Medical device and method for detecting electrical signal noise

Abstract

A medical device is configured to sense electrical signals and determine that a signal-to-noise ratio criterion is satisfied based on stored electrical signal segments in response to sensed electrophysiology events. The medical device is configured to determine, from one of the stored electrical signal segments, an increased-gain signal segment in response to determining that the signal-to-noise ratio criterion is satisfied. The medical device determines a noise metric from the increased-gain signal segment. In response to the noise metric satisfying a noise detection criterion, the stored electrical signal segment associated with the increased-gain signal segment can be classified as a noise segment.

Description

Technical Field

[0001] This disclosure generally relates to a medical device and method for detecting electrical signal noise. Background Technology

[0002] Medical devices can sense electrophysiological signals from the heart, brain, nerves, muscles, or other tissues. Such devices can be implantable and wearable, or external devices that use implantable and / or surface (skin) electrodes to sense electrophysiological signals. In some cases, such devices can be configured to deliver therapy based on sensed electrophysiological signals. For example, implantable or external pacemakers, cardioverter-defibrillators, cardiac monitors, etc., sense cardiac electrical signals from a patient's heart. Pacemakers or cardioverter-defibrillators can deliver therapeutic electrical stimulation to the heart via electrodes carried by one or more medical electrical leads and / or electrodes on the housing of the medical device. Electrical stimulation may include signals such as pacing pulses or rhythm changes or defibrillation shocks. In some cases, medical devices can 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 the sensed cardiac electrical signals. Upon detection of abnormal rhythms (e.g., bradycardia, tachycardia, or fibrillation), one or more appropriate electrical stimulation signals can be delivered to restore or maintain a more normal cardiac rhythm. For example, an implantable cardioverter defibrillator (ICD) can deliver a pacing pulse to a patient’s heart when bradycardia or tachycardia is detected, or deliver a cardioverter defibrillator (CV / DF) shock to the heart when tachycardia or fibrillation is detected.

[0003] Medical devices can sense cardiac electrical signals from the ventricles and deliver electrical stimulation therapy to the ventricles using electrodes carried by transvenous medical electrical leads. Cardiac signals sensed within the ventricles using endocardial electrodes typically have high signal strength and quality, enabling reliable sensing of near-field cardiac electrical events, such as ventricular R waves sensed from within the ventricles. In some proposed or available ICD systems, extracardiac leads may be coupled to the ICD, where sensing cardiac signals from outside the heart presents challenges in accurately sensing cardiac electrical events. In various medical devices or systems, implantable, percutaneous, or skin (skin) electrodes can be positioned for sensing electrophysiological signals by the medical device, which can be implantable, external, or wearable. Such devices may include those configured to monitor electrophysiological signals for medical conditions or health purposes (including, but not limited to, fitness trackers, watches, or other medical or fitness devices). Summary of the Invention

[0004] Generally, this disclosure relates to a medical device and technique for detecting noise in electrical signals sensed by a medical device. Electrical signal noise can be detected in electrophysiological signals such as, but not limited to, cardiac electrical signals, neural signals, brain signals, or muscle signals. Noise detection techniques can be used in conjunction with various patient monitoring devices and / or treatment delivery devices, including devices for monitoring a patient's heart rate. For example, the detection of noise in cardiac electrical signals can be included in heart rate monitoring and arrhythmia detection methods such as rapid arrhythmia detection algorithms to avoid erroneous arrhythmia detection in the presence of cardiac electrical signal noise such as electromagnetic interference (EMI) or non-cardiac myoelectric potential signals. A device operating according to the techniques disclosed herein can determine whether a signal-to-noise ratio (SNR) criterion is met based on the electrical signal sensed by the device and increase the gain of an electrical signal segment in response to determining that the SNR criterion is met. The device can determine a noise metric from the signal segment with increased gain. Electrical signal segments associated with the signal segment with increased gain can be classified as noise based on the noise metric. The noise detection technique disclosed herein can improve electrophysiological signal monitoring by suppressing or ignoring noise segments and can prevent the delivery of unnecessary treatments (or prevent necessary treatments) in medical devices, including those with treatment delivery capabilities.

[0005] In some examples, mobile devices such as those disclosed herein can be configured to detect ventricular tachycardias, such as ventricular tachycardia (VT) or ventricular fibrillation (VF), based on detecting a ventricular rate faster than the tachycardia detection rate within at least a predetermined number of ventricular cycles. The VT or VF rate can be detected by sensing R waves from a cardiac electrical signal, determining the ventricular interval or RR interval (RRI) between consecutively sensed R waves, and counting the number of ventricular intervals shorter than the VT or VF detection interval. Non-cardiac noise may be oversensed as ventricular R waves due to the variability of cardiac signal amplitude and / or due to the occurrence of non-cardiac noise such as skeletal muscle potentials during patient activity. Oversensing of non-cardiac noise may cause the medical device to erroneously increase the count of VT or VF intervals when a potentially normal sinus rhythm may be present. Medical devices operating according to the techniques disclosed herein can detect noise in segments of the cardiac electrical signal that may be occurring during a series of ventricular intervals, including the tachycardia detection interval. The device is configured to improve the detection of non-cardiac noise by determining when signal-to-noise ratio criteria are met and to increase the gain of cardiac signal segments being evaluated for noise detection to reveal potential low-amplitude non-cardiac noise pulses. When noise is detected in the cardiac electrical signal and arrhythmia detection criteria such as the threshold number of rapid arrhythmia intervals are met, arrhythmia detection can be suppressed to avoid false arrhythmia detection and unnecessary treatment delivery.

[0006] In one example, this disclosure provides a medical device including a sensing circuit, a memory, and a control circuit. The sensing circuit is configured to sense at least one electrical signal and sense electrophysiological events from the at least one electrical signal. The control circuit is coupled to the sensing circuit and the memory and is configured to store electrical signal segments of the at least one electrical signal sensed by the sensing circuit in the memory in response to each of a series of electrophysiological events sensed by the sensing circuit. The control circuit is configured to determine, based on the stored electrical signal segments, whether a signal-to-noise ratio (SNR) criterion is met, and to determine, in response to the determination that the SNR criterion is met, a signal segment with increased gain from one of the cardiac electrical signal segments. The control circuit is configured to determine a noise metric from the signal segment with increased gain, determine that the noise metric meets a noise detection criterion, and to classify the stored electrical signal segments associated with the signal segment with increased gain as noise segments in response to the noise metric meeting the noise detection criterion. The control circuit may determine, based on at least one electrical signal, whether a rapid arrhythmia detection criterion is met for the purpose of detecting rapid arrhythmias and to prevent rapid arrhythmia detection in response to the stored electrical signal segments being classified as noise segments.

[0007] In another example, this disclosure provides a method comprising sensing at least one electrical signal, sensing an electrophysiological event from the at least one electrical signal, and storing electrical signal segments from the at least one electrical signal in response to each of a series of sensed electrophysiological events. The method further comprises determining, based on the stored electrical signal segments, that a signal-to-noise ratio (SNR) criterion is met; determining, in response to determining that the SNR criterion is met, a signal segment with increased gain from one of the stored cardiac electrical signal segments; and determining a noise metric from the signal segment with increased gain. The method includes determining that the noise metric meets a noise detection criterion and, in response to the noise metric meeting the noise detection criterion, classifying the stored cardiac electrical signal segments associated with the signal segment with increased gain as noise segments. The method may include determining, based on at least one electrical signal, that a rapid arrhythmia detection criterion is met for detecting rapid arrhythmias and stopping rapid arrhythmia detection in response to the stored electrical signal segments being classified as noise segments.

[0008] In another example, this disclosure provides a non-transitory computer-readable medium storing a set of instructions that, when operated by control circuitry of a medical device, cause the medical device to sense at least one electrical signal, sense an electrophysiological event from the at least one electrical signal, and store electrical signal segments from the at least one electrical signal in response to each of a series of sensed electrophysiological events. The instructions further cause the medical device to determine, based on the stored electrical signal segments, that a signal-to-noise ratio (SNR) criterion is met; in response to determining that the SNR criterion is met, to determine a signal segment with increased gain from one of the stored electrical signal segments; to determine a noise metric from the signal segment with increased gain; and in response to the noise metric meeting a noise detection criterion, to classify the stored electrical signal segments associated with the signal segment with increased gain as noise segments. The instructions may further cause the medical device to determine, based on at least one electrical signal, that a rapid arrhythmia detection criterion is met for detecting rapid arrhythmias and to prevent rapid arrhythmia detection in response to the stored electrical signal segments being classified as noise segments.

[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 set forth 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 It is a conceptual diagram based on an example ICD.

[0013] Figure 4 Yes, it can be included in Figure 3 The circuit diagram of the sensing circuit in the ICD.

[0014] Figure 5 It is used by, according to an example, such as Figure 3 A flowchart of a method for using an ICD medical device to detect non-cardiac noise in cardiac electrical signals.

[0015] Figure 6 The diagram illustrates a first cardiac electrical signal and a second cardiac electrical signal, analyzed by a medical device according to an example, to determine whether a signal-to-noise ratio criterion is met in order to increase the gain of the differential signal used for noise detection.

[0016] Figure 7 This is a flowchart, based on some examples, of a method performed by a medical device to determine noise metrics and classify cardiac electrical signals into noisy or non-noise segments.

[0017] Figure 8 It is a graphical representation of the segmented cardiac electrical signal and the corresponding first-order differential signal.

[0018] Figure 9 This is a flowchart of an example method for determining the overall morphological amplitude of cardiac electrical signal segments used to detect the morphology of rapid arrhythmias.

[0019] Figure 10 This is a flowchart of an example method for detecting the morphology of rapid arrhythmias in segments of cardiac electrical signals based on an overall morphological signal width metric.

[0020] Figure 11 This is a flowchart of an example method for controlling rapid arrhythmia detection and treatment delivery by performing noise detection disclosed herein via a medical device.

[0021] Figure 12 This is a flowchart for an alternative method for the detection and treatment of rapid cardiac arrhythmias controlled by medical devices.

[0022] Figure 13 This is a flowchart of a method performed by a medical device, according to another example, for detecting non-cardiac noise in response to detection noise and suppressing ventricular rapid arrhythmias. Detailed Implementation

[0023] Generally, this disclosure describes a medical device and technique for detecting noise in electrical signals, such as cardiac electrical signals, sensed by a medical device. In some examples, the medical device may be configured to sense cardiac electrical events from the cardiac electrical signals, such as atrial P waves accompanied by atrial myocardial depolarization and / or ventricular R waves accompanied by ventricular myocardial depolarization. The medical device may determine heart rate or rhythm and the need for treatment delivery based on at least the sensed cardiac electrical events. For example, atrial or ventricular tachyarrhythmias may be detected by the medical device based on the sensed cardiac electrical signals. In some examples, the medical device may be configured to sense R waves accompanied by ventricular depolarization from the cardiac electrical signals for use in controlling ventricular pacing and detecting ventricular tachyarrhythmias. Ventricular tachyarrhythmias may be detected in response to sensing a threshold number of R waves occurring within a time interval from a preceding R wave less than the tachyarrhythmia detection interval. Non-cardiac electrical noise present in cardiac signals, such as electromagnetic interference (EMI) or skeletal muscle electromyographic signals, may be oversensed as R waves, leading to erroneous short RRIs being identified as ventricular tachyarrhythmia intervals. In some cases, variability in R wave signal intensity due to patient movement or other factors can cause oversensing of non-cardiac noise, resulting in relatively short RRIs being counted in tachyarrhythmia detections when the underlying rhythm may actually be a normal sinus rhythm. Incorrect tachyarrhythmia detections can lead to CV / DF shocks or other tachyarrhythmia treatments delivered by medical devices, such as anti-tachyarrhythmic pacing (ATP), when treatment may not be necessary.

[0024] In some examples, the medical device performing the techniques disclosed herein may be included in an extracardiac ICD system. As used herein, the term “extracardiac” refers to a location outside the blood vessels surrounding the patient’s heart, the heart, and the pericardium. Implantable electrodes carried by extracardiac leads may be positioned outside the thoracic cavity (outside the thoracic cavity and sternum) or inside the thoracic cavity (below the thoracic cavity or sternum), but are generally not in close contact with myocardial tissue. In other examples, transvenous extracardiac leads may carry implantable electrodes that can be positioned within a vein but outside the heart, for example, within an internal thoracic vein, jugular vein, or other vein, for sensing cardiac electrical signals. Changes in patient position or patient physical activity, as well as other factors, may cause variations in the amplitude of cardiac event signals (e.g., P wave amplitude, R wave amplitude, and T wave amplitude) in signals sensed from extracardiac or extracardiac locations. Furthermore, the presence and amplitude of skeletal muscle myoelectric potential signals in cardiac electrical signals may be highly variable due to changes in patient physical activity and posture. Cardiac signals sensed via extracardiac or extracorporeal electrodes may be more susceptible to signal amplitude variability and noise contamination, such as due to myocardial potentials or environmental EMI, than cardiac signals sensed using transvenous intracardiac electrodes.

[0025] The medical device and techniques disclosed herein provide a method for detecting noise, such as electromyographic noise, by increasing the gain of a noisy cardiac electrical signal being analyzed to avoid underdetection of signal noise by a noise detection algorithm. By increasing the gain of the cardiac electrical signal, non-cardiac noise can be detected more reliably, thereby enabling the suppression of erroneous rapid arrhythmia detection due to oversensitivity of non-cardiac noise. As disclosed herein, the medical device can detect noise from a cardiac electrical signal based on one or more noise metrics determined from segments of the cardiac electrical signal. When the amplitude of a noise pulse in the cardiac electrical signal is low, for example, less than a threshold, the gain of the cardiac electrical signal is increased to intentionally increase the amplitude of the noise pulse to improve the likelihood of detecting non-cardiac noise present in the cardiac electrical signal that may lead to erroneous cardiac event sensing.

[0026] This document describes noise detection techniques in conjunction with an ICD configured to sense cardiac electrical signals using an implantable extracardiac (or extracorporeal) medical lead carrying sensing and therapeutic delivery electrodes. However, aspects disclosed herein can be utilized in conjunction with other cardiac medical devices or systems, and more generally with other medical devices or systems configured to sense electrical signals that may become noise-corrupted. For example, the noise detection techniques described in conjunction with the accompanying figures can be implemented in any implantable or external medical device enabled to sense electrophysiological signals, including signals from the brain, nerves, and muscles. Noise detection techniques can be used in conjunction with medical devices configured to sense cardiac electrical events from cardiac signals received from a patient's heart via sensing electrodes, including implantable pacemakers, ICDs, or cardiac monitors coupled to non-venous, transvenous, pericardial, or epicardial sensing 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. The noise detection devices and techniques disclosed herein can be implemented in a variety of medical devices that use implantable or external electrodes to sense electrophysiological signals that may be disrupted by noise.

