Device for detecting excessive sensing of cardiac events

Abstract

A medical device is configured to detect an alternating pattern of signal features determined from consecutive segments of a cardiac electrical signal and determine an overall morphology metric from at least one segment of the cardiac electrical signal. The device is configured to detect a cardiac event overdrive in response to detecting the alternating pattern and the overall morphology metric not meeting a tachyarrhythmia morphology criterion. The medical device can refrain from detecting tachyarrhythmias in response to detecting the cardiac event overdrive.

Description

Technical Field

[0001] This disclosure generally relates to medical device systems and methods for detecting over-sensitivity of cardiac events in cardiac electrical signals. 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's housing. The electrical stimulation may include signals such as pacing pulses or cardioverter-defibrillator (CV / DF) shocks. In some cases, the medical device may sense cardiac electrical signals that accompany intrinsic or pacing-induced depolarization of the heart and control the delivery of stimulation signals to the heart based on these sensed signals. Upon detection of abnormal rhythms such as bradycardia, tachycardia, or fibrillation, one or more appropriate electrical stimulation signals may be delivered to restore or maintain a more normal cardiac rhythm. For example, an ICD may deliver pacing pulses to a patient's heart upon detection of bradycardia or tachycardia, or deliver CV / DF shocks to the heart upon detection of tachycardia or fibrillation.

[0003] An intervenous digital rectum (ICD) senses cardiac electrical signals within the heart chambers and delivers 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, without oversensing far-field events from other heart chambers, such as P waves. In some proposed or available ICD systems, non-venous leads may be coupled to the ICD, presenting new challenges for accurately sensing cardiac electrical events from outside the heart chambers. Summary of the Invention

[0004] Generally, this disclosure relates to techniques for detecting oversensing of cardiac events from cardiac electrical signals and for suppressing arrhythmia detection in response to the detection of oversensing of cardiac events. In some cases, the oversensing cardiac event may be a P wave, which is mistakenly sensed as an R wave from the cardiac electrical signal. Oversensing P waves can be counted for detection of ventricular tachyarrhythmias that result in anti-tachyarrhythmic pacing or CV / DV shock. Medical devices such as pacemakers or ICDs operating according to the techniques disclosed herein can detect P wave oversensing and, based on a detection threshold criterion reached in response to the detection of oversensing P waves, ventricular tachyarrhythmias are not detected. In this way, when oversensing is detected, tachyarrhythmia treatment, such as anti-tachycardia pacing and / or one or more CV / DV shocks, can be blocked.

[0005] In some examples, cardiac electrical signals are sensed via a cardiovascular external lead for sensing cardiac events (e.g., R waves), and cardiac electrical stimulation therapy is delivered via a cardiovascular external electrode based on the sensed cardiac events. A medical device operating according to the techniques disclosed herein can sense cardiac events from a first cardiac electrical signal and detect oversensitization of the cardiac events from the first cardiac electrical signal by determining the characteristics of consecutive time segments of a second cardiac electrical signal. The device can detect oversensitization of cardiac events based on identifying alternating patterns of the characteristics of the second cardiac electrical signal. Detection of oversensitization of cardiac events may include verifying that consecutive segments of the second cardiac electrical signal presenting alternating patterns of signal characteristics do not include tachyarrhythmic morphologies.

[0006] In one example, this disclosure provides a medical device including a cardiac electrical signal sensing circuit and a control circuit. The cardiac electrical signal sensing circuit is configured to sense at least one cardiac electrical signal and detect cardiac events from the at least one cardiac electrical signal. The control circuit is configured to, in response to each of a plurality of cardiac events detected from the at least one cardiac electrical signal, determine signal features from segments of the at least one cardiac electrical signal, detect alternation patterns of the signal features determined from consecutive segments of the at least one cardiac electrical signal, determine an overall morphological measure from each segment of the at least one consecutive segment, and detect cardiac event oversensitization in response to the overall morphological measure not meeting the morphological criteria for tachyarrhythmia and detecting the alternation pattern. The control circuit, in response to detecting cardiac event oversensitization, stops the detection of arrhythmias.

[0007] In another example, this disclosure provides a method comprising sensing at least one cardiac electrical signal and detecting cardiac events from the at least one cardiac electrical signal. The method includes, in response to each of a plurality of cardiac events detected from the at least one cardiac electrical signal, determining signal features from segments of the at least one cardiac electrical signal, detecting an alternation pattern of the signal features determined from consecutive segments of the at least one cardiac electrical signal, and determining a global morphological measure from each segment of the at least one consecutive segment. The method further includes determining that the global morphological measure does not meet a tachyarrhythmia morphological criterion, detecting cardiac event oversensitization and the alternation pattern in response to the global morphological measure not meeting the tachyarrhythmia morphological criterion, and halting the detection of arrhythmia in response to the detection of cardiac event oversensitization.

[0008] In another example, this disclosure provides a non-transitory computer-readable storage medium storing a set of instructions that, when executed by control circuitry of a medical device, cause the medical device to sense at least one cardiac electrical signal, detect cardiac events from the at least one cardiac electrical signal, and, in response to each of a plurality of cardiac events detected from the at least one cardiac electrical signal, determine signal features from segments of the at least one cardiac electrical signal. The medical device further detects alternating patterns of the signal features determined from consecutive segments of the at least one cardiac electrical signal, determines an overall morphological measure from each segment of the at least one consecutive segment, determines that the overall morphological measure does not meet a tachyarrhythmia morphological criterion, and, in response to the overall morphological measure not meeting the tachyarrhythmia morphological criterion and detecting the alternating pattern, detects cardiac event oversensitization. The medical device then stops the detection of arrhythmias in response to the detection of cardiac event oversensitization.

[0009] This overview is intended to provide an overview of the subject matter described in this disclosure. It is not intended to provide an exclusive or exhaustive interpretation of the apparatus and methods described in detail in the following figures and description. Further details of one or more examples are illustrated in the following figures and description. Attached Figure Description

[0010] Figure 1A and Figure 1B This is a conceptual diagram of an extra-cardiac ICD system configured to sense cardiac electrical events and deliver cardiac electrical stimulation therapy, based on an example.

[0011] Figures 2A to 2C Therefore, with Figures 1A to 1B The illustration shows a conceptual diagram of a patient with an extra-cardiac ICD system implanted, with different implantation configurations.

[0012] Figure 3 This is a schematic diagram based on an instance of the ICD.

[0013] Figure 4 Is included Figure 3 A diagram of the circuit system in the sensing circuit of an ICD.

[0014] Figure 5 This is a flowchart of a method for detecting hypersensitivity to cardiac events, based on an example.

[0015] Figure 6A This is a conceptual diagram of a method for detecting alternating patterns of cardiac signal characteristics based on an example.

[0016] Figure 6B This is a diagram of cardiac electrical signal segments stored over a time interval in response to an R-wave sensing event signal.

[0017] Figure 7 This is a flowchart of a method for determining a global morphological metric based on an example, which is used to verify suspected real sensed cardiac events in alternating signal characteristic patterns of cardiac electrical signal segments.

[0018] Figure 8 This is a flowchart of a method for verifying suspected real sensed cardiac events in cardiac electrical signal segments based on a global morphological metric, based on another example.

[0019] Figure 9 This is a flowchart of a method for detecting P-wave oversensing and suppressing ventricular tachyarrhythmia detection in response to the detection of P-wave oversensing, based on an example. Detailed Implementation

[0020] Generally, this disclosure describes techniques for detecting cardiac events oversensing by a medical device or system. In some instances, the medical device may be configured to sense R waves accompanied by ventricular depolarization for use in controlling ventricular pacing and detecting ventricular tachyarrhythmias. Ventricular tachyarrhythmias may be detected in response to a threshold number of R waves being sensed occurring within a time interval smaller than the tachyarrhythmia detection interval. In some cases, atrial P waves accompanied by atrial depolarization may be oversensed as R waves. When P waves are incorrectly sensed as R waves within the tachyarrhythmia interval where R waves are actually sensed, oversensing P waves can cause the medical device to count ventricular tachyarrhythmia intervals, potentially leading to erroneous ventricular tachyarrhythmia detection and inappropriate CV / DF shocks or other treatments delivered by the cardiac medical device, such as anti-tachyarrhythmic pacing (ATP). By identifying P wave oversensing, ventricular tachyarrhythmia detection due to P wave oversensing (PWOS) can be suppressed. Medical devices that implement the techniques disclosed herein can detect excessive sensing of cardiac events for the purpose of controlling treatment of tachyarrhythmias.

[0021] In some instances, the medical device system performing the techniques disclosed herein may be an extracardiac ICD system. As used herein, the term "extracardiac" refers to a location outside the blood vessels surrounding the heart, the heart, and the pericardium. Implantable electrodes carried by extracardiac leads may be positioned outside the thoracic cavity (outside the thoracic cavity and sternum) or inside the thoracic cavity (below the sternum), but are generally not in close contact with myocardial tissue. The techniques disclosed herein for detecting P-wave oversensing can be applied to cardiac electrical signals sensed using extracardiac electrodes.

[0022] This article describes techniques for detecting cardiac event oversensing in conjunction with an ICD 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 techniques for detecting P-wave oversensing, as described in conjunction with the accompanying figures, can be implemented in any implantable or extravascular medical device that enables the sensing of intrinsic cardiac electrical events from cardiac signals received from a patient's heart via sensing electrodes, including implantable pacemakers, ICDs, or cardiac monitors coupled to transvenous, 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.

[0023] Furthermore, while the techniques disclosed herein are described as being used to detect P wave oversensing as R wave, these techniques can be used to detect oversensing of other cardiac events, such as the potential for erroneous atrial tachyarrhythmia detection due to R wave oversensing as P wave. Atrial P waves can be sensed from cardiac electrical signals received, for example, by leaded electrodes or leadless pacemakers in the atrium, and R wave oversensing as P wave can be detected.

[0024] Figure 1A and Figure 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, based on an example. 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 Figure 1B This is described in the context of an ICD system 10, which is capable of delivering a high-voltage CV / DF shock in response to the detection of a tachyarrhythmia and, in some instances, a cardiac pacing pulse. However, the techniques disclosed herein for detecting hypersensitivity to cardiac events can be implemented in other cardiac devices configured to sense cardiac events and, for example, determine the interval of cardiac events or heart rate, for determining heart rate or rhythm and controlling cardiac electrical stimulation therapy.

[0025] 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 instances, 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 leads 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.

[0026] 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 further 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.

[0027] The elongated lead body 18 has a proximal end 27 and a distal end 25, the proximal end including a lead connector (not shown) configured to connect to an ICD connector assembly 17, and the distal end including one or more electrodes. Figure 1A and Figure 1B In the example shown, 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 a separate defibrillation electrode, in which case each of electrodes 24 and 26 can be activated independently.

[0028] Electrodes 24 and 26 (and in some instances, housing 15) are referred to herein as defibrillation electrodes because they are used alone or together 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 in lieu 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 functionality 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 applications of high-voltage cardioversion / defibrillation shock therapy 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.

[0029] 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 electrodes / sensing electrodes because they are typically configured for use in low-voltage applications, for example, 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.

[0030] 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 instances, the housing 15 of the ICD 14 is used in combination with one or more electrodes from the sensing electrode vectors 24, 26, 28, and / or 30. Various sensing electrode vectors utilizing combinations of electrodes 24, 26, 28, and 30 and the housing 15 are described below for acquiring a first cardiac electrical signal and a second cardiac electrical signal using corresponding first and second sensing electrode vectors selectable by a sensing circuitry system included in the ICD 14.

[0031] exist Figure 1A and Figure 1BIn the example shown, electrode 28 is located proximally 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 examples, a third pacing / sensing electrode may be located distally to defibrillator electrode 26. Electrodes 28 and 30 are shown 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 examples, lead 16 may include fewer or more pacing / sensing electrodes and / or defibrillator electrodes than in the example shown here.

[0032] In the example shown, lead 16 extends centrally subcutaneously or submuscularly on 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 lead 16 is shown as extending 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 angled 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.

[0033] Electrical conductors (not shown) extend from a lead connector at the proximal lead end 27 through one or more cavities of the elongated lead body 18 of lead 16 to electrodes 24, 26, 28, and 30 positioned along the distal portion 25 of lead body 18. The elongated electrical conductors included within lead body 18 (which may be separate, corresponding insulated conductors within 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 the circuitry of ICD 14 (such as treatment delivery circuitry and / or sensing circuitry) via connectors in connector assembly 17 (including associated electrical feedthroughs through 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 sensing 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.

[0034] 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 examples, 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.

[0035] In the example shown, the lead body 18 includes a curved distal portion 25 with two "C"-shaped curves that together resemble the Greek letter ε (epsilon). Defibrillation electrodes 24 and 26 are each carried by 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 the pacing / sensing electrodes 28 and 30 are positioned. In some cases, the 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 the defibrillation electrodes 24 and 26 are laterally offset from the pacing / sensing electrodes 28 and 30.

[0036] Other examples of cardiovascular external leads, including one or more defibrillation electrodes and one or more pacing and sensing electrodes carried by a curved, serpentine, wavy, or zigzag distal portion of a lead body 18, which can be implemented using the techniques described herein, are generally disclosed in pending U.S. Patent Publication No. 2016 / 0158567 (Marshall et al.). However, the techniques disclosed herein are not limited to any particular lead body design. In other examples, the lead body 18 is a flexible, elongated lead body without any pre-formed shape, bend, or curvature.

[0037] The ICD 14 analyzes cardiac electrical signals received from one or more sensing electrode vectors to monitor abnormal rhythms such as bradycardia, ventricular tachycardia (VT), or ventricular fibrillation (VF). The ICD 14 can analyze the heart rate and morphology of cardiac electrical signals to monitor tachyarrhythmias using any of a variety of tachyarrhythmia detection techniques.

