Medical device for detecting tachyarrhythmia

Abstract

A medical device is configured to determine time intervals between successive cardiac events sensed from a cardiac electrical signal, to increase a value of a tachyarrhythmia interval count in response to each determined time interval that is detected as a tachyarrhythmia interval. The device is further configured to detect normal sinus rhythm events and to decrease the value of the tachyarrhythmia interval count in response to detecting a threshold number of normal sinus rhythm events.

Description

Technical Field

[0001] This disclosure generally relates to a medical device and a method for detecting rapid cardiac arrhythmias using the medical device. Background Technology

[0002] Medical devices such as pacemakers and implantable cardioverter-defibrillators (ICDs) deliver therapeutic electrical stimulation to a patient's heart via electrodes carried by one or more medical electrical leads and / or electrodes on the device housing. The electrical stimulation may include signals such as pacing pulses or cardioversion / defibrillation shocks. In some cases, the medical device may sense cardiac electrical signals accompanying intrinsic or pacing-induced depolarization of the heart and control the delivery of stimulation signals to the heart based on the sensed cardiac electrical signals. Upon detection of an abnormal rhythm (e.g., bradycardia, tachycardia, or fibrillation), one or more appropriate electrical stimulation signals may be delivered to restore or maintain a more normal heart rhythm. For example, an ICD may deliver a pacing pulse to a patient's heart upon detection of bradycardia or tachycardia, or deliver a cardioversion / defibrillation (CV / DF) shock to the heart upon detection of tachycardia or fibrillation.

[0003] An intracardiac disc (ICD) can sense cardiac electrical signals within the heart chambers and deliver electrical stimulation therapy to the chambers using electrodes carried by transvenous medical leads. Cardiac signals sensed within the heart chambers typically possess high signal strength and quality, enabling reliable sensing of near-field cardiac electrical events, such as ventricular R waves sensed from within the ventricles. In some proposed or available ICD systems, non-transvenous leads can be coupled to the ICD, presenting new challenges in accurately sensing cardiac electrical events from sensing sites outside the heart. Summary of the Invention

[0004] In general, this disclosure relates to techniques for detecting tachyarrhythmias and avoiding erroneous tachyarrhythmia detection in the presence of variability in cardiac signal amplitude, such as electromagnetic interference (EMI) or electromyographic signals, and / or cardiac electrical signal noise. Detection of ventricular tachyarrhythmias, such as ventricular tachycardia (VT) or ventricular fibrillation (VF), can be based on detecting a ventricular rate faster than the tachyarrhythmia detection rate over at least a predetermined number of ventricular cycles. The VT or VF rate can be detected by sensing R waves from the cardiac electrical signal, determining the ventricular interval or RR interval (RRI) between consecutively sensed R waves, and counting the number of ventricular intervals shorter than the VT or VF detection interval. Due to variability in cardiac signal amplitude and / or due to intervals caused by non-cardiac noise, other cardiac events (e.g., P waves or T waves and / or non-cardiac noise) may be oversensed as ventricular R waves. This oversensing can lead to an increased count of VT or VF intervals when an underlying normal sinus rhythm (NSR) may be present. A medical device operating according to the technology disclosed herein can detect NSR beats occurring during a series of ventricular intervals, including the tachyarrhythmia detection interval. The device is configured to decrease the value of a tachyarrhythmia interval counter in response to the detection of an NSR beat that meets reset criteria. When a potential NSR is present, the tachyarrhythmia interval counter can be decreased to a predetermined value to prevent the value of the tachyarrhythmia interval counter from reaching a VT or VF detection threshold.

[0005] In one embodiment, this disclosure provides a medical device including a cardiac electrical signal sensing circuit, a control circuit, and a treatment delivery circuit. The cardiac electrical signal sensing circuit is configured to receive and sense cardiac events from cardiac electrical signals. The control circuit is configured to determine time intervals between consecutively sensed cardiac events, detect tachyarrhythmia intervals from the determined time intervals, increment a tachyarrhythmia interval count in response to the detection of each detected tachyarrhythmia interval, and detect normal sinus rhythm intervals from the determined time intervals. The control circuit determines when a normal sinus rhythm interval with a reset threshold number is detected and decrements the tachyarrhythmia interval count in response to the detection of a reset threshold number of normal sinus rhythm intervals. After decrementing the tachyarrhythmia interval count, the control circuit determines when the tachyarrhythmia interval count subsequently reaches a tachyarrhythmia detection threshold and detects a tachyarrhythmia in response to the tachyarrhythmia interval count reaching the tachyarrhythmia detection threshold. In response to the detection of a rapid arrhythmia, the treatment delivery circuit provides treatment for the rapid arrhythmia.

[0006] In another embodiment, this disclosure provides a method comprising sensing cardiac events from cardiac electrical signals, determining time intervals between consecutively sensed cardiac events, detecting tachyarrhythmic intervals based on the determined time intervals, incrementing a tachyarrhythmic interval count in response to the detection of each detected tachyarrhythmic interval, and detecting normal sinus rhythm intervals from the determined time intervals. The method further comprises determining when a reset threshold number of normal sinus rhythm intervals is detected and decrementing the tachyarrhythmic interval count in response to the detection of the reset threshold number of normal sinus rhythm intervals. After decrementing the tachyarrhythmic interval count, the method may further comprise determining when the tachyarrhythmic interval count subsequently reaches a tachyarrhythmia detection threshold and detecting a tachyarrhythmia in response to the tachyarrhythmia interval count reaching the tachyarrhythmia detection threshold. The method may include delivering tachyarrhythmia treatment in response to the detection of a tachyarrhythmia.

[0007] In another embodiment, this disclosure provides a non-transitory computer-readable medium storing a set of instructions that, when executed by control circuitry of a medical device, cause the medical device to sense cardiac events from cardiac electrical signals, determine time intervals between consecutively sensed cardiac events, detect tachyarrhythmia intervals from the determined time intervals, increment a tachyarrhythmia interval count in response to the detection of each detected tachyarrhythmia interval, determine when a normal sinus rhythm interval of a reset threshold number is detected, and decrement a tachyarrhythmia interval count in response to the reset threshold number of detected normal sinus rhythm intervals. After decrementing the tachyarrhythmia interval count, the instructions may further cause the device to determine that the tachyarrhythmia interval count subsequently reaches a tachyarrhythmia detection threshold, detect a tachyarrhythmia in response to the tachyarrhythmia interval count reaching the tachyarrhythmia detection threshold, and deliver tachyarrhythmia treatment in response to the detection of a tachyarrhythmia.

[0008] This invention is intended to provide an overview of the subject matter described herein. It is not intended to provide an exclusive or exhaustive explanation of the apparatus and methods described in detail in the following drawings and description. Further details of one or more embodiments are set forth in the following drawings and description. Attached Figure Description

[0009] Figure 1A and 1B This is a conceptual diagram of an extravascular ICD system configured, according to one embodiment, to sense cardiac electrical events and deliver cardiac electrical stimulation therapy.

[0010] Figures 2A-2C This is a conceptual diagram of a patient who has had an extra-cardiovascular ICD system implanted. The implantation structure of this system differs from...Figures 1A-1B The layout shown.

[0011] Figure 3 This is a conceptual diagram of an ICD based on one embodiment.

[0012] Figure 4 It can be included in Figure 3 The circuit diagram of the sensing circuit in the ICD.

[0013] Figure 5 This is a flowchart of a method for controlling a rapid arrhythmia interval counter according to one embodiment.

[0014] Figure 6A This is a flowchart of a method for setting an NSR interval threshold according to one embodiment.

[0015] Figure 6B This is a flowchart of a method for controlling the adjustment of a ventricular tachyarrhythmia interval counter according to another embodiment.

[0016] Figure 7 This is a flowchart of a method for detecting NSR pulsation according to some embodiments.

[0017] Figure 8 This is a diagram of an embodiment of a notch-filtered cardiac electrical signal segment from which cardiac signal segment pulsation characteristics are determined for use in detecting NSR pulsations.

[0018] Figure 9 This is a diagram of another embodiment of a notch-filtered cardiac electrical signal segment from which cardiac signal segment pulsation characteristics are determined for use in detecting NSR pulsations.

[0019] Figure 10 This is a flowchart of a method for determining an overall morphological measure of the morphology of rapid arrhythmias used to detect cardiac signal fragments, according to one embodiment.

[0020] Figure 11 This is a flowchart of a method for detecting rapid arrhythmia morphology of cardiac electrical signal segments according to another embodiment.

[0021] Figure 12 This is a flowchart of a method for detecting ventricular tachyarrhythmias performed by an ICD according to some embodiments. Detailed Implementation

[0022] In summary, this disclosure describes techniques for detecting tachyarrhythmias using a medical device. The medical device can be configured to sense R waves accompanying ventricular depolarization from cardiac electrical signals for controlling ventricular pacing and detecting ventricular tachyarrhythmias. Ventricular tachyarrhythmias can be detected in response to a threshold number of R waves occurring at intervals shorter than the tachyarrhythmia detection interval (referred to as RRI). Cardiac events (e.g., P waves or T waves) and / or non-cardiac noise (e.g., EMI or electromyographic signals) may be oversensed as R waves, leading to erroneous RRIs being identified as ventricular tachyarrhythmia intervals. In some cases, variations in R wave signal intensity due to patient movement or other factors may lead to oversensing of cardiac events and / or non-cardiac noise, resulting in relatively short RRIs being counted in the detection of tachyarrhythmias when the underlying rhythm may actually be a normal sinus rhythm. An incorrect detection of tachyarrhythmia may result in a CV / DF shock or other tachyarrhythmia treatment delivered by a medical device, such as anti-tachyarrhythmic pacing (ATP), when such treatment may not be necessary.

[0023] A medical device performing the technology disclosed herein detects NSR (or non-tachyarrhythmic) beats when the count of the tachyarrhythmia interval is not zero, and resets or adjusts the count of the tachyarrhythmia interval to a lower value in response to the detection of an NSR beat. In this way, when an NSR beat event is detected, it indicates the presence of an underlying normal sinus rhythm, and by decreasing the value of the tachyarrhythmia interval counter once or multiple times during counter increments after each tachyarrhythmia interval detection, the detection of RRI-based tachyarrhythmias can be prolonged or jointly suppressed.

[0024] In some embodiments, a medical device performing the techniques disclosed herein may be included in an extracardiac ICD system. As used herein, the term “extracardiac” refers to a location outside the blood vessels surrounding the patient’s heart, the heart, and the pericardium. Implantable electrodes carried by extracardiac leads may be placed extrathoracically (outside the thoracic cavity and sternum) or intrathoracically (below the thoracic cavity or sternum), but typically not in close contact with myocardial tissue. Changes in patient position or patient physical activity, as well as other factors, may cause variations in the amplitude of cardiac event signals (e.g., P-wave amplitude, R-wave amplitude, and T-wave amplitude) in signals sensed from extracardiac locations. For example, signals sensed extracardiac may be more susceptible to amplitude variations and noise contamination than signals sensed intracardiac due to myoelectric potentials or environmental EMI. The techniques disclosed herein for adjusting tachyarrhythmia interval counter values ​​based on NSR beat monitoring can be applied to cardiac electrical signals sensed using extracardiac electrodes and are not intended to be limiting. As described herein, analysis of RRI and cardiac electrical signal morphology is performed to detect ventricular beats that may be NSR beats.

[0025] This article describes tachyarrhythmia detection techniques in conjunction with ICDs and implantable extravascular medical leads carrying sensing and therapeutic delivery electrodes. However, the aspects disclosed herein can be used in conjunction with other cardiac medical devices or systems. For example, the tachyarrhythmia detection techniques described with reference to the accompanying figures can be implemented in any implantable or external medical device capable of sensing intrinsic cardiac electrical events via sensing electrodes received from the patient's heart. These include implantable pacemakers, ICDs, or cardiac monitors connected to venous, pericardial, or epicardial leads carrying sensing and therapeutic delivery electrodes; leadless pacemakers, ICDs, or cardiac monitors with housing-based sensing electrodes; and external or wearable pacemakers, defibrillators, or cardiac monitors coupled to external, surface, or skin electrodes.

[0026] Furthermore, while the illustrative embodiments presented herein relate to the detection of ventricular tachyarrhythmias, the disclosed techniques can also be implemented in medical devices configured to detect (and optionally treat) atrial tachyarrhythmias. In this case, when the PP interval occurring between consecutively sensed atrial P waves is shorter than the atrial tachyarrhythmia detection interval, the atrial tachyarrhythmia interval counter can be increased. Based on the analysis of the PP interval and P wave morphology, cardiac electrical signals that can be sensed from inside or outside the atrium can be analyzed to detect atrial NSR beats. When atrial NSR beats are detected according to the methods disclosed herein, the value of the atrial tachyarrhythmia interval counter can be decreased.

[0027] Figure 1A and 1B This is a conceptual diagram of an extra-cardiac ICD system 10 configured to sense cardiac electrical events and deliver cardiac electrical stimulation therapy according to one embodiment. Figure 1A This is a front view of the ICD system 10 implanted in patient 12. Figure 1B This is a side view of the ICD system 10 implanted in the patient 12. The ICD system 10 includes an ICD 14 connected to cardiovascular external electrical stimulation and sensing leads 16. Figure 1A and 1B This is described in the context of an ICD system 10 capable of delivering a high-voltage CV / DF shock in response to the detection of a tachyarrhythmia, and in some embodiments, delivering a cardiac pacing pulse. However, the techniques disclosed herein for detecting tachyarrhythmias can be implemented in other cardiac devices configured to sense cardiac events and determine a heart rate for controlling cardiac electrical stimulation therapy.

[0028] The ICD 14 includes a housing 15 forming a hermetically sealed enclosure that protects the internal components of the ICD 14. The housing 15 of the ICD 14 may be formed of a conductive material, such as titanium or a titanium alloy. The housing 15 may function as an electrode (sometimes referred to as a "can" electrode). The housing 15 may be used as an active can electrode for delivering CV / DF shocks or other high-voltage pulses delivered using high-voltage therapeutic circuitry. In other embodiments, the housing 15 may be used to deliver unipolar low-voltage cardiac pacing pulses and / or for sensing cardiac electrical signals in conjunction with electrodes carried by lead 16. In other cases, the housing 15 of the ICD 14 may include multiple electrodes on an external portion of the housing. One or more external portions of the housing 15 that serve as one or more electrodes may be coated with a material such as titanium nitride, for example, to reduce post-stimulation polarization artifacts.

[0029] The ICD 14 includes a connector assembly 17 (also referred to as a connector block or header) that includes an electrical feedthrough through a housing 15 to provide electrical connection between a conductor extending within the lead body 18 of the lead 16 and electronic components included within the housing 15 of the ICD 14. As will be described in more detail herein, the housing 15 may house one or more processors, memories, transceivers, cardiac electrical signal sensing circuitry, therapeutic delivery circuitry, power supplies, and other components for sensing cardiac electrical signals, detecting heart rhythm, and controlling and delivering electrical stimulation pulses to treat abnormal heart rhythms.

[0030] The elongated lead body 18 has a proximal end 27 comprising a lead connector (not shown) configured to connect to an ICD connector assembly 17, and a distal end 25 comprising one or more electrodes. Figure 1A and 1B In the embodiments described herein, the distal portion 25 of the lead body 18 includes defibrillation electrodes 24 and 26 and pacing / sensing electrodes 28 and 30. In some cases, defibrillation electrodes 24 and 26 may form a defibrillation electrode together, as they can be configured to be activated simultaneously. Alternatively, defibrillation electrodes 24 and 26 may form separate defibrillation electrodes, in which case each of electrodes 24 and 26 can be activated independently.

[0031] Electrodes 24 and 26 (and in some embodiments, housing 15) are referred to herein as defibrillation electrodes because they are used individually or collectively to deliver high-voltage stimulation therapy (e.g., cardioversion or defibrillation shock). Electrodes 24 and 26 may be elongated coil electrodes and generally have a relatively large surface area for delivering high-voltage electrical stimulation pulses compared to pacing electrode 28 and sensing electrode 30. However, in addition to or instead of high-voltage stimulation therapy, electrodes 24 and 26 and housing 15 may also be used to provide pacing functionality, sensing functionality, or both pacing and sensing functionality. In this sense, the use of the term "defibrillation electrode" herein should not be construed as limiting electrodes 24 and 26 to high-voltage cardioversion / defibrillation shock therapy applications only. For example, either electrode 24 or 26 may be used as a sensing electrode in a sensing vector to sense cardiac electrical signals and determine the need for electrical stimulation therapy.

[0032] Electrodes 28 and 30 are relatively small surface area electrodes that can be used to sense cardiac electrical signals and, in some configurations, can be used to deliver relatively low-voltage pacing pulses. Electrodes 28 and 30 are referred to as pacing / sensing electrodes because they are typically configured for use in low-voltage applications, such as as cathodes or anodes for delivering pacing pulses and / or sensing cardiac electrical signals, in contrast to delivering high-voltage CV / DF shocks. In some cases, electrodes 28 and 30 may provide pacing functionality only, sensing functionality only, or both.

[0033] The ICD 14 can sense cardiac electrical signals corresponding to the electrical activity of the heart 8 via a combination of sensing electrode vectors including combinations of electrodes 24, 26, 28, and / or 30. In some embodiments, the housing 15 of the ICD 14 is used in combination with one or more of the electrodes 24, 26, 28, and / or 30 in the sensing electrode vectors. Various sensing electrode vectors utilizing combinations of electrodes 24, 26, 28, and 30 with the housing 15 are described below for sensing first and second cardiac electrical signals using corresponding first and second sensing electrode vectors selectable by sensing circuitry included in the ICD 14.

[0034] exist Figure 1A and Figure 1BIn the embodiments illustrated herein, electrode 28 is located proximal to defibrillator electrode 24, and electrode 30 is located between defibrillator electrodes 24 and 26. One, two, or more pacing / sensing electrodes may be carried by lead body 18. For example, in some embodiments, a third pacing / sensing electrode may be located distal to defibrillator electrode 26. Electrodes 28 and 30 are illustrated as loop electrodes; however, electrodes 28 and 30 may comprise any of several different types of electrodes, including loop electrodes, short coil electrodes, hemispherical electrodes, directional electrodes, or segmented electrodes, etc. Electrodes 28 and 30 may be positioned along lead body 18 at other locations, not limited to those shown. In other embodiments, lead 16 may include fewer or more pacing / sensing electrodes and / or defibrillator electrodes than in the embodiments shown herein.

[0035] In the illustrated embodiment, lead 16 extends centrally subcutaneously or submuscularly over the thoracic cavity 32 from connector assembly 27 of ICD 14 toward the center of the patient 12's torso (e.g., toward the xiphoid process 20 of patient 12). Near the xiphoid process 20, lead 16 bends or turns upward, subcutaneously or submuscularly, above the thoracic cavity and / or sternum 22. Although in Figure 1A The description indicates that the lead 16 extends laterally from and substantially parallel to the sternum 22, but the distal portion 25 of the lead 16 can be implanted at other locations, such as above the sternum 22, offset to the right or left of the sternum 22, or at an angle laterally from the sternum 22 to the left or right. Alternatively, the lead 16 can be placed along other subcutaneous or submuscular pathways. The path of the cardiovascular lead 16 may depend on the location of the ICD 14, the arrangement and location of the electrodes carried by the lead body 18, and / or other factors.

