defibrillation shock to the electrodes using the energy stored in the therapeutic delivery capacitor; wherein the operating circuitry is configured to perform the method described in any of the foregoing examples.

[0026] Another illustrative, non-limiting example takes the form of an automated external defibrillator (AED) comprising: a plurality of electrodes adapted for placement on a patient’s torso, wherein at least two electrodes are paddle electrodes adapted for external defibrillation; operating circuitry coupled to the plurality of electrodes, the operating circuitry including a battery, analysis circuitry for analyzing cardiac signals from the electrodes, a therapeutic delivery capacitor for storing energy for defibrillation shocks, a charger configured to charge the therapeutic delivery capacitors using power from the battery, and therapeutic output circuitry for delivering defibrillation shocks to the paddle electrodes using the energy stored in the therapeutic delivery capacitors; wherein the operating circuitry is configured to perform the method described in any of the foregoing examples.

[0027] This summary is intended to provide an overview of the subject matter of this patent application. It is not intended to provide an exclusive or exhaustive explanation of the invention. A detailed description is included to provide further information regarding this patent application. Attached Figure Description

[0028] In accompanying drawings that are not necessarily drawn to scale, similar numbers may describe similar parts in different views. Similar numbers with different letter suffixes may represent different instances of similar parts. The accompanying drawings are illustrated in general terms by way of example and not limitation, of the various embodiments discussed in this document.

[0029] Figure 1 This illustrates a method for analyzing cardiac signals in a defibrillator;

[0030] Figure 2 The detection of electrical cardiac events is illustrated in the diagram.

[0031] Figures 3-4 This illustrates the defibrillator shock delivery and its effect on cardiac signals;

[0032] Figures 5-7 This is a block diagram of a new method for delivering defibrillation treatment;

[0033] Figures 8-10 It shows the use of Figures 5-7 The method of defibrillator shock delivery;

[0034] Figures 11-13 The analytical steps for characterizing R and T waves are shown;

[0035] Figures 14-15 An illustrative implantable defibrillator is shown; and

[0036] Figure 16 The operating circuitry of an example defibrillator is shown. Detailed Implementation

[0037] The following detailed examples focus on subcutaneous implantable defibrillators (SICDs). However, the invention is not limited to specific defibrillator placements. Embodiments of the invention can be used with various defibrillator types, including implantable defibrillators (whether intravenous, subcutaneous, epicardial, retrosternal, etc.), wearable defibrillators, and automated external defibrillators (AEDs). In any case, an output shock that causes or accelerates arrhythmia may occur.

[0038] Typically, defibrillators function by sensing cardiac signals, most commonly electrical signals, although other signals (sound, motion, blood pressure, oxygenation, etc.) can sometimes be collected. The cardiac signals are analyzed to determine if there is an arrhythmia requiring defibrillation. The most common method is to count cardiac cycles (“beats”) to calculate the beat rate, while also observing various characteristics of the cardiac signal shape (“morphology”). This can include matching to a template (whether through correlation, wavelet transform, principal component analysis, etc.) and observing the signal width and its changes over time.

[0039] Cardiac cycle counting can be performed in various ways. Some systems and recommendations involve capturing blocks of cardiac signal and identifying repeating cycles within them, such as through autocorrelation. Most implantable systems currently use cycle detection methods continuously by comparing the cardiac signal to a time-varying threshold; when the time-varying threshold is crossed, a new cardiac cycle can be announced. Each cardiac cycle consists of multiple “waves,” with the main components conventionally named the P wave, QRS complex, and T wave. Cardiac cycle detection typically focuses on detecting the R wave to indicate ventricular rate. Since the most dangerous arrhythmias often originate in the ventricles, the R wave is usually the primary focus of cycle detection.

[0040] Figure 1 A general method for analyzing cardiac signals in a defibrillator is illustrated. This method is iterative and can be initiated with the announcement of a newly detected cardiac event, as indicated in box 10. Once a cardiac event is detected, it can be termed a “beat.” Next, it can be determined in the beat confirmation whether the new detection originated from the heart and / or was correctly counted 12. For example, noise and / or over-detection can be identified in box 12, causing the new detection to be rejected and the process to return to box 10.

[0041] If a beat is confirmed at point 12, the method proceeds to rhythm analysis. Some methods of rhythm analysis rely on beat rate calculation as a first-level analysis. If the beat rate is above the ventricular fibrillation (VF) threshold, the most recently detected beat can be classified as malignant. If the beat rate is in the ventricular tachycardia (VT) zone, the beat can be further analyzed using factors such as width, morphology, or other factors to differentiate between sinus tachycardia (which may be accompanied by movement) and ventricular tachycardia (whether monomorphic or polymorphic). If the beat rate is in the VT zone and the beat is found to be caused by ventricular tachycardia, the beat can be reclassified as malignant.

[0042] In some systems, rhythm analysis tracks multiple counters, such as by tracking monomorphic ventricular tachycardia (MVT) beats, VF beats, and normal beats. For example, one or more detection interval number (NID) counters can be used; when the NID counter exceeds a defibrillation threshold, the method proceeds to box 16. In other systems, an X / Y filter can be used, where X tracks the number of malignant beats in the most recent set of Y confirmed beats. Again, if the X / Y threshold is met, the method proceeds to box 16. If a condition does not require defibrillation, the method returns to box 10 to await the next detection.

[0043] Box 16 relates to charging. Implantable and wearable defibrillators, as well as AED systems, typically operate on battery power with battery voltages far below the voltage / power levels required for effective defibrillation. For example, a SICD system can use a battery source with an output voltage of approximately 9 volts to deliver a 1350-volt defibrillation shock at 80 joules of energy; a transvenous system may have a battery with an output of 3 or 6 volts, simultaneously generating a 40-joule shock with a peak voltage of 750 volts. Wearable systems and AEDs can have larger batteries, as well as greater energy levels and voltages. Therefore, each of these defibrillators will use a charger to boost the battery output voltage to a much higher value and store the charger's output on one or more therapeutic delivery capacitors until the therapeutic energy level is stored.

[0044] When charging begins at 16, the method returns to detection 10 and continues looping through boxes 10, 12, 14, and 16 until the charging procedure is complete. During charging, most modern systems continue processing beats in boxes 12 and 14 to ensure continued detection of arrhythmias.

[0045] In the existing system, once the charging operation is complete, the path from pulsation detection to electric shock is different. More specifically, after charging is complete, the next new pulsation detection from box 10 bypasses boxes 12 and 14. Instead, as indicated by line 20, the next new pulsation detection prompts for reconfirmation and electric shock delivery 18.

[0046] Reconfirmation may include checking whether recently sensed cardiac data continues to indicate the need for treatment, such as by determining whether the beat rate, calculated using one or more intervals between detected beats before charging is complete, is above a threshold. Some examples may include further reconfirmation criteria, such as those disclosed in U.S. Patent No. 9,149,637, the disclosure of which is incorporated herein by reference.

[0047] Some examples may have a two-part charging operation. First, charging is performed to a treatment threshold, typically a set voltage. Once the initial charging sequence is complete, a reconfirmation is performed, such as using the method in U.S. Patent No. 9,149,637, either by capturing a cardiac event and confirming that the beat rate is above the threshold, or by other criteria as needed. As the reconfirmation completes, capacitor charging restarts with a “top-off”, because the reconfirmation takes several seconds, during which leakage current in the high-voltage capacitor and associated circuitry can reduce the stored energy. The “top-off” occurs quickly (e.g., typically less than 2 seconds). When the “top-off” is complete, an attempt is made to synchronize by sensing a new beat. If a new beat is detected, treatment is delivered; if no beat is detected within a preset time interval, asynchronous defibrillation is initiated.

[0048] When an electric shock is delivered at point 18 in response to a new pulse detection, this is considered a synchronous shock. If no new pulse is detected within a predetermined time period after charging is complete, the existing system will deliver an asynchronous shock. For example, a 1 to 2 second delay (depending on the system) after charging is complete without a newly detected pulse can trigger a shock. In some cases, this method of shock delivery can be dangerous to the patient, as further explained below.

