Medical device for reduced power for arrhythmia detection

Abstract

A medical device and method conserves power for monitoring cardiac arrhythmias. The device includes a sensing circuit configured to sense a cardiac signal, a power source, and a control circuit having a processor powered by the power source. The control circuit is configured to operate in a normal state by waking the processor to analyze the cardiac electrical signal to determine a status of a cardiac arrhythmia. The control circuit switches from the normal state to a power conservation state that includes waking the processor at a lower rate than during the normal state.

Description

TECHNICAL FIELD

[0001] The present disclosure relates generally to medical devices, and in particular, to a device and method for detecting cardiac arrhythmias with reduced power requirements during a power conservation state. BACKGROUND

[0002] A variety of medical devices for monitoring a patient's physiological condition and / or delivering therapy have been clinically implanted or proposed for clinical implantation in patients and / or have been incorporated into wearable medical devices. For example, some implantable medical devices (IMDs) can employ one or more elongated electrical leads that carry stimulation electrodes, sensing electrodes, and / or other sensors. The IMDs can deliver therapy to or monitor the condition of various organs, nerves, muscles, or tissues, such as the heart, brain, stomach, spinal cord, pelvic floor, etc. Implantable medical leads can be configured to position electrodes or other sensors at desired locations for delivery of electrical stimulation or sensing of physiological conditions. For example, electrodes or sensors can be carried along a distal portion of a lead that extends subcutaneously, transvenously, or submuscularly. A proximal portion of the lead can be coupled to an implantable medical device housing that contains circuitry, such as signal generation circuitry and / or sensing circuitry.

[0003] Some IMDs, such as cardiac pacemakers or implantable cardioverter-defibrillators (ICDs), provide therapeutic electrical stimulation to a patient's heart through electrodes carried by one or more implantable leads and / or the housing of the pacemaker or ICD. The leads can be transvenous, for example, advanced through one or more veins into the heart to position endocardial electrodes in close proximity to heart tissue. Other leads can be non-transvenous leads implanted outside the heart (e.g., implanted epicardially, pericardially, or subcutaneously). The electrodes are used to sense intrinsic cardiac electrical signals to monitor the rhythm of the heart and to deliver electrical stimulation pulses to the heart to address abnormal rhythms.

[0004] IMDs capable of delivering electrical stimulation to treat abnormal heart rhythms generally sense signals representative of the heart's intrinsic depolarization and analyze the sensed signals to identify abnormal rhythms. Upon detection of an abnormal rhythm, the device can deliver appropriate electrical stimulation therapy to restore a more normal rhythm or, in some cases, withhold therapy when the abnormal rhythm does not respond to therapy. For example, upon detection of bradycardia or tachycardia using endocardial or epicardial electrodes, a pacemaker or ICD can deliver low voltage pacing pulses to the heart. Upon detection of a rapid ventricular tachycardia or fibrillation using electrodes carried by a transvenous lead or a non-transvenous lead, an ICD can deliver high voltage cardioversion or defibrillation shocks to the heart. When a ventricular tachycardia is determined to be a supraventricular tachycardia caused by a conductive atrial tachyarrhythmia, ventricular tachycardia therapy can be withheld. The type of therapy delivered and its effectiveness in restoring a normal rhythm depends at least in part on the type of electrodes used to deliver the electrical stimulation and their location relative to the heart tissue. Data or information related to the detection of abnormal rhythms can be stored in the implantable device for upload to an external device for diagnostic and patient monitoring purposes and for use by a clinician in selecting a therapy plan. SUMMARY

[0005] In general, the present disclosure relates to techniques for conserving power required from a power source of a medical device configured to detect cardiac arrhythmias. The disclosed techniques can be implemented in an IMD, such as a cardiac rhythm monitor, pacemaker, or ICD, or a wearable medical device, such as a medical device incorporated into a watch, belt, watchband, vest, or other wearable substrate. A medical device operating according to the techniques disclosed herein is configured to operate in at least two different cardiac arrhythmia monitoring states, e.g., a normal state and a power conservation state. During the power conservation state, less power from the power source of the medical device is used in monitoring for cardiac arrhythmias and determining the status of the cardiac arrhythmias than during the normal state. In some examples, power is conserved during the power conservation state by reducing at least the frequency or rate at which a processor is awakened to analyze cardiac electrical signals to determine the status of the cardiac arrhythmias, as compared to the rate at which the processor is awakened during the normal state. In some examples, the processor is awakened to analyze cardiac electrical signals to determine the status of a rapid atrial arrhythmia, referred to herein as "AT / AF," which can include atrial tachycardia, atrial flutter, and / or atrial fibrillation.

[0006] In one example, the disclosure provides a medical device comprising: a sensing circuit configured to sense a cardiac signal; a power source; and a control circuit comprising a processor powered by the power source. The control circuit is configured to operate in a normal state by waking up the processor at a first rate to analyze the cardiac signal to determine a status of a cardiac arrhythmia and switch from the normal state to a power conservation state that uses less power from the power source than the normal state in determining the status of the cardiac arrhythmia. Operating in the power conservation state comprises waking up the processor at a second rate that is less than the first rate at which the processor is woken up during the normal state.

[0007] In another example, the disclosure provides a method comprising: sensing a cardiac signal, operating in a normal state by waking up a processor at a first rate to analyze the cardiac signal to determine a status of a cardiac arrhythmia; and switching from the normal state to a power conservation state that uses less power in determining the status of the cardiac arrhythmia than the normal state. Operating in the power conservation state can comprise waking up the processor at a second rate that is less than the first rate at which the processor is woken up.

[0008] In another example, the 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 a cardiac signal; operate in a normal state by waking up a processor of the medical device at a first rate to analyze the cardiac signal to determine a status of a cardiac arrhythmia; and switch from the normal state to a power conservation state that uses less power in determining the status of the cardiac arrhythmia than the normal state. Operating in the power conservation state can comprise waking up the processor at a second rate that is less than the first rate at which the processor is woken up during the normal state.