[0036] Electrical conductors (not shown) pass through one or more lumens of the elongated lead body 18 of lead 16 from a lead connector at the proximal lead end 27 to electrodes 24, 26, 28, and 30 positioned along the distal portion 25 of the lead body 18. The elongated electrical conductors contained within the lead body 18 (which may be separate, corresponding insulated conductors within the lead body 18) are each electrically coupled to the respective defibrillation electrodes 24 and 26 and pacing / sensing electrodes 28 and 30. The respective conductors electrically couple electrodes 24, 26, 28, and 30 to circuitry (e.g., treatment delivery circuitry and / or sensing circuitry) of the ICD 14 via connectors in the connector assembly 17 (including associated electrical feedthroughs through the housing 15). The electrical conductors transmit treatment from the treatment delivery circuitry within the ICD 14 to one or more of the defibrillation electrodes 24 and 26 and / or the pacing / sensing electrodes 28 and 30, and transmit sensed electrical signals generated by the patient's heart 8 from one or more of the defibrillation electrodes 24 and 26 and / or the pacing / sensing electrodes 28 and 30 to the sensing circuitry within the ICD 14.

[0037] The lead body 18 of lead 16 may be formed of a non-conductive material (including silicone, polyurethane, fluoropolymers, mixtures thereof, and / or other suitable materials) and shaped to form one or more cavities in which one or more conductors extend. The lead body 18 may be tubular or cylindrical. In other embodiments, the distal portion 25 (or all) of the elongated lead body 18 may have a flat, strip, or paddle-shaped shape. The lead body 18 may be formed with a pre-shaped distal portion 25, which is typically straight, curved, bent, serpentine, wavy, or serrated.

[0038] In the illustrated embodiment, the lead body 18 includes a curved distal portion 25 having two "C"-shaped curves together resembling the Greek letter epsilon "ε". Defibrillation electrodes 24 and 26 are each carried from one of the two corresponding C-shaped portions of the distal portion 25 of the lead body. The two C-shaped curves extend or bend in the same direction away from the central axis of the lead body 18, along which pacing / sensing electrodes 28 and 30 are positioned. In some cases, pacing / sensing electrodes 28 and 30 may be substantially aligned with the central axis of the straight proximal portion of the lead body 18, such that the midpoints of defibrillation electrodes 24 and 26 are laterally offset from pacing / sensing electrodes 28 and 30.

[0039] Other embodiments of cardiovascular external leads, including one or more defibrillation electrodes and one or more pacing and sensing electrodes carried by a curved, serrated, wavy, or zigzag distal portion of the lead body 18, can be implemented using the techniques described herein, as generally disclosed in U.S. Patent Publication No. 2016 / 0158567 (Marshall et al.). However, the techniques disclosed herein are not limited to any particular lead body design or electrode arrangement. In other embodiments, the lead body 18 is a flexible, elongated lead body without any pre-formed shape, bend, or curvature.

[0040] The ICD 14 analyzes cardiac electrical signals received from one or more sensing electrode vectors to monitor abnormal rhythms, such as cardiac arrest, bradycardia, ventricular tachycardia (VT), or ventricular fibrillation (VF). The ICD 14 can analyze the heart rate and morphology of the cardiac electrical signals to monitor tachyarrhythmias according to any of several tachyarrhythmia detection techniques. These tachyarrhythmia detection techniques can implement aspects of the methods disclosed herein for detecting NSR beats and / or reducing the value of a tachyarrhythmia interval counter to suppress or prolong the process of detecting tachyarrhythmias upon detection of an NSR beat.

[0041] The ICD 14 generates and delivers electrical stimulation therapy in response to the detection of tachyarrhythmias (e.g., VT or VF) using a therapeutic delivery electrode vector selectable from any of the available electrodes 24, 26, 28, 30 and / or housing 15. The ICD 14 may deliver antitachycardia pacing (ATP) in response to VT detection, and in some cases may deliver ATP prior to a CV / DF shock or during high-voltage capacitor charging to attempt to avoid the need for a CV / DF shock. If ATP fails to terminate VT or when VF is detected, the ICD 14 may deliver one or more CV / DF shocks via one or both of the defibrillation electrodes 24 and 26 and / or housing 15. The ICD 14 may deliver a CV / DF shock individually or together using electrodes 24 and 26 as cathodes (or anodes) and housing 15 as an anode (or cathode). The ICD 14 can use the pacing electrode vector of the housing 15 containing one or more of electrodes 24, 26, 28 and 30 and the ICD 14 to generate and deliver other types of electrical stimulation pulses, such as post-shock pacing pulses or bradycardia pacing pulses.

[0042] ICD 14 is shown as a subcutaneous implantation along the left side of patient 12, along the thoracic cavity 32. In some cases, ICD 14 may be implanted between the left posterior axillary line and the left anterior axillary line of patient 12. However, ICD 14 may be implanted in other subcutaneous or submuscular locations within patient 12. For example, ICD 14 may be implanted in a subcutaneous pouch in the chest region. In this case, lead 16 may extend subcutaneously or submuscularly from ICD 14 toward the manubrium of sternum 22, and bend downwards or turn from the manubrium to the desired subcutaneous or submuscular location. In yet another embodiment, ICD 14 may be placed in the abdomen. Lead 16 may also be implanted in other extracardiac or extravascular locations. For example, as per [reference to...] Figures 2A to 2C As described, the distal portion 25 of the lead 16 can be implanted under the sternum / pleural cavity in the substernal space. Figure 1A and 1B This is illustrative in nature and should not be considered as limiting the practice of the techniques disclosed herein.

[0043] External device 40 is shown communicating telemetry with ICD 14 via communication link 42. External device 40 may include processor 52, memory 53, display 54, user interface 56, and telemetry unit 58. Processor 52 controls the operation of external device and processes data and signals received from ICD 14. Display 54, which may include a graphical user interface, displays data and other information to the user for viewing parameters of ICD operation and programming, as well as cardiac electrical signals retrieved from ICD 14.

[0044] User interface 56 may include a mouse, touchscreen, keypad, etc., to enable a user to interact with external device 40 to initiate a telemetry session with ICD 14 for retrieving and / or transmitting data to ICD 14, including programmable parameters for controlling cardiac event sensing and treatment delivery. Telemetry unit 58 includes a transceiver and antenna configured for bidirectional communication with telemetry circuitry contained in ICD 14, and configured to operate in conjunction with processor 52 for sending and receiving data related to ICD functionality via communication link 42.

[0045] For example, A communication link 42 is established between the ICD 14 and the external device 40 via Wi-Fi, a Medical Implantable Communication Service (MICS), or other RF or communication frequency bandwidth or communication protocol. Data stored or acquired by the ICD 14, including physiological signals or associated data derived therefrom, device diagnostic results, and the history of detected episodes and delivered treatments, can be retrieved by the external device 40 from the ICD 14 upon request.

[0046] External device 40 may be embodied as a programmer used in a hospital, clinic, or physician's office to retrieve data from ICD 14 and program the operating parameters and algorithms in ICD 14 to control ICD functions. External device 40 may alternatively be embodied as a home monitor or a handheld device. External device 40 can be used to program cardiac signal sensing parameters, heart rhythm detection parameters, and treatment control parameters used by ICD 14. In some embodiments, external device 40 may be used to program at least some control parameters for detecting cardiac events and tachyarrhythmias according to the techniques disclosed herein into ICD 14.

[0047] Figures 2A-2C Patient 12 is different Figures 1A-1B The diagram shows a conceptual arrangement of an implantable extravascular ICD system 10. Figure 2A This is a front view of patient 12 who has system 10 implanted. Figure 2B This is a side view of patient 12 with system 10 implanted. Figure 2C This is a transverse view of a patient 12 with system 10 implanted. In this arrangement, the cardiovascular external guide 16 of system 10 is at least partially implanted below the sternum 22 of patient 12. The guide 16 extends subcutaneously or submuscularly from ICD 14 toward xiphoid process 20, and bends or turns within the anterior mediastinum 36 in a substernal position near xiphoid process 20 and extends upward.

[0048] The anterior mediastinum 36 can be considered as being transversely defined by the pleura 39, posteriorly defined by the pericardium 38, and anteriorly defined by the sternum 22 (see [reference]).Figure 2C The distal portion 25 of the guide 16 may extend substantially within the loose connective tissue and / or substernal muscle tissue of the anterior mediastinum 36 along the posterior aspect of the sternum 22. A guide implanted such that the distal portion 25 is substantially within the anterior mediastinum 36 may be referred to as a “substernal guide”.

[0049] exist Figures 2A to 2C In the example described, the lead 16 is located substantially below the center of the sternum 22. However, in other cases, the lead 16 may be implanted such that it is laterally offset from the center of the sternum 22. In some cases, the lead 16 may extend laterally such that, in addition to or in place of the sternum 22, the distal portion 25 of the lead 16 is below / below the pleural cavity 32. In other embodiments, the distal portion 25 of the lead 16 may be implanted in other extracardiac intrathoracic locations, including the pleural cavity or the pericardium 38 surrounding and adjacent to the pericardium 38 of the heart 8.

[0050] Figure 3 This is a conceptual diagram of a circuit that may be included in ICD 14 according to one embodiment. The electronic circuitry system is enclosed within housing 15. Figure 3 The ICD (illustrated schematically as electrodes) includes software, firmware, and hardware that collaboratively monitor cardiac electrical signals, determine when electrical stimulation therapy is needed, and deliver therapy as needed based on a programmed therapy delivery algorithm and control parameters. The ICD 14 can be coupled to a cardiovascular lead, such as lead 16 carrying cardiovascular external electrodes 24, 26, 28, and 30, for delivering electrical stimulation pulses to the patient's heart and for sensing cardiac electrical signals.

[0051] The ICD 14 includes control circuitry 80, memory 82, therapeutic delivery circuitry 84, cardiac electrical signal sensing circuitry 86, and telemetry circuitry 88. A power supply 98 provides power to the ICD 14's circuitry (including each of components 80, 82, 84, 86, and 88) as needed. The power supply 98 may include one or more energy storage devices, such as one or more rechargeable or non-rechargeable batteries. Connections between the power supply 98 and each of the other components 80, 82, 84, 86, and 88 will be made from... Figure 3 The overall block diagram is for understanding purposes, but is not shown for clarity. For example, power supply 98 may be connected to one or more charging circuits included in treatment delivery circuitry 84 to charge a holding capacitor included in treatment delivery circuitry 84, which discharges at appropriate times under the control of control circuitry 80 to generate electrical pulses according to a treatment protocol. Power supply 98 may also be connected as needed to components of cardiac electrical signal sensing circuitry 86, such as sensing amplifiers, analog-to-digital converters, switching circuit systems, etc., to perform the cardiac electrical signal sensing functionality of sensing circuitry 86 as described herein.

[0052] Figure 3 The circuitry shown represents the functionality contained in ICD 14 and may include any discrete and / or integrated electronic circuitry components implementing analog and / or digital circuitry capable of producing the functionality attributed herein to ICD 14. Functionality associated with one or more circuits may be performed by separate hardware, firmware, or software components, or integrated within general-purpose hardware, firmware, or software components. For example, cardiac event sensing, NSR beat detection, and tachyarrhythmia detection may be performed collaboratively by sensing circuitry 86 and control circuitry 80, and may include operations implemented in a processor or other signal processing circuitry included in control circuitry 80, which executes instructions and control signals stored in memory 82, such as blanking and timing, and sensing threshold amplitude signals sent from control circuitry 80 to sensing circuitry 86.

[0053] The various circuitry of the ICD 14 may include application-specific integrated circuits (ASICs), electronic circuitry, processors (shared, dedicated, or grouped) and memory, combinational logic circuitry, state machines, or other suitable components or combinations thereof that provide the described functionality, executing one or more software or firmware programs. The specific form of the software, hardware, and / or firmware used to implement the functionality disclosed herein will be determined primarily by the specific system architecture employed in the ICD and the specific detection and treatment delivery methods employed by the ICD. Providing software, hardware, and / or firmware to implement the described functionality within the context of any modern implantable cardiac device system, based on the disclosure herein, is within the capabilities of those skilled in the art.

[0054] Memory 82 may comprise any volatile, non-volatile, magnetic, or electrically non-transitory computer-readable storage medium, such as random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically erasable programmable ROM (EEPROM), flash memory, or any other memory device. Furthermore, memory 82 may comprise a non-transitory computer-readable medium storing instructions that, when executed by one or more processing circuits, cause control circuitry 80 and / or other ICD components to perform various functions belonging to ICD 14 or those ICD components. The non-transitory computer-readable medium storing instructions may comprise any of the media listed above.

[0055] The control circuit 80 communicates, for example, via a data bus with the treatment delivery circuit 84 and the sensing circuit 86, for sensing cardiac electrical activity, detecting heart rhythm, and controlling the delivery of cardiac electrical stimulation therapy in response to the sensed cardiac signals. The treatment delivery circuit 84 and the sensing circuit 86 are electrically coupled to electrodes 24, 26, 28, 30 and housing 15 carried by leads 16, which can serve as common or ground electrodes or as active canned electrodes for delivering CV / DF shock pulses or cardiac pacing pulses.

[0056] Sensing circuitry 86 may be selectively connected to electrodes 28, 30 and / or housing 15 to monitor the electrical activity of a patient's heart. Sensing circuitry 86 may also be selectively connected to defibrillation electrodes 24 and / or 26 for use in a sensing electrode vector together or in combination with one or more of electrodes 28, 30 and / or housing 15. Sensing circuitry 86 may be able to selectively receive cardiac electrical signals from at least two sensing electrode vectors of available electrodes 24, 26, 28, 30 and housing 15. In some instances, at least two cardiac electrical signals from two different sensing electrode vectors may be received simultaneously by sensing circuitry 86. Sensing circuitry 86 may simultaneously monitor one or both of the cardiac electrical signals for sensing cardiac electrical events and / or generating digitized cardiac signal waveforms for analysis by control circuitry 80. For example, sensing circuitry 86 may include switching circuitry for selecting which of electrodes 24, 26, 28, 30 and housing 15 are coupled to a first sensing channel 83 and which electrodes are coupled to a second sensing channel 85 of sensing circuitry 86.

[0057] Each sensing channel 83 and 85 can be configured to amplify, filter, and digitize cardiac electrical signals received from selected electrodes coupled to the respective sensing channel to improve signal quality for detecting cardiac electrical events (e.g., R waves) or performing other signal analyses. The cardiac event detection circuitry within sensing circuitry 86 may include one or more sensing amplifiers, filters, rectifiers, threshold detectors, comparators, analog-to-digital converters (ADCs), timers, or combinations thereof. Figure 4 Other analog or digital components are further described. The cardiac event sensing threshold can be automatically adjusted by the sensing circuit 86 under the control of the control circuit 80 based on a time period and the value of the sensing threshold determined by the control circuit 80, stored in the memory 82, and / or controlled by the hardware, firmware, and / or software of the control circuit 80 and / or the sensing circuit 86.

[0058] When a cardiac event is detected based on a sensing threshold crossing, the first sensing channel 83 can generate a sensed event signal (e.g., an R-wave sensing event signal) that is transmitted to the control circuit 80. (See below for further details.) Figures 5 to 12The event signal sensed from the first sensing channel 83 is used by the control circuit 80 to trigger the storage of a time segment of a second cardiac electrical signal from the second sensing channel 85 for processing and analysis to detect NSR beats and adjust the ventricular tachyarrhythmia interval counter. The memory 82 can be configured to store a predetermined number of cardiac electrical signal segments in a cyclic buffer under the control of the control circuit 80, for example, at least one, two, three, or other numbers of cardiac electrical signal segments. Each segment can be written to the memory 82 within an extended time interval before and after the trigger R-wave sensing event signal generated by the first sensing channel 83. The control circuit 80 can access the stored cardiac electrical signal segments to verify the R-wave sensing of the first sensing channel 83 and appropriate tachyarrhythmia interval detection, which can be performed before meeting tachyarrhythmia detection criteria and actual tachyarrhythmia detection.

[0059] The control circuit 80 also uses R-wave sensing event signals to determine the RRI (Regular Response Index) to detect tachyarrhythmias and determine treatment needs. The RRI is the time interval between consecutively sensed R waves and can be determined between consecutive R-wave sensing event signals received from the sensing circuit 86. For example, the control circuit 80 may include a timing circuit 90 for determining the RRI between consecutive R-wave sensing event signals received from the sensing circuit 86 and for controlling various timers and / or counters for controlling the timing of treatment deliveries by the treatment delivery circuit 84. The timing circuit 90 may additionally set a time window (e.g., a morphological template window, a morphological analysis window) or perform other timing-related functions of the ICD 14, including synchronizing the electric shock or other treatment delivered by the treatment delivery circuit 84 with the sensed cardiac events.

[0060] The control circuit 80 is also shown to include a tachyarrhythmia detector 92, configured to analyze signals received from the sensing circuit 86 to detect tachyarrhythmia episodes. The tachyarrhythmia detector 92 may be implemented in the control circuit 80 as hardware, software, and / or firmware for processing and analyzing signals received from the sensing circuit 86 for detecting VT and / or VF. The timing circuit 90 uses the timing of R-wave sensing event signals received from the sensing circuit 86 to determine the RRI between consecutively sensed event signals. The tachyarrhythmia detector 92 may include comparators and counters for counting the RRIs determined by the timing circuit 92, the RRIs falling within various rate detection regions for determining ventricular rates or performing other rate- or interval-based assessments for detecting and distinguishing VT and VF.

[0061] For example, the tachyarrhythmia detector 92 can compare the RRI determined by timing circuitry 90 with one or more tachyarrhythmia detection intervals, such as tachycardia detection intervals and fibrillation detection intervals. RRIs falling within a detection interval are counted by the corresponding VT interval counter or VF interval counter, and in some cases by a combination of VT / VF interval counters included in the tachyarrhythmia detector 92. When the interval counter value reaches a detection threshold number, a ventricular tachyarrhythmia can be detected by the tachyarrhythmia detector 92. The tachyarrhythmia detector 92 can be configured to perform further signal analysis to determine whether other detection criteria, such as R-wave morphology criteria, episodic criteria, and noise and oversensitivity rejection criteria, are met before detecting VT or VF. Furthermore, in conjunction with… Figures 5-12 An embodiment is described in which parameters can be determined by a rapid arrhythmia detector 92 based on cardiac electrical signals received from a sensing circuit 86, said cardiac electrical signals being used to detect NSR beats for adjusting the value of a VT or VF interval counter.

[0062] To support these additional analyses, sensing circuitry 86 can transmit digitized cardiac electrical signals (e.g., electrocardiogram (ECG) signals) to control circuitry 80 for morphological analysis performed by tachyarrhythmia detector 92. Cardiac electrical signals from selected sensing vectors (e.g., from first sensing channel 83 and / or second sensing channel 85) can be filtered and amplified, provided to a multiplexer, and subsequently converted into multi-bit digital signals by an analog-to-digital converter; all of this is included in sensing circuitry 86 for storage in memory 82. Memory 82 may include one or more loop buffers to temporarily store segments of digital cardiac electrical signals for analysis by control circuitry 80. Control circuitry 80 may be a microprocessor-based controller employing digital signal analysis techniques to characterize the digitized signals stored in memory 82, employing any of a variety of signal processing methods for analyzing cardiac signals and cardiac event waveforms (e.g., R waves) to identify and classify individual beats and patient rhythms. As described below, the processing and analysis of the digital signal may include determining the signal characteristics used to detect NSR beats and verifying the absence of tachyarrhythmic morphologies in cardiac electrical signal segments associated with VT / VF interval counts greater than a reset threshold. In some embodiments, when the number of signal segments meeting the tachyarrhythmia morphology detection criteria is less than the tachyarrhythmia morphology reset threshold, and the number of detected NSR beats meets the NSR reset threshold, the value of the VT and / or VF interval counter can be adjusted from its current value to a positive, lower, non-zero value. In some embodiments, the VT and / or VF interval counter may be reduced to a predetermined value or reduced by a predetermined amount not equal to the number of detected NSR beats. In other embodiments, the value of the VT and / or VF interval counter may be adjusted from its current value to 0.