[0049] To understand the arrhythmias associated with defibrillation shocks, it is important to first review how defibrillators detect new heartbeats. Figure 2 The detection of electrical cardiac events is illustrated graphically. The cardiac electrical signal is shown at 50, with the standard symbols for the P wave, QRS complex, and T wave displayed at 52, aligned with the components of signal 50. A “detection curve” is applied as a series of dashed lines, including line 60 on the left side of the graph, which persists over time until it intersects the cardiac signal line at 62, at which point the event is announced as the detection of a new cardiac cycle or beat. After detection 62, a refractory period is enforced, as indicated at 64, during which no further beats can be announced. Detection period 66 follows refractory period 64, again decaying over time until another interaction with the cardiac electrical signal line occurs at 68, indicating another refractory period 70, followed by another detection period 72.

[0050] In practice, the height of the detection curve during the detection periods (60, 66, 72) is typically proportional to the height of the detected event during the refractory periods 64 and 70. For example, detection period 66 can define a threshold for detecting cardiac events starting from a first percentage of the R-wave height, which can be the peak during the refractory period 64, or one or more previous refractory periods, for example, calculated as a running average. Many variations of this method have been disclosed in the art, such as in U.S. Patent Nos. 5,709,215 and 8,565,878 and U.S. Pre-Grant Publication No. 20040049120, the disclosures of which are incorporated herein by reference.

[0051] Figures 3-4 The defibrillator shock delivery and its effect on cardiac signals are shown. Figure 3 The patient's positive outcome is shown. The system processes the received cardiac signal 100 and detects new beats at 102, 104, and 106, collecting data that can be used to determine whether to continue detecting the arrhythmia to be treated. The end-of-charge label is indicated at 110, which in this example indicates full charge. The next beat to be detected occurs at 112, and a shock is delivered at 114. If desired, a predetermined delay can exist between detection 112 and shock delivery 114, typically less than 200 milliseconds or even less. In other examples, shock 114 may follow more or less immediately (i.e., as quickly as any lag allowed by the system processing cardiac signal 100 and detecting the event at 112). After shock delivery 114, a blanking period 116 can be enforced, during which the defibrillator's sensing circuitry recovers from any transient electrical signals following the shock. In this example, the event detected at 112 is a fibrillation cycle, and the patient can be seen transitioning to a more or less normal rhythm during and after the vanishing period, with P waves, QRS complexes, and T waves visible.

[0052] Figure 4 The patient's negative outcome is shown. Here, the cardiac signal is displayed at 150. The T wave in the cardiac signal is very prominent, exceeding half the size of the R wave. This large T wave leads to overdetection of the cardiac signal, with detection 152 occurring on the R wave and detection 154 occurring on the T wave. If the potential actual beat rate is, for example, in the range of approximately 90 bpm or higher, the detected signal can be double-counted, causing the device to observe a beat rate of 180 bpm or higher. At such a high (miscalculated) heart rate, the device is likely to identify a treatable condition and prepare to deliver an electric shock.

[0053] exist Figure 4In the diagram, the shock ending at 158 ​​occurs after the R-wave detection at 156 and before the subsequent T-wave detection at 162. If this occurs, the T-wave becomes a synchronous event, and the shock delivered at 164 can occur on the T-wave itself. The T-wave represents a vulnerable portion of the cardiac cycle, and a shock delivered to the T-wave can trigger a vital sign (VF), which is what happened in this example. Therefore, during and after the blanking period 166, the patient experiences a VF as shown at 168. This VF then requires treatment with a defibrillator. Not only was the first shock unnecessary, but as a result of T-wave oversensing, a potentially fatal condition (VF) was triggered, requiring further shocks. Figures 3-4 The new and alternative methods for the synchronization procedure shown are desirable.

[0054] Figures 5-7 This is a block diagram of a new method for delivering defibrillation therapy. Figure 5 In this example, the charging completion label is marked at 200; for this example and the examples below, charging completion label 200 can refer to the completion of “fully charged” as described above, although in other examples it can be the initial charging completion. At 202, the method continues to sense cardiac signals to detect the next heartbeat. When a beat is detected, the method proceeds to beat analysis 204. During beat analysis 204, the beat detected from box 202 is characterized as an R wave or a T wave. If the beat is characterized as an R wave, the method proceeds to box 206 and then executes the first shock protocol 208. If the beat is characterized as a T wave, the method proceeds to box 210 and then executes the second shock protocol. The two shock protocols illustrated are different from each other. In several examples, the second shock protocol at 212 delivers a shock later than the first shock protocol at 208 relative to the beat detected at 202. This could be due to waiting for the next detected beat, or by implementing a delay period, as shown below. Figure 6 and Figure 7 shown.

[0055] It should be noted that the characterization performed in box 204 is not necessarily clinically definitive. It is possible that the beat detected at 202 is neither a T wave nor an R wave due to the lack of sinus rhythm, which can occur if fibrillation or certain ventricular tachyarrhythmias are present. The aim is to characterize the beat in box 204 to determine which pathway is followed between 206 / 208 and 210 / 212. Because the primary impact of additional analysis is to avoid shocking the T wave, which can be tricky in cases of overdetection of R and T waves, naming the characterization in box 204 as an "R wave" or "T wave" is merely a convenient nomenclature. The following combination can be used... Figures 11-13 The steps shown and discussed, along with other examples in this paper, are used to perform the characterization at position 204 as a result of the analysis.

[0056] Figure 6 Another illustrative example is shown. When charging is complete at 250, the method moves to pulsation detection 252. When a pulsation is detected, the method then performs pulsation analysis at 254, which results in the pulsation being characterized as an R-wave or a T-wave. If the pulsation is characterized as an R-wave, the method proceeds to box 256 and then to box 258, where a delay and shock routine are performed. The delay in box 258 can be, for example, but not limited to, a relatively short delay in the range of about 1 to about 350 milliseconds; in one example, the delay from the synchronization event is about 100 milliseconds. The delay can be omitted in some examples, where the shock is delivered only at 258 immediately after the characterization in box 254 is complete.

[0057] If a pulsation in box 254 is characterized as a T wave, the method instead routes to box 262 via box 260, where the pulsation already characterized as a T wave in box 254 is "skipped." "Skipping" means that no shock is synchronously delivered to the pulsation already characterized as a T wave. Instead, the method waits for the next detection at box 264. When the next pulsation is detected in box 264, the method can directly proceed to box 258 to delay and deliver the shock.

[0058] In alternative examples, as indicated by line 270, the next detected pulsation at 264 can again undergo analysis of box 254. In some examples, a single “skipped” pulsation is allowed, and line 270 is omitted. In other examples, using line 270, there can be two or more skipped pulsations. To prevent extensive delays, the method may allow only a maximum number of “skipped” pulsations, such as 2, 3, or 4 skipped pulsations, before the pulsation is automatically characterized as an R-wave and follows path 256. In other examples, there may be no maximum number of “skipped” pulsations, but there is a maximum treatment time after the charge completion box 250 can be enforced, such as limiting the time between box 250 and box 258 to an interval, for example, in the range of approximately 1 to approximately 3 seconds. In practice, a maximum delay can help ensure that the shock energy remains above a threshold because the high-power capacitor used for shock delivery and the associated switches used to control the treatment output can each have a leakage current that dissipates the stored energy to the point where the therapeutic efficacy can be reduced. In other examples, if needed, the repeat analysis at 254, which causes the path at 260 / 262 to be followed, is used to reopen the reconfirmation analysis, thereby potentially avoiding the shock entirely.

[0059] Figure 6 The examples in [the document] can be based on Figure 5The language is used to represent the first electric shock protocol, where the path at 256 / 258 is used as the first electric shock protocol, and the path from 260 / 262 / 264 (which may be repeated) to 258 is used as the second electric shock protocol.