[0027] The illustrative examples presented herein relate to sensing cardiac electrical signals for the detection of ventricular tachyarrhythmias. However, the disclosed techniques can be implemented in medical devices configured to sense atrial and / or ventricular cardiac events to detect various cardiac rhythms such as bradycardia, tachycardia, fibrillation, etc. For example, a cardiac device using the disclosed noise detection techniques can be configured to sense P waves, for example, for detecting (and optionally treating) atrial tachyarrhythmias. In this case, the medical device can count PP intervals, which are smaller than the atrial tachyarrhythmia detection interval, occurring between consecutively sensed atrial P waves. Cardiac electrical signals that can be sensed from within or outside the atrium can be analyzed based on the analysis of cardiac electrical signals using the techniques disclosed herein to detect non-cardiac noise. Atrial tachyarrhythmia episodes can be suppressed based on non-cardiac noise detection.

[0028] More generally, the disclosed techniques can be used in any device configured to determine heart rate from sensed cardiac electrical signals, such as a fitness tracker, watch, or other heart rate monitor. When cardiac electrical signals are disrupted by non-cardiac noise, the determined heart rate may be incorrect, for example, overestimated because non-cardiac noise signals are incorrectly sensed as cardiac events.

[0029] 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 rapid arrhythmia, and in some examples, a cardiac pacing pulse. However, the techniques disclosed herein for detecting non-cardiac noise can be implemented in other cardiac devices configured to sense cardiac events and, for example, determine the cardiac event interval or heart rate, for use in determining heart rate or rhythm and controlling cardiac electrical stimulation therapy.

[0030] 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 examples, 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.

[0031] 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.

[0032] 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.

[0033] Electrodes 24 and 26 (and in some examples, 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 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.

[0034] 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.

[0035] 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 examples, the housing 15 of the ICD 14 is used in combination with one or more electrodes of the sensing electrode vectors 24, 26, 28, and / or 30. Various sensing electrode vectors utilizing combinations of electrodes 24, 26, 28, and 30 with the housing 15 are described below for sensing first and second cardiac electrical signals using corresponding first and second sensing electrode vectors selectable by sensing circuitry included in the ICD 14.

[0036] 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.

[0037] 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. The techniques disclosed herein are not limited to a specific path for the lead 16 or the final location of the electrodes 24, 26, 28, and 30.

[0038] Electrical conductors (not shown) extend from the lead connector at the proximal lead end 27 through one or more cavities of the elongated lead body 18 of the lead 16 to electrodes 24, 26, 28, and 30 positioned along the distal portion 25 of the lead body 18. The elongated electrical conductors included within the lead body 18 (which may be separate, corresponding insulated conductors within the lead body 18) are each electrically coupled to the respective defibrillation electrodes 24 and 26 and pacing / sensing electrodes 28 and 30. The respective conductors electrically couple the electrodes 24, 26, 28, and 30 to the circuitry of the ICD 14 (such as treatment delivery circuitry and / or sensing circuitry) via connectors in the connector assembly 17 (including associated electrical feedthroughs through the housing 15). The electrical conductors transmit treatment from the treatment delivery circuitry within the ICD 14 to one or more of the defibrillation electrodes 24 and 26 and / or the pacing / sensing electrodes 28 and 30, and transmit 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.

[0039] 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.

[0040] 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.

[0041] 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.), which is incorporated herein by reference in its entirety. 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.

[0042] 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 rapid arrhythmias according to any of a variety of rapid arrhythmia detection techniques. Example techniques for detecting rapid arrhythmias are described in conjunction with the flowcharts presented herein.

[0043] The ICD 14 generates and delivers electrical stimulation therapy in response to the detection of rapid arrhythmias (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 ATP in response to VT detection, and in some cases may deliver ATP prior to 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 CV / DF shocks alone or in combination with 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.

[0044] ICD 14 is shown subcutaneously implanted on the left side of patient 12 along thoracic cavity 32. In some cases, ICD 14 may be implanted between the left posterior axillary line and the left anterior axillary line of patient 12. However, ICD 14 may be implanted in other subcutaneous or submuscular locations 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.

[0045] 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.

[0046] 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.

[0047] 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, results of device diagnostics, and the history of detected rhythmic episodes and delivered treatments, can be retrieved by the external device 40 from the ICD 14 upon request.

[0048] 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 monitoring 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 noise detection according to the techniques disclosed herein into ICD 14.

[0049] 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 patient 12 with system 10 implanted. Figure 2B This is a side view of patient 12 with system 10 implanted. Figure 2C This is a transverse view of a patient 12 with system 10 implanted. In this arrangement, the cardiovascular external lead 16 of system 10 is at least partially implanted below the sternum 22 of patient 12. Lead 16 extends subcutaneously or submuscularly from ICD 14 toward xiphoid process 20, and bends or turns within the anterior mediastinum 36 in a substernal position near xiphoid process 20 and extends upward.

[0050] 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”.

[0051] 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.

[0052] In various example implantation sites of the cardiovascular lead 16 and electrodes 24, 26, 28, and 30, the cardiac signal sensed by the ICD 14 may be contaminated by skeletal muscle electromyography (EMG) and / or environmental EMI. In some cases, repetitive motion or sustained muscle contraction may generate EMG noise pulses that contaminate the cardiac electrical signal sensed by the ICD 14. Some noise pulses may be oversensed as cardiac events, such as R waves, leading to erroneous heart rate determination. In some cases, the noise detection algorithm may fail to detect the noise, even when some noise pulses are oversensed as cardiac events. If the noise detection algorithm does not detect the noise, but some noise pulses are oversensed as cardiac events, the heart rate may be overestimated. False rapid arrhythmia detections may be made, or bradycardia pacing may be suppressed when actually needed. When the noise detection algorithm does not detect the noise, erroneously sensed cardiac events may go unchecked. Therefore, the techniques disclosed herein provide improvements in non-cardiac noise detection by including gain adjustments that can be used to increase the amplitude of noise pulses in the cardiac electrical signal to allow for easier detection of noise pulses as described below. The increased gain signal can be used to detect noise without changing the gain of the signal used to sense cardiac events. In this way, noise pulses present in the cardiac electrical signal can be detected and identified as noise more reliably, so that corrective action can be taken if the noise pulse is missensed (oversensed) as a cardiac event.

[0053] Figure 3 This is based on a conceptual diagram of an example ICD 14. The electronic circuitry system is enclosed within a housing 15. Figure 3 The ICD (illustrated schematically as electrodes) includes software, firmware, and hardware that collaboratively monitor cardiac electrical signals, determine when electrical stimulation therapy is needed, and deliver therapy as needed based on a programmed therapy delivery algorithm and control parameters. The ICD 14 can be coupled to 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.

[0054] 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 3The 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.

[0055] Figure 3 The 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 the detection of noise for the detection of events based on cardiac event interval suppression sensing or for the prevention of rapid arrhythmias 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 operates instructions and control signals stored in memory 82, such as blanking intervals and timing periods, and sensing threshold amplitude signals sent from control circuitry 80 to sensing circuitry 86.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] A cardiac electrical signal sensing circuit 86 (also referred to herein as "sensing circuit" 86) may be selectively coupled to electrodes 28, 30 and / or housing 15 to monitor the electrical activity of a patient's heart. Sensing circuit 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. In some examples, sensing circuit 86 may be able to selectively receive cardiac electrical signals from at least two sensing electrode vectors from 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 circuit 86. Sensing circuit 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 circuit 80. For example, the sensing circuit 86 may include a switching circuit system for selecting which of the electrodes 24, 26, 28, 30 and housing 15 is coupled to the first sensing channel 83, and which electrode is coupled to the second sensing channel 85 of the sensing circuit 86.

[0060] 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 time period 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.

[0061] 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 sensed event signal to trigger the storage of time segments of the cardiac electrical signal for processing and analysis, in order to detect noise in the cardiac electrical signal as described below. In some examples, the sensing circuit 86 senses at least one cardiac electrical signal received by 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, where each cardiac electrical signal segment corresponds to a detected R-wave, for noise detection processing and analysis. A single cardiac electrical signal sensed by the first sensing channel 83 can be used for R-wave detection and analysis of cardiac electrical signal segments for noise detection. In other examples, an R-wave is detected from a first cardiac electrical signal sensed by the first sensing channel 83 and segments of a second cardiac electrical signal sensed by a second sensing channel 85 can be buffered, where each segment corresponds to an R-wave sensed from the first cardiac electrical signal. Noise detection can be based on segmented analysis of the second cardiac electrical signal. The second cardiac electrical signal can be received via a different pair of sensing electrodes 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 can be received by the same pair of sensing electrodes 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.

[0062] Memory 82 can be configured to store a predetermined number of cardiac electrical signal segments, such as at least one, two, three, or other numbers of cardiac electrical signal segments, in a cyclic buffer under the control of control circuitry 80. Each segment can be written to memory 82 over a time interval extending before and after the R-wave sensing event signal generated by the first sensing channel 83. When detection based on a predetermined number of rapid arrhythmia intervals requires confirmation of the R-wave sensed by the first sensing channel 83, control circuitry 80 can access the stored cardiac electrical signal segments, which can precede rapid arrhythmia detection. In some examples, the R-wave sensed by the first sensing channel 83 can be suppressed when a relevant cardiac electrical signal segment (including the time of the sensed R-wave) buffered from the second sensing channel 85 is classified as a noise segment. In other examples, the sensed R-wave can be used to determine the RRI that can be counted as a rapid arrhythmia interval, but only when a threshold number of cardiac electrical signal segments are classified as noise segments if rapid arrhythmia detection criteria are met. (See below for example in conjunction with...) Figures 5 to 8 This describes a method for classifying cardiac electrical signals into noise segments.

[0063] The control circuit 80 also uses R-wave sensing event signals to determine the RRI (Relaxed Intent Rate) to detect rapid arrhythmias and determine treatment needs. The RRI is the time interval between continuously sensed R waves and can be determined between consecutive R-wave sensing event signals received by the control circuit 80 from the sensing circuit 86. For example, the control circuit 80 may include a timing circuit 90 for determining the RRI between consecutive R-wave sensing event signals received from the sensing circuit 86 and for controlling various timers and / or counters for controlling the timing of treatment delivery by the treatment delivery circuit 84. The timing circuit 90 may additionally set time windows (such as morphological template windows, morphological analysis windows) or perform other timing-related functions of the ICD 14, including synchronizing cardioversion shocks or other treatments delivered by the treatment delivery circuit 84 with sensed cardiac events.

[0064] Control circuitry 80 is also shown to include a rapid arrhythmia detector 92 configured to analyze signals received from sensing circuitry 86 to detect rapid arrhythmias. The rapid arrhythmia detector 92 can detect rapid arrhythmias based on cardiac events detected from sensed cardiac electrical signals that meet rapid arrhythmia criteria, such as a threshold number of detected cardiac events occurring within a rapid arrhythmia interval. In some examples, rapid arrhythmia detection based on the detection of non-cardiac noise using techniques disclosed herein can be suppressed by detecting the threshold number of detected cardiac events each occurring within a rapid arrhythmia interval. The rapid arrhythmia detector 92 can 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. The rapid arrhythmia detector 92 may include a comparator and a counter for counting RRIs falling into various rate detection zones as determined by timing circuitry 90 to determine ventricular rate or to perform other rate-based or interval-based assessments of R-wave sensing event signals, thereby detecting and distinguishing VT and VF.

[0065] For example, the rapid arrhythmia detector 92 can compare the RRI determined by the timing circuit 90 with one or more rapid arrhythmia detection interval zones (such as tachycardia detection interval zones and fibrillation detection interval zones). RRIs falling within a detection interval zone 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 rapid arrhythmia 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. For VT or VF to be detected, the corresponding VT or VF interval counter needs to reach a threshold "Number of Detection Intervals" (NID).

[0066] 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. As an example, the NID required 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 NID threshold, the tachyarrhythmia detector 92 can detect ventricular tachyarrhythmias. The NID can be programmable, ranging from as low as 12 to as high as 40, without any limitations. VT intervals 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.

[0067] The rapid arrhythmia 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. Examples of parameters that can be determined from cardiac electrical signals received from sensing circuit 86 for detection that may lead to the prevention of VT or VF detection are described below.

[0068] To support these additional analyses, sensing circuitry 86 can transmit digitized electrocardiogram (ECG) signals to control circuitry 80 for morphological analysis performed by rapid arrhythmia 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 the digitized signals may include determining signal characteristics for detecting noise present in the cardiac electrical signals. When noise is detected, RRI-based rapid arrhythmia detection can be stopped to prevent rapid arrhythmia treatment. Alternatively, rapid arrhythmia treatment can be stopped in response to a rapid arrhythmia detection that also detects noise.

[0069] The treatment 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 treatment delivery circuit 84 according to control signals received from the control circuit 80. The control circuit 80 may include various timers or counters that control when to deliver cardiac pacing pulses. 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 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.

[0070] 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 circuit, such as an H-bridge, which determines the electrodes used for delivering cardiopulmonary bypass or defibrillation pulses and the pulse waveform.

[0071] In some examples, the high-voltage treatment circuit configured to deliver CV / DF shock pulses may be controlled by control circuitry 80 to deliver pacing pulses, such as ATP, post-shock pacing pulses, or ventricular pacing pulses. In other examples, treatment delivery circuitry 84 may include low-voltage treatment circuitry for generating and delivering pacing pulses for various pacing needs.

[0072] It should be recognized that the method for detecting noise disclosed herein can be implemented in a medical device that monitors cardiac electrical signals by 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.

[0073] 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.

[0074] 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.

[0075] In some examples, the sensing circuit 86 includes a second sensing channel 85 for sensing a second cardiac electrical signal. For example, the second sensing channel 85 may receive raw cardiac electrical signals 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 the housing 15. In some examples, the second sensing channel 85 may be selectively coupled to other sensing electrode vectors, which may form relatively long bipolars having a greater interelectrode distance or spacing than the sensing electrode vectors coupled to the first sensing channel 83. In some cases, the second sensing electrode vectors may, but not necessarily, be approximately orthogonal to the first channel sensing electrode vectors. 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 can be used by control circuitry 80 for analysis and noise detection. Compared to the relatively short bipolar coupled to the first sensing channel, the long bipolar coupled to the second sensing channel 85 can provide a relatively far-field or more global cardiac signal. 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 have only one common electrode, but not both.

[0076] 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, amplifiers, or other signal processing circuitry systems, such that two different signals are sensed by the respective sensing channels 83 and 85, and different analyses can be performed on these 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 the 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 circuitry 80 for analysis for noise detection. 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 received via the same sensing electrode vector in some examples.

[0077] exist Figure 4In 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.

[0078] 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 can be Σ-Δ converters (SDCs), but other types of ADCs can also be used. In some examples, the outputs of ADCs 63 and 73 can 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.

[0079] 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 to pass cardiac electrical signals, such as the R wave typically found in this frequency range. Filter 74 of the second sensing channel 85 may have a bandpass of approximately 2.5 to 100 Hz. In some examples, the second sensing channel 85 may also include a notch filter 76 to filter noise signals at 60 Hz or 50 Hz.