[0063] The treatment delivery circuit 84 includes a charging circuit, one or more charge storage devices, such as one or more high-voltage capacitors and / or low-voltage capacitors, and a switching circuit that controls when the one or more capacitors discharge across a selected pacing electrode vector or CV / DF shock vector. Charging of the capacitor to a programmed pulse amplitude and discharging of the capacitor to a programmed pulse width can be performed by the treatment delivery circuit 84 according to control signals received from the control circuit 80. The control circuit 80 may include various timers or counters that control when cardiac pacing pulses are delivered. For example, the timing circuit 90 may include a programmable digital counter set by the microprocessor of the control circuit 80 for controlling the basic pacing time interval associated with various pacing modes or ATP sequences delivered by the ICD 14. The microprocessor of the control circuit 80 may also set the amplitude, pulse width, polarity, or other characteristics of the cardiac pacing pulses based on programmed values ​​stored in memory 82.

[0064] In response to the detection of VT or VF, control circuit 80 can control treatment delivery circuit 84 to deliver treatment, such as ATP and / or CV / DF therapy. Treatment can be delivered by initiating charging of a high-voltage capacitor via a charging circuit, both of which are included in treatment delivery circuit 84. Charging is controlled by control circuit 80, which monitors the voltage on the high-voltage capacitor, which is transmitted to control circuit 80 via a charging control line. When the voltage reaches a predetermined value set by control circuit 80, a logic signal is generated across the entire capacitor line and transmitted to treatment delivery circuit 84, thereby terminating charging. CV / DF pulses are transmitted to the heart via a control bus through the output circuit of treatment delivery circuit 84 under the control of timing circuit 90. The output circuit may include an output capacitor through which the charged high-voltage capacitor discharges via a switching circuit (e.g., an H-bridge) that determines the electrodes for delivering cardioversion or defibrillation pulses and pulse waveforms.

[0065] In some embodiments, a high-voltage treatment circuit configured to deliver CV / DF shock pulses may be controlled by control circuitry 80 to deliver pacing pulses, for example, to deliver ATP, post-shock pacing pulses, or ventricular pacing pulses during atrioventricular block or bradycardia. In other embodiments, treatment delivery circuitry 84 may include a low-voltage treatment circuit for generating and delivering pacing pulses for various pacing needs.

[0066] It should be recognized that the method disclosed herein for detecting tachyarrhythmias can be implemented in a medical device that monitors cardiac electrical signals via sensing circuit 86 and control circuit 80 without therapeutic delivery capability, or in a medical device that monitors cardiac electrical signals and delivers cardiac pacing therapy via therapeutic delivery circuit 84 without high-voltage therapeutic capability (e.g., cardioversion / defibrillation shock capability), and vice versa. In some cases, the medical device can be configured to communicate with another medical device capable of delivering therapy in response to tachyarrhythmia detection.

[0067] Control parameters used by control circuit 80 to sense cardiac events and control treatment delivery can be programmed into memory 82 via telemetry circuit 88. Telemetry circuit 88 includes a transceiver and an antenna for communication with external device 40 (in...) using RF communication or other communication protocols as described above. Figure 1A (As shown in the image) Communication. Under the control of the control circuit 80, the telemetry circuit 88 can receive downlink telemetry from the external device 40 and send uplink telemetry to the external device 40.

[0068] Figure 4This is a circuit diagram according to one embodiment of a sensing circuit 86 having a first sensing channel 83 and a second sensing channel 85. The first sensing channel 83 may be selectively coupled to a first sensing electrode vector via a switching circuit included in the sensing circuit 86, the first sensing electrode vector including at least one electrode carried by a cardiovascular lead 16 for receiving a first cardiac electrical signal. The first sensing channel 83 may be coupled to a sensing electrode vector as a short bipolar, having a relatively shorter interelectrode distance or spacing than a second electrode vector coupled to the second sensing channel 85. The first sensing channel 83 may be coupled to a sensing electrode vector that is substantially vertical (when the patient is in an upright position) or substantially aligned with the cardiac axis to increase the likelihood of a relatively high R-wave signal amplitude relative to the P-wave signal amplitude. In one embodiment, the first sensing electrode vector may include pacing / sensing electrodes 28 and 30, as shown. In other embodiments, the first sensing electrode vector coupled to the sensing channel 83 may include defibrillation electrodes 24 and / or 26, for example, a sensing electrode vector between pacing / sensing electrode 28 and defibrillation electrode 24, or between pacing / sensing electrode 30 and one of defibrillation electrodes 24 or 26. In other embodiments, the first sensing electrode vector may be between defibrillation electrodes 24 and 26.

[0069] Sensing circuitry 86 includes a second sensing channel 85 that receives a second cardiac electrical signal from a second sensing vector, such as a vector comprising an electrode 24, 26, 28, or 30 carried by a lead 16 mating with housing 15. In some embodiments, the second sensing channel 85 may be selectively coupled to other sensing electrode vectors that may form relatively long bipolars having an interelectrode distance or interval greater than that of the sensing electrode vector coupled to the first sensing channel 83. In some cases, the second sensing electrode vector may be substantially orthogonal to the first channel sensing electrode vector, but this is not necessary. For example, as shown, defibrillation electrode 26 and housing 15 may be coupled to the second sensing channel 85 to provide the second cardiac electrical signal. As described below, the second cardiac electrical signal received by the second sensing channel 85 via the long bipolar can be used by control circuitry 80 to analyze and detect NSR beats. Compared to the relatively short bipolar coupled to the first sensing channel, the long bipolar coupled to the second sensing channel 85 can provide a relatively far-field or more global cardiac signal. The specific electrodes indicated as being coupled to the first sensing channel 83 and the second sensing channel 85 are shown as illustrative embodiments and are not intended to be limiting. In other embodiments, any vector selected from available electrodes (e.g., electrodes 24, 26, 28, 30 and / or housing 15) may be included in the sensing electrode vectors coupled to the first and second sensing channels 83 and 85. The sensing electrode vectors coupled to the first sensing channel 83 and the second sensing channel 85 may be different sensing electrode vectors; they may have no common electrode or only one common electrode, but not both.

[0070] In other embodiments, the sensing electrode vectors may be the same; however, the two sensing channels 83 and 85 may include different filters or other processing circuitry to facilitate different analyses of the two signals, such as different signal feature determinations. For example, the first sensing channel may filter and process the received cardiac electrical signals to sense a first signal for detecting R waves in response to R-wave sensing threshold crossing for determining RRI. The second sensing channel 85 may filter and process the received cardiac electrical signals to sense a second signal passed to the control circuitry 80 for determining and analyzing signal waveform morphology and specific morphological features to detect NSR beats.

[0071] exist Figure 4 In the illustrated embodiment, the electrical signal generated across the first sensing electrode vector (e.g., electrodes 28 and 30) is received by the first sensing channel 83, and the electrical signal generated across the second sensing electrode vector (e.g., electrode 26 and housing 15) is received by the second sensing channel 85. The cardiac electrical signal is provided as a differential input signal to the pre-filters and preamplifiers 62 or 72 of the first sensing channel 83 and the second sensing channel 85, respectively. Non-physiological high-frequency and DC signals can be filtered by low-pass or band-pass filters included in each pre-filter and preamplifier 62 and 72, and high-voltage signals can be removed by protection diodes included in the pre-filters and preamplifiers 62 and 72. The pre-filter 62 and preamplifier 72 can amplify the pre-filtered signal by a gain of 10 to 100, or 17.5 in one embodiment, and can convert the differential signal into a single-ended output signal, which is passed to the analog-to-digital converter (ADC) 63 in the first sensing channel 83 and the ADC 73 in the second sensing channel 85. Pre-filters and amplifiers 62 and 72 can provide anti-aliasing filtering and noise reduction before digitization.

[0072] ADCs 63 and 73 convert the first cardiac electrical signal from an analog signal to a first digital bitstream and the second cardiac electrical signal to a second digital bitstream, respectively. In one embodiment, ADCs 63 and 73 may be Σ-Δ converters (SDCs), but other types of ADCs may also be used. In some embodiments, the outputs of ADCs 63 and 73 may be provided to a decimator (not shown), which acts as a low-pass filter to increase the resolution of the first and second cardiac electrical signals and reduce their sampling rate.

[0073] The digital outputs of ADC 63 and ADC 73 are each fed to their respective filters 64 and 74, which may be digital bandpass filters. Bandpass filters 64 and 74 may have the same or different bandpass frequencies. For example, filter 64 may have a bandpass of approximately 13 Hz to 39 Hz to pass cardiac electrical signals, such as the R wave typically found in this frequency range. Filter 74 of the second sensing channel 85 may have a bandpass of approximately 2.5 to 100 Hz. In some embodiments, the second sensing channel 85 may also include a notch filter 76 to filter noise signals at 60 Hz or 50 Hz.

[0074] The bandpass-filtered signal in the first sensing channel 83 is passed from filter 64 to rectifier 65 to generate a filtered and rectified signal. The first sensing channel 83 includes an R-wave detector 66 for sensing a cardiac event in response to a first cardiac electrical signal crossing an R-wave sensing threshold. The R-wave detector 66 may include an automatically adjusting sensing amplifier, comparator, and / or other detection circuitry that compares the filtered and rectified cardiac electrical signal to the R-wave sensing threshold in real time and generates an R-wave sensing event signal 68 when the cardiac electrical signal intersects the R-wave sensing threshold outside of a sensing blanking interval. The R-wave sensing threshold may be a multi-level sensing threshold, as disclosed in commonly assigned U.S. Patent No. 10,252,071 (Cao et al.). In short, a multi-level sensing threshold may have a value for an initial sensing threshold that is maintained for a time interval, which may be equal to the tachycardia detection interval or the expected R-wave to T-wave interval, and then decreases to a second sensing threshold, which is maintained until the decrease time interval expires. After a falling time interval, the sensing threshold decreases to a minimum sensing threshold, which may correspond to a programmed sensitivity sometimes referred to as the "sensing floor." In other embodiments, the R-wave sensing threshold used by the R-wave detector 66 may be set to an initial value based on a determined peak amplitude during the most recent post-sensing blanking interval and decays linearly or exponentially over time until the minimum sensing threshold is reached. The techniques described herein are not limited to the specific behavior of the sensing threshold. Instead, other decaying, gradually adjusted, or otherwise automatically adjusted sensing thresholds may be used.

[0075] A notch-filtered digital cardiac electrical signal 78 from the second sensing channel 85 can be passed to a memory 82 for buffering segments of the second cardiac electrical signal 78 within predetermined time intervals in response to each R-wave sensing event signal 68 generated by the first sensing channel 83. In some embodiments, the buffered segments of the second cardiac electrical signal 78 are rectified by a rectifier 75 before being stored in the memory 82. In some cases, both the filtered unrectified signal 78 and the rectified signal 79 are passed to a control circuit 80 and / or the memory 82 for determining the characteristics of multiple segments of the second cardiac electrical signal, wherein each segment extends over a time interval containing a time point of the R-wave sensing event signal generated by the first sensing channel 83, triggering the storage of the signal segment in the memory 82.

[0076] When a tachyarrhythmic interval of a threshold number has been detected, control circuitry 80 can buffer a second cardiac electrical signal segment in memory 82 and retrieve the stored signal segment from memory 82 for analysis. As described herein, analysis of the second cardiac electrical signal segment can be performed for detecting NSR beats and for detecting tachyarrhythmic morphology signal segments. For example, control circuitry 80 can be configured to detect NSR beats by determining an NSR morphology matching score and specific sensing event signal characteristics from a second cardiac electrical signal segment corresponding to an R wave sensed by a first sensing channel 83 at an RRI greater than the NSR interval threshold. When an NSR beat is detected based on an overall waveform morphology matching an NSR R wave template and at least one specific waveform characteristic conforming to an NSR threshold criterion, additional analysis can be performed to detect ventricular tachyarrhythmic morphology present in the second cardiac electrical signal time segment. Time segments of notch-filtered, rectified signal 79 received from the second sensing channel 85 can be used to detect each time segment with a ventricular tachyarrhythmic morphology. In some embodiments, when a first threshold number of NSR beats is detected and fewer than a second threshold number of ventricular tachyarrhythmia morphological signal fragments are detected, the VT interval counter and / or VF interval counter can be reset to below their current values ​​to suppress or delay tachyarrhythmia detection. In this way, erroneous VT or VF detections due to intermittent or continuous oversensing of cardiac events or noise can be avoided when a potential NSR is present, especially in the presence of varying R-wave amplitudes (e.g., due to changes in patient position).

[0077] like Figure 4 The configuration of sensing channels 83 and 85 shown is illustrative in nature and should not be considered as a limitation on the techniques described herein. Sensing channels 83 and 85 of sensing circuit 86 may include more than Figure 4More or fewer components are shown and described. For example, in other embodiments, a single sensing channel may be provided for sensing cardiac electrical signals, sensing R waves from that channel to generate an R-wave sensing event signal, and analyzing segments of the cardiac electrical signals from that channel to detect NSR morphology. In some embodiments, Figure 4 Some of the components shown can be shared between sensing channels 83 and 85. For example, one or more of the pre-filters and pre-amplifiers 62 / 72, ADCs 63 / 73, and / or filters 64 / 74 can be shared components between sensing channels 83 and 85, where a single sense signal output is split into two sensing channels for subsequent processing and analysis. As disclosed herein, sensing circuitry 86 and control circuitry 80 include circuitry configured to perform the functions of ICD14 in the detection of tachyarrhythmias.

[0078] Figure 5 This is a flowchart 100 of a method for controlling a tachyarrhythmia interval counter in a tachyarrhythmia detection technique according to one embodiment. In the various embodiments presented herein, an R-wave is sensed by a first sensing channel 83 of sensing circuitry 86 based on an R-wave sensing threshold crossing. The RRI is determined by timing circuitry 90 between consecutively sensed R-wave pairs. These RRIs are compared to tachyarrhythmia detection intervals. When an RRI falls within the VT detection interval range—for example, less than a VT detection interval threshold and greater than a VF detection interval threshold—and VT detection is enabled by the user, the VT interval counter value is incremented at block 102. When an RRI is less than a VF detection interval threshold, the VF interval counter value is incremented. In some cases, a combined VT / VF interval counter increments in response to each RRI less than a VT detection interval threshold.

[0079] At block 104, control circuitry 80 identifies and counts NSR events. In some embodiments, NSR events are identified and counted by identifying and counting the NSR interval. The NSR interval is the RRI that is greater than the NSR interval threshold. The following is in conjunction with... Figure 6AA method for establishing an NSR interval threshold is described. In other embodiments, identifying an NSR event includes identifying an NSR beat morphology. An NSR beat morphology can be identified by analyzing cardiac electrical signal segments within a beat morphology time interval that includes the time of a sensed R wave, and determining at least one morphological feature determined from the cardiac electrical signal segments within the beat morphology time interval that meets the NSR beat morphology criteria. In some embodiments, an NSR interval can be identified and counted when at least one morphological feature determined from a cardiac electrical signal segment associated with an NSR interval meets the NSR beat morphology criteria. A cardiac electrical signal segment that meets the NSR beat morphology criteria can be associated with an NSR interval by including the time of a sensed R wave associated with the NSR interval, for example, the end of an RRI identified as an NSR interval.

[0080] To detect VT or VF, a corresponding VT or VF interval counter needs to reach a certain number of intervals to detect (NID) the tachyarrhythmia. For example, the NID for detecting VT might require the VT interval counter to reach 32 VT intervals counted from the most recent 32 consecutive RRIs. In one embodiment, the NID for detecting VF can be programmed to be 18 VF intervals from the most recent 24 consecutive RRIs, or in another embodiment, it can be programmed to be 30 VF intervals from 40 consecutive RRIs. VF can be detected when the VF interval counter reaches the desired NID within a specified number of recent RRIs. In other embodiments, the NID can be programmable and range from as low as 12 to as high as 40 without any limitation, detecting VT or VF intervals continuously or discontinuously from a predetermined number of recent RRIs. In some cases, a combined VT / VF interval counter can count both VT and VF intervals and detect tachyarrhythmia episodes based on the fastest interval detected when a specified NID is reached. When the NID is programmed relatively high (e.g., 30 VF intervals out of 40 consecutive RRIs), intermittent episodes of oversensitivity due to noise or R-wave amplitude variability are more likely to occur than when the NID is programmed relatively low. Therefore, short, erroneous tachyarrhythmic intervals can accumulate over a relatively large number of consecutive RRIs, potentially leading to false VF detections. Therefore, based on RRIs and / or NSR morphological characteristics, during tachyarrhythmic interval counting, cardiac events highly probable to be NSR events can be identified by reducing the tachyarrhythmic interval counters (one or more) in response to detected NSR events to prolong or delay tachyarrhythmia detection.

[0081] The NSR event criteria applied at box 104 for identifying and counting NSR events may require that the R wave sensed at an RRI is greater than an NSR interval threshold, that the RRI identified as greater than the NSR interval threshold is stable compared to other RRIs identified as greater than the NSR interval threshold (with low variability or difference between them), and / or that the R wave occurs during the occurrence of multiple consecutive RRIs that are stable and greater than the NSR interval threshold. Additionally or alternatively, NSR event criteria may be applied to one or more cardiac electrical signal waveform morphology features. For example, NSR event criteria may require matching the overall waveform morphology and / or one or more specific morphological features of the sensed R wave to an NSR R wave morphology template, such as amplitude, polarity, polarity pattern, time of absolute peak, maximum slope, signal area, signal width, or any combination thereof, to match the corresponding NSR R wave reference value for the specific feature within a matching threshold range. In some embodiments, low variability of specific morphological features between beats occurring at RRIs greater than the NSR threshold interval may be required to meet NSR beat criteria.

[0082] As shown below Figures 6A-9 In one embodiment, control circuit 80 can identify RRIs longer than the NSR interval threshold and determine whether a segment of the second cardiac electrical signal corresponding to an R wave sensed from the first cardiac electrical signal during the NSR interval meets the NSR morphological criteria. When the currently sensed R wave appears at an RRI longer than the NSR threshold interval and has at least one morphological feature conforming to the NSR morphological criteria, an NSR event can be identified and counted at block 104. As described below... Figure 7 and 8 The NSR morphology criteria can be applied to signal characteristics determined from relatively short time segments of a second cardiac electrical signal, including the time point at which the R wave is sensed from a first cardiac electrical signal associated with the detected NSR interval, in order to characterize the R wave signal. As previously stated, a second cardiac electrical signal is not necessarily required. A single cardiac electrical signal can be used to sense the R wave at the NSR interval and perform morphological analysis on a segment of the cardiac electrical signal containing the sensed R wave to detect the NSR morphology.

[0083] At block 106, control circuitry 80 may further analyze segments of the second cardiac electrical signal corresponding to each sensed R wave to identify and count segments exhibiting an overall morphology likely to be a ventricular tachyarrhythmia morphology. One or more overall morphological features may be determined from the analysis of sampling points across time-region segments of the second cardiac electrical signal, which may include the time point of the R-wave sensing event signal but extend beyond the expected R-wave width earlier and / or later than the R-wave sensing event signal time point. The ventricular tachyarrhythmia morphology criteria applied at block 106 may be applied to morphological measures determined from relatively long segments of the second ECG signal, which are longer than the relatively short segments used in block 104 to identify NSR beats. Both the longer and shorter segments are within one cardiac cycle and include the time of the R-wave sensing event signal. The relatively long segment of the second cardiac electrical signal evaluated at box 106 extends beyond the expected width of the sensed R wave to characterize the similarity of the second cardiac electrical signal segment to the waveform of ventricular tachyarrhythmias, such as fibrillation waves which may have a sinusoidal morphology. As an example, the overall morphological features determined at box 106 for detecting the morphology of tachyarrhythmias may include amplitude morphology measures and / or signal width morphology measures. The following is in conjunction with... Figure 10 and 11 This describes a method for identifying a segment of the overall morphological signal of a tachyarrhythmia at box 106. Overall morphological features that can be used to detect the morphology of a tachyarrhythmia may include maximum slope, some peaks, total signal area, pulse count, low slope content, normalized mean rectified amplitude, or other morphological features. Examples of overall morphological features may include any signal feature or measure determined using sampling points that span a time interval longer than the expected NSR R wave width and are associated with the tachyarrhythmia waveform.