[0038] 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 pacing electrode vectors, including one or more of electrodes 24, 26, 28 and 30 and the housing 15 of the ICD 14, to generate and deliver other types of electrical stimulation pulses, such as post-shock pacing pulses or bradycardia pacing pulses.

[0039] ICD 14 is shown subcutaneously implanted along the left side of patient 12 along thoracic 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 in patient 12. For example, ICD 14 may be implanted in a subcutaneous pouch in the pectoral muscle region. In this case, lead 16 may extend subcutaneously or submuscularly from ICD 14 toward the manubrium of sternum 22, and bend or turn downward from the manubrium and extend to the desired subcutaneous or submuscular location. In yet another example, ICD 14 may be placed in the abdomen. Lead 16 may also be implanted in other 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 below the sternum / thoracic cavity in the substernal space. Figure 1A and Figure 1B This is illustrative in nature and should not be considered as limiting the practice of the techniques disclosed herein.

[0040] 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 ICD operation and programmed parameters, as well as cardiac electrical signals retrieved from ICD 14.

[0041] 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 included in ICD 14 and configured to operate in conjunction with processor 52 for transmitting and receiving ICD-related data via communication link 42.

[0042] Can be used such as 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 radio frequency (RF) links such as RF or communication frequency bandwidth or communication protocols. Data stored or acquired by the ICD 14, including physiological signals or associated data derived therefrom, device diagnostic results, and the history of detected rhythmic episodes and delivered treatments, can be retrieved by the external device 40 from the ICD 14 upon request.

[0043] 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 rate detection parameters, and treatment control parameters used by ICD 14. In some examples, external device 40 may be used to program at least some control parameters used in detecting hypersensitivity of cardiac events according to the techniques disclosed herein into ICD 14.

[0044] Figures 2A to 2C Therefore, with Figures 1A to 1B The diagram shows a concept of a patient 12 with an extra-cardiovascular ICD system 10 implanted, arranged in different implantation configurations. Figure 2A This is a front view of a patient 12 with an implanted ICD system 10. Figure 2B This is a side view of patient 12 who has an ICD system 10 implanted. Figure 2C This is a transverse view of a patient 12 with an ICD system 10 implanted. In this arrangement, the cardiovascular external lead 16 of the system 10 is at least partially implanted below the sternum 22 of the patient 12. The lead 16 extends subcutaneously or submuscularly from the ICD 14 toward the xiphoid process 20, and bends or turns within the anterior mediastinum 36 in a substernal position near the xiphoid process 20 and extends upward.

[0045] 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”.

[0046] exist Figures 2A to 2C In the example shown, 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 examples, the distal portion 25 of the lead 16 may be implanted in other intrathoracic locations outside the cardiovascular system, including the pleural cavity or the pericardium 38 surrounding and adjacent to the pericardium of the heart 8.

[0047] Figure 3 This is a schematic diagram based on an example ICD 14. The electronic circuitry system is enclosed within the housing 15 (in... 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 cardiovascular leads, 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.

[0048] The ICD 14 includes control circuitry 80, memory 82, treatment delivery circuitry 84, cardiac electrical signal sensing circuitry 86, and telemetry circuitry 88. A power supply 98 powers the circuitry of the ICD 14, including each of the required components 80, 82, 84, 86, and 88. 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 general block diagram is understood but is not shown for clarity. For example, power supply 98 may be coupled to one or more charging circuits included in treatment delivery circuitry 84 for charging 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 coupled as needed to components of cardiac electrical signal sensing circuitry 86, such as sensing amplifiers, analog-to-digital converters, switching circuit systems, etc.

[0049] Figure 3The circuitry shown represents the functionality included in ICD 14 and may include any discrete and / or integrated electronic circuitry components that implement analog and / or digital circuitry capable of producing the functionality attributed herein to ICD 14. The functionality associated with one or more circuits may be implemented by separate hardware components, firmware components, or software components, or integrated within common hardware components, firmware components, or software components. For example, cardiac event sensing and detection of hypersensitive cardiac events may be performed cooperatively by sensing circuitry 86 and control circuitry 80, and may include operations implemented in a processor or other signal processing circuitry system included in control circuitry 80, which executes instructions and control signals stored in memory 82, such as blanking intervals and timing intervals, and sensing threshold amplitude signals sent from control circuitry 80 to sensing circuitry 86.

[0050] The various circuitry of the ICD 14 may include application-specific integrated circuits (ASICs), electronic circuitry, a processor (shared, dedicated, or grouped) and memory executing one or more software or firmware programs, combinational logic circuitry, state machines, or other suitable components or combinations thereof that provide the described functionality. 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. Given the disclosure herein, providing software, hardware, and / or firmware to implement the described functionality within the context of any modern implantable cardiac device system is within the capabilities of those skilled in the art.

[0051] Memory 82 may include 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 include 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 include any of the media listed above.

[0052] 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, and 30 carried by leads 16 and a housing 15, which may serve as common or ground electrodes or as active canned electrodes for delivering CV / DF shock pulses or cardiac pacing pulses.

[0053] Sensing circuitry 86 may be selectively coupled 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 coupled 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 capable of selectively receiving cardiac electrical signals from at least two sensing electrode vectors of available electrodes 24, 26, 28, 30 and housing 15. In some examples, 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 a switching circuitry system for selecting which of electrodes 24, 26, 28, 30 and housing 15 is coupled to a first sensing channel 83 and which electrode is coupled to a second sensing channel 85 of sensing circuitry 86.

[0054] 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 such as R waves or performing other signal analyses. The cardiac event detection circuitry system within sensing circuit 86 may include one or more sensing amplifiers, filters, rectifiers, threshold detectors, comparators, analog-to-digital converters (ADCs), timers, or other analog or digital components, such as in combination. Figure 4 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 timing interval and 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.

[0055] When a cardiac event is detected based on a sensing threshold, the first sensing channel 83 can generate a sensing event signal, such as an R-wave sensing event signal, which is transmitted to the control circuit 80. The control circuit 80 uses the sensing event signal to trigger the storage of time-segmented segments of the cardiac electrical signal for post-processing and analysis to detect excessive sensing of cardiac events, as combined below. Figures 5 to 9As described. In some examples, sensing circuit 86 senses at least one cardiac electrical signal received from a sensing electrode vector selected from available electrodes (e.g., electrodes 24, 26, 28, 30) and housing 15, for detecting R waves and buffering multiple cardiac electrical signal segments, each corresponding to a detected R wave, for processing and analysis to detect P wave oversensitization. A single cardiac electrical signal sensed by first sensing channel 83 can be used for R wave detection and analysis of cardiac electrical signal segments for PWOS detection. In other examples, an R wave is detected from a first cardiac electrical signal sensed by first sensing channel 83, and segments of a second cardiac electrical signal sensed by second sensing channel 85 can be buffered, each segment corresponding to an R wave sensed from the first cardiac electrical signal. PWOS detection can be based on analysis of the second cardiac electrical signal segments. The second cardiac electrical signal can be received via a different sensing electrode pair coupled to the second sensing channel 85 than the sensing electrode pair coupled to the first sensing channel 83, for sensing the first cardiac electrical signal, and / or the second cardiac electrical signal can be received by the same sensing electrode pair, but processed differently by the second sensing channel 85, for example, filtered differently, to produce a second cardiac electrical signal that is different from the first cardiac electrical signal sensed by the sensing circuit 86.

[0056] The memory 82 can be configured to store a predetermined number of cardiac electrical signal segments in a circulating buffer under the control of the control circuit 80, such as at least one cardiac electrical signal segment, two cardiac electrical signal segments, three cardiac electrical signal segments, or other numbers of cardiac electrical signal segments. Each segment can be written into the memory 82 over a time interval extending before and after the R-wave sensing event signal generated by the first sensing channel 83. When the detection based on a predetermined number of rapid arrhythmia intervals requires confirmation of the R-wave sensed by the first sensing channel 83, the control circuit 80 can access the stored cardiac electrical signal segments, which can precede the rapid arrhythmia detection.

[0057] Control circuit 80 also uses R-wave sensing event signals to determine the RR interval (RRI) to detect tachyarrhythmias and determine the need for treatment. RRI is the time interval between consecutive sensed R waves and can be determined between consecutive R-wave sensing event signals received from sensing circuit 86. For example, control circuit 80 may include timing circuitry 90 for determining the RRI between consecutive R-wave sensing event signals received from sensing circuit 86 and for controlling various timers and / or counters for controlling the timing of treatment delivery by treatment delivery circuitry 84. Timing circuitry 90 may additionally set time windows (such as morphological template windows, morphological analysis windows) or perform other timing-related functions of ICD 14, including synchronizing cardioversion shocks or other treatments delivered by treatment delivery circuitry 84 with sensed cardiac events.

[0058] Control circuitry 80 is also shown to include a tachyarrhythmia detector 92 configured to analyze signals received from sensing circuitry 86 to detect tachyarrhythmias. Tachyarrhythmia detector 92 may detect tachyarrhythmias based on cardiac events detected from sensed cardiac electrical signals that meet tachyarrhythmia criteria, such as the threshold number of detected cardiac events occurring at tachyarrhythmia intervals. Tachyarrhythmia detector 92 may be implemented in control circuitry 80 as hardware, software, and / or firmware for processing and analyzing signals received from sensing circuitry 86 for detecting VT and / or VF. In some examples, timing circuitry 90 uses the timing of R-wave sensed event signals received from sensing circuitry 86 to determine the RRI between sensed event signals. Tachyarrhythmia detector 92 may include comparators and counters for counting RRIs determined by timing circuitry 90 that fall within various rate detection zones to determine ventricular rate or perform other rate-based or interval-based evaluations of the R-wave sensed event signals, thereby detecting and distinguishing VT and VF.

[0059] 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. For example, the VF detection interval threshold can be set from 300 milliseconds (ms) to 350 milliseconds (ms). For example, if the VF detection interval is set to 320 ms, the VF interval counter will count RRIs less than 320 ms. When VT detection is enabled, the VT detection interval can be programmed to be in the range of 350 ms to 420 ms, or 400 ms as an example. To detect VT or VF, the corresponding VT or VF interval counter needs to reach a threshold number of intervals to detect (NID) tachyarrhythmias.

[0060] For example, the NID for detecting VT may require a VT interval counter to reach 32 VT intervals counted from the most recent 32 consecutive RRIs. Similarly, the NID for detecting VF may be programmed to be 18 VF intervals from the most recent 24 consecutive RRIs or 30 VF intervals from 40 consecutive RRIs. When the VT or VF interval counter reaches the detection threshold, the tachyarrhythmia detector 92 can detect ventricular tachyarrhythmias. The NID is programmable and ranges from as low as 12 to as high as 40 without any intentional limitation. VT or VF intervals can be detected continuously or discontinuously from a specified 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.

[0061] The tachyarrhythmia detector 92 can be configured to perform additional signal analysis to determine whether other detection criteria, such as R-wave morphology criteria, episodic criteria, and noise and hypersensitivity suppression criteria, are met before detecting VT or VF. Figures 5 to 9 Examples of parameters that can be determined from cardiac electrical signals received from sensing circuit 86 are described for detecting oversensing of cardiac events that could lead to the prevention of VT or VF detection.

[0062] To support these additional analyses, sensing circuitry 86 can transmit digitized electrocardiogram (ECG) signals to control circuitry 80 for morphological analysis performed by tachyarrhythmia detector 92 to detect and differentiate heart rhythms. Cardiac electrical signals from selected sensing vectors (e.g., from first sensing channel 83 and / or second sensing channel 85) can be passed through filters and amplifiers, 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 digital cardiac electrical signal segments for analysis by control circuitry 80. Control circuitry 80 may be a microprocessor-based controller that employs digital signal analysis techniques to characterize the digitized signals stored in memory 82 to identify and classify patient heart rhythms using any of a variety of signal processing methods for analyzing cardiac signals and cardiac event waveforms (e.g., R waves). As described below, the processing and analysis of digital signals may include determining signal characteristics for detecting patterns of oversensitivity, and verifying the absence of tachyarrhythmic morphologies in ECG signal segments presenting the detected oversensitivity patterns. When tachyarrhythmic morphologies are absent and alternating patterns of signal characteristics are detected, RRI-based tachyarrhythmia detection may be blocked to inhibit tachyarrhythmia treatment.

[0063] The therapeutic delivery circuit 84 includes a charging circuit system, one or more charge storage devices, such as one or more high-voltage capacitors and / or low-voltage capacitors, and a switching circuit system 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 therapeutic 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 circuitry 80 can schedule and control treatment delivery circuitry 84 to generate and deliver treatments, such as ATP and / or CV / DF therapy. Treatment can be generated by initiating the charging of a high-voltage capacitor via a charging circuit, both of which are included in treatment delivery circuitry 84. Charging is controlled by control circuitry 80, which monitors the voltage on the high-voltage capacitor, which is transmitted to control circuitry 80 via a charging control line. When the voltage reaches a predetermined value set by control circuitry 80, a logic signal is generated across the entire capacitor line and transmitted to treatment delivery circuitry 84, thereby terminating charging. Under the control of timing circuitry 90, the output circuitry of treatment delivery circuitry 84 delivers CV / DF pulses to the heart via a control bus. The output circuitry may include an output capacitor through which the charged high-voltage capacitor discharges via a switching circuitry system (e.g., an H-bridge) that determines the electrodes for delivering cardiopulmonary bypass or defibrillation pulses and the pulse waveform.

[0065] In some examples, the high-voltage therapeutic 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 examples, therapeutic delivery circuitry 84 may include low-voltage therapeutic circuitry for generating and delivering pacing pulses for various pacing needs.