[0009] This summary is intended to provide an overview of the subject matter described in this disclosure. It is not intended to provide an exclusive or exhaustive explanation of the apparatus and methods described in detail in the accompanying drawings and description below. Further details of one or more examples are set forth in the accompanying drawings and in the description below. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 is a conceptual diagram of one example of an IMD system configured to detect cardiac arrhythmias and deliver cardiac electrical stimulation therapy.

[0011] Figure 2 is a conceptual diagram of a leadless cardiac pacemaker positioned within the right atrium for sensing atrial signals and delivering cardiac pacing pulses.

[0012] Figure 3 is a conceptual diagram of an example configuration of a medical device configured to detect cardiac arrhythmias and switch between a normal state and a power saving state to detect cardiac arrhythmias.

[0013] Figure 4 is a conceptual diagram of cardiac arrhythmia detection operating states between which IMD control circuitry can switch according to some examples.

[0014] Figure 5 is a flowchart of operations performed by a medical device for detecting atrial arrhythmias in a normal operating state according to one example.

[0015] Figure 6 is a flowchart of operations performed by a medical device in a power saving state of atrial arrhythmia monitoring according to one example.

[0016] Figure 7 is a flowchart of a method for medical device control of AT / AF monitoring and detection operating states according to another example.

[0017] Figure 8 is a flowchart of a method for medical device control of atrial arrhythmia detection states according to another example. DETAILED DESCRIPTION

[0018] In general, this disclosure describes techniques for conserving power used for detecting and monitoring cardiac arrhythmias by a medical device. In various examples, the device can be an IMD, such as an implantable cardiac monitor, a pacemaker, or an ICD. In other examples, the medical device is an external, wearable medical device, such as an external cardiac monitor incorporated into a watch, a belt, a watchband, a vest, or other wearable substrate, or an external pacemaker, as examples. The medical device is configured to detect and report cardiac arrhythmias, which can or can not be treated by the medical device, e.g., through delivery of electrical stimulation therapy. In some examples, atrial arrhythmias that can lead to, e.g., ventricular therapy inhibition can be detected.

[0019] To detect arrhythmias, medical devices typically sense cardiac signals to detect periodic cardiac events and determine cardiac event intervals. The medical device processes the sensed cardiac event intervals and / or the sensed event signal waveforms according to an implemented arrhythmia detection algorithm. The cardiac signals can be cardiac electrical signals used to detect cardiac event signals that accompany myocardial depolarization. In other examples, the medical device can sense cardiac mechanical signals that accompany myocardial contraction, e.g., from an impedance sensor, an acoustic sensor, a pressure sensor, an accelerometer, or other motion sensor, for detecting or confirming arrhythmias. Processing the sensed cardiac signals consumes considerable power as a processor providing power to execute the arrhythmia detection algorithm and / or determine a status of an arrhythmia (e.g., redetecting a persistent arrhythmia, detecting an arrhythmia termination, determining an incidence of an arrhythmia, or other arrhythmia episode information, all of which can be determined from the processed signals and stored in a memory of the medical device for reporting to a clinician for diagnostic and therapy management purposes).

[0020] Accordingly, arrhythmia monitoring algorithms executed by a processor of a medical device consume current from a power source of the medical device. The useful life of an IMD used to monitor arrhythmias and / or perform other functions (e.g., for delivering cardiac pacing or other cardiac electrical stimulation therapy) can be shortened, which can be critical to maintaining life or maintaining quality of life. In an externally worn device, the power consumed for arrhythmia monitoring can increase the frequency of necessary battery charging or replacement. The technology disclosed herein conserves power of a medical device for detecting at least some arrhythmias (e.g., atrial arrhythmias) that can not be considered a serious threat to life or can not be treated by the medical device, but can be tracked for diagnostic reporting purposes and / or distinguished from other types of more serious arrhythmias.

[0021] Figure 1is a conceptual diagram of one example of an IMD system 10 configured to detect cardiac arrhythmias and deliver cardiac electrical stimulation therapy. The system 10 is capable of sensing atrial P-waves attendant to atrial heart muscle depolarization and detecting AT and / or AF, collectively referred to herein as “AT / AF,” based on analysis of the sensed P-waves. The AT / AF detection, also referred to herein as “atrial arrhythmia detection,” method can include analysis of time intervals related to P-waves, e.g., PP intervals between consecutively sensed P-waves, P-wave to R-wave ratio (attendant to ventricular heart muscle depolarization), PR intervals, RP intervals, and / or P-wave signal morphology. In accordance with the technology disclosed herein, the IMD system 10 is configured to operate in a normal state to sense P-waves and detect AT / AF, and in a power conservation state to sense P-waves and detect AT / AF. The IMD 14 can switch between the normal state and the power conservation state to provide detection and reporting of AT / AF episodes during both states, while conserving power consumed for AT / AF detection during the power conservation state as compared to the normal state.

[0022] The system 10 includes an IMD 14 coupled to transvenous leads 16, 17, and 18 for sensing cardiac electrical signals and delivering cardiac electrical stimulation therapy in each of the right atrium (RA), right ventricle (RV), and left ventricle (LV) of the heart 8. In this example, the IMD 14 is configured as a multi-chamber pacemaker and defibrillator capable of delivering cardiac resynchronization therapy (CRT). CRT includes delivering pacing pulses in the LV, RV, and / or RA to improve mechanical synchronization of the left and right ventricles with each other and / or with the atria, thereby facilitating more efficient pumping of the heart 8. Accordingly, the IMD 14 is coupled to three leads 16, 17, and 18 in this example to provide multi-chamber sensing and pacing.