[0060] Figure 7 Another example is shown. The method in question begins with charge completion at box 300, followed by pulsation detection 302. When a pulsation is detected, it is analyzed at 304 and characterized as an R-wave 306 or a T-wave 308. If the pulsation is characterized as an R-wave 306, a first delay is implemented at 308 prior to the shock delivery 310. The first delay can be a fixed delay, such as a delay in the range of 0 to 300 milliseconds, or approximately 100 milliseconds. In another example, the first delay can be a variable delay calculated using the interval between detected pulsations or other factors. In one example, the first delay can be calculated using the interval between previously detected events by determining the average of earlier detected events and subtracting the interval between the pulsation detected at 302 and the pulsation preceding it from that average. The duration of the first delay can be short enough to be characterized as “immediate,” i.e., within 300 milliseconds or less after the pulsation is detected or characterized. In systems using a digital clock as a reference for the analysis step, the first delay can be as short as a single clock cycle.

[0061] Conversely, if the pulsation detected in box 304 is characterized as a T-wave, the method proceeds to box 312 and applies a second delay as shown at 314 before delivering the shock at 310. The second delay can be a fixed delay longer than the first delay; for example, the second delay can be an amount in the range of 100 to 400 milliseconds longer than the first delay. In one example, the second delay exceeds the first delay by 350 milliseconds. In another example, the first delay is 100 milliseconds, and the second delay is 350 milliseconds. In yet another example, the second delay is a variable delay calculated using the intervals between detected pulsations. For example, the second delay can be calculated as the sum of two previous intervals, minus the interval between the pulsation detected at 302 and its preceding pulsations.

[0062] The following section will discuss several more specific calculations of the first and second delays in further detail. Figure 7 It can be used Figure 5 The language is used to represent the first electric shock protocol, where the sequence of boxes 306, 308, and 310 is the first electric shock protocol, and the sequence of boxes 312, 314, and 310 is the second electric shock protocol.

[0063] Figures 8-10 It shows the use of Figures 5-7 The method of defibrillator shock delivery. Each figure is shown assuming that capacitor charging (whether initial charging or full charging, if full charging is part of the method) is completed. FromFigure 8 Initially, Example 350 shows a heart signal with a detected beat at 352. For naming purposes, the detected beat at 352 can be the "Nth" beat, and is the first detected beat after charging is complete. Assuming no shock is delivered, a subsequent beat is detected at 360, and can be considered the N+1th beat. If the Nth beat 352 is characterized as an R wave, a shock is delivered as shown at 354 (this may mean that the N+1th beat 360 will not occur). On the other hand, if the Nth beat 352 is characterized as a T wave, the method skips the shock delivery at the Nth beat 352, instead waiting until the N+1th beat is detected at 360. The shock is then delivered as indicated by 362. It is clear that only one of the shocks 354 and 362 will actually occur.

[0064] Figure 9 Another scenario is shown. Here, again, example 400 is shown as occurring after the capacitor charging (and / or full charging) is complete. A detected pulse appears at 402. Pulse 402 is analyzed to characterize it as an R wave or a T wave. If pulse 402 is characterized as an R wave, a shock is delivered immediately at 404. If pulse 402 is characterized as a T wave, the method returns to sensing another heartbeat detection. In this example, no additional pulse is detected before timeout 406 occurs. Timeout 406 can be calculated based on the time from the end of charging (not shown in the figure), or, as shown, from the time the pulse is detected at 402. At 408, timeout 406 triggers asynchronous shock delivery. Illustrative timeout 406 can be one second, although a range conceivable from approximately 500 milliseconds to 2.5 seconds, or longer if desired, is possible. Timeout 406 can have a duration selected to prevent excessive drop in therapeutic energy levels due to leakage current. It is important to understand that only one of the two electric shocks, 404 and 408, is actually delivered.

[0065] Although Figures 8-9 Usually corresponds to Figure 6 The method shown, but Figure 10 Showing with Figure 7 Corresponding examples. Figure 10Example 450 restarts after the capacitor has finished charging. A detected pulse occurs at 452, and this pulse 452 is analyzed to characterize it as an R-wave or a T-wave. If pulse 452 is characterized as an R-wave, a shock is delivered as shown in 456 after the relatively short first delay period 454 expires. If pulse 452 is characterized as a T-wave, the method waits for the relatively long second delay period 460 to expire and delivers a shock at 462. In this example, it is not important whether a second pulse is detected after pulse 452. It is clear that only one of shocks 456 or 462 occurs.

[0066] The first delay period 454 can be fixed or variable, and can be similar to the above for... Figure 7 The delay 1,308 describes this. In some examples, the physician may be asked to select a first delay period 454. If variable, any suitable method may be used to determine the first delay period. For example, if desired, the first delay period 454 may be calculated in advance by calculating the width of the R wave during normal cardiac activity or the width of the beat detected during an ongoing arrhythmia. The first delay period 454 can then be calculated as a fraction, such as 25% to 125% of the calculated width, or about 80% to about 100% of the calculated width. The first delay period 454 may alternatively be calculated using the intervals between detected events, such as by averaging the ongoing intervals and subtracting the interval immediately preceding the detected beat 452 from that average.

[0067] Similarly, the second delay period 460 can be fixed or it can be variable. The second delay period 460 is preferably longer than the first delay period. For example, the second delay period 460 can be longer than the first delay by an amount ranging from 100 to 400 milliseconds. In one example, the second delay period 460 exceeds the first delay by 350 milliseconds, where the first delay period is fixed or variable. In another example, the first delay is 100 milliseconds and the second delay is 350 milliseconds, where both are fixed. In yet another example, the second delay period is fixed and in the range of approximately 100 to approximately 400 milliseconds. In yet another example, the second delay is a variable delay calculated using the interval between detected beats. For example, the second delay can be calculated as the sum of two previous intervals, minus the interval between the beat detected at 302 and its preceding beats. In yet another example, the second delay is determined by analyzing cardiac cycles detected during normal heart rhythm to calculate the T-wave width, which can be a portion of the T-wave width, the entire T-wave width, or the entire T-wave width plus a portion of the T-wave width and / or a fixed added delay.

[0068] Figures 11-13 The analytical steps for characterizing R and T waves are shown.Figure 11 The diagram illustrates the labeling of detected events for analytical purposes. An exemplary cardiac signal is shown at 500, where the charging time ends at charging end label 502. Because charging can proceed quite quickly (less than 2 seconds in some examples), some beats 510, 520, 530 may occur before charging begins. Several beats are detected at 510, 520, 530, 540, where beat 540 occurs after charging end label 502, and other beats occur before it. Beat 540 is used as a reference point to label these beats. Thus, beat 540 is the Nth beat, beat 530 is the N-1th beat 532, beat 520 is the N-2th beat 522, and beat 510 is the N-3th beat. The intervals between beats are labeled as intervals I 534, I-1 524, and I-2 514. When described in this way, N-2, N-1, and the Nth ECG event are consecutively detected ECG events, with N-2 being the earliest in time. This designation will be used in the following discussion.

[0069] In some examples, intervals can be used to help characterize the Nth beat 540 as an R wave or a T wave. In one example, only interval 532 is analyzed by comparing it to the RT interval range. If interval 532 is within the RT interval range, the Nth beat 540 can be characterized as a T wave in this example; otherwise, the Nth beat 540 is characterized as an R wave. Some further examples combine interval analysis with the analysis of the beat itself, including the use of amplitude analysis, as described in further detail below.

[0070] like Figure 7 and Figure 10 The intervals used can also be used to determine the shock delay. In one example, the first delay (a shorter delay is used if the synchronous beat is characterized as an R wave) is calculated by averaging intervals I-1522 and I-2512 and subtracting interval I532. The second delay can then be calculated by adding intervals I-1522 and I-2512 and subtracting interval I532. Alternatively, the first delay can be a fixed delay or the second delay can be a fixed delay, while still using the above calculation for the other of these two delays. In yet another example, the first delay can be calculated using the above calculation, and the second delay is determined by adding a fixed duration to the first delay. As previously stated, each of the first and second delays can alternatively be a fixed delay.