[0066] It should be recognized that the method for detecting excessive cardiac events disclosed herein 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 pacemaker that monitors cardiac electrical signals and delivers cardiac pacing therapy via therapeutic delivery circuit 84 without high-voltage therapeutic capabilities such as cardioversion / defibrillation shock capability.

[0067] Control parameters used by control circuitry 80 for sensing cardiac events and controlling treatment delivery can be programmed into memory 82 via telemetry circuitry 88. Telemetry circuitry 88 includes a transceiver and an antenna for communicating with external device 40 (in...) using RF communication or other communication protocols as described above. Figure 1A (As shown in the diagram) 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.

[0068] Figure 4 This is a diagram of a circuit system included in a sensing circuit 86 having a first sensing channel 83 and a second sensing channel 85, according to one example. The first sensing channel 83 may be selectively coupled to a first sensing electrode vector via a switching circuit system 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. In some examples, the first sensing channel 83 may be coupled to a sensing electrode vector that is a short bipolar vector 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 approximately vertical (when the patient is in an upright position) or approximately 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 example, the first sensing electrode vector may include pacing / sensing electrodes 28 and 30. In other examples, the first sensing electrode vector coupled to sensing channel 83 may include defibrillator electrodes 24 and / or 26, for example, a sensing electrode vector between pacing / sensing electrode 28 and defibrillator electrode 24 or between pacing / sensing electrode 30 and either defibrillator electrode 24 or 26. In other examples, the first sensing electrode vector may be located between defibrillator electrodes 24 and 26.

[0069] In some examples, sensing circuitry 86 includes a second sensing channel 85 for sensing a second cardiac electrical signal. For example, the second sensing channel 85 may receive a raw cardiac electrical signal from a second sensing electrode vector, such as from a vector comprising an electrode 24, 26, 28, or 30 carried by a lead 16 mating with housing 15. In some examples, the second sensing channel 85 may be selectively coupled to other sensing electrode vectors, which may form a relatively long bipolar structure having an interelectrode distance or spacing greater than that of the sensing electrode vector coupled to the first sensing channel 83. In some cases, the second sensing electrode vector may, but not necessarily, be approximately orthogonal to the first channel sensing electrode vector. For example, defibrillation electrode 26 and housing 15 may be coupled to the second sensing channel 85 to provide a second cardiac electrical signal. As described below, the second cardiac electrical signal received by the second sensing channel 85 via the long bipolar structure can be used by control circuitry 80 for the analysis and detection of P-wave oversensing (when an atrial P wave is incorrectly sensed as an R wave by the first sensing channel 83). Compared to the relatively short bipolar line coupled to the first sensing channel, the long bipolar line coupled to the second sensing channel 85 can provide a relatively far-field or more global cardiac signal. In a relatively global signal, the amplitude of the P wave may be relatively higher or lower than the near-field signal received by the first sensing channel 83 and used to sense the R wave to determine the RRI (depending on the electrode's position relative to the atrium). In other examples, any vector selected from available electrodes (e.g., electrodes 24, 26, 28, 30) and / or housing 15 may be included in the sensing electrode vector coupled to the second sensing channel 85. The sensing electrode vectors coupled to the first sensing channel 83 and the second sensing channel 85 may be different sensing electrode vectors, which may not have a common electrode or may have only one common electrode, but not both.

[0070] However, in other examples, the sensing electrode vectors coupled to the first sensing channel 83 and the second sensing channel 85 may be the same. The two sensing channels 83 and 85 may include different filters or other signal processing circuitry systems, such that two different signals are sensed by the respective sensing channels, and different analyses can be performed on the two signals. For example, the first sensing channel 83 may sense a first cardiac electrical signal by filtering and processing the received cardiac electrical signal used to detect the R-wave in response to an R-wave sensing threshold exceeding the threshold for determining RRI. The second sensing channel 85 may sense a second cardiac electrical signal different from the first cardiac electrical signal by filtering and processing the received cardiac electrical signal, to segment the signal and pass it to the control circuit 80 for determining and analyzing the signal waveform morphology and specific morphological characteristics, for detecting alternating signal characteristics, and for detecting segments with rapid arrhythmia morphology. The first sensing channel 83 may apply a relatively narrow bandpass filter, and the second sensing channel 85 may apply a relatively wide bandpass filter and notch filter to provide two different sensed cardiac electrical signals.

[0071] exist Figure 4 In the illustrative example shown, 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 and second sensing channels 83 and 85, respectively. Non-physiological high-frequency and DC signals may be filtered by low-pass or band-pass filters included in each pre-filter and preamplifier 72, and high-voltage signals may be removed by protection diodes included in the pre-filters and preamplifiers 62 and 72. The pre-filters 62 and 72 can amplify the pre-filtered signal with a gain between 10 and 100, and in one example, a gain of 17.5, and can convert the differential signal into a single-ended output signal 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. The pre-filter 62 and amplifier 72 provide anti-aliasing filtering and noise reduction before digitization.

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

[0073] The digital outputs of ADCs 63 and 73 are respectively fed to corresponding 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 for passing 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 Hz to 100 Hz. In some examples, the second sensing channel 85 may further 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 system 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 crosses the R-wave sensing threshold outside 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 an initial sensing threshold held for a time interval, which may be equal to the tachycardia detection interval or the expected R-wave to T-wave interval, and then descends to a second sensing threshold held until the end of a descending time interval, which may be 1 second to 2 seconds long. After a falling time interval, the sensing threshold decreases to a minimum sensing threshold, which may correspond to a programmable sensitivity sometimes referred to as the "sensing lower limit." In other examples, the R-wave sensing threshold used by the R-wave detector 66 may be set to an initial value based on a peak amplitude determined during the most recent 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 specific behavior of the sensing threshold or specific R-wave sensing techniques. Instead, other decaying, gradually adjusted, or otherwise automatically adjusted sensing thresholds may be utilized.

[0075] In response to the R-wave sensing event signal 68 generated by the first sensing channel 83, 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. In some examples, 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 control circuitry 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 covering a point in time in the R-wave sensing event signal generated by the first sensing channel 83.

[0076] Control circuit 80 is configured to detect tachyarrhythmias based on cardiac events detected from at least one cardiac electrical signal sensed by sensing circuit 86. For example, control circuit 80 may be configured to detect a tachyarrhythmia when each of a threshold number of detected cardiac events occurs at a tachyarrhythmia interval. When a lower threshold number of tachyarrhythmia intervals has been detected before reaching a detection threshold, control circuit 80 may buffer segments of the sensed cardiac electrical signal in memory 82 and retrieve the stored signal segments from memory 82 for analysis. In some examples, the RRI for detecting tachyarrhythmia intervals is determined based on a first cardiac electrical signal sensed by first sensing channel 83, and when a lower threshold number of tachyarrhythmia intervals are detected, cardiac electrical signal segments are buffered from a second cardiac electrical signal received by control circuit 80 from second sensing channel 85 for P-wave oversensing analysis. Analysis of the second cardiac electrical signal segments can be performed for detecting P-wave oversensing, as described below. Figures 5 to 9 As described. In other examples, a single cardiac electrical signal sensed by sensing circuit 86 is used to determine the RRI for detecting tachyarrhythmia intervals and to buffer both cardiac electrical signal segments. The buffered cardiac electrical signal segments are analyzed to detect signs of hypersensitivity to cardiac events.

[0077] For example, control circuit 80 may be configured to determine signal features from each of a plurality of consecutive second cardiac electrical signal segments for detecting alternating patterns of signal features as indications of PWOS. When an indication of PWOS is detected based on the determined alternating patterns of signal features, further analysis may be performed on at least one of the alternating patterns of second cardiac electrical signal segments to detect a rapid arrhythmia morphology present in that segment. Time segments of the notch-filtered rectified signal 79 received from the second sensing channel 85 may be used to detect rapid arrhythmia morphologies. In some examples, as described below, at least one segment of the second cardiac electrical signal corresponding to a suspected true R wave is identified based on the detected alternating patterns of signal features. An indication of PWOS is detected when no rapid arrhythmia morphology is detected in any of the plurality of second cardiac electrical signal segments identified as suspected true R waves in the alternating patterns. Detection of a threshold number of PWOS indications may cause control circuit 80 to halt rapid arrhythmia detection and treatment delivery circuit 84 to halt rapid arrhythmia treatment.

[0078] 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... Figure 4The document shows and describes more or fewer components, and some components may be shared between sensing channels 83 and 85. For example, one or more of the pre-filter 62 and pre-amplifier 72, ADC 63 / 73 and / or filter 64 / 74 may be shared components between sensing channels 83 and 85, wherein a single sensing signal output is split into two sensing channels for subsequent processing and analysis. Sensing circuitry 86 and control circuitry 80 include circuitry configured to perform functionality attributable to ICD 14, as disclosed herein, in detecting excessive sensing of cardiac events and in suppressing or preventing the detection of tachyarrhythmias.

[0079] Figure 5 This is a flowchart 100 of a method for detecting cardiac event oversensing, based on one example. In the various examples presented herein, the detected cardiac event oversensing is PWOS when the first sensing channel 83 exceeds the intentionally sensed R-wave based on an R-wave sensing threshold. PWOS occurs when the P-wave of the cardiac electrical signal exceeds the R-wave sensing threshold, causing the first sensing channel 83 to generate an erroneous R-wave sensing event signal that is transmitted to the control circuitry 80. However, it should be understood that the techniques for detecting cardiac event oversensing can be applied to detect R-wave oversensing when the P-wave is intentionally sensed by the sensing circuitry of a medical device. In this case, R-wave oversensing occurs when the R-wave of the cardiac electrical signal crosses the P-wave sensing threshold, causing the sensing circuitry to generate an erroneous P-wave sensing event signal.

[0080] At block 102, sensing circuit 86 senses a cardiac event based on a cardiac event sensing threshold exceeding the threshold of a first cardiac electrical signal. The cardiac electrical signal may be a near-field signal used to increase the likelihood of sensing a cardiac event in the desired cardiac chamber (e.g., a ventricle or atrium) without oversensing cardiac events in adjacent cardiac chambers (e.g., atria or ventricles). In one example, the cardiac event sensed at block 102 is intended to be based on an R-wave exceeding the sensed R-wave threshold detected by the first sensing channel 83 of sensing circuit 86 as described above.

[0081] At block 104, control circuitry 80 can determine one or more signal features from cardiac electrical signal segments that temporally correspond to the sensing event signal generated by first sensing channel 83. The signal features can be determined based on a second cardiac electrical signal sensed via a sensing electrode vector, which is different from the sensing electrode vector used to sense the first cardiac electrical signal from which the cardiac event is sensed. Compared to the first cardiac electrical signal, the second cardiac electrical signal may be a relatively far-field or more global cardiac signal, and / or may be filtered or processed differently to enhance the specificity and sensitivity of the morphological analysis for detecting alternating signal features and morphological signal segments of rapid arrhythmias. For example, a sensing electrode vector with an inter-electrode distance greater than that of the first sensing electrode vector can be used to sense the second cardiac electrical signal. Alternatively, the second cardiac electrical signal segment may be filtered with a relatively wide-pass filter to preserve the characteristics of the cardiac electrical signal waveform, and in some examples, filtered with a notch filter to attenuate 50Hz to 60Hz noise. In other examples, the first and second cardiac electrical signals are received by the same sensing electrode vector, but are processed differently, such as being filtered differently, to produce a first cardiac electrical signal that is different from the second cardiac electrical signal.

[0082] At box 104, segments of the second cardiac electrical signal within a predetermined time interval can be buffered in memory 82. The predetermined time interval covers the point in time from which a cardiac event is sensed from the first cardiac electrical signal. For example, in response to a signal from the first sensing channel 83 (see...) Figure 4 For each R-wave sensing event signal 68 received, the control circuit 80 may buffer time segments of the second cardiac electrical signal 78 (and, in some examples, the rectified signal 79) from the second sensing channel 85 in the memory 82. These time segments may extend from a time point earlier than the time when the R-wave sensing threshold is exceeded to a time point later than the time point when the R-wave sensing threshold exceeds the threshold that caused the first sensing channel 83 to generate the R-wave sensing event signal 68. The duration of these time segments may be from 300 ms to 500 ms, for example, a duration of 360 ms, including sampling points before and after the R-wave sensing event signal. For example, as combined with... Figure 6B As described, when the sampling rate is 256Hz, the 360ms segment may include 92 sampling points, of which 24 sampling points appear 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 that is earlier in time than the R-wave sensing event signal.

[0083] Control circuit 80 can determine one or more signal features from each segment of the second cardiac electrical signal. In one example, at least the maximum peak-to-peak amplitude occurring during a time segment of the second cardiac electrical signal is determined. The maximum peak-to-peak amplitude on the time segment of the second cardiac electrical signal can be determined as the absolute difference between the minimum sample point amplitude and the maximum sample point amplitude. Therefore, control circuit 80 may include a peak detector that stores the values ​​of the minimum and maximum peak values ​​detected in a comparative analysis of the sample point amplitudes of the digitized, notch-filtered cardiac signal. In this example of determining the maximum peak-to-peak amplitude, the cardiac electrical signal segment is an unrectified signal. In other examples, a rectified signal may be used, and the maximum peak amplitude may be determined. A series of maximum peak-to-peak amplitudes, such as at least three to twelve maximum peak-to-peak amplitudes determined from a corresponding number of buffered second cardiac electrical signal segments, can be stored in memory 82 so that it can be used for analysis of cardiac event oversensitivity detection.