[0084] At blocks 104 and 106, control circuitry 80 can determine one or more signal features from each of a plurality of segments of the second cardiac electrical signal, wherein each segment corresponds to (e.g., buffered in response to) a sensed event signal generated by the first sensing channel 83. The signal features can be compared with NSR beat criteria and / or ventricular tachyarrhythmia morphological criteria to identify and count NSR beat and ventricular tachyarrhythmia morphological signal segments, respectively. As described above, the second cardiac electrical signal can be a relatively far-field or more comprehensive cardiac signal compared to the first cardiac electrical signal and is filtered or processed differently to enhance the specificity and sensitivity of the morphological analysis used to detect NSR beat and ventricular tachyarrhythmia morphological signal segments. For example, the second cardiac electrical signal can be sensed using a sensing electrode vector having an inter-electrode distance greater than that of the first sensing electrode vector. Additionally or alternatively, segments of the second cardiac electrical signal can be filtered by relatively wide bandpass and notch filters to attenuate 50-60 Hz noise. Segments of the second cardiac electrical signal within a predetermined time interval can be buffered in memory 82. The predetermined time interval includes the time points of cardiac events (e.g., R waves) sensed from the first cardiac electrical signal.

[0085] For example, in response to each R-wave sensing event signal 68 received from the first sensing channel 83, the control circuit 80 may buffer a time segment of the second cardiac electrical signal 78 from the second sensing channel 85 in the memory 82. The time segment may extend from a point earlier than the R-wave sensing threshold crossing to a point later than the R-wave sensing threshold crossing that caused the first sensing channel 83 to generate the R-wave sensing event signal. This time segment may be a duration of 300 to 500 ms, such as 360 ms, which includes sampling points before and after the R-wave sensing event signal. For example, at a sampling rate of 256 Hz, a 360 ms segment may include 92 sampling points, where 24 sampling points occur after the R-wave sensing event signal stored in the trigger signal segment, and 68 sampling points extend from an R-wave sensing event signal that is temporally earlier than the R-wave sensing event signal. The entire segment (e.g., all 92 sampling points) can be used to determine the overall morphological measure for identifying and counting ventricular tachyarrhythmia segments, and a portion of the entire segment (e.g., including 48 sampling points at sensed R wave time points) can be used to determine the pulsatility characteristics for identifying and counting NSR beats.

[0086] At block 108, control circuit 80 compares the value of the VT and / or VF interval counter with a reset threshold value less than NID. When the VT or VF interval counter is less than or equal to the predetermined reset threshold value, at block 102, control circuit 80 continues counting VT / VF intervals and identifies and counts NSR beats and tachyarrhythmia morphological signal segments. In some embodiments, the reset threshold is a value of 6 VF intervals. Additionally or alternatively, when VT detection is enabled, the reset threshold value 7 can be applied to the combined VT / VF interval counter. For example, the NID used for VF detection can be a count of 30 VF intervals from the most recent 40 RRIs. In this embodiment, when the value of the VF interval counter is equal to or greater than 7, or the value of the combined VT / VF interval counter is equal to or greater than 8, and when the NSR and tachyarrhythmia morphological reset criteria are also met, at least the VF interval counter reset is enabled (the "Yes" branch at block 108). When VT detection is enabled, at box 108, the reset of the VT interval counter and / or the combined VT / VF interval counter can be enabled when at least one tachyarrhythmia interval counter reaches a predetermined reset threshold.

[0087] At block 108, when the tachyarrhythmia interval counter is greater than its corresponding reset threshold, at block 110, control circuit 80 compares the count of detected NSR events with the NSR reset criteria. In some embodiments, if the count of NSR events at block 110 is less than the NSR reset threshold, control circuit 80 proceeds to block 116 to check if VT or VF detection criteria are met. For example, if VT NID, VF NID, or a combination of VT / VF NID is met, VT or VF can be detected at block 118, and treatment, such as ATP and / or cardioversion or defibrillation, can be delivered.

[0088] If the tachyarrhythmia detection criteria are not met at box 116, the process returns to box 102 to continue updating the VT / VF interval counters for various VT, VF, and / or combinations and identifying NSR events and tachyarrhythmia morphological segments. In one embodiment, the NSR reset threshold may be set to at least two NSR events in eight consecutive sensed R waves (or eight consecutive RRIs). Control circuitry 80 may determine the number of reset thresholds required to reach an NSR event in response to detecting an NSR beat morphology associated with each of the NSR intervals corresponding to the reset threshold number.

[0089] The NSR reset criterion applied at box 110 may require at least one NSR event from a necessary number of NSR events to occur within the two most recent two of eight (or other predetermined number) consecutively sensed R waves. Each NSR event may be detected based on the detected NSR interval and / or the detected NSR pulsation pattern. Thus, the NSR reset criterion may require the detection of a first threshold number of NSR events from a first predetermined number of sensed R waves and a second threshold number of NSR events from a second predetermined number of sensed R waves. The first threshold number of NSR events may be equal to or greater than the second threshold number of NSR events. The first predetermined number of sensed R waves is greater than the second predetermined number of sensed R waves. The first predetermined number of sensed R waves may overlap with or include the second predetermined number of sensed R waves. For example, when it is necessary to detect two NSR events in eight consecutively sensed R waves, it may be necessary to detect at least one of the two NSR events in the two most recent two of the eight consecutively sensed R waves.

[0090] In some embodiments, the required number of NSR events can be set based on the programmed NID required to detect tachyarrhythmias. For example, when the NID is relatively high, a greater number of NSR events may be needed to adjust the tachyarrhythmia interval counter compared to when the NID is relatively low. To illustrate, if the NID for detecting VF is 30 VF intervals out of 40 consecutive RRIs, the NSR reset threshold for NSR events might be at least 4 out of the most recent 16 sensed R waves, while if the NID is 18 VF intervals out of 30 consecutive RRIs, the NSR reset threshold might be 2 NSR events out of 8 sensed R waves. The following is in conjunction with... Figures 7 to 9 This describes a technique for identifying NSR events and determining when the NSR event count reaches the NSR reset threshold.

[0091] When the NSR event count meets the NSR reset criteria (e.g., greater than or equal to the NSR reset threshold) at box 110, in box 112, control circuit 80 compares the ventricular tachyarrhythmia morphology count value with the value of the suppression reset threshold. When the number of signal segments identified as having tachyarrhythmia morphology is greater than or equal to the value of the suppression reset threshold, control circuit 80 suppresses the reset or adjusts the VT, VF, and / or combination VT / VF interval counters. For example, the value of the suppression reset threshold could be the tachyarrhythmia morphology count of 6 out of the most recently sensed R waves. When five or fewer of the 8 cardiac signal segments are identified as having ventricular tachyarrhythmia morphology, the reset of the VT, VF, and / or combination VT / VF interval counters is enabled or allowed. However, when six or more cardiac electrical signal segments have been identified and counted as having tachyarrhythmia morphology, the reset of the tachyarrhythmia interval counters is suppressed (withheld) (the "No" branch at box 112). When the number of identified tachyarrhythmic signal segments equals or exceeds the withhold reset threshold, adjustments to the VT, VF, and / or VT / VF interval counters based on detected NSR events cannot be performed. In this way, when evidence of a true tachyarrhythmia is detected based on overall morphological measurements, the ventricular tachyarrhythmia interval counter is not reset. Segments identified as having a ventricular tachyarrhythmia morphology may be located among eight (or other predetermined) second cardiac electrical signal segments of NSR events detected at the reset threshold number. For example, if two of the eight consecutive signal segments are identified as NSR beats based on the NSR beat criterion, and all six or at least a portion of the remaining signal segments of the eight consecutive signal segments are identified as having a tachyarrhythmia morphology, then no tachyarrhythmia interval counter adjustment is performed (the "No" branch at box 112). Before returning to box 102, the VT / VF interval counting continues, and the control circuit 80 can determine in box 116 whether one of the VT, VF, or VT / VF interval counters has reached its respective NID. If so, the control circuit 80 can detect the tachyarrhythmia, and the treatment delivery circuit 84 can deliver VT or VF treatment in box 118 according to the programmed tachyarrhythmia treatment.

[0092] When the NSR event count meets the NSR reset criteria and the tachyarrhythmia morphology count is less than the suppression reset threshold (the "Yes" branch of block 112), at block 114, control circuitry 80 can adjust one or more of the VT interval counter, VF interval counter, and / or combined VT / VF interval counter. In one embodiment, the VF interval counter is adjusted from its current value to a predetermined value, for example, to value 3. As another embodiment, the combined VT / VF interval counter can be adjusted from its current value to the value of the current VT interval counter and the adjusted value of the VF interval counter, or to a predetermined value. When VT detection is enabled, the VT interval counter can be adjusted from its current value to a predetermined value, for example, to value 2. The adjustment performed at block 114 always decreases the value of the corresponding counter. If all reset criteria are met, but the value of one of the counters is less than the predetermined reset value of that counter, the counter is not increased to the reset value. For example, the VF interval counter may be greater than the reset threshold, for example, 8 or more, but the VT interval counter may be at value 1. The VF interval counter can be reset to value 3, and the VT interval counter can remain at value 1. In this embodiment, the combined VT / VF interval counter can be adjusted to value 4 based on the currently adjusted VT and VF interval counter values.

[0093] In some embodiments, a tachyarrhythmia interval counter value greater than a reset threshold (as determined at block 108) can be reduced from its current value to a value at least zero or a value greater than zero and less than the reset threshold. In other embodiments, a tachyarrhythmia interval counter value can be reduced from its current value to an adjustment value based on the current value of the tachyarrhythmia interval counter. For example, when the current value of the tachyarrhythmia interval counter is any value greater than 15, the value can be reduced to a proportional, predetermined value of 10 at block 114. For example, when the current value is greater than the reset threshold 8 but less than or equal to 15, the value can be reduced to a proportional, predetermined value of 3. Thus, the reduced reset value can be based on the current value of the tachyarrhythmia counter. In some embodiments, predetermined reset values ​​are defined for different ranges of the current tachyarrhythmia interval counter value. In other embodiments, the reset value is set as a fraction or portion of the current tachyarrhythmia interval counter. For example, at box 114, the tachyarrhythmia interval counter can be reduced to a positive integer value that is approximately one-third, one-half, or other portion of the current value of the tachyarrhythmia interval counter.

[0094] In other embodiments, the tachyarrhythmia counter can be adjusted at block 114 by a decrement set to a predetermined value, which can be a fixed value or adjusted based on the current value of a programmed NID and / or tachyarrhythmia interval counter. The reduction in the tachyarrhythmia interval counter may or may not be equal to the number of identified NSR events. For example, if six out of eight second cardiac electrical signal segments are identified as NSR beats associated with an NSR interval, the tachyarrhythmia counter value can be reduced by six but not below a predetermined minimum (e.g., not less than one). If two NSR beats are identified, the tachyarrhythmia interval counter value can be reduced by two but not below the predetermined minimum. In other embodiments, the tachyarrhythmia counter can be reduced to a predetermined value, which can be zero or any positive value less than its current value.

[0095] After adjusting the VT / VF interval counter at box 114, control circuit 80 returns to box 102 to continue counting when a VT / VF interval is detected. In response to meeting reset criteria at boxes 108, 110, and 112, control circuit 80 may adjust the VT / VF interval counter once or multiple times at box 114. After decrementing the value of the tachyarrhythmia interval counter once or multiple times at box 114, control circuit 80 may subsequently determine at box 116 that the tachyarrhythmia interval counter has reached a tachyarrhythmia detection threshold, such as a programmed NID, and detect a tachyarrhythmia at box 118 in response to the tachyarrhythmia interval counter value reaching the tachyarrhythmia detection threshold. In response to control circuit 80 detecting a tachyarrhythmia, treatment delivery circuit 84 may deliver tachyarrhythmia treatment at box 118.

[0096] As described above, it should be understood that the techniques described herein for adjusting VT and / or VF interval counters based on detecting NSR events and tachyarrhythmia morphology signal segments can be applied to adjusting atrial tachyarrhythmia counters used for detecting atrial tachyarrhythmias. A P wave can be sensed by sensing circuitry in response to a cardiac signal crossing a P wave sensing threshold, and the PP interval can be determined and compared with one or more atrial tachyarrhythmia detection intervals to calculate the atrial tachyarrhythmia interval. Various NSR beat criteria and tachyarrhythmia morphology criteria can be applied to cardiac electrical signals to determine when reset criteria are met, thereby adjusting the atrial tachyarrhythmia interval counter.

[0097] Figure 6A This is a flowchart 200 of a method for setting an NSR interval threshold according to one embodiment. The NSR interval threshold can be used to identify and count NSR events, for example, in Figure 5In box 104. In box 202, control circuitry 80 sets a long cycle length threshold. The long cycle length threshold can be set based on a programmed ventricular tachyarrhythmia detection interval threshold. For example, the long cycle length threshold can be set to a predetermined interval longer than the longest tachyarrhythmia detection interval. When VF detection is enabled but VT detection is not enabled, the long cycle length threshold can be set to a predetermined interval greater than the VF detection interval threshold. For example, the VF detection interval threshold can be set to 300 to 350 milliseconds (ms). For example, if the VF detection interval is set to 320 ms, RRIs less than 320 ms will be counted by the VF interval counter. The long cycle length threshold can be set to 60 ms or longer, or up to 380 ms.

[0098] When VT detection is enabled, the VT detection interval can be programmed to be in the range of 350 to 420 ms, or 400 ms for example. In this case, the long cycle length threshold can be set to be 60 ms longer than the VT detection interval, whichever is longer between the VF and VT detection intervals. In an embodiment where the VT interval is programmed to be 400 ms, the long cycle length threshold can be set to 460 ms. After setting the long cycle length threshold at block 202, the control circuit 80 can adjust the long cycle length threshold at any time the ventricular tachyarrhythmia detection parameters are reprogrammed by the user. For example, if VT detection becomes enabled or disabled, or if the VT detection interval threshold or the VF detection interval threshold is reprogrammed to a different value, the control circuit 80 can adjust the long cycle length threshold to a predetermined interval longer than the longest programmed ventricular tachyarrhythmia detection interval used for enabling tachyarrhythmia detection.

[0099] At box 204, an R-wave signal is sensed from a first cardiac electrical signal. The RRI is determined by control circuitry 80 between continuously received R-wave sensing event signals. When the first sensing channel 83 (see...) Figure 4 When an R-wave is sensed, the VT, VF, and / or combined VT / VF interval counters can be adjusted in response to the detection of an RRI within the corresponding VT detection interval region or VF detection interval region. At block 206, control circuitry 80 compares each RRI to a long period length threshold. When an RRI is longer than the long period length threshold, it is stored in a long period length buffer at block 210. Memory 82 can be configured with a first-in-first-out buffer for storing a predetermined number of long period lengths. In various embodiments, up to 8 to 12 long period lengths can be stored in the buffer. Newly detected long period lengths may overwrite the oldest long period length stored in the buffer. In one embodiment, 11 long period lengths are stored in the long period length buffer of memory 82. If the RRI is not longer than the period length threshold at block 206, the process can return to block 204 to sense the next R-wave.

[0100] At block 212, the NSR interval threshold is updated based on the long period lengths stored in the long period length buffer. The NSR interval threshold can be set based on the mean, median, mode, range, or other statistical parameters of the buffered long period lengths. Before updating the NSR interval threshold at block 212, one or more of the stored long period lengths may be rejected as outliers. A narrower range of long period lengths can be selected from the buffer in memory 82, or another subset of the stored long period lengths can be selected for setting the NSR interval threshold. In one embodiment, the median of the earliest 9 long period lengths stored in the long period length buffer is used to set the NSR interval threshold at block 212. The NSR interval threshold can be set as a fraction or percentage of the median. In one example, the NSR interval is set to 75% of the median of the earliest 9 long period lengths stored in the buffer, which stores up to 11 long period lengths.

[0101] This process of storing long cycle lengths and updating the NSR interval threshold can be performed once daily, or periodically with a greater or lesser frequency. In other embodiments, the process of storing long cycle lengths and updating the NSR interval threshold can be performed on a beat-by-beat basis, with each detected long cycle length used to update the long cycle length buffer on a first-in, first-out basis. The NSR interval threshold can be updated each time the long cycle length buffer is updated. In other embodiments, the NSR interval threshold can be set to a fixed, predetermined value.

[0102] Figure 6B This is a flowchart 250 of a method for controlling the adjustment of a ventricular tachyarrhythmia interval counter according to another embodiment. At block 214, the RRI at the end of the currently sensed R wave is compared with an NSR interval threshold. This can be based on... Figure 6A The implementation uses examples to establish the NSR interval threshold. In other embodiments, the NSR interval threshold can be set as a predetermined fixed interval, an interval based on the longest programmed tachyarrhythmia detection interval, an interval based on a previously determined RRI greater than the longest programmed tachyarrhythmia detection interval (e.g., the average RRI determined during a known sinus rhythm), or other methods. If the RRI is less than or equal to the NSR threshold, the current beat (corresponding to the currently sensed R wave) is not detected as an NSR beat at box 216. The process can return to box 214 to sense the next R wave and determine the next RRI. In other embodiments, when the NSR beat criterion is not met at box 218, a tachyarrhythmia morphology classification can be determined at box 222 to update the morphology buffer as described below.

[0103] When the current RRI is greater than the NSR threshold at box 214, the control circuit 80 can analyze a segment of the second cardiac electrical signal corresponding to the currently sensed R wave at box 218 to determine whether an NSR pulsation pattern has been detected to support the detection of NSR pulsation. The following is in conjunction with... Figures 7-9 Examples of describing second cardiac electrical signals and examples of applying them to the detection of NSR pulsation morphology at box 218.

[0104] When the NSR pulsation morphology criterion is not met at box 218, the current R-wave sensing event signal is not detected as an NSR pulsation at box 216. At box 216, the NSR pulsation classification buffer can be updated on a first-in-first-out basis based on the detection of a non-NSR pulsation. In response to the detection of an NSR morphology at box 218, an NSR pulsation is detected at box 220. The control circuit 80 updates the NSR pulsation classification buffer and / or the NSR pulsation count accordingly at box 221. The buffer may be included in memory 82 for classifying and storing eight consecutive pulsations as NSR pulsations or non-NSR pulsations on a first-in-first-out basis. The control circuit 80 can then determine the NSR pulsation count as the number of X NSR pulsations in the YR wave sensing event.