[0080] 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 the 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.), which is incorporated herein by reference in its entirety. In short, the multi-level sensing threshold may have an initial sensing threshold held for a period of time, 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 the descending time interval, which may be 1 second to 2 seconds long. After the fall 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.

[0081] 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.

[0082] In some examples, the second sensing channel 85 may include a filter 77. Filter 77 may be a first-order derivative filter for receiving a notch-filtered signal from a notch filter 76 and generating a first-order differential signal 81 (e.g., where the i-th sample of the first-order differential signal is the difference between the i-th sample point of the notch-filtered signal and the first i-1 sample points of the notch-filtered signal). In other examples, higher-order differential signals, such as second-order or higher-order differential signals, may be output by the derivative filter 77. In still other examples, the derivative filter 77 may be a high-pass filter with a sharp cutoff frequency, such as, for example, a 50Hz, 60Hz, 80Hz, or 100Hz high-pass filter. Filter 77 may be configured to generate a filtered signal that removes low-frequency cardiac event signals without removing higher-frequency noise pulses, which may be 50Hz or higher. The differential (or filtered) signal 81 may be buffered in a memory 82 and passed to control circuitry 80 for processing and analysis to detect noise contamination presumed to be present in both the first cardiac electrical signal 68 and the second cardiac electrical signal 78. In some examples, the differential signal 81 may be buffered in memory 82 and rectified by rectifier 75 before being processed and analyzed by control circuitry 80. In other examples, the differential signal 81 is buffered in memory 82 without rectification and processed and analyzed by control circuitry 80 to detect noise contamination as described below.

[0083] Control circuit 80 is configured to detect rapid arrhythmias 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 rapid arrhythmias when a detection threshold number of cardiac events each occur with a rapid arrhythmia interval. When a lower threshold number of rapid arrhythmia intervals has been detected before reaching the NID rapid arrhythmia 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 rapid arrhythmia intervals is determined based on a first cardiac electrical signal sensed by first sensing channel 83, and when a lower threshold number of rapid arrhythmia intervals is detected, cardiac electrical signal segments are buffered from a second cardiac electrical signal received by control circuit 80 from second sensing channel 85 for noise analysis. As described below, analysis of the second cardiac electrical signal segments may be performed for use in detecting non-cardiac noise before reaching a detection threshold number of rapid arrhythmia intervals (NID). In other examples, a single cardiac electrical signal sensed by sensing circuit 86 is used to sense R waves to determine RRI and count rapid arrhythmia intervals, and is buffered to store cardiac electrical signal segments for use in detecting noise, wherein each buffered segment is associated with a sensed R wave.

[0084] For example, control circuit 80 may be configured to determine the maximum amplitude from each of multiple consecutive cardiac electrical signal segments to determine whether a signal-to-noise ratio (SNR) criterion is met. If so, control circuit 80 may increase signal gain to intentionally increase the amplitude of noise pulses in the cardiac electrical signal segments. By increasing signal gain, non-cardiac noise pulses can be more easily detected as noise. Increasing gain improves noise detection, allowing potential oversensitization of noise pulses as R waves, which may lead to the detection of rapid arrhythmia intervals. One or more noise metrics may be determined from the increased gain signal to determine whether a noise criterion is met. When a threshold number of cardiac electrical signal segments meet the noise criterion, the detection of rapid arrhythmias based on the threshold number of rapid arrhythmia intervals or other detection criteria may be suppressed or inhibited. In other examples, the RRI associated with cardiac electrical signal segments identified as noise contamination may be ignored and not used for counting rapid arrhythmia intervals. In some examples, time segments of the notch-filtered rectified signal 79 received from the second sensing channel 85 can be used to detect noise segments that could lead to the inhibition of rapid arrhythmia detection.

[0085] 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 4 The 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, where 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 in response to the detection of non-cardiac noise as disclosed herein, and in the detection of non-cardiac noise and the suppression or inhibition of rapid arrhythmia intervals or episodes.

[0086] Figure 5 This is a flowchart 100 of an example method for detecting non-cardiac noise in cardiac electrical signals. In the various examples presented herein, non-cardiac noise pulses, such as skeletal muscle potentials, can be oversensed by sensing circuitry 86 as R-waves (or other cardiac event signals corresponding to depolarization / repolarization of cardiac tissue). For example, when the noise pulse exceeds the R-wave detector 66 ( Figure 4When the R-wave sensing threshold is exceeded, an erroneous R-wave sensing event signal 68 may be generated at the rapid arrhythmia interval closest to the previous R-wave sensing event signal, resulting in an increase in the VT or VF interval counter. However, it should be understood that when the P-wave is sensed by the sensing circuitry of a medical device, the technique disclosed herein for detecting non-cardiac noise can be applied to oversensing noise that is likely to be detected. In this case, oversensing of non-cardiac noise pulses occurs when noise pulses in the cardiac electrical signal exceed the P-wave sensing threshold, causing the sensing circuitry to generate an erroneous P-wave sensing event signal. The erroneous P-wave sensing event signal can be counted as a rapid arrhythmia interval, toward meeting the criteria for atrial rapid arrhythmia detection. Furthermore, Figure 5 The method shown is applicable to detecting noise in any electrical signal sensed by a medical device used to monitor or detect electrophysiological event signals. The techniques in flowchart 100 can be used to detect noise signals that may disrupt the electrical signal.

[0087] At block 102, sensing circuitry 86 senses a cardiac event based on a cardiac event sensing threshold exceeded by the cardiac electrical signal. In some examples, the cardiac electrical signal is received by a first sensing channel via a sensing electrode vector in a relatively near field 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 exceed the sensed R-wave based on an R-wave sensing threshold detected by the first sensing channel 83 of sensing circuitry 86 as described above. In other medical applications, electrophysiological events, such as action potentials or depolarization or repolarization of excitable tissue, can be sensed at block 102 from electrical signals sensed by a medical device.

[0088] At block 104, control circuitry 80 may buffer segments of electrical signals in memory 82 for noise analysis in response to an electrophysiological event sensed at block 102. In response to detecting noise in the buffered signal segments associated with the sensed electrophysiological event, control circuitry 80 may perform noise analysis to suppress the sensed electrophysiological event (or suppress or prevent detection of conditions based on the sensed electrophysiological event). Control circuitry 80 may buffer signal segments in memory 82 at block 104 for further analysis and processing as described below. In some examples, the buffered signal segments originate from the same signal from which the event was detected at block 102, while in other examples the buffered signal segments are different signals, for example, sensed using different sensing electrodes and / or generated by sensing circuitry 84 using different filtering, amplification, etc., than the first signal.

[0089] The buffered segment can be a cardiac electrical signal received from the second sensing channel 85 and can be notched to attenuate 50-60Hz noise. In some examples, the second sensing channel 85 receives the cardiac electrical signal via a different sensing electrode vector to sense a second cardiac electrical signal different from the first cardiac electrical signal used to sense a cardiac event at block 102. In other examples, the same sensing electrode vector is used to receive a single cardiac electrical signal for both sensing a cardiac event and buffering a segment of the cardiac electrical signal for noise detection. When using the same sensing electrode vector, different filtering or other signal processing can be used to generate a first sensed cardiac electrical signal for detecting a cardiac event at block 102 and a second sensed cardiac electrical signal for buffering the signal segment at block 104 for noise analysis.

[0090] The segments of the second cardiac electrical signal can be buffered during a predetermined time interval, which includes the time point from when the first cardiac electrical signal senses a cardiac event. For example, in response to the first sensing channel 83 (see...) Figure 4 Upon receiving the R-wave sensing event signal 68, the control circuit 80 can 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. This time segment can extend from a time point earlier than the time when an R-wave sensing threshold is exceeded to a time point later than the time point when the first sensing channel 83 generates the R-wave sensing event signal 68. The duration of this time segment can be from 300 ms to 500 ms, for example, a duration of 360 ms, including sample points before and after an R-wave sensing event signal. For example, as combined with... Figure 6 As described, when the sampling rate is 256Hz, the 360ms segment may include 92 sample points, of which 24 sample points occur after the stored R-wave sensing event signal of the trigger signal segment and 68 sample points extend from the R-wave sensing event signal that is earlier in time than the R-wave sensing event signal.

[0091] At block 106, control circuitry 80 determines a metric of signal strength. Determining the metric of signal strength may include determining the maximum signal amplitude during a buffered signal segment associated with the sensed electrophysiological event. For example, control circuitry 80 may determine the signal strength metric as the maximum amplitude of a buffered cardiac signal during a signal segment. In one example, control circuitry 80 determines the maximum amplitude of a rectified signal segment (or the absolute maximum amplitude of a non-rectified signal segment). As further described below, the maximum signal amplitude of each of a plurality of buffered signal segments may be determined, and the maximum signal amplitude among the maximum signal amplitudes may be used as a signal strength metric to determine whether a signal-to-noise ratio criterion is met at block 110.

[0092] At block 108, control circuitry 80 determines a measure of the intensity or amplitude of possible noise during the buffered signal segmentation. In one example, control circuitry 80 determines the noise intensity measure by determining a differential signal from the buffered signal segmentation. For example, control circuitry 80 can determine a first-order differential signal by determining the difference between each pair of consecutive sample points of a notch-filtered cardiac electrical signal segment. In other examples, higher-order differential signals, such as second-order or higher-order differential signals, can be determined. Alternatively, the differential signal can be generated by a high-pass filter with a sharp-angle cutoff frequency, for example, a cutoff frequency of at least 50 Hz or 60 Hz when the sampling frequency is 256 Hz. In one example, the maximum absolute amplitude of the differential signal of the buffered signal segment is determined as a noise intensity measure at block 108.

[0093] At block 110, control circuitry 80 determines whether a signal-to-noise ratio (SNR) criterion is met based on a signal strength metric and a noise intensity metric. In some examples, control circuitry 80 may determine whether the SNR criterion is met based on a signal strength metric and / or a noise intensity metric determined from multiple signal segments, which may be sequentially buffered signal segments. For example, the maximum signal strength metric determined from multiple signal segments and the noise intensity metric determined from the current signal segment may be compared with the SNR criterion to determine whether the current signal segment is detected as a noise segment. The number of signal segments from which control circuitry 80 determines the maximum signal strength metric may occur during a predetermined time interval expected to include at least one real electrophysiological event, such as at least one real R wave, as described below. Figure 6 Further described. Signal-to-noise ratio (SNR) standards may include one or more requirements, applied individually or in combination to one or more signal strength measures and / or one or more noise strength measures, for example, as one or more ratios of signal strength measures to noise strength measures.

[0094] In some examples, the signal-to-noise ratio (SNR) metric includes a signal strength metric and a noise strength metric. The signal strength metric can be applied to a maximum signal strength measure, such as the maximum amplitude determined from one or more preceding most recent buffered signal segments. The maximum signal strength measure is an indication of the amplitude of the expected cardiac event signal that may have occurred during the preceding signal segments. The noise strength metric can be applied to a noise strength measure of the currently buffered signal segment, such as the maximum amplitude of the differential signal in the currently buffered signal segment. In this example, control circuitry 80 identifies the maximum amplitude from the most recent buffered signal segment as an indication of the cardiac event signal strength and identifies the maximum amplitude of the differential signal in the currently buffered signal segment as an indication of the signal strength in the currently buffered signal segment. At block 110, control circuitry 80 uses these measures to determine when the SNR metric is met. In other examples, control circuitry 80 may determine a ratio of the maximum signal strength measure to the maximum noise strength measure and compare this ratio to a minimum ratio threshold to determine when the SNR metric is met.

[0095] Figure 6 Figure 200 illustrates a first cardiac electrical signal 202 and a second cardiac electrical signal 232, analyzed according to a method for determining whether a signal-to-noise ratio criterion is met in order to increase the gain of the differential signal. In the first cardiac electrical signal 202, two genuine R waves 204 and 206 are sensed by a first sensing channel 83, generating corresponding R-wave sensing event signals 208 and 210. However, due to non-cardiac noise present in the first cardiac electrical signal 202, two noise pulses 212 and 214 are each sensed by an R-wave detector 66, generating erroneous R-wave sensing event signals 216 and 218. Each of the R-wave sensing event signals 208, 210, 216, and 218, indicating a ventricular sensing event, triggers a segment of the second cardiac electrical signal 232 during corresponding time intervals 233, 235, 241, and 243.

[0096] Each time interval 233, 235, 241, and 243 may extend before and after the times of the corresponding R-wave sensing event signals 208, 210, 216, and 218, such that the corresponding buffered second cardiac electrical signal segment includes sample points before and after the time of the corresponding R-wave sensing event signal. As indicated above, in one example, the duration of each time interval 233, 235, 241, and 243 is approximately 360 ms, such that when the sampling rate is 256 Hz, the corresponding second cardiac electrical signal segment buffered during this time interval includes 92 sample points, of which 24 sample points occur after the stored R-wave sensing event signal of the trigger signal segment and 68 sample points extend from the R-wave sensing event signal that is temporally earlier than the R-wave sensing event signal. Each cardiac electrical signal segment corresponding to the corresponding time interval 233, 235, 241, or 243 contains the time of a single R-wave sensing event signal.

[0097] Control circuit 80 determines the maximum absolute amplitude 234 of the buffered cardiac electrical signal segment during time interval 233, the maximum absolute amplitude 242 of the buffered cardiac electrical signal segment during time interval 241, and the maximum absolute amplitudes 244 and 236 of the buffered cardiac electrical signal segment during corresponding time intervals 243 and 235. This process of determining the maximum amplitude of each buffered second cardiac electrical signal segment can correspond to the above... Figure 5 A measure of the R-wave signal intensity is defined at box 106. These maximum amplitudes 234, 242, 244, and 236 can be stored in a first-in-first-out (FIFO) buffer, such that the maximum amplitude of each of the multiple second cardiac electrical signal segments is buffered in a rolling FIFO buffer. The buffer can store a predetermined number of maximum amplitudes, for example, 3 to 10 maximum amplitudes corresponding to the most recent 3 to 10 cardiac electrical signal segments and associated R-wave sensing event signals.

[0098] In other examples, the maximum amplitude buffer may store each of the maximum amplitudes determined based on a second cardiac electrical signal segment buffered in response to each R-wave sensing event signal during at least predetermined time intervals 252, 254. In some examples, the predetermined time interval, referred to as the maximum amplitude buffer time interval, may be one to two seconds long. The maximum amplitude buffer time interval is selected such that at least one true R wave is expected to occur during time intervals 252 or 254. For example, when time intervals 252, 254 are 1.2 seconds, a true R wave (e.g., R wave 234 or R wave 236) is expected to occur within 1.2 seconds when the true heart rate is as low as 50 beats per minute. The maximum amplitude buffer time interval may correspond to or be based on a lower pacing rate time interval or the patient's expected resting heart rate. Each maximum amplitude determined from each cardiac electrical signal segment buffered during 1.2 seconds, 1.5 seconds, 2.0 seconds, or other selected time intervals may be stored in the maximum amplitude buffer. In this scenario, the number of maximum amplitudes stored in the maximum amplitude buffer can be variable because, depending on how many non-cardiac noise pulses are oversensed and the actual ventricular rate, different numbers of R-wave sensing event signals may occur during each fixed predetermined time interval 252, 254, and thus different numbers of cardiac electrical signal segments. When the ventricular blanking interval is set to 150 ms and the maximum amplitude buffer time interval is set to 1.2 seconds, the maximum possible number of R-wave sensing event signals is eight, resulting in eight corresponding cardiac electrical signal segments and eight maximum amplitudes stored in the maximum amplitude buffer.