[0071] Figure 12The diagram illustrates how to calculate the RT interval. The cardiac electrical signal is displayed at 550, and a beat is detected at 552. The refractory period is defined at 554, and the R wave occurring within this period is shown. The T wave detection period is then defined after the refractory period, as indicated by 556. For example, the refractory period can have a duration of 80 to 160 milliseconds or more or less, and the T wave period can have a duration of 120 to 200 milliseconds or more or less. Preferably, the sum of the refractory period 554 and the T wave detection period 556 is at least 300 milliseconds. In this case, the RT interval is then calculated by identifying the peak value (R wave peak) during the refractory period 554 (as indicated by the arrow at 560) and the peak value (T wave peak) during the T wave detection period 556 (as indicated by the arrow at 562), and calculating the interval 564 between them. In an alternative approach, the detection time point at 552 (i.e., where the cardiac electrical signal crosses the detection threshold) can be used as the start of the RT interval, while the T-wave peak detected during the T-wave detection period is used instead as the end of the RT interval.

[0072] For a given system, the RT interval can be calculated at any time. For example, for chronic disease devices (implants and wearable devices), the RT interval can be calculated by the device with physician assistance during device fitting or implantation to ensure that the correct peaks are labeled. In other examples, the RT interval can be calculated again for chronic disease devices when rhythm analysis does not indicate the presence of any arrhythmia. In other examples, the RT interval can be "calculated" during an ongoing arrhythmia, such as an arrhythmia that has triggered capacitor charging (at least as identified by the device). While the reliability of attempting RT interval calculation during an arrhythmia may be slightly lower, it is still possible to perform the calculation if needed.

[0073] The RT interval can then be used to set a range for the RT interval, which can be used to characterize the detected pulsation as an R wave or a T wave. For example, the RT interval range can be used... Figure 12 The calculated RT interval is adjusted by adding / subtracting 20, 30, 40, 50, 60, or 70 milliseconds, or by adding or subtracting a percentage (e.g., 10, 20, 30, and 40). Using... Figure 11 According to naming conventions, if the I interval 532 is within the RT interval range, then in the interval-only example, the Nth beat can be characterized as a T wave. If desired, other factors (such as amplitude or magnitude analysis) can be combined with the use of RT interval analysis.

[0074] Figure 13The amplitude peaks are shown as being able to name events N-1 and N-2. The cardiac signal 590 is displayed, and the two detected beats are shown at 592 and 594, labeled N-1 592 and N-2 594. For each detected beat, the positive and negative peak values ​​are labeled. Thus, the N-1 beat 592 has a positive peak PP1 and a negative peak NP1, and the N-2 beat 594 has a positive peak PP2 and a negative peak. NP2. These peak values ​​can be used to analyze whether the amplitude or magnitude indicates that a T-wave has occurred.

[0075] In one example, an analysis is performed to determine whether pulses 592 and 594 show a large-small (i.e., N-2 "greater than" N-1), small-large (i.e., N-1 "greater than" N-2), or similar amplitude patterns. Each of the large-small and small-large amplitude patterns indicates that the R-wave and T-wave have been detected sequentially. In one example, these patterns can be determined by calculating one or more ratios. The rectified peak ratio can be calculated as:

[0076] Rectified peak ratio = max(|PP1|, |NP1|) / max(|PP2|, |NP2|)

[0077] The peak-to-peak ratio can also be calculated as:

[0078] Peak-to-peak ratio = (|PP1| + |NP1|) / (|PP2| + |NPT2|)

[0079] Here, each of |PP1|, |NP1|, |PP2|, and |NP2| represents the rectified peak amplitude in each formula. Some examples may use only the rectified peak ratio and (see again) Figure 11 The interval is 532, as shown below:

[0080] a) If the rectified peak ratio is within the similarity limit, the Nth beat is characterized as a T wave only if I is within the RT interval; otherwise, it is characterized as an R wave.

[0081] b) If the rectified peak ratio is below the similarity limit, the Nth beat is characterized as an R-wave; and

[0082] c) If the rectified peak ratio is above the similarity limit, then only if I is within or below the RT interval,

[0083] The Nth beat is characterized as a T wave; otherwise, it is characterized as an R wave.

[0084] Wherein, as needed, the similarity threshold is defined as a range close to 1, such as 0.80 to 1.20, or higher or lower (the lower limit is any value from 0.65 to 0.99, and the upper limit is any value from 1.01 to 1.35). The RT interval range can be variable, such as based on Figure 12 The calculations / analyses shown can also be fixed, such as 200 to 300 milliseconds. Alternatively, each of a), b), and c) above can be replaced with peak-to-peak ratio. In yet another alternative, both rectified peak ratio and peak-to-peak ratio are used, as explained below:

[0085] 1) If the peak-to-peak ratio is within the similarity limit, the Nth beat is characterized as a T wave only when the peak-to-peak ratio is higher than the minimum and the interval I is within the RT interval range; otherwise, the Nth beat is characterized as an R wave.

[0086] 2) If the rectified peak ratio is below the similarity limit, the Nth beat is characterized as an R-wave;

[0087] 3) If the peak-to-peak ratio is higher than the similarity limit, the Nth beat is characterized as a T only if the peak-to-peak ratio is higher than the minimum and the interval I is within or below the RT interval; otherwise, the Nth beat is characterized as an R wave.

[0088] The minimum value is a lower bound set in the range of approximately 0.6 to approximately 0.9; in one example, the minimum value is set to 0.8. In another example, tests 1) and 2) can be as shown, and test 3) is modified to compare I with the maximum value of the RT interval that is greater than the range of RT intervals; for example, the maximum value of the RT interval can be 350 ms and the range of the RT intervals can be 200 to 300 milliseconds.

[0089] In another example, RT interval estimation (whether measured or pre-set) is used, and a two-layer analysis is performed, as shown below:

[0090] i) If the rectified peak ratio is within the similarity limit, the Nth pulsation is characterized as an R-wave.

[0091] ii) If the rectified peak ratio is above the similarity limit, the Nth beat is characterized as a T wave unless the interval I is not similar to the RT interval estimate.

[0092] iii) If the rectified peak ratio is below the similarity limit, the Nth beat is characterized as an R wave unless the interval I is similar to the RT interval estimate.

[0093] In this example, "similar to the RT interval estimate" can mean relatively close similarity, such as within + / - 50 milliseconds (although other bounds in the range of approximately 10 to approximately 70 milliseconds can be used), while "dissimilar to the RT interval estimate" can mean relatively wide dissimilarity, such as being more than + / - 100 milliseconds away from the RT interval estimate (again, other bounds in the range of approximately 40 to approximately 120 milliseconds can be used). In other examples, the dissimilar / similar bounds can be the same.

[0094] It is understandable that various combinations of intervals and amplitudes can be used. In another example, phase can be used to distinguish between R-waves and T-waves. For example, by identifying... Figure 13 The positive and negative peak values ​​shown can characterize N-3, N-2, and N-1 detections as biphasic or monophasic. A rule set can be generated to characterize each beat:

[0095] - If PP > 1.5 * |NP|, then single-phase is positive.

[0096] - If |NP| > 1.5 * PP, then single-phase is negative.

[0097] - Otherwise, it is biphasic.

[0098] Depending on the sensing vector used to sense the cardiac electrical signal, the QRS complex and T wave can fall into different categories: monophasic positive, monophasic negative, and biphasic. If so, polarity can be used to distinguish the R wave from the T wave, as follows:

[0099] - If phase N-3 = phase N-1 and phase N-2 ≠ phase N-1, and the rectified peak ratio is higher than the similarity limit, then the Nth beat is characterized as a T wave;

[0100] Otherwise, the Nth beat is characterized as an R wave.

[0101] Whether such a function is enabled can depend on whether the cardiac electrical signals (whether captured under physician supervision or in a non-bedridden setting), particularly the R wave or QRS complex, are biphasic. For example, a defibrillator may sense one or more cardiac cycles before or during the detection of an arrhythmia to determine whether the patient's cardiac signals associated with the R wave (and / or T wave, optionally) are typically monophasic or biphasic. In any case, the T wave is usually monophasic, and if the T wave and R wave have the same polarity for a given sensing vector, phase analysis used to distinguish between the T wave and R wave may be useless; therefore, the system can enable or disable the phase analysis used to distinguish between the R wave and T wave as needed.