[0023] The IMD 14 includes a connector assembly 12 coupled to a housing 15 that encloses electrical circuitry configured to perform IMD functions, as further described below with respect to the processor, cardiac electrical signal sensing circuitry, and therapy delivery circuitry. The connector assembly 12, sometimes referred to as a “header,” is hermetically sealed to the housing 15 and, in this example, includes three connector bores for receiving proximal lead connectors 40, 42, and 44 of each of the respective leads 16, 17, and 18 to provide electrical communication between electrodes carried by the distal portions of each lead and the sensing and therapy delivery circuitry enclosed by the housing 15. The housing 15 is formed of a biocompatible material, such as stainless steel or a titanium alloy. In some examples, the housing 15 can include an insulative coating over at least the exterior of the housing 15. Examples of the insulative coating include parylene, urethane, PEEK, or polyimide, among others. The housing 15 can be hermetically sealed to enclose and protect the IMD circuitry from blood and body fluids. Figure 3 The processor, cardiac electrical signal sensing circuitry, and therapy delivery circuitry are further described below. The connector assembly 12, sometimes referred to as a “header,” is hermetically sealed to the housing 15 and, in this example, includes three connector bores for receiving proximal lead connectors 40, 42, and 44 of each of the respective leads 16, 17, and 18 to provide electrical communication between electrodes carried by the distal portions of each lead and the sensing and therapy delivery circuitry enclosed by the housing 15. The housing 15 is formed of a biocompatible material, such as stainless steel or a titanium alloy. In some examples, the housing 15 can include an insulative coating over at least the exterior of the housing 15. Examples of the insulative coating include parylene, urethane, PEEK, or polyimide, among others. The housing 15 can be hermetically sealed to enclose and protect the IMD circuitry from blood and body fluids.

[0024] The leads coupled to IMD 14 include RA lead 16, RV lead 17, and coronary sinus (CS) lead 18. RA lead 16 can carry a distal tip electrode 20 and a ring electrode 22 proximal ly spaced from tip electrode 20 for sensing atrial electrical signals (e.g., P-waves) and delivering RA pacing pulses. RA lead 16 can be positioned such that its distal end is located in the RA and superior vena cava, and includes an insulated electrical conductor extending from each of electrodes 20 and 22 through an elongated lead body to a proximal lead connector 40.

[0025] RV lead 17 includes pacing electrodes 28 and sensing electrodes 30, shown as tip electrode 28 and a ring electrode 30 proximally spaced from tip electrode 28. Electrodes 28 and 30 provide sensing and pacing in the RV, and each electrode is connected to a respective insulated conductor within the body of RV lead 17. The proximal ends of each insulated conductor are coupled to a proximal lead connector 42. RV lead 17 is positioned such that its distal end is in the RV for sensing RV electrical signals, such as R-waves accompanying ventricular depolarization, and delivering pacing pulses in the RV. In some examples, IMD 14 is capable of delivering high voltage pulses for cardioversion or defibrillation of heart 8 in response to detecting a tachyarrhythmia. In this case, RV lead 17 can include defibrillation electrodes 24 and 26, which can be elongated coil electrodes for delivering high voltage cardiac cardioversion / defibrillation (CV / DF) therapy, also referred to as “shocks” or “shock pulses.”

[0026] Defibrillation electrode 24 can be referred to as an “RV defibrillation electrode” or “RV coil electrode” because it is carried along the body of RV lead 17 such that it is positioned substantially within the RV when distal pacing electrode 28 and sensing electrode 30 are positioned for pacing and sensing in the RV. For example, tip electrode 28 can be positioned at an endocardial location at the RV apex. Defibrillation electrode 26 can be referred to as a “superior vena cava (SVC) defibrillation electrode” or “SVC coil electrode” because it is carried along the body of RV lead 17 such that it is positioned at least partially along the SVC when the distal end of RV lead 17 is advanced within the RV. While electrodes 24 and 26 are referred to herein as defibrillation electrodes, it should be understood that electrodes 24 and 26 can be used for sensing cardiac electrical signals, delivering cardiac pacing pulses, or delivering anti-tachyarrhythmia pacing (ATP) therapy, and are not necessarily limited only to use for delivering high voltage CV / DV shock pulses. Each of electrodes 24, 26, 28, and 30 is connected to a respective insulated conductor extending within the body of lead 17. The proximal ends of the insulated conductors are coupled to respective connectors carried by proximal lead connector 42, e.g., DF-4 connectors, at the proximal end of lead 17 for providing electrical connections to IMD 14.

[0027] The CS lead 18 can be advanced within the vasculature on the left side of the heart through the coronary sinus and a cardiac vein (CV). The CS lead 18 is shown as a four-pole lead having four electrodes 32, 34, 36, and 38, which can be selected in various bipolar or unipolar electrode vectors for sensing cardiac electrical signals from the LV and delivering cardiac pacing pulses to the LV, e.g., during CRT delivery. In other examples, the CS lead 18 can include one or more electrodes for sensing cardiac electrical signals and delivering pacing pulses to the LV. The electrodes 32, 34, 36, and 38 are each coupled to respective insulated conductors within the body of the CS lead 18, which provide electrical and mechanical connection to a proximal lead connector 44 that is coupled to the IMD connector assembly 12.

[0028] The various pacing and sensing electrodes 20, 22, 28, 30, 32, 34, 36, and 38 can be selected in bipolar combinations for sensing and pacing in the respective RA, RV, or LV. In some examples, the housing 15 is usable as an electrode, sometimes referred to as a “can” electrode, for selection in a unipolar pacing or sensing electrode vector with any of the electrodes 20, 22, 28, 30, 32, 34, 36, or 38. The IMD housing 15 can act as a subcutaneous defibrillation electrode in combination with one or both of the RV coil electrode 24 and the SVC coil electrode 26 for delivering CV / DF shocks to the heart 8. It will be recognized that many sensing and electrical stimulation electrode vectors are available using the various electrodes carried by one or more of the leads 16, 17, and 18.