[0099] In the illustrated example, the maximum amplitude buffering interval 252, which can be 1.2 seconds long or of another choice, extends from the most recent cardiac electrical signal segment (or from the associated R-wave sensing event signal 218) buffered during interval 243 and includes any preceding cardiac electrical signal segments (or maximum amplitudes) already buffered within the maximum amplitude buffering interval 252. In other examples, the maximum amplitude buffer in memory 82 is configured to store up to a fixed number of maximum amplitudes on a first-in, first-out basis, such as eight maximum amplitudes, each with a corresponding timestamp. When a maximum amplitude is determined for a given cardiac electrical signal segment, the maximum amplitude may be buffered in memory 82 along with its timestamp. The maximum amplitudes that occur within the maximum amplitude buffering interval 252 from the current maximum amplitude timestamp and are stored in the maximum amplitude buffer along with their timestamps can be evaluated to identify likely R waves from among the maximum amplitudes.

[0100] Therefore, for each cardiac electrical signal segment, the maximum amplitude can be identified along with a timestamp that occurred within a maximum amplitude buffer interval earlier than the current maximum amplitude (or the current buffered signal segment). In the example of maximum amplitude buffer interval 252, maximum amplitude 244, as well as earlier maximum amplitudes 234 and 242 that occurred within maximum amplitude buffer interval 252, are evaluated to identify the maximum amplitude with the highest probability of becoming an R-wave during the maximum amplitude buffer interval. In other examples, the maximum amplitude can be evaluated from the beginning of the maximum amplitude, the R-wave sensing event signal, or the cardiac electrical signal segment and time-wise forward rather than backward as described herein within the maximum amplitude buffer interval. However, this can delay the determination of whether the current cardiac electrical signal segment meets the signal-to-noise ratio criterion by one to two seconds of the maximum amplitude buffer interval, which can result in noise detection being later than time-wise backward from the current maximum amplitude.

[0101] The maximum amplitude 234 of the maximum amplitude buffered during the time interval 252 is identified by the control circuit 80. This maximum amplitude 234, originating from the buffered maximum amplitudes 234, 242, and 244 during the one- to two-second maximum amplitude buffering time interval 252, is presumed to be the true R-wave amplitude (corresponding to R-wave 204 in this case) and is unlikely to be a relatively low-amplitude non-cardiac noise pulse, for example, caused by skeletal muscle myoelectric potentials. The two lower maximum amplitudes 242 and 244 could be non-cardiac noise pulses oversensed as R-waves. This maximum amplitude 234 of the signal segment originating from multiple buffers can be determined by the control circuit 80 as a signal strength metric, for example, in... Figure 5 The maximum signal amplitude may need to be determined from multiple consecutively buffered signal segments, as shown in box 106. Therefore, determining the signal strength metric may require identifying the maximum signal amplitude from multiple consecutively buffered signal segments.

[0102] The next R-wave sensing event signal 210 triggers the buffering of the next cardiac electrical signal segment (during time interval 235), and the maximum amplitude 236 during the next cardiac electrical signal segment is buffered in the first-in-first-out maximum amplitude buffer, thereby replacing the oldest maximum amplitude 234. Other maximum amplitudes 242 and 244 that occurred most recently during the previous cardiac electrical signal segments (associated with time intervals 241 and 243, respectively) within a fixed predetermined time interval 254 remain in the maximum amplitude buffer. Now, the largest maximum amplitude stored in the maximum amplitude buffer is the maximum amplitude 236, presumably the true R-wave amplitude (corresponding to R-wave 206), because it is the highest amplitude stored in the maximum amplitude buffer.

[0103] In this way, the maximum amplitude of each buffered cardiac electrical signal segment occurring during the shift intervals, as represented by intervals 252 and 254, is buffered, such that the likely true R-wave amplitude can be identified as an indicator of R-wave signal intensity during each time interval 252, 254. The maximum amplitude can be determined from shift intervals 252, 254 and... Figure 5 The signal strength threshold at box 110 is compared to determine whether the first criterion of the signal-to-noise ratio standard is met. In one example, the signal strength threshold is set as a percentage or portion of the ADC range of the sensing channel. For example, in an example of a segment of a rectified cardiac electrical signal from a second cardiac electrical signal buffer sensed by the second sensing channel 85, ADC 73 may have a range of 127 ADC units. The maximum amplitude may be compared to 30%, 40%, 50%, or other percentages or fractions of the maximum ADC range. In one example, the maximum amplitude is compared to one-third of an ADC range of 127 units or 42 ADC units. When the maximum absolute maximum amplitude is greater than 42 ADC units, the R-wave signal strength is considered to meet the first criterion of the signal-to-noise ratio standard. Figure 5 The signal-to-noise ratio criterion applied at box 110 is one standard. In other examples, the signal strength threshold can be set based on previously confirmed R-wave amplitude, the average amplitude of sample points during a segment of cardiac electrical signals or another time interval, or based on another reference amplitude. The signal strength threshold can be selected such that a signal strength metric greater than the threshold is likely to correspond to a relatively high R-wave amplitude or a real electrophysiological event being sensed by a medical device.

[0104] In addition to determining whether the signal strength standard is met at box 110, the control circuit 80 can also... Figure 5 The control circuit 80 determines whether the noise intensity criterion is met at box 110. In one example, the control circuit 80 determines the noise intensity metric by determining the first-order differential signal of the current cardiac electrical signal segment. Figure 6 Using time interval 252 as an example, the first-order differential signal of the most recent cardiac electrical signal segment (corresponding to time interval 243) is determined. The maximum amplitude of this differential signal is determined and compared to a noise intensity threshold. The noise intensity threshold can also be defined as a percentage or fraction of the ADC range. In one example, the maximum amplitude of the differential signal of the most recent cardiac electrical signal segment in time interval 252 is compared to approximately 10% (or other percentage) of the ADC range as a percentage or fraction lower than the signal intensity threshold applied to the maximum amplitude to determine whether a signal intensity criterion is met. For example, when the ADC range is 127 ADC units, the noise intensity threshold could be 13 ADC units. The noise intensity criterion applied at box 110 is met when the maximum amplitude of the differential signal of the current segment 243 is less than the noise intensity threshold of 13 ADC units.

[0105] In some examples, the lowest maximum amplitude buffered in a FIFO buffer, or the maximum amplitude of the currently buffered signal, may be assumed to be an oversensitized noise signal and used as a noise intensity measure. However, the lowest maximum amplitude may be a real event signal if lower frequencies are not segmented from the buffered signal corresponding to the frequency of the real electrophysiological event signal to remove possible real electrophysiological event signals (e.g., real R-wave signals) before determining the noise intensity measure. For example, the lowest maximum amplitude may be a low-amplitude R-wave or fibrillation wave that should not be presumed to be a noise impulse or suppressed as possible noise.

[0106] When in Figure 5 When both the signal strength criterion and the noise strength criterion are met at box 110, the control circuit 80 determines that the signal-to-noise ratio (SNR) criterion is met. Typically, the signal strength criterion is met when the inferred R-wave amplitude of the most recent cardiac electrical signal segment is greater than a predetermined portion of the ADC range or another selected signal strength threshold. The noise strength criterion is met when the maximum amplitude of the current differential signal segment is less than a predetermined portion of the ADC range or another selected noise strength threshold. In other examples, the control circuit 80 may determine the ratio of the maximum signal strength metric to the current noise strength metric and compare this expected SNR to a minimum acceptable SNR threshold. When the ratio of the maximum signal strength metric to the current noise strength metric is greater than the minimum ratio threshold, the control circuit 80 determines that the SNR criterion is met.

[0107] When the signal-to-noise ratio (SNR) criterion is met, control circuit 80 increases the gain of the cardiac electrical signal used to detect noise at block 112, for example, by doubling it. For example, control circuit 80 may adjust the gain of the differential signal of the current cardiac electrical signal segment 243 at block 112 before determining the noise metric from the differential signal segment at block 114. It should be understood that the gain increase may be applied to the cardiac electrical signal segment before or after the segmentation of the differential signal. The gain of a high-pass filtered signal, a first-order or higher-order differential signal, or any cardiac electrical signal segment being used by control circuit 80 to determine the noise metric may be adjusted at block 112 to increase the amplitude of noise pulses that may be present in the signal. When the SNR criterion is not met at block 110, control circuit 80 does not adjust the gain of the signal used to determine the noise metric and may proceed directly to block 114 without changing the signal gain.

[0108] Control circuit 80 determines a noise metric from the current signal segment at block 114 to detect that segment as a noise segment (or not a noise segment). In one example, control circuit 80 may determine a noise impulse count as a noise metric. The noise impulse count can be determined by combining the following... Figure 7As described, the noise metric is determined by counting pulses defined by consecutive zero-crossings of the differential signal segments. In other examples, control circuitry 80 may determine the noise metric by: counting the number of “swings” or oscillations of the signal during the signal segments; counting the number of inflection points in the signal segments; counting the number of peaks; counting the number of threshold crossovers; determining the integral or sum of the amplitude of the rectified sample point over the signal segments; determining the average amplitude over the signal segments; determining the high-frequency content of the signal; detecting episodes or intervals where the frequency is continuously above a noise frequency threshold; or other metrics related to the number and / or amplitude of noise pulses in the signal segments. In other examples, a noise detector may be included in sensing circuitry 86 or control circuitry 80 configured to detect noise pulses based on the amplitude and / or frequency content of the signal. For example, the noise detector may detect the duration interval of high-frequency content associated with noise disruption in cardiac electrical signals (e.g., intervals as low as 100 ms or less, intervals of 100 to 500 ms or longer). After increasing the gain of the signal segments used for noise detection, medical devices can utilize various noise detection techniques to detect noise pulses from the increased gain signal.

[0109] In the next cardiac electrical signal segment during time interval 235, the maximum amplitude of the differential signal is likely to exceed the noise intensity threshold due to the presence of a large real R-wave signal associated with peak amplitude 236. In this case, the maximum amplitude of the current differential signal is greater than the noise intensity threshold. Therefore, the signal-to-noise ratio criterion for time interval 254 is not met because the noise intensity criterion is not met. The gain of the differential signal during time interval 235 remains unchanged, and control signal 80 advances to block 114 to determine the noise metric from the differential signal of the cardiac electrical signal segment during time interval 235 without gain adjustment. (See below for further details.) Figure 7 The description follows an example to determine the noise metric at box 114.

[0110] Control circuit 80 determines at block 116 when a noise criterion is met based on the determined noise metric and may classify the current cardiac electrical signal segment as a noise segment at block 118. When the noise criterion is not met at block 116, the current cardiac electrical signal segment is not classified as a noise segment. The process may return to block 102 to wait for the next sensing event signal to repeat the process for the next electrical signal segment buffered in response to the next sensing event signal.

[0111] Figure 7This is a flowchart 300 illustrating methods for determining noise metrics and classifying cardiac electrical signal segments as noisy or non-noisy segments, based on some examples. In some examples, the noise metric may be determined from a first-order (or other higher-order) differential signal based on notch-filtered cardiac electrical signal segments buffered from a second sensing channel 85. Figure 5 Analyze the differential signal at box 114 to determine the noise metric, instead of as described above when... Figure 5 The gain is changed when the signal-to-noise ratio standard is not met at position 110. Figure 5 When the signal-to-noise ratio criterion is met at box 110, the noise metric is determined from the differential signal after increasing the gain of the differential signal, for example, doubling the gain.

[0112] At block 302, control circuitry 80 can determine the zero-crossing points of segments of the differential signal. The differential signal can be received and buffered from second sensing channel 85 as described above, or determined by control circuitry 80 based on segments of cardiac electrical signals buffered from second sensing channel 85. Zero-crossing points can be determined by identifying a pair of sample points of the differential signal crossing the zero-crossing point, the pair including a sample point (positive or negative) immediately preceding the zero-crossing point and a second sample point (negative or positive) immediately following the zero-crossing point. The sample point with the smallest absolute value in this pair is identified by control circuitry 80 and set to zero amplitude to delineate the zero-crossing point and define the end point of a signal pulse and the start point of the next consecutive signal pulse. In some cases, one of the sample points in the pair at the zero-crossing point may have zero amplitude, and the second sample point may be positive or negative. The zero-amplitude sample point can be selected as the zero-crossing point defining the end point of a signal pulse and the start point of the next signal pulse. Zero-crossing sample points are separated and defined as follows: Figure 8 The diagram shows a continuous pulse of the differential signal.

[0113] Figure 8 This is a graphical representation 400 of the cardiac electrical signal segment 401 and the corresponding first-order differential signal 410. (See above for details.) Figure 6 As typically described, cardiac electrical signal segment 401 is buffered during time segment 402 in response to an R-wave sensing event signal. The R-wave sensing event signal may be associated with a real R-wave or an oversensitized noise signal. The first-order differential signal 410 of cardiac electrical signal segment 401 is determined by hardware, firmware, and / or software included in sensing circuitry 86 and / or control circuitry 80 for analysis to detect noise contamination. A pair of sample points 404a and 404b includes the last sample point 404a before the zero-crossing of the first-order differential signal 410 and the earliest sample point 404b after the zero-crossing. The absolute values ​​of sample points 404a and 404b are compared by control circuitry 80, and... Figure 7 The minimum absolute value sample point at frame 302 is set to zero amplitude to define the continuous pulse of the differential signal 410.

[0114] Continue to refer to the diagram Figure 7 and Figure 8 Differential signals in Figure 7 The rectifier at frame 304 is used to generate Figure 8 The rectified differential signal 420 is shown. Each pulse of the rectified differential signal 420, such as pulse 422, is defined by two consecutive zero-point sample points 424 and 426. For example, the zero-point sample point 424 may be a minimum absolute amplitude sample point 404a or 404b that is set to zero to mark the end of the previous pulse and the beginning of pulse 422.

[0115] The control circuit 80 determines at block 306 whether the signal-to-noise ratio standard is met, for example, based on the combination Figure 5 and 6 The example technique described is used to determine this. The gain of the rectified differential signal 420 is increased at block 308, for example, by doubling or adding another selected factor, to produce an increased gain signal while meeting the signal-to-noise ratio criterion, for example... Figure 8 The increased gain signal 430.

