Noise detection based on the overall morphology of cardiac electrical signals for suppressing ventricular tachyarrhythmia detection

Abstract

The present disclosure relates to noise detection based on the overall morphology of cardiac electrical signals for suppressing ventricular tachyarrhythmia detection. A medical device system such as a cardiovascular implantable cardioverter defibrillator (ICD) senses R waves from a first cardiac electrical signal through a first sensing channel, and stores a time segment of a second cardiac electrical signal in response to each sensed R wave. The medical device system determines a morphology parameter associated with signal noise based on the time segment of the second cardiac electrical signal, detects noisy signal segments based on the signal morphology parameter; and stops detecting tachyarrhythmia attacks in response to detecting a threshold number of noisy signal segments.

Description

[0001] This application is a divisional application of an invention patent application with an international application date of 2017 / 7 / 26, an international application number of PCT / US2017 / 043828, an application number of 201780046449.3 entering the Chinese national phase, and entitled "Noise detection based on the overall morphology of cardiac electrical signals for suppressing ventricular tachyarrhythmia detection". Technical Field

[0002] The present disclosure generally relates to a medical device system and method for detecting noise in cardiac electrical signals and discontinuing ventricular tachyarrhythmia detection in response to detecting the noise. Background Art

[0003] Medical devices such as cardiac pacemakers and implantable cardioverter defibrillators (ICDs) provide therapeutic electrical stimulation to the patient's heart through electrodes carried by one or more medical electrical leads and / or electrodes on the housing of the medical device. The electrical stimulation may include signals such as pacing pulses or cardioversion shocks or defibrillation shocks. In some cases, the medical device can sense the cardiac electrical signals accompanying the intrinsic depolarization of the heart or the depolarization induced by pacing, and control the delivery of the stimulation signal to the heart based on the sensed cardiac electrical signals. When abnormal rhythms such as bradycardia, tachycardia or fibrillation are detected, one or more appropriate electrical stimulation signals can be delivered to restore or maintain a more normal rhythm of the heart. For example, the ICD can deliver pacing pulses to the patient's heart when bradycardia or tachycardia is detected, or deliver cardioversion shocks or defibrillation shocks to the heart when tachycardia or fibrillation is detected. The ICD can sense cardiac electrical signals in the heart chambers, and use electrodes carried by transvenous medical electrical leads to deliver electrical stimulation therapy to the heart chambers. The cardiac signals sensed within the heart are typically of high signal strength and quality for reliable sensing of cardiac electrical events, such as R waves. In other examples, non-transvenous leads may be coupled to an ICD, in which case cardiac signal sensing presents new challenges for accurately sensing cardiac electrical events. Summary of the invention

[0004] In general, the present disclosure relates to techniques for detecting noise-contaminated cardiac electrical signal segments and rejecting ventricular tachyarrhythmia detection in response to detecting the noisy signal segments. A medical device system operating according to the techniques disclosed herein can determine signal morphology parameters of cardiac electrical signal segments that extend beyond an expected QRS signal width to identify the noisy signal segments based on the morphology parameters.

[0005] In one example, the present disclosure provides a medical device, including a sensing circuit having a first sensing channel, the first sensing channel being configured to receive a first cardiac electrical signal and sense an R wave in response to the first cardiac electrical signal crossing a sensing amplitude threshold, and the sensing circuit having a second sensing channel, the second sensing channel being configured to receive a second cardiac electrical signal. The second sensing channel receives the second cardiac electrical signal via a sensing electrode vector different from a sensing electrode vector used by the first sensing channel. The medical device further includes a memory and a control circuit coupled to the sensing circuit and the memory. The control circuit is configured to store a time segment of the second cardiac electrical signal in the memory for each of the plurality of R waves sensed by the first sensing channel. The control circuit is configured to: for each of the plurality of stored time segments, determine a morphology parameter associated with signal noise from the stored time segment, and detect the corresponding stored time segment as a noisy signal segment based on the morphology parameter determined for the stored time segment. The control circuit stops detecting a tachyarrhythmia episode in response to detecting at least a threshold number of the stored time segments as noisy signal segments.

[0006] In another example, the present disclosure provides a method, comprising: sensing an R wave by a first sensing channel of a sensing circuit of a medical device in response to a first cardiac electrical signal crossing a sensing amplitude threshold, the first cardiac electrical signal being received by the first sensing channel via a first sensing electrode vector coupled to the medical device; storing a time segment of a second cardiac electrical signal in a memory for each of the plurality of R waves sensed by the first sensing channel, the second cardiac electrical signal being received via a second sensing electrode vector coupled to the medical device and different from the first sensing electrode vector. The method further comprises: determining a morphology parameter associated with signal noise according to the stored time segment for each of the plurality of stored time segments, detecting the corresponding stored time segment as a noisy signal segment based on the morphology parameter determined for the stored time segment; and stopping detecting a tachyarrhythmia episode in response to detecting at least a threshold number of the stored time segments as noisy signal segments.

[0007] In another example, the present disclosure provides a non-transitory computer-readable storage medium, comprising a set of instructions, which, when executed by a control circuit of a medical device, cause the medical device to: sense an R wave through a first sensing channel of a sensing circuit of the medical device in response to a first cardiac electrical signal crossing a sensing amplitude threshold, the first cardiac electrical signal being received by the first sensing channel via a first sensing electrode vector coupled to the medical device; store a time segment of a second cardiac electrical signal in a medical device memory in response to each of the multiple R waves sensed by the first sensing channel, the second cardiac electrical signal being received by a second sensing channel of the medical device via a second sensing electrode vector; for each of the multiple stored time segments, determine a morphological parameter associated with signal noise according to the stored time segment and detect the corresponding stored time segment as a noisy signal segment based on the morphological parameter determined for the stored time segment; and stop detecting a rapid arrhythmia attack in response to detecting at least a threshold number of the stored time segments as noisy signal segments.

[0008] The present summary is intended to provide an overview of the subject matter described in the present disclosure. The present summary is not intended to provide an exclusive or exhaustive explanation of the apparatus and methods described in detail in the following figures and the specification. Further details of one or more examples are set forth in the following figures and the specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1A and Figure 1B is a conceptual diagram of an extracardiovascular ICD system according to an example.

[0010] FIG. 2A to FIG. 2C Different implant configurations are used to implant Figure 1A Conceptual diagram of a patient with an extracardiac ICD system.

[0011] Figure 3 is a conceptual diagram of a distal portion of a cardiovascular external lead having an electrode configuration according to another example.

[0012] Figure 4 Based on an example Figures 1A to 2C Schematic diagram of an ICD.

[0013] Figure 5 Based on an example Figure 4 Schematic diagram of the circuit system included in the sensing circuit.

[0014] Figure 6 Can be included in Figure 5 FIG. 5 is a graph showing the attenuation characteristics of the notch filter in the sensing circuit. FIG.

[0015] Figure 7 Based on an example Figures 1A to 2C Flow chart of a method performed by an ICD for sensing and validating R waves for tachyarrhythmia detection.

[0016] Figure 8 is a graphical representation of filtered cardiac electrical signals and amplitude ratio thresholds that may be applied to confirm an R-wave sensing event.

[0017] Fig. 9 Can be stored in Figures 1A to 2C An example of a lookup table of amplitude ratio thresholds in the memory of an ICD for confirming R-wave sensing events.

[0018] Fig.10 is a flow chart of a method for detecting tachyarrhythmias by an ICD according to one example.

[0019] Fig.11 is a flow chart of a method for detecting tachyarrhythmias by an ICD according to another example.

[0020] Fig.12 Based on another example Figure 4 Schematic diagram of the circuit system included in the sensing circuit.

[0021] Fig.13 is a flow chart of a method for detecting tachyarrhythmia by an ICD according to yet another example.

[0022] Fig.14 is a flow chart of a method performed by an ICD for discontinuing ventricular tachyarrhythmia detection in response to an overall morphology suppression rule.

[0023] Fig.15 , Fig.16 and Fig.17 is a flow chart of an illustrative method for determining gross morphology parameters of a cardiac electrical signal that can be used to detect noisy signal segments.

[0024] Fig.18 is used to Fig.15 , Fig.16 and Fig.17 Flow chart of a method for comparing overall morphological parameters with noisy segment detection criteria and detecting cardiac electrical signal segments as noisy segments.

[0025] Fig.19 It is a timing diagram depicting a time segment, on which morphology parameters, amplitude parameters and signal width parameters related to the baseline noise can be determined to determine whether the corresponding time period is a noisy segment.

[0026] Fig. 20 is a flow chart of a method for comparing an overall morphology parameter with a noise detection criterion and detecting the segment as a noisy segment according to another example. DETAILED DESCRIPTION

[0027] In general, the present disclosure describes techniques for detecting noise contamination of cardiac electrical signals in a medical device system and ceasing to detect ventricular tachyarrhythmias in response to the detection of the noise. The medical device system can be any implantable or external medical device capable of sensing cardiac electrical signals, including an implantable pacemaker, implantable cardioverter-defibrillator (ICD), cardiac resynchronization therapy (CRT) device, or cardiac monitor coupled to extracardiovascular, transvenous, epicardial, or intrapericardial leads carrying sensing electrodes; a leadless pacemaker, ICD, or cardiac monitor with housing-based sensing electrodes; and an external pacemaker, defibrillator, or cardiac monitor coupled to external electrodes, body surface electrodes, or skin electrodes.

[0028] However, these techniques are described in conjunction with implantable medical leads that carry extra-cardiovascular electrodes. As used herein, the term "extra-cardiovascular" refers to a location outside of the blood vessels, heart, and pericardium surrounding the patient's heart. The implantable electrodes carried by the extra-cardiovascular leads can be positioned extra-thoracic (outside the chest cavity and sternum) or intra-thoracic (below the chest cavity or sternum), but are generally not in close contact with myocardial tissue. The technology disclosed herein provides a method for detecting noisy signals acquired using extra-cardiovascular electrodes and ceasing to detect ventricular tachycardia (VT) and ventricular fibrillation (VF) when signal noise is identified.

[0029] Figure 1A and Figure 1B is a conceptual diagram of an extracardiovascular ICD system 10 according to one example. Figure 1A is a front view of ICD system 10 implanted in patient 12 . Figure 1B 1 is a side view of an ICD system 10 implanted in a patient 12. The ICD system 10 includes an ICD 14 connected to an extracardiac electrical stimulation and sensing lead 16. The ICD system 10 is described in the context of an ICD system 10 capable of providing defibrillation shocks and / or cardioversion shocks as well as pacing pulses. Figure 1A and Figure 1B .

[0030] ICD 14 includes a housing 15 that forms an airtight seal that protects the internal components of ICD 14. The housing 15 of ICD 14 can be formed of a conductive material such as titanium or a titanium alloy. The housing 15 can act as an electrode (sometimes referred to as a metal shell electrode). The housing 15 can be used as an active metal shell electrode for delivering cardioversion / defibrillation (CV / DF) shocks or other high-voltage pulses delivered using a high-voltage therapy circuit. In other examples, the housing 15 can be used to deliver unipolar low-voltage cardiac pacing pulses in conjunction with a lead-based cathode electrode and for sensing cardiac electrical signals in conjunction with a lead-based electrode. In other instances, the housing 15 of ICD 14 can include multiple electrodes on an external portion of the housing. The (multiple) external portions of the housing 15 that act as (multiple) electrodes can be coated with materials such as titanium nitride.

[0031] ICD 14 includes a connector assembly 17 (also referred to as a connector block or connector header) that includes electrical feedthroughs that intersect housing 15 to provide electrical connections between conductors extending within lead bodies 18 of leads 16 and electronic components included within housing 15 of ICD 14. As will be described in further detail herein, housing 15 may house one or more processors, memory, transceivers, electrical cardiac signal sensing circuitry, therapy delivery circuitry, power supplies, and other components for sensing cardiac electrical signals, detecting cardiac rhythms, and controlling and delivering electrical stimulation pulses for treating abnormal cardiac rhythms.

[0032] Lead 16 includes an elongated lead body 18 having a proximal end 27 including a lead connector (not shown) configured to connect to ICD connector assembly 17 and a distal end 25 including one or more electrodes. Figure 1A and Figure 1B In the example shown, the distal portion 25 of the lead 16 includes defibrillation electrodes 24 and 26 and pacing / sensing electrodes 28, 30, and 31. In some cases, the defibrillation electrodes 24 and 26 can form a defibrillation electrode together because they can be configured to be activated simultaneously. Alternatively, the defibrillation electrodes 24 and 26 can form separate defibrillation electrodes, in which case each of the electrodes 24 and 26 can be activated independently. In some instances, the defibrillation electrodes 24 and 26 are coupled to electrically isolated conductors, and the ICD 14 may include a switching mechanism to allow the electrodes 24 and 26 to be used as a single defibrillation electrode (e.g., activated simultaneously to form a common cathode or anode) or as separate defibrillation electrodes (e.g., activated individually, one as a cathode and one as an anode; or activated one at a time, one as an anode or cathode and the other remains inactive, wherein the housing 15 acts as an active electrode).

[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 can be elongated coil electrodes and typically have a relatively high surface area for delivering high voltage electrical stimulation pulses compared to low voltage pacing and sensing electrodes 28, 30, and 31. However, in addition to or in lieu of high voltage stimulation therapy, electrodes 24 and 26 and housing 15 can also be used to provide pacing functions, sensing functions, or both pacing functions and sensing functions. In this sense, the use of the term "defibrillation electrodes" herein should not be construed as limiting electrodes 24 and 26 to only high voltage cardioversion / defibrillation shock therapy applications. For example, electrodes 24 and 26 can be used in a pacing electrode vector to deliver extracardiovascular pacing pulses such as ATP pulses and / or in a sensing vector to sense cardiac electrical signals and detect VT and VF.

[0034] Electrodes 28, 30, and 31 are relatively small surface area electrodes for delivering low voltage pacing pulses and for sensing cardiac electrical signals. Electrodes 28, 30, and 31 are referred to as pacing / sensing electrodes because they are generally configured for low voltage applications, e.g., as cathodes or anodes for delivering pacing pulses and / or sensing cardiac electrical signals. In some instances, electrodes 28, 30, and 31 may provide only pacing functionality, only sensing functionality, or both.

[0035] exist Figure 1A and Figure 1B In the example shown, electrode 28 is positioned proximal to defibrillation electrode 24, and electrode 30 is positioned between defibrillation electrodes 24 and 26. A third pacing / sensing electrode 31 may be positioned distal to defibrillation electrode 26. Figure 1A and Figure 1B In the example of FIG. 1 , electrodes 28 and 30 are illustrated as ring electrodes, and electrode 31 is illustrated as a hemispherical tip electrode. However, electrodes 28, 30, and 31 may include any of a variety of different types of electrodes, including ring electrodes, short coil electrodes, hemispherical electrodes, directional electrodes, segmented electrodes, etc., and may be positioned anywhere along distal portion 25 of lead 16 and are not limited to the illustrated locations. Further, electrodes 28, 30, and 31 may have similar types, shapes, sizes, and materials or may be different from one another.

[0036] Lead 16 extends from connector assembly 27 of ICD 14 centrally toward the center of the torso of patient 12 (e.g., toward xiphoid process 20 of patient 12) subcutaneously or submuscularly above thorax 32. At a location proximal to xiphoid process 20, lead 16 bends or turns and extends upwardly above thorax and / or sternum, subcutaneously or submuscularly, substantially parallel to sternum 22. Although in Figure 1A and Figure 1B2 is shown as being laterally offset from the sternum 22 and extending substantially parallel to the sternum, but the lead 16 may be implanted at other locations, such as above the sternum 22, offset to the right or left of the sternum 22, angled laterally from the sternum 22 toward the left or right, etc. Alternatively, the lead 16 may be placed along other subcutaneous or submuscular routes. The path of the cardiovascular external lead 16 may depend on the location of the ICD 14, the arrangement and location of the electrodes carried by the lead distal portion 25, and / or other factors.

[0037] The conductor (not shown) extends from the lead connector at the proximal lead end 27 through one or more lumens of the elongated lead body 18 of the lead 16 to electrodes 24, 26, 28, 30 and 31 positioned along the distal portion 25 of the lead body 18. The lead body 18 can have a tubular or cylindrical shape. In other examples, the distal portion 25 (or all) of the elongated lead body 18 can have a flat, ribbon or paddle shape. The lead body 18 of the lead 16 can be formed of a non-conductive material including silicone, polyurethane, fluoropolymer, mixtures thereof, and other suitable materials and is shaped to form one or more lumens in which the one or more conductors extend. However, the technology disclosed herein is not limited to this configuration or to any particular lead body design.

[0038] The elongated electrical conductors contained within lead body 18 are each electrically coupled to corresponding defibrillation electrodes 24 and 26 and pacing / sensing electrodes 28, 30, and 31, which may be separate corresponding insulated conductors within the lead body. The corresponding conductors electrically couple electrodes 24, 26, 28, 30, and 31 to circuitry, such as therapy delivery circuitry and / or sensing circuitry, of ICD 14 via connections in connector assembly 17 including associated electrical feedthroughs that cross housing 15. The electrical conductors transmit therapy from the therapy delivery circuitry within ICD 14 to one or more of defibrillation electrodes 24 and 26 and / or pacing / sensing electrodes 28, 30, and 31, and transmit sensed electrical signals from one or more of defibrillation electrodes 24 and 26 and / or pacing / sensing electrodes 28, 30, and 31 to sensing circuitry within ICD 14.

[0039] The ICD 14 may obtain electrical signals corresponding to the electrical activity of the heart 8 via a sensing vector combination including a combination of electrodes 28, 30, and / or 31. In some examples, the housing 15 of the ICD 14 is used in the sensing electrode vector in combination with one or more of the electrodes 28, 30, and / or 31. The ICD 14 may even obtain cardiac electrical signals using a sensing vector including one or both of the defibrillation electrodes 24 and / or 26 (e.g., between electrodes 24 and 26 or one of electrodes 24 or 26 combined with one or more of electrodes 28, 30, 31) and / or the housing 15.

[0040] The ICD 14 analyzes the cardiac electrical signals received from one or more of the sensing vectors to monitor for abnormal rhythms, such as bradycardia, VT, or VF. The ICD 14 may analyze the heart rate and / or the morphology of the cardiac electrical signals to monitor for tachyarrhythmias according to any of a variety of tachyarrhythmia detection techniques. An example technique for detecting tachyarrhythmias is described in U.S. Pat. No. 7,761,150 (Ghanem et al.).