[0084] In other examples, the polarity (positive or negative) of the maximum absolute peak amplitude can be determined at box 104 from one or more signal features identified in each second cardiac electrical signal segment. In still other examples, the signal features determined at box 104 may be the maximum slope of the second cardiac electrical signal, the total area (e.g., the integral or sum of the amplitudes at the sampling points), or other features expected to alternate when the sensing event signal generated by the first sensing channel corresponds to an alternating pattern of R and P waves (e.g., PRP or RPR). In some examples, two or more signal features may be identified from each segment to detect an alternating pattern of combinations of two or more signal features.

[0085] At block 106, control circuitry 80 compares continuously defined signal characteristics and / or event intervals with criteria for detecting alternating patterns of signal characteristics. For example, alternating patterns of relatively high and relatively low maximum peak-to-peak amplitudes of a second cardiac electrical signal segment can be detected at block 106. In other examples, alternating patterns of event signal polarity can be detected at block 106. In yet another example, event time intervals can be determined between continuously sensed event signals generated by a first sensing channel to detect alternating patterns of long and short event intervals. The alternating patterns detected at block 106 may be a pair of high and low maximum peak-to-peak amplitudes (e.g., high-low or low-high), a pair of positive and negative event polarities (e.g., positive-negative or negative-positive), and / or a pair of long and short event intervals (e.g., long-short or short-long). In other examples, at block 106, at least three alternating patterns of consecutive event signal characteristics are required to detect the alternating pattern. Using the example of maximum peak-to-peak amplitude, at box 106, a relative peak-to-peak amplitude pattern of high-low-high or low-high-low can be detected as an alternating pattern. The following is combined with... Figure 6AMethods and standards are described for detecting alternating patterns of relatively high and low maximum peak-to-peak amplitude differences and relatively long and short intervals.

[0086] When no alternating pattern is detected (No branch of block 106), control circuit 80 may not perform further signal analysis to detect cardiac event oversensing. The process may return to block 102 to continue sensing cardiac events. In response to the detection of an alternating pattern of at least one signal feature from consecutive second cardiac electrical signal segments (Yes branch of block 106), such as alternating peak-to-peak amplitude, control circuit 80 may determine an overall morphological feature from one or more second cardiac electrical signal segments corresponding to the alternating signal feature pattern at block 108.

[0087] In some examples, when the alternating signal characteristic pattern indicates that the middle segment of the cardiac electrical signal among three consecutive segments is an oversensing event, for example, based on the high-low-high peak-to-peak amplitude, control circuit 80 can identify the first and third segments of the cardiac electrical signal as corresponding to the suspected real-sensing cardiac event. The overall morphological characteristics can be determined from the first and third segments identified as the suspected real-sensing cardiac event (e.g., a real-sensing R wave). When the alternating pattern indicates that the first and third segments of the second cardiac electrical signal are oversensing events, for example, based on the low-high-low peak-to-peak amplitude, the overall morphological characteristics can be determined from the middle (second) segment of the three consecutive segments. In this case, the middle segment is identified as the second cardiac electrical signal segment corresponding to the suspected real-sensing event. In some examples, at block 110, one or more overall morphological characteristics of the signal segment suspected only of being a real-sensing R wave can be compared with tachyarrhythmia morphological criteria. In other examples, one or more overall morphological features may be identified from all segments that are determined to present alternating feature patterns in the analysis at box 106, and compared with morphological criteria for tachyarrhythmias at box 110.

[0088] Each overall morphological feature is determined from the analysis of sample points spanning the second cardiac electrical signal segment. As an example, the overall morphological features determined at box 108 may include amplitude morphology measures and / or signal width morphology measures. Overall morphological features that can be used to detect the morphology of tachyarrhythmias may include maximum slope, number of peaks, total signal area, pulse count, low slope content, normalized average rectified amplitude, or other morphological features. Examples of overall morphological features may include any signal feature or measure associated with the tachyarrhythmia waveform. The following is combined with... Figures 7 to 8 The description is used to determine the overall morphological features at box 108.

[0089] At box 110, one or more general morphological features may be compared with tachyarrhythmia morphological criteria. When the general morphological features meet the tachyarrhythmia morphological criteria, no cardiac event oversensing is detected. As further described below, the tachyarrhythmia morphological criteria may require at least one of an amplitude morphology measure or a signal width morphology measure to be greater than a corresponding threshold as an indication of tachyarrhythmia waveform morphology. When the general morphological features at box 110 do not meet the tachyarrhythmia morphological criteria (“No” branch), an indication of cardiac event oversensing is detected at box 112. This detection at box 112 indicates that at least one of the second cardiac electrical signal segments corresponds to the oversensing cardiac event. When the general morphological features do not meet the criteria used to detect tachyarrhythmia morphology at box 110, for example, for at least one cardiac electrical signal segment identified as a suspected real sensed cardiac event, the suspected real sensed cardiac event is verified. In the absence of signs of tachyarrhythmic patterns, this verification of real sensed cardiac events (the "No" branch of box 110), and the detection of alternating signal characteristic patterns, leads to the detection of signs of oversensing at box 112.

[0090] Conversely, when the overall morphological characteristics of at least one second cardiac electrical signal segment are determined to meet the morphological criteria for tachyarrhythmias, that at least one second cardiac electrical signal segment can be identified as a suspected real-sensing cardiac event in an alternating signal characteristic pattern, which has not been verified and no signs of hypersensing have been detected (the "Yes" branch of box 110). (See below for further details.) Figure 7 and Figure 8 The general morphological features described, identified at box 108, can be compared with the criteria at box 110, which distinguishes between possible tachyarrhythmia morphologies and possible true cardiac event signal morphologies, such as true R waves. The process returns to box 102 to continue sensing cardiac events based on the first cardiac electrical signal and to monitor for cardiac event oversensing as needed.

[0091] Control circuitry 80 may include a counter or buffer that tracks the number of times oversensing signs are detected at block 112 from a specified number of recently sensed cardiac events. At block 114, the counter may be incremented or a flag may be set to indicate oversensing sign detection performed at block 112. For example, a first-in-first-out (FIFO) buffer may store a specified number of flags. When an alternating pattern is detected and the morphological criteria for tachyarrhythmia are not met, the flag may be set high (e.g., set to 1) to indicate that an oversensing sign has been detected. When no alternating pattern is detected, or the morphological criteria for tachyarrhythmia are met, the flag may be set low (e.g., set to 0) to indicate that no oversensing sign has been detected. In some examples, the FIFO buffer may be updated on a beat-by-beat basis as an oversensing sign is detected (or not detected), with the oldest flag value being discarded. The buffer may store a predetermined number of flags, for example, up to 32 (or more) corresponding to up to 32 (or more) consecutively sensed cardiac events. The detection of signs of oversensing performed at box 112 indicates that at least one of the second cardiac electrical signal segments in the alternating characteristic pattern corresponds to the suspected real oversensing event, such as a P wave that is mistakenly sensed as an R wave.

[0092] At box 116, the number of oversensing sign detections (or the number of oversensing sign flags set in a buffer storing a specified number of flags in a first-in-first-out manner) can be compared to an oversensing detection threshold. For example, if X oversensing signs are detected during a series of Y sensed cardiac event signals sensed from a first cardiac electrical signal, cardiac event oversensing is detected at box 120. In one example, if a percentage of sensed event signals received from the first sensing channel 83 exceeds a threshold (e.g., 20%, 25%, 30%, 35%, 40%, or other percentage) resulting in oversensing sign detection based on analysis of multiple consecutive second cardiac electrical signal segments, oversensing is detected at box 120. For example, cardiac event oversensing is detected if 3 oversensing sign detections occur on 12 consecutive R-wave sensed event signals, or if 4 oversensing sign detections occur on 16 consecutive R-wave sensed event signals, or if 8 oversensing sign detections occur on 32 R-wave sensed event signals. In these examples, each sign of hypersensitivity can be detected based on the analysis of three consecutive segments of the second cardiac electrical signal.

[0093] If the threshold for detecting excessive cardiac event sensing is not reached at box 116, the process can return to box 102 without any treatment delivery adjustment by the treatment delivery circuitry at box 118. When excessive cardiac event sensing is detected at box 120, control circuitry 80 can halt arrhythmia detection at box 122. In some cases, control circuitry 80 can, in response to excessive cardiac event sensing detection, cause treatment delivery circuitry 80 to halt arrhythmia treatment at box 122. For example, scheduling of cardiac electrical stimulation treatment can be prevented in response to the detection of excessive cardiac event sensing. As combined below... Figure 9 As described, when other tachyarrhythmia detection criteria are met at box 121, such as the number of thresholds for the sensed cardiac event rate or RRI at box 121 being less than the tachyarrhythmia detection interval, tachyarrhythmia detection can be blocked at box 122 in response to the detection of cardiac event oversensing.

[0094] In other examples, consecutively determined RRIs can be buffered in memory 82 in a first-in-first-out manner to store a specified number of RRIs. When all slots of the buffer are filled with RRI values, each RRI smaller than the tachyarrhythmia detection interval can be counted as a tachyarrhythmia interval. When a threshold number of tachyarrhythmia intervals is counted in the buffer, control circuitry 80 can determine at block 121 that a tachyarrhythmia rate criterion is met. However, RRIs smaller than the tachyarrhythmia detection interval, which temporally correspond to a flag set in response to the detection of cardiac oversensitivity, can be ignored and are not counted for the threshold number of tachyarrhythmia detection intervals reached. In this way, arrhythmia detection can be prevented by ignoring RRIs consistent with cardiac oversensitivity detection.

[0095] Anti-tachyarrhythmic therapy, such as multiple ATP and / or CV / DF shocks, can be prevented by inhibiting or stopping tachyarrhythmia detection at box 122 to avoid inappropriate treatment delivery due to cardiac event hypersensitivity. In this way, the performance of medical devices for detecting and treating tachyarrhythmias is improved by detecting cardiac event hypersensitivity and avoiding inappropriate or unnecessary treatment responses from the medical device due to cardiac event hypersensitivity.

[0096] Figure 6AThis is a conceptual diagram 150 of a method for detecting alternating patterns of cardiac signal characteristics according to one example. Two examples 151a and 151b are depicted, wherein an alternating high-low-high maximum peak-to-peak amplitude pattern is detected in example 151a, and an alternating low-high-low maximum peak-to-peak amplitude pattern is detected in example 151b. In these examples 151a and 151b, a first sensing channel 83 is configured to sense R-waves based on R-wave sensing threshold exceedances of a first cardiac electrical signal. In response to each R-wave sensing threshold exceedance, R-wave sensing event signals 190, 191, 192, 194, 195, and 196 are generated by sensing circuitry 86. In the individual examples 151a and 151b, R-wave sensing event signals 190, 191, and 192 are three consecutive R-wave sensing event signals, and R-wave sensing event signals 194, 195, and 196 are three consecutive R-wave sensing event signals. Each R-wave sensing event signal 190 to 196 triggers a second cardiac electrical signal 78 generated by the second sensing channel 85 at corresponding time intervals 153, 155, 157, 163, 165, and 167 (see...). Figure 4 The second cardiac electrical signal can be stored in segments, where each individual time interval covers the time point at which the trigger R-wave sensing event signal (190, 191, 192, 194, 195, and 196) occurs. The signal segments can be buffered in memory 82 when sensed, such that the signal segments can be stored at each time interval 153, 155, 157, 163, 165, and 167, which begins before and ends after the corresponding trigger R-wave sensing event signal.

[0097] Figure 6B It is in response to the R-wave sensing event signal 191 (corresponding to Figure 6AIllustration 220 shows a second cardiac electrical signal segment 221 stored over time interval 155 (shown as time interval 155 and R-wave sensing event signal 191, with the same numbering). Time segment 155 begins after the previous R-wave sensing event signal 190 and ends before the next R-wave sensing event signal 192. The expected sampling rate (e.g., 128 Hz or 256 Hz) of the second cardiac electrical signal (from sensing channel 85) is buffered in memory 82 until the R-wave sensing event signal 191 is received, at which point the expected number of sampling points before R-wave sensing event signal 191 (e.g., 68 sampling points when the sampling rate is 256 Hz) and the expected number of sampling points after R-wave sensing event signal 191 (e.g., 24 sampling points appearing after R-wave sensing event signal 191) are stored in a designated buffer (memory 82) as the second cardiac electrical signal segment 221. In other examples, higher or lower sampling rates, such as 512 Hz or 128 Hz, may be used. Higher or lower numbers of sample 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. In various examples, the length of the time interval 155 storing the second cardiac electrical signal segment 221 for analysis can be between 100 ms and 500 ms, and in one example it is 360 ms. Sample points of the second cardiac electrical signal buffered before the start of time segment 155 and after the previous time segment 153 can be discarded.

[0098] In some examples, the second cardiac electrical signal segment 221 is a non-rectified signal, such that the maximum peak-to-peak amplitude 154 can be determined as the absolute difference between the maximum sample point amplitude 222 and the minimum sample point amplitude 224 detected on signal segment 155. In other examples, the maximum peak value, minimum peak value, or maximum peak value of the rectified signal can be determined. In the example shown, control circuitry 80 determines the maximum peak-to-peak amplitude of the second cardiac electrical signal during each time segment of time segments 153, 155, 157, 163, 165, and 167. For example, the maximum peak-to-peak amplitude A2 154 is determined based on the second cardiac electrical signal segment 221 stored on time segment 155 as the absolute difference between the maximum peak sample point amplitude 222 and the minimum peak sample point amplitude 224. (See again...) Figure 6AThe maximum peak amplitude A1 152 is determined from the second cardiac electrical signal segment stored on time segment 153; the maximum peak-to-peak amplitude A3 156, etc., is determined based on the second cardiac electrical signal segment stored on time segment 157. The maximum and minimum sampling point amplitudes used to determine the peak-to-peak amplitudes 152, 154, 156, 162, 164, and 166 can occur at any time during the corresponding time segments 153, 155, 157, 163, 165, and 167, and are not necessarily the amplitudes at R-wave sensing event signals 190, 191, 192, 194, 195, and 196.