[0116] When the signal-to-noise ratio (SNR) criterion is not met, the rectified differential signal 420 without gain adjustment is analyzed to detect noise segments. The process in flowchart 300 proceeds from block 306 to block 310 without increasing the gain of the rectified differential signal at block 308 before performing noise analysis. Note that the gain of the differential signal 420 is increased to increase the amplitude of non-cardiac noise pulses to facilitate noise pulse counting and noise disruption detection. The gain of the cardiac electrical signal is not increased at block 308 to facilitate R-wave sensing. R-wave sensing from the selected cardiac electrical signal is performed separately and independently of the gain adjustment applied to the differential signal 420 for noise detection. The R-wave can be sensed from the cardiac electrical signal before determining that the SNR criterion is met and before making gain adjustments to the differential signal.

[0117] At block 310, control circuitry 80 determines the pulse detection threshold amplitude. The pulse detection threshold amplitude can be determined based on the maximum amplitude analyzed by either the rectified differential signal 420 or the augmented gain signal 430 for noise detection based on a signal-to-noise ratio (SNR) criterion. For example, the maximum peak amplitude 428 of the rectified differential signal 420 (when the SNR criterion is not met) or the maximum peak amplitude 438 of the augmented gain signal 430 (when the SNR criterion is met) can be determined by determining the maximum amplitude of the corresponding differential signal 428 or 438 during time segment 402. The pulse detection threshold amplitude can be set as a fraction or percentage of the maximum amplitude (428 or 438), for example, half (or another fraction) of the maximum maximum amplitude. In one example, the pulse detection threshold amplitude is set to one-eighth of the maximum amplitude of the rectified first-order differential signal (420 or 430).

[0118] exist Figure 7 At box 312, the pulse detection threshold amplitude is compared with the suspected noise threshold amplitude. When the pulse detection threshold amplitude, i.e., the fraction or percentage of the maximum amplitude of the differential signal segment, is less than the suspected noise threshold, the control circuit 80 may classify the segment as a non-noise segment at box 320. In other examples, the maximum amplitude of the differential signal segment may be directly compared with the suspected noise threshold amplitude. When the pulse detection threshold amplitude is less than the suspected noise threshold, it is determined at box 320 that the current cardiac electrical signal segment is not contaminated by noise. The suspected noise threshold may be set to a value of 1 ADC unit in some examples, but in various examples it may be set to a value of 5 ADC units or less, or another selected threshold.

[0119] Refer again Figure 8 When the maximum pulse amplitude 428 is less than a threshold amplitude (or a pulse detection threshold amplitude set as a portion of the maximum amplitude 428 is less than a suspected noise threshold), noise in the cardiac electrical signal segment 401, which is observed as a noise pulse in the rectified differential signal 420, may go undetected without increasing the gain. However, by increasing the gain of the differential signal 420 to generate an increased gain signal 430, the pulse detection threshold amplitude, set based on the increased (e.g., doubled) maximum pulse amplitude 438, may meet or exceed the suspected noise threshold. This allows the control circuit 80 to determine that the cardiac electrical signal segment 401 is suspected of containing noise and enables analysis of the increased gain signal 430 to determine whether the corresponding signal segment 401 is corrupted by noise.

[0120] When low-amplitude electromyographic noise is present in a signal segment, such as that represented by the signal pulse of signal segment 401 and the first-order differential signal 410, oversensitization of the electromyographic noise can lead to VT or VF NID. When this electromyographic noise is not identified or detected, incorrect VT or VF detection may be made, resulting in treatment delivery. By increasing the gain of the first-order differential signal while meeting the signal-to-noise ratio criteria, the electromyographic noise pulse becomes more detectable, enabling the identification of noise-contaminated signal segments and thus avoiding incorrect VT or VF detection and unnecessary VT or VF treatment.

[0121] Refer again Figure 7When the pulse detection threshold amplitude at block 312 is greater than or equal to the suspected noise threshold, control circuit 80 identifies and counts noise pulses present in the differential signal segment to determine whether the segment contains noise. Each pulse of the rectified differential signal 420 (when the signal-to-noise ratio criterion is not met) defined by sample points between two consecutive zeros or the differential signal 430 rectified with increased gain (when the signal-to-noise ratio criterion is met) can be counted. In some examples, control circuit 80 may count a pulse as a noise pulse only if the pulse meets the noise pulse criterion at block 314.

[0122] Noise pulse criteria may include pulse amplitude criteria and / or pulse width criteria. For example, a pulse may be counted as a noise pulse at box 314 when it has an amplitude greater than the pulse detection threshold amplitude and a pulse width less than or equal to the pulse width threshold, defined by the number of sample points between consecutive zeros defining the pulse. Depending in part on the sampling rate, the pulse width threshold may be set to six or fewer sample points, but may be set to other values. When the maximum amplitude between consecutive zeros is less than or equal to the pulse detection threshold amplitude and / or the number of sample points between consecutive zeros is greater than the pulse detection threshold width, the pulse is not counted as a noise pulse at box 314.

[0123] At block 316, control circuit 80 compares the number of pulses that meet the noise pulse criterion and are therefore counted as noise pulses at block 314 with a threshold count. When the counted number of noise pulses is less than the threshold count, the cardiac electrical signal segment from which the differential signal is derived is classified as a non-noise segment at block 320. The current cardiac electrical signal segment is determined to be uncontaminated by noise. The associated R-wave sensing event signal is inferred to be a genuine sensed R-wave or at least not a non-cardiac noise signal. This determination based on the second cardiac electrical signal can be extended to the first cardiac electrical signal such that when the noise pulse count determined based on one cardiac electrical signal is less than the noise threshold count, both signals are determined to be clean signals without non-cardiac noise contamination. However, when the counted number of noise pulses is equal to or exceeds the threshold count, the cardiac electrical signal segment can be classified as a noise segment at block 322. This classification can be extended to the first cardiac electrical signal such that the R-wave sensing event signal that triggers the buffer of the second cardiac electrical signal may be an erroneously sensed R-wave due to non-cardiac noise.

[0124] In some examples, before classifying the cardiac electrical signal segment as a noise segment at block 322, control circuitry 80 may determine at block 318 whether a rapid arrhythmia morphology exists in the cardiac signal segment. The presence of a rapid arrhythmia morphology excludes classifying the signal segment as a noise segment to avoid halting rapid arrhythmia detection due to noise when signs of a rapid arrhythmia morphology are detected in the cardiac electrical signal segment. Signs of a rapid arrhythmia morphology may be detected at block 318 based on an overall morphological analysis of the signal segment. Instead of counting individual pulses in the differential signal segment, the overall morphology of the cardiac electrical signal segment (e.g., signal segment 401) may be analyzed to assess the morphology of the overall waveform 405 that the noise pulse 407 may be riding. For example, control circuitry 80 may use, for example, […]. Figure 8 The rectified signal segment 403 in the process determines the signal amplitude and signal width measurement of the overall signal segment. This is used in... Figure 7 The method for determining the overall morphological signal amplitude and overall morphological signal width measure for detecting signs of rapid arrhythmia at box 318 is described below in conjunction with Figure 1. Figure 5-10 This can be described. For example, the overall morphological signal amplitude and signal width associated with a sinusoidal fibrillation waveform can be detected as indications of rapid arrhythmia morphology.

[0125] When a rapid arrhythmia morphology is determined to be present (the "Yes" branch of box 318), the control circuit 80 may classify the cardiac electrical signal segment as a non-noise segment at box 320, even if the noise pulse count meets the threshold count used to detect non-cardiac noise at box 316. When no rapid arrhythmia morphology is detected at box 318 (the "No" branch), the cardiac electrical signal segment is detected as a noise segment at box 322 in response to the noise pulse count meeting the threshold count at box 316.

[0126] Figure 9 This is a flowchart 500 based on an example method for determining the overall morphological amplitude of cardiac electrical signal segments used to detect the morphology of rapid arrhythmias. (See above for reference.) Figure 6 Typically described, this refers to buffering each segment of the cardiac electrical signal analyzed to determine overall morphological measures. It can usually be found in... Figure 7 The method in flowchart 500 at box 318 is used to analyze cardiac electrical signal segments that may be suspected of being noise contamination signals.

[0127] At block 502, a segment of the second cardiac electrical signal stored on a trigger-based basis in response to an R-wave sensing event signal can be rectified. In some 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 502, 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 502. Figure 8 The diagram shows a rectified signal segment 403 buffered during time segment 402. The rectified signal segment obtained at block 502, for example, segment 403, may correspond to, as in combination with... Figure 7 Signal segments identified as suspicious noise segments based on the maximum amplitude of the differential signal and the number of noise pulses in the differential signal, as described.

[0128] Continue to refer to Figure 8 and Figure 9 At block 504, control circuitry 80 determines the maximum absolute amplitude 408 of the rectified notch-filtered signal segment 403. The maximum absolute amplitude 408 can be determined from all sample points spanning the selected signal segment 403. As described above, when the sampling rate is 256 Hz, a 360 ms segment of the second cardiac electrical signal can include 92 sample points, of which 24 sample points occur after the stored R-wave sensing event signal that triggered the signal segment and 68 sample points extend from the R-wave sensing event signal that is earlier in time.

[0129] At box 506, the amplitudes of all sample points in the rectified signal segment are summed, representing the area 406 of the rectified signal segment 403. At box 508, based on the maximum absolute amplitude 408 determined at box 504 and the summed sample point amplitudes (area 406) determined at box 506, the overall morphological amplitude 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 sample points in the notch filter and rectified signal segment 403 normalized to the maximum amplitude 408. For example, the NRA can be determined as four times the summed amplitude (area 406) divided by the maximum absolute amplitude 408, which can be truncated to an integer value. This NRA can be... Figure 7 Box 318 was identified as the overall morphological amplitude quantity for use in detecting rapid arrhythmia morphology based on sample points of signal segments extending before and after the R-wave sensing event signal. (If it is possible to...) Figure 8As seen in the diagram, the overall morphological amplitude determined by the maximum amplitude 408 and area 406 represents the amplitude of the potential cardiac signal waveform 405 that an individual non-cardiac noise pulse 407 might ride upon. Therefore, combined with Figure 7 The noise pulse count described is useful in detecting non-cardiac noise pulses 407 that may contaminate the overall cardiac signal waveform 405; however, the following overall morphological amplitude and overall morphological width measurements are useful in detecting the overall morphology of the potential cardiac signal waveform 405 in the signal segment 403 that may correspond to the waveform morphology of a rapid arrhythmia.

[0130] For example, the overall morphological amplitude determined by dividing the weighted area 406 by the maximum amplitude 408 can be negatively correlated with the probability that a signal segment sample point is at the baseline amplitude during time segment 402. The higher the overall morphological amplitude, the lower the probability that the signal is at the baseline amplitude at any given time point during signal segment 402. The relatively low probability that signal 403 is at the baseline during time segment 402 can be associated with rapid arrhythmia morphologies, such as ventricular fibrillation morphologies that may resemble a sinusoidal signal. When the overall morphological amplitude exceeds a threshold, the cardiac electrical signal segment is more likely to have a rapid arrhythmia morphology. When the overall morphological amplitude is less than a threshold, the probability that the signal is at the baseline amplitude at a given time point during time segment 402 of signal segment 403 is higher. The relatively high probability that a signal sample point is at the baseline during time segment 402 can be associated with a relatively narrow R-wave signal occurring during the signal segment, where the baseline amplitude portion of the signal segment occurs before and after the R-wave sensing event signal. Therefore, when no rapid arrhythmia morphology is detected and the noise pulse count reaches the threshold count value, as described above, the R-wave sensing event signal associated with cardiac electrical signal segmentation may correspond to non-cardiac noise pulses rather than real R waves.

[0131] When the overall morphological amplitude exceeds the "Yes" branch of the predetermined threshold box 510, a sign of a potential large-amplitude cardiac signal corresponding to a rapid arrhythmia morphology is detected at box 516. In this case, the detection of the rapid arrhythmia morphology is excluded as described above. Figure 7 The signal segments are detected as noise segments as described. No rapid arrhythmia morphology was detected at box 512 when the NRA is less than or equal to the NRA threshold (the "No" branch of box 510). This depends on the combination above. Figure 7The described pulse count analysis can detect segmented data as noisy segments. The NRA threshold applied at box 510 for detecting rapid arrhythmias 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 four and normalized to the maximum absolute amplitude. The NRA threshold used to detect rapid arrhythmia morphology in cardiac electrical signal segments can depend on various factors, such as the amplification and number of summed sample points, the amplification factor of the summed sample points, or the weighting factor.

[0132] Figure 10 This is a flowchart 550 of an example method for detecting the morphology of rapid arrhythmias in segments of cardiac electrical signals based on an overall morphological signal width metric. The process of flowchart 550 can be executed by an ICD 80 to... Figure 7 The overall shape signal width metric is determined at box 318. Boxes 502 and 504 correspond to the combination above. Figure 9 The boxes are described with the same numbering. In box 502, the segmentation of the rectified cardiac electrical signal after notch filtering is defined, for example... Figure 8 The signal segment 403 shown can be used to determine the maximum absolute amplitude 408 of the signal segment 403 at box 504.

[0133] Continue to refer to Figure 8 and Figure 10 The control circuit 80 determines a pulse amplitude threshold 412 at block 552 based on the maximum absolute amplitude 408 determined at block 504. This pulse amplitude threshold 412 can be used to identify the signal pulse with the largest signal width among all signal pulses occurring during time segment 402 of the cardiac electrical signal segment 403. For example, the pulse amplitude threshold 412 used to determine the overall morphological signal width metric can be set to half of the maximum absolute amplitude 408 of the rectified notch-filtered signal segment 403.

[0134] At block 554, control circuitry 80 determines the signal width of all signal pulses in the second cardiac electrical signal segment 403. Each signal pulse in signal segment 403 can be identified by identifying two consecutive zero-amplitude or baseline amplitude sample points of the rectified signal segment 403. All signal pulses between two consecutive baseline amplitude sample points are identified. In some examples, signal pulses can be identified from the non-rectified signal segment 401 to enable identification between zero-crossing points. The signal width of each identified signal pulse is determined as the number of sample points (or corresponding time intervals) between a pair of consecutive baseline amplitude sample points (or zero-crossing points). At block 556, the absolute maximum amplitude of each rectified signal pulse is determined. At block 558, all signal pulses in the rectified signal segment 403 having an absolute maximum amplitude greater than or equal to the pulse amplitude threshold 412 are identified. For example, at block 558, all signal pulses with a maximum amplitude at least half of the maximum absolute amplitude 408 determined at block 504 are identified. Control circuit 80 determines the maximum signal pulse width of all identified signal pulses at block 560. The number of sample points of the signal pulse spanning each identifier is counted and compared to determine the maximum signal pulse width from all signal pulses identified at block 558 as having an amplitude of at least pulse amplitude threshold 412. Maximum pulse width, for example... Figure 8 The pulse width 414 in the figure is identified at box 560 and is determined as a measure of the overall morphological signal width used to detect the morphology of rapid arrhythmias (e.g., in...). Figure 7 (at box 318). This maximum signal pulse width 414 is expected to be the pulse width of the potential cardiac signal waveform 405.