[0041] The ICD 14 generates and delivers electrical stimulation therapy in response to detection of a tachyarrhythmia (e.g., VT or VF). The ICD 14 may deliver ATP in response to VT detection, and in some cases, may deliver ATP before a CV / DF shock or during charging of a high-voltage capacitor in an attempt to avoid the need to deliver a CV / DF shock. ATP may be delivered using an extracardiac pacing electrode vector selected from any one of electrodes 24, 26, 28, 30, 31 and / or housing 15. The pacing electrode vector may be different from the sensing electrode vector. In one example, cardiac electrical signals are sensed between pacing / sensing electrodes 28 and 30 and between one of pacing / sensing electrodes 28 or 30 and housing 15, and ATP pulses are delivered between a pacing / sensing electrode 30 used as a cathode electrode and a defibrillation electrode 24 used as a return anode electrode. In other examples, pacing pulses may be delivered between a pacing / sensing electrode 28 and either (or both) of a defibrillation electrode 24 or 26 or between a defibrillation electrode 24 and a defibrillation electrode 26. These examples are not intended to be limiting, and it should be recognized that other sensing electrode vectors and pacing electrode vectors may be selected based on individual patient needs.

[0042] If ATP does not successfully terminate VT or when VF is detected, ICD 14 can deliver one or more cardioversion or defibrillation (CV / DF) shocks via one or both of defibrillation electrodes 24 and 26 and / or housing 15. ICD 14 can use electrodes 24 and 26, alone or together, as cathodes (or anodes) and housing 15 as anodes (or cathodes) to deliver CV / DF shocks. ICD 14 can generate and use a pacing electrode vector including electrodes 24, 26, 28, 30, and 31 and one or more of housing 15 of ICD 14 to deliver other types of electrical stimulation pulses, such as post-shock pacing pulses or bradycardia pacing pulses.

[0043] Figure 1A and Figure 1BThe present invention is illustrative in nature and should not be considered to limit the practice of the technology disclosed herein. In other examples, lead 16 may include less than three pacing / sensing electrodes or more than three pacing / sensing electrodes and / or a single defibrillation electrode or more than two electrically isolated or electrically coupled defibrillation electrodes or electrode segments. Pacing / sensing electrodes 28, 30 and / or 31 may be positioned elsewhere along the length of lead 16. For example, lead 16 may include a single pacing / sensing electrode 30 between defibrillation electrodes 24 and 26 and no pacing / sensing electrode at the distal end of defibrillation electrode 26 or the proximal end of defibrillation electrode 24. Various example configurations of cardiovascular external leads and electrodes and sizes that can be implemented in conjunction with the cardiovascular extra-cardiovascular pacing technology disclosed herein are described in U.S. Publication No. 2015 / 0306375 (Marshall et al.) and U.S. Publication No. 2015 / 0306410 (Marshall et al.).

[0044] ICD 14 is shown as being implanted subcutaneously on the left side of patient 12's body along thorax 32. In some instances, 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 at other subcutaneous or submuscular locations within patient 12. For example, ICD 14 may be implanted in a subcutaneous pocket in the pectoralis region. In this case, lead 16 may extend subcutaneously or submuscularly from ICD 14 toward the manubrium of sternum 22 and bend or turn subcutaneously or submuscularly downward from the manubrium and extend to a desired location. In yet another example, ICD 14 may be placed in the abdomen. Lead 16 may also be implanted in other extracardiac locations. For example, as described with respect to FIG. 2A to FIG. 2C As depicted, the distal portion 25 of the lead 16 may be implanted in the substernal space beneath the sternum / thoracic cavity.

[0045] External device 40 is shown in telemetric communication with ICD 14 via communication link 42. External device 40 may include a processor, a display, a user interface, a telemetry unit, and other components for communicating with ICD 14 to transmit and receive data via communication link 42. A radio frequency (RF) link, such as Wi-Fi or Medical Implant Communications Service (MICS) or other RF or communications bandwidth, establishes a communications link 42 between the ICD 14 and the external device 40 .

[0046] The external device 40 may be embodied as a programmer used in a hospital, clinic, or surgeon's office to retrieve data from the ICD 14 and program operating parameters and algorithms in the ICD 14 for controlling ICD functions. The external device 40 may be used to program R-wave sensing parameters, cardiac rhythm detection parameters, and therapy control parameters used by the ICD 14. Data stored or acquired by the ICD 14, including physiological signals or associated data derived therefrom, device diagnostics, and a history of detected rhythm episodes and delivered therapies, may be retrieved from the ICD 14 by the external device 40 following an interrogation command. Alternatively, the external device 40 may be embodied as a home monitor or handheld device.

[0047] FIG. 2A to FIG. 2C Is implanted with Figure 1A and Figure 1B A conceptual diagram of a patient 12 with an extracardiovascular ICD system 10 arranged in different implant configurations is shown in FIG. Figure 2A is a front view of patient 12 having ICD system 10 implanted therein. Figure 2B is a side view of patient 12 having ICD system 10 implanted therein. Figure 2C is a lateral view of a patient 12 implanted with an ICD system 10. In this arrangement, a cardiovascular external lead 16 of the system 10 is at least partially implanted beneath a sternum 22 of the patient 12. The lead 16 extends subcutaneously or submuscularly from the ICD 14 toward the xiphoid process 20 and bends or turns at a location proximal to the xiphoid process 20 and extends upward within the anterior mediastinum 36 in a substernal position.

[0048] The anterior mediastinum 36 can be viewed as being bounded laterally by the pleura 39, posteriorly by the pericardium 38, and anteriorly by the sternum 22. In some instances, the anterior wall of the anterior mediastinum 36 can also be formed by the transverse thoracic muscle and one or more costal cartilages. The anterior mediastinum 36 includes a certain amount of loose connective tissue (such as alveolar tissue), adipose tissue, some lymphatic vessels, lymph glands, substernal muscle tissue, small side branches of the internal thoracic artery or vein, and the thymus. In one example, the distal portion 25 of the lead 16 extends substantially along the posterior side of the sternum 22 within the loose connective tissue and / or substernal muscle tissue of the anterior mediastinum 36.

[0049] Leads that are implanted so that the distal portion 25 is substantially within the anterior mediastinum 36 may be referred to as "substernal leads." FIG. 2A to FIG. 2C, lead 16 is positioned substantially centrally below sternum 22. However, in other examples, lead 16 may be implanted such that it is laterally offset from the center of sternum 22. In some examples, lead 16 may extend laterally such that distal portion 25 of lead 16 is below / under thoracic cavity 32 (in addition to or in lieu of sternum 22). In other examples, distal portion 25 of lead 16 may be implanted in other extracardiovascular intrathoracic locations including the pleural cavity or around and near but generally not within the perimeter of pericardium 38 of heart 8. Other implant locations and lead and electrode arrangements that may be used in conjunction with the cardiac pacing techniques described herein are generally disclosed in the above-referenced patent applications.

[0050] Figure 3 is a conceptual diagram showing a curved distal end portion 25' having a lead body 18' Figures 1A to 2C 1 '. The lead body 18' can be formed to have a curved, bent, meandering or zigzag shape along the distal portion 25'. In the example shown, the defibrillation electrodes 24' and 26' are carried along the curved portion of the lead body 18'. The pacing / sensing electrode 30' is carried between the defibrillation electrodes 24' and 26'. The pacing / sensing electrode 28' is carried at the proximal end of the proximal defibrillation electrode 24'. In this example, no electrode is provided at the distal end of the defibrillation electrode 26'.

[0051] like Figure 3 , the lead body 18' may be formed to have a curved distal portion 25' including two "C" shaped curves, which together may resemble the Greek letter epsilon "epsilon". Defibrillation electrodes 24' and 26' are each carried by one of the two corresponding C-shaped portions of the lead body distal portion 25', which extend or curve away from the central axis 33 of the lead body 18' in the same direction. In the example shown, the pacing / sensing electrode 28' is at the proximal end of the C-shaped portion carrying electrode 24', and the pacing / sensing electrode 30' is at the proximal end of the C-shaped portion carrying electrode 26'. In some instances, the pacing / sensing electrodes 28' and 30' may be generally aligned with the central axis 33 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 electrodes 28' and 30'. Other examples of cardiovascular external leads that can be implemented utilizing the pacing techniques described herein are generally disclosed in U.S. Patent Publication No. 2016 / 0158567 (Marshall et al.), which include one or more defibrillation electrodes and one or more pacing and sensing electrodes carried by a curved, meandering, wavy, or serrated distal portion of the lead body.

[0052] Figure 41 is a schematic diagram of an ICD 14 according to an example. The electronic circuit system enclosed in the housing 15 (in Figure 4 The ICD 14 includes software, firmware, and hardware that collaborate to monitor cardiac electrical signals, determine when electrical stimulation therapy is needed, and deliver therapy on demand according to programmed therapy delivery algorithms and control parameters. The software, firmware, and hardware are configured to detect tachyarrhythmias and deliver anti-tachyarrhythmia therapy, for example, to detect ventricular tachyarrhythmias and in some cases distinguish between VT and VF to determine when ATP or CV / DF shocks are needed. The ICD 14 is coupled to cardiovascular external leads such as lead 16 carrying external cardiovascular electrodes 24, 26, 28, 30, and 31 (if present) to deliver electrical stimulation pulses to the patient's heart and sense cardiac electrical signals.

[0053] ICD 14 includes control circuitry 80, memory 82, therapy delivery circuitry 84, sensing circuitry 86, and telemetry circuitry 88. Power supply 98 provides power to the circuitry of ICD 14, including each of components 80, 82, 84, 86, and 88, when needed. Power supply 98 may include one or more energy storage devices, such as one or more rechargeable or non-rechargeable batteries. Connections between power supply 98 and each of the other components 80, 82, 84, 86, and 88 will be based on the Figure 4 , but for clarity, the connections are not shown. For example, the power supply 98 can be coupled to a low voltage (LV) charging circuit and a high voltage (HV) charging circuit included in the therapy delivery circuit 84 to charge the low voltage capacitors and high voltage capacitors respectively included in the therapy delivery circuit 84 for generating corresponding low voltage pacing pulses such as bradycardia pacing pulses, post-shock pacing pulses, or ATP pulses, or for generating high voltage pulses such as CV / DF shock pulses. In some examples, the high voltage capacitors rather than the low voltage capacitors are charged and used to deliver ATP pulses, post-shock pacing pulses, or other pacing pulses. The power supply 98 is also coupled to components of the sensing circuit 86 as needed, such as a sensing amplifier, an analog-to-digital converter, a switching circuit system, etc.

[0054] Figure 4The functional blocks shown in represent the functions included in the ICD 14 and may include any discrete and / or integrated electronic circuit components that implement analog circuits and / or digital circuits capable of producing the functions attributed to the ICD 14 herein. The various components may include application specific integrated circuits (ASICs), electronic circuits, processors (shared, dedicated, or groups) and memories that execute one or more software or firmware programs, combinational logic circuits, state machines, or other suitable components or combinations of components that provide the described functions. The specific form of software, hardware, and / or firmware used to implement the functions disclosed herein will be determined primarily by the specific system architecture employed in the ICD and the specific detection and therapy delivery methods employed by the ICD. In view of the disclosure herein, it is within the ability of those skilled in the art to provide software, hardware, and / or firmware for implementing the described functions in the context of any modern ICD system.

[0055] Memory 82 may include any volatile, nonvolatile, magnetic, or electrically non-transitory computer-readable storage medium, such as random access memory (RAM), read-only memory (ROM), nonvolatile RAM (NVRAM), electrically erasable programmable ROM (EEPROM), flash memory, or any other memory device. In addition, 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 or other ICD components to perform various functions attributed to ICD 14 or those ICD components. The non-transitory computer-readable medium storing instructions may include any of the media listed above.

[0056] The functions of the ICD 14 attributed to this article may be embodied as one or more integrated circuits. Depicting different features as components is intended to highlight different functional aspects and does not necessarily imply that such components must be implemented by separate hardware or software components. Instead, the functions associated with one or more components may be performed by separate hardware, firmware, or software components, or integrated within common hardware, firmware, or software components. For example, cardiac event sensing operations and rapid arrhythmia detection operations may be performed by sensing circuit 86 under the control of control circuit 80, and may include operations implemented in a processor or other signal processing circuit system included in control circuit 80 that executes instructions stored in memory 82 and control signals such as blanking intervals and timing periods and sensing threshold amplitude signals sent from control circuit 80 to sensing circuit 86.

[0057] The control circuit 80 communicates with the therapy delivery circuit 84 and the sensing circuit 86, for example, via a data bus, to sense cardiac electrical activity, detect cardiac rhythm, and control the delivery of cardiac electrical stimulation therapy in response to sensed cardiac signals. The therapy delivery circuit 84 and the sensing circuit 86 are electrically coupled to the leads 16 (e.g., Figures 1A to 3 ) carries electrodes 24, 26, 28, 30 and 31 (if present, as shown) Figure 1A and Figure 2A as shown) and a housing 15 which may serve as a common electrode or ground electrode or as an active metal shell electrode for delivering CV / DF shock pulses or cardiac pacing pulses.

[0058] The sensing circuit 86 can be selectively coupled to the electrodes 28, 30, 31 and / or the housing 15 to monitor the electrical activity of the patient's heart. In addition, the sensing circuit 86 can be selectively coupled to the defibrillation electrodes 24 and / or 26 for use in a sensing electrode vector. The sensing circuit 86 is enabled to selectively receive cardiac electrical signals from at least two sensing electrode vectors from the available electrodes 24, 26, 28, 30, 31 and the housing 15. At least two cardiac electrical signals from two different sensing electrode vectors can be received simultaneously by the sensing circuit 86, and the sensing circuit 86 can monitor one or both of the cardiac electrical signals at a time to sense the cardiac electrical signals. For example, the sensing circuit 86 may include a switching circuit system for selecting which of the electrodes 24, 26, 28, 30, 31 and the housing 15 to couple to, for example, as in combination Figure 5 and Fig.12 The described sensing channels 83 or 85 include cardiac event detection circuitry. The switching circuitry may include a switch array, a switch matrix, a multiplexer, or any other type of switching device suitable for selectively coupling components of the sensing circuit 86 to selected electrodes. The cardiac event detection circuitry within the sensing circuit 86 may include one or more sense amplifiers, filters, rectifiers, threshold detectors, comparators, analog-to-digital converters (ADCs), or other devices such as a combination of a plurality of sense amplifiers, filters, rectifiers, threshold detectors, comparators, analog-to-digital converters (ADCs), or other devices such as a plurality of sense amplifiers, filters, rectifiers, threshold detectors, comparators, analog-to-digital converters (ADCs), or other devices such as a plurality of sense amplifiers, filters, rectifiers, threshold detectors, comparators, analog-to-digital converters (ADCs), or other devices such as a plurality of sense amplifiers, filters, rectifiers, threshold detectors, comparators, analog-to-digital converters (ADCs), or other devices such as a plurality of sense amplifiers, filters, rectifiers, threshold detectors, comparators, analog-to-digital converters (ADCs), or other devices such as a plurality of sense amplifiers, filters, rectifiers, threshold detectors, threshold detectors, comparators, threshold detectors ... Figure 5 and Fig.12 The cardiac event sensing threshold may be automatically adjusted by sensing circuit 86 under the control of control circuit 80 based on a timing period and sensing threshold determined by control circuit 80, stored in memory 82, and / or controlled by hardware of control circuit 80 and / or sensing circuit 86.

[0059] In some examples, the sensing circuit 86 includes a plurality of sensing channels 83 and 85 for acquiring cardiac electrical signals from a plurality of sensing vectors selected from electrodes 24, 26, 28, 30, 31 and housing 15. Each sensing channel 83 and 85 can be configured to amplify, filter and digitize the cardiac electrical signals received from the selected electrodes coupled to the corresponding sensing channel to improve the signal quality for detecting cardiac events such as R waves. For example, each sensing channel 83 and 85 can include a pre-filter and an amplifier for filtering and amplifying the signals received from the selected electrode pair. The resulting raw cardiac electrical signals can be transmitted from the pre-filter and the amplifier to the cardiac event detection circuit system in at least one sensing channel 83 to sense cardiac events in real time from the received cardiac electrical signals. As disclosed herein, the sensing channel 83 can be configured to sense cardiac events such as R waves based on a cardiac event sensing threshold, and the second sensing channel 85 can be configured to transmit the digitized cardiac electrical signals obtained from the different sensing electrode vectors to the control circuit 80 for confirming the cardiac events sensed by the first sensing channel 83.

[0060] When a cardiac event is detected based on a sensing threshold crossing, the first sensing channel 83 may generate a sensing event signal such as an R-wave sensing event signal that is transmitted to the control circuit 80. The sensing event signal is used by the control circuit 80 to trigger storage of a time segment of the second cardiac electrical signal for post-processing and analysis to confirm the following, for example, in combination with Figures 7 to 9 The described R-wave sensing event signal. The memory 82 can be configured to store a predetermined number of cardiac electrical signal segments, such as at least one, two or other number of cardiac electrical signal segments, in a circular buffer under the control of the control circuit 80. Each segment can be written to the memory 82 within a time interval extended before and after the R-wave sensing event signal generated by the first sensing channel 83. When confirmation of the R wave sensed by the first sensing channel 83 is required based on the detection of a predetermined number of tachyarrhythmia intervals, the control circuit 80 can access the stored cardiac electrical signal segments, and the detection can be prior to the tachyarrhythmia detection.

[0061] The R-wave sensed event signal is also used by the control circuit 80 to determine the RR interval (RRI) in order to detect tachyarrhythmias and determine the need for treatment. The RRI is the time interval between consecutive sensed R waves, and can be determined between consecutive R-wave sensed event signals received from the sensing circuit 86. For example, the control circuit 80 may include a timing circuit 90, which is used to determine the RRI between consecutive R-wave sensed event signals received from the sensing circuit 86, and is used to control various timers and / or counters used to control the timing of therapy delivery by the therapy delivery circuit 84. In addition, the timing circuit 90 can set time windows such as morphology template windows, morphology analysis windows, or perform other timing-related functions of the ICD 14, including synchronizing the cardioversion shock or other therapy delivered by the therapy delivery circuit 84 with sensed cardiac events.