[0105] After updating the NSR beat classification buffer, or during simultaneous or parallel processing, control circuitry 80 can determine at block 222 whether the current second cardiac electrical signal segment corresponding to the currently sensed R wave meets the overall morphological criteria for tachyarrhythmias. If so, the tachyarrhythmia morphology classification buffer can be updated at block 224 on a first-in, first-out basis. In one embodiment, the tachyarrhythmia morphology classification buffer stores, for example, classifications of 6 to 12 signal segments or 8 signal segments as tachyarrhythmia morphological segments or non-tachyarrhythmia morphological segments. In some embodiments, tachyarrhythmia morphology analysis is skipped at block 222 when the second cardiac electrical signal segment is determined to be an NSR beat. In other embodiments, tachyarrhythmia morphology analysis for detecting the second cardiac electrical signal segment as having a tachyarrhythmia morphology can be performed before detecting the NSR beat, and the analysis for detecting the NSR beat can be skipped when the second cardiac electrical signal segment is detected as a tachyarrhythmia morphology signal segment. In other embodiments, when the tachyarrhythmia morphology criteria are met, the segment can be classified as a tachyarrhythmia morphology segment regardless of whether the NSR beat criterion is met. Tachyarrhythmia morphology classification can replace NSR beat classification. In this case, the NSR buffer may not be updated to include NSR beat classification in response to meeting the NSR beat criterion, unless the same signal segment does not meet the tachyarrhythmia morphology criteria.

[0106] At box 226, control circuit 80 determines whether the VT interval counter, VF interval counter, and / or combined VT / VF interval counter have reached the above-mentioned combination. Figure 5 The value of the reset threshold. For example, if the VF interval counter has reached a value of 7 or higher, or the combined VT / VF interval counter has reached a value of 8 or higher, then the reset threshold is met at block 226. If not, control circuit 80 suppresses any adjustment to the tachyarrhythmia interval counter and returns to block 214. In response to reaching the reset threshold, control circuit 80 determines at block 228 whether the NSR reset criterion and the tachyarrhythmia morphology reset criterion are met. As described above... Figure 5 The NSR event count may need to be greater than the NSR reset threshold, and the tachyarrhythmia morphology count may need to be less than the suppression reset threshold. When an NSR beat associated with each NSR interval is detected based on the NSR morphology, the control circuit 80 can determine the NSR reset threshold number for the detected NSR interval.

[0107] If the reset criterion is not met at box 228, the tachyarrhythmia interval counter is not adjusted, and the process can return to box 214. When the reset criterion is met, the control circuit 80 adjusts the tachyarrhythmia interval counter to a predetermined value or according to a predetermined specification. For example, as described above... Figure 5 As described, the VF interval counter can decrease from its current value to a value of 3. If the VT interval counter is enabled, it may decrease to a value of 2. The combined VT / VF interval counter can be adjusted to count the combination of the adjusted VT interval counter value and the adjusted VF interval counter value. In response to the reset criterion being met at box 228, it can be combined as described above. Figure 5 The method involves making other predetermined or proportional adjustments to the tachyarrhythmia interval counter.

[0108] In some embodiments, regardless of the value of the tachyarrhythmia interval counter, it can be based on Figure 6A The method updates the NSR interval threshold based on the ongoing long-cycle length. However, according to... Figure 6B The method, based on NSR interval thresholds and NSR beat morphology, can be performed only after the value of at least one tachyarrhythmia interval counter is greater than zero or other predetermined threshold values. For example, as combined with the following... Figure 12 Generally, NSR beat detection can be enabled when the VF interval counter is 3 or higher and / or the VT interval counter is 2 or higher. In other embodiments, the buffering of long cycle lengths and the determination of NSR interval thresholds can begin when the tachyarrhythmia interval counter is active, for example, at a non-zero value or at an R-sense confirmation threshold of 2, 3 or other predetermined values.

[0109] Figure 7 This is a flowchart 300 of a method for detecting NSR pulsation. At block 301, control circuitry 80 establishes an NSR R-wave morphology template and NSR pulsation characteristic values. The NSR morphology template and NSR pulsation characteristic values ​​represent the expected R-wave morphology during NSR pulsation. In some embodiments, the NSR template can be acquired during a slow, non-paced ventricular rhythm to represent a normal QRS waveform generated by depolarization conduction from the sinoatrial node. At block 301, in order to establish the template and pulsation characteristic values, control circuitry 80 can acquire a predetermined number of R-wave signals (or QRS complexes) from cardiac electrical signals received from sensing circuitry 86 during a known NSR period. For example, NSR can be manually confirmed by a user using external device 40, or automatically determined by control circuitry 80 by detecting a normal heart rate (e.g., less than the rate of rapid arrhythmias associated with the VT / VF detection interval) and / or regular, stable R-wave signals. For example, three or more R-wave signals can be acquired at block 301. These R-wave signals can be notch-filtered signals received from the second sensing channel 85, each signal corresponding to an R-wave sensing event signal received from the first sensing channel 83. The notch-filtered R-wave signal segments can be time-aligned relative to the corresponding R-wave sensing event signals. In other embodiments, different reference time points or sample numbers can be used to align the R-wave signal segments, such as the maximum peak or other reference points. The notch-filtered R-wave signals can then be averaged to obtain an averaged R-wave signal, thereby establishing an NSR R-wave morphological template for detecting NSR pulsations. Wavelet transform coefficients can be determined from the averaged R-wave signal, for example, using the Haar wavelet transform method. The digitized averaged R-wave signal and / or wavelet transform coefficients can be stored as an NSR morphological template in memory 82. In other embodiments, the NSR morphological template can be generated from the wavelet transform of a single R-wave signal acquired during NSR. As described below, the processing performed to generate the NSR morphological template and compare unknown signal segments with the NSR morphological template can include other techniques in the time domain or transform techniques other than wavelet transform methods.

[0110] At block 301, control circuit 80 establishes a reference NSR pulsation characteristic value, which can be determined from the average R-wave signal also used to generate the NSR morphology template. The reference NSR pulsation characteristic value determined at block 301 may include R-wave polarity pattern, peak time interval, and normalized width metric. The following section combines... Figure 8 and Figure 9 This describes an embodiment of a technique for determining these specific NSR pulsation characteristics. Reference NSR pulsation characteristic values ​​are stored in memory 82 to determine when NSR pulsation morphology criteria are met.

[0111] In response to the detection of an RRI greater than the NSR threshold interval at block 302, control circuit 80 determines a morphological matching score at block 304. The morphological matching score is determined between an established NSR R-wave morphological template and a second cardiac electrical signal segment in response to the currently sensed R-wave buffer (ending the RRI greater than the NSR threshold). The morphological matching score can be determined by performing a wavelet transform on the second ECG signal segment to generate a set of wavelet coefficients for an unknown ECG waveform present in the second ECG signal segment. The wavelet coefficients can have predetermined weights on the amplitude representing the frequency components of the signal waveform. These wavelet coefficients can be compared with wavelet coefficients established for the NSR R-wave morphological template to determine the morphological matching score. The morphological matching score represents the correlation between the wavelet coefficients of the NSR R-wave morphological template and the wavelet coefficients of the waveform present in the second cardiac electrical signal segment, which can be aligned with the template based on predetermined reference points (e.g., sampling points spanning the R-wave sensing threshold). Various template or morphological matching techniques for determining the correlation between the NSR R-wave template or reference and the unknown cardiac electrical signal waveform can be used to determine the morphological matching score. This technique can include various waveform correlation analyses to identify multiple reference points or feature points along the signal waveform and / or other defined waveform characteristics (e.g., positive and / or negative waveform area, amplitude, zero crossings, inflection points, peak slope, etc.). The determination of the NSR R wave morphology is not limited to specific matching techniques used to detect the correlation between unknown cardiac electrical signal segments and known NSR R wave templates or references.

[0112] At block 306, a template match score determined from a selected matching technique can be compared to an NSR match score threshold. The match score threshold can be set to 60, 70, or another predetermined value below which unknown cardiac signal waveforms are not considered NSR R waves. In one embodiment, the morphological match score threshold is set to 61 when the morphological match score ranges from 1 to 100. When the morphological match score is less than this threshold, at block 308, the current beat is not detected as an NSR beat. When the morphological match score is equal to or greater than the NSR match threshold, control circuitry 80 can determine each specific NSR beat feature from the second cardiac electrical signal segment at block 309 and compare them with reference NSR beat features at block 310.

[0113] Combined with the following text Figure 8 and 9The pulsation features defined in block 309 may include one or more of the polarity pattern of the peak values ​​of the cardiac electrical signal waveform, the maximum peak time, the normalized width measure, or other pulsation features. At block 310, these features, determined from a second cardiac electrical signal segment including the R-wave time sensed from the first cardiac electrical signal, can be compared to reference values. When the pulsation features match the reference features according to predefined matching criteria, the NSR pulsation morphology is detected at block 314. When the pulsation features do not match the reference features, for example, within a specified range, no NSR pulsation is detected at block 308. Figure 5 Box 104 or Figure 6B At box 218, analysis based on the corresponding second cardiac electrical signal segments in boxes 304-314 is performed to classify the cardiac electrical signal segments and the corresponding currently sensed R waves as NSR or non-NSR beats. Therefore, the detection of NSR beats may include detecting the NSR morphology from the second cardiac electrical signal over a time period corresponding to the R wave sensed from the first cardiac electrical signal at an RRI, where the RRI is the NSR interval (e.g., greater than an NSR interval threshold) from a previous cardiac event (sensed R wave or ventricular pacing pulse). When an NSR beat is detected based on the detected NSR interval and the detected NSR morphology (which may include overall waveform shape and specific beat characteristics), at box 104 ( Figure 5 ) or box 221( Figure 6B The NSR beat classification buffer is updated at ( ) to control the adjustment of the tachyarrhythmia interval counter when the NSR beat classification stored in the buffer meets the reset criteria.

[0114] In some embodiments, the NSR beat detection criteria applied to the morphological matching score and / or specific morphological beat features for detecting NSR beats can be adjustable, and the NSR beat detection criteria can include various thresholds, matching intervals, differences, or ranges. When a relatively low number of NSR beat reset thresholds is needed to reduce the tachyarrhythmia interval counter, the control circuit 80 can apply a more stringent matching criterion. When a relatively high number of NSR beat reset thresholds is needed to reduce the tachyarrhythmia interval counter, the morphological matching criterion can be adjusted to a less stringent criterion. For example, when the NSR reset threshold is set to identify 2 NSR beats from 8 consecutive sensed R waves, a relatively high morphological matching score, such as 71 or higher, may be required, and / or the specific beat feature may need to be within a relatively stringent range for each reference value, such as 15% to 20%. When the NSR reset threshold is set to a relatively high number of NSR beats, such as 4 from the most recent 10 sensed R waves, the morphological matching score threshold can be lower, such as 61 or lower. Specific pulsation characteristics may need to be within a relatively wide range of the corresponding reference values, such as 25% to 30%.

[0115] Figure 8 This is a diagram of one embodiment of notch-filtered cardiac electrical signal segment 350. Figure 7 At box 309, cardiac signal segment pulsation characteristics are determined from the notch-filtered cardiac electrical signal segment 350 for detecting NSR pulsation. The cardiac signal segment 350 may include a predetermined number of sampling points before and after the R-wave sensing event signal 352 generated by the sensing circuit 86. In one embodiment, the cardiac signal segment 350 for determining pulsation characteristics includes 48 sampling points acquired at a sampling rate of 256 Hz, wherein the R-wave sensing event signal 352 is aligned with a twenty-fourth sampling point. In other embodiments, higher or lower sampling rates, such as 512 Hz or 128 Hz, may be used. Correspondingly higher or lower numbers of sampling points can be used to analyze cardiac signal segments extending over the same or similar time intervals before and after the point at which the R-wave is sensed.

[0116] R-wave sensing event signal 352 can be generated when cardiac signal segment 350 crosses an R-wave sensing threshold, but it can also be generated when, for example, different cardiac electrical signals from one of the different sensing channels 83 and 85 cross the R-wave sensing threshold. For example, the first sensing channel 83 can generate R-wave sensing event signal 352 in response to a first cardiac electrical signal received by the first sensing channel 83 crossing the R-wave sensing threshold. Cardiac signal segment 350 can be buffered in memory 82 from a second cardiac electrical signal 78 received by the control circuit 80 from the second sensing channel 85. R-wave sensing event signal 352 from the first sensing channel 83 is used as a time marker for selecting stored start and end sampling points from the second cardiac electrical signal. Thus, the first sensing channel 83 can be used to sense R-waves, and the second sensing channel 85 can be used to acquire cardiac signal segments from different sensing vectors and / or sensing channels with different filtering or other signal processing characteristics. Each second cardiac electrical signal segment 350 corresponds to R-wave sensing event signal 352 because segment 350 spans a time interval containing R-wave sensing event signal 352.

[0117] A relatively short time segment 350 of the second cardiac electrical signal can be used to determine specific pulsatility features for detecting NSR beats, the second cardiac electrical signal including and optionally focusing on the time points spanned by the R-wave sensing threshold and the first cardiac electrical signal. Signal features determined as “pulsatility features” from the relatively short time segment (e.g., 48 sampling points (sampled at 256 Hz) or approximately 180 to 200 ms of the second cardiac electrical signal) are characterized within time intervals corresponding to an isolated R-wave to verify that the signal features match the NSR R-wave features. The time segment may at least correspond to the expected width of the NSR R-wave or NSRQRS waveform. In other embodiments, the time segment may at least correspond to the expected duration of the QT or RT interval. In some embodiments, the relatively short time interval of the second cardiac electrical signal segment used to determine the pulsatility features for classifying NSR beats is part of a longer time interval 360 of the second cardiac electrical signal segment used to determine an overall morphological measure for classifying the second cardiac electrical signal segment as a tachyarrhythmia morphology, as described below. Figure 10 and 11 As stated above.

[0118] One characteristic identified from cardiac signal segment 350 can be its peak polarity pattern. The R-wave signal can be biphasic, with a distinct positive peak and a distinct negative peak. At other times, the R-wave signal may have a monophasic polarity pattern characterized by a single dominant peak (positive or negative). Control circuitry 80 can be configured to identify and differentiate four polarity patterns occurring within a relatively narrow time segment of the second cardiac electrical signal: biphasic with a positive peak followed by a negative peak; biphasic with a negative peak followed by a positive peak; monophasic with a positive dominant peak; or monophasic with a negative dominant peak. Polarity pattern values ​​can be assigned to each possible polarity pattern for buffering a predetermined number of cardiac signal segments in memory 82. For example, the four polarity patterns listed above can be assigned values ​​from 1 to 4, respectively. In other embodiments, the polarity patterns identified by control circuitry 80 may not be limited to the four patterns listed above; control circuitry 80 can be configured to identify fewer, more, or different polarity patterns than the four listed herein. The identified polarity patterns can be tailored to an individual patient or based on the implantation location of the sensing electrode vector. The polarity pattern characterizes the R-wave polarity pattern over a short period of time (e.g., approximately 180 to 200 ms) during NSR, including the R-wave sensing event signal. For example, the R-wave signal may include more than two significant peaks in the three-phase signal, or the signal may have a polarity pattern including a pronounced split positive peak and / or a pronounced split negative peak.

[0119] The control circuit 80 can determine the polarity mode of the cardiac signal segment 350 by determining the maximum positive amplitude 354 (of the maximum peak value 353) and the maximum negative amplitude 356 (of the minimum peak value 355). The maximum absolute values ​​of the maximum positive and negative amplitudes 354 and 356 are identified and can be used by the control circuit 80 to set a polarity mode amplitude threshold. If the absolute values ​​of both the maximum positive amplitude 354 and the minimum negative amplitude 356 are greater than the polarity mode amplitude threshold, the cardiac signal segment 350 is determined to have a biphasic polarity mode. If only one of the maximum amplitudes 354 or 356 is greater than the polarity mode amplitude threshold, the cardiac signal segment is determined to have a uniphasic polarity mode.

[0120] In the illustrative embodiment, the polarity mode amplitude threshold is set to 25% of the maximum of the maximum positive amplitude 354 and the absolute minimum negative amplitude 356. Figure 8 In the specific embodiment shown, the absolute value of the maximum positive amplitude 354 is greater than the absolute value of the minimum negative amplitude 356. Therefore, the control circuit 80 uses the maximum positive amplitude 354 to set the polarity mode amplitude threshold to 25% of the maximum positive amplitude 354. The absolute value of the minimum negative amplitude 356 is compared with the polarity mode amplitude threshold. Because it is greater than the polarity mode amplitude threshold, i.e., greater than 25% of the maximum positive amplitude 354 in this embodiment, the cardiac signal segment 350 is determined to have a biphasic polarity mode.

[0121] Control circuit 80 can further determine that the positive peak 353 occurs earlier in time than the negative peak 355, thus prioritizing the generation of a biphasic, positive peak polarity pattern. The number of sampling points for the maximum peak 353 and the minimum peak 355 can be compared to determine whether the biphasic pattern prioritizes positive or negative peaks. The sampling points in the cardiac signal segment 350 can be numbered consecutively from beginning to end; for example, when the cardiac signal segment 350 includes 48 sampling points, they are numbered from 1 to 48. The lower number of sampling points for the maximum peak 353 and the higher number of sampling points for the minimum peak 355 indicate the first polarity pattern of positive peaks. Control circuit 80 can store a value in memory 82 indicating that the polarity pattern of the cardiac signal segment 160 is biphasic, with positive peaks prioritizing.

[0122] The second pulsating feature determined from the relatively short cardiac signal segment 350 may be a peak time interval 358. In an embodiment of biphasic polarity mode, the peak time interval 358 may be determined as the time interval between a maximum peak 353 and a minimum peak 355. For cardiac signal segment 350, this peak time interval 358 may be determined and stored in memory 82 as the difference between the corresponding number of sampling points for the maximum positive peak 353 and the minimum negative peak 355. The peak time interval 358 may be determined from a selected, specified reference time point during signal segment 350 to the maximum peak, wherein this reference time point may vary depending on the peak polarity mode described below.

[0123] Figure 9 This is a diagram of cardiac signal segment 370 with an example notch filter exhibiting a single-phase polarity mode. Signal segment 370 can be combined as described above. Figure 8 As described, the signal is acquired as a predetermined number of sampling points centered on the R-wave sensing event signal 372, for example, 48 sampling points sampled at 256 Hz. The relatively short signal segment 370 may be part of a relatively long segment 380 from the second cardiac electrical signal buffer, used to determine an overall morphological measure for detecting the rapid arrhythmia morphology of that segment, for example, as combined below. Figure 10 and 11 The amplitude 374 of the maximum positive peak value 373 is used by the control circuit 80 to set the polarity mode amplitude threshold because it is greater than the amplitude 376 of the minimum negative peak value 375 (absolute value). In this embodiment, the absolute value of the minimum negative amplitude 376 is less than the polarity mode amplitude threshold, which can be set to one-quarter of the maximum positive amplitude 374. Therefore, the maximum positive peak 373 is the only dominant peak. The control circuit 80 identifies the cardiac signal segment 370 as having a single-phase, positive peak polarity mode and stores the polarity mode value indicating this polarity mode of the cardiac signal segment 370 in the memory 82.

[0124] When the peak polarity mode is determined to be single-phase, the control circuit 80 can determine the peak time interval 378 using a different method than the method used to determine the peak time interval 358 of the bi-phase polarity mode signal 350, such as... Figure 8 As shown. The peak time interval 378 of the single-phase signal 370 can be determined as the time interval or the difference in the number of sampling points between the R-wave sensing event signal 372 and the main peak value, which is the maximum positive peak value 373 in this embodiment.