[0099] Once three consecutive peak-to-peak amplitudes are determined from three consecutively stored segments of the second cardiac electrical signal, the differences between these consecutive peak-to-peak amplitudes are determined. In Example 151a, a first amplitude difference D1 158 is determined between amplitude A1 152 and amplitude A2 154. A second amplitude difference D2 160 is determined between the second amplitude A2 154 and the third amplitude A3 156. The first amplitude difference D158 and the second amplitude difference D2 160 between the three consecutively determined peak-to-peak amplitudes 152, 154, and 156 can be compared with a difference threshold to detect alternating patterns of peak-to-peak amplitudes in the second cardiac electrical signal segment.

[0100] The difference threshold can be a fixed value or set based on the maximum peak-to-peak amplitude determined by at least one of three consecutively defined peak-to-peak amplitudes 152, 154, and 156. In some examples, the larger of the two amplitudes being compared is identified, and the difference threshold is set as a percentage of the larger amplitude. For example, in first example 151a, the absolute value of the first difference D1 158 is compared as a percentage of the first larger maximum peak-to-peak amplitude A1 152. The second difference D2 160 is compared as a percentage of the third (larger) maximum peak-to-peak amplitude A3 156. As an example, the percentage of the maximum peak-to-peak amplitude used to set the difference threshold can be from 15% to 30%, and in one example it is 22%. When the absolute value of the difference D1 158 is greater than 22% of the peak-to-peak amplitude A1 152 and the difference D2 160 is greater than 22% of the peak-to-peak amplitude A3 156, the control circuit 80 detects a high-low-high alternating pattern. R-wave sensing event signal 191, corresponding to the low peak-to-peak amplitude A2154 in the detected high-low-high pattern, is the suspected oversensitized P wave. R-wave sensing event signals 190 and 192, corresponding to the high peak-to-peak amplitudes 152 and 156 in the second cardiac electrical signal segments stored at time intervals 153 and 157, respectively, can be identified as the suspected true sensed R waves. Control circuit 80 can increment the oversensitized cardiac event sign counter or set an oversensitized cardiac event sign flag to track the number of times an oversensitized cardiac event pattern is identified on three consecutive R-wave sensing event signals.

[0101] In addition to detecting the high-low-peak-peak amplitude pattern, control circuitry 80 can verify the stability of alternating peak-to-peak amplitudes A1 152 and A3 156. These first amplitudes 152 and third amplitudes 156, which correspond to the actual sensed R-wave, may need to be within each other's stability thresholds. In one example, the difference D3 161 between peak-to-peak amplitudes A1 152 and A3 156 may need to be less than a threshold percentage of the highest maximum peak-to-peak amplitude (A1 152 in this example) among the three signal segments, for example, less than 50%. The requirement that D3 be less than the stability threshold requires that the maximum peak-to-peak amplitudes A1 152 and A3 156 of the signal segments corresponding to the two suspected actual R-wave sensing event signals 190 and 192 are stable, and this stability threshold can be set based on the highest maximum peak-to-peak amplitude.

[0102] In some examples, the maximum peak amplitude of the R-wave sensed from the first sensing channel can be used to perform a comparison of signal amplitude differences for detecting high-low-high or low-high-low patterns. A first difference and a second difference between three consecutive sensed R-waves of the first cardiac electrical signal can be compared to corresponding thresholds, which may differ from the threshold applied to the maximum peak-to-peak amplitude difference determined from the segmentation of the second cardiac electrical signal. In one example, the difference between the first and second sensed R-wave amplitudes needs to be greater than 20% (or other percentage) of the largest of the first and second sensed R-wave amplitudes. Alternatively, the difference between the first and second maximum peak amplitudes determined from the second cardiac electrical signal needs to be greater than 20% or a multiple of the highest of the first and second maximum peak amplitudes, for example, 20% of 1.5 times the highest maximum peak amplitude.

[0103] In other examples, additional criteria may be applied as a means of detecting PWOS signs before counting the alternating patterns of the detected signal features. For example, the polarity (positive or negative) of the maximum peak amplitude of the unrectified signal may be determined for each segment of the second cardiac electrical signal or for at least several segments suspected of being oversensitized events. In other examples, in Figure 5 At box 106, the RR intervals 180 and 182 between the continuous R-wave sensing event signals 190 and 191 and the continuous R-wave sensing event signals 191 and 192 can be compared with the alternating mode detection standard.

[0104] For example, the sum of RR intervals 180 and 182 may need to fall within a threshold range, such as greater than 380 ms or other fast interval thresholds and less than 1200 ms or other slow interval thresholds. This threshold range may correspond to the expected range of RR intervals for true non-tachyarrhythmias. When at least one of three consecutive R-wave sensing event signals 190, 191, or 192 is an oversensitized P wave, the sum of the two RR intervals 180 and 182 may represent the true RR interval. Therefore, their sum should fall within the expected RR interval range.

[0105] RR intervals 180 and 182 can be compared to each other, or their difference can be compared to a difference threshold, to verify the presence of possible long-short patterns of RPR patterns corresponding to R-wave sensing event signals 190, 191, and 192. In some examples, a short-long or long-short pattern is detected when one RR interval 180 or 182 is shorter than the other RR interval 182 or 180 by a threshold percentage (e.g., less than 60%, 50%, 40%, or other percentages). Alternatively or additionally, at least one of two consecutive RR intervals may need to be smaller than a threshold interval, e.g., a threshold interval less than 360 ms to 400 ms. In some cases, the threshold interval is set as the tachyarrhythmia detection interval plus an offset, e.g., 40 ms longer than the VT or VF detection interval. This short interval combined with alternating amplitude patterns may be an indication of PWOS.

[0106] These examples of comparative analysis of RR intervals can be performed on RR intervals determined between consecutive R-wave sensing event signals generated by the first sensing channel 83. Alternatively, any or all of these examples of comparative analysis of RR intervals can be performed by determining the RR interval between the maximum peak amplitude or R-wave sensing threshold amplitude exceeding the second cardiac electrical signal. The determination of long and short RR interval patterns in combination with high and low amplitude patterns can lead to the control circuit 80 detecting a PWOS indication. As described below, tachyarrhythmia morphology criteria can be applied to one or more second cardiac electrical signal segments exhibiting alternating signal characteristic patterns before detecting the alternating pattern as an indication of PWOS.

[0107] In the second example 151b, the control circuit 80 is configured to detect low-high-low patterns of the maximum peak-to-peak amplitude of a second cardiac electrical signal buffered on time segments 163, 165, and 167, triggered by corresponding R-wave sensing event signals 194, 195, and 196. In this case, a first amplitude difference D1 168 is determined between the first maximum peak-to-peak amplitude A1 162 and the second maximum peak-to-peak amplitude A2 164 (e.g., A1 minus A2). A second amplitude difference D2 170 is determined between the second maximum peak-to-peak amplitude A2 164 and the third maximum peak-to-peak amplitude A3 166 (e.g., A2 minus A3). The absolute value of D1 168 can be compared with a difference threshold set based on one of the amplitudes A1 162, A2 164, or A3 166, for example, as a percentage of the higher second maximum peak-to-peak amplitude A2 164. In one example, the difference threshold is set to 22% of A2 164 (the larger of A1 and A2). The second amplitude difference D2 170 can also be compared with a difference threshold set as a percentage of the higher second maximum peak-to-peak amplitude A2 164. When both the first amplitude difference D1 168 and the second amplitude difference D2 170 are greater than a percentage of the second maximum peak amplitude A2 164, the control circuit 80 detects a low-high-low maximum peak-to-peak amplitude pattern.

[0108] In addition to detecting low-to-high peak-to-peak amplitude patterns, control circuitry 80 can verify the stability of alternating low-to-peak amplitudes A1 162 and A3 166. These first amplitudes 162 and third amplitudes 166, which may correspond to oversensitized P waves, may need to be within each other's stability thresholds. In one example, the difference D3 171 between A1 162 and A3 166 may need to be less than a threshold percentage of the maximum of these two low-to-peak amplitudes (A1 162 in this example), for example, less than 50%. D3 being less than the stability threshold requirement, for example, a stability threshold set based on the higher peak of the alternating low-to-peak amplitudes A1 162 and A3 166, requires that the peak-to-peak amplitudes of the second cardiac electrical signal segment corresponding to the two suspected oversensitized P waves be stable.

[0109] Therefore, once a low-high-low or high-low peak-to-peak amplitude pattern is detected based on a continuous peak-to-peak amplitude difference greater than a difference threshold, for three consecutive signal segments of an alternating pattern to be detected as a signal feature, it may be necessary that the difference between the first and third peak-to-peak amplitudes be less than a stability threshold. The difference threshold can be set as a percentage of the highest maximum peak-to-peak amplitude among all three consecutive signal segments or the two signal segments being compared. The stability threshold can be set as a percentage of the higher of the first and third peak-to-peak amplitudes. It should be understood that in other examples, the difference threshold and stability threshold may be defined differently from the specific example given here. For example, the difference threshold and stability threshold used to detect alternating signal feature patterns may be based on a percentage of the lower peak-to-peak amplitude among the maximum peak-to-peak amplitudes instead of the highest maximum peak-to-peak amplitude, or based on the average or median peak-to-peak amplitude of all segments or only the segments corresponding to the suspected true R-wave, a predetermined threshold, etc.

[0110] As described above, additional criteria, such as the polarity of multiple maximum peak amplitudes in the first time segment 163 and the third time segment 165 and / or the second time segment 165, can be compared with polarity criteria used to detect signs of PWOS. In other examples, consecutive RR intervals 184 and 186 can be compared with each other, or their difference can be compared with an RR interval difference threshold, to verify the detection of short-long patterns of RRI to support the detection of a low-high-low maximum peak-to-peak amplitude pattern that indicates that the first R-wave sensing event signal 194 and the third R-wave sensing event signal 196 are suspected oversensitized P waves, and the second, intermediate R-wave sensing event signal 195 is the suspected true R wave. In response to the detection of a low-high-low pattern, an oversensitivity sign counter can be incremented, or an oversensitivity sign flag can be set to track the number of alternating patterns of consecutively identified second cardiac electrical signal characteristics detected.

[0111] Even if two possible P waves are oversensitized in a series of three R-wave sensing event signals 194, 195, and 196, the oversensitivity sign counter can be incremented by 1 or a single flag can be set. In some examples, a set of three overlapping, moving segments of the second cardiac electrical signal can be evaluated to detect alternating signal characteristic patterns. For example, the third R-wave sensing event signal 196 can be the second R-wave sensing event signal in the set of the next three consecutive R-wave sensing event signals, which can also meet the oversensitivity sign criteria (in a high-low-high pattern). When using three (or other selected number) moving sets of consecutively determined maximum peak-to-peak amplitudes (or other signal characteristics) to detect alternating signal characteristic patterns, the oversensitivity sign counter can be incremented by one (or a single set of oversensitivity sign flags) in response to each detection of the alternating signal characteristic pattern. An oversensitivity detection threshold set to detect X oversensitivity signs out of Y consecutive sensing events can take into account the possible double count of some suspected oversensitivity events in the detected alternating patterns.

[0112] In other examples, the consecutive sets of the second cardiac electrical signal segments may not overlap. For example, three signal segments corresponding to three consecutive R-wave sensing event signals may be analyzed, and then the control circuit 80 may wait for the next three R-wave sensing event signals to analyze the next three non-overlapping segments of the second cardiac electrical signal. For each set of signal segments detected as an alternating signal characteristic pattern, the oversensitivity sign counter may be incremented by 1. In other examples, the oversensitivity sign counter (or the number of sign sets) may be incremented by the number of suspected oversensitivity cardiac events in each detected alternating signal characteristic pattern, for example, by 1 in example 151a and by 2 in example 151b.

[0113] Figure 7 This is a flowchart 200 based on an example of a method for determining a global morphological metric used to verify suspected real sensed cardiac events in alternating signal characteristic patterns of cardiac electrical signal segments. (See attached...) Figure 6B The overall description allows for buffering analysis of each cardiac electrical signal segment to determine overall morphological measures. The method described in flowchart 200 is typically available in... Figure 5Execution is performed at frames 108 and 110 to analyze at least one second cardiac electrical signal segment from a continuous series of segments exhibiting alternating signal characteristic patterns for detecting tachyarrhythmia morphology. For example, when three segments of the second cardiac electrical signal exhibit alternating patterns, the first and third segments can be analyzed to determine an overall morphological measure when the alternating patterns indicate that the second and middle segments correspond to an oversensitized P wave and the first and third segments correspond to a suspected true R wave. The second middle segment can be analyzed to determine an overall morphological measure when the alternating patterns indicate that the second middle segment corresponds to a suspected true sensed cardiac event and the first and third segments correspond to a suspected oversensitized event. In other examples, all segments included in the detected alternating pattern sequence can be analyzed to determine an overall morphological measure.

[0114] Figure 7 The method corresponds to the analysis of one-second cardiac electrical signal segments, used to verify suspected real cardiac events in alternating signal characteristic patterns based on the absence of morphological signs of rapid arrhythmias. At block 202, a second cardiac electrical signal segment stored on a trigger-based basis in response to an R-wave sensing event signal can be rectified. In some examples, 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 202, control circuitry 80 can retrieve the buffered rectified signal segment from memory 82. In other examples, the notch-filtered signal segment can be buffered in memory 82, and control circuitry 80 can perform rectification on the stored signal segment at block 202. The rectified signal segment obtained at block 202 can correspond to a signal segment identified as a suspected real sensed cardiac event based on a detected high-low-high or low-high-low alternating signal characteristic pattern, such as a real sensed R-wave, as described above. Figure 6A As described.