[0135] The overall morphological signal width metric can be correlated with the probability that signal segment 401 has a rapid arrhythmia morphology. For example, a relatively high overall morphological signal width metric could 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 could be an indication of a relatively narrow true R wave occurring during time segment 402 of cardiac electrical signal segment 401 or the absence of a true cardiac signal. When a relatively wide signal pulse is not detected from rectified cardiac electrical signal segment 403, oversensitized non-cardiac noise pulses may be present and may have triggered the buffering of cardiac signal segment 401.

[0136] Control circuit 80 at block 562 compares the maximum pulse width 414, identified at block 560, with a pulse width threshold. In one example, the pulse width threshold is set to 20 sample points when the sampling rate is 256 Hz. When the maximum signal pulse width is less than or equal to the width threshold, control circuit 80 does not detect a rapid arrhythmia morphology at block 564. A maximum signal pulse width less than or equal to the width threshold may correspond to a real, relatively narrow R wave, such as during sinus rhythm, or to a non-cardiac noise pulse. When the maximum signal pulse width is less than or equal to the width threshold (no rapid arrhythmia morphology detected at block 318), and at least the threshold number of pulses are counted from the differential signal (…). Figure 7 When the frame 316 is in place, the control circuit 80 can... Figure 7 Noise segments were detected at frame 322.

[0137] When the maximum pulse width at box 562 exceeds a width threshold, a relatively wide maximum signal pulse width can be detected as an indication of a rapid arrhythmia waveform morphology at box 564. Even when counting noise pulses of a threshold number from the differential signal 410 originating from cardiac electrical signal segment 401, indications of rapid arrhythmia morphology in signal segment 401 exclude the detection of noise segments. When detecting rapid arrhythmia morphology based on an overall morphological signal width metric, signal segments may not be detected as noise segments.

[0138] In some cases, such as when noise-only pulses exist in segments of the cardiac electrical signal, it is possible to... Figure 10 Box 558 indicates that there is no signal pulse with a maximum amplitude greater than the pulse amplitude threshold. In this case, the overall morphological width metric is not determined, and no rapid arrhythmia morphology is detected. Cardiac electrical signal segments can be detected as noise segments based on noise pulse count.

[0139] In various examples, both the overall morphological amplitude and the overall morphological signal width metric can be determined (in... Figure 7 According to the box at position 318 respectively Figure 9 and Figure 10 The technique is used to compare the overall morphological amplitude and the overall morphological signal width with the corresponding rapid arrhythmia morphology threshold. In some examples, it may be necessary for both the overall morphological amplitude and the overall morphological signal width to be less than or equal to the corresponding rapid arrhythmia morphology threshold in order to prevent the rapid arrhythmia morphology from being detected, thus enabling the detection of noise segments. When either the overall morphological amplitude or the overall morphological signal width is greater than the corresponding rapid arrhythmia morphology threshold, in Figure 7At box 318, indications of rapid arrhythmia morphology can be detected in the cardiac electrical signal segment, thus excluding the detection of noisy segments. In other examples, it may be necessary for both the overall morphological amplitude and signal width metric to be greater than the corresponding rapid arrhythmia morphology threshold in order to detect rapid arrhythmia morphology and exclude the detection of noisy segments. If one of the overall morphological metrics, such as amplitude or width metric, is less than or equal to the corresponding rapid arrhythmia morphology threshold, the rapid arrhythmia morphology criteria may not be met at box 318, thus allowing the signal segment to be detected as a noisy segment at box 322.

[0140] pass Figure 9 The method determined the overall morphological amplitude and through Figure 10 The overall morphological signal width metric determined by the method can be combined for use in... Figure 7 At box 318, signs of rapid arrhythmia morphology are detected to prevent the detection of noise segments as described above. Segments of cardiac electrical signals with relatively high overall morphological amplitude and / or relatively high overall morphological signal width metrics are signs of rapid arrhythmia morphology and are not counted as noise segments that may prevent the detection and subsequent treatment of rapid arrhythmias in order to maintain high sensitivity for rapid arrhythmia detection.

[0141] Figure 11 This is a flowchart 600 of an example method for the detection and treatment of rapid arrhythmias controlled by a medical device. At block 602, the control circuitry 80 of the ICD 14 determines whether criteria for enabling signal analysis to detect noise segments are met. In one example, the criteria for enabling analysis for noise detection require a threshold number of rapid arrhythmia intervals. For example, a threshold number of VT and / or VF intervals less than the NID required to detect VT or VF may trigger signal analysis for the detection of signal segments contaminated by noise. For example, three, five, eight, or other selected numbers of RRIs falling within the VT and / or VF interval region may be required to enable signal analysis for noise detection at block 602.

[0142] In other examples, noise analysis criteria can be met when patient activity signals indicate that the patient is engaged in physical activity. For example, patient activity metrics can be determined from signals from an accelerometer or another physiological sensor included in ICD 14. Noise analysis can be enabled at box 602 when patient activity metrics indicate that the patient is engaged in physical activity above a resting or predetermined threshold level.

[0143] In other examples, heart rate threshold changes based on R-wave sensed event signals may satisfy noise analysis criteria at box 602. For example, an increase in heart rate with an RRI less than a predetermined threshold interval, a decrease in the median RRI threshold, or other heart rate measures could be an indication that noise pulses are being oversensed. Therefore, in some cases, the criteria used to enable noise analysis based on heart rate may not require the RRI to fall within the rapid arrhythmia interval region. Rapidly occurring increases in heart rate or heart rates exceeding the sub-rapid arrhythmia threshold rate may satisfy the noise analysis criteria at box 602.

[0144] In some examples, noise analysis criteria may require a combination of two or more criteria. For example, a threshold heart rate or rapid arrhythmia interval count and a threshold patient activity level may be required to enable noise analysis at box 602. When the criteria for enabling signal analysis for noise detection are met at box 602, control circuitry 80 waits for the next R-wave sensing event signal from sensing circuitry 86 at box 606 and buffers the corresponding cardiac electrical signal segment at box 608. In some examples, cardiac electrical signal segments are buffered from a second cardiac electrical signal from second sensing channel 85 when the first sensing channel 83 senses an R-wave from a first cardiac electrical signal. In other examples, cardiac electrical signal segments may be buffered from the same cardiac electrical signal from which an R-wave is sensed.

[0145] At box 610, control circuit 80 performs noise analysis to classify cardiac electrical signals into noisy or non-noise segments. Control circuit 80 can then perform this analysis based on the above. Figure 5-10 Any example techniques described classify cardiac electrical signals into noise or non-noise segments. Generally, noise metrics such as noise pulse count, inflection point count, integral or summation of sample point amplitudes, high-frequency content, or other noise metrics related to the number, frequency, and / or amplitude of noise pulses can be determined from the differential signal of the cardiac electrical signal. The noise metric can be determined after increasing the gain of the differential signal when the signal-to-noise ratio criterion is met as described above. When the noise metric exceeds a noise threshold, the segment can be classified as a noise segment. When a rapid arrhythmia morphology is detected, for example, based on the combination of... Figure 8-10 The described technique can classify segments into non-noise segments, such that noise segment classification is stopped when the noise metric exceeds the noise segment threshold but a rapid arrhythmia morphology is detected.

[0146] Control circuit 80 updates the noise segment count at block 612. A first-in-first-out buffer in memory 82 can be set with a flag indicating the classification of each cardiac electrical signal segment being analyzed. The buffer can store a flag value (e.g., 1 = noise segment and 0 = non-noise segment) for each of a predetermined number of cardiac electrical signal segments. For example, the buffer can store the classification of each of six, eight, ten, twelve, or other selected numbers of consecutive cardiac electrical signal segments analyzed on a first-in-first-out basis. A Y / X counter that is updated with each new signal segment classification can be implemented in control circuit 80.

[0147] At block 614, control circuitry 80 determines when one or more rapid arrhythmia detection criteria are met. In some examples, the rapid arrhythmia detection criteria applied at block 610 may include interval-based criteria, such as a desired NID achieved by a VT interval counter, VF interval counter, or a combination of VT / VF interval counters of rapid arrhythmia detection circuitry 92. In other examples, determining at block 610 whether a rapid arrhythmia detection criterion to be met or not met may be based on QRS waveform morphology, meeting morphology-based criteria, or a combination of interval- or rate-based criteria and morphology-based criteria.

[0148] If the criteria for rapid arrhythmia detection are not met at box 614, control circuitry 80 can return to box 602 to continue signal analysis for noise detection, as long as the criteria for enabling noise detection are still met at box 602. When the criteria for enabling signal analysis for noise detection become unmet (e.g., patient activity, heart rate, and / or VT and / or VF interval counts are below the corresponding thresholds for enabling noise detection), the count of the noise segment can be cleared at box 604. For example, the buffer storing signal segment classifications as noise or non-noise segments can be cleared or reset to all non-noise segment values ​​at box 604.

[0149] When at least one criterion for detecting rapid arrhythmias is determined to be met at block 614, control circuit 80 may compare the current noise segment count with the stop criterion at block 616. For example, when the number of counted noise segments reaches or exceeds the stop threshold, the stop criterion is met, and rapid arrhythmia detection based on at least one met rapid arrhythmia detection criterion is stopped by control circuit 80 at block 620. When, for example, NID is reached and the threshold number of cardiac electrical signal segments has been classified as noise segments, control circuit 80 does not detect VT or VF at block 620. In some examples, a single noise segment may meet the stop criterion. When control circuit 80 detects a noise segment, the associated sensed R wave may be suppressed, resulting in NID not being reached.

[0150] Rapid arrhythmia treatment programmed to be delivered in response to VT or VF detection was not scheduled or delivered. In other examples, VT or VF detection may be performed in response to meeting the rapid arrhythmia detection criteria at box 614, but treatment may be stopped if the number of noise segments meets or exceeds the stop criteria. When the stop criteria are not met at box 616, for example, when the noise segment count is less than the stop threshold, a rapid arrhythmia is detected at box 618 by control circuitry 80 based on meeting the rapid arrhythmia detection criteria. Treatment, such as ATP and / or CV / DF shock, may be delivered in response to rapid arrhythmia detection.

[0151] Figure 12 This is flowchart 650, which describes an alternative method for the detection and treatment of rapid cardiac arrhythmias controlled by medical devices. Figure 12 In the middle, the boxes with the same number correspond to those combined above. Figure 11 The functionality described for boxes with similar numbering. Figure 12 During the process, when the noise analysis criteria are met at box 602, the control circuit 80 classifies each cardiac electrical signal segment into noise or non-noise at box 610.

[0152] After classifying the cardiac electrical signal segments at block 610, control circuitry 80 can be configured to ignore R-wave sensing event signals associated with the cardiac electrical signal segments. In some examples, control circuitry 80 may ignore R-wave sensing event signals without determining the RRI when a segment is classified as a noisy segment. Figure 12 In the example shown, the control circuitry can determine at block 652 whether an RRI ending with an R-wave sensing event signal associated with the current cardiac electrical signal segment is a rapid arrhythmia interval.

[0153] If so, control circuit 80 determines at block 654 whether the current cardiac electrical signal segment is classified as a noise segment. If the signal segment associated with the R-wave sensing event signal that terminates the rapid arrhythmia is classified as a noise segment (the "Yes" branch of block 654), control circuit 80 does not count the rapid arrhythmia interval as a VT or VF interval at block 656. The process returns to block 602. If the RRI is a rapid arrhythmia interval and the signal segment is not classified as a noise segment (the "No" branch of block 654), the RRI is counted as a rapid arrhythmia interval at block 658.

[0154] When at least one criterion for rapid arrhythmia detection is met at box 614, for example, by achieving NID via a VT or VF interval counter, VT or VF is detected at box 618 and programmed treatment is delivered at box 618. In this way, rapid arrhythmia detection is effectively prevented or not performed in response to the RRI, which is a rapid arrhythmia interval but associated with an R-wave sensing event signal corresponding to a cardiac electrical signal segment classified as a noise segment.

[0155] Figure 13 This is a flowchart 700 of a method performed by an ICD 14 according to another example for detecting non-cardiac noise and suppressing ventricular rapid arrhythmias in response to detection noise. At blocks 702 and 704, sensing circuitry 86 can receive two different cardiac electrical signals. In some examples, sensing circuitry 86 can select two different sensing electrode vectors 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 passed to sensing circuitry 86 as vector selection control signals.

[0156] The first sensing electrode vector selected at box 702 for sensing the first cardiac electrical signal can be a relatively short bipolar, 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 may include electrodes that are relatively very close to each other and relatively very close to the ventricular chambers compared to the second sensing vector selected at box 704, to provide sensing of a relatively “near-field” ventricular signal for sensing the R wave. The first sensing electrode vector can 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 for reliable R wave sensing. However, the first sensing electrode vector is not limited to any particular inter-electrode spacing or orientation and can be selected as any available electrode pair.

[0157] The second sensing electrode vector for receiving the second cardiac electrical signal at block 704 can 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 can be selected as a vector between one of the pacing sensing electrodes 28 or 30 and the ICD housing 15, a 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 electrode vector can be orthogonal or nearly orthogonal to the first sensing electrode vector, but the first and second sensing vectors do not need to be orthogonal. Compared to the first sensing electrode vector, the second sensing electrode vector can receive a relatively global or far-field cardiac electrical signal. The second cardiac electrical signal received by the second sensing channel 85 at block 304 can be analyzed by control circuitry 80 to detect noise interference in both the first and second cardiac electrical signals. In other examples, the first and second cardiac electrical signals sensed at blocks 702 and 704 can be received from the same sensing electrode vector, such that sensing circuit 86 receives a single cardiac electrical signal. However, two different sensing channels 83 and 85 of sensing circuit 86 can process the raw received signal. This sensing circuit has different filtering and / or other signal processing features to sense two different cardiac electrical signals, one sensed by the first sensing channel 83 for detecting the R wave and the other sensed by the second sensing channel 85 for detecting noise and performing rapid arrhythmia morphology analysis. In yet another example, a single cardiac signal is used to sense the R wave and buffered for detecting noise corruption of the cardiac signal.

[0158] 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 706. 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 706, the control circuit 80 is triggered at block 708 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 sample points before and after the R-wave sensing event signal time. The segments of the second cardiac electrical signal may or may not be temporally focused 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 sample 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 sample points at a sampling rate of 256 Hz or approximately 200 ms. In another example, the buffered segment is at least 92 sample points, or approximately 360 ms, sampled at 256 Hz, and can be used for analysis to detect noise present in the cardiac electrical signal segment.

[0159] 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-wave sensing confirmation threshold is not reached at box 714 as described below, the previously stored segment may never be analyzed for noise detection and will 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 noise detection, that segment is overwritten by the next segment corresponding to the next R-wave sensing event signal.