[0102] In another example, event shape can be used to distinguish between R waves and T waves. Shape or morphology (terms that are interchangeable) can be analyzed using width, which can be determined using the methods described in U.S. Patent 10,582,870, the disclosure of which is incorporated herein by reference. For example, R waves, or QRS complexes, are typically narrower than T waves. If the R wave width is known for a given patient and defibrillator system (particularly for chronic disease devices such as wearable or implantable defibrillator systems), it is possible to analyze N-1 detected events to see if they have a width matching that of an R wave, in which case, for example, if the Nth detection falls within the RT interval, it can be characterized as a T wave. If the N-1 events do not match an R wave, then due to… Figures 5-7 The purpose of the method is that the Nth detection can be characterized as an R-wave.

[0103] Alternatively, morphology can be analyzed using analyses such as correlated waveform analysis (CWA), where a sample-by-sample comparison is made between the captured signal associated with the pulsation and a pre-stored static or dynamic template. Morphology can rely on transforms such as principal component analysis (PCA) or wavelet transform, where the components of the captured signal are first separated and then compared to characterize similarities or dissimilarities. Frequency analysis, such as Fast Fourier Transform (FFT), can be used to characterize the detected pulsations. Using any such morphological analysis, the characterization of R-waves and T-waves can be performed by observing whether an alternation pattern can be identified, and if so, which of the N-3, N-2, and N-1 pulsations is likely an R-wave or a T-wave. Assuming consistent detection of cardiac events, it can be further inferred that if N-3 and N-1 are R-waves and N-2 is likely a T-wave, then the Nth detection will also be a T-wave. The use of interval analysis (RT interval estimation or range) can be combined with this type of shape assessment.

[0104] For example, the rule set can be as follows:

[0105] - If shape N-3 is similar to shape N-1, and shape N-2 is not similar to shape N-1, and the rectified peak ratio is above the similarity limit, then the Nth beat can be characterized as a T wave;

[0106] Otherwise, the Nth beat is characterized as an R wave.

[0107] In this example, the shape similarity of N-3 to N-1 and the dissimilarity with N-2 show alternating shape patterns. Alternating shape patterns, in turn, suggest T-wave oversensing, and therefore the rectified peak ratio is used here to determine whether odd beats (N-3, N-1) or event beats (N-2, N) are possible R waves. Conversely, if N-3 and N-1 are dissimilar, no pattern can be collected, and analysis indicates a randomly changing signal (such as PVT or VF), which means concerns about proarrhythmic shocks are alleviated. If morphology is used and no pattern is found, it is because... Figures 5-7 The purpose of this method is to automatically characterize the Nth detected event as an R-wave.

[0108] The previous examples presented dynamic shape analysis by comparing N-3 with N-1, and N-2 with either N-1 or N-3, where the basis for comparison constantly changes or is updated with recent detection data. In static analysis, stored templates or numbers can be used. For example, for width, it is possible to compare N-3 with N-2 and / or N-1 in dynamic analysis, or to compare the width of each of N-3, N-2, and N-1 with predetermined limits to characterize a pulsation as wide or narrow. With other shape analyses (CWA, PCA, wavelet, or FFT), static templates can be stored, whether for point-by-point data of CWA, component features of PCA, specific wavelets, or specific frequency components, where the analysis determines whether a pulsation matches a stored static template. Each pulsation can then be classified as a match or a mismatch, again determining whether an alternating pattern exists.

[0109] It can be noted that in the examples so far, the pulsation N itself is not analyzed for shape or amplitude, and only the interval preceding N is used in the analysis. The reason for omitting the pulsation N is that the incoming data for the pulsation N is incomplete when the analysis is triggered. For example, the shock delivery may be invoked to synchronize the shock delivery with the pulsation N before the data required to measure the width or perform CWA, PCA, wavelet, or FFT shape analysis is fully collected.

[0110] In another example, one or more features of the pulsation N can also be used, particularly including the amplitude. See again... Figure 12 Given a detector 552, the amplitude indicated at 570 can be determined by waiting for the inflection point of the cardiac electrical signal before invoking the shock delivery. If so, amplitude 570 can be used for any of the above comparisons, for example, by observing whether the peak values ​​for similar time placements for any of detectors N-3, N-2, and N-1 have amplitudes similar to amplitude 570. Therefore, the set of rules can be as follows:

[0111] - If the amplitudes N-2, N-1, and N are low-high-low, and the amplitudes of N-1 and N-3 are similar, then the Nth beat is characterized as a T wave; or

[0112] - If the amplitude N-1 is greater than the amplitude N, and the interval I is within the RT interval range, then the Nth beat is characterized as a T wave;

[0113] Otherwise, the Nth beat is characterized as an R wave.

[0114] Other factors and combinations thereof may be used alternatively to characterize the Nth beat as an R wave or a T wave. The various illustrations provided are not intended to limit the invention to these specific analyses.

[0115] This invention can be applied to wearable defibrillator systems, AEDs, or implantable systems. As a specific example, Figures 14-15 An illustrative implantable system is shown. Alternative implantable systems may include epicardial systems, or entirely intravenous or intracardiac systems.

[0116] Figure 14 The illustrative system shown is relative to the heart 600. The system shown can be a subcutaneous implantable device, such as the Boston Scientific Emblem SICD system. Figure 14 The system can alternatively implant the lead in a retrosternal location or into an internal thoracic vein, as shown in various published patents and / or published patent applications. The canister 602 can be implanted near the left axilla, where lateral, anterior, or posterior locations are possible. Lead 604 couples the canister 602 to electrodes 606, 608, and 610, which are shown implanted along the patient's sternum, typically on the left or right side. In another example, the canister can be located in an anterior position (axillary or pectoral muscle, if desired), with the lead wrapped around the back of the patient's chest. Figure 14 The system may include an external programmer 620 configured to communicate with the implant 602.

[0117] Figure 10 The system is a transvenous system, schematically shown relative to the heart 650, with the patient's ribs omitted for clarity. The canister 652 is positioned in a high pectoral muscle position, where the lead 654 is connected to the vascular system and enters the heart, for example via the subclavian vein. The lead 654 may include a superior vena cava coil electrode 656, a right ventricular coil electrode 658, and one or two ventricular sensing / pacing electrodes 660, 662. A programmer is again shown at 670, and the programmer is configured to communicate with the implanted system. The system may also include a left ventricular lead (not shown).

[0118] Figure 14 or Figure 15Communication between any of the systems can be inductive, RF (such as using Medradio or Bluetooth), or via any other suitable communication medium. This communication can be used to configure the implantable system for sensing, treatment, or other features, to load new software or firmware onto the implantable system, and to retrieve information about system operation, such as device status, treatment history, diagnostic data (related to both the device and the patient), or other suitable data. The programmer may include the circuitry necessary for processing, storing, displaying, telemetry / RF communication, etc., for these purposes.

[0119] Figure 14 and Figure 15 The canisters typically contain the operating circuitry for implantable systems. Figure 16 An illustrative example is shown. Tank 700 houses operating circuitry including a control module 710, which may be or include a microcontroller and various associated application-specific integrated circuits (ASICs). Memory 712 is provided for storing operating data and instruction sets for the operation of control module 710. A signal processing section is shown at 714 and may include appropriate analog and / or digital circuitry required to process the received cardiac electrical signals, including filtering, analog-to-digital conversion, and any dedicated ASIC, such as a morphological analysis ASIC. The signal processing section 714 is operatively linked to I / O components that may include switching circuitry and DC and / or MRI blocking sub-circuitries, which are in turn coupled to feedthrough and / or connector 724.

[0120] The operating circuitry may also include a power supply 720, such as a main battery or a rechargeable battery. As indicated by 722, a high-voltage (HV) sub-circuit is also provided and includes a charger and an HV capacitor for defibrillation treatment. For example, the charger may include a voltage boosting circuit, such as a transformer, for generating a high-voltage output temporarily stored on the HV capacitor for therapeutic purposes. The HV sub-circuit 722 is also linked to I / O 716. Control of the HV output can be achieved using an H-bridge circuit, as is known in the art.