[0062] The control circuit 80 is also shown to include a tachyarrhythmia detector 92 that is configured to analyze signals received from the sensing circuit 86 to detect tachyarrhythmia episodes. The tachyarrhythmia detector 92 may be implemented in the control circuit 80 as hardware and / or firmware that processes and analyzes signals received from the sensing circuit 86 to detect VT and / or VF. In some examples, the timing of the R-wave sensed event signals received from the sensing circuit 86 is used by the timing circuit 90 to determine the RRI between the sensed event signals. The tachyarrhythmia detector 92 may include a comparator and a counter that counts the RRIs determined by the timing circuit 92 that fall into various rate detection regions used to determine the ventricular rate or to perform other rate-based or interval-based assessments to detect and distinguish VT and VF.

[0063] For example, the tachyarrhythmia detector 92 may compare the RRI determined by the timing circuit 90 to one or more tachyarrhythmia detection interval regions, such as a tachycardia detection interval region and a fibrillation detection interval region. RRIs that fall within the detection interval regions are counted by a corresponding VT interval counter or a VF interval counter, and in some cases are counted in a combined VT / VF interval counter included in the tachyarrhythmia detector 92. When the interval counter reaches a detection threshold, a ventricular tachyarrhythmia may be detected by the tachyarrhythmia detector 92. The tachyarrhythmia detector 92 may be configured to perform other signal analysis to determine whether other detection criteria are met before detecting VT or VF, such as an R wave morphology criterion, an onset criterion, and a noise and oversensing suppression criterion. In combination Fig.10 , Fig.11 and Fig.13Examples of other parameters that may be determined based on cardiac electrical signals received by sensing circuit 86 for use in determining the state of tachyarrhythmia detection suppression rules that may cause cessation of VT or VF detection are described.

[0064] To support these additional analyses, the sensing circuit 86 may transmit digitized electrogram (ECG) signals to the control circuit 80 for morphology analysis performed by the tachyarrhythmia detector 92 to detect and distinguish cardiac rhythms. The cardiac electrical signals from the selected sensing vector, such as from the first sensing channel 83 and / or the second sensing channel 85, may be transmitted through filters and amplifiers, provided to a multiplexer, and thereafter converted to multi-bit digital signals by an analog-to-digital converter for storage in the memory 82, the filters, amplifiers, multiplexers, and analog-to-digital converters all being included in the sensing circuit 86. The memory 82 may include one or more circular buffers to temporarily store segments of the digital cardiac electrical signals for analysis by the control circuit 80 to confirm R waves sensed by the sensing channel 83, determine morphology match scores, detect T wave oversensing, detect noise contamination, and more functions as further described below.

[0065] The control circuit 80 may be a microprocessor-based controller that employs digital signal analysis techniques to characterize the digitized signals stored in the memory 82 in order to identify and classify the patient's cardiac rhythm using any of a number of signal processing methods for analyzing cardiac signals and cardiac event waveforms, such as R waves. Examples of devices and algorithms that may be adapted to utilize the techniques for performing R-wave sensing and confirmation and tachyarrhythmia detection described herein are generally disclosed in the following patents: U.S. Pat. No. 5,354,316 (Keimel); U.S. Pat. No. 5,545,186 (Olson et al.); U.S. Pat. No. 6,393,316 (Gillberg et al.); U.S. Pat. No. 7,031,771 (Brown et al.); U.S. Pat. No. 8,160,684 (Ghanem et al.); and U.S. Pat. No. 8,437,842 (Zhang et al.).

[0066] The therapy delivery circuit 84 includes: charging circuitry; one or more charge storage devices, such as one or more high voltage capacitors and / or low voltage capacitors; and switching circuitry that controls when the capacitor(s) are discharged across a selected pacing electrode vector or CV / DF shock vector. The capacitors may be charged to a programmed pulse amplitude and discharged for a programmed pulse width by the therapy delivery circuit 84 in accordance with a control signal received from the control circuit 80. The timing circuit 90 of the control circuit 80 may include various timers or counters that control when ATP or other cardiac pacing pulses are delivered. For example, the timing circuit 90 may include a programmable digital counter that is set by a microprocessor of the control circuit 80 to control basic time intervals 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, which may be based on programmed values ​​stored in the memory 82.

[0067] During pacing, an escape interval counter within the timing circuit 90 is reset when an R wave is sensed as indicated by a signal from the sensing circuit 86. In accordance with the selected pacing mode, when the escape interval counter expires, a pacing pulse is generated by the pulse output circuit of the therapy delivery circuit 84. The pacing output circuit is coupled to the desired pacing electrode via a switch matrix to discharge one or more capacitors across the pacing load. The escape interval counter is reset when a pacing pulse is generated and thereby controls the basic timing of cardiac pacing functions including ATP. The duration of the escape interval is determined by the control circuit 80 via the data / address bus. When the escape interval counter is reset by sensing an R wave, the count value present in the escape interval counter can be used to measure the RRI by the timing circuit 90 as described above so as to detect the occurrence of various arrhythmias by the tachyarrhythmia detector 92.

[0068] The memory 82 may include a read-only memory (ROM) in which resides a stored program that controls the operation of the control circuit 80. The memory 82 may further include a random access memory (RAM) or other memory device configured as a plurality of recirculating buffers capable of maintaining a series of measured RRIs, counts, or other data for analysis by the tachyarrhythmia detector 92 to predict or diagnose arrhythmias.

[0069] In response to detecting a ventricular tachycardia, ATP therapy may be delivered by loading a protocol from a microprocessor included in the control circuit 80 into the timing circuit 90 according to the type and rate of the detected tachycardia. In the event that a higher voltage cardioversion pulse or defibrillation pulse is required, for example, the tachyarrhythmia is VF or VT and is not terminated via ATP therapy, the control circuit 80 activates the cardioversion and defibrillation control circuit system included in the control circuit 80 to initiate charging of the high voltage capacitor via the charging circuit under the control of the high voltage charge control line, both of which are included in the therapy delivery circuit 84. The voltage on the high voltage capacitor is monitored via the voltage capacitor line, which is transmitted to the control circuit 80. When the voltage reaches a predetermined value set by the control circuit 80, a logic signal is generated on the capacitor full line that is transmitted to the therapy delivery circuit 84 to terminate charging. The defibrillation pulse or cardioversion pulse is delivered to the heart via the control bus by the output circuit of the therapy delivery circuit 84 under the control of the timing circuit 90. The output circuit determines the electrodes and pulse waveforms used to deliver the cardioversion pulse or defibrillation pulse. The therapy delivery and control circuitry generally disclosed in any of the above-referenced patents may be implemented in ICD 14 .

[0070] The control parameters used by control circuit 80 to detect cardiac rhythm and control therapy delivery can be programmed into memory 82 via telemetry circuit 88. Telemetry circuit 88 includes a circuit for communicating with external device 40 (eg, Figure 1A The telemetry circuit 88 may include a transceiver and antenna for communication with the patient 12 (as shown). Under the control of the control circuit 80, the telemetry circuit 88 may receive downlink telemetry from the external device 40 and send uplink telemetry to the external device. In some cases, the telemetry circuit 88 may be used to transmit and receive communication signals to / from another medical device implanted in the patient 12.

[0071] Figure 5 8 is a diagram of the circuit system included in the first sensing channel 83 and the second sensing channel 85 of the sensing circuit 86 according to one example. The first sensing channel 83 can be selectively coupled to the first sensing electrode vector via the switching circuit system (not shown) to receive the first cardiac electrical signal, and the first sensing electrode vector includes Figures 1A to 2CElectrodes carried by the cardiovascular external lead 16 shown. The first sensing channel 83 can be coupled to a sensing electrode vector that is a short dipole having a relatively short inter-electrode distance or spacing compared to the second electrode vector coupled to the second sensing channel 85. In the example shown, the first sensing electrode vector can include pacing / sensing electrodes 28 and 30. In other examples, depending on the inter-electrode spacing and position of the distal portion 25 of the lead 16, the first sensing electrode vector coupled to the sensing channel 83 can include pacing / sensing electrodes 30 and 31 and in some cases pacing / sensing electrodes 28 and 31. In other examples, for example, the first sensing channel 83 can be selectively coupled to a sensing electrode vector that includes the defibrillation electrodes 24 and / or 26, for example, a sensing electrode vector between the pacing / sensing electrode 28 and the defibrillation electrode 24, between the pacing / sensing electrode 30 and either of the defibrillation electrodes 24 or 26, or between the pacing / sensing electrodes 26 and 31. In some examples, the first sensing electrode vector can be between the defibrillation electrodes 24 and 26.

[0072] The sensing circuit 86 includes a second sensing channel 85 that receives a second cardiac electrical signal from a second sensing vector, such as a vector including electrode 30 and housing 15 as shown or a vector including electrode 28 and housing 15. The second sensing channel 85 can be selectively coupled to other sensing electrode vectors that can form a long dipole having a greater inter-electrode distance or spacing than the sensing electrode vector coupled to the first sensing channel 83. As described below, the second cardiac electrical signal received by the second sensing channel 85 via the long dipole can be used by the control circuit 80 for morphological analysis (including, for example, as combined with Fig.10 In other examples, any vector selected from available electrodes, such as electrodes 24, 26, 28, 30 and / or 31 and / or housing 15, can be included in the sensing electrode vector coupled to second sensing channel 85.

[0073] The electrical signals generated across the input electrodes 28 and 30 of the sensing channel 83 and across the input electrodes 30 and 15 of the sensing channel 85 are provided as differential input signals to the pre-filters and pre-amplifiers 62 and 72, respectively. Non-physiological high frequency and DC signals may be filtered by a low pass or band pass filter included in each of the pre-filters and pre-amplifiers 62 and 72, and high voltage signals may be removed by protection diodes included in the pre-filters and pre-amplifiers 62 and 72. The pre-filters and pre-amplifiers 62 and 72 may amplify the pre-filtered signals by a gain between 10 and 100 and in one example by a gain of 17.5, and may convert the differential signals to single-ended output signals that are transmitted to an analog-to-digital converter (ADC) 63 in the first sensing channel 83 and an ADC 73 in the second sensing channel 85. The pre-filters and amplifiers 62 and 72 may provide anti-aliasing filtering and noise reduction prior to digitization.

[0074] ADC 63 and ADC 73 convert the first cardiac electrical signal from an analog signal into a first digital bit stream and convert the second cardiac electrical signal into a second digital bit stream, respectively. In one example, ADC 63 and ADC 73 may be Sigma-Delta Converters (SDCs), but other types of ADCs may be used. In some examples, the outputs of ADC 63 and ADC 73 may be provided to a decimator (not shown) that acts as a digital low-pass filter that increases the resolution and reduces the sampling rate of the corresponding first and second cardiac electrical signals.

[0075] In the sensing channel 83, the digital output of the ADC 63 is transmitted to the filter 64, which may be a digital bandpass filter having a bandpass of approximately 10 Hz to 30 Hz for transmitting cardiac electrical signals such as R waves that typically occur in this frequency range. The bandpass filtered signal is transmitted from the filter 64 to the rectifier 65 and then to the R-wave detector 66. The R-wave detector 66 may include an automatically adjusted sense amplifier, comparator, and / or other detection circuit system that compares the filtered and rectified first cardiac electrical signal to an 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.

[0076] The R-wave sensing threshold may be controlled by the sensing circuit 86 and / or the control circuit 80 to a multi-level sensing threshold, as disclosed in U.S. Patent Application No. 15 / 142,171 (Cao et al., filed April 29, 2016). Briefly, the multi-level sensing threshold may have a starting sensing threshold that is maintained for a time interval equal to the tachycardia detection interval, and then drops to a second sensing threshold that is maintained until the expiration of a falling time interval, which may be 1 second to 2 seconds in length. The sensing threshold drops to a minimum sensing threshold after the falling time interval. The starting sensing threshold may be the lower of a predetermined percentage of the most recent previous sensed R-wave peak amplitude and a maximum sensing threshold limit determined using a sensitivity-related gain and a programmed sensitivity setting. In other examples, the R-wave sensing threshold used by the R-wave detector 66 may be set to a starting value based on the previous R-wave peak amplitude and decay linearly or exponentially over time until the minimum sensing threshold is reached. However, the technology of the present application is not limited to a particular behavior of the sensing threshold. Alternatively, other automatically adjusted sensing thresholds may be utilized.

[0077] In some examples, the filtered digitized cardiac electrical signal (output of filter 64) from sensing channel 83 can be stored in memory 82 for signal processing by control circuit 80 for detecting tachyarrhythmia attacks. In one example, the output of rectifier 64 is transmitted to differentiator 67, which determines an N-order differential signal 69 transmitted to memory 82. Differential signal 69 is sometimes also referred to as a "difference signal" because each sample point of differential signal 69 can be determined as the difference between the i-th input sample point and the corresponding iN input sample point. Control circuit 80 can retrieve the stored signal from memory 82 for signal analysis to be performed by tachyarrhythmia detector 92 according to the implemented tachyarrhythmia detection algorithm. For example, a T wave oversensing algorithm implemented in tachyarrhythmia detector 92 may detect evidence of T wave oversensing from first order difference signal 69 produced by differentiator 67, as described in U.S. Patent Application No. 62 / 367,221 (Attorney Docket No. C00013321.USP1, Cao et al.) Other examples of methods for detecting T wave oversensing using a differential signal that may be performed by tachyarrhythmia detector 92 are generally disclosed in U.S. Patent No. 7,831,304 (Cao et al.).

[0078] The second cardiac electrical signal digitized by ADC 73 can be transmitted to filter 74 for bandpass filtering, for example, from 10 Hz to 30 Hz. In some examples, sensing channel 85 includes notch filter 76. Notch filter 76 can be implemented in firmware or hardware and is provided to attenuate 50 Hz to 60 Hz electrical noise, muscle noise and other electromagnetic interference (EMI) or electrical noise / artifacts in the second cardiac electrical signal. Compared to intracardiac electrodes, using, for example, Figures 1A to 3 The cardiac electrical signals acquired by the cardiovascular external electrodes shown in are more likely to be contaminated by 50 Hz to 60 Hz electrical noise, muscle noise and other EMI, electrical noise / artifacts. Therefore, a notch filter 76 can be provided to significantly attenuate the amplitude of signals in the range of 50 Hz to 60 Hz, wherein the signals in the range of approximately 1 Hz to 30 Hz corresponding to the typical cardiac electrical signal frequencies are minimally attenuated. Figure 6 An example of a notch filter designed with minimal computational requirements and its filtering characteristics is described.

[0079] The output signal 78 of the notch filter 76 can be transmitted from the sensing circuit 86 to the memory 82 under the control of the control circuit 80 so that a segment of the second cardiac electrical signal 78 is stored in a temporary buffer of the memory 82. For example, the timing circuit 90 of the control circuit 80 can set a time interval or a plurality of sampling points relative to the R wave sensing event signal 68 received from the first sensing channel 83, and the second cardiac electrical signal 78 is stored in the memory 82 within the time interval or the plurality of sampling points. Figures 7 to 13 The buffered second cardiac electrical signal segments are described as being analyzed by the control circuit 80 on an as-needed triggered basis to confirm the R-wave sensed by the first sensing channel 83 .

[0080] Notch filter 76 may be implemented as a digital filter for real-time filtering performed by firmware as part of sensing channel 85 or by control circuit 80 to filter the buffered digital output of filter 74. In some examples, the output of filter 74 of sensing channel 85 may be stored in memory 82 at time segments defined with respect to R-wave sense event signal 68 prior to filtering by notch filter 76. When control circuit 80 is triggered to analyze the stored second cardiac electrical signal to confirm the R-wave sense event signal, for example, as in conjunction with Figure 7 , Fig.10 , Fig.11 and Fig.13As described, the notch filter 76 may be applied to the stored segments of the second cardiac electrical signal prior to further processing and analysis thereof. In this manner, if it is determined that the R-wave sensed by the first sensing channel 83 does not require analysis of the stored signal segments, the firmware implemented to perform the operation of the notch filter 76 need not be executed.

[0081] The configuration of sensing channels 83 and 85 is illustrative in nature and should not be considered to limit the technology described herein. Figure 5 The sensing channels 83 and 85 of the sensing circuit 86 may include more or fewer components than shown and described in the drawings. However, the first sensing channel 83 is configured to detect an R-wave from the first cardiac electrical signal in real time, for example, in hardware-implemented components, based on the first cardiac electrical signal crossing an R-wave sensing threshold, and the second sensing channel 85 is configured to provide the second cardiac electrical signal for storage in the memory 82 for post-processing and analysis by the control circuit 80, thereby confirming the R-wave sensing event signal generated by the first sensing channel 83.

[0082] Figure 6 is a graph 50 of the attenuation characteristics of the notch filter 76 of the second sensing channel 85. In one example, the notch filter 76 is implemented as a digital filter in firmware. The output of the digital notch filter can be determined by the firmware implemented in the second sensing channel 85 according to the following equation:

[0083] Y(n)=(x(n)+2x(n-2)+x(n-4)) / 4

[0084] Wherein, x(n) is the amplitude of the nth sample point of the digital signal received by the notch filter 76 for a sampling rate of 256 Hz, x(n-2) is the amplitude of the n-2 sample point and x(n-4) is the amplitude of the n-4 sample point. Y(n) is the amplitude of the nth sample point of the notch-filtered, digital second cardiac electrical signal. Figure 6 The graph 50 of represents the resulting attenuation of the amplitude Y(n) as a function of frequency. At a frequency of 60 Hz, the attenuation of the amplitude of Y(n) is -40 decibels (dB). At a frequency of 50 Hz, the attenuation is -20 dB, and at 23 Hz, which may be typical for the R wave of the cardiac electrical signal, the attenuation is limited to -3 dB. Therefore, the notch filter 76 can provide highly attenuated 50 Hz and 60 Hz noise, muscle noise, other EMI, and other electrical noise / artifacts while passing the lower frequency cardiac signal in the second cardiac electrical signal output of the sensing channel 85. Although the notch filter 76 may not attenuate frequencies close to the maximum frequency of 128 Hz, the filter 74 of the second sensing channel 85, which may be a bandpass filter, can sufficiently reduce the higher frequency range signal content above 60 Hz.