[0029] It will be recognized that alternative lead systems can be substituted for the three-lead system shown Figure 1 Although a particular multi-chamber IMD and lead system is shown in Figure 1 disclosed herein can be implemented in single-chamber, dual-chamber, or multi-chamber cardiac pacemakers, which can or can not include CRT or CV / DF capabilities. Such devices can be coupled to one or more transvenous leads, such as leads 16, 17, and 18, which can each be used to position electrodes in one or more of the ventricles. In some examples, a single lead can include ventricular electrodes for sensing and stimulation in a ventricle and one or more atrial electrodes for sensing in an atrium. In other examples, non-transvenous or extracardiac leads extending subcutaneously, submuscularly, or substernally can be used to place electrodes and / or other sensors to sense cardiac signals and detect cardiac arrhythmias therefrom. Examples of other IMDs, such as cardiovascular external IMD systems, in which the techniques disclosed herein can be implemented are generally disclosed in U.S. Patent No. 10,045,710 (Higgins et al.).

[0030] The external device 50 is shown in wireless telemetry communication with the IMD 14 over a communication link 60. As A radio frequency (RF) link, such as Wi-Fi, Medical Implant Communication Service (MICS), or other communication bandwidth, can be used to establish the communication link 60. The external device 50 can be referred to as a "programmer" that is used by a physician, technician, nurse, clinician, or other qualified user to program operational parameters in the IMD 14. The external device 50 can be positioned in a clinic, hospital, or other medical facility. The external device 50 can alternatively be embodied as a home monitor or hand-held device that can be used in a patient's home or other location to allow the patient or other user to interact with or remotely monitor the patient and IMD 14 operation. In one example, the external device 50 can correspond to a MYCARE LINK® patient monitor commercially available from Medtronic, Inc. of Minneapolis, MN. TM patient monitor.

[0031] The external device 50 can be used to program IMD operational parameters, such as sensing and therapy delivery control parameters, into the IMD 14. The external device 50 includes an external processor 52, memory 53, a display 54, a user interface 56, and a telemetry unit 58. The external processor 52 controls the external device operations and processes data and signals received from the IMD 14. The external processor 52 provides therapy delivery data, cardiac electrical signal data, arrhythmia episode data, such as AT / AF data, and / or other device related or patient related data retrieved from the IMD 14 to the user display 54 for generating displays of the data for observation and review by a clinician.

[0032] The user display 54 generates displays of data received from the IMD 14 and can include a graphical user interface that facilitates programming of one or more sensing parameters, arrhythmia detection parameters, therapy delivery parameters, etc. by a user interacting with the external device 50. The external device 50 can display other data and information related to IMD function to the user for viewing IMD operation and programmed parameters and cardiac electrical signals or other physiological data retrieved from the IMD 14 during an interrogation session. The user interface 56 can include a mouse, touch screen or other pointing device, keyboard, and / or keypad that enables a user to interact with the external device 50 to initiate telemetry sessions with the IMD 14 for retrieving data from and / or transmitting data to the IMD 14, as well as for selecting and programming desired sensing and therapy delivery control parameters, tachyarrhythmia detection algorithms, and other operational parameters into the IMD 14. Normal state and power saving state operational parameters for detecting arrhythmias can be programmed using the external device 50 in accordance with the techniques disclosed herein.

[0033] The external telemetry unit 58 includes a transceiver and antenna configured for bidirectional communication with an implanted transceiver and antenna included in the IMD 14. In some examples, the external device 50 can include a programming head that is placed proximate to the IMD 14 to establish and maintain a communication link, and in other examples, the external device 50 and the IMD 14 can be configured to communicate using distance telemetry algorithms and circuitry that do not require the use of a programming head and do not require user intervention to maintain the communication link. It is contemplated that the external device 50 can be wired or wirelessly connected to a communication network through the telemetry unit 58 in order to transmit data to a central database or computer, allowing for remote management of the patient. The remote patient management system can be configured to enable a clinician to view cardiac electrical signal data, atrial tachyarrhythmia episode data, and AT / AF detection operational status received from the IMD 14 using the presently disclosed technology.

[0034] Figure 2 is a conceptual view of a leadless cardiac pacemaker positioned within the right atrium for sensing atrial signals and delivering cardiac pacing pulses to the heart 8. The pacemaker 100 can be configured to sense P-waves and deliver atrial pacing pulses in the absence of a sensed P-wave. The pacemaker 100 can be a leadless pacemaker including a housing 105 that encloses pacemaker circuitry. The pacemaker 100 can include two or more housing-based electrodes 102, 104, and 106. A distal tip electrode 102 can be a button, spherical, or helical electrode extending from a distal end 112 of the pacemaker 100. One or more ring electrodes 104 and 106 can be disposed along a longitudinal sidewall of the housing 105, e.g., encircling the generally cylindrical housing 105. Electrode 104 is shown proximate the distal end 112, and electrode 106 is shown at a proximal interval opening proximate a proximal end 110 of the pacemaker 100. The distal tip electrode 104 can be used as a pacing cathode electrode, while either of the ring electrodes 104 and 106 as a return anode. The electrodes 104 and 106 can be used to sense atrial signals, as a bipolar pair or paired with the tip electrode 102.

[0035] The tip electrode 102 can be deployed in atrial myocardial tissue to provide single chamber atrial sensing and pacing of the pacemaker 100. In other examples, the tip electrode 102 can be positioned in or near the His bundle for delivering pacing pulses to the native ventricular conduction system, providing ventricular pacing. In such cases, atrial and ventricular signals can be sensed by the pacemaker 100, and ventricular pacing can be delivered, which can be synchronized with atrial P-waves.