[0121] One or more leads 730 may be coupled to connector 724. One or more leads 730 may include one or more electrodes 732, 734 suitable for sensing and / or therapeutic delivery purposes. Canister 700 may be an hermetically sealed and conductive housing having one or more surfaces suitable for use as electrodes for therapeutic delivery or sensing purposes. Wearable defibrillators or AEDs may have... Figure 16 The circuit elements and modules shown are similar, except that the output circuit has a higher power level to some extent, and the signal capture circuit can be configured to capture the surface signal of the cardiac ECG, which can be similar to the signal captured by SICD, but is usually at a lower signal voltage.

[0122] Wearable defibrillators can take the form of a vest and may have electrodes built into it, such that the shock electrodes are positioned anteriorly and posteriorly on the patient's upper chest, including or excluding lateral (e.g., armpit) electrodes; in some wearable defibrillators, a dose of conductive gel can be expelled immediately before shock delivery if needed. The commercially available ZollLifevest is one example; additional examples of various vest designs appear in U.S. Patents 5,944,669 and 6,065,154, the disclosure of which is incorporated herein by reference. Wearable defibrillators and AEDs may have electronic modules housed to protect the shock during delivery, but do not necessarily have a conductive housing like typical implanted systems. In some examples, wearable defibrillators and AEDs may have rechargeable batteries.

[0123] Unlike wearable defibrillators, AEDs typically consist of electrodes on conductive leads placed on the patient's body. These electrodes do not require any type of vest for carrying, and are generally positioned on the front of the patient's chest, with one electrode positioned more laterally and lower (typically on the left and below the heart) and the other more upperally and medially to the right. Various other specific design features of wearable and AED systems are well known to those skilled in the art. Example embodiments of an AED are illustrated in U.S. Patent 7,463,922, the disclosure of which is incorporated herein by reference. AEDs are commercially available, for example, Phillip's Heartstart AED and Defibtech Lifeline, among others.

[0124] The illustrative, non-limiting example with reference to the foregoing description and figures takes the form of a defibrillator device (such as device 602, 652, and / or 700), comprising: a plurality of electrodes (606, 608, 610, and / or housing 602; 656, 658, 660, 662, and / or housing 652 or 732, 734, and / or housing 700) adapted to capture cardiac electrical signals and / or deliver electrical therapy to a patient; and an output device (716, 722) for delivering a defibrillation shock using one or more electrodes. The output device includes a charger and a therapeutic delivery capacitor (722, wherein the charger and capacitor may also take the form described in U.S. Patent 7,769,445, disclosed herein by reference); operating circuitry (710, 712, 714, 716) configured to use cardiac electrical signals from electrodes to detect and analyze the cardiac cycle to sense cardiac events, and to use the output device to determine whether and when to deliver a defibrillation shock; wherein the operating circuitry is configured to perform the following operations: determining the need for a defibrillation shock ( Figure 1Boxes 12 and 14 are used to determine the need for an electric shock, which, if a shock is needed, causes box 16 to be invoked, and, if a defibrillation shock is needed, causes the output device to charge the treatment delivery capacitor to a predetermined shock threshold. Figure 1 (Box 16 in the middle); after the treatment delivery capacitor is charged to the predetermined shock threshold ( Figure 1 After charging is completed at 20 points, proceed to box 18 and proceed. Figures 5-7 (Analysis in the text): Sensing the Nth ECG event (202, 252, 302); characterizing the Nth ECG event as an R wave or a T wave (204, 254, 304); and: if the Nth ECG event is an R wave (206, 256, 306), then delivering a defibrillation shock according to the first shock protocol (208, 258, 308); or if the Nth ECG event is a T wave (210, 260, 312), then delivering a defibrillation shock according to the second shock protocol (212, 262 / 264, 314).

[0125] Additionally or alternatively, the operating circuitry is configured such that delivering a defibrillation shock according to the first shock protocol includes delivering a defibrillation shock after the expiration of the first shock delay following the Nth ECG event; and delivering a defibrillation shock according to the second shock protocol includes delivering a defibrillation shock after the expiration of the second shock delay following the Nth ECG event. As described above, the first shock delay may be almost immediate; a single clock cycle or a delay of up to 350 milliseconds may be used; in some examples, the second delay is a fixed delay, while in other examples, the second delay may cover waiting for the occurrence of other events, rather than a fixed delay or anything beyond that.

[0126] Additionally or alternatively, the operating circuitry is configured to set the second shock delay as follows: sense each of N-1, N-2, and N-3 ECG events, wherein the N-1 ECG event precedes the Nth ECG event, the N-2 ECG event precedes the N-1 ECG event, and the N-3 ECG event precedes the N-2 ECG event, each of the Nth, N-1, N-2, and N-3 ECG events representing a continuous detection of a cardiac event; determine an interval I1, which represents the interval from the N-1 ECG event to the Nth ECG event; determine an interval I2, which represents the interval from the N-2 ECG event to the N-1 ECG event; determine an interval I3, which represents the interval from the N-3 ECG event to the N-2 ECG event; and set the second shock delay to be equal to {I2 + I3 – I1}.

[0127] Additionally or optionally, the operating circuitry is configured to set the first shock delay to be equal to 0 or the greater of the average of I2 and I3 minus I1.

[0128] Additionally or optionally, the operating circuitry is further configured such that: issuing a defibrillation shock according to the second shock protocol includes sensing the next ECG event during a predetermined timeout interval, and: if the next ECG event is sensed during the predetermined timeout interval, issuing a defibrillation shock after the detection of the next ECG event, or issuing a defibrillation shock after the predetermined interval has expired if no other ECG event is sensed.

[0129] Additionally or alternatively, the operating circuitry is further configured such that: issuing a defibrillation shock according to the second shock protocol includes: sensing the next ECG event during a predetermined timeout interval, and: issuing a defibrillation shock after the predetermined timeout interval expires if no other ECG event is sensed; or if the next ECG event is sensed during the predetermined timeout interval, characterizing the next ECG event as an R wave or a T wave, and: if the next ECG event is an R wave, issuing a defibrillation shock using the first shock protocol; or if the next ECG event is a T wave, then: sensing a subsequent ECG event following the next ECG event and issuing a defibrillation shock after detecting the subsequent ECG event, or issuing a defibrillation shock after the predetermined timeout interval expires if no other ECG event following the next ECG event is sensed.

[0130] Additionally or optionally, the operating circuit is further configured to characterize the Nth ECG event as an R wave or T wave by: sensing each of the N-1 and N-2 ECG events, wherein the N-1 ECG event precedes the Nth ECG event, and the N-2 ECG event precedes the N-1 ECG event, each of the Nth, N-1, and N-2 ECG events representing a continuous detection of cardiac events; observing the interval between the Nth and N-1 ECG events; determining the amplitude of each of the N-1 and N-2 ECG events; and calculating the peak-to-peak ratio as: N The ratio of the amplitude of the N-1 ECG event to the amplitude of the N-2 ECG events; determining whether the peak ratio falls within the similarity range, and: if the peak ratio falls within the similarity range, if the interval is within the RT interval, then the Nth ECG event is characterized as a T wave, otherwise the Nth ECG event is characterized as an R wave; if the peak ratio is above the similarity range, if the interval is within the RT interval, then the Nth ECG event is characterized as a T wave, otherwise the Nth ECG event is characterized as an R wave; or if the peak ratio is below the similarity range, then the Nth ECG event is characterized as an R wave.

[0131] Additionally or alternatively, the operating circuitry is also configured to calculate the RT interval range by: sensing a reference cardiac event; defining a refractory period and a T-wave period for identifying first and second peaks associated with the reference cardiac event; identifying the maximum peak during the refractory period as the first peak; identifying the maximum value during the T-wave period as the second peak; determining the RT interval of the reference cardiac event as the interval between the first and second peaks; and setting the RT interval range around the RT interval.