[0160] 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 706 by determining the RRI at block 710 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 rapid arrhythmia detection circuit 92, which adjusts the rapid arrhythmia interval counter at block 312. If the RRI is longer than the tachycardia detection interval (TDI), the rapid arrhythmia 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 712. If the RRI is shorter than or equal to the FDI, the VF interval counter is incremented at block 712. In some examples, if the RRI is less than the TDI, the combined VT / VF interval counter is incremented.

[0161] After updating the rapid arrhythmia interval counter at box 712, the rapid arrhythmia detector 92 compares the counter value with the R-sensing confirmation threshold at box 714 to determine if noise analysis criteria are met, and compares it with the VT detection threshold and VF detection threshold at box 732 to determine if the corresponding NID is met. If the VT or VF detection interval counter has reached the R-sensing confirmation threshold, the "Yes" branch of box 714 analyzes, for example, a second cardiac electrical signal from sensing channel 85 to detect noise corruption in signal segments that could cause the first sensing channel 83 to generate erroneous R-wave sensing event signals, resulting in an increase in the VT and / or VF counter at box 712. The R-sensing confirmation threshold can be a VT or VF interval count value greater than one or another higher threshold count value. Different R-sensing confirmation thresholds can be applied to the VT interval counter and the VF interval counter. For example, the R-sensing confirmation threshold could be count two for the VT interval counter and count three for the VF interval counter. In other examples, the R-sensing confirmation threshold is a higher number, such as five 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 individual VT and VF counters, or alternatively, to a combined VT / VF interval counter, the R-sensing confirmation threshold may be applied. 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 712, only the VF interval counter is updated in response to the RRI determination, and at box 714, the R-sensing confirmation threshold may be applied to the VF interval counter.

[0162] If, at box 714, none of the rapid arrhythmia interval counters have reached the R-wave sensing confirmation threshold, the control circuit 80 waits at box 708 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 714, for example when the VF interval counter is greater than 2, the control circuit 80 begins analyzing the second cardiac electrical signal segments to detect noise segments.

[0163] At block 716, 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, the stored second cardiac electrical signal segment is notch-filtered and rectified at block 716 by control circuitry 80, for example, via a notch filter and rectifier implemented in software, firmware, or hardware. In other examples, such as Figure 4 The notch filter signal is received from the second sensing channel 85 and buffered in the memory 82 for retrieval by the control circuit 80. As described above, the notch filter can be implemented to attenuate line frequency noise at 50Hz and 60Hz.

[0164] At block 718, control circuitry 80 determines a signal strength metric and a noise strength metric for use when identifying noise segments after an R-wave sensing confirmation threshold has been reached. In some examples, the signal strength metric and noise metric may be determined from a second cardiac electrical signal segment of each notch-filtered signal buffer in response to an R-wave sensing event. In one example, control circuitry 80 may determine the signal strength metric as the maximum amplitude of the rectified signal segment of the notch-filtered signal. Additionally, control circuitry 80 may determine the noise strength metric by determining the rectified differential signal (or high-pass filtered signal) at block 718 and determining its maximum amplitude as the noise strength metric. In some examples, control circuitry 80 may use the maximum amplitude of each buffered signal segment during a predetermined time interval (e.g., 1.2 seconds) and the maximum amplitude of the current differential signal segment to determine at block 720 whether a signal-to-noise ratio criterion is met.

[0165] As shown above Figure 5As described, the maximum amplitude of all segments during the time interval can be compared to a signal strength threshold (e.g., one-third of the dynamic range of the ADC or other selected threshold), and the maximum amplitude of the differential signal of the current cardiac electrical signal segment can be compared to a noise intensity threshold, such as 13 ADC units or other predetermined or selected values. A signal-to-noise ratio (SNR) criterion is met at box 720 when the maximum amplitude is greater than the signal strength threshold and the maximum differential signal amplitude of the current signal segment is less than the noise intensity threshold. In other examples, the ratio of the maximum amplitude during a predetermined time interval to the maximum differential signal amplitude of the current signal segment can be compared to a SNR threshold ratio to determine whether the SNR criterion is met at box 720.

[0166] When the signal-to-noise ratio (SNR) criterion is met, the control circuit 80 increases the gain of the differential signal at block 722. Otherwise, the gain remains unchanged. The control circuit 80 uses either the differential signal with constant gain or the differential signal with increased gain at block 724 to determine a noise metric, such as noise pulse count. This is used in conjunction with the above... Figure 7-8 The method for determining the noise metric by determining the noise impulse count as described can be performed at box 724. In other examples, different noise metrics, such as any of the examples given above, can be determined from the current signal segment.

[0167] In addition to determining the noise metric, the control circuit 80 may optionally determine the overall morphological metric at block 726 for use as described above. Figure 9 and Figure 10 As typically described, the morphology of the rapid arrhythmia waveform is detected at box 726. Based on the noise pulse count (or other noise metric) and the rapid arrhythmia waveform morphology metric, when determined, the current second cardiac electrical signal segment can be classified at box 728. As described above, when the noise metric meets the noise detection threshold and the overall morphology metric does not meet the rapid arrhythmia morphology criteria, the control circuit 80 can classify the segment as a noise segment at box 728. When the noise metric is less than or equal to the noise detection threshold or at least one overall morphology metric meets the rapid arrhythmia morphology criteria, the control circuit 80 can classify the segment as a non-noise segment at box 728.

[0168] After classifying the current segment, control circuit 80 can determine at block 732 whether the VT interval counter, VF interval counter, or combined VT / VF interval counter has reached the NID. If the VT interval counter, VF interval counter, or combined VT / VF interval counter has not reached the threshold detection interval (NID), control circuit 80 returns to block 710 to continue determining RRI and analyzing the second cardiac electrical signal segment (block 714), provided that the R sensing confirmation threshold is met. If the R sensing confirmation threshold is no longer met at block 714, the noise segment counter or buffer can be cleared at block 715.

[0169] When the NID is reached at box 732, control circuit 80 determines at box 734 whether the stop detection threshold number for the noise segment has been reached, based on the values ​​of the VT interval counter and / or VF interval counter. In response to the stop threshold number of the most recent cardiac electrical signal segment being classified as a noise segment, VT or VF detection based on the NID being reached is stopped at box 734. In one example, if at least two of the most recent eight cardiac electrical signal segments are classified as noise segments, the stop detection threshold is met at box 734. VT or VF detection (and any associated VT or VF treatment) is stopped by control circuit 80 at box 736. When the most recent signal segment of the threshold number is classified as a noise segment, control circuit 80 does not detect ventricular tachyarrhythmias, even when tachyarrhythmia detection criteria such as NID are met. As long as NID continues to be met, control circuit 80 can continue to classify and count noise segments as new R waves are sensed to determine at box 734 whether the stop threshold is still met.

[0170] In some examples, control circuitry 80 may determine at block 738 whether a termination criterion has been met when detection has been stopped. Termination of a fast rhythm may be detected based on a predetermined number of RRIs greater than the rapid arrhythmia detection interval, or when the mean, median, or other measure of RRIs determined during a predetermined time interval is greater than the rapid arrhythmia detection interval. For example, rapid arrhythmia termination may be detected at block 738 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) are detected after NID is met. In one example, termination is detected at block 738 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 738 when a predetermined time interval has elapsed and the median RRI is greater than the VT detection interval. For example, if the median RRI of the most recent 12 RRIs is always greater than the VT detection interval by at least 20 seconds or other predetermined time segments, the control circuit 80 may detect termination at block 738. In response to detecting termination, the control circuit 80 may reset the VT interval counter and the VF interval counter, as well as the noise fraction count, and return to block 710.

[0171] When the NID is met at box 732 and the inhibition threshold is not reached at box 734 (e.g., less than the threshold number of classified noise segments), a VT or VF event is detected at box 740. In response to VT / VF detection, the treatment delivery circuit 84 can deliver VT or VF treatment at box 742. It should be understood that criteria other than the NID criteria may be applied before VT or VF is detected at box 740. For example, it may be necessary to disqualify various P-wave hypersensing inhibition criteria, T-wave hypersensing inhibition criteria, supraventricular tachycardia (SVT) inhibition criteria, etc., and / or it may be necessary to detect VT / VF at box 740 and meet rapid arrhythmia initiation criteria, rapid arrhythmia morphology criteria, etc., before delivering treatment at box 742.

[0172] In other examples, VT / VF detection could be performed in response to meeting detection criteria, such as achieving NID at box 732, but VT / VF treatment could be stopped at box 736 if a stop threshold is reached or the number of detected noise segments is exceeded. Treatment delivery circuit 84 can stop VT or VF treatment until the stop threshold is no longer met and rapid arrhythmias are still detected. When the stop threshold is no longer met and termination of the detected VT or VF has not been detected at box 738, treatment delivery circuit 84 can deliver the stopped treatment. If it is determined that the detected VT or VF should be terminated at box 738 while treatment is stopped, the noise segment count and VT / VF interval counter can be cleared and the process can return to box 710 without frequent treatment delivery.

[0173] 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.

[0174] 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, which corresponds 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 required program code in the form of instructions or data structures and is accessible by a computer).

[0175] 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 logic arrays (FPLAs), or other equivalent integrated or discrete logic circuit systems. Therefore, the term "processor" as used herein can refer to any of the foregoing structures or any other structures suitable for implementing the techniques described herein. Furthermore, these techniques can be implemented entirely within one or more circuit or logic elements.

[0176] 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 combinations different from the specific combinations presented in the accompanying drawings. It should be understood that various modifications may be made to the reference examples without departing from the scope of this disclosure and the appended claims and examples.

[0177] Example 1. A medical device comprising: a sensing circuit configured to sense at least one electrical signal and sense a plurality of electrophysiological events from the at least one electrical signal; a memory; and a control circuit coupled to the sensing circuit and the memory and configured to: store in the memory, in response to each of the plurality of electrophysiological events sensed by the sensing circuit, segments of electrical signals from the at least one electrical signal sensed by the sensing circuit; determine that a signal-to-noise ratio (SNR) criterion is met based on the stored electrical signal segments; determine, in response to determining that the SNR criterion is met, a signal segment with increased gain from one of the stored electrical signal segments; determine a noise metric from the signal segment with increased gain; determine that the noise metric meets a noise detection criterion; and classify one of the stored electrical signal segments associated with the signal segment with increased gain as a noise segment in response to the noise metric meeting the noise detection criterion.

[0178] Example 2. The device according to Example 1, wherein the control circuit is further configured to determine whether the signal-to-noise ratio criterion is satisfied by determining a differential signal from at least one of the plurality of stored electrical signal segments; and to determine that the differential signal satisfies the signal-to-noise ratio criterion.

[0179] Example 3. The device according to any one of Examples 1 to 2, wherein the control circuit is configured to determine whether the signal-to-noise ratio criterion is satisfied by determining a maximum amplitude from each of the plurality of stored electrical signal segments; and to determine that the maximum amplitude satisfies the signal-to-noise ratio criterion.

[0180] Example 4. The device according to Example 3, wherein the control circuit is configured to determine that the maximum amplitude satisfies the signal-to-noise ratio criterion by determining the largest maximum amplitude among the maximum amplitudes determined from each of the plurality of stored electrical signal segments; and to determine that the largest maximum amplitude is greater than a signal strength threshold.

[0181] Example 5. The device according to any one of Examples 1 to 4, wherein the control circuit is configured to determine that the signal-to-noise ratio criterion is met by determining the maximum differential signal amplitude from at least one of the plurality of stored electrical signal segments; and to determine that the maximum differential signal amplitude is less than a noise intensity threshold.

[0182] Example 6. The device according to any one of Examples 1 to 5, wherein the control circuit is configured to determine whether the signal-to-noise ratio criterion is met by determining the maximum amplitude from each of the electrical signal segments stored in a predetermined time interval.

[0183] Example 7. The device according to any one of Examples 1 to 6, wherein the control circuit is configured to determine the signal segment with increased gain by determining the most recent differential signal segment among the electrical signal segments; and to increase the gain of the most recent differential signal among the electrical signal segments.

[0184] Example 8. The device according to any one of Examples 1 to 7, wherein the control circuit is further configured to determine a pulse amplitude threshold based on the signal segmentation with increased gain; and to determine the noise metric in response to the pulse amplitude threshold being greater than a suspected noise threshold amplitude.

[0185] Example 9. The device according to any one of Examples 1 to 8, wherein the control circuitry is configured to determine the noise metric by identifying the signal pulses that indicate the signal segments with increased gain; and to determine the count of the identified signal pulses.

[0186] Example 10. The device according to Example 9, wherein the control circuitry is configured to identify the signal pulse by determining the maximum amplitude of the signal segment with increased gain; setting a pulse amplitude threshold based on the maximum amplitude; identifying consecutive pairs of zero-crossing points of the signal segment with increased gain; determining the maximum pulse amplitude between each consecutive pair of zero-crossing points; determining the number of sample points between each consecutive pair of zero-crossing points; and identifying the signal pulse in response to the maximum pulse amplitude being greater than the pulse amplitude threshold and the number of sample points being greater than a predetermined width threshold.

[0187] Example 11. The device according to any one of Examples 1 to 10, wherein the sensing circuit is configured to sense the at least one electrical signal by sensing at least one cardiac electrical signal and to sense the plurality of electrophysiological events by sensing a plurality of cardiac electrical events from the at least one cardiac electrical signal; and the control circuit is configured to store the electrical signal segment by storing a cardiac electrical signal segment from the at least one cardiac electrical signal in response to each of the plurality of cardiac electrical events sensed by the sensing circuit.

[0188] Example 12. The device according to Example 11, wherein the control circuitry is further configured to determine, based on the at least one cardiac electrical signal, that a rapid arrhythmia detection criterion is met for detecting a rapid arrhythmia; and to prevent rapid arrhythmia detection in response to one of the stored cardiac electrical signal segments associated with the increased gain signal segment being classified as a noise segment.

[0189] Example 13. The device according to any one of Examples 11 to 12, wherein the control circuitry is further configured to classify each of the stored cardiac electrical signal segments as either a noise segment or a non-noise segment; determine a threshold number of the stored cardiac electrical signal segments classified as noise segments; and prevent rapid arrhythmia detection in response to the threshold number of the stored cardiac electrical signal segments being classified as noise segments.

[0190] Example 14. The device according to any one of Examples 11 to 13, further comprising a treatment delivery circuit configured to generate rapid arrhythmia treatment in response to the control circuit detecting a rapid arrhythmia based on the at least one cardiac electrical signal; wherein the control circuit is further configured to classify each of the stored cardiac electrical signal segments into one of a noise segment or a non-noise segment; determine a threshold number of the stored cardiac electrical signal segments classified as noise segments; and detect a rapid arrhythmia by means of the at least one cardiac electrical signal in response to meeting a rapid arrhythmia detection criterion; and the treatment delivery circuit is configured to stop the rapid arrhythmia treatment in response to the threshold number of the stored cardiac electrical signal segments being classified as noise segments.