[0036] The electrodes 102, 104, and 106 can be positioned at locations along the pacemaker 100 other than shown. The electrodes 102, 104, and 106 (and the housing 105) can be positioned in the right atrium, the right ventricle, the left atrium, the left ventricle, or other locations in the heart 8.Figure 1 The electrodes carried by the leads 16, 17, and 18 (e.g., the electrodes shown in FIG. 1) can be, but are not limited to, titanium, platinum, iridium, or alloys thereof, and can include a low-polarization coating such as titanium nitride, iridium oxide, ruthenium oxide, platinum black, etc. The housing 105 is formed of a biocompatible material such as stainless steel or a titanium alloy. In some examples, the housing 105 can include an insulating coating. Examples of insulating coatings include parylene, urethane, PEEK, or polyimide, etc. The entire housing 105 can be insulated, but only the electrodes 102, 104, and 106 are not insulated.

[0037] The pacemaker 100 is configured to sense atrial P-waves and detect AT / AF by analyzing time intervals associated with sensed P-waves and / or P-wave morphology. As disclosed herein, the pacemaker 100 can switch between at least two different atrial arrhythmia detection operating states (e.g., a normal state and a power saving state). During the power saving state, atrial sensing, the rate at which the processor is awakened to process atrial signals, and / or the number of steps or criteria analyzed for detecting AT / AF can be reduced to conserve power consumed in detecting atrial arrhythmias, thereby extending the useful life of the power source of the pacemaker 100 compared to AT / AF detection without the power saving state.

[0038] While the pacemaker 100 is shown within the RA, it should be understood that a leadless pacemaker can be positioned in or on the heart 8 so as to sense cardiac signals and detect arrhythmias. The power saving techniques disclosed herein are not limited to use with medical devices having atrial electrodes placed within the RA, such as Figure 1 and 2 as shown, can also be implemented in various medical devices having electrodes and / or sensors configured to sense cardiac signals and detect arrhythmias therefrom. In some examples, detecting an atrial arrhythmia does not require sensing atrial P-waves. For example, an atrial arrhythmia can be detected by analysis of RR interval variability, where each RR interval is the time interval between two consecutive sensed R-waves from a cardiac electrical signal. The power saving state techniques disclosed herein can be implemented in devices that perform arrhythmia detection using ventricular signals, as generally disclosed in U.S. Patent No. 7,623,922 B2 (Sarkar et al.) and U.S. Patent No. 9,486,155 B2 (Sarkar et al.). The techniques disclosed herein that employ a power saving state to reduce power consumed for monitoring arrhythmias can be implemented in conjunction with any arrhythmia detection technique that utilizes processing circuitry to determine a state of an arrhythmia.

[0039] Figure 3 is a conceptual diagram of an example configuration of a medical device configured to detect an arrhythmia and switch between a normal state and a power saving state to detect the arrhythmia. Referring to Figure 1 the multi-chamber IMD 14 described inFigure 3 The circuit system shown has sensing, pacing, and cardioversion / defibrillation capabilities and is coupled to carrier electrodes 20, 22, 24, 26, 28, 30, 32, and 34 (as well as 36 and 38). Figure 3 (Not shown in the image) Three leads. However, it should be understood that, in combination with Figure 3 The circuits and components shown and described may be included Figure 2 In a pacemaker 100 or other cardiac rhythm monitoring or therapeutic delivery IMD or wearable medical device, to provide the functionality disclosed herein for switching between a normal state and a power-saving state to monitor and detect cardiac arrhythmias.

[0040] The techniques disclosed herein primarily describe a power-saving state for monitoring and detecting atrial tachyarrhythmias (e.g., AT / AF). AT / AF may not be treatable with electrical stimulation therapy delivered by an IMD. However, AT / AF can be monitored to provide important cardiac rhythm information and data to clinicians caring for the patient. Atrial tachyarrhythmias may not be immediately life-threatening, but can be an important diagnostic and prognostic condition that enhances clinicians' ability to manage patients, for example, with prescription medications, IMDs, or other means, to avoid more serious arrhythmias and stroke. Therefore, physicians may desire an IMD that can monitor cardiac rhythms to provide AT / AF information without significantly reducing the IMD's lifespan, thereby enabling more critical monitoring and detection of ventricular tachyarrhythmias and / or delivery of cardiac pacing therapy and CV / DF shocks. Therefore, the operating states for monitoring and detecting arrhythmias are described as being used for AT / AF detection. However, upon consideration, the aspects disclosed herein for switching between normal and power-saving states, as well as the techniques for reducing power consumption during power-saving states compared to normal states when detecting arrhythmias, can be used to monitor and detect other types of arrhythmias, including, in some instances, ventricular tachyarrhythmias.

[0041] The IMD 14 includes control circuitry 80, memory 82, treatment delivery circuitry 84, cardiac signal sensing circuitry 86 (also referred to herein as “sensing circuitry 86”), telemetry circuitry 88, activity sensor 96, and power supply 98. Figure 3 The various circuits represented herein can be combined on one or more integrated circuit boards, which include specific integrated circuits (ASICs), electronic circuits, processors (shared, dedicated, or grouped) and memory, combinational logic circuits, state machines, or other suitable components that execute one or more software or firmware programs to provide the described functions.