[0132] Additionally or alternatively, the operating circuitry is also configured to calculate the RT interval range by: sensing a reference ECG event by observing the crossover of the cardiac electrical signal with respect to a cardiac event detection threshold, and identifying a first time point at the crossover; defining a T-wave period for identifying the T-wave peak; identifying the maximum peak during the T-wave period, and identifying a second time point at the maximum peak during the T-wave period; determining the RT interval for the reference cardiac event as the interval between the first and second time points; and setting the RT interval range around the RT interval.

[0133] Additionally or alternatively, the operating circuitry is also configured to sense at least N-1 and N-2 ECG events, wherein the N-1 ECG event occurs after the N-2 ECG event and before the Nth ECG event.

[0134] Additionally or alternatively, the operating circuit is configured to characterize the Nth ECG event as an R wave or T wave by: calculating the rectified peak ratio of the N-1 and N-2 ECG events as the ratio of the maximum rectified peak value of the N-1 ECG event to the maximum rectified peak value of the N-2 ECG event; calculating the peak-to-peak ratio of the N-1 and N-2 ECG events as the ratio of the sum of the amplitudes of the maximum positive and negative peaks associated with the N-1 sensed ECG event and the sum of the amplitudes of the maximum positive and negative peaks associated with the N-2 ECG event; and observing the Nth ECG event... The interval between the Nth and N-1th ECG events; and: if the rectified peak ratio is within a first range, if the interval is within the RT interval range and the peak-to-peak ratio is higher than a second threshold, then the Nth ECG event is characterized as a T wave, otherwise the Nth ECG event is characterized as an R wave; if the rectified peak ratio is lower than the first range, then the Nth ECG event is characterized as an R wave; if the rectified peak ratio is higher than the first range, if the interval is less than the RT interval estimate and the peak-to-peak ratio is higher than the second threshold, then the Nth ECG event is characterized as a T wave, otherwise the Nth ECG event is characterized as an R wave.

[0135] Additionally or alternatively, the operating circuitry is configured to characterize the Nth ECG event as an R-wave or a T-wave by: observing the interval between the Nth and N-1th ECG events; determining the amplitude of each of the N-1th and N-2th ECG events; calculating the peak-to-peak ratio as the ratio of the amplitude of the N-1th ECG event to the amplitude of the N-2th ECG event; determining whether the peak-to-peak ratio falls within a similarity range, and: if the peak-to-peak ratio falls within a similarity range, and if the interval is within the RT interval range, then the Nth ECG event is characterized as a T-wave, otherwise the Nth ECG event is characterized as an R-wave; if the peak-to-peak ratio is above a similarity range, and if the interval is within the RT interval range, then the Nth ECG event is characterized as a T-wave, otherwise the Nth ECG event is characterized as an R-wave; or if the peak-to-peak ratio is below a similarity range, then the Nth ECG event is characterized as an R-wave.

[0136] Alternatively or additionally, the operating circuitry is configured to sense an N-1th ECG event preceding the Nth ECG event and characterize the Nth ECG event as an R wave or a T wave by: determining the interval from the N-1th ECG event to the Nth ECG event; comparing the interval with a range of RT intervals; and if the interval is within the range of RT intervals, characterizing the Nth sensed ECG event as a T wave; otherwise, characterizing the Nth ECG event as an R wave.

[0137] Alternatively or additionally, the operating circuitry is configured such that the RT interval range and RT interval estimate are calculated by analyzing one or more cardiac cycles. Alternatively or additionally, the operating circuitry is configured such that the RT interval range and RT interval estimate are preset.

[0138] Additionally or alternatively, the operating circuitry is configured to characterize the Nth ECG event as an R-wave or a T-wave by detecting at least one previous ECG event and determining one or more of the intervals or amplitudes associated with the previous ECG events that indicate whether the Nth ECG event should be characterized as an R-wave or a T-wave.

[0139] Alternatively or additionally, the operating circuitry is configured to characterize the Nth ECG event as an R wave or a T wave by detecting at least one previous ECG event and analyzing the morphology of at least one previous ECG event.

[0140] Additionally or alternatively, the defibrillator device may take the form of a wearable defibrillator and may also include a vest carrying electrodes.

[0141] Alternatively or additionally, the defibrillator device may take the form of an automated external defibrillator, wherein the electrodes are paddle electrodes.

[0142] Additionally or alternatively, the operating circuitry and output devices are housed in a conductive canister that serves as one of the electrodes, and one or more electrodes are also carried on leads attached to the canister, the leads being configured to pass through a blood vessel and attach to the heart, such that the defibrillator device takes the form of a transvenous implantable defibrillator.

[0143] Alternatively or additionally, the operating circuitry and output devices are housed in a conductive canister that serves as one of the electrodes, and one or more electrodes are also carried on leads attached to the canister that are configured for subcutaneous placement, such that the defibrillator device takes the form of a subcutaneously implantable defibrillator.

[0144] Each of these unrestricted examples can exist independently or can be combined with one or more other examples in various permutations or combinations.

[0145] The above detailed description includes references to the accompanying drawings, which form part of the detailed description. The drawings illustrate, by way of illustration, specific embodiments in which the invention can be practiced. These embodiments are also referred to herein as “examples.” These examples can also include elements other than those shown or described. However, the inventors also contemplate examples that provide only those elements shown or described. Furthermore, the inventors contemplate examples of any combination or arrangement of those elements (or one or more aspects thereof) shown or described, whether relating to a particular example (or one or more aspects thereof) or to other examples (or one or more aspects thereof) shown or described herein.

[0146] In the event of any inconsistency between the usage in this document and any other document incorporated by reference, the usage in this document shall prevail.

[0147] In this document, the terms “a” or “an” are common in patent documents and include one or more, and are not related to any other instance or use of “at least one” or “one or more”. Furthermore, in the following claims, the terms “first,” “second,” and “third,” etc., are used merely as labels and are not intended to impose numerical requirements on their objects.

[0148] The methods described herein can be implemented, at least in part, by a machine or computer. Some examples can include computer-readable or machine-readable media encoded with instructions operable to configure an electronic device to perform the methods described in the examples above. Implementations of these methods can include code, such as microcode, assembly language code, high-level language code, etc. This code can include computer-readable instructions for performing various methods. The code can form part of a computer program product. Furthermore, in one example, the code can be tangibly stored on one or more volatile, non-transitory, or non-volatile tangible computer-readable media, such as during execution or at other times. Examples of such tangible computer-readable media can include, but are not limited to, hard disks, removable disks or optical discs, magnetic tape cassettes, memory cards or memory sticks, random access memory (RAM), read-only memory (ROM), etc.

[0149] The above description is intended to be illustrative and not restrictive. For example, the above examples (or one or more aspects thereof) can be used in combination with each other. Other embodiments can be used, such as those used by those skilled in the art after reviewing the above description.

[0150] An abstract is provided to comply with 37C.FR §1.72(b) and to enable the reader to quickly determine the nature of the technical disclosure. It should be understood that this document is not intended to construe or limit the scope or meaning of the claims.

[0151] Furthermore, in the above detailed description, various features may be grouped together to simplify this disclosure. This should not be construed as meaning that disclosed features of non-claims are essential to any claim. Rather, the subject matter of the invention may be present in fewer than all features of a particular disclosed embodiment. Therefore, the following claims are incorporated herein by way of example or embodiment, wherein each claim exists independently as a separate embodiment, and these embodiments are contemplated to be combined with each other in various combinations or arrangements. The scope of the invention should be determined by reference to the appended claims and the full scope of their equivalents.