[0085] When using a different sampling rate other than 256 Hz, the number of sampling points indicated in the above equation for determining the notch filtered signal may be modified as desired, however, the resulting frequency response may or may not be consistent with Figure 6 The frequency response shown in FIG. 7 is the same as that shown in FIG. 7A . The notch filter 76 uses minimal computations with only two additions and three shifts required. In other examples, other digital filters may be used to attenuate 50 Hz and 60 Hz. For example, for a sampling rate of 256 Hz, the filtered signal Y(n) may be determined as Y(n)=(x(n)+x(n-1)+x(n-2)+x(n-3)) / 4, which has a ratio of 0.01 to 0.01 at 50 Hz and 60 Hz. Figure 6 The frequency response shown is less attenuated, but acts as a better amplifier at higher frequencies (greater than 60 Hz). Figure 6 The frequency response shown is a low pass notch filter with greater attenuation.

[0086] Figure 7 1 is a flow chart 100 of a method performed by ICD 14 for sensing and confirming an R wave for tachyarrhythmia detection according to one example. At blocks 102 and 104, sensing circuit 86 selects two different sensing electrode vectors for receiving a first cardiac electrical signal by first sensing channel 83 and receiving a second cardiac electrical signal by second sensing channel 85. The two sensing electrode vectors may be selected by a switching circuit system included in sensing circuit 86 under the control of control circuit 80. In some examples, the two sensing electrode vectors are programmed by a user and retrieved from memory 82 by control circuit 80 and transmitted to sensing circuit 86 as a vector selection control signal.

[0087] The first sensing vector selected at box 102 for obtaining the first cardiac electrical signal can be a relatively short dipole, for example, between electrodes 28 and 30 of lead 16 or between electrodes 28 and 24 or other electrode combinations as described above. The relatively short dipoles can include electrodes that are relatively very close to each other and relatively very close to the ventricular heart chamber compared to other available sensing electrode pairs. The first sensing vector can be a vertical sensing vector (relative to the patient's upright or standing position) or generally aligned with the heart axis to maximize the amplitude of the R wave in the first cardiac electrical signal for reliable R wave sensing.

[0088] The second sensing electrode vector used to obtain the second cardiac electrical signal at box 104 can be a relatively long dipole with a larger inter-electrode distance than the first sensing electrode vector. For example, the second sensing electrode vector can be selected as a vector between one of the pacing sensing electrodes 28 or 30 and the ICD housing 15, between one of the defibrillation electrodes 24 or 26 and the housing 15, or other combinations of an electrode and the housing 15 along the distal portion of the lead 16. In some examples, this sensing vector can be orthogonal or nearly orthogonal to the first sensing vector, but it is not required that the first sensing vector and the second sensing vector are orthogonal vectors. Compared with the first sensing electrode vector, the second sensing electrode vector can provide a relatively more global or far-field cardiac electrical signal. The second cardiac electrical signal obtained at box 104 can be used for waveform morphology analysis by the rapid arrhythmia detector 92 of the control circuit 80, and for cardiac signal analysis to confirm the R wave sensing event signal generated by the first sensing channel 83 of the sensing circuit 86.

[0089] At box 106, the sensing circuit 86 may generate an R-wave sense event signal in response to the first sensing channel 83 detecting that the first cardiac electrical signal crosses the R-wave sensing threshold. The R-wave sense event signal may be transmitted to the control circuit 80. In response to the R-wave sense event signal, the "yes" branch of box 106 is performed downward, and the control circuit 80 is triggered at box 108 to store a segment of the second cardiac electrical signal (sensing vector 2, box 104) received from the second sensing channel 85 in a circular buffer of the memory 82. The length of the digitized segment of the second cardiac electrical signal may be 100ms to 500ms, for example, including sampling points before and after the time of the R-wave sense event signal, and the sampling points may or may not be centered in time with the R-wave sense event signal received from the sensing circuit 86. For example, the segment may extend 100ms after the R-wave sense event signal and the duration may be 200ms to 500ms, so that the segment extends from approximately 100ms to 400ms before the R-wave sense event signal to 100ms after the R-wave sense event signal. In other examples, the segment may be centered on the R-wave sensed event signal or extend a greater number of sampling points after the R-wave sensed event signal than before it. In one example, the buffered segment of the cardiac electrical signal is at least 50 sampling points or approximately 200 ms acquired at a sampling rate of 256 Hz. In another example, the buffered segment is at least 92 sampling points or approximately 360 ms sampled at 256 Hz and may be used for morphology analysis, noise analysis, T wave oversensing, and / or other analysis performed by the tachyarrhythmia detector 92 to detect VT or VF. In combination Fig.10Other analyses of the buffered second cardiac electrical signal for detecting VT or VF, or ceasing VT or VF detection, are described that may be performed by the tachyarrhythmia detector 92. The memory 82 may be configured to store a predetermined number of second cardiac electrical segments, such as at least 1 and in some cases two or more cardiac electrical signal segments, in a circular buffer such that the oldest segment is overwritten by the newest segment. However, if the R-wave confirmation threshold is not reached as described below, the previously stored segment may never be analyzed for R-wave confirmation before being overwritten. In some examples, a single segment of the second cardiac electrical signal may be stored and, if the segment is not required for confirmation of an R-wave sensed by the first channel, the segment is overwritten by the next segment corresponding to the next R-wave sensed event signal.

[0090] In addition to buffering the segment of the second cardiac electrical signal, the control circuit 80 also responds to the R-wave sensed event signal generated at box 106 by determining the RRI that ends with the current R-wave sensed event signal and starts with the most recent previous R-wave sensed event signal at box 110. The timing circuit 90 of the control circuit 80 can transmit the RRI timing information to the tachyarrhythmia detection circuit 92, which adjusts the tachyarrhythmia interval counter at box 112. If the RRI is longer than the tachycardia detection interval (TDI), the tachyarrhythmia interval counter remains unchanged. If the RRI is shorter than the TDI but longer than the fibrillation detection interval (FDI), that is, if the RRI is in the tachycardia detection interval area, the VT interval counter is increased at box 112. If the RRI is shorter than or equal to the FDI, the VF interval counter is increased at box 112. In some examples, if the RRI is less than the TDI, the combined VT / VF interval counter is increased.

[0091] After updating the tachyarrhythmia interval counter at box 112, the tachyarrhythmia detector 92 compares the counter value to the R sensing confirmation threshold at box 114 and compares the counter value to the VT and VF detection thresholds at box 132. If the VT or VF detection interval counter has reached the R sensing confirmation threshold, the "yes" branch of box 114, the second cardiac electrical signal from the sensing channel 85 is analyzed to confirm the R wave sensed by the first sensing channel 83 at box 106. The R sensing confirmation threshold can be a VT or VF interval count greater than or equal to the count having one or the other higher 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 can be a count of two on the VT interval counter and a count of three on the VF interval counter. In other examples, the R sensing confirmation threshold is a higher number, such as five or higher, but can be less than the number of intervals required to detect VT or VF. In addition to or in lieu of applying an R-sense confirmation threshold to the separate VT and VF counters, an R-sense confirmation threshold may be applied to the combined VT / VF interval counter.

[0092] If none of the tachyarrhythmia interval counters reaches the R sensing confirmation threshold at box 114, the control circuit 80 waits for the next R wave sensing event signal at box 108 to buffer the next segment of the second cardiac electrical signal. If the R sensing confirmation threshold is reached at box 114, the control circuit 80 determines the maximum amplitude of the buffered signal segment stored for the most recent R wave sensing event signal at box 116. The maximum amplitude can be determined based on a differential signal determined based on the buffered signal segment. For example, an n-order differential signal can be determined based on the buffered signal segment by determining the difference between the i-th and in-th signal sampling points of the buffered signal segment. In one example, a 4-order differential signal is determined.

[0093] The maximum absolute value of the differential signal is estimated as the amplitude of an event in the second cardiac electrical signal that is sensed as an R wave from the first cardiac electrical signal. The time of the maximum absolute value of the signal is identified as the time of the event in the second cardiac electrical signal. When the R wave is not the first R wave to be confirmed since the R sensing confirmation threshold is reached, the control circuit 80 determines the amplitude ratio at box 118 as the ratio of the maximum absolute value determined at box 116 to the event amplitude determined for the most recently confirmed R wave sensing event based on the second cardiac electrical signal. At box 120, the control circuit 80 calculates the time interval from the most recent event of the second cardiac electrical signal that was confirmed as an R wave sensing event to the time of the event determined at box 116.

[0094] When the R wave is the first R wave to be confirmed after reaching the R sensing confirmation threshold, it can be assumed that the first confirmation event on the second cardiac electrical signal occurs simultaneously with the R wave sensing event signal with a default maximum amplitude. The default maximum amplitude can be set to be equal to the amplitude of the R wave sensed by the first sensing channel 83, a nominal value (e.g., 1 millivolt) or a previously determined R wave amplitude or an average R wave amplitude determined based on the second cardiac electrical signal. Alternatively, the maximum absolute amplitude of the differential signal and its time can be identified and stored as an initial value for determining the amplitude ratio and time for the next R wave to be confirmed at boxes 118 and 120. In other examples, the amplitude ratio can be determined for the first R wave to be confirmed after reaching the R sensing confirmation threshold, for example, based on the previous time or default R wave amplitude before reaching the R sensing confirmation threshold. The first R wave can be confirmed based on this amplitude ratio and / or the time since the previous R wave sensing event signal.

[0095] At box 122, the control circuit 80 determines a ratio threshold to be applied to the amplitude ratio based on the time interval determined at box 120. In one example, the ratio threshold is retrieved from a lookup table stored in a memory. In other examples, the ratio threshold can be calculated based on the time interval determined at box 120. The ratio threshold can be a variable threshold that decreases as the time interval since the last confirmed R wave increases. Therefore, the time interval determined at box 120 is used to determine what ratio threshold should be applied to the amplitude ratio determined at box 118 in order to confirm the R wave sensed by the first sensing channel 83. The ratio threshold can decrease in a linear manner, an exponential manner, or a step-wise manner, or a combination thereof. For example, the ratio threshold can decrease with a continuous slope or decay rate over some portions of the time since the last confirmed R wave, and can remain constant over other portions of the time since the last confirmed R wave. In combination Figure 8 and Fig. 9 Examples of time-varying ratio thresholds and methods for determining the ratio threshold at block 122 are described.

[0096] At block 124, the control circuit 80 compares the ratio threshold determined at block 122 to the amplitude ratio determined at block 118. If the amplitude ratio is equal to or greater than the ratio threshold, an R-wave sense event is confirmed at block 126. If the amplitude ratio is less than the ratio threshold, an R-wave sense event is not confirmed at block 128. The event may be an oversensed T wave, P wave, muscle noise, electromagnetic interference, or other or non-cardiac electrical noise that has been oversensed by the first sensing channel 83.

[0097] At box 130, the control circuit 80 adjusts the unconfirmed beat counter. If the R-wave sensed event is not confirmed, the unconfirmed beat counter increases by one count. If the R-wave sensed event is confirmed at box 126, the unconfirmed beat counter can remain at its current value or decrease. In some examples, the unconfirmed beat counter tracks how many of the most recent predetermined number of consecutive R-wave sensed event signals generated by the first sensing channel 83 are unconfirmed in an xout of y manner. For example, the unconfirmed beat counter can track how many of the most recent 12 R-wave sensed event signals were not confirmed as R waves based on the amplitude ratio comparison performed at box 124.

[0098] In addition to counting how many beats have not been confirmed at block 130, data related to the most recent n events analyzed by the control circuit 80 may also be stored in a rolling buffer. For example, data for the most recent twelve events analyzed to confirm an R-wave sensed event signal may be stored. The stored data may include event amplitudes, amplitude ratios, event timing, the time interval since the most recently confirmed event, and whether the event was confirmed.

[0099] Although according to Figure 7 The example of confirming or not confirming an R-wave sensed event signal based on an amplitude ratio determined from a second cardiac electrical signal, but it should be recognized that other features of the second cardiac signal may be compared to the R-wave confirmation criteria in addition to or in lieu of the event amplitude as described above. For example, the peak conversion rate, event area, event signal width, or other features of a buffered cardiac electrical signal segment may be compared to a corresponding threshold to confirm the event as an R-wave. The threshold may be defined as the minimum ratio of the feature relative to a similar feature of the most recent previous event confirmed as an R-wave, or may be a threshold that is compared directly to a feature determined from the buffered cardiac electrical signal segment that is unrelated to the previous event.

[0100] If any of the tachyarrhythmia interval counters adjusted at box 112 reaches the number of intervals (NID) for detecting tachyarrhythmias, as determined at box 132, the tachyarrhythmia detector 92 of the control circuit 80 determines at box 134 whether an inhibition rule is satisfied before detecting a tachyarrhythmia. In one example, the NID required to detect VT can be a count of 16 VT intervals, which are RRIs that fall within a predetermined VT interval range or region. The NID for detecting VF can be a count of 30 VF intervals out of the last 40 RRIs, where the VF intervals are RRIs that fall within a predetermined VF interval range or region. If the NID is reached, one or more inhibition rules can be applied to inhibit VT or VF detection based on the RRI count satisfying the NID. The following, for example, in conjunction with Fig.10 , Fig.11 and Fig.13 Various suppression rules are described. At least one suppression rule can be related to the number of R waves sensed by the first sensing channel 83 that have not been confirmed by the analysis of the second cardiac electrical signal. Another suppression rule can be related to the combination of Figures 14 to 19 The described detection of noisy signal fragments is related to that based on the overall morphological analysis.

[0101] For example, the unconfirmed beat counter updated at box 130 can be compared to a suppression rule criterion at box 134. The suppression rule criterion can be a suppression threshold that requires at least x out of y events to be not confirmed R waves. For example, if at least 3, at least 4, at least 6, or other predetermined number of events out of the most recent 12 events (or other predetermined number of events) analyzed to confirm an R-wave sensed event signal are not confirmed R waves, the suppression rule is satisfied, the "yes" branch of box 134. Pending VT or VF detection based on reaching NID at box 132 is stopped at box 140, and anti-tachyarrhythmia therapy is not delivered.

[0102] If all suppression rules are not met, the "NO" branch of block 134 does not stop pending detection of a VT or VF episode. VT or VF is detected based on the corresponding VT or VF interval counter reaching the corresponding NID at block 136. Control circuit 80 controls therapy delivery circuit 84 to deliver appropriate anti-tachyarrhythmia therapy, e.g., ATP or cardioversion / defibrillation shock, according to programmed therapy control parameters.

[0103] Figure 8 is a graphical representation of a filtered second cardiac electrical signal 200 and an amplitude ratio threshold 210 that may be applied to Figure 7 The amplitude ratio determined at block 118 of the control circuit 80 based on the second cardiac electrical signal is used to confirm the R-wave sensing event signal from the first sensing channel 83. The amplitude ratio is not a sensing threshold that is compared in real time with the second cardiac electrical signal 200. The first sensing channel 83 can operate by sensing the R-wave when the first cardiac electrical signal crosses the R-wave amplitude sensing threshold defined in mV. However, the second cardiac electrical signal provided by the second sensing channel 85 to the control circuit 80 is not compared in real time with the amplitude sensing threshold when it is acquired. Instead, as combined Figure 7 As described, if the first sensing channel 83 generates an R-wave sensing event signal, the second cardiac electrical signal is buffered in the memory 82, and if the rapid arrhythmia interval counter reaches the R-wave confirmation threshold, the buffered signal is post-processed to determine whether the ratio of the maximum amplitude determined based on the buffered signal segment to the maximum amplitude determined based on the previous confirmed R wave of the second cardiac electrical signal reaches or exceeds the ratio threshold 210.

[0104] The ratio threshold 210 is shown with respect to the second cardiac electrical signal 200 because the ratio threshold 210 is not a fixed value but varies over time. The ratio threshold 210 decreases as the time since the R wave 202 is confirmed increases. This time-varying ratio threshold is why the control circuit 80 Figure 7 The time since the last confirmed R-wave sensed event is determined at block 120 in order to determine, at block 122, a value of a ratio threshold that is applied to the amplitude ratio to confirm or not confirm an R-wave sensed event signal.

[0105] The cardiac electrical signal 200 may be generated by the second sensing channel 85 by filtering, amplifying and digitizing the cardiac electrical signal received by the second sensing electrode vector. Although the signal 200 is conceptually shown as having only a positive waveform, it should be understood that the signal 200 may have a positive portion and a negative portion and need not be a rectified signal. Figure 7 At block 116 of the present invention, the absolute value of the maximum peak amplitude, positive or negative, is determined from the stored second cardiac electrical signal segment. The cardiac electrical signal 200 includes an R wave 202, a T wave 204, a P wave 206, and a subsequent R wave 240. The R wave 202 represents a confirmed event occurring at a time point 205. The time point 205 is as described above in conjunction with Figure 7 The sampling points of the maximum absolute values ​​of the differential signal determined in response to the R-wave sensing event signal 250 are described.

[0106] If an R wave sensing event signal occurs during blanking interval 214 after time point 205 of the previous confirmed R wave 202, a new R wave sensing event is not confirmed. Sensing channel 83 may have sensed the same R wave 202 twice, or may have sensed non-cardiac electrical noise as an R wave.

[0107] After the blanking interval, at a point in time corresponding to the expiration of the blanking interval 214, the ratio threshold 210 is equal to the starting value 220, which may be set to 0.6 in one example, but may be in a range between 0.4 and 0.7 in other examples. In one embodiment, the ratio threshold 210 is stored in a lookup table and retrieved from the memory 82 by the control circuit 80 for comparison with the amplitude ratio determined in response to the R-wave sense event signal from the first sensing channel.

[0108] Fig. 9is an example of a lookup table 300 of ratio thresholds 304 that may be stored in the memory 82 for corresponding event time intervals, which may be stored as corresponding sampling point numbers 302. If the blanking interval 214 is approximately 150 ms, then when the sampling rate is 256 Hz, the first sampling point at which the maximum amplitude may be determined as an event time point is at sampling point 38. In other examples, the blanking interval 214 may be longer or shorter than 150 ms, and the first sampling point number stored in the lookup table 300 will correspond to the sampling point number at which the blanking interval 214 expires after the confirmed event time point 205 that is considered to be a "zero" sampling point.