[0042] The cardiac signal sensing circuit 86 can include multiple sensing channels, e.g., an atrial sensing channel 87 and a ventricular sensing channel 89. The atrial sensing channel can be configured to receive cardiac electrical signals, e.g., by the RA electrodes 20 and 22, to sense atrial P-waves and generate an atrial EGM signal that can be passed to the control circuit 80 for analysis by the processor 92 for atrial arrhythmia detection. The ventricular sensing channel 89 can receive cardiac electrical signals, e.g., by the RV electrodes 24 and 26 and / or the CS electrodes 32, 34, 36, and 38 (only electrodes 32 and 34 are shown for clarity, Figure 3 The ventricular sensing channel 89 includes circuitry for detecting ventricular R-waves and for generating a ventricular EGM signal that can be passed to the control circuit 80 for detecting ventricular arrhythmias. When the IMD 14 is a multi-chamber device, separate RV and LV sensing channels can be provided for sensing ventricular electrical signals from the respective RV electrodes 24 and 26 and the CS electrodes 32, 34, 36, and 38.

[0043] Each atrial sensing channel 87 and ventricular sensing channel 89 can include a respective pre-filter and amplifier circuit that includes a high-pass filter that removes DC offset, e.g., a 2.5 to 5 Hz high-pass filter, or a wide-band filter with a 2.5 Hz to 100 Hz pass-band to remove direct current offset and high frequency noise. The pre-filter and amplifier circuit can further include an amplifier to amplify the "raw" cardiac electrical signal that is passed to an analog-to-digital converter (ADC) included in each sensing channel 87 and 89. The ADC can pass a multi-bit digital EGM signal to the control circuit 80 for detecting cardiac events and determining the patient's heart rhythm. The digital signal from the ADC of each respective channel 87 and 89 can be passed to a rectifier and amplifier circuit included in the sensing circuit 86 that can include a rectifier, a band-pass filter, and an amplifier for passing a filtered and rectified cardiac electrical signal to a respective cardiac event detector, e.g., a P-wave detector in the atrial channel 87 and an R-wave detector in the ventricular channel 89.

[0044] The cardiac event detector of each respective channel 87 and 89 can include a sense amplifier or other detection circuitry that compares an incoming rectified cardiac electrical signal to a cardiac event sense threshold amplitude, which can be an automatically adjusted threshold. When the incoming signal exceeds the sense threshold amplitude, the cardiac event detector generates a cardiac sense event signal that is passed to control circuit 80. In response to an R-wave detector sensing an R-wave, an R-wave sense event signal can be passed from ventricular sense channel 89 to control circuit 80. The R-wave sense event signal can be used by timing circuit 94 for scheduling ventricular pacing pulses and determining a ventricular rate interval or RR interval (between two consecutively received R-wave sense event signals). Control circuit 80 can determine a ventricular rhythm from the determined RR intervals, which can be combined with analysis performed by processor 92 on a ventricular EGM signal received from sensing circuit 86.

[0045] Control circuit 80 can receive a P-wave sense event signal from atrial sense channel 87 each time a P-wave detector included in atrial sense channel 87 senses an atrial P-wave due to an atrial signal received by electrodes 20 and 22 exceeding a P-wave sense threshold. Timing circuit 94 can use the P-wave sense event signal to schedule atrial and / or ventricular pacing pulses and determine an atrial rate by determining a PP interval between consecutively received P-wave sense event signals. Processor 92 is configured to execute an atrial tachyarrhythmia detection algorithm, for example, by executing instructions stored in memory 82, which can include analysis of PP intervals (and / or other cardiac event intervals, such as PR, RP, and RR intervals) and / or atrial EGM signal morphology. Control circuit 80 is configured to“wake up” processor 92 to process atrial signal information for AT / AF detection or for determining a status of a detected AT / AF episode. As used herein, the term“wake up” with respect to processor 92 refers to a power control operation during which current or power is provided from power source 98 to processor 92 to enable the processor to perform processing functions. Processor 92 can be placed into a“sleep” by suppressing or minimizing current applied to processor 92 when not energized for performing processing functions.

[0046] While examples of AT / AF detection described herein generally refer to sensing P-waves and / or R-waves from cardiac electrical signals used for AT / AF detection, it should be recognized that sensing circuit 86 can include or be coupled to other sensors for sensing cardiac signals, detecting periodic cardiac events (e.g., corresponding to atrial contractions and / or ventricular contractions), and producing cardiac sensed event signals and / or signal waveforms that are passed to control circuit 80 for use in detecting AT / AF. Thus, sensing circuit 86 can be configured to sense cardiac mechanical signals and / or cardiac electrical signals for use in detecting cardiac arrhythmias. Sensing circuit 86 can sense impedance signals using electrodes coupled to sensing circuit 86. In other examples, sensing circuit 86 can include or be coupled to acoustic sensors, motion sensors, pressure sensors, or other mechanical sensors enclosed by IMD housing 15, mounted on housing 15, or carried by leads coupled to sensing circuit 86 for producing cardiac signals.

[0047] As disclosed herein, control circuit 80 can operate according to a normal operating state during which control circuit 80 wakes processor 92 at a rate or frequency based on wake-up criteria established for the normal state. In some examples, the rate at which processor 92 is woken during the normal state can be as frequently as each time an atrial sensed event signal (e.g., a P-wave sensed event signal) is received from atrial sensing channel 87. Control circuit 80 is further configured to switch between the normal operating state and a power conservation state during which control circuit 80 can reduce the frequency or rate at which processor 92 is woken in order to perform an atrial arrhythmia detection algorithm or determine a status of an atrial arrhythmia. During the power conservation state, control circuit 80 can additionally or alternatively adjust sensing control parameters used by atrial sensing channel 87 to reduce current from power source 98 required to sense atrial P-waves (or atrial mechanical events). For example, amplifiers, ADCs, filters, or other circuitry in atrial sensing channel 87 can be disabled or disconnected from power source 98. In some examples, P-wave sensing control parameters are adjusted to intentionally cause P-wave undersensing and effectively reduce the frequency or rate at which processor 92 is woken for atrial signal processing for atrial arrhythmia detection.