Claims

1. A defibrillator device, comprising: Multiple electrodes adapted to capture cardiac electrical signals and / or deliver electrical therapy to the patient; An output device for delivering defibrillation shocks using one or more electrodes, the output device including a charger and a treatment delivery capacitor; Operating circuitry is configured to use cardiac electrical signals from electrodes to detect and analyze the cardiac cycle to sense cardiac events and to determine whether and when to use the output device to deliver a defibrillation shock. The operating circuit is configured to perform the following operations: Determine the need for a defibrillation shock, and if a defibrillation shock is required, cause the output device to charge the treatment delivery capacitor to a predetermined shock threshold. After the treatment delivery capacitor is charged to a predetermined shock threshold: a) Detect the Nth ECG event; b) Characterize the Nth electrocardiographic event as an R wave or a T wave; and: If the Nth ECG event is an R wave, then the defibrillation shock is delivered according to the first shock protocol; or If the Nth ECG event is a T wave, then the defibrillation shock is delivered according to the second shock protocol. The operating circuit is further configured to characterize the Nth electrocardiographic event as an R wave or a T wave in the following manner: Each of N-1 and N-2 ECG events is sensed, wherein the N-1 ECG event precedes the Nth ECG event, and the N-2 ECG event precedes the N-1 ECG event, and each of the Nth, N-1, and N-2 ECG events represents a continuous detection of cardiac events; Observe the interval between the Nth and N-1th electrocardiographic events; Determine the amplitude of each of the N-1 and N-2 ECG events; The peak-to-peak ratio is calculated as the ratio of the amplitude of the N-1 ECG events to the amplitude of the N-2 ECG events. Determine whether the peak ratio falls within the similarity range, and: If the peak ratio falls within the similarity range, and if the interval is within the RT interval range, then the Nth ECG event is characterized as a T wave; otherwise, the Nth ECG event is characterized as an R wave. If the peak ratio is higher than the similarity range, and if the interval is within the RT interval range, then the Nth ECG event is characterized as a T wave; otherwise, the Nth ECG event is characterized as an R wave; or If the peak ratio is below the similarity range, the Nth ECG event is characterized as an R wave.

2. The defibrillator device according to claim 1, wherein, The operating circuit is configured such that: Delivering the defibrillation shock according to the first shock protocol includes: delivering the defibrillation shock after the expiration of the first shock delay following the Nth electrocardiographic event; and Delivering the defibrillation shock according to the second shock protocol includes delivering the defibrillation shock after the second shock delay following the Nth ECG event has expired.

3. The defibrillator device according to claim 1, wherein, The operating circuit is configured to set the second electric shock delay as follows: Sensing each of N-1, N-2, and N-3 ECG events, wherein the N-1 ECG event precedes the Nth ECG event, the N-2 ECG event precedes the N-1 ECG event, and the N-3 ECG event precedes the N-2 ECG event, and each of the Nth, N-1, N-2, and N-3 ECG events represents continuous detection of cardiac events; Determine the interval I1, where I1 represents the interval from the N-1th ECG event to the Nth ECG event; Determine the interval I2, where I2 represents the interval from the N-2th ECG event to the N-1th ECG event; Determine the interval I3, where I3 represents the interval from the N-3th ECG event to the N-2th ECG event; and The second shock delay is set to be equal to {I2+I3–I1}.

4. The defibrillator device according to claim 3, wherein, The operating circuit is configured to set the first shock delay to 0 or the greater of the average of I2 and I3 minus I1.

5. The defibrillator device according to claim 1, wherein, The operating circuit is further configured such that: Delivering the defibrillation shock according to the second shock protocol includes: sensing the next electrocardiographic event during a predetermined timeout interval, and choosing one of the following: If the next ECG event is sensed during the predetermined timeout interval, the defibrillation shock is delivered after the next ECG event is detected, or The defibrillation shock is delivered after a predetermined interval has elapsed if no other ECG event is detected.

6. The defibrillator device according to claim 1, wherein, The operating circuit is further configured such that: Delivering the defibrillation shock according to the second shock protocol includes: sensing the next electrocardiographic event during a predetermined timeout interval, and choosing one of the following: The defibrillation shock is delivered after a predetermined interval has elapsed if no other ECG event is detected; or If the next ECG event is sensed during the predetermined timeout period, the next ECG event is characterized as an R wave or a T wave, and: If the next ECG event is an R wave, then the defibrillation shock is delivered using the first shock protocol; or If the next ECG event is a T wave, then one of the following two options will be chosen: Sensing subsequent ECG events after the next ECG event, and delivering the defibrillation shock upon detection of the subsequent ECG event, or The defibrillation shock is delivered after the predetermined timeout interval expires if no further ECG event is detected following the next ECG event.

7. The defibrillator device according to claim 1, wherein, The operating circuit is also configured to sense at least N-1 and N-2 ECG events, wherein the N-1 ECG event occurs after the N-2 ECG event and before the Nth ECG event.

8. The defibrillator device according to claim 7, wherein, The operating circuit is configured to characterize the Nth electrocardiographic event as an R wave or a T wave in the following manner: The rectified peak ratio of the N-1 and N-2 ECG events is calculated as: the ratio of the maximum rectified peak value of the N-1 ECG event to the maximum rectified peak value of the N-2 ECG events; The peak-to-peak ratio of the N-1 and N-2 ECG events is calculated as the ratio of the sum of the amplitudes of the largest positive and negative peaks associated with the N-1 sensed ECG events to the sum of the amplitudes of the largest positive and negative peaks associated with the N-2 ECG events. Observe the interval between the Nth and N-1th electrocardiographic events; and: If the rectified peak ratio is within a first range, if the interval is within the RT interval range and the peak-to-peak ratio is higher than a second threshold, then the Nth ECG event is characterized as a T wave; otherwise, the Nth ECG event is characterized as an R wave. If the rectified peak ratio is lower than the first range, the Nth ECG event is characterized as an R wave; If the rectified peak ratio is higher than the first range, if the interval is less than the estimated RT interval and the peak-to-peak ratio is higher than the second threshold, then the Nth ECG event is characterized as a T wave; otherwise, the Nth ECG event is characterized as an R wave.

9. The defibrillator device according to claim 7, wherein, The operating circuit is configured to characterize the Nth electrocardiographic event as an R wave or a T wave in the following manner: Observe the interval between the Nth and N-1th electrocardiographic events; Determine the amplitude of each of the N-1 and N-2 ECG events; The peak-to-peak ratio is calculated as the ratio of the amplitude of the N-1 ECG events to the amplitude of the N-2 ECG events. Determine whether the peak ratio falls within the similarity range, and: If the peak ratio falls within the similarity range, and if the interval is within the RT interval range, then the Nth ECG event is characterized as a T wave; otherwise, the Nth ECG event is characterized as an R wave. If the peak ratio is higher than the similarity range, and if the interval is within the RT interval range, then the Nth ECG event is characterized as a T wave; otherwise, the Nth ECG event is characterized as an R wave; or If the peak ratio is below the similarity range, the Nth ECG event is characterized as an R wave.

10. The defibrillator device according to claim 1, wherein, The operating circuit is configured to sense an N-1th cardiac electrical signal preceding the Nth ECG event, and to characterize the Nth ECG event as an R wave or a T wave in the following manner: Determine the interval from the N-1th ECG event to the Nth ECG event; Compare the interval with the RT interval range; and If the interval is within the range of the RT interval, the Nth sensed ECG event is characterized as a T wave; otherwise The Nth electrocardiographic event is characterized as an R wave.

11. The defibrillator device according to claim 1, wherein, The operating circuit is configured to characterize the Nth ECG event as an R-wave or a T-wave by detecting at least one previous ECG event and determining one or more of the intervals or amplitudes associated with the previous ECG event that indicate whether the Nth ECG event should be characterized as an R-wave or a T-wave.

12. The defibrillator device according to claim 1, wherein, The operating circuit is configured to characterize the Nth ECG event as an R wave or a T wave by detecting at least one previous ECG event and analyzing the morphology of the at least one previous ECG event.

13. The defibrillator device according to any one of claims 1-12, wherein it takes the form of: Wearable defibrillators also include a vest carrying the electrodes; or An automated external defibrillator, wherein the electrodes are paddle electrodes.

14. The defibrillator device according to any one of claims 1-12, wherein, The operating circuitry and the output device are housed in a conductive canister, which serves as one of the electrodes, and one or more of the electrodes are also carried on leads attached to the canister, such that the defibrillator is configured for implantation in a patient.

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