[0109] The ratio threshold is stored for the first sampling point number entry as a starting ratio threshold 220, which is 0.6 in this example. If the control circuit 80 receives an R-wave sense event signal from the first sensing channel 83, and the detection interval counter is equal to or greater than the R-wave confirmation threshold, the maximum event amplitude and event time are determined based on the buffered second cardiac electrical signal. The event time can be determined as the sampling point number since the event time 205 of the most recently confirmed R-wave 202. If the event time is determined to be the sampling point number 38, the control circuit 80 retrieves the ratio threshold stored in the lookup table 300 for the sampling point number 38, which is 0.6 in this example. This ratio threshold is applied to the amplitude ratio determined based on the maximum amplitude of the buffered second cardiac electrical signal to the maximum amplitude determined based on the most recently confirmed R-wave 202.

[0110] Refer again Figure 8 , the ratio threshold 210 is shown decreasing at a constant decay rate 222 until the first time interval 216 expires. The time interval 216 can be defined to start at the time point 205 of the confirmed event 202 or when the blanking interval 205 expires. The time interval 216 can extend up to 1 second from the time point 205 of the most recently confirmed R-wave 202. In one example, the decay rate 222 can be about 0.3 / second, so that if the time interval 216 is about 1 second, the ratio threshold 224 is 0.3 when the starting ratio threshold 220 is 0.6.

[0111] Beginning at the expiration of time interval 216, ratio threshold 210 remains at constant value 224 until second time interval 218 expires. Constant value 224 is a ratio of approximately 1 / 3 (0.3) in one example, but may be between 1 / 5 (0.2) and 1 / 2 (0.5) in other examples. Value 224 may remain for up to 500 ms (for a total time interval 218 of up to 1.5 seconds) after time interval 216 expires. This change from decay rate 222 to constant value 224 is reflected in lookup table 300 as ratio threshold 0.3 starting at sample point number 256 and extending to sample point number 383.

[0112] At the expiration of the time interval 218, the ratio threshold 210 is stepped down to an intermediate ratio threshold 226 and then decays at a constant rate 228 until the ratio threshold reaches a minimum ratio threshold 230. The step-wise decrease from the constant value 224 may be to a ratio threshold of approximately 1 / 6 to 1 / 4. In one example, the ratio threshold is decreased from approximately 1 / 3 (0.3) to an intermediate ratio threshold of 1 / 5 (0.2) at 0.5 seconds after the expiration of the time interval 216. This change is reflected in the lookup table 300 as a ratio threshold of 0.2 at the sampling point 384 (0.5 seconds after the sampling point 256).

[0113] The second decay rate 228 can be the same as the decay rate 222 or a slower decay rate, so that the ratio threshold 210 reaches the minimum ratio threshold 230 (e.g., 1 / 32 (0.03), 1 / 64 (0.015)) or other predetermined minimum ratio approximately 2.5 seconds (sampling point number 640) after the time point 205 of the previous confirmed R wave 202. Fig. 9 ) captures the behavior of the ratio threshold 210 moving forward in time from the confirmed R-wave 202. For example, at the example decay rate 222 of 0.3 / sec, the ratio threshold is 0.587 at sample point number 48, and so on.

[0114] The values ​​listed here and reflected in the lookup table 300 for the ratio thresholds 220, 224, 226 and 230 and the time intervals 216 and 218 are illustrative in nature; other values ​​less than or greater than the listed values ​​may be used to implement the time-varying ratio amplitudes for confirming R-wave sensing events. The values ​​of the ratio thresholds and time intervals used to control the change from one ratio threshold to another, or the decay rate and total decay interval, will depend in part on the sampling rate, which is 256 Hz in the example provided but may be greater or less than 256 Hz in other examples.

[0115] Refer again Figure 8, if the first sensing channel 83 generates an R-wave sensing event signal 252, the control circuit 80 is triggered to store a time segment 254 of the second cardiac electrical signal 200 in the memory 80. The time segment 254 can be 360ms in one example, and can be between 300ms and 500ms in other examples. If the VT interval counter or the VF interval counter or the combined VT / VF interval counter has reached the R-wave confirmation threshold, the control circuit 80 determines the maximum amplitude based on the buffered cardiac signal time segment. As described above, the maximum amplitude can be the maximum absolute value of the x-order differential signal determined based on the second cardiac electrical signal 200. The maximum amplitude can be determined based on a portion of the stored cardiac signal time segment. For example, the maximum amplitude can be determined based on a segment 255 that is a sub-segment or a portion of the stored time segment 254. When the length of the total time segment 254 is 360ms to 500ms, the length of the segment 255 can be approximately 50ms to 300ms, for example, a length of 200ms. Segments 255 may be defined relative to the time at which the R-wave sensing event signal 252 is received.

[0116] The sampling point number 197 at which the maximum amplitude occurs within the time segment 255 represents the number of sampling points since the event time 205 (sampling point number zero) of the most recently confirmed R-wave 202. The sampling point number 197 is determined as the event time of the maximum amplitude of the cardiac signal time segment 255. The control circuit 80 uses this sampling point number to look up the corresponding ratio threshold 304 in the lookup table 300. For example, the maximum amplitude during the time segment 255 obtained in response to the R-wave sensing event signal 252 may occur at the sampling point number 197 approximately 0.77 seconds after the event time point 205. The stored ratio threshold for the sampling point number 197 may be approximately 0.4 for a decay rate 222 of approximately 0.3 / second (or 0.0012 per sampling point) starting from the starting value 220, which in this example is 0.6 starting at the sampling point number 38. If the amplitude ratio of the maximum amplitude determined at sampling point number 197 during time segment 255 to the maximum amplitude determined for confirming R-wave 202 is greater than or equal to 0.4, then R-wave sense event 252 is confirmed. In this example, the cardiac electrical signal has a lower baseline amplitude during interval 255, and therefore, R-wave sense event signal 252 is not confirmed. Control circuit 80, as combined with Figure 7 The unacknowledged event counter is incremented as described.

[0117] Similarly, the control circuit 80 may receive the R-wave sense event signal 256 and determine the maximum amplitude during the time segment 259 defined relative to the R-wave sense event signal 256 of the buffered cardiac electrical signal segment 258. The event time sample point number 403 at which the maximum amplitude occurs since the event time 205 is used to look up the ratio threshold from the lookup table 300. In this case, the amplitude ratio determined from the buffered second cardiac electrical signal during the time segment 259 exceeds the ratio threshold 210 at the event time sample point number 403 corresponding to the R-wave 240 of the maximum amplitude during the time segment 259. The R-wave sense event signal 256 is confirmed by the control circuit 80. In this way, the second cardiac electrical signal from the sensing channel 85 is analyzed only when the R-wave sense event confirmation condition is met, such as the tachyarrhythmia interval counter is active and has reached a threshold count, which may be less than the required number of intervals for detecting a VT or VF episode. The R-wave sense event of the first sensing channel is confirmed based on post-processing of the buffered second cardiac electrical signal.

[0118] Fig.10 4 is a flowchart 400 of a method for detecting tachyarrhythmias by the ICD 14 according to another example. The operations performed at blocks 102 to 114, 132, 136, 138, and 140 in the flowchart 400 may generally be similar to Figure 7 At blocks 102 and 104, two different sensing electrode vectors are selected by the sensing circuit 86 for receiving the first cardiac electrical signal by the first sensing channel 83 and receiving the second cardiac electrical signal by the second sensing channel 85, as described above in conjunction with Figure 5 and Figure 7 as described.

[0119] At box 106, the sensing circuit 86 can generate an R-wave sensing event signal in response to the first sensing channel 83 detecting that the first cardiac electrical signal crosses the R-wave sensing threshold. The R-wave sensing event signal can be transmitted to the control circuit 80. In response to the R-wave sensing event signal, the control circuit 80 is triggered at box 108 to store a segment of the second cardiac electrical signal received from the second sensing channel 85 in a circular buffer of the memory 82. The length of the digitized segment of the second cardiac electrical signal, which can be defined in time relative to the time of the R-wave sensing event signal received from the sensing circuit 86, can be, for example, 100ms to 500ms. In one example, the buffered segment of the cardiac electrical signal is at least 92 sampling points obtained at a sampling rate of 256Hz, or approximately 360ms, 68 of which can precede the sampling point at which the R-wave sensing event signal is received and 24 of which can extend after the sampling point at which the R-wave sensing event signal is received.

[0120] In addition to buffering the segments of the second cardiac electrical signal, the control circuit 80 responds to the R-wave sensed event signal generated at block 106 by determining the RRI that ends with the current R-wave sensed event signal and begins with the most recent previous R-wave sensed event signal at block 110. The timing circuit 90 of the control circuit 80 may communicate the RRI timing information to the tachyarrhythmia detection circuit 92, which adjusts the tachyarrhythmia detection counter at block 112, as described above in conjunction with Figure 7 as described.

[0121] After updating the VT interval counter and the VF interval counter at box 112, the tachyarrhythmia detector 92 compares the interval counter value to the R sensing confirmation threshold at box 114 and compares the counter value to the VT and VFNID detection thresholds at box 132. If the VT or VF interval counter has reached the R sensing confirmation threshold, the "yes" branch of box 114, the second cardiac electrical signal from the sensing channel 85 is analyzed to confirm the R wave sensed by the first sensing channel 83 at box 106. In one example, the R sensing confirmation threshold is count two on the VT interval counter and count three on the VF interval counter. Figure 7 Other examples are given.

[0122] If either of the interval counters has not reached the R-sense confirmation threshold at block 114, the control circuit 80 waits for the next R-wave sense event signal in order to buffer the next segment of the second cardiac electrical signal at block 108. In some cases, the oldest buffered cardiac signal segment may be overwritten by the next cardiac signal segment and never analyzed to confirm an R-wave or for any other purpose because the buffered cardiac signal segment does not need to be analyzed while the VT and VF interval counters are inactive (at count zero) or remain below the R-sense confirmation threshold.

[0123] If the R sensing confirmation threshold is reached at block 114, the control circuit 80 applies a notch filter to the stored second cardiac electrical signal segment at block 416. The notch filter applied at block 416 may be combined with Figure 6 The notch filter significantly attenuates 50 Hz to 60 Hz electrical noise, muscle noise, other EMI, and other noise / artifacts in the stored second cardiac electrical signal segment. Using the notch filtered segment, the control circuit 80 performs multiple analyses on the segment to determine whether any suppression rules are met. As described below, if the suppression rules are met, the pending VT or VF episode detection based on reaching the NID threshold at box 132 can be stopped.

[0124] As combined Figure 7 As described, the amplitude ratio may be determined at block 418 to confirm that an R-wave sensing event signal has triggered a buffer of the currently stored second cardiac electrical signal segment. The determination made at block 418 may include Figure 7 The amplitude ratio is used at box 428 to update the R-wave confirmation suppression rule.

[0125] At block 418, the maximum peak amplitude for determining the amplitude ratio may be determined from a portion of the stored cardiac signal segments. For example, if 360 ms or 500 ms segments were stored at block 108, only a 200 ms segment centered in time about the R-wave sensing event signal, e.g., approximately 52 sampling points sampled at 256 Hz, may be analyzed to determine the amplitude ratio at block 418. A longer signal segment than required to determine the amplitude ratio at block 418 may be stored at block 108 so that the longer segment may be used for other signal analysis procedures performed by tachyarrhythmia detector 92 as described below, e.g., for determining baseline noise parameters and for use in conjunction with the R-wave sensing event signal. Figures 14 to 19 Other overall morphological parameters for detecting noisy signal segments are described.

[0126] When the current R-wave sense event signal is not the first R-wave sense event signal confirmed since the R-sense confirmation threshold was reached at block 114, the control circuit 80 may determine the event interval as the time interval or number of sampling points from the maximum peak amplitude to the previous confirmed R-wave sense event at block 418. At block 428, the control circuit 80 may compare the amplitude ratio to a ratio threshold, which may be determined as a function of the R-sense confirmation threshold. Figure 8 and Fig. 9 The event interval determined using the described use is retrieved from a lookup table stored in memory 82. If the amplitude ratio is greater than the ratio threshold, then the sensed R-wave is confirmed. If the amplitude ratio is less than the ratio threshold, then the sensed R-wave is not confirmed.

[0127] At box 428, X of the Y unconfirmed beat counters may be updated by the tachyarrhythmia detector 92 to reflect the number of unconfirmed R-wave sensed event signals in the most recent Y R-wave sensed event signals. For example, X of the Y counters may count how many R waves in the most recent 12 R-wave sensed event signals were not confirmed as R waves. If X of the Y counts reach a suppression threshold, e.g., if at least 3, 4, 5, or another predetermined number of R-wave sensed event signals in the 12 R-wave sensed event signals were not confirmed as R waves, then the R-wave suppression rule for stopping tachyarrhythmia detection is satisfied. A flag or logic value may be set by the control circuit 80 to indicate that the R-wave suppression rule is satisfied. Updating the R-wave suppression rule at box 428 may include combining Figure 7 The operations described with respect to blocks 122 , 124 , 126 , 128 , 130 , and 134 .

[0128] At boxes 420, 422, 424 and 426, other cardiac signal parameters can be determined based on the notch filtered cardiac signal segments to update the states of other tachyarrhythmia detection suppression rules at corresponding boxes 430, 432, 434 and 436. In some examples, the digitized cardiac electrical signal from the first sensing channel 83 can be analyzed and used to update the state of the tachyarrhythmia detection stop rule. For example, the notch filtered cardiac electrical signal from the second sensing channel 85 can be analyzed at boxes 420, 422 and 426 to update the overall morphology suppression rule, the beat morphology suppression rule and the noise suppression rule at boxes 430, 432 and 436, respectively. The differential signal 69 (see Figure 424) from the first sensing channel 83 can be analyzed at box 424. Figure 5 ) is analyzed to update the T wave oversensing (TWOS) rule at box 434.

[0129] At block 420, one or more overall morphology parameters may be determined based on the notch-filtered second cardiac signal segment. The overall morphology parameters may include, but are not limited to, low slope content, noise pulse count, normalized rectified amplitude, maximum signal width, or other noise metrics. Fig.15 , Fig.16 and Fig.17 Examples of global morphology parameters that may be determined at block 420 are described. Other examples of global morphology parameters that may be determined are generally disclosed in U.S. Pat. No. 7,761,150 (Ghanem et al.) and U.S. Pat. No. 8,437,842 (Zhang et al.), cited above. The global morphology parameters may be determined using the entire second cardiac signal segment stored at block 108 or a portion of the stored segment. In one example, at least 92 sampling points, approximately 360 ms, which may be a portion of the stored segment or the entire stored segment, are analyzed to determine the global morphology parameters. The portion of the signal segment analyzed to determine the global morphology metric extends beyond an expected QRS signal width such that at least a portion of the segment analyzed corresponds to an expected baseline portion. In this manner, at least one global morphology parameter determined (such as, in combination with Fig.15 The noise pulse count described herein is related to non-cardiac signal noise that may occur during the baseline portion, such as non-cardiac myoelectric noise or electromagnetic interference (EMI).

[0130] The state of the overall morphology suppression rule is updated at block 430 using the overall morphology parameter. The overall morphology parameter is determined from the signal segment to determine whether the signal segment is noisy, and therefore whether the second cardiac electrical signal is noisy. The noisy segment may include multiple noise signal pulses that are evidence of non-cardiac muscle (electromyographic) noise, EMI, or other non-cardiac noise signals. The noisy signal segment may be an indication of the following situation: the R-wave sense event signal during the noisy signal segment is unreliable for assisting VT or VF detection. Therefore, the overall morphology analysis can analyze signal segment sample points that are not limited to R waves, but can extend along an expected baseline portion in the segment before triggering the stored R-wave sense event signal for the signal segment. By performing a signal morphology analysis that includes the expected baseline portion (which is referred to as a "overall morphology analysis" because it involves analysis of the entire signal segment or an extended portion of the signal segment that extends beyond only the expected R wave or QRS waveform), noise pulses can be identified and detected to enable detection of noisy signal segments.

[0131] A criterion or threshold may be applied to each of the determined overall morphology parameters, and the overall morphology suppression rule may be satisfied when a desired number of the overall morphology parameters satisfy the criterion or threshold applied to the corresponding parameter. For example, if at least two of the three overall morphology parameters satisfy the noise detection criterion, the overall morphology suppression rule is satisfied. At block 430, the control circuit 80 may set a flag or logic signal indicating this. Figures 14 to 19 Methods for determining overall morphology parameters and whether overall morphology suppression rules are satisfied are described.

[0132] At box 422, a morphology match score is determined based on the stored second cardiac electrical signal segment. The morphology match score can be determined by performing a wavelet transform or other morphology matching analysis on a portion of the stored segment, such as at least 48 signal sampling points or approximately 190ms, and can be performed using the notch filtered signal generated at box 416. The morphology matching analysis may include: aligning a selected portion of the stored segment with a previously determined known R-wave template; and determining a morphology match score. The morphology match score can have a possible value range from 0 to 100 and indicates how well the morphology of the second cardiac signal segment matches the known R-wave template. The wavelet transform method as generally disclosed in U.S. Patent No. 6,393,316 (Gillberg et al.) is an example of a morphology matching method that can be performed at box 422 to determine a match score.

[0133] Other morphological matching methods that can be implemented by the tachyarrhythmia detector 92 can compare the waveform, amplitude, slope, time inflection point, number of peaks, or other features of the stored second cardiac electrical signal with a known R-wave template. More specifically, waveform duration or width, waveform polarity, waveform positive slope, waveform negative slope, and / or other waveform features can be used alone or in combination to characterize the similarity between the unknown waveform and the known R-wave template. The morphological matching method can use one morphological feature of the stored second cardiac electrical signal or a combination of two or more morphological features to determine a match with a known R-wave template. A posture-independent method for determining a morphological matching score including generating a posture-independent R-wave template for template matching can be performed, as generally disclosed in pre-granted U.S. Patent Application No. 2016 / 0022166 (Stadler et al.). Other beat morphology matching techniques that can be used at box 422 are generally disclosed in U.S. Patent No. 8,825,145 (Zhang et al.) and U.S. Patent No. 8,983,586 (Zhang et al.).

[0134] The morphology match scores are used by the tachyarrhythmia detector 92 at box 432 to update the beat morphology suppression rule. In one example, the beat morphology suppression rule may be satisfied when a minimum number of morphology match scores out of a predetermined number of recent morphology match scores exceed a match score threshold. For example, the beat morphology suppression rule is satisfied if at least three of eight of the most recent morphology match scores exceed a match score threshold of 50, 60, 70, or other score threshold. A relatively high match score that exceeds a selected match score threshold indicates that the unknown beat matches a known R-wave template and is therefore a normal R-wave rather than a VT or VF beat. Therefore, when a threshold number of the most recent morphology match scores out of these most recent morphology match scores are determined to be normal R-waves, the beat morphology suppression rule is satisfied, and the control circuit 80 can set a flag or logic signal indicating this.