[0125] In addition to peak time interval and peak polarity pattern, it can be seen from ( Figure 8 and Figure 9 The relatively short cardiac signal segments 350 and 370 are identified (e.g., in...). Figure 7The third pulsation feature (at box 309) can be a normalized width measure. The normalized width measure is determined as an indicator of the narrowness of the sensed R-wave. When the signal waveform in the second cardiac electrical signal corresponding to the R-wave sensed from the first cardiac electrical signal is relatively narrow, it is likely a true R-wave. When the signal waveform is wide, the signal may be an oversensitized signal, such as a P-wave, T-wave, or non-cardiac noise, or even a fibrillation wave. To obtain a width measure related to the waveform width of the signal corresponding to the R-wave sensing event in time, cardiac signal segments 350 or 370 can be rectified, and the amplitudes of all sampled points can be summed to obtain the “area” defined by the rectified signal segment 350 or 370. The area of ​​signal 350 or 370 can be divided by the maximum absolute value of the maximum peak amplitude 354 or 374 or the minimum peak amplitude 356 or 376 of the corresponding signal segment (which can be considered as the “height” of the signal segment). When sampling points within a short second cardiac electrical signal segment include relatively low amplitude signal points, the normalized width metric will be relatively low; for example, around the true R-wave peak, indicating a steep and relatively narrow signal waveform as evidence of a true NSR R-wave. When the signal waveform is relatively wide, sampling points spanning a shorter second cardiac electrical signal segment will typically include higher amplitudes relative to the maximum peak value, resulting in a higher normalized width metric, which is evidence for an NSR R-wave.

[0126] Each of the three beat characteristics (i.e., peak polarity pattern, peak time interval, and normalized width measure) can be identified and stored for analysis of a second cardiac electrical signal segment for each buffer used to detect NSR beats. Reference values ​​for peak polarity pattern, peak time interval, and normalized width measure can be pre-defined in [the relevant data]. Figure 7 Box 301 is constructed based on an NSR R-wave template (e.g., based on the overall average of multiple, time-aligned NSR R-waves). This can be achieved using a combination of... Figure 8 and Figure 9 The described pulsation feature determination technique is used to establish pulsation feature reference values. In this way, the pulsation features of a cardiac signal segment determined from a signal segment acquired during an unknown heart rhythm can be compared with similar reference values ​​of NSR R-wave template pulsation features to detect NSR pulsations and update the NSR pulsation classification buffer.

[0127] When each pulsation feature falls within the threshold range of a reference feature, or matches a reference value in the case of a polarity pattern, a signal segment can be classified as an NSR pulsation, and this classification is stored in the NSR pulsation classification buffer. As an illustrative example, when the peak distance is within 7 sampling points of a reference peak distance, the peak distance is determined to be a matching NSR reference feature. When the normalized width metric is within 30 ADC units of a reference width metric, the normalized width metric is determined to be a matching NSR reference feature. When both pulsation features match their respective NSR reference features, the polarity pattern matches the NSR polarity pattern, and the overall morphology matching score is greater than a matching score threshold (e.g., 60), the segment can be classified as an NSR pulsation in the NSR buffer. Otherwise, the segment may be classified as a non-NSR pulsation in the NSR buffer.

[0128] Figure 10 This is a flowchart 400 of a method for determining a general morphological measure for detecting morphology of tachyarrhythmias, according to one embodiment. The method of flowchart 400 can be used in... Figure 5 Box 106 or Figure 6B Execution is performed at box 218 to analyze the second ECG signal segment for detecting evidence of tachyarrhythmia morphology. Figure 10 In one embodiment, a general morphological amplitude is determined to detect the rapid arrhythmia morphology of a second cardiac electrical signal segment. The time interval for buffering the second cardiac electrical signal segment to determine the general morphological measure can be longer than the time interval for determining the pulsational characteristics as described above. For example, all sampling points spanning a time interval can be used to determine the general morphological measure, which is approximately twice the time interval used to determine the pulsational characteristics. For example, at a sampling rate of 256 Hz, a 360 ms segment of the second cardiac electrical signal may include 92 sampling points, of which 24 sampling points occur after the R-wave sensing event signal stored in the trigger signal segment, and 68 sampling points extend from the R-wave sensing event signal in time earlier than the R-wave sensing event signal. In this way, the second cardiac electrical signal segment used to detect the pulsational characteristics as described above can start later (closer to the sensed R wave) and end at the same sampling points as the second cardiac electrical signal segment used to detect the rapid arrhythmia morphology (after the sensed R wave).

[0129] At block 402, a segment of the second cardiac electrical signal stored on a trigger-based basis in response to an R-wave sensing event signal can be rectified. In some embodiments, a 360ms segment of the notch-filtered second cardiac electrical signal can be rectified by a rectifier 75 included in the second sensing channel 85. At block 402, the buffered, rectified signal segment can be retrieved from memory 82 by control circuitry 80. In other embodiments, a notch-filtered segment of the second cardiac electrical signal can be buffered in memory 82, and control circuitry 80 can perform rectification of the stored signal segment at block 402. Control circuitry 80 can determine the maximum absolute amplitude of the rectified, notch-filtered signal segment at block 404. The maximum absolute amplitude can be determined from all sampling points spanning a relatively long segment of the second cardiac electrical signal.

[0130] At block 406, the amplitudes of all sampled points of the rectified signal segment are summed. At block 408, based on the maximum absolute amplitude determined at block 404 and the total sampled point amplitudes determined at block 406, the overall shape metric of the signal segment is determined as the Normalized Rectified Amplitude (NRA). In one embodiment, the NRA is determined as a predetermined weight or multiple of the sum of the amplitudes of all sampled points of the notch-filtered and rectified signal segment normalized to the maximum amplitude. For example, the NRA can be determined as four times the sum divided by the maximum absolute amplitude, which can be truncated to an integer value. This NRA can be... Figure 5 The frame at position 105 or Figure 6B The value at frame 222 was determined as the overall morphological amplitude for detecting the morphology of tachyarrhythmias.

[0131] The overall morphological amplitude can be negatively correlated with the probability that a signal segment sampling point is at baseline amplitude during the time interval of the signal segment. A higher overall morphological amplitude indicates a lower probability that the signal is at baseline amplitude at any given time point during a relatively long time interval of the signal segment, including the sensed R-wave signal. This relatively low probability of the signal being at baseline during this time interval can be associated with tachyarrhythmia morphologies, such as ventricular fibrillation morphologies, which can resemble a sinusoidal waveform and have a lower number of sampling points at any given time point of the baseline signal segment compared to the NSR R-wave. When the overall morphological amplitude exceeds a tachyarrhythmia morphology threshold, the second cardiac electrical signal segment is more likely to have a tachyarrhythmia morphology. When the overall morphological amplitude is less than this threshold, the probability that the signal is at baseline amplitude at a given time point during a relatively long time interval of the signal segment extends earlier from the sensed R-wave. During a relatively long signal segment time interval, a relatively high probability that the signal sampling point is at the baseline can be associated with a real, relatively narrow NSR R-wave signal that occurs during the signal segment, where the baseline amplitude portion of the signal segment occurs before and after the real R-wave.

[0132] At box 410, the NRA is compared to a tachyarrhythmia threshold. The tachyarrhythmia threshold used to detect the overall morphology of tachyarrhythmias can be between 100 and 150, and in some embodiments is 125, for example, when 92 samples are summed and multiplied by a factor of four and normalized by the maximum absolute amplitude. The threshold applied at box 410 to distinguish between tachyarrhythmia and non-tachyarrhythmia morphologies in the second cardiac electrical signal segment will depend on various factors, such as the sampling rate, the magnification and number of summed samples, the factor of the summed samples, or the weighting factor, etc.

[0133] When the NRA at box 410 is greater than the tachyarrhythmia threshold, evidence of a tachyarrhythmia morphology is detected, which rules out adjusting the tachyarrhythmia interval counter to a lower value. When, for example, the threshold count of the second cardiac signal segment is based on a relatively high overall morphological amplitude, indicating a tachyarrhythmia morphology, the control circuit 80 can detect the tachyarrhythmia morphology and... Figure 5 Box 106 (or Figure 6B The tachyarrhythmia morphology classification buffer used for counting tachyarrhythmia morphological segments is updated at boxes 222 and 224. When the NRA is less than the tachyarrhythmia threshold at box 410, no tachyarrhythmia morphology is detected at box 414, which is based at least on the overall morphological amplitude but can be detected based on other overall morphological measures.

[0134] Figure 11 This is a flowchart 450 of a method for detecting tachyarrhythmia morphology in a second cardiac electrical signal segment according to another embodiment. In this embodiment, tachyarrhythmia morphology detection is based on an overall morphological signal width metric. For example, the process of flowchart 450 can be performed by an ICD 14 for... Figure 5 The frame at position 106 or Figure 6B The overall shape signal width metric is determined at box 222. Boxes 402 and 404 correspond to the above combination. Figure 10 The same numbered boxes are described. In box 402, a notch-filtered, rectified signal segment obtained from the second sensing channel 85 is analyzed, including time points of the R-wave sensing event signal generated by the first sensing channel 83, to detect the overall morphology indicating tachyarrhythmias. At box 404, control circuitry 80 determines the maximum absolute amplitude of the rectified signal segment.

[0135] Control circuit 80 determines a pulse amplitude threshold at block 452 based on the maximum absolute amplitude determined at block 404. This pulse amplitude threshold can be used to identify the signal pulse with the largest signal width among all signal pulses occurring during the time interval of the second cardiac electrical signal segment. For example, the pulse amplitude threshold used to determine the overall morphological signal width metric can be set to half the maximum absolute amplitude of the rectified, notch-filtered signal segment.

[0136] At box 454, control circuitry 80 determines the signal width of all signal pulses corresponding to the second cardiac electrical signal segment of the currently sensed R wave. Signal pulses can be identified by recognizing two consecutive zero-amplitude or baseline amplitude sampling points (or two consecutive zero-crossing points) of a rectified signal segment. All signal pulses between two consecutive baseline amplitude sampling points are identified at box 454. The signal width of each identified signal pulse is determined as the number of sampling points (or the corresponding time interval) between a pair of consecutive baseline amplitude sampling points.

[0137] At box 456, the maximum amplitude of each signal pulse is determined. At box 458, all signal pulses with a maximum amplitude greater than the pulse amplitude threshold determined at box 452 are identified. For example, all signal pulses with a maximum amplitude at least half of the maximum absolute amplitude determined at box 404 are identified. At box 460, the maximum signal pulse width is determined by comparing the signal pulse widths of all signal pulses with a maximum amplitude at least equal to the pulse amplitude threshold. At box 460, the maximum signal pulse width among all identified signal pulses that meet the amplitude threshold requirement can be determined as a measure of the overall morphological signal width.

[0138] At block 462, control circuitry 80 compares the maximum signal pulse width with a tachyarrhythmia width threshold. In one embodiment, the tachyarrhythmia width threshold is set between 15 and 25 sampling points, for example, 20 sampling points when the sampling rate is 256 Hz. When the maximum signal pulse width is less than or equal to the width threshold, control circuitry 80 does not detect tachyarrhythmia morphology based on the signal width metric at block 468. However, tachyarrhythmia morphology can be detected based on another overall morphology metric, such as combining... Figure 10 The overall morphological amplitude is described.

[0139] The overall morphological signal width metric was correlated with the probability of signal segments exhibiting tachyarrhythmic morphologies. For example, a relatively high overall morphological signal width metric might be evidence of tachyarrhythmic morphologies, such as ventricular fibrillation waves that are relatively wide compared to narrow NSR R waves. Conversely, a relatively low overall morphological signal width metric might be evidence of relatively narrow NSR R waves occurring during the time interval of a second cardiac electrical signal segment.

[0140] When the maximum pulse width at box 462 exceeds the threshold for tachyarrhythmia morphology, tachyarrhythmia morphology is detected at box 464. A relatively wide signal pulse is evidence of tachyarrhythmia morphology within the segment of the second cardiac electrical signal being analyzed. Evidence of tachyarrhythmia morphology can be excluded, for example, in… Figure 5 The box at position 114 or Figure 6B Reset or adjust the tachyarrhythmia interval counter at box 240, even when NSR beats have been detected. When fewer than the threshold number of the analyzed cardiac electrical signal segments is determined to have a tachyarrhythmia morphology, NSR beat detection supports resetting or adjusting the tachyarrhythmia interval counter to avoid VT or VF detection due to variations in R wave amplitude and / or exceeding the noise incidence rate of the desired NID.

[0141] Depend on Figure 10 The method determines the overall morphological amplitude and is determined by Figure 11 The overall shape signal width metric determined by the method can be determined by the control circuit 80, and used in combination to... Figure 5 Box 106 or Figure 6B Tachyarrhythmia morphology is detected at box 222. In some embodiments, evidence of tachyarrhythmia morphology based on overall morphology metrics prevents the tachyarrhythmia interval counter from being reset or adjusted, regardless of NSR beat detection. A second cardiac electrical signal segment with a relatively high overall morphological amplitude and / or a relatively high overall morphological signal width metric is evidence of tachyarrhythmia morphology. In various embodiments, both the overall morphological amplitude and overall morphological signal width metrics can be determined and compared with their respective tachyarrhythmia morphology thresholds. In some embodiments, for a signal segment to be identified and counted as a tachyarrhythmia overall morphological signal segment, it may only be necessary for either the overall morphological amplitude or the overall morphological signal width metric to be greater than the corresponding tachyarrhythmia morphology threshold. When tachyarrhythmia morphology criteria are met, for example, when at least one or both of the overall morphological amplitude and overall morphological signal width metrics are less than the corresponding tachyarrhythmia morphology threshold, the threshold number of the identified NSR beats can be used to reset or adjust the tachyarrhythmia interval counter.

[0142] Figure 12 This is a flowchart 500 of a method for detecting ventricular tachyarrhythmias performed by an ICD 14 according to some embodiments. At blocks 502 and 504, two different sensing electrode vectors can be selected by sensing circuitry 86 for receiving a first cardiac electrical signal via a first sensing channel 83 and a second cardiac electrical signal via a second sensing channel 85, respectively (see...). Figure 4The two sensing electrode vectors can be selected by a switching circuit included in the sensing circuit 86 under the control of the control circuit 80. In some embodiments, the two sensing electrode vectors are programmed by the user and retrieved from the memory 82 by the control circuit 80 and transmitted to the sensing circuit 86 as vector selection control signals.

[0143] The first sensing vector selected at box 502 for sensing the first cardiac electrical signal can be a relatively short bipolar vector, for example, between electrodes 28 and 30, or between electrodes 28 and 24 of lead 16, or other electrode combinations as described above. The relatively short bipolar vector may include electrodes that are relatively close to each other and relatively close to the ventricular chambers compared to the second sensing vector selected at box 504, to provide sensing of a relatively “near-field” ventricular signal for sensing the R wave. The first sensing vector can be a vertical sensing vector (relative to the patient’s upright or standing position) or generally aligned with the cardiac axis to maximize the R wave amplitude in the first cardiac electrical signal for reliable R wave sensing. However, the first sensing vector is not limited to any particular inter-electrode spacing or orientation and can be selected as any available electrode pair.

[0144] At block 504, the second sensing electrode vector for obtaining the second cardiac electrical signal can be a relatively long bipolar vector with an interelectrode distance greater than that of the first sensing electrode vector. For example, the second sensing electrode vector can be selected as a vector between one of the pacing sensing electrodes 28 or 30 and the ICD housing 15, between one of the defibrillation electrodes 24 or 26 and the housing 15, or between an electrode and the housing 15 along the distal portion of the lead 16. In some embodiments, the second sensing vector can be orthogonal or nearly orthogonal to the first sensing vector, but the first and second sensing vectors do not need to be orthogonal. Compared to the first sensing electrode vector, the second sensing electrode vector can receive a relatively more global or far-field cardiac electrical signal. At block 504, the second cardiac electrical signal received by the selected second sensing vector can be analyzed by control circuitry 80 to detect NSR morphology and overall morphology of tachyarrhythmias. In other embodiments, sensing vector 1 and sensing vector 2 can be the same sensing vector. In some embodiments, sensing vector 1 and sensing vector 2 are the same sensing vector, but are received by two different sensing channels of sensing circuitry 86 with different filtering and / or other signal processing characteristics to sense two different cardiac electrical signals, one for detecting R waves and the other for performing morphological analysis to detect NSR beats and tachyarrhythmia morphologies. In other embodiments, a single sensing channel may be provided to sense the cardiac electrical signal for sensing R waves and perform morphological analysis for detecting NSR beats and tachyarrhythmia morphologies.

[0145] At block 506, in response to the first sensing channel 83 detecting that a first cardiac electrical signal crosses an R-wave sensing threshold, sensing circuit 86 can generate an R-wave sensing event signal. The R-wave sensing event signal can be passed to control circuit 80. In response to the R-wave sensing event signal, control circuit 80 is triggered at block 508, down the "yes" branch of block 506, to store segments of the second cardiac electrical signal received from the second sensing channel 85 (via a second sensing vector selected at block 504) within a predetermined time interval. These segments of the second cardiac electrical signal can be stored in a circular buffer of memory 82, which is configured to store multiple sequential segments, the storage of each segment being triggered by the R-wave sensing event signal generated by the first sensing channel 83. For example, the digitized segment of the second cardiac electrical signal can be 100 to 500 ms long, including sampling points before and after the time of the R-wave sensing event signal. The segments of the second cardiac electrical signal may or may not be time-focused on the R-wave sensing event signal received from sensing circuit 86. For example, the segment may extend 100 ms after the R-wave sensing event signal and last for 200 to 500 ms, such that the segment extends from approximately 100 to 400 ms before the R-wave sensing event signal to 100 ms after the event. In other embodiments, the segment may be focused on the R-wave sensing event signal, or may extend a greater number of sampling points after the R-wave sensing event signal than before it. In one embodiment, the buffered segment of the second cardiac electrical signal is at least 50 sampling points obtained at a sampling rate of 256 Hz or approximately 200 ms. In another embodiment, the buffered segment is at least 92 sampling points, or approximately 360 ms, sampled at 256 Hz, and can be used for analysis to detect NSR beats and for other analyses to confirm R-wave sensing, such as analysis of noisy signal segments or oversensing.

[0146] Memory 82 can be configured to store a predetermined number of second cardiac electrical signal segments (e.g., at least one, and in some cases, two or more) in a circular buffer, such that the oldest segment is overwritten by the newest segment triggered by the currently sensed R wave. In some embodiments, each segment is analyzed to detect NSR beat morphology and update the NSR beat classification buffer. As described below, in other embodiments, if the R-sensing confirmation threshold number for the tachyarrhythmia interval is not reached at block 514, previously stored segments may never be analyzed for NSR beat detection and may be overwritten. In some embodiments, at least one segment of the second cardiac electrical signal can be stored, and if NSR beat detection is not required for adjusting the tachyarrhythmia interval counter, this segment can be overwritten by the next segment corresponding to the next sensed R wave event signal.

[0147] In addition to buffering a segment of the second cardiac electrical signal, control circuit 80 responds to the R-wave sensing event signal generated at block 506 by determining the RRI at block 510. The RRI ends with the current R-wave sensing event signal and begins with the most recent preceding R-wave sensing event signal. Timing circuit 90 of control circuit 80 can transmit the RRI timing information to tachyarrhythmia detection circuit 92, which adjusts the tachyarrhythmia interval counter at block 512. If the RRI is longer than the tachycardia detection interval (TDI), the tachyarrhythmia interval counter remains unchanged. If the RRI is shorter than the TDI but longer than the fibrillation detection interval (FDI), for example, if the RRI is in the tachycardia detection interval region, the VT interval counter is incremented at block 512. If the RRI is shorter than or equal to the FDI, the VF interval counter is incremented at block 512. In some embodiments, if the RRI is less than the TDI, a combined VT / VF interval counter is incremented.

[0148] After updating the tachyarrhythmia interval counter at box 512, the tachyarrhythmia detector 92 compares the counter value with the R-sensing confirmation threshold at box 514 and the VT and VF detection thresholds at box 536. If the VT or VF detection interval counter has reached the R-sensing confirmation threshold, i.e., the "Yes" branch of box 514, a second cardiac electrical signal buffered from sensing channel 85 can be analyzed to detect NSR beats, used to adjust the VT and VF interval counters as needed. The second cardiac electrical signal can also be analyzed to detect various types of oversensing, which may cause the first sensing channel 83 to generate erroneous R-wave sensing event signals, resulting in an increase in the VT and / or VF counters at box 512. The R-sensing confirmation threshold can be a count of VT or VF intervals greater than one or another higher threshold.