[0048] The control circuit 80 includes a timing circuit 94 and a processor 92. The control circuit 80 can receive P-wave sensed event signals, R-wave sensed event signals, and / or digital cardiac electrical signals from the sensing circuit 86 for detecting cardiac arrhythmias and controlling therapy delivery functions. For example, the P-wave sensed event signals and R-wave sensed event signals can be passed to the timing circuit 94 to inhibit a predetermined atrial or ventricular pacing pulse, respectively. The timing circuit 94 can set a pacing escape interval in response to a cardiac sensed event signal. For example, an atrial pacing escape interval can be started in response to a P-wave sensed event signal. A ventricular pacing escape interval can be started in response to an R-wave sensed event signal or a P-wave sensed event signal. Expiration of the pacing escape interval causes the therapy delivery circuit 84 to deliver a pacing pulse to the appropriate heart chamber through a pacing electrode vector selected from the available electrodes. If a cardiac event signal is received prior to expiration of the pacing escape interval, the elapsed time on the pacing escape interval timer or counter is determined to be a cardiac event interval, e.g., a PP interval or an RR interval. The cardiac event intervals determined by the timing circuit 94 can be used by the processor 92 to detect cardiac arrhythmias, such as AT / AF.

[0049] The control circuit 80 can retrieve programmable therapy delivery control parameters, such as pacing rates and pacing pulse amplitudes, pacing pulse widths, and CV / DF shock energies controlled by the timing circuit, from the memory 82, which are passed to the therapy delivery circuit 84 for controlling electrical stimulation pulse delivery. In addition to providing control signals to the therapy delivery circuit 84, the control circuit 80 can also provide sensing control signals to the sensing circuit 86, e.g., P-wave and R-wave sensing thresholds, sensitivity, and / or various blanking and refractory intervals applied to the cardiac electrical signals, to control sensing of P-waves and R-waves by the respective atrial channel 87 and ventricular channel 89.

[0050] The therapy delivery circuit 84 generates electrical pacing pulses that are delivered to the patient's heart through available electrodes coupled to the IMD 14, e.g., electrodes 20, 22, 24, 26, 28, 30, 32, 34, 36, and 38, and the can 15. The therapy delivery circuit 84 can include a charging circuit 120, a switching circuit 122, and an output circuit 124. The charging circuit 120 can include one or more hold capacitors that can be charged to a pacing pulse amplitude that is a multiple of the battery voltage signal of the power source 98 under the control of a voltage regulator. The pacing pulse amplitude can be set based on control signals from the control circuit 80. The switching circuit 122 can control when the hold capacitors of the charging circuit 120 are coupled to the output circuit 124 for delivery of a pacing pulse. For example, the switching circuit 122 can include a switch that is activated by a timing signal received from the timing circuit 94 upon expiration of a pacing escape interval and remains closed for a programmed pacing pulse width to enable the hold capacitors of the charging circuit 120 to discharge. The hold capacitors, pre-charged to the pacing pulse voltage amplitude, are discharged through an output capacitor of the output circuit 124 across a selected electrode pacing vector for the programmed pacing pulse duration. The output circuit can include a plurality of output capacitors and switching circuitry for selectively discharging the hold capacitors through the desired output capacitor and pacing electrode vector. Examples of pacing circuitry generally disclosed in U.S. Patent No. 5,507,782 (Kieval et al.) and U.S. Patent No. 8,532,785 (Crutchfield et al.) can be implemented in the pacemaker 14 for charging the pacing capacitors to a predetermined pacing pulse amplitude under the control of the control circuit 80 to generate and deliver pacing pulses.

[0051] When the IMD 14 is capable of delivering high-voltage CV / DF shock therapy in addition to cardiac pacing therapy, the therapy delivery circuit 84 can include one or more high-voltage hold capacitors and one or more low-voltage capacitors in the charging circuit 120. For example, a transformer can be used to charge the high-voltage hold capacitors to a voltage corresponding to the programmed shock energy. Thus, the charging circuit 120 can include a transformer to step down the battery voltage of the power source 98 to enable charging of the high-voltage rated capacitors to a voltage much greater than the battery voltage. Charging of the high-voltage capacitors (or combination of capacitors) by the charging circuit 120 can be performed under the control of the processor 92 that receives feedback signals from the therapy delivery circuit 84 to determine when to charge the high-voltage capacitors to a voltage corresponding to the programmed shock energy. A charging complete signal can be communicated from the processor 92 to the charging circuit 120 to terminate charging. One example of a high-voltage charging circuit and its operation is generally disclosed in U.S. Patent No. 8,195,291 (Norton et al.).

[0052] Pacemaker 14 can include one or more sensors for monitoring physiological signals of the patient other than cardiac electrical signals sensed by sensing circuit 86. For example, IMD 14 can include a patient activity sensor 96, which can include a motion sensor such as an accelerometer for detecting patient motion resulting from patient physical activity. Signals from activity sensor 96 passed to control circuit 80 can be analyzed by processor 92 to determine a measure of patient physical activity, sometimes referred to as "rate responsive pacing," for controlling pacing rate as a function of the patient's level of physical activity. In some examples, processor 92 is awakened at predetermined time intervals to determine a patient activity measure, which can be determined by determining a threshold crossing count and / or an integral of the motion sensor signal. For example, processor 92 can be awakened by control circuit 80 at two second time intervals to determine an updated patient activity measure from the activity sensor signal, determine an updated sensor indicated pacing rate, and adjust the pacing rate interval accordingly.

[0053] In other examples, in addition to or instead of activity sensor 96, IMD 14 can include other sensors such as a pressure sensor, an optical sensor, an acoustic sensor, a temperature sensor, a pH sensor, or any combination thereof. Processor 92 can determine a measure related to a patient condition from a sensor signal or combination of sensor signals used to determine patient-related diagnostic data that can be stored in memory 82 and / or used to control therapy delivered by therapy delivery circuit 84.