[0135] The difference between the beat morphology suppression rule and the overall morphology suppression rule is that the beat morphology suppression rule is based on the analysis of the suspicious R wave signal to determine the possibility that it is a normal R wave. In other words, the beat morphology suppression rule is applied to stop VT or VF detection based on verifying a normal ventricular beat (or at least identifying a beat that is unlikely to be a VT or VF beat). The overall morphology suppression rule is based on the analysis of a longer time interval in the signal segment than the beat morphology suppression rule, so that signal morphology parameters related to non-cardiac noise pulses (for example, during the baseline portion of the second cardiac electrical signal) can be detected. The overall morphology suppression rule is applied to stop VT or VF detection based on detecting a noisy signal segment that may interfere with reliable VT or VF detection or cause erroneous VT or VF detection.

[0136] At block 424, a TWOS parameter is determined based on the stored digitized cardiac electrical signal. In some cases, the TWOS parameter is determined based on the first order difference signal 69 received from the first sensing channel 83, as described above in conjunction with Figure 5As described. The first order difference signal is determined by subtracting the amplitude of the n-1 sampling point from the nth sampling point. Alternatively, the second cardiac electrical signal from the sensing channel 85 before or after notch filtering can be used to determine TWOS parameters to detect TWOS based on morphological analysis of the stored cardiac signal, such as generally disclosed in U.S. Patent Application No. 62 / 367,221 (Attorney Docket No. C00013321.USP1, Cao et al.) cited above. The tachyarrhythmia detector 92 can be configured to perform a T wave oversensing suppression algorithm by determining the differential filtered cardiac electrical signal and the TWOS parameters, such as generally disclosed in U.S. Patent No. 7,831,304 (Cao et al.) cited above. Other aspects of detecting TWOS that can be used to determine TWOS parameters based on the first and / or second cardiac electrical signals are generally disclosed in U.S. Patent No. 8,886,296 (Patel et al.) and U.S. Patent No. 8,914,106 (Charlton et al.).

[0137] At block 434, tachyarrhythmia detector 92 uses the TWOS parameter(s) determined for the currently stored cardiac signal segment to update the status of the TWOS suppression rule as satisfied or not satisfied. For example, if one or more TWOS parameters indicate that the R-wave sensed event signal generated by first sensing channel 83 is likely to be an oversensed T-wave, a TWOS event counter may be updated at block 434. If the TWOS event counter reaches a threshold, the TWOS suppression rule is satisfied. Control circuitry 80 may set a flag or logic signal indicating when the TWOS suppression rule is satisfied.

[0138] Other noise parameters may be determined at box 426 to identify oversensing due to noise artifacts. The noise parameters determined at box 426 may include determining a peak amplitude based on the second cardiac electrical signal segment that has been notched filtered. All or a portion of the stored signal segment may be used to determine one or more amplitude peaks. In other examples, the first cardiac electrical signal segment may be notched filtered and may be used to determine the noise parameters at box 426. The peak amplitude determined at box 426 may include the maximum peak amplitude determined at box 418 for determining the amplitude ratio. The maximum peak amplitude of one or more stored cardiac signal segments is compared to the noise detection criteria to determine whether the noise suppression rule is satisfied at box 436. The control circuit 80 sets a flag or logic signal at box 436 to indicate the state of the noise suppression rule. A method for determining noise parameters at box 426 and updating the noise suppression rule at box 436 is generally disclosed in U.S. Patent Application No. 62 / 367,170 (Greenhut et al., Attorney Docket No. C000013169.USP1).

[0139] After adjusting the VT interval counter and the VF interval counter at box 112, the tachyarrhythmia detector 92 compares the interval counters to the VT and VF NID detection thresholds at box 132. If the VT or VF interval counter has reached the NID, the tachyarrhythmia detector 92 checks the status of the inhibition rule at box 440. If the inhibition criteria are met based on the status of one or more inhibition rules at box 440, the "yes" branch of box 440 stops VT or VF detection based on the RRI analysis at boxes 110, 112 and 132 at box 140. No VT or VF therapy is delivered. The process returns to box 110 to determine the next RRI when the next R wave sense event signal is received from the sensing channel 83.

[0140] If the suppression criteria are not met, the "NO" branch of block 440, a VT or VF episode is detected at block 136 based on which VT or VF interval counter has reached its corresponding NID threshold. The control circuit 80 controls the therapy delivery circuit 84 to deliver therapy at block 138 based on the type of episode detected and the programmed therapy delivery control parameters.

[0141] In some examples, the suppression criteria applied at box 440 only require that a single suppression rule be satisfied in order for the tachyarrhythmia detector 92 to cease VT or VF detection. In other examples, two or more suppression rules may be required to be satisfied before RRI-based VT or VF detection is ceased. In still other examples, one suppression rule may be associated with another suppression rule so that the suppression criteria are satisfied at box 440. For example, an R-wave confirmation suppression rule may be used to satisfy the suppression criteria only when the overall morphology suppression rule is also satisfied. In this case, the R-wave confirmation suppression rule alone cannot be used to satisfy the suppression criteria at box 440. The overall morphology suppression rule may be used only together with the R-wave confirmation suppression rule, alone, or in combination with another rule to satisfy the suppression criteria.

[0142] The suppression rules updated at blocks 428-436 may be programmatically enabled or disabled by a user using external device 40. Control circuitry 80 may determine which parameters are needed at blocks 418-426 to update the status of suppression rules that are only enabled or programmed "on."

[0143] Fig.11 5 is a flow chart of a method for detecting tachyarrhythmias by the ICD 14 according to another example. Figure 7 and Fig.10In the example of , the number of RRIs falling into the corresponding VT or VF interval range or region determined according to the first sensing electrode vector 102 is tracked by the corresponding VT and VF interval counters. At block 132, the counts of the VT and VF interval counters are compared to the corresponding VT and VF NID thresholds. Fig.11 The boxes with the same numbers in the Figure 7 and Fig.10 The boxes shown in FIG. 1 correspond to the boxes with similar numbers.

[0144] In other examples, the second cardiac electrical signal received by the second sensing channel 85 from the second electrode vector at box 104 can also be used to determine the RRI and determine whether the NID threshold is reached at decision box 438. The tachyarrhythmia detector 92 may include a second VT and VF interval counter for counting the RRI determined based on the second cardiac electrical signal received by the second sensing channel 85. The second VT and VF interval counter can be updated at box 415 based on the RRI determined based on the second cardiac electrical signal received via the second sensing electrode vector 104.

[0145] In one example, after reaching the R sensing confirmation threshold at block 114, tachyarrhythmia detector 92 may begin updating the second VT and VF interval counters at block 415. The process of updating the second VT and VF interval counters starting from an initial zero count may include: Figure 7 The amplitude ratio is compared to the ratio threshold as described in blocks 122, 124, 126 and 128 of FIG. 12 to confirm an R wave at block 428. If R wave sensing is confirmed at block 126, the R wave confirmation suppression rule is updated at block 428 based on the confirmed R wave sensing event, and the tachyarrhythmia detector 92 compares the event interval determined at block 418 to the VT and VF interval regions at block 415. The event interval determined at block 418 is the time interval from the most recently confirmed R wave event time to the event time of the maximum absolute amplitude of the time segment stored for the most recently R wave sensing event signal.

[0146] If the most recent R-wave sensed event signal is confirmed at box 428, the event interval can be compared to the VT and VF interval regions defined as the same interval region as the RRI application determined at box 112 for the R-wave sensed event signal generated by the first sensing channel 83 at box 415. If the event interval determined for the confirmed R-wave at box 418 falls into the VT interval region, the second VT interval counter is increased at box 415. If the event interval falls into the VF interval region, the second VF interval counter is increased at box 415. In some examples, if the event interval falls into the VT or VF interval region, the combined VT / VF interval counter is increased.

[0147] If one of the first VT or VF interval counters (or combined VT / VF interval counters) applied to the RRI determined based on the first sensing channel 83 reaches the NID at box 132, the tachyarrhythmia detector 92 can compare the second VT and VF interval counters to the second NID requirement at box 438. The second VT NID and the second VF NID used by the tachyarrhythmia detector 92 can be less than the VT NID and VF NID applied to the first VT and VF interval counters at box 132. In some examples, the second VT and VF interval counters begin to be updated after the R sensing confirmation threshold is reached at box 114. Therefore, the count of the second VT and VF interval counter can be less than the first VT and VF interval counter (the counter adjusted at box 112). The count of the second VT and VF interval counter can fall behind the first VT and VF interval counter by the number of intervals required to reach the R sensing confirmation threshold. For example, if the first VT interval counter is required to have a count of at least 2 or the first VF interval counter is required to have a count of at least 3 in order to reach the R sensing confirmation threshold at box 114, the second VT or VF interval counter can have a count of at least 2 or 3, respectively, which is less than the corresponding first VT or VF interval counter.

[0148] If one of the second VT or VF interval counters reaches the second NID, the "yes" branch of block 438 indicates that the tachyarrhythmia detector 92 has detected a second NID based on the above description in conjunction with the Fig.10 The state of the suppression rules updated at blocks 428 through 436 as described above is used to determine whether the suppression criteria are met at block 440. If neither of the second VT or VF interval counters has reached the second NID at block 438, the "No" branch of block 438, then the tachyarrhythmia detector 92 does not proceed to check the suppression criteria at block 440. Instead, the tachyarrhythmia detector 92 may wait for the corresponding first VT or VF interval counter to reach the first VT or VF NID at block 132 and wait for the corresponding second VT or VF interval counter to reach the corresponding second NID at block 438. For example, in order to proceed to block 440 to determine whether the suppression criteria are met and subsequently detect VT at block 136 or stop VT detection at block 140, the first VT interval counter is required to reach the first VT NID at block 132 and the second VT interval counter is required to reach the second VT NID at block 438. Similarly, in order to proceed to box 440 to determine whether the suppression criteria are met and then detect VF at box 136 or stop VF detection at box 140, the first VF interval counter is required to reach the first VF NID at box 132 and the second VF interval counter is required to reach the second VF NID at box 438.

[0149] Fig.12Based on another example Figure 4 A diagram of the circuit system included in the sensing circuit of FIG. Fig.12 , the components with the same number in sensing channels 83 and 85 are combined with Figure 5 Like numbered parts described and shown herein correspond to each other. Figure 5 In the example of , the first sensing channel 83 is configured to sense the R wave in real time through the R wave detector 66 and generate the R wave sensing event signal 68, which is transmitted to the timing circuit 90 when the R wave is sensed. The second sensing channel 85 is configured to transmit the filtered digitized output signal 78 to the memory 82 to store the second cardiac electrical signal segment when triggered by the R wave sensing event signal 68 from the first sensing channel 83, without performing real-time R wave sensing from the second cardiac electrical signal.

[0150] exist Fig.12 In the example of , the second sensing channel 85 is configured to transmit the digitized filtered output signal 78 to the memory 82 for storing the second cardiac electrical signal segment as described above. In addition, the sensing channel 85 is configured to perform real-time R-wave sensing from the second cardiac electrical signal. In this case, the second sensing channel 85 includes a rectifier 75 for rectifying the digitized and bandpass filtered signal output of the filter 74. The rectified signal is transmitted from the rectifier 75 to the R-wave detector 77. The R-wave detector may include a sense amplifier, a comparator, or other R-wave detection circuit system configured to apply an automatically adjusted R-wave sensing threshold to the rectified signal so as to sense an R-wave in response to a positive R-wave sensing threshold crossing.

[0151] The second sensing channel 85 can generate an R-wave sensing event signal 79, which is transmitted in real time to the timing circuit 90 for determining the RRI based on the second cardiac electrical signal. The RRI can be determined as a time interval or a sampling point count between consecutively received R-wave sensing event signals 79. The timing circuit 90 can transmit the RRI determined based on the R-wave sensing event signal 79 from the second sensing channel 85 to the rapid arrhythmia detector 92 for updating the second VT and VF interval counter based on the RRI determined based on the real-time sensing of the R wave by the second sensing channel 85.

[0152] exist Fig.11 In the flowchart 500, the second VT and VF interval counter is updated by the tachyarrhythmia detector 92 at box 415 based on the R wave confirmed at box 428 as a result of post-processing the stored second cardiac electrical signal segment. Fig.11In the example of , the second sensing channel 85 does not sense the R wave in real time (signal segments can be recorded, but an R wave sensing event signal is not generated in real time because the R wave is sensed based on the R wave sensing threshold). Fig.12 In the present invention, the second sensing channel 85 is configured to sense the R wave in real time from the second cardiac electrical signal received by the second sensing vector 104, and therefore, the rapid arrhythmia detector 92 can update the second VT and VF interval counter based on the real-time sensing of the R wave by the second sensing channel 85.

[0153] Fig.13 is a flowchart 550 of a method for detecting rapid arrhythmia by ICD 14 according to another example, in which the second sensing channel 85 is configured to sense R waves from a second cardiac electrical signal in real time, and in addition, the control circuit 80 is configured to confirm the R waves sensed by the first sensing channel 83 by post-processing the second cardiac electrical signal. Fig.13 The boxes with the same number in Figure 7 and / or Fig.11 Like numbered blocks shown in and described in conjunction with FIG.

[0154] exist Fig.13 In the example of FIG. 1 , at block 105, the R-wave detector 77 of the sensing channel 85 generates an R-wave sensing event signal 79 ( Fig.12 ). The second R-wave sensing threshold may be an automatically adjusted threshold and may be different from the R-wave sensing threshold used by the R-wave detector 66 of the first sensing channel 83. The timing circuit 90 determines the RRI between consecutive R-wave sensing event signals 79 received from the second sensing channel 85 at box 105, and transmits the determined RRI to the tachyarrhythmia detector 92. At box 419, the tachyarrhythmia detector 92 adjusts the second VT interval counter or the second VF interval counter in response to each RRI determined at box 105, both of which interval counters may be X-in-Y type counters. In this example, the second VT and VF interval counters of the tachyarrhythmia detector 92 may be updated in real time, similar to the first VT and VF interval counters used to count the RRI determined based on the first cardiac electrical signal. The second VT and VF interval counters may be updated on a beat-by-beat basis without requiring the R-sensing confirmation threshold (box 114) to be reached first.

[0155] If the tachyarrhythmia detector 92 determines at box 132 that the first VT NID or the first VF NID is reached, the tachyarrhythmia detector 92 compares the second VT and VF interval counters with the second VT NID and the second VF NID, respectively, at box 439. In this case, the second VT NID and the second VF NID can be the same as the first VT NID and the first VF NID because the first and second VT interval counters and the first and second VF interval counters are all updated in response to the real-time sensed R-wave. If the second VT or VF NID has not been reached (the "No" branch of box 430), the tachyarrhythmia detector 92 can return to box 132 to wait for the VT or VF NID threshold to be reached based on the real-time sensed R-wave of both the corresponding first and second sensing channels 83 and 85.

[0156] If a corresponding second VT or VF NID is reached at box 439 when a first VT or VF NID is reached at box 132, then tachyarrhythmia detector 92 determines at box 440 whether the suppression criteria are met, as previously described in conjunction with Fig.10 The pending VT or VF detection based on real-time detection of tachyarrhythmic intervals from the first and second cardiac electrical signals is stopped at box 140 in response to satisfying the suppression criteria, or the VT or VF detection is confirmed at box 135 if the suppression rules are not satisfied. The control circuit 80 controls the therapy delivery circuit to deliver anti-tachyarrhythmia therapy in response to VT or VF detection at box 138.

[0157] Fig.14 is a flowchart 600 of a method performed by the ICD 14 for responding to satisfying an overall morphology suppression rule (block 430, Fig.10 , Fig.11 and Fig.13 ) and stop VT or VF detection. Fig.14 Blocks 102 to 114, 132, 136, 138 and 140 correspond to the above combined Fig.10 , Fig.11 and Fig.13 Boxes with the same number are described.

[0158] As described above, if the R sensing confirmation threshold is reached at block 114, the control circuit 80 applies a notch filter to the stored second cardiac electrical signal segment at block 416. The notch filter applied at block 416 may be combined with Figure 6 The notch-filtered second cardiac electrical signal segment is used at blocks 602, 604 and 606 to determine morphological parameters associated with baseline noise (block 602), maximum signal amplitude (block 604) and maximum signal width (block 606). Fig.15 , Fig.16 and Fig.17 An example of a method that may be performed by the control circuit 80 to determine a baseline noise parameter, determine a signal amplitude parameter, and determine a signal width parameter is described. The method performed at blocks 602, 604, and 608 may correspond to Fig.10 , Fig.11 and Fig.13 The overall morphological parameters are determined at box 420.

[0159] These parameters are compared to noise detection criteria at block 608. If the noise detection criteria are met at block 608, the second cardiac signal segment being analyzed is determined to be a noisy segment at block 610. Noise contamination of a signal segment may be caused by muscle (electromyographic) noise, EMI, or other non-cardiac electrical noise sources.

[0160] In response to detecting a noisy segment at box 610 ("yes" branch), after reaching the R-wave confirmation threshold at box 114, the control circuit 80 increases the noisy segment count at box 614 to track the number of segments identified as noisy based on the morphology parameter. The state of the overall morphology suppression rule is updated at box 430 based on the value of the noisy segment count. When the segment is not detected as noisy, the "no" branch of box 610, the overall morphology suppression rule can be updated at box 430 to track the number of noisy segments detected from a predetermined number of analyzed segments or from the most recent R-wave sensing event signal. The overall morphology suppression rule can be satisfied based on the noisy segment count value. If a threshold number of noisy segments are detected, the suppression rule is satisfied at box 430. For example, if at least two of the most recent eight (or other predetermined number) analyzed cardiac electrical signal segments are classified as noisy, the suppression rule is updated at box 430 to be satisfied. If less than two of the most recent eight analyzed cardiac electrical signal segments are classified as noisy, the suppression rule is updated to be not satisfied.