[0115] At block 204, control circuitry 80 determines the maximum absolute amplitude of the rectified, notch-filtered signal segment. The maximum absolute amplitude can be determined from all sampling points spanning the selected signal segment. As described above, when the sampling rate is 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 that is temporally earlier than the R-wave sensing event signal. At block 204, the sampling point with the maximum amplitude in the rectified signal is determined.

[0116] At box 206, the amplitudes of all sampled points in the rectified signal segment are summed. At box 208, based on the maximum absolute amplitude determined at box 204 and the summed sampled point amplitudes determined at box 206, the overall shape metric of the signal segment is determined as the Normalized Rectified Amplitude (NRA). In one example, the NRA is determined as a predetermined multiple or weighted sum of the amplitudes of all sampled points in the notch filter and rectified signal segment, normalized to the maximum amplitude. For example, the NRA could be determined as four times the summed amplitude divided by the maximum absolute amplitude, which could be truncated to an integer value. Figure 5 At frame 108, this NRA can be determined as the overall morphological amplitude.

[0117] The overall morphological amplitude is inversely 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 corresponds to a lower probability that the signal is at baseline amplitude at any given time point during the time interval of the signal segment. This relatively low probability of the signal being at baseline during this time interval can be associated with tachyarrhythmic morphologies, such as ventricular fibrillation morphologies, which can resemble sinusoidal signals. A second cardiac electrical signal segment is more likely to have a tachyarrhythmic morphology when the overall morphological amplitude exceeds a threshold used to verify a suspected true sensed R wave. When the overall morphological amplitude is below the threshold, the probability that the signal is at baseline amplitude at a given time point during the time interval of the signal segment is higher. A relatively high probability that a signal sample point is at baseline during the time interval of the signal segment can be associated with a true, relatively narrow R wave signal occurring during the signal segment, where the baseline amplitude portion of the signal segment appears before and after the true R wave.

[0118] Therefore, when the overall morphological amplitude exceeds the true sensing event threshold, the indication of a true sensing R wave is not confirmed. In this case, the suspected true sensing event is not verified, ruling out the detection of signs of oversensitivity. At box 210, the NRA is compared to the true sensing event threshold. The true sensing event threshold used to verify a suspected true cardiac event can be set between 100 and 150, and in some examples is set to 125, such as when 92 sample points are summed and multiplied by a weighting factor of 4 and normalized to the maximum absolute amplitude. The threshold applied at box 210 to distinguish true sensing R waves from tachyarrhythmic morphologies in the second cardiac electrical signal segment will depend on various factors, such as the amplification factor and the number of summed sample points, the multiple of summed sample points, or the weighting factor.

[0119] In response to an NRA less than a true sensing event threshold, control circuitry 80 may verify the suspected true cardiac event based on the alternating signal characteristic pattern at block 212. When the NRA is greater than (or equal to) the true event threshold at block 210, the suspected true sensing event is not verified at block 214. Signs of tachyarrhythmia morphology are detected at block 216. (Reference) Figure 5 In response to signs of rapid arrhythmia patterns based on NRA greater than the true sensing event threshold, no signs of oversensing were detected even though alternating signal characteristic patterns were detectable (the "Yes" branch of box 110).

[0120] When in Figure 5 The overall morphological amplitude determined at frame 108 (based on) Figure 7 The method detected signs of tachyarrhythmia morphology when the threshold at box 210 was greater than the true sensing event threshold. Figure 5 Box 110) excludes the detection of signs of oversensing. When at least one (or all) of the multiple second cardiac electrical signal segments corresponding to the suspected real R-wave signal in the alternating pattern of signal segments are verified based on an overall morphological amplitude less than or equal to the threshold of the real sensing event, the control circuit 80 does not detect signs of tachyarrhythmia morphology and may detect signs of oversensing in response to the verification of the alternating pattern of multiple suspected real sensing events and the characteristics of the second cardiac electrical signal segments. In this case, Figure 5 No signs of tachyarrhythmia were detected at box 110, resulting in signs of hypersensitivity being detected at box 112.

[0121] Figure 8 This is flowchart 250, based on another example, of a method for verifying suspected real sensed cardiac events in cardiac electrical signal segments based on overall morphological metrics. The process in flowchart 250 can be executed by ICD 14 for... Figure 5 The overall shape signal width metric is determined at box 108. Boxes 202 and 204 correspond to the above combination. Figure 7 The same numbered boxes are described. The notch-filtered rectified signal segment determined at box 202 can correspond to the suspected real sensed cardiac event based on the detected alternating signal characteristic pattern. At box 204, the notch-filtered rectified signal segment can be used to determine the maximum absolute amplitude of the signal segment.

[0122] Control circuit 80 determines a pulse amplitude threshold at block 252 based on the maximum absolute amplitude determined at block 204. 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.

[0123] At box 254, control circuitry 80 determines the signal width of all signal pulses in the second cardiac electrical signal segment. Each signal pulse in the signal segment can be identified by recognizing two consecutive zero amplitude or baseline amplitude sampling points in the rectified signal segment (or two consecutive zero crossings in the non-rectified signal segment). At box 254, all signal pulses between two consecutive baseline amplitude sampling points are identified. In some examples, signal pulses can be identified from the non-rectified signal segment so that signal pulses can be identified between zero crossings. The signal width of each identified signal pulse is determined as the number of sampling points (or corresponding time intervals) between a pair of consecutive baseline amplitude sampling points (or zero crossings). At box 256, the absolute maximum amplitude of each rectified signal pulse is determined. At box 258, all signal pulses having an absolute maximum amplitude greater than or equal to the pulse amplitude threshold determined at box 252 are identified. For example, at box 258, all signal pulses with a maximum amplitude at least half of the maximum absolute amplitude determined at box 204 are identified. At box 260, the maximum signal pulse width is determined by comparing the signal pulse widths of all signal pulses identified at box 258 as having a maximum amplitude that is at least the pulse amplitude threshold. Among all signal pulses identified at box 258, the maximum pulse width identified at box 260 can be determined as... Figure 5 The overall shape signal width measurement at frame 108.

[0124] The overall morphological signal width metric can be correlated with the probability of a signal segment exhibiting a rapid arrhythmia morphology. For example, a relatively high overall morphological signal width metric may be an indication of a rapid arrhythmia morphology, such as a relatively wide ventricular fibrillation wave. Conversely, a relatively low overall morphological signal width metric may be an indication of a relatively narrow true R wave appearing during the time interval of the second cardiac electrical signal segment. Suspected true sensed R waves can be validated by a relatively low overall morphological signal width metric, supporting the detection of signs of hypersensitivity based on the detected alternating signal characteristic patterns.

[0125] At block 262, control circuit 80 compares the maximum pulse width identified at block 260 with a true sensed cardiac event width threshold. In one example, the true sensed cardiac event width threshold is set to 20 sampling points when the sampling rate is 256 Hz. When the maximum signal pulse width is less than the width threshold, control circuit 80 verifies the suspected true cardiac event at block 264. A maximum signal pulse width less than or equal to the width threshold may correspond to a true, relatively narrow R wave, for example, during sinus rhythm. Verification of the suspected true sensed cardiac event when an alternating pattern of signal characteristics is detected can support the detection of cardiac event oversensitization. In response to the detection of an alternating pattern at block 106 and verification of at least one suspected true cardiac sensing event based at least on an overall morphological signal width metric less than the true sensed event width threshold, [further details can be added]. Figure 5 Oversensing was detected at box 112.

[0126] When the maximum pulse width at box 262 exceeds the width threshold, the suspected real sensed cardiac event is not verified at box 266. Instead, a relatively wide maximum signal pulse width can be detected at box 268 as an indication of a tachyarrhythmic morphology within the segment of the second cardiac electrical signal being analyzed. Indications of a tachyarrhythmic morphology rule out [the possibility of] [a specific event]. Figure 5 Box 112 is used to verify the suspected real sensed cardiac events and detect signs of oversensing, even though alternating patterns of second cardiac electrical signal segmentation features have been detected.

[0127] In various examples, both the overall morphological amplitude and the overall morphological signal width measure can be determined (in... Figure 5 At frame 110, according to Figure 7 and Figure 8 (technology), and in Figure 5 The value at box 110 is compared with a true cardiac event criterion or threshold. In some examples, both the overall morphological amplitude and the overall morphological signal width metric may be required to meet the true cardiac sensing event criterion; for example, both may need to be less than or equal to the corresponding threshold to validate a suspected true cardiac sensing event and allow for the detection of hypersensitivity signs. When only one of the overall morphological amplitude or the overall morphological signal width is greater than the corresponding true cardiac sensing event threshold, in Figure 5 At box 110, signs of tachyarrhythmia morphology were detected in the second cardiac electrical signal segment, ruling out the detection of signs of oversensing. In other examples, it may be necessary for at least one of the overall morphological amplitude and signal width measures of multiple suspected true cardiac event signal segments to be less than or equal to the corresponding true cardiac event threshold in order to detect signs of oversensing based on alternating signal characteristic patterns.

[0128] Depend on Figure 7The method determines the overall morphological amplitude and is determined by Figure 8 The overall morphological signal width measures determined by the method can be used in combination to verify suspected true R waves in alternating signal characteristic patterns. In some examples, indications of tachyarrhythmic morphology based on overall morphological measures prevented verification of suspected true R waves and ruled out detection of signs of oversensitivity. Segments of the second cardiac electrical signal with relatively high overall morphological amplitude and / or relatively high overall morphological signal width measures are indications of tachyarrhythmic morphology.

[0129] Figure 9 This is a flowchart 300 of an example method performed by an ICD 14 for detecting P-wave oversensing and suppressing ventricular tachyarrhythmia detection in response to the detection of P-wave oversensing. At blocks 302 and 304, 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. Under the control of control circuitry 80, the two sensing electrode vectors can be selected by a switching circuitry system included in sensing circuitry 86. In some examples, the two sensing electrode vectors are programmed by the user and retrieved from memory 82 by control circuitry 80, and transmitted to sensing circuitry 86 as vector selection control signals.

[0130] The first sensing electrode vector selected at box 302 for obtaining the first cardiac electrical signal may be a relatively short bipolar electrode, 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 electrode may include electrodes that are relatively close to each other and relatively close to the ventricular chamber compared to the second sensing vector selected at box 304, to provide sensing of a relatively “near-field” ventricular signal for sensing the R wave. The first sensing vector may be a vertical sensing vector (relative to the patient’s upright or standing position) or approximately aligned with the cardiac axis to maximize the amplitude of the R wave in the first cardiac electrical signal, thereby enabling reliable R wave sensing. However, the first sensing electrode vector is not limited to any particular inter-electrode spacing or orientation and may be selected as any available electrode pair.

[0131] The second sensing electrode vector used to obtain the second cardiac electrical signal at block 304 may be a relatively long bipolar electrode with an interelectrode distance greater than that of the first sensing electrode vector. For example, the second sensing electrode vector may be selected as the vector between one of the pacing sensing electrodes 28 or 30 and the ICD housing 15, the vector between one of the defibrillation electrodes 24 or 26 and the housing 15, or other combinations along the distal portion of lead 16 and an electrode of the housing 15. In some examples, this second sensing vector may 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 may receive a relatively global or far-field cardiac electrical signal. Control circuitry 80 may analyze the second cardiac electrical signal received by the second sensing vector selected at block 304 to detect P-wave oversensing. In other examples, the sensing vectors 1 and 2 selected at blocks 302 and 304 for sensing the first and second cardiac electrical signals may be the same sensing electrode vectors, such that the sensing circuit 86 receives a single cardiac electrical signal, but the two different sensing channels 83 and 85 of the sensing circuit 86 process the raw received signal. The sensing circuit has different filtering and / or other signal processing features to sense two different cardiac electrical signals, one by the first sensing channel 83 for detecting the R wave, and the other by the second sensing channel for performing signal feature and morphological analysis.

[0132] In response to the first sensing channel 83 detecting that a first cardiac electrical signal exceeds an R-wave sensing threshold, the sensing circuit 86 may generate an R-wave sensing event signal at block 306. The R-wave sensing event signal may be transmitted to the control circuit 80. In response to the R-wave sensing event signal, i.e., the downlink "yes" branch of block 306, the control circuit 80 is triggered at block 308 to store segments of the second cardiac electrical signal received from the second sensing channel 85 within a predetermined time interval. The segments of the second cardiac electrical signal may be stored in a circular buffer of memory 82, configured to store multiple sequential segments, wherein the storage of each segment is triggered by the R-wave sensing event signal generated by the first sensing channel 83. For example, the digitized segments of the second cardiac electrical signal may be 100 ms to 500 ms long, including sampling points before and after the R-wave sensing event signal time. The segments of the second cardiac electrical signal may or may not be time-concentrated on the R-wave sensing event signal received from the 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 it. In other examples, the segment may be centered on the R-wave sensing event signal or extend a greater number of sampling points after the R-wave sensing event signal than before it. In one example, the buffered segment of the cardiac electrical signal is obtained with at least 50 sampling points at a sampling rate of 256 Hz or approximately 200 ms. In another example, the buffered segment is at least 92 sampling points, or approximately 360 ms, sampled at 256 Hz, and can be used to analyze the detection of P-wave oversensing.

[0133] Memory 82 can be configured to store a predetermined number of second cardiac electrical segments in a cyclic buffer, for example, at least one, and in some cases two or more cardiac electrical signal segments, such that the oldest segment is overwritten by the newest segment. However, if the R-sense confirmation threshold is not reached at box 314 described below, the previously stored segment may never be analyzed for P-wave oversensitization detection and may be overwritten. In some examples, at least one segment of the second cardiac electrical signal may be stored, and if it is not needed for P-wave oversensitization detection, that segment is overwritten by the next segment corresponding to the next R-wave sensing event signal.