[0191] Example 15. The device according to any one of Examples 11 to 14, wherein the control circuitry is further configured to determine a plurality of cardiac event intervals based on a plurality of sensed cardiac electrical events; determine a first threshold number of the plurality of cardiac event intervals as rapid arrhythmia intervals; and store the cardiac electrical signal segments for determining, in response to determining that the first threshold number of the plurality of cardiac event intervals are rapid arrhythmia intervals, the signal-to-noise ratio criterion is met.

[0192] Example 16. The device according to Example 15, wherein the control circuitry is configured to determine that a rapid arrhythmia detection criterion is met by determining that a plurality of cardiac event intervals of a second threshold number are rapid arrhythmia intervals, the second threshold number being greater than the first threshold number.

[0193] Example 17. The device according to any one of Examples 11 to 16, wherein the control circuitry is further configured to determine at least one overall morphological waveform metric from said one of the stored cardiac electrical signal segments associated with said increased gain signal segments; determine that said overall morphological waveform metric satisfies a rapid arrhythmia morphological criterion; and, in response to said overall morphological waveform metric satisfying the rapid arrhythmia morphological criterion, prevent said one of the stored cardiac electrical signal segments associated with said increased gain signal segments from being classified as a noise segment.

[0194] Example 18. The device according to any one of Examples 1 to 17, wherein the control circuitry is further configured to control treatment based on the electrophysiological event sensed by the sensing circuitry; and to ignore the electrophysiological event sensed by the sensing circuitry and associated with one of the stored electrical signal segments classified as the noise segment.

[0195] Example 19. A method comprising: sensing at least one electrical signal; sensing a plurality of electrophysiological events from the at least one electrical signal; storing electrical signal segments from the at least one electrical signal in response to each of the plurality of sensed electrophysiological events; determining whether a signal-to-noise ratio (SNR) criterion is met based on the stored electrical signal segments; determining a signal segment with increased gain from one of the stored electrical signal segments in response to determining that the SNR criterion is met; determining a noise metric from the signal segment with increased gain; determining that the noise metric meets a noise detection criterion; and classifying the one of the stored electrical signal segments associated with the signal segment with increased gain as a noise segment in response to the noise metric meeting the noise detection criterion.

[0196] Example 20. The method according to Example 19, wherein determining that the signal-to-noise ratio criterion is satisfied includes: determining a differential signal from at least one of the plurality of stored electrical signal segments; and determining that the differential signal satisfies the signal-to-noise ratio criterion.

[0197] Example 21. The method according to any one of Examples 19-20, wherein determining that the signal-to-noise ratio criterion is satisfied comprises: determining a maximum amplitude from each of the plurality of stored electrical signal segments; and determining that the maximum amplitude satisfies the signal-to-noise ratio criterion.

[0198] Example 22. The method according to Example 21, wherein the control circuit is configured to determine that the signal-to-noise ratio criterion is satisfied by determining the largest maximum amplitude among the largest amplitudes determined from each of the plurality of stored electrical signal segments; and to determine that the largest maximum amplitude is greater than a signal strength threshold.

[0199] Example 23. The method according to any one of Examples 19 to 22, wherein determining that the signal-to-noise ratio criterion is satisfied comprises: determining a maximum differential signal amplitude from at least one of the plurality of stored electrical signal segments; and determining that the maximum differential signal amplitude is less than a noise intensity threshold.

[0200] Example 24. The method according to any one of Examples 19 to 23, wherein determining that the signal-to-noise ratio criterion is satisfied includes determining the maximum amplitude from each of the electrical signal segments stored within a predetermined time interval.

[0201] Example 25. The method according to any one of Examples 19 to 24, wherein determining the signal segment with increased gain comprises: determining the most recent differential signal segment among the electrical signal segments; and increasing the gain of the most recent differential signal among the electrical signal segments.

[0202] Example 26. The method according to any one of Examples 19 to 25 further includes: determining a pulse amplitude threshold based on the signal segmentation with increased gain; and determining the noise metric in response to the pulse amplitude threshold being greater than a suspected noise threshold amplitude.

[0203] Example 27. The method according to any one of Examples 19 to 26, wherein determining the noise metric comprises: identifying signal pulses of the signal segment with increased gain; and determining a count of the identified signal pulses.

[0204] Example 28. The method according to Example 27, wherein identifying the signal pulse includes: determining the maximum amplitude of the signal segment with increased gain to identify the signal pulse; setting a pulse amplitude threshold based on the maximum amplitude; identifying consecutive pairs of zero-crossing points of the signal segment with increased gain; determining the maximum pulse amplitude between each consecutive pair of zero-crossing points; determining the number of sample points between each consecutive pair of zero-crossing points; and identifying the signal pulse in response to the maximum pulse amplitude being greater than the pulse amplitude threshold and the number of sample points being greater than a predetermined width threshold.

[0205] Example 29. A method according to any one of Examples 19 to 28, wherein sensing the at least one electrical signal comprises: sensing at least one cardiac electrical signal; sensing the plurality of electrophysiological events comprises sensing a plurality of cardiac electrical events from the at least one cardiac electrical signal; and storing the electrical signal segments comprises storing a cardiac electrical signal segment from the at least one cardiac electrical signal in response to each of the plurality of cardiac electrical events sensed by the sensing circuit.

[0206] Example 30. The method according to Example 29 further includes: determining, based on the at least one cardiac electrical signal, that it meets the criteria for detecting rapid arrhythmia in order to detect rapid arrhythmia; and stopping rapid arrhythmia detection in response to the classification of one of the stored cardiac electrical signal segments associated with the signal segment with increased gain as a noise segment.

[0207] Example 31. The method according to any one of Examples 29-30 further includes: classifying each of the stored cardiac electrical signal segments as either a noise segment or a non-noise segment; determining a threshold number of the stored electrical signal segments classified as noise segments; and stopping rapid arrhythmia detection in response to the threshold number of the stored electrical signal segments being classified as noise segments.

[0208] Example 32. The method according to any one of Examples 29 to 31, further comprising: classifying each of the stored cardiac electrical signal segments as either a noise segment or a non-noise segment; determining a threshold number of the stored cardiac electrical signal segments classified as noise segments; detecting a rapid arrhythmia by means of the at least one cardiac electrical signal in response to meeting a rapid arrhythmia detection criterion; and stopping the rapid arrhythmia detection in response to the threshold number of the stored cardiac electrical signal segments being classified as noise segments.

[0209] Example 33. The method according to any one of Examples 19 to 32, further comprising: determining a plurality of cardiac event intervals based on a plurality of sensed cardiac electrical events; determining a first threshold number of the plurality of cardiac event intervals as rapid arrhythmia intervals; and storing the cardiac electrical signal segments for determining, in response to determining that the first threshold number of the plurality of cardiac event intervals are rapid arrhythmia intervals, the signal-to-noise ratio criterion is met.

[0210] Example 34. The method according to Example 33 further includes: determining whether the plurality of cardiac event intervals of a second threshold number are rapid arrhythmia intervals to meet the rapid arrhythmia detection criteria, wherein the second threshold number is greater than the first threshold number.

[0211] Example 35. The method according to any one of Examples 19-34, further comprising: determining at least one overall morphological waveform metric from said one of the stored cardiac electrical signal segments associated with said increased gain signal segments; determining that said overall morphological waveform metric satisfies a rapid arrhythmia morphological criterion; and preventing said one of the stored cardiac electrical signal segments associated with said increased gain signal segments from being classified as a noise segment in response to said overall morphological waveform metric satisfying the rapid arrhythmia morphological criterion.

[0212] Example 36. The method according to any one of Examples 19 to 35 further includes: controlling treatment based on the electrophysiological event sensed by the sensing circuit; and ignoring the electrophysiological event sensed by the sensing circuit and associated with one of the stored electrical signal segments classified as the noise segment.

[0213] Example 37. A non-transitory computer-readable medium storing a set of instructions, which, when operated by control circuitry of a medical device, cause the medical device to: sense at least one electrical signal; sense a plurality of electrophysiological events from the at least one electrical signal; store electrical signal segments from the at least one electrical signal in response to each of the plurality of sensed electrophysiological events; determine whether a signal-to-noise ratio (SNR) criterion is met based on the stored electrical signal segments; determine a signal segment with increased gain from one of the stored electrical signal segments in response to determining that the SNR criterion is met; determine a noise metric from the signal segment with increased gain; and determine that the noise metric meets a noise detection criterion; and classify the one of the stored electrical signal segments associated with the signal segment with increased gain as a noise segment in response to the noise metric meeting the noise detection criterion.

Claims

1. A medical device, the medical device comprising: A sensing circuit configured to sense at least one electrical signal and sense a plurality of electrophysiological events from the at least one electrical signal; Memory; as well as A control circuit, coupled to the sensing circuit and the memory, is configured to: In response to each of the plurality of electrophysiological events sensed by the sensing circuit, electrical signal segments of the at least one electrical signal sensed by the sensing circuit are stored in the memory. Based on the stored electrical signal segments, it is determined whether the signal-to-noise ratio standard is met; In response to determining that the signal-to-noise ratio criterion is met, a signal segment with increased gain is determined from one of the stored electrical signal segments; Noise metrics are determined from the segments of the signal with increased gain; The noise metric is determined to meet the noise detection standard. as well as In response to the noise metric satisfying the noise detection criterion, one of the stored electrical signal segments associated with the increased gain signal segment is classified as a noise segment.

2. The device of claim 1, wherein the control circuit is further configured to determine that the signal-to-noise ratio criterion is met by one or more of the following steps: (a) Determine a differential signal from at least one of the plurality of stored electrical signal segments and determine that the differential signal satisfies the signal-to-noise ratio criterion; (b) Determine the maximum amplitude from each of the plurality of said stored electrical signal segments and determine that said maximum amplitude satisfies the signal-to-noise ratio criterion; (c) Determine the maximum differential signal amplitude from at least one of the plurality of stored electrical signal segments and determine that the maximum differential signal amplitude is less than a noise intensity threshold; as well as (d) Determine the maximum amplitude from each of the electrical signal segments stored within a predetermined time interval.

3. The device of claim 2, wherein the control circuit is configured to determine that the maximum amplitude satisfies the signal-to-noise ratio criterion by means of the following steps: Determine the largest maximum amplitude from each of the determined maximum amplitudes among the plurality of stored electrical signal segments; The maximum amplitude is determined to be greater than the signal strength threshold.

4. The device according to any one of claims 1 to 3, wherein the control circuit is configured to determine the signal segmentation with increased gain by means of the following steps: Determine the most recent differential signal segment among the electrical signal segments; and Increase the gain of the most recent differential signal in the electrical signal segment.

5. The device according to any one of claims 1 to 3, wherein the control circuit is further configured to: The pulse amplitude threshold is determined based on the signal segmentation with increased gain; and The noise metric is determined in response to the pulse amplitude threshold being greater than the suspected noise threshold amplitude.

6. The device according to any one of claims 1 to 3, wherein the control circuit is configured to determine the noise metric by means of the following steps: The signal pulse that identifies the signal segment with increased gain; and Determine the count of the signal pulses identified.

7. The device of claim 6, wherein the control circuitry is configured to identify the signal pulse by means of the following steps: Determine the maximum amplitude of the signal segment with increased gain; Set the pulse amplitude threshold based on the maximum amplitude; A series of consecutive pairs that identify the zero-crossing points of the signal segments with increased gain; Determine the maximum pulse amplitude between each consecutive pair of zero-crossing points; Determine the number of sample points between each consecutive pair of zero-crossing points; as well as The signal pulse is identified in response to the maximum pulse amplitude being greater than the pulse amplitude threshold and the number of sample points being greater than a predetermined width threshold.

8. The device according to any one of claims 1 to 3, wherein: The sensing circuit is configured to sense the at least one electrical signal by sensing at least one cardiac electrical signal and to sense the plurality of electrophysiological events by sensing a plurality of cardiac electrical events from the at least one cardiac electrical signal; as well as The control circuit is configured to store the electrical signal segment by storing a segment of the cardiac electrical signal from the at least one cardiac electrical signal in response to each of the plurality of cardiac electrical events sensed by the sensing circuit.

9. The device according to claim 8, wherein the control circuit is further configured to: Based on the at least one cardiac electrical signal, determine whether the rapid arrhythmia detection criteria are met for the purpose of detecting rapid arrhythmias; and Rapid arrhythmia detection is prevented in response to one of the stored cardiac electrical signal segments associated with the increased gain signal segment being classified as a noise segment.

10. The device according to claim 8, wherein the control circuit is further configured to: Each of the stored cardiac electrical signal segments is classified into either a noise segment or a non-noise segment; The stored ECG signal segments, whose threshold number is determined, are classified into noise segments; and Rapid arrhythmia detection is prevented in response to the number of stored cardiac electrical signal segments classified as noise segments.

11. The device of claim 8, further comprising a treatment delivery circuit configured to generate rapid arrhythmia treatment in response to the control circuit detecting a rapid arrhythmia based on the at least one cardiac electrical signal; The control circuit is further configured as follows: Each of the stored cardiac electrical signal segments is classified into either a noise segment or a non-noise segment; The stored ECG signal segments, whose threshold number is determined, are classified into noise segments; and Rapid arrhythmia is detected by responding to at least one cardiac electrical signal in response to meet the criteria for rapid arrhythmia detection; and The treatment delivery circuit is configured to halt the treatment of the rapid arrhythmia in response to the threshold number of stored cardiac electrical signal segments being classified as noise segments.

12. The device according to claim 8, wherein the control circuit is further configured to: Multiple cardiac event intervals are determined based on the sensed multiple cardiac electrical events; The plurality of cardiac event intervals that determine the first threshold number are rapid arrhythmia intervals; and The cardiac electrical signal segments are stored for use in response to determining that the signal-to-noise ratio criterion is met in response to determining that the plurality of cardiac event intervals of the first threshold number are rapid arrhythmia intervals.

13. The device of claim 12, wherein the control circuit is configured to determine that a rapid arrhythmia detection criterion is met by determining that a second threshold number of the plurality of cardiac event intervals is a rapid arrhythmia interval, the second threshold number being greater than the first threshold number.

14. The device of claim 8, wherein the control circuit is further configured to: Determine at least one overall morphological waveform measure from one of the stored cardiac electrical signal segments associated with the increased gain signal segments; The overall morphological waveform measurement is determined to meet the morphological criteria for rapid arrhythmias. as well as In response to the overall morphological waveform metric satisfying the rapid arrhythmia morphology criteria, the classification of one of the stored cardiac electrical signal segments associated with the increased gain signal segment as a noise segment is prevented.

15. The device according to any one of claims 1 to 3, wherein the control circuit is further configured to: Treatment is controlled based on the electrophysiological events sensed by the sensing circuit; and Ignore the electrophysiological event sensed by the sensing circuit and associated with one of the stored electrical signal segments classified as the noise segment.

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