[0161] The next signal segment is taken at block 612 and undergoes the same analysis at blocks 602 to 610 to determine whether the segment is noisy based on the noise detection criteria applied at block 608. Fig.19As described, the next signal segment that will undergo analysis to detect a noisy signal segment may not correspond to the next continuous R-wave perception event signal. In some cases, the next signal segment retrieved at box 612 corresponds to an R-wave perception event signal that occurs at least 300ms or another predetermined time limit after the stored R-wave perception event signal that triggered the currently analyzed signal segment. In this way, the signal segments analyzed to be identified as noisy signal segments may sometimes be continuous and at other times may be non-continuous. For the purpose of determining the overall morphological parameters, R-wave perception event signals that occur at RRIs that are less than a predetermined time limit may be skipped. In other examples, each R-wave perception event signal that occurs outside the post-sensing blanking interval is analyzed to determine the overall morphological parameters.

[0162] In response to reaching the NID at block 132, the control circuit 80 determines at block 440 whether the suppression criteria are met based on the RRI determined from the cardiac electrical signals received by the first sensing channel 83 via the first sensing vector 102. Fig.14 In the example of FIG. 4 , the control circuit 80 checks the status of the overall morphology suppression rule updated at box 430. If the overall morphology suppression rule is satisfied when the NID is reached at box 132, e.g., if at least two of the most recent eight signal segments analyzed are detected as noisy segments as given in the example above, VT or VF detection based on reaching the NID at box 132 is stopped at box 140; no therapy is delivered.

[0163] This process of analyzing signal segments to detect noisy segments may be repeated as long as the R-sense confirmation threshold remains met or until VT or VF is detected. When the NID is reached and the overall morphology suppression rule (and any other suppression rules applied at block 440 as previously described herein) is not met, VT or VF is detected at block 136. The control circuit 80 controls the therapy delivery circuit 84 to deliver therapy, such as ATP or electric shock therapy, in accordance with the programmed therapy. It should be understood that in some examples, the VT or VF detection performed at block 136 may require that a second NID be reached based on an RRI determined based on a second cardiac electrical signal, such as in combination with Fig.11 and Fig.13 as described.

[0164] Fig.15 is performed by ICD 14 according to an example so as to Fig.14 Flowchart 700 of a method for determining a morphology parameter associated with baseline noise at block 602 of FIG. The morphology parameter associated with baseline noise is referred to herein as a baseline noise parameter and is Fig.15 In the example of FIG. 5 , the morphology parameter associated with the baseline noise is the signal pulse count during a signal segment.

[0165] At box 702, a first-order difference signal can be determined based on a notch-filtered second cardiac electrical signal segment. In one example, the length of the stored segment is at least 360 ms, so that the first-order difference signal is determined using, for example, sampling points within a 360 ms segment of the second cardiac electrical signal after notch filtering. The 360 ​​ms segment can include sampling points before and after the R-wave sensing event signal. For example, when the sampling rate is 256 Hz, the 360 ​​ms segment can include 92 sampling points, wherein 24 of the sampling points occur after the R-wave sensing event signal that triggers storage of the signal segment, and 68 sampling points are earlier in time than the R-wave sensing event signal and extend from the R-wave sensing event signal. By processing a relatively small number of sampling points that occur after the R-wave sensing event signal, the control circuit 80 does not need to wait for a long time after the R-wave sensing event signal to obtain all the sampling points required to determine the baseline noise parameter (and other overall morphology parameters), thereby minimizing the signal processing delay for detecting noise and updating the overall morphology suppression rule. The first-order difference signal is calculated by calculating the consecutive differences between the sampling points A(n)-A(n-1), where n is the number of sampling points, which in the example given above ranges from 1 to 92; A(n) is the amplitude of the nth sampling point; and A(n-1) is the amplitude of the immediately preceding n-1 sampling points.

[0166] At block 704, zero crossings are set by identifying consecutive sampling points of the differential signal with opposite polarities. For example, a positive sampling point after a negative sampling point is identified as a zero crossing, or a negative sampling point after a positive sampling point is identified as a zero crossing. The control circuit 80 compares the absolute values ​​of the two signal sampling points identified as zero crossings. The sampling point of the differential signal with a smaller absolute value amplitude is set to zero amplitude to clearly define each zero crossing, where two consecutive zero crossings define a baseline noise pulse.

[0167] At box 706, the differential signal with the set zero crossing is rectified. At box 708, a noise pulse amplitude threshold is determined. The noise pulse amplitude threshold can be determined based on the maximum amplitude of the rectified differential signal within the entire segment being analyzed, in the example given above, within 360ms. The noise pulse amplitude threshold can be set to a fraction or a percentage of the maximum amplitude of the rectified differential signal. For example, the noise pulse amplitude threshold can be set to one eighth of the maximum amplitude of the rectified differential signal.

[0168] At box 710, signal pulses within the analyzed segment are identified and counted. Signal pulses are identified by comparing the amplitude of the sampling points of the rectified differential signal that occur between two consecutive zero crossings to a noise pulse amplitude threshold. If the rectified differential signal amplitude crosses the noise pulse amplitude threshold, then the signal pulses are identified and counted at box 710. The control circuit 80 can traverse the entire stored signal segment or a selected portion thereof that is earlier in time than the QRS complex is extended to include the baseline signal portion, so as to identify and count all pulses in the analyzed segment that exceed the noise pulse amplitude threshold. Fig.14 The baseline noise parameter determined at block 602 is the count of identified signal pulses determined at block 710. Other techniques that may be implemented to determine a baseline noise parameter such as muscle noise pulse count at block 602 are generally disclosed in U.S. Pat. No. 8,435,185 (Ghanem et al.).

[0169] Fig.16 is based on an example used in Fig.14 Flowchart 800 of a method for determining an amplitude parameter at block 605 of FIG. 802, the notch-filtered signal segment is rectified, for example, as described above in conjunction with Fig.15 The 360 ​​ms segment is rectified. The control circuit 80 determines the maximum absolute amplitude of the rectified notch filtered segment at box 804. The amplitudes of all sampling points of the analyzed rectified signal segment are summed at box 806. At box 808, a normalized rectified amplitude (NRA) is determined based on the maximum absolute amplitude determined at box 804 and the summed sampling point amplitude determined at box 806. In one example, the NRA is determined as the ratio of a predetermined multiple of the sum of all sampling point amplitudes of the notch filtered and rectified signal segment to the maximum absolute amplitude. For example, the NRA can be determined as the summed amplitude divided by four times the maximum absolute amplitude, and the result can be truncated to an integer value. It can be Fig.14 This NRA is determined as an amplitude parameter at block 604 of the present invention. The higher the value of this amplitude parameter, the greater the likelihood that the signal segment contains a valid R wave of a VT or VF episode. When the amplitude parameter is greater than the shockable beat amplitude threshold, the signal segment can be identified as a "shockable beat", as described below in conjunction with Fig.18 described.

[0170] Fig.17 can be executed by the control circuit 80 so as to Fig.14 Flowchart 810 of a method for determining a signal width parameter at block 606 of FIG. 802 and 804 correspond to the above with reference to FIG. Fig.16The notch filtered rectified signal segments determined at block 802 and the maximum absolute amplitude of the rectified signal segments determined at block 804 are used to calculate the maximum absolute amplitude of the rectified signal segments. Fig.14 At block 604, the signal amplitude parameter is determined and Fig.14 The signal width parameter is determined at block 606 of FIG. However, in other examples, the signal width parameter may also be used in conjunction with Fig.15 The signal amplitude parameter and the signal width parameter are determined from a differential signal with a set zero crossing point for determining the pulse count as described, rather than from a notch-filtered rectified signal segment.

[0171] The control circuit 80 determines a pulse amplitude threshold based on the maximum absolute amplitude at block 812. This pulse amplitude threshold is used to identify a signal pulse with a maximum signal width in the second cardiac electrical signal segment. The pulse amplitude threshold determined at block 812 may be the same as the pulse amplitude threshold determined at block 812. Fig.15 For example, the pulse amplitude threshold for determining the signal width parameter may be set to half the maximum absolute amplitude of the rectified notch-filtered signal segment, while Fig.15 The noise pulse amplitude threshold used to determine the signal pulse count can be set to one eighth of the maximum amplitude of the rectified difference signal segment.

[0172] pass Fig.16 The signal amplitude parameters determined by the method and by Fig.17 The signal width parameters determined by the method are used to identify signal pulses that are more likely to be R waves of potential VT or VF rhythms than baseline noise pulses. Signal segments with relatively large signal amplitude parameters and / or relatively large signal width parameters are likely to be heartbeats of VT or VF rhythms rather than noise and are referred to herein as "potentially shockable beats." When a potentially shockable beat is detected based on a larger signal amplitude parameter and / or signal width parameter, a more stringent standard can be applied to detect the signal segment as a noisy segment to avoid stopping VT or VF detection based on a potentially shockable beat. The signal segment including the potentially shockable beat is required to meet the higher noise detection standard in order to prove that the signal segment is detected in box 614 ( Fig.14 ) counts signal segments as noisy segments, which may result in satisfying the overall morphology suppression rule and stopping VT or VF detection. Otherwise, potentially shockable beats counted as noisy segments based on less stringent noise detection criteria may result in stopping or delaying VT or VF detection during true tachyarrhythmia episodes.

[0173] At block 814, the control circuit 80 determines the signal width of all pulses of the segment as the number of sampling points (or corresponding time intervals) between a pair of consecutive zero crossings of the rectified signal. At block 816, the maximum peak value of each pulse is determined. All pulses having a maximum peak value greater than or equal to the pulse amplitude threshold determined at block 812, such as greater than half of the maximum absolute amplitude, are identified. At block 820, a pulse having a maximum pulse width is identified among the pulses having a maximum peak amplitude of at least the pulse amplitude threshold. This maximum pulse width is within Fig.14 is determined as a signal width parameter at block 606 .

[0174] Fig.18 900 is a flowchart of a method for comparing overall morphological parameters with noise detection criteria and detecting segments as noisy segments. The process of flowchart 900 may be performed at Fig.14 At block 902, control circuit 80 retrieves the overall morphology parameters determined at blocks 602, 604, and 606 for comparison with the noise detection criteria. At block 904, the NRA is compared to a potential shockable beat amplitude threshold. Fig.16 When the NRA is determined as described, the potentially shockable beat amplitude threshold can be set between 100 and 150, and in some examples, to 140. If the NRA is greater than the threshold, then the signal segment likely includes a true R wave of a VT or VF episode and is therefore a potentially shockable beat if it occurs during a VT or VF interval.

[0175] At block 906, the maximum pulse width is compared to a potentially shockable beat width threshold. If both the NRA and the maximum pulse width of the signal segment at blocks 904 and 906 are greater than the corresponding amplitude threshold and width threshold, the segment is identified as a potentially shockable beat at block 908. In one example, when the sampling rate is 256 Hz, the potentially shockable beat width threshold is set to 20 samples. At block 910, the baseline noise parameter (e.g., combined with the baseline noise parameter) is determined. Fig.15 The signal pulse count of the segment is compared to a first noisy segment threshold. If the signal pulse count is greater than the noisy segment threshold, for example, greater than 12, the segment is detected as a noisy segment at block 916. In response to detecting a noisy segment, the noisy segment count is incremented. Fig.14 The box 614 is increased by one.

[0176] If the pulse count is less than the first noisy segment threshold, the "No" branch of box 910, the segment is not detected as a noisy segment, and as long as the R sensing confirmation threshold is still reached at box 114 and VT or VF has not been detected, the process returns to box 902 to retrieve the overall morphology parameters of the next signal segment.

[0177] If the segment is not identified as a potentially shockable beat, the "NO" branch of box 904 or the "NO" branch of box 906, then at box 914, the identified signal pulse count is compared to a second noisy segment threshold. The second noisy segment threshold can be less than the first noisy segment threshold. If the segment is not identified as a potentially shockable beat based on the amplitude parameter and the signal width parameter, a less stringent criterion, such as a lower noisy segment threshold, can be applied to classify the segment as a noisy segment. In one example, the second noisy segment threshold is six. If the pulse count exceeds the second noisy segment threshold, then the segment is detected as a noisy segment at box 916 and will be classified as a noisy segment. Fig.14 The control circuit 80 counts at block 614. Otherwise, the segment is not detected as a noisy segment (the "No" branch of block 914), and the overall morphological parameters of the next segment are taken at block 902.

[0178] When the noisy segment count reaches or exceeds the suppression threshold, for example, two noisy segments are counted among the eight most recent analyzed segments, the overall morphological suppression rule is satisfied, as described above in conjunction with Fig.14 The segment is classified as noisy based on the count of positive or negative signal pulses in the originally stored segment having a differential signal absolute amplitude greater than a noise pulse amplitude threshold. Fig.18 In an example of, the number of signal pulses required to detect a noisy segment when the segment is identified as a potentially shockable beat based on a relatively large amplitude parameter and / or a relatively large signal width parameter is less than the number of signal pulses required to detect the segment when the noisy segment is not identified as a potentially shockable beat. Fig.18 In the example of , both the amplitude parameter and the signal width parameter need to exceed the corresponding amplitude threshold and width threshold in order to identify the segment as a potentially shockable beat. In other examples, only one of the amplitude parameter or the signal width parameter may need to exceed its corresponding threshold in order to identify the segment as a potentially shockable beat.

[0179] Fig.19 9 is a timing diagram 950 depicting a time segment within which morphology parameters associated with baseline noise, amplitude parameters, and signal width parameters may be determined. An R-wave sensing event signal 952 occurring at time 962 may cause an R-wave confirmation threshold to be reached. A next R-wave sensing event signal 953 at time 963 triggers storage of a time segment 970 of a second cardiac electrical signal segment. A portion 972 of the time segment 970 extends before the R-wave sensing event signal 953 and a portion 974 extends after the R-wave sensing event signal 953. Overall morphology parameters may be determined for the time segment 970 and the overall morphology parameters may be analyzed to determine whether noise detection criteria are met based on the time segment 970. Figures 15 to 18 The method detects segment 970 as a noisy segment.

[0180] The next R-wave sensing event signal 954 occurs within a predetermined time limit 980 from time 963. Thus, in some examples, analysis of the time segment corresponding to the R-wave sensing event signal 954 is skipped. The second cardiac electrical signal segment may be stored for the R-wave sensing event signal 954 and may be used for other signal analysis to confirm sensing the R-wave and / or determine the status of other suppression rules, but in some examples, not for overall morphology suppression rule analysis. In one example, the time limit 980 may be 300 ms, but may be longer or shorter than this value. The time limit 980 may be set to achieve a processing time for the analysis of the time segment 970 to be performed before starting the analysis of the next time segment. The next R-wave sensing event signal 955 occurs at a time 965 after the time limit 980 expires. The time segment 975 buffered in the memory 82 in response to the R-wave sensing event signal 955 is analyzed to determine whether it is a noisy segment.

[0181] R-wave sensing event 956 at time 966 occurs after time limit 980 has expired in order to Figures 15 to 18 The method of analyzing the time segment 976 of the second cardiac electrical signal. The R wave sensing event signal 957 appears within the time limit 980 after the R wave sensing event signal 956, so as to Fig.19 The example of skipping the analysis of the corresponding time segment. The next time segment 978 corresponding to the R-wave perception event 958 at time 968 is the earliest R-wave perception event that occurs after the expiration of the time limit 980 and is therefore analyzed to determine whether the segment 978 is a noisy segment. In this way, when one or more event segments corresponding to the R-wave perception events that occur within the predetermined time limit 980 are skipped, the time segments of the second cardiac electrical signal may sometimes correspond to continuous R-wave perception event signals and sometimes correspond to non-continuous R-wave perception event signals.

[0182] Fig. 20 920 is a flowchart of a method for comparing an overall morphology parameter to a noise detection criterion and detecting a segment as a noisy segment according to another example. In some examples, each second cardiac electrical signal time segment corresponding to each R-wave sensing event signal received after reaching the R-sensing confirmation threshold is analyzed without requiring the R-wave sensing event signal to be received in the same manner as described above. Fig.19 The post-sensing blanking interval may be applied after each R-wave sensing event signal, e.g. Figure 8The blanking interval 214 of the post-sensing detection is set to exclude R-wave sensing event signals that expire earlier than the post-sensing blanking interval. The post-sensing blanking interval can be, for example, 150 ms. The second cardiac electrical signal segments buffered for each consecutive R-wave sensing event signal that occurs outside the post-sensing blanking interval can be analyzed. Fig.19 In the example of the predetermined time limit 980 shown, the time limit 980 can be set to zero so that each R-wave sensing event signal after expiration of the post-sensing blanking interval results in an overall morphology analysis of the corresponding second cardiac electrical signal segment (after reaching the R-sensing confirmation threshold).

[0183] Boxes 902 to 908 correspond to Fig.18 The segments parameters are retrieved at block 902, and the NRA and maximum pulse width are compared to the corresponding shockable beat amplitude and width thresholds at blocks 904 and 906. If both the NRA and maximum pulse width are greater than their corresponding amplitude and width thresholds (the "yes" branches of both blocks 904 and 906), the segment is classified as a potentially shockable beat at block 908. In this example, when the segment is classified as a potentially shockable beat, the noisy segment threshold is not compared. The segment does not cause the overall morphology suppression rule to be satisfied, so that if the NID ( Fig.14 If the R sensing confirmation threshold is still met and no VT or VF attack is detected, the process returns to frame 902 to retrieve the next stored segment parameters of the second cardiac electrical signal segment.

[0184] If one or both of the NRA and the maximum pulse width are less than their corresponding thresholds (the "No" branch of block 904 and / or block 906), then the signal pulse count determined for the segment is compared to a noisy segment threshold at block 922. The noisy segment threshold may be a pulse count of 8, 10, 12, or other predetermined threshold, which will depend in part on the duration of the signal segment being analyzed. If the pulse count is not greater than the noisy segment threshold, the "No" branch is taken and the segment is not classified as noisy and does not cause an error in the signal segment. Fig.14 The noisy segment count is increased at block 614. If the pulse count is greater than the noisy segment threshold, such as a pulse count of 12 or more, the segment is classified as a noisy segment at block 924. The noisy segment count is Fig.14 The overall morphology suppression rule state is updated at block 430. If the overall morphology suppression rule is satisfied, for example, based on the noisy segment count reaching a threshold (e.g., at least two of the last eight analyzed segments are classified as noisy), as determined at block 440, then the overall morphology suppression rule is satisfied. If the NID is reached based on the first cardiac electrical signal, then Fig.14VT / VF detection is stopped at box 140 and treatment is stopped.