[0134] In addition to buffering the segmentation of the second cardiac electrical signal, control circuit 80 responds to the R-wave sensing event signal generated at block 306 by determining the RRI at block 310 that ends with the current R-wave sensing event signal and begins with the most recent previous R-wave sensing event signal. Timing circuit 90 of control circuit 80 can transmit RRI timing information to tachyarrhythmia detection circuit 92, which adjusts the tachyarrhythmia interval counter at block 312. 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 312. If the RRI is shorter than or equal to the FDI, the VF interval counter is incremented at block 312. In some examples, if the RRI is less than the TDI, the combined VT / VF interval counter is incremented.

[0135] After updating the tachyarrhythmia interval counter at box 312, the tachyarrhythmia detector 92 compares the counter value with the R-sensing confirmation threshold at box 314, and with the VT detection threshold and VF detection threshold at box 332. If the VT or VF detection interval counter has reached the R-sensing confirmation threshold, the "Yes" branch of box 314 analyzes a second cardiac electrical signal from sensing channel 85 to detect P-wave oversensing, which may cause the first sensing channel 83 to generate an erroneous R-wave sensing event signal, resulting in an increase in the VT and / or VF counter at box 312. The R-sensing confirmation threshold may be a VT or VF interval count value greater than one or another higher threshold count value. Different R-sensing confirmation thresholds may be applied to the VT interval counter and the VF interval counter. For example, the R-sensing confirmation threshold may be a count of 2 for the VT interval counter and a count of 3 for the VF interval counter. In other examples, the R-sensing confirmation threshold is a higher number, such as 5 or higher, but may be less than the number of VT or VF 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, applying the R-sensing confirmation threshold to the combined VT / VF interval counter. It should be recognized that in some examples, VT detection may not be enabled, and VF detection may be enabled. In this case, at box 312, only the VF interval counter is updated in response to the RRI determination, and at box 314, the R-sensing confirmation threshold can be applied to the VF interval counter.

[0136] If, at box 314, none of the tachyarrhythmia interval counters have reached the R-wave sensing confirmation threshold, the control circuit 80 waits at box 308 for the next R-wave sensing event signal to buffer the next segment of the second cardiac electrical signal. If the R-wave sensing confirmation threshold is reached at box 314, for example when the VF interval counter is greater than 2, the control circuit 80 begins analyzing the second cardiac electrical signal segment to detect P-wave oversensing.

[0137] At block 316, control circuitry 80 can retrieve one or more notch-filtered signal segments stored in memory 82. In some examples, after reaching an R-sensing confirmation threshold, at block 316, control circuitry 80 performs notch filtering on the stored second cardiac electrical signal segment, for example, a notch filter implemented via firmware. In other examples, such as Figure 4 As shown, a notch-filtered signal is received from the second sensing channel 85 and buffered in memory 82 for retrieval by the control circuit 80. After reaching the R-wave sensing confirmation threshold, the control circuit 80 determines the maximum peak-to-peak amplitude based on each consecutive unrectified, notch-filtered second cardiac electrical signal segment buffered in response to the R-wave sensing event signal. The maximum peak-to-peak amplitude is determined for at least three consecutive buffered cardiac signal segments to enable the determination of the two amplitude differences between two consecutive pairs of maximum peak-to-peak amplitudes, as described above. Figure 6A As described. At box 318, control circuit 80 determines the difference between consecutively defined peak-to-peak amplitudes.

[0138] Once three consecutive, defined peak-to-peak amplitudes are available, allowing two consecutive amplitude differences to be determined at block 318, control circuit 80 can apply a standard for detecting the alternating pattern of peak amplitudes at block 320. The standard applied at block 320 corresponds to the combination described above. Figure 6A The example described. It should be understood that in some cases, the peak-to-peak amplitudes of three consecutive buffered cardiac electrical signal segments may not be available when the R-sensing confirmation threshold is first reached, because the determination of the peak-to-peak amplitudes from the buffered segments may not begin until the R-sensing confirmation threshold is reached. More than two R-wave sensing event signals and corresponding buffered second cardiac electrical signal segments may be required before the first determination of the alternation pattern can be made at box 320.

[0139] As described above, the control circuit 80 can detect the alternation pattern of maximum peak-to-peak amplitudes by determining the maximum peak-to-peak amplitude of three consecutive segments, identifying the highest maximum amplitude of two consecutive determined peak-to-peak amplitudes, setting a difference threshold as a percentage of the highest maximum peak-to-peak amplitude, and then comparing the difference between the two consecutive determined maximum peak-to-peak amplitudes with the difference threshold. The difference between two consecutive peak-to-peak amplitudes is determined from the three consecutive determined peak-to-peak amplitudes. (This is in conjunction with...) Figure 6A As described in Example 151a, two consecutive differences can be compared to a first set of criteria used to detect a high-low-high pattern. If no high-low-high pattern is detected, two consecutive differences can be compared to a second set of criteria used to detect a low-high-low pattern, such as in combination. Figure 6A Example 151b describes this. In other examples, control circuit 80 may first apply a low-high-low amplitude difference criterion, and if that is not met, then apply a high-low-high amplitude difference criterion, or apply low-high-low and high-low-high criteria in parallel, to detect alternating patterns of maximum peak-to-peak amplitudes in three consecutive second cardiac electrical signal segments.

[0140] When no alternation pattern is detected at block 320, control circuit 80 may determine at block 332 whether the number of VT and / or VF intervals required for VT or VF detection has been reached. If the VT interval counter, VF interval counter, or combined VT / VF interval counter has not reached the threshold number of detection intervals (NID), control circuit 80 returns to block 310 to continue determining RRI and analyzing the second cardiac electrical signal segment (block 314), provided that the R sensing confirmation threshold is met.

[0141] When an alternating pattern is detected at block 320, control circuit 80 identifies, at block 322, which of the three consecutive segments corresponds to the suspected real sensed R wave based on the identified alternating pattern. For example, when a high-low-high amplitude pattern is identified, the first and third cardiac electrical signal segments are identified as corresponding to the suspected real sensed R wave, while the second and intermediate cardiac electrical signal segments are identified as the suspected oversensitized P wave. When a low-high-low amplitude pattern is detected at block 320, the intermediate cardiac electrical signal segment is identified as corresponding to the suspected real sensed R wave, and the first and third cardiac electrical signal segments are identified as the suspected oversensitized P wave segments, corresponding to the suspected false R wave sensing event signal.

[0142] At box 326, a general morphological metric is determined for multiple cardiac electrical signal segments identified as corresponding to the suspected true sensed R wave. This general morphological metric can be determined by processing and analyzing one or both of the rectified, notch-filtered segments and / or unrectified, notch-filtered segments of the second cardiac electrical signal, as described above. Figures 7 to 8 As described. Therefore, the notch-filtered signal segment can be rectified at block 324 (e.g., by...). Figure 4 The second sensing channel 85), and the control circuit 80 can use rectified notch-filtered signal segmentation at block 326 to determine the overall shape metric. The overall shape metric may include amplitude and signal width metrics, as described above. Figure 7 and Figure 8As described. When multiple suspected true R-wave cardiac electrical signal segments with alternating signal characteristic patterns identified at box 328 include tachyarrhythmic morphologies, multiple suspected true R waves are not verified as true sensed R waves based on meeting the tachyarrhythmic morphology criteria. In response to the detection of at least one tachyarrhythmic morphology in the alternating pattern of the signal segments at box 328, VT or VF detection due to suspected PWOS is suppressed by suppressing the detection of PWOS signs at box 330, even if the alternating pattern of the signal segments may be detected. For example, as in combination Figure 7 and Figure 8 As described, when either the overall morphological amplitude or the overall morphological signal width measure is greater than the corresponding true sensing event threshold, the suspected true sensing R wave may not be verified. In this case, tachyarrhythmia morphology is detected at box 328, and no PWOS sign detection is performed at box 330, even though an alternating peak-to-peak amplitude pattern is detected at box 320. At box 330, the oversensitivity sign flag can be set to 0, or the PWOS counter can be adjusted based on the number of times PWOS signs have been detected on the last Y R-wave sensing event signals.

[0143] When the morphological criteria for tachyarrhythmias are not met—for example, when both the overall morphological amplitude feature and the overall morphological signal width feature are less than the true sensing event threshold—no tachyarrhythmia morphology is detected for a given signal segment at box 328. The suspected true R-wave sensing event is verified. In response to multiple suspected true R-wave sensing events verified in the alternating patterns of signal features, a PWOS sign is detected at box 334. At box 334, the PWOS sign flag can be set to 1, or the PWOS counter can be adjusted to increase the number of times a PWOS sign has been detected on the last Y R-wave sensing event signals.

[0144] At box 328, when the overall morphological parameters meet the morphological criteria for tachyarrhythmias, the suspected true R-wave sensing event signal segment is not necessarily identified as an erroneous R-wave. However, when the morphological criteria for tachyarrhythmias are met, for example, when one or both overall morphological measures exceed the true sensing event signal threshold, the suspected true sensing R-wave signal segment cannot be verified and may represent a true ventricular tachyarrhythmia signal segment. In the presence of relatively high overall morphological amplitude and / or relatively high overall morphological signal width measures, VT or VF detection is prevented due to possible PWOS, both of which are associated with tachyarrhythmia morphology. When the overall morphological measures are relatively low, the suspected R-wave sensing event signal may be a true R-wave, but with relatively low amplitude, which may lead to frequent PWOS when the R-wave sensing threshold is set based on the maximum peak amplitude of the sensed signal. In this case, PWOS sign detection is performed at box 334.

[0145] As long as the R-sensing confirmation threshold is met at box 314, the control circuit 80 continues to analyze segments of the second cardiac electrical signal to detect PWOS signs (boxes 316 to 328). If the VT and VF interval counters no longer meet the R-sensing confirmation threshold at box 314, the PWOS sign counter or buffer can be cleared or reset. The next time the R-sensing confirmation threshold is reached, the PWOS sign counter or buffer can start counting PWOS detections or set the PWOS sign buffer flag in a first-in-first-out manner. When NID is reached at box 332, the control circuit 80 determines at box 336 whether PWOS has been detected based on the values ​​of the VT and / or VF interval counters. For PWOS to be detected and for VT or VF detection to be blocked, for example, the number of PWOS sign flags stored in the first-in-first-out buffer or the value of the PWOS sign counter needs to reach a threshold number. For example, if the PWOS event flag is set to "1" for at least 8 of the most recent 32 buffered segments of the second cardiac electrical signal, then PWOS is detected at box 336. The oversensing threshold applied to the PWOS sign counter or flag can be a fixed threshold or an adjustable threshold based on NID. For example, when NID is relatively low, the control circuit 80 can set the oversensing threshold to a relatively low value, while when NID is relatively high, the oversensing threshold can be increased.

[0146] At box 342, VT or VF detection is blocked, and in response to PWOS detection at box 336, treatment for ventricular tachyarrhythmia is not delivered. As long as NID continues to be met, control circuitry 80 can continue to update the PWOS sign counter as new R waves are sensed to determine at box 336 whether the oversensing threshold is still met. In some examples, control circuitry 80 can determine at box 344 whether termination criteria are met when PWOS detection does not occur. Termination of a fast rhythm can be detected based on a predetermined number of RRIs greater than the tachyarrhythmia detection interval, or when the average, median, or other measure of RRIs determined within a predetermined time interval is greater than the tachyarrhythmia detection interval. For example, tachyarrhythmia termination can be detected at box 344 when a threshold number of RRIs longer than the VT detection interval (e.g., when VT detection is enabled) or longer than the VF detection interval (e.g., when VT detection is not enabled) is detected after NID is met. In one example, termination is detected at block 344 when at least eight consecutive long RRIs (e.g., greater than the VT detection interval) are detected. In another example, control circuitry 80 may detect termination at block 344 when a predetermined time interval has elapsed and the median RRI is greater than the VT detection interval. For example, control circuitry 80 may detect termination at block 344 when 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. In response to the detection of termination, control circuitry 80 may reset the VT interval counter and the VF interval counter and return to block 310.

[0147] When NID is met at box 332 and PWOS is not detected at box 336, a VT or VF episode is detected at box 338. In response to VT / VF detection, the treatment delivery circuit 84 can deliver VT or VF treatment at box 340. It should be understood that other criteria may be applied prior to detecting VT or VF at box 338. For example, various noise suppression criteria, T-wave hypersensitivity suppression criteria, supraventricular tachycardia (SVT) suppression criteria, etc., may need to be met before VT / VF detection at box 338.

[0148] It should be understood that, based 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 omitted entirely (e.g., not all described actions or events are necessary for practicing the methods). Furthermore, in some examples, 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 may be performed by a combination of units or circuits associated with, for example, a medical device.

[0149] In one or more examples, the described functionality may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functionality may be stored on a computer-readable medium in the form of one or more instructions or code and may be executed by a hardware-based processing unit. The computer-readable medium may 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 is accessible by a computer).

[0150] 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, as used herein, the term "processor" can refer to any of the foregoing structures or any other structure suitable for implementing the techniques described herein. Furthermore, these techniques can be implemented entirely within one or more circuit or logic elements.

[0151] 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 may be made to the referenced examples without departing from the scope of this disclosure and the following claims.

[0152] Further embodiments that may be combined with other embodiments described herein are described in the following terms. Any features described as a part of these terms may be used on or in combination with other embodiments described herein to produce yet more further embodiments.