[0149] Different R-sensing confirmation thresholds can be applied to the VT interval counter and the VF interval counter. For example, the R-sensing confirmation threshold could be a count of two on the VT interval counter and a count of three on the VF interval counter. In other embodiments, the R-sensing confirmation threshold is a higher number, such as five or higher, but may be less than the number of intervals required to detect VT or VF. In addition to applying the R-sensing confirmation threshold to the individual VT and VF counters, or alternatively, to the combined VT / VF interval counters, the R-sensing confirmation threshold can also be applied. It should be recognized that in some embodiments, VT detection may not be enabled, and VF detection may be enabled in ICD 14. In this case, in response to the RRI determination, only the VF interval counter is updated at block 512, and the R-sensing confirmation threshold can be applied to the VF interval counter at block 514.

[0150] If any rapid arrhythmia interval counter at box 514 does not reach the R-sensing confirmation threshold, control circuitry 80 waits at box 508 for the next R-wave sensing event signal to buffer the next segment of the second cardiac electrical signal. If the R-sensing confirmation threshold is reached at box 514, for example, when the VF interval counter value is at least 2 or the VT interval counter value is at least 3, control circuitry 80 begins analyzing the second cardiac electrical signal segment for detecting NSR beats. In various embodiments, additional analyses of the second cardiac electrical signal segment may also be performed to confirm the sensed R wave, detect various types of oversensing, and / or detect evidence of supraventricular tachyarrhythmias (SVT).

[0151] At block 516, control circuitry 80 can retrieve one or more notch-filtered signal segments stored in a cyclic buffer of memory 82 for performing various signal analyses that can confirm or reject rapid arrhythmia interval detection. In some embodiments, the stored second cardiac electrical signal segment is notch-filtered by control circuitry 80 (e.g., a notch filter implemented by firmware) after an R-sensing confirmation threshold is reached. In other embodiments, such as Figure 4 As shown, the notch-filtered signal received from the second sensing channel 85 is buffered in memory 82 for retrieval by the control circuit 80. As described above, for some analyses performed on the second cardiac electrical signal to detect NSR pulsations and tachyarrhythmia morphologies, notch-filtered, rectified segments of the second cardiac electrical signal can be used. In other analyses, unrectified, notch-filtered segments of the second cardiac electrical signal are used by the control circuit 80.

[0152] At block 516, control circuitry 80 may perform various analyses to detect oversensing signal segments. Oversensing signal segments may be detected based on analysis of a second cardiac electrical signal segment, which is performed to detect noise that may be oversensed as erroneous R-waves from the first cardiac electrical signal. At block 516, noise signal segments that can be identified as oversensing signal segments may include noise signals caused by non-myocardial noise (myoelectric potentials), electromagnetic interference, or other electrical noise. At block 516, oversensing signal segments may be additionally or alternatively identified based on analysis of the second cardiac electrical signal segment to detect possible cardiac event oversensing, such as T-wave oversensing or P-wave oversensing that leads to erroneous R-wave sensing event signals generated by the first sensing channel. At block 516, multiple analyses may be performed to detect different types of possible oversensing of stored R-wave sensing event signals that lead to triggering the second cardiac electrical signal segment. In some embodiments, the results of the oversensing analysis performed at block 516 may be used to set a VT / VF detection rejection rule at block 518, as described below. Various embodiments of analysis for identifying second cardiac electrical signal segments that are actually or potentially noise-related or oversensitized by cardiac events, which can be performed at block 516, are described in U.S. Patent Nos. 10,406,373 (Zhang et al.) and 9,956,423 (Zhang et al.).

[0153] At block 520, control circuitry 80 may set an NSR reset criterion applied to detected NSR beats to determine when to adjust the tachyarrhythmia interval counter. In some embodiments, control circuitry 80 may set the NSR reset criterion at block 520 based on an oversensing analysis performed at block 516. The NSR reset criterion may be set based on a history of noise signal segment detection, a history of oversensing detection, and / or a programmed NID required to detect VT or VF. For example, if one or more second cardiac electrical signal segments have been identified as noise signal segments, SVT signal segments, or oversensing of T waves or P waves, the threshold number of NSR beats required to reset or adjust the tachyarrhythmia interval counter may be reduced. Noise signal segments, SVT signal segments, T wave oversensing, or P wave oversensing may be detected based on analysis of the second cardiac electrical signal segments, which may include determining various characteristics of the signal segments and / or morphological analysis of the second cardiac electrical signal segments. These analyses may correspond to any analyses disclosed in the foregoing references. Any technique for detecting oversensing or noise in cardiac electrical signal segments may be applied at block 516. When no noise or oversensing detection is performed, the number of NSR beats required to reset the tachyarrhythmia interval counter can be set to a relatively high threshold, for example, at least three NSR beats detected out of eight analyzed cardiac electrical signal segments. When a signal segment is identified as an oversensing segment due to the detection of a cardiac event or potential or actual oversensing of non-cardiac noise, the chance of detecting a short RRI and counting it as a tachyarrhythmia interval increases in the presence of potential NSR. Therefore, when one or more segments are detected as noisy and / or one or more segments are identified as oversensing T waves or P waves, the NSR reset threshold used to adjust the tachyarrhythmia interval counter can be reduced to, for example, two or even one NSR beat detected.

[0154] Additionally or alternatively, the NSR reset criteria set in box 520 can be based on the currently programmed NID used to detect VT or VF. For example, when the VF NID is set to 30 VF intervals out of the most recent 40 RRIs, the threshold number for NSR beats can be set relatively high, such as 4 out of 8. When the VF NID is set relatively low, such as 18 VF intervals out of 24 RRIs, the threshold number for NSR beats can be set relatively low, such as 2 NSR beats detected out of the 6 segments analyzed.

[0155] In some embodiments, in addition to setting the number of NSR reset thresholds required for resetting or adjusting the NSR beat detection for tachyarrhythmia interval counters, control circuitry 80 may set criteria for detecting each NSR beat at block 520 based on the NSR reset threshold. For example, as described above, when the NSR reset threshold is relatively low (e.g., three NSR beats or less), the morphological match score threshold and / or specific beat feature threshold for detecting NSR beats may be set relatively higher or more stringent. When relatively few NSR beat detections are required to reset the VT and / or VF interval counters, a higher morphological match score (e.g., greater than 70), a smaller difference threshold from a reference beat feature (e.g., within 20% of the reference beat feature), and all three specific beat features within the correspondingly different thresholds from the reference NSR R wave feature may be required to detect NSR beats. When a relatively high number of NSR beats need to be detected (e.g., four or more), the morphological criteria may be slightly less stringent, for example, a lower morphological matching threshold (e.g., greater than 60), a larger difference from a specific reference beat feature (e.g., within 30% of the reference beat feature), and / or fewer beat features required to match the reference heartbeat feature (e.g., only one or two matching heartbeat features). It should be recognized that in other embodiments, block 520 for setting the NSR reset criteria is optional, and the NSR reset criteria and NSR beat detection threshold may be predetermined, fixed values ​​that cannot be automatically adjusted by the control circuitry 80.

[0156] At box 526, a second cardiac electrical signal segment is analyzed to classify the segment as an NSR beat or a non-NSR beat. This analysis may include interval-based and / or morphology-based analyses as described above. Interval-based NSR beat detection can be performed at box 526 by detecting intervals equal to or greater than the NSR threshold (which may be combined with...). Figure 6A The RRI (as described) is used for detection. For a predetermined number of previously detected NSR intervals, the NSR intervals may need to fall within the regularity of the RRI differences. In some embodiments, the NSR interval detection criteria may need to detect a predetermined number of consecutive NSR intervals and be stable (within each other's variability or difference thresholds) before classifying each NSR interval as an NSR beat. When the interval-based criteria are met for the currently sensed R wave, at box 530, the NSR beat classification buffer can be updated to provide an updated count of NSR beats in Y consecutive sensed R waves. In this embodiment that relies solely on RRI analysis to detect NSR beats, the analysis of a second cardiac electrical signal segment for NSR beat detection can be omitted.

[0157] Additionally or alternatively, morphological analysis can be applied to a second cardiac electrical signal segment to detect NSR pulsation. For example, as in combination with Figure 6B and7 The method describes that when the RRI of the sensed R wave is greater than the updated NSR interval threshold, the corresponding second cardiac electrical signal segment can be analyzed to detect the NSR beat morphology associated with the NSR interval. Second cardiac electrical signal analysis may include determining whether the signal waveform morphology matches a previously established NSR R wave template and / or determining whether a specific beat feature determined from a relatively short portion of the buffered second cardiac electrical signal segment matches a reference NSR R wave morphological feature. At box 526, NSR beats can be detected based solely on RRI analysis, solely on morphological analysis of the second cardiac electrical signal, or a combination of both. At box 530, the NSR beat classification buffer can be updated, and the NSR beat count can be increased.

[0158] At box 528, a general morphological metric is determined from the cardiac electrical signal segment to detect the morphology of rapid arrhythmias present in the second cardiac electrical signal segment. (As described above, in conjunction with...) Figure 10 and 11 The overall morphological metric may include an overall morphological amplitude measure and an overall morphological signal width measure. When either the overall morphological amplitude measure or the overall morphological signal width measure is greater than the corresponding tachyarrhythmia morphological threshold, the segment can be identified and counted (at box 530) as a tachyarrhythmia morphological signal segment. In some embodiments, when a segment meets the tachyarrhythmia morphological criteria, it is classified as a non-NSR beat in the NSR buffer, regardless of whether it meets the NSR beat criteria. Therefore, when a segment meets the tachyarrhythmia morphological criteria, the same segment that meets the NSR beat criteria may not be considered an NSR beat.

[0159] At block 532, control circuitry 80 determines whether all reset criteria are met. For example, control circuitry 80 may verify that at least one of the VT and / or VF interval counters has reached a reset threshold value. For example, when VT detection is enabled, the VF counter value may be required to be at least 7, or the combined VT / VF counter value may be required to be at least 8. When the VT and / or VF interval counters are confirmed to have reached at least one reset threshold value, control circuitry 80 may apply the NSR reset threshold established at block 520 and verify that the value of the tachyarrhythmia morphology counter is less than the suppression reset threshold number. Reset criteria are met at block 532 when the number of NSR beat classifications stored in the NSR beat classification buffer reaches the NSR reset threshold and the number of tachyarrhythmia morphology classifications stored in the tachyarrhythmia morphology classification buffer is less than the suppression reset threshold number.

[0160] Control circuit 80 can adjust the VT and / or VF (and / or combined VT / VF) interval counters at block 534. As described above, the VT, VF, and / or combined VT / VF counters can each be reduced to a predetermined value, reduced by a predetermined amount (reduced to a specified minimum value), or reduced by a predetermined portion or fraction of the current value of the respective counter. In some embodiments, at block 514, each tachyarrhythmia interval counter can be adjusted to and not less than an R-sensing confirmation threshold applied to the respective tachyarrhythmia interval counter. In the embodiments given above, the VF interval counter is adjusted from its current value when the reset criterion is met to value 2, and the VT interval counter is adjusted from its current value when the reset criterion is met to value 3. In this way, the R-sensing confirmation threshold continues to be met at block 514, enabling continuous analysis of the buffered second cardiac electrical signal segment to detect NSR beats.

[0161] In other embodiments, the adjustment at box 534 is based on the current tachyarrhythmia counter value. For illustration, if the VF interval counter is 10 or less, it can be reset to value 3 at box 534. If the VF interval counter is greater than 10 but less than 20, it can be reset to value 8. If the VF interval counter is 20 or more, it may be reset to value 12. In the foregoing embodiments, the tachyarrhythmia interval counter is adjusted according to a predetermined specification, which is not necessarily equal to the number of detected NSR beats. In other examples, in response to each detected NSR beat that is highly correlated, for example, with the wavelet coefficients of the NSR R wave template and the specific beat characteristics of the NSR R wave template, the adjustment at box 534 may be a subtraction of one, and the R wave may not be confirmed due to evidence of noise or oversensitization detected in the second ECG signal segment at box 516. In this way, the VT and / or VF interval counters can be dynamically adjusted up or down based on the RRI and the detected NSR beats in combination with other R wave confirmation criteria applied at box 516.

[0162] In some embodiments, control circuitry 80 may adjust the NID required for detecting VT or VF (box 537) in response to an adjustment of the threshold number of the tachyarrhythmia interval counter based on NSR beat detection (box 535). As defined in box 535, when the tachyarrhythmia interval counter is adjusted by three, five, or other threshold numbers based on satisfying the NSR reset criterion at box 534, control circuitry 80 may increase the NID threshold for VT and / or VF detection at box 537. For example, due to satisfying the NSR reset criterion, when the VF interval counter is adjusted a number of times (e.g., at least three times), the nominal NID for 30 VF intervals out of 40 RRIs for VF detection may increase to the NID for 45 VF intervals out of 60 RRIs.

[0163] After adjusting the tachyarrhythmia interval counter at box 534 (and optionally adjusting NID at box 537), the control circuit 80 can continue checking whether NID has been reached at box 536, and if not, determine RRI at box 510. As long as the R-sensing confirmation threshold is met at box 514, the analysis of the second cardiac electrical signal segment continues. When the reset criterion is not met at box 532, the control circuit 80 can determine at box 536 whether NID has been reached based on the values ​​of the VT and / or VF interval counters.

[0164] In some embodiments, the result of the oversensing analysis performed at box 516 can be used to set a VT / VF detection rejection rule at box 518 when the NID required for VT or VF detection is reached at box 536. VT or VF detection based on the NID threshold met at box 536 can be suppressed at box 542 when the noise or oversensing criterion used to set the rejection rule is met (box 518). When VT / VF detection is suppressed, VT or VF treatment is suppressed at box 542. Various embodiments of VT / VF detection rejection rules that can be applied based on noise and / or oversensing analysis of a second cardiac electrical signal segment are described in U.S. Patent No. 10,406,373 (Zhang et al.) and U.S. Patent No. 9,956,423 (Zhang et al.).

[0165] After suppressing VT / VF detection and treatment at block 542, control circuitry 80 can determine at block 543 whether termination criteria are met. Termination of the rapid rate of the sensed R wave (which satisfies NID) can be detected based on a predetermined number of RRIs greater than the tachyarrhythmia detection interval, or when the average, median, or other metric of RRIs determined within a predetermined time interval is greater than the tachyarrhythmia detection interval. For example, termination can be detected at block 543 when a threshold number of RRIs longer than the VT detection interval (when VT detection is enabled) or longer than the VF detection interval (when VT detection is disabled) is detected after NID is met. In one embodiment, termination is detected at block 543 when at least eight consecutive long RRIs greater than the VT detection interval are detected, for example. In another embodiment, termination can be detected at block 543 when a predetermined time interval has elapsed and the median RRI is greater than the VT detection interval. For example, if the median RRI of the most recent 12 RRIs is always greater than the VT detection interval by at least 20 seconds or other predetermined time period, the control circuit 80 may detect termination in block 543. In response to detecting termination, the control circuit 80 may reset the VT and VF interval counters to zero and return to block 510.

[0166] If the NID (box 536) is met, and the VT / VF rejection rule is not satisfied at box 518, the control circuit 80 may detect a VT / VF episode at box 544. It should be understood that while the NID may be met, other criteria (e.g., failure to meet the rejection rule at box 518) may be required to actually detect VT or VF and initiate a treatment response. In response to the VT / VF detection at box 544, the treatment delivery circuit 84 may begin charging the capacitor at box 546 to prepare for delivering a CV / DF shock. In some embodiments, during charging, the control circuit 80 may continue analyzing the RRI and / or a second cardiac electrical signal segment for detecting NSR beats. If a threshold number of NSR beats is detected at box 548, the tachyarrhythmia interval counter may be adjusted at box 534. For example, a reset criterion that was not met at box 532 prior to the detection of VT or VF at box 544 may be met at box 548 during capacitor charging. When the reset criterion is met during charging at block 548, the tachyarrhythmia interval counter can be adjusted at block 534. Since the NID is no longer met after adjusting the tachyarrhythmia interval counter at block 534, the treatment delivery circuit 84 cancels VT / VF treatment and terminates capacitor charging that begins at block 546. In other embodiments, once the NID is met at block 536, resulting in the detection of VT / VF at block 544, and capacitor charging begins at block 546, the reset of the VT / VF interval counter can be suppressed (block 548 can be omitted).

[0167] If the NID is met at box 536 and no NSR pulsation is detected during capacitor charging (or the NSR reset criterion is still not met or not checked), VT or VF treatment is delivered at box 550. It should be understood that other VT / VF rejection criteria may be applied after VT / VF is detected and during charging. For example, it may be necessary to keep various noise rejection criteria, T-wave hypersensitivity rejection criteria, P-wave hypersensitivity rejection criteria, SVT rejection criteria, etc., unmet during charging at box 546 before delivering treatment at box 550.

[0168] The method disclosed herein is used to detect potential NSRs when a rapid ventricular rate is detected, for example, due to noise or hypersensitivity of cardiac events. When a probability counter of tachyarrhythmia intervals is used to detect VT or VF, continuous tachyarrhythmia intervals are not required; intermittent episodes of noise or hypersensitivity, especially in the presence of R-wave amplitude variability, can lead to NID. NSR beats may occur during and / or between intermittent episodes of noise or hypersensitivity. By identifying NSR beats during tachyarrhythmia interval counting according to the technique disclosed herein, the tachyarrhythmia interval counter can be adjusted to a lower value to reduce the likelihood of erroneous tachyarrhythmia detection, while still allowing for tachyarrhythmia detection with high sensitivity and specificity. Therefore, the functionality of the medical device performing the present disclosure is improved by integrating a specified method for detecting NSR beats and a prescribed adjustment of a tachyarrhythmia interval counter in response to NSR beat detection, because this improvement results in a reduction in the rate of erroneous tachyarrhythmia detection and unnecessary treatment delivery without reducing the rate of true tachyarrhythmia detection and necessary treatment delivery.

[0169] It should be understood that, depending on the examples, certain actions or events in any of the methods described herein may be performed in a different order, may be added, combined, or may be omitted entirely (e.g., not all described actions or events are necessary for practicing the methods). Furthermore, in some instances, actions or events may be performed simultaneously rather than sequentially, for example, through multithreaded processing, interrupt handling, or multiple processors. Additionally, for clarity, although some aspects of this disclosure are described as being performed by a single circuit or unit, it should be understood that the techniques of this disclosure can be performed by a combination of units or circuits associated with, for example, a medical device.

[0170] In one or more examples, the described functionality can be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functionality can be stored on a computer-readable medium in the form of one or more instructions or code and can be executed by a hardware-based processing unit. The computer-readable medium can include a computer-readable storage medium corresponding to a tangible medium such as a data storage medium (e.g., RAM, ROM, EEPROM, flash memory, or any other medium that can be used to store the desired program code in the form of instructions or data structures and that can be accessed by a computer).

[0171] Instructions can be executed by one or more processors, such as one or more digital signal processors (DSPs), general-purpose microprocessors, application-specific integrated circuits (ASICs), field-programmable arrays (FPLAs), or other equivalent integrated or discrete logic circuit systems. Therefore, the term "processor" as used herein can refer to any of the foregoing structures or any other structure suitable for implementing the techniques described herein. Furthermore, the techniques can be implemented entirely within one or more circuit or logic elements.