[0185] exist Fig.18 In the example of , a segment classified as a potentially shockable beat can still be classified as a noisy segment based on a higher, more stringent pulse count threshold ( Fig.18 In block 910). Fig. 20 In the example of , all second cardiac electrical signal segments that are identified as potentially shockable beats based on the signal amplitude parameter and / or the signal width parameter are not classified as noisy segments and do not result in cessation of VT / VF detection and treatment. At least one or both of the amplitude parameter and the width parameter are required to be less than their corresponding potentially shockable beat amplitude threshold and width threshold in order to compare the signal pulse count to the noisy segment threshold at box 922 and detect a noisy segment at box 924.

[0186] Thus, in the foregoing description, a method and apparatus for discontinuing ventricular tachyarrhythmia detection in response to detecting noise contamination of cardiac electrical signal segments in an extracardiovascular ICD system has been presented with reference to specific embodiments. In other examples, the various methods described herein may include steps performed in a different order or combination than the illustrative examples shown and described herein. It should be understood that various modifications may be made to the referenced embodiments without departing from the scope of the present disclosure and the following claims.

[0187] The following numbered examples illustrate one or more aspects of the disclosure.

[0188] Example 1. A method, comprising: sensing a plurality of R waves by a first sensing channel of a sensing circuit of a medical device system in response to a first cardiac electrical signal crossing a sensing amplitude threshold, the first cardiac electrical signal being received by the first sensing channel via a first extracardiovascular sensing electrode vector coupled to the medical device system; storing a time segment of a second cardiac electrical signal in a memory for each of the plurality of R waves sensed by the first sensing channel, the second cardiac electrical signal being received via a second sensing electrode vector coupled to the medical device system and different from the first sensing electrode vector; for each of the plurality of stored time segments: determining a morphological parameter associated with signal noise based on the stored time segment; detecting the corresponding stored time segment as a noisy signal segment based on the morphological parameter determined for the stored time segment; and stopping detecting a rapid arrhythmia attack in response to detecting at least a threshold number of the stored time segments as noisy signal segments.

[0189] Example 2. The method as described in Example 1 further includes: before determining the morphological parameters, filtering the time segment of the second cardiac electrical signal by a notch filter.

[0190] Example 3. A system as described in any of Examples 1 and 2, further comprising: determining a plurality of intervals between consecutive R waves in the R wave sensed by the first sensing channel; determining that at least a predetermined number of the plurality of intervals are less than a rapid arrhythmia detection interval; and determining the morphological parameters in response to a predetermined number of the plurality of intervals being less than the rapid arrhythmia detection interval.

[0191] Example 4. A method as described in any of Examples 1 to 3, wherein determining the morphological parameters includes: identifying signal pulses occurring during the time segment of the second cardiac electrical signal; and determining a count of the identified signal pulses.

[0192] Example 5. A method as described in Example 4, wherein identifying the signal pulse includes: identifying the zero crossing point of the second cardiac electrical signal during the time segment; determining that the second cardiac electrical signal crosses a noise pulse amplitude threshold between two consecutive zero crossing points; and identifying the signal pulse in response to the second cardiac electrical signal crossing the noise pulse amplitude threshold between two consecutive zero crossing points.

[0193] Example 6. The method as described in any one of Examples 1 to 5 further includes: determining at least one of a signal width parameter or a signal amplitude parameter of the stored time segment; detecting a potentially shockable beat based on at least one of the signal width parameter or the signal amplitude parameter; comparing the morphology parameter with a first noisy segment threshold in response to detecting the potentially shockable beat; determining that the morphology parameter determined for the corresponding stored signal segment is greater than or equal to the first noisy segment threshold; and detecting the corresponding stored time segment as a noisy signal segment in response to the morphology parameter determined for the stored signal segment being greater than or equal to the first noisy segment threshold.

[0194] Example 7. The method as described in Example 6 further includes: comparing the morphology parameter with a second noisy segment threshold in response to not detecting a potentially shockable beat based on at least one of the signal width parameter or the signal amplitude parameter; determining that the morphology parameter is greater than or equal to the second noisy segment threshold, the second noisy segment threshold being less than the first noisy segment threshold; and detecting the stored time segment as a noisy signal segment in response to the morphology parameter being greater than or equal to the second noisy segment threshold, the second noisy segment threshold being less than the first noisy segment threshold.

[0195] Example 8. The method as described in any one of Examples 1 to 7 further includes: determining at least one of a signal width parameter and / or a signal amplitude parameter based on the stored time segment; determining that the stored time segment is not a potentially shockable beat based on at least one of the signal width parameter and / or the signal amplitude parameter; comparing the morphology parameter with a noisy segment threshold in response to determining that the stored time segment is not a potentially shockable beat; and determining that the corresponding stored time segment is a noisy signal segment in response to the morphology parameter determined for the stored time segment being greater than or equal to the noisy segment threshold.

[0196] Example 9. A method as described in Example 8, wherein determining the signal width parameter includes: identifying the zero crossing points of the second cardiac electrical signal during the stored time segment; determining that the second cardiac electrical signal crosses a pulse amplitude threshold between two consecutive zero crossing points; identifying a signal pulse in response to the second cardiac electrical signal crossing the pulse amplitude threshold between two consecutive zero crossing points; determining the pulse width of each identified signal pulse as the time interval between the two consecutive zero crossing points of each corresponding identified signal pulse; and determining the signal width parameter as the maximum pulse width among the determined pulse widths.

[0197] Example 10. The method as described in any of Examples 8 and 9 further includes: determining the amplitude parameter by the following operations: determining the sum of the absolute amplitudes of all sampling points of the time segment; and normalizing the sum by the maximum sampling point amplitude of the time segment; comparing the amplitude parameter with a shockable beat amplitude threshold; determining that the amplitude parameter is greater than the shockable beat amplitude threshold; comparing the signal width parameter with a shockable beat width threshold; determining that the signal width parameter is greater than the shockable beat width threshold; and detecting the potentially shockable beat when the amplitude parameter is greater than the shockable beat amplitude threshold and the signal width parameter is greater than the shockable beat width threshold.

[0198] Example 11. The method as described in any one of Examples 1 to 10 further includes: increasing a noisy signal segment count in response to detecting the noisy signal segment; determining a plurality of intervals between consecutive R waves in the R wave sensed by the first sensing channel; determining that a predetermined number of the plurality of intervals are less than a rapid arrhythmia detection interval; comparing the value of the count with a suppression threshold in response to detecting that the predetermined number of the plurality of intervals are less than the rapid arrhythmia detection interval, and determining that the value of the noisy signal segment count is equal to or greater than the suppression threshold; and stopping detecting the rapid arrhythmia attack in response to the value of the noisy signal segment count being equal to or greater than the suppression threshold.

[0199] Example 12. The method as described in any one of Examples 1 to 11 further includes: determining the morphological parameters of the first time segment of the second cardiac electrical signal corresponding to the first perceived R wave; determining whether the next perceived R wave appears within a predetermined time limit from the first perceived R wave; determining that the next perceived R wave appears within the predetermined time limit; and skipping determining the morphological parameters according to the time segment corresponding to the next perceived R wave of the second cardiac electrical signal in response to the next perceived R wave appearing within the predetermined time limit.

[0200] Example 13. The method of any one of Examples 1 to 12, further comprising: sensing the first cardiac electrical signal via at least one electrode carried by a cardiovascular external lead coupled to the ICD.

[0201] Example 14. The method as described in any one of Examples 1 to 13, further comprising: sensing the first cardiac electrical signal by the first sensing electrode vector having a first inter-electrode spacing; and sensing the second cardiac electrical signal by the second sensing electrode vector having a second inter-electrode spacing, the second inter-electrode spacing being greater than the first inter-electrode spacing.

[0202] Example 15. The method as described in any one of Examples 1 to 14 further includes: increasing the noisy segment count in response to detecting the noisy signal segment; determining a plurality of intervals between consecutive R waves in the R wave sensed by the first sensing channel; detecting that a predetermined number of the plurality of intervals are less than a tachyarrhythmia detection interval; comparing the value of the noisy segment count with a suppression threshold in response to detecting that the predetermined number of the plurality of intervals are less than the tachyarrhythmia detection interval; determining that the value of the count is less than the suppression threshold; detecting the tachyarrhythmia attack in response to the value of the count being less than the suppression threshold; and controlling the therapy delivery circuit of the medical device system to deliver the anti-tachyarrhythmia therapy in response to detecting the tachyarrhythmia attack.

[0203] Example 16. A non-transitory computer-readable storage medium, comprising a set of instructions that, when executed by a control circuit of an extracardiovascular implantable cardioverter-defibrillator (ICD), cause the extracardiovascular ICD to: sense a plurality of R waves by a first sensing channel of a sensing circuit of the extracardiovascular ICD in response to a first cardiac electrical signal crossing a sensing amplitude threshold, the first cardiac electrical signal being received by the first sensing channel via a first extracardiovascular sensing electrode vector coupled to the extracardiovascular ICD; store a time segment of a second cardiac electrical signal in an ICD memory in response to each of the plurality of R waves sensed by the first sensing channel, the second cardiac electrical signal being received by a second sensing channel of the extracardiovascular ICD via a second extracardiovascular sensing electrode vector; determine, for each of the plurality of stored time segments, a morphological parameter associated with signal noise based on the stored time segment, and detect the corresponding stored time segment as a noisy signal segment based on the morphological parameter determined for the stored time segment; and stop detecting a rapid arrhythmia attack in response to detecting at least a threshold number of the stored time segments as noisy signal segments.

Claims

1. A medical device system, comprising: A sensing circuit configured to: receiving a first cardiac electrical signal; sensing a plurality of R waves from the first cardiac electrical signal, and receiving a second cardiac electrical signal different from the first cardiac electrical signal; Memory; as well as a control circuit coupled to the sensing circuit and the memory, the control circuit being configured to: storing a signal segment of the second cardiac electrical signal in the memory for each R wave of the plurality of R waves sensed by the sensing circuit from the first cardiac electrical signal; determining a morphology parameter from each signal segment of the second cardiac electrical signal; and and determining at least one signal segment of the second cardiac electrical signal as a noisy signal segment based on the morphology parameters determined for each respective signal segment; and In response to determining the at least one signal segment as a noisy signal segment, detecting a tachyarrhythmia episode is ceased.

2. The system according to claim 1, characterized in that The control circuit is further configured to: determining a plurality of RR intervals between consecutive R waves in the R wave sensed by the sensing circuit; determining that at least a threshold number of the plurality of RR intervals are each less than a tachyarrhythmia detection interval; and In response to determining that at least the threshold number of RR intervals of the plurality of RR intervals are each less than the tachyarrhythmia detection interval, the at least one signal segment is determined to be a noisy signal segment based on the morphology parameter.

3. The system according to claim 2, characterized in that The control circuit is configured to: The morphology parameter is determined from each signal segment of the second cardiac electrical signal by: identifying signal pulses in the signal segment; and determining a count of the identified signal pulses; and By determining that the count of the signal pulses of the at least one signal segment is greater than a threshold, it is determined that the at least one signal segment is a noisy signal segment.

4. The system according to claim 3, characterized in that The control circuit is configured to identify the signal pulses in the signal segment by: determining that the second cardiac electrical signal crosses a noise pulse amplitude threshold; and In response to the second cardiac electrical signal crossing the noise pulse amplitude threshold, signal pulses in the signal segment are identified.

5. The system according to any one of claims 1 to 4, characterized in that: The control circuit is further configured to: determining the morphology parameter from each signal segment of the second cardiac electrical signal by determining an amplitude parameter from each signal segment; and determining said at least one signal segment of said second cardiac electrical signal as a noisy signal segment by at least determining that said amplitude parameter of said at least one signal segment is less than a shockable beat amplitude threshold, Specifically, the control circuit is configured to determine the amplitude parameter of each signal segment by: determining a maximum amplitude of said signal segments; determining a sum of the amplitudes of the sampling points of the signal segment; and The amplitude parameter is determined by determining a ratio of the maximum amplitude to a multiple of the sum of the sampling point amplitudes.

6. The system according to any one of claims 1 to 5, characterized in that: The control circuit is further configured to: determining the morphology parameter from each signal segment of the second cardiac electrical signal by determining a signal width parameter from each signal segment; and determining the at least one signal segment of the second cardiac electrical signal as a noisy signal segment by at least determining that the signal width parameter of the at least one signal segment is less than a shockable beat width threshold, Specifically, the control circuit is configured to determine the signal width parameter of each signal segment in the following manner: identifying a plurality of signal pulses in the signal segment; determining a signal width of each of the plurality of signal pulses; determining a maximum signal width among the determined signal widths; and The signal width parameter is determined as the maximum signal width.

7. The system according to any one of claims 1 to 6, characterized in that: The control circuit is further configured to: store the signal segment of the second cardiac electrical signal, the signal segment including sampling points occurring before and after the time of a corresponding R wave of the plurality of R waves sensed by the sensing circuit from the first cardiac electrical signal.

8. The system according to any one of claims 1 to 7, characterized in that: further comprising a therapy delivery circuit, and wherein: The control circuit is further configured to: determining a plurality of RR intervals between consecutive R waves of the R waves sensed by the sensing circuit from the first cardiac electrical signal; determining that at least a first threshold number of RR intervals of the plurality of RR intervals are each equal to or less than a tachyarrhythmia detection interval; determining that less than a second threshold number of the stored signal segments are noisy signal segments based on the morphology parameter determined for each respective signal segment; and responsive to determining that the first threshold number of the plurality of RR intervals is equal to or less than the tachyarrhythmia detection interval and that fewer than the second threshold number of the stored signal segments are noisy signal segments, detecting a tachyarrhythmia; and The therapy delivery circuit is configured to deliver anti-tachyarrhythmia therapy in response to the control circuit detecting the tachyarrhythmia.

9. A method for detecting noise in a cardiac electrical signal, comprising: receiving a first cardiac electrical signal; sensing an R wave from the first cardiac electrical signal; receiving a second cardiac electrical signal different from the first cardiac electrical signal; storing a signal segment of the second cardiac electrical signal in response to each of a plurality of R waves sensed from the first cardiac electrical signal; determining a morphology parameter from each signal segment of the second cardiac electrical signal; determining at least one signal segment of the second cardiac electrical signal as a noisy signal segment based on the morphology parameters determined for each respective signal segment; and In response to determining the at least one signal segment as a noisy signal segment, detecting a tachyarrhythmia episode is ceased.

10. The method according to claim 9, characterized in that Further including: determining a plurality of RR intervals between consecutive R waves sensed from the first cardiac electrical signal; determining that at least a threshold number of the plurality of RR intervals are each less than a tachyarrhythmia detection interval; as well as In response to determining that at least the threshold number of RR intervals of the plurality of RR intervals are each less than the tachyarrhythmia detection interval, determining the at least one signal segment as a noisy signal segment based on the morphology parameter, Specifically include: The morphology parameter is determined from each signal segment of the second cardiac electrical signal by: identifying signal pulses in the signal segment; and determining a count of said signal pulses; and determining that the at least one signal segment is a noisy signal segment by determining that the count of the signal pulses of the at least one signal segment is greater than a threshold, Specifically, identifying the signal pulse in the signal segment includes: determining that the second cardiac electrical signal crosses a noise pulse amplitude threshold; In response to the second cardiac electrical signal crossing the noise pulse amplitude threshold, signal pulses in the signal segment are identified.

11. The method according to claim 9 or 10, characterized in that include: determining the morphology parameter from each signal segment of the second cardiac electrical signal by determining an amplitude parameter of the signal segment; Wherein determining the at least one signal segment of the second cardiac electrical signal as a noisy signal segment comprises: at least determining that the amplitude parameter of the at least one signal segment is less than a shockable beat amplitude threshold, Specifically, determining the amplitude parameter of the signal segment includes: determining a maximum amplitude of said signal segments; Determining the sum of the amplitudes of the sampling points of the signal segment; and The amplitude parameter is determined by determining a ratio of the maximum amplitude to a multiple of the sum of the sampling point amplitudes.

12. The method according to any one of claims 9 to 11, characterized in that include: determining the morphology parameter from each signal segment of the second cardiac electrical signal by determining a signal width parameter; as well as determining that the at least one signal segment of the second cardiac electrical signal is a noisy signal segment by at least determining that the signal width parameter is less than a shockable beat width threshold, Specifically, determining the signal width parameter includes: identifying a plurality of signal pulses in the signal segment; determining a signal width of each of the plurality of signal pulses; determining a maximum signal width among the determined signal widths; and The signal width parameter is determined as the maximum signal width.

13. The method according to any one of claims 9 to 12, characterized in that: Storing the signal segment of the second cardiac electrical signal includes storing sampling points of the second cardiac electrical signal that occur before and after the time of a corresponding R wave of the plurality of R waves sensed from the first cardiac electrical signal.

14. A non-transitory computer readable medium storing a set of instructions that, when executed by control circuitry of a medical device, cause the medical device to: receiving a first cardiac electrical signal; sensing an R wave from the first cardiac electrical signal; receiving a second cardiac electrical signal different from the first cardiac electrical signal; storing a signal segment of the second cardiac electrical signal in response to each of a plurality of R waves sensed from the first cardiac electrical signal; determining a morphology parameter from each signal segment of the second cardiac electrical signal; determining at least one signal segment of the second cardiac electrical signal as a noisy signal segment based on the morphology parameters determined for each respective signal segment; and In response to determining the at least one signal segment as a noisy signal segment, detecting a tachyarrhythmia episode is ceased.

15. The non-transitory computer readable medium of claim 14, wherein: The set of instructions, when executed by the control circuit of the medical device, further causes the medical device to: determining a plurality of RR intervals between consecutive R waves sensed from the first cardiac electrical signal; determining that at least a first threshold number of RR intervals of the plurality of RR intervals are each equal to or less than a tachyarrhythmia detection interval; determining that fewer than a second threshold number of the stored signal segments are noisy signal segments based on the morphology parameter determined for each respective signal segment; detecting a tachyarrhythmia in response to determining that the first threshold number of the plurality of RR intervals is equal to or less than the tachyarrhythmia detection interval and that fewer than the second threshold number of the stored signal segments are noisy signal segments; as well as Anti-tachyarrhythmia therapy is delivered in response to detecting the tachyarrhythmia.

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