[0153] 1. A method comprising: sensing at least one cardiac electrical signal; detecting cardiac events from the first cardiac electrical signal; determining signal features from segments of the at least one cardiac electrical signal in response to each of a plurality of cardiac events detected from the at least one cardiac electrical signal; detecting an alternation pattern of the signal features determined from consecutive segments of the at least one cardiac electrical signal; determining a global morphological measure from each segment of the at least one segment of the consecutive segments; determining that the global morphological measure does not meet a morphological criterion for tachyarrhythmias; detecting cardiac event oversensitization in response to the global morphological measure not meeting the morphological criterion for tachyarrhythmias and the detection of the alternation pattern; and halting the detection of arrhythmias in response to the detection of signs of cardiac event oversensitization.

[0154] 2. The method according to Clause 1, the method further comprising, in response to detecting the alternation pattern, identifying at least one segment of a cardiac electrical signal corresponding to at least one suspected real-felt cardiac event based on the alternation pattern; and determining the overall morphological measure from the at least one segment corresponding to the suspected real-felt cardiac event.

[0155] 3. The method according to any one of Clauses 1 to 2, the method further comprising detecting a tachyarrhythmia based on a cardiac event detected from the at least one cardiac electrical signal that meets the criteria for a tachyarrhythmia; and generating a treatment in response to the detection of a tachyarrhythmia.

[0156] 4. The method according to any one of claims 1 to 3, the method further comprising detecting an indication of a tachyarrhythmia morphology in response to the overall morphological measure determined from each segment of at least one segment of the continuous segments that satisfies the tachyarrhythmia morphology criteria; and, in response to detecting the alternation pattern, preventing the oversensing of the cardiac event when the overall morphological measure from at least one continuous segment of the continuous segments satisfies the tachyarrhythmia morphology criteria.

[0157] 5. The method according to any one of clauses 1 to 4, wherein detecting the alternation pattern of the signal features comprises determining a first signal feature from a first signal segment of the at least one cardiac electrical signal, determining a second signal feature from a second signal segment of the at least one cardiac electrical signal, and determining a third signal feature from a third signal segment of the at least one cardiac electrical signal, the first signal segment, the second signal segment, and the third signal segment respectively corresponding to a first cardiac event, a second cardiac event, and a third cardiac event continuously detected from the at least one cardiac electrical signal; setting a first difference threshold based on one of the first signal feature or the second signal feature; determining a first difference between the first signal feature and the second signal feature; setting a second difference threshold based on one of the second signal feature or the third signal feature; determining a second difference between the second signal feature and the third signal feature; comparing the second difference with the second difference threshold; and detecting the alternation pattern in response to the first difference being greater than the first difference threshold and the second difference being greater than the second difference threshold.

[0158] 6. The method according to Clause 5, the method further comprising determining each of the first signal feature, the second signal feature and the third signal feature by determining the maximum peak-to-peak amplitude from the first signal segment, the second signal segment and the third signal segment, respectively.

[0159] 7. The method according to any one of clauses 5 or 6, the method further comprising determining a third difference between the first signal feature and the third signal feature; determining that the third difference is less than a stability threshold; and detecting the alternation pattern based on the fact that the first difference and the second difference are respectively greater than the first difference threshold and the second difference threshold, and the third difference is less than the stability threshold.

[0160] 8. The method according to any one of clauses 1 to 7, wherein the alternation pattern of detecting the signal feature includes an alternation pattern of detecting at least one of the polarity of peak-to-peak amplitude, cardiac event interval, or maximum peak amplitude.

[0161] 9. The method according to any one of Clauses 1 to 8, wherein determining the overall morphological measure comprises determining the maximum amplitude of the segment; determining the sum of the amplitudes of a plurality of sample points of the segment; and dividing the sum by the maximum amplitude.

[0162] 10. The method according to any one of clauses 1 to 9, wherein determining the overall morphological measure includes identifying a plurality of signal pulses of the segment; determining the signal width of each of the plurality of signal pulses; and determining a maximum signal width from the determined signal widths.

[0163] 11. The method according to any one of claims 1 to 10, the method further comprising: determining a first overall morphology metric by determining an overall morphology signal width metric; determining a second overall morphology metric by determining an overall morphology signal width metric; determining that the overall morphology amplitude is less than or equal to a first threshold; determining that the overall morphology signal width metric is less than or equal to a second threshold; verifying a suspected real sensed cardiac event in response to both the overall morphology amplitude being less than or equal to the first threshold and the overall morphology signal width metric being less than or equal to the second threshold; and detecting cardiac event oversensitization in response to detecting the alternation pattern and verifying the suspected real sensed cardiac event.

[0164] 12. The method according to any one of clauses 1 to 11, the method further comprising detecting signs of oversensitivity by detecting alternating patterns of the signal features during a predetermined number of consecutive segments; determining a threshold number of times the signs of oversensitivity have been detected, wherein the threshold number is a proportion of the number of cardiac event intervals between consecutively detected cardiac events from the at least one cardiac electrical signal required to detect the arrhythmia; and detecting cardiac event oversensitivity in response to determining that the signs of oversensitivity have been detected a threshold number of times.

[0165] 13. The method according to Clause 12, the method further comprising adjusting the threshold number in response to a change in the number of cardiac event intervals required to detect the arrhythmia.

[0166] 14. The method according to any one of claims 1 to 13, the method further comprising sensing a first cardiac electrical signal in the at least one cardiac electrical signal via a first sensing electrode vector; detecting the cardiac event from the first cardiac electrical signal; sensing a second cardiac electrical signal of the at least one cardiac electrical signal via a second sensing electrode vector different from the first sensing electrode vector; determining the signal features from the second cardiac electrical signal; and detecting the alternation pattern of the signal features determined from successive segments of the second cardiac electrical signal.

[0167] 15. The method according to any one of Clauses 1 to 14, the method further comprising not scheduling arrhythmia treatment in response to detecting oversensitivity of the cardiac event.

[0168] 16. The method according to any one of claims 1 to 15, the method further comprising determining two consecutive cardiac event intervals between consecutive cardiac events of the plurality of cardiac events; determining that the sum of the two consecutive cardiac event intervals falls within a threshold range; and determining the signal features of the alternation pattern for detecting the alternation pattern in each consecutive segment of the consecutive cardiac events corresponding to each of the consecutive cardiac events in the two consecutive cardiac event intervals.

[0169] 17. A non-transitory computer-readable medium storing a set of instructions, which, when executed by control circuitry of a medical device, causes the medical device to sense at least one cardiac electrical signal; detect cardiac events from the at least one cardiac electrical signal; determine signal features from segments of the at least one cardiac electrical signal in response to each of a plurality of cardiac events detected from the at least one cardiac electrical signal; detect an alternation pattern of the signal features determined from consecutive segments of a second cardiac electrical signal; determine an overall morphological metric from each segment of at least one segment of the consecutive segments of the second cardiac electrical signal; determine that the overall morphological metric does not meet a morphological criterion for tachyarrhythmia; detect cardiac event oversensitization in response to the overall morphological metric not meeting the morphological criterion for tachyarrhythmia and the detection of the alternation pattern; and prevent detection of arrhythmias in response to the detection of cardiac event oversensitization.

Claims

1. A medical device comprising: A cardiac electrical signal sensing circuit, wherein the cardiac electrical signal sensing circuit is configured as follows: Detect at least one cardiac electrical signal; Detect cardiac events from at least one cardiac electrical signal; Control circuit, the control circuit being configured to: In response to each of a plurality of cardiac events detected from the at least one cardiac electrical signal, signal features are determined from segments of the at least one cardiac electrical signal; Detecting alternating patterns of signal features determined from continuous segments of the at least one cardiac electrical signal; From each segment of at least one of the continuous segments of the at least one cardiac electrical signal, an overall morphological measure is determined by determining at least one of the amplitude or signal width measures. The overall morphological measure was compared with the morphological criteria for tachyarrhythmias; It was determined that the overall morphological measure did not meet the morphological criteria for tachyarrhythmias. In response to the overall morphological metric failing to meet the morphological criteria for tachyarrhythmias and the detection of the alternation pattern, cardiac event oversensitization is detected; and In response to the detection of an oversensitivity to the cardiac event, the detection of tachyarrhythmias is stopped.

2. The medical device according to claim 1, wherein the control circuit is further configured as follows: In response to the detection of the alternation pattern, at least one segment of the cardiac electrical signal corresponding to at least one suspected real sensed cardiac event is identified based on the alternation pattern; and The overall morphological measure is determined from the at least one segment corresponding to the suspected real sensed cardiac event.

3. The medical device according to any one of claims 1-2, wherein the control circuit is further configured to detect tachyarrhythmia based on the cardiac event detected from the at least one cardiac electrical signal that meets the criteria for tachyarrhythmia; The medical device further includes a treatment delivery circuit configured to generate treatment in response to the control circuit detecting a rapid arrhythmia.

4. The medical device according to any one of claims 1-2, wherein the control circuit is further configured to: In response to the overall morphological measure determined from each segment of at least one segment of a continuous segment satisfying the morphological criteria for tachyarrhythmia, indications of tachyarrhythmia morphology are detected; and When the overall morphological measure from at least one of the consecutive segments satisfies the morphological criteria for tachyarrhythmia, the oversensing of the cardiac event is prevented in response to the detection of the alternation pattern.

5. The medical device according to any one of claims 1-2, wherein the control circuit is configured to detect the alternating pattern of the signal characteristics by: A first signal feature is determined from a first signal segment of the at least one cardiac electrical signal, a second signal feature is determined from a second signal segment of the at least one cardiac electrical signal, and a third signal feature is determined from a third signal segment of the at least one cardiac electrical signal, wherein the first signal segment, the second signal segment, and the third signal segment correspond to a first cardiac event, a second cardiac event, and a third cardiac event continuously detected from the at least one cardiac electrical signal, respectively. A first difference threshold is set based on either the first signal feature or the second signal feature; Determine the first difference between the first signal feature and the second signal feature; It is determined that the first difference is greater than the first difference threshold; A second difference threshold is set based on either the second signal feature or the third signal feature; Determine the second difference between the second signal feature and the third signal feature; It is determined that the second difference is greater than the second difference threshold; and The alternation pattern is detected in response to the first difference being greater than the first difference threshold and the second difference being greater than the second difference threshold.

6. The medical device of claim 5, wherein the control circuit is configured to determine each of the first signal feature, the second signal feature, and the third signal feature by determining a first maximum peak-to-peak amplitude, a second maximum peak-to-peak amplitude, and a third maximum peak-to-peak amplitude, respectively, from the first signal segment, the second signal segment, and the third signal segment.

7. The medical device according to claim 5, wherein the control circuit is further configured as follows: Determine the third difference between the first signal feature and the third signal feature; It is determined that the third difference is less than the stability threshold; and The alternation pattern of the signal features is detected based on the fact that the first difference and the second difference are respectively greater than the first difference threshold and the second difference threshold, and the third difference is less than the stability threshold.

8. The medical device according to any one of claims 1-2, wherein the control circuit is configured to detect the alternation pattern of the signal characteristics by detecting an alternation pattern of at least one of the polarity of peak-to-peak amplitude, cardiac event interval, or maximum peak amplitude.

9. The medical device according to any one of claims 1-2, wherein the control circuitry is configured to determine the overall morphological measure by: (a) Determine the maximum amplitude of the segment; determine the sum of the amplitudes of multiple sample points of the segment; and divide the sum by the maximum amplitude; or (b) Identify the multiple signal pulses of the segment; determine the signal width of each of the multiple signal pulses; And determine the maximum signal width from the determined signal width.

10. The medical device according to any one of claims 1-2, wherein the control circuit is further configured to: The first overall morphological measure is determined by determining the overall morphological amplitude. The second overall morphological measure is determined by determining the overall morphological signal width measure; The overall morphological amplitude is determined to be less than or equal to a first threshold. The overall morphological signal width metric is determined to be less than or equal to a second threshold. In response to the overall morphological amplitude being less than or equal to the first threshold and the overall morphological signal width measurement being less than or equal to the second threshold, the suspected real sensed cardiac event is verified. and In response to detecting the alternating pattern and verifying the suspected real sensed cardiac event, the cardiac event oversensing is detected.

11. The medical device according to any one of claims 1-2, wherein the control circuit is further configured to: Indications of over-sensitivity are detected by detecting alternating patterns of the signal characteristics during a predetermined number of consecutive segments; Determine that the signs of oversensitivity have been detected a threshold number of times, wherein the threshold number is a proportion of the number of cardiac event intervals between consecutively detected cardiac events from the at least one cardiac electrical signal required to detect the arrhythmia; and In response to determining that the signs of oversensitization have been detected a threshold number of times, the cardiac event oversensitization is detected.

12. The medical device of claim 11, wherein the control circuitry is configured to adjust the threshold number in response to a change in the number of cardiac event intervals required to detect the arrhythmia.

13. The medical device according to any one of claims 1-2, wherein: The sensing circuit is configured as follows: A first cardiac electrical signal is sensed via a first sensing electrode vector; The cardiac event is detected from the first cardiac electrical signal; and A second cardiac electrical signal is sensed via a second sensing electrode vector different from the first sensing electrode vector; and The control circuit is configured as follows: The signal characteristics are determined from the second cardiac electrical signal; and The alternating pattern of the signal characteristics determined from continuous segments of the second cardiac electrical signal is detected.

14. The medical device according to any one of claims 1-2, wherein the control circuitry is configured to not schedule arrhythmia treatment in response to detecting an oversensitivity of the cardiac event.

15. The medical device according to any one of claims 1-2, wherein the control circuit is further configured to: Determine the interval between two consecutive cardiac events between the plurality of cardiac events; Determine that the sum of the intervals between the two consecutive cardiac events falls within a threshold range; and The signal features for detecting the alternation pattern are determined from each consecutive segment of the consecutive segments of the consecutive cardiac events corresponding to the two consecutive cardiac event intervals.

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