[0172] Therefore, a medical device has been presented in the foregoing description with reference to specific examples. It should be understood that the various aspects disclosed herein can be combined in different combinations than those shown in the accompanying drawings. It should be understood that various modifications can be made to the referenced embodiments without departing from the scope of this disclosure and the appended claims and / or embodiments.

[0173] Example 1. A method comprising: sensing cardiac events from a first cardiac electrical signal; determining time intervals between consecutive cardiac events sensed from the first cardiac electrical signal; detecting a plurality of tachyarrhythmic intervals from the determined time intervals, each of the plurality of tachyarrhythmic intervals being less than a tachyarrhythmic detection interval threshold; incrementing a tachyarrhythmic interval count in response to detecting each of the plurality of detected tachyarrhythmic intervals; and detecting a normal sinus rhythm interval from the determined time intervals, the normal sinus rhythm interval being greater than a certain threshold. At a normal sinus rhythm interval threshold; determining a normal sinus rhythm interval at which a first reset threshold number is detected; in response to the first reset threshold number of the detected normal sinus rhythm interval, reducing the tachyarrhythmia interval count; after reducing the tachyarrhythmia interval count, determining that the tachyarrhythmia interval count subsequently reaches a tachyarrhythmia detection threshold; detecting a tachyarrhythmia in response to the tachyarrhythmia interval count reaching the tachyarrhythmia detection threshold; and delivering tachyarrhythmia treatment in response to the detection of a tachyarrhythmia.

[0174] Example 2. According to the method of Example 1, the detection of a normal sinus rhythm interval includes setting a long interval threshold; detecting a plurality of long intervals from a determined time interval, each of the plurality of long intervals being greater than the long interval threshold; determining a normal sinus rhythm interval threshold based on the plurality of long intervals; and detecting a normal sinus rhythm interval in response to a time interval determined between consecutive cardiac events sensed from a first cardiac electrical signal being greater than the determined normal sinus rhythm interval threshold.

[0175] Example 3. The method according to Example 2 further includes setting the long interval threshold to a predetermined interval that is longer than the tachyarrhythmia detection interval.

[0176] Example 4. A method according to any one of Examples 1-3, wherein determining a first reset threshold number for detecting the normal sinus rhythm interval further includes determining a normal sinus rhythm interval of the first threshold number from a second cardiac electrical signal detected from a first predetermined number of cardiac events; and determining a normal sinus rhythm interval of a second threshold number from a second predetermined number of cardiac events, wherein the first predetermined number of cardiac events is greater than and includes the second predetermined number of cardiac events.

[0177] Example 5. The method according to any one of Examples 1-4 further includes sensing a second cardiac electrical signal different from the first cardiac electrical signal; detecting a normal sinus rhythm morphology from the second cardiac electrical signal, the second cardiac electrical signal corresponding to the time of a cardiac event sensed from the first cardiac electrical signal during a detected normal sinus rhythm interval; detecting normal sinus rhythm beats associated with the normal sinus rhythm interval based on the detected normal sinus rhythm morphology; and determining the detected normal sinus rhythm intervals of the first reset threshold number in response to detecting a normal sinus rhythm beat associated with each of the normal sinus rhythm intervals of the first reset threshold number.

[0178] Example 6. According to the method of Example 5, detecting a normal sinus rhythm morphology includes determining a morphological matching score between a second cardiac electrical signal and a predetermined normal sinus rhythm template; determining that the morphological matching score is greater than a matching threshold; determining a plurality of pulsation features from a first time interval of the second cardiac electrical signal, the first time interval including the time point of a cardiac event sensed from the first cardiac electrical signal; determining that the plurality of pulsation features meet a beat feature matching criterion; and detecting a normal sinus rhythm morphology in response to determining that the morphological matching score is greater than the matching threshold and that the plurality of pulsation features meet the beat feature matching criterion.

[0179] Example 7. According to the method of Example 6, wherein the control circuit is further configured to set at least one of the matching threshold and the threshold of the pulsation feature matching criterion based on a first reset threshold.

[0180] Example 8. The method according to any one of Examples 6-7, wherein detecting multiple pulsation features includes determining one or more polarity patterns of signal peaks of the second cardiac electrical signal during a first time interval; a peak time interval from a reference time point to the maximum peak amplitude during the first time interval; or a normalized width measure determined by summing the amplitudes of all sampled points of the second cardiac electrical signal during the first time interval and dividing by the maximum peak amplitude.

[0181] Example 9. The method according to any one of Examples 1-8 further includes determining a second reset threshold number for the tachyarrhythmia interval count that is greater than the number of tachyarrhythmia intervals; in response to the tachyarrhythmia interval count being greater than the second reset threshold number and the first reset threshold number for the detected normal sinus rhythm, decreasing the value of the tachyarrhythmia interval count; and reducing the value of the tachyarrhythmia interval count to a value greater than zero and less than the value of the second reset threshold.

[0182] Example 10. The method according to any one of Examples 1-9 further includes determining a current value of the tachyarrhythmia interval count in response to a first reset threshold number of detected normal sinus rhythm intervals; and reducing the tachyarrhythmia interval count value to an adjusted value based on the current value of the tachyarrhythmia interval count value.

[0183] Example 11. The method according to any one of Examples 1-10 further includes setting a first reset threshold based on a rapid arrhythmia detection threshold.

[0184] Example 12. The method of any one of Examples 1-11 further includes sensing a second cardiac electrical signal different from a first cardiac electrical signal; determining at least one overall morphological measure from the second cardiac electrical signal within an overall morphological time interval, the overall morphological time interval including a time point of a cardiac event sensed from the first cardiac electrical signal associated with a detected normal sinus rhythm interval; determining that the at least one overall morphological measure is greater than a tachyarrhythmia morphology threshold; detecting tachyarrhythmia morphology in response to the overall morphological measure being greater than the tachyarrhythmia morphology threshold; increasing the tachyarrhythmia morphology count for each tachyarrhythmia morphology detection; determining that the tachyarrhythmia morphology count is less than a third reset threshold; and decreasing the tachyarrhythmia interval count value in response to the detection of a first reset threshold number of normal sinus rhythm intervals and a tachyarrhythmia morphology count less than the third reset threshold.

[0185] Example 13. The method according to Example 12 further includes determining at least one morphological feature from the morphological time interval of the second cardiac electrical signal, the morphological time interval including the time point of a cardiac event sensed from the first cardiac electrical signal associated with the detected normal sinus rhythm interval, the overall morphological time interval being greater than the morphological time interval; determining that at least one morphological feature meets the normal sinus rhythm morphological criteria; and in response to determining that at least one morphological feature meets the normal sinus rhythm morphological criteria in each of the normal sinus rhythm intervals of a first reset threshold number, determining that a normal sinus rhythm interval of the first reset threshold number is detected.

[0186] Example 14. The method of any one of Examples 12-13 further includes, in response to a first reset threshold number of detected normal sinus rhythm intervals and a tachyarrhythmia morphology count equal to or greater than a third reset threshold, suppressing the reduction of the tachyarrhythmia interval count.

[0187] Example 15. The method of any one of Examples 12-14, wherein determining at least one overall morphological metric comprises at least one of: (a) determining an overall morphological amplitude quantity by determining a maximum amplitude from sampling points spanning a second time interval of a second cardiac electrical signal; determining the sum of amplitudes of all sampling points spanning the second time interval of the second cardiac electrical signal; determining the overall morphological metric by dividing the sum by the maximum amplitude; or (b) determining an overall morphological signal width metric by: identifying a plurality of signal pulses spanning the second time interval of the second cardiac electrical signal; determining the signal width of each of the plurality of signal pulses; and determining a maximum signal width from the determined signal widths.

[0188] Example 16. The method of any one of Examples 1-15 further includes setting a first reset threshold number to a first value; sensing a second cardiac electrical signal different from the first cardiac electrical signal; detecting at least one segment of the second cardiac electrical signal as an oversensing segment; and adjusting the first reset threshold number from the first value to a second value different from the first value in response to detecting at least one segment as an oversensing segment.

[0189] Example 17. The method of any one of Examples 1-16 further includes reducing the tachyarrhythmia interval count by a predetermined reduction, said predetermined reduction being one of the fixed reductions; an adjustable reduction based on a tachyarrhythmia detection threshold; or an adjustable reduction based on the value of the tachyarrhythmia interval count.

[0190] Example 18. The method of any one of Examples 1-16 further includes reducing the tachyarrhythmia interval count to a predetermined value of at least zero.

[0191] Example 19. The method of any one of Examples 1-16 further includes determining that the value of the tachyarrhythmia interval count is greater than a confirmation threshold number of tachyarrhythmia intervals; after determining that the value of the tachyarrhythmia interval count is greater than the confirmation threshold number of tachyarrhythmia intervals, detecting the normal sinus rhythm interval; and in response to a first reset threshold number of the detected normal sinus rhythm interval, reducing the tachyarrhythmia interval count value to the confirmation threshold number of tachyarrhythmia intervals.

[0192] Example 20. The method of any one of Examples 1-19 further includes receiving a first cardiac electrical signal via a first sensing electrode vector, the first sensing electrode vector including a first pair of cardiovascular external electrodes carried by a cardiovascular external lead.

[0193] Example 21. A non-transitory computer-readable medium storing a set of instructions, when executed by control circuitry of a medical device, causing the medical device to sense cardiac events from cardiac electrical signals; determine time intervals between consecutive cardiac events sensed from the cardiac electrical signals; detect a plurality of tachyarrhythmia intervals from the determined time intervals, each of the plurality of tachyarrhythmia intervals being less than a tachyarrhythmia detection interval threshold; increment a tachyarrhythmia interval count in response to detecting each of the plurality of detected tachyarrhythmia intervals; and in response to detecting a normal sinus The system detects normal sinus intervals; determines that a first reset threshold number of normal sinus intervals has been detected; in response to the first reset threshold number of the detected normal sinus intervals, reduces the value of the tachyarrhythmia interval count; after reducing the value of the tachyarrhythmia interval count, determines that the tachyarrhythmia interval count subsequently reaches the value of the tachyarrhythmia detection threshold; in response to the value of the tachyarrhythmia interval count reaching the tachyarrhythmia detection threshold, detects tachyarrhythmias; and in response to the detected tachyarrhythmias, delivers tachyarrhythmia treatment.

Claims

1. A medical device comprising: The cardiac electrical signal sensing circuit is configured as follows: Receive the first cardiac electrical signal; Sensing cardiac events from the first cardiac electrical signal; The control circuit is configured as follows: Determine the time interval between consecutive cardiac events sensed from the first cardiac electrical signal; Multiple rapid arrhythmia intervals are detected within a defined time interval, each of which is less than a rapid arrhythmia detection interval threshold. In response to detecting each of the plurality of rapid arrhythmia intervals, the value of the rapid arrhythmia interval count is increased; Detect normal sinus rhythm intervals within a defined time interval, wherein the normal sinus rhythm interval is greater than a normal sinus rhythm interval threshold; A normal sinus rhythm interval was detected that determined the first reset threshold number; In response to the first reset threshold number of the detected normal sinus rhythm intervals, the value of the tachyarrhythmia interval count is reduced; as well as After decreasing the value of the tachyarrhythmia interval count, it is determined that the tachyarrhythmia interval count subsequently reaches the tachyarrhythmia detection threshold; In response to the value of the rapid arrhythmia interval count reaching the rapid arrhythmia detection threshold, a rapid arrhythmia is detected; as well as A treatment delivery circuit is configured to deliver treatment for the tachyarrhythmia in response to the detection of a tachyarrhythmia by a control circuit.

2. The apparatus according to claim 1, wherein, The control circuit is also configured to detect the normal sinus rhythm interval in the following manner: Set a long interval threshold; Multiple long intervals are detected from the determined time intervals, each of which is greater than the long interval threshold; The normal sinus rhythm interval threshold is determined based on the multiple long intervals; as well as The normal sinus rhythm interval is detected in response to a time interval determined between consecutive cardiac events sensed from the first cardiac electrical signal being greater than a determined normal sinus rhythm interval threshold.

3. The apparatus according to claim 2, wherein, The control circuit is configured as follows: The long interval threshold is set to a predetermined interval that is longer than the tachyarrhythmia detection interval.

4. The apparatus according to any one of claims 1-3, wherein: The control circuit is further configured to determine the normal sinus rhythm interval of the first reset threshold number by detecting it in the following manner: Determine that a first threshold number of normal sinus intervals are detected from a first predetermined number of sensed cardiac events; and Determine the number of normal sinus intervals detected from a second predetermined number of sensed cardiac events that are within a second threshold number. Wherein, the first predetermined number of sensed cardiac events is greater than the second predetermined number of sensed cardiac events and includes the second predetermined number of cardiac events.

5. The apparatus according to any one of claims 1-3, wherein: The cardiac electrical signal sensing circuit is also configured to sense a second cardiac electrical signal that is different from the first cardiac electrical signal; The control circuit is further configured to: Normal sinus rhythm morphology is detected from the second cardiac electrical signal, which corresponds to the time of cardiac events sensed from the first cardiac electrical signal during the detected normal sinus rhythm interval. Based on the detected normal sinus rhythm morphology, normal sinus rhythm beats associated with the normal sinus rhythm interval are detected; as well as In response to detecting a normal sinus rhythm beat associated with each of the normal sinus rhythm intervals of the first reset threshold number, it is determined that the normal sinus rhythm interval of the first reset threshold number has been detected.

6. The apparatus according to claim 5, wherein, The control circuit is configured to detect the normal sinus rhythm morphology in the following manner: Determine the morphological matching score between the second cardiac electrical signal and a predetermined normal sinus rhythm template; The morphological matching score is determined to be greater than the matching threshold; Multiple pulsation features are determined from a first time interval of the second cardiac electrical signal, the first time interval including the time point of the cardiac event sensed from the first cardiac electrical signal; Determine that the plurality of pulsation features meet the pulsation feature matching criteria; as well as In response to determining that the morphological matching score is greater than the matching threshold and that the plurality of pulsation features meet the pulsation feature matching criteria, the normal sinus rhythm morphology is detected.

7. The apparatus according to claim 6, wherein, The control circuit is further configured to: At least one of the matching threshold and the threshold of the pulsation feature matching standard is set based on the first reset threshold.

8. The apparatus according to any one of claims 6-7, wherein, The control circuit is configured to detect the plurality of pulsation features by determining one or more of the following: The polarity pattern of the signal peak of the second cardiac electrical signal during the first time interval; The peak time interval from the reference time point to the maximum peak amplitude during the first time interval; or It determines the normalized width metric by summing the amplitudes of all sample points of the second cardiac electrical signal within the first time interval and dividing by the maximum peak amplitude.

9. The apparatus according to any one of claims 1-3, wherein, The control circuit is further configured to: Determine that the count of rapid arrhythmia intervals is greater than the second reset threshold number of rapid arrhythmia intervals; In response to the rapid arrhythmia interval count being greater than the second reset threshold and the first reset threshold for detecting normal sinus rhythm, the value of the rapid arrhythmia interval count is decreased; and Reduce the tachyarrhythmia interval count to a value greater than zero and less than the second reset threshold.

10. The apparatus according to any one of claims 1-3, wherein, The control circuit is further configured to: In response to the first reset threshold number of the detected normal sinus rhythm interval, the current value of the tachyarrhythmia interval count is determined; as well as The value of the tachyarrhythmia interval count is reduced to an adjusted value based on the current value of the tachyarrhythmia interval count.

11. The apparatus according to any one of claims 1-3, wherein, The control circuit is also configured to set the first reset threshold based on the rapid arrhythmia detection threshold.

12. The apparatus according to any one of claims 1-3, wherein: The sensing circuit is also configured to sense a second cardiac electrical signal that is different from the first cardiac electrical signal; and The control circuit is further configured to: At least one overall morphological measure is determined from the second cardiac electrical signal within an overall morphological time interval, the overall morphological time interval including time points of cardiac events sensed from the first cardiac electrical signal associated with the detected normal sinus rhythm interval; Determine that at least one overall morphological metric is greater than the morphological threshold for tachyarrhythmias; In response to the overall morphological metric being greater than the tachyarrhythmia morphology threshold, tachyarrhythmia morphology is detected; For each tachyarrhythmia morphology detection, increase the tachyarrhythmia morphology count; The count of the rapid arrhythmia morphology is determined to be less than the third reset threshold; In response to the detection of a first reset threshold number of normal sinus rhythm intervals and the rapid arrhythmia morphology count being less than the third reset threshold, the value of the rapid arrhythmia interval count is reduced.

13. The apparatus according to claim 12, wherein, The control circuit is further configured to: At least one pulsation morphology feature is determined from the pulsation morphology time interval of the second cardiac electrical signal, the pulsation morphology time interval including the time point of cardiac events sensed from the first cardiac electrical signal associated with the detected normal sinus rhythm interval, the overall morphology time interval being greater than the pulsation morphology time interval. Determine that at least one pulsation morphology characteristic meets the criteria for normal sinus rhythm pulsation; and In response to determining that each normal sinus rhythm beat meets the first reset threshold number of normal sinus rhythm intervals among the at least one beat morphology feature, it is determined that the first reset threshold number of normal sinus rhythm intervals is detected.

14. The apparatus according to claim 12, wherein, The control circuit is further configured to suppress the reduction of the tachyarrhythmia interval count in response to the detection of a first reset threshold number of normal sinus rhythm intervals and the tachyarrhythmia morphology count being equal to or greater than the third reset threshold.

15. The apparatus according to claim 12, wherein, The control circuit is configured to determine the at least one overall morphological measure by at least one of the following: (a) Determine the total morphological amplitude in the following manner: The maximum amplitude is determined from the sampling points spanning the second time interval of the second cardiac electrical signal; Determine the sum of the amplitudes of the sampling points spanning the second time interval of the cardiac electrical signal; and The overall morphological measure is determined by dividing the sum by the maximum amplitude; or (b) Determine the overall morphological signal width metric using the following method: Identify multiple signal pulses spanning the second time interval of the second cardiac electrical signal; Determine the signal width of each of the plurality of signal pulses; as well as The maximum signal width is determined from the defined signal width.

16. The apparatus according to any one of claims 1-3, wherein: The sensing circuit is configured to sense a second cardiac electrical signal that is different from the first cardiac electrical signal; The control circuit is further configured to: Set the first reset threshold number to a first value; At least one segment of the second cardiac electrical signal is detected as an oversensing segment; In response to detecting the at least one segment as an oversensing segment, the first reset threshold number is adjusted from the first value to a second value different from the first value.

17. The apparatus according to any one of claims 1-3, wherein, The control circuit is configured to reduce the rapid arrhythmia interval count by a predetermined amount, the predetermined amount being one of the following: Fixed reduction; Based on the adjustable amount of the rapid arrhythmia detection threshold; or The adjustable amount based on the value of the rapid arrhythmia interval count.

18. The apparatus according to any one of claims 1-3, wherein, The control circuit is configured to reduce the tachyarrhythmia interval count to a predetermined value of at least zero.

19. The apparatus according to any one of claims 1-3, wherein, The control circuit is configured as follows: The value of the rapid arrhythmia interval count is determined to be greater than the confirmation threshold number of rapid arrhythmia intervals; After determining that the value of the tachyarrhythmia interval count is greater than the confirmation threshold number of tachyarrhythmia intervals, the normal sinus rhythm interval is detected; as well as In response to the detection of the first reset threshold number of normal sinus rhythm intervals, the tachyarrhythmia interval count is reduced to the confirmation threshold number of tachyarrhythmia intervals.

20. The apparatus according to any one of claims 1-3, wherein, The sensing circuit is configured to receive the first cardiac electrical signal via a first sensing electrode vector, the first sensing electrode vector including a first pair of cardiovascular external electrodes carried by a cardiovascular external lead that can be coupled to the medical device.

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