[0054] Memory 82 can include computer-readable instructions that, when executed by processor 92 of control circuit 80, cause control circuit 80 to perform various functions attributed to IMD 14 (or pacemaker 100) throughout this disclosure. The computer-readable instructions can be encoded within memory 82. Memory 82 can include any non-transitory computer-readable storage media including any volatile, non-volatile, magnetic, optical, or electrical media, such as a random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically-erasable programmable ROM (EEPROM), flash memory, or other digital media.

[0055] Power source 98 supplies power to each of the other circuits and components of IMD 14 as needed. Power source 98 can include one or more energy storage devices, such as one or more rechargeable or non-rechargeable batteries. Connections between power source 98 and control circuit 80 are shown, but connections between power source 98 and the other circuits and components are not shown for clarity, but are to be understood to be similar to those between power source 98 and control circuit 80. Figure 3 Figure 3 ​The general block diagram can be used for understanding. For example, power supply 98 can power charging circuit 120 to charge holding capacitors to the pacing voltage amplitude, supply current to switch 122 and other circuitry included in treatment delivery circuitry 84 to generate and deliver electrical stimulation pulses to the patient's heart as needed. Power supply 98 also supplies power to telemetry circuitry 88, sensing circuitry 86, activity sensor 96, and memory 82 as needed. As described herein, control circuitry 80 can control when power supply 98 is coupled to processor 92 and atrial sensing channel 87 based on power-saving states to reduce the current consumption of power supply 98 required for detecting and monitoring AT / AF.

[0056] IMD 14 may include telemetry circuitry 88, which includes a transceiver and an antenna for, for example, communicating with an external programmer or home monitor (such as...). Figure 1 The external device 50 shown transmits and receives data via a radio frequency (RF) communication link. For example, when the external device 50 ( Figure 1 When used as a programmer or home monitor to transmit programming commands to and retrieve data from the IMD 14, the telemetry circuit 88 may be able to communicate bidirectionally with the external device 50. Cardiac electrical signals, marker channel data depicting the timing of cardiac event sensing and pacing, currently programmed parameters, or other data can be transmitted by the telemetry circuit 88. Specifically, cardiac signal episodes representing detected arrhythmias (including AT / AF episodes) can be stored in memory 82 and transmitted by the telemetry circuit 88. Programmable control parameters and programming commands used to control cardiac electrical signal sensing and cardiac pacing can be received by the telemetry circuit 88 and stored in memory 82 for access by the control circuit 80.

[0057] The functionality attributed to the medical device herein can be embodied in one or more processors, controllers, hardware, firmware, software, or any combination thereof. Depiction of different features as separate circuit systems is intended to highlight different functional aspects and does not necessarily imply that such features are implemented by separate hardware, firmware, or software components or through any particular circuit architecture. Rather, the functionality associated with one or more of the circuitry described herein can be performed by the same or different hardware, firmware, or software components, or integrated within common hardware, firmware, or software components. As disclosed herein, the operation of the circuitry included in the medical device should not be interpreted as reflecting a specific form of hardware, firmware, and software that is required to practice the described technology. It is believed that the particular form of software, hardware, and / or firmware will be determined primarily by the particular system architecture employed in the medical device and by the particular sensing and therapy delivery circuitry employed by the medical device. In view of the disclosure herein, providing software, hardware, and / or firmware to accomplish the described functionality in the context of any modern medical device is within the capabilities of one of skill in the art. For example, the processor 92 can be configured to execute firmware stored in the memory 82 to detect AT / AF, while P-wave sensing, PP interval determination, or counting of P-wave sensed events can be implemented in hardware included in the sensing circuitry 86 and control circuitry 80.

[0058] Figure 4 Conceptual diagram 150 of the arrhythmia detection operating states between which the control circuit 80 can switch according to some examples. An IMD that performs the technology disclosed herein can be configured to operate in at least a normal atrial arrhythmia detection state 152 (also referred to herein as “normal state” 152) and a power- saving atrial arrhythmia detection state 154 (also referred to herein as “power-saving state” 154). The control circuit 80 can switch from the normal state 152 to the power-saving state 154 (path 160) when conditions or criteria for power-saving detection of atrial arrhythmias are met. The conditions for switching to the power-saving state are described below, e.g., in connection with FIG. 2, and can include, for example, a threshold duration of operating in the normal state, a threshold duration of detected AT / AF episodes, or a threshold duration of no atrial sensing. During the power-saving state, one or more operations can be suspended or reduced in frequency to reduce power consumed for detecting atrial arrhythmias. However, atrial arrhythmias can still be detected or monitored during the power-saving state. Atrial arrhythmia monitoring can not be completely disabled during the power-saving state 154. However, the power used to detect arrhythmias during the power-saving state 154 is less than the power used to detect arrhythmias during the normal state 152. Figure 5

[0059] ​When the conditions or criteria for returning to the normal state 152 are met, the control circuit 80 can switch directly from the power conservation state 154 back to the normal state 152 (path 162). In some examples, one condition for switching back to the normal state can be a maximum duration spent in the power conservation state 154. Other examples of conditions or criteria for switching between the normal state 152 and the power conservation state 154 are described below in connection with various flowcharts presented herein.

[0060] In some examples, the control circuit 80 can switch from the power conservation state 154 to a third confirmation state 156 (path 164). During the confirmation state 156, the IMD can determine whether the conditions that caused the control circuit 80 to switch to the power conservation state still exist. If the conditions that caused the control circuit 80 to switch from the normal state 152 to the power conservation state 154 still exist, the control circuit 80 can switch from the confirmation state 156 back to the power conservation state 154 (path 166). If the conditions do not exist, the control circuit 80 can switch from the confirmation state 156 to the normal state 152 (path 168). In other examples, the control circuit 80 can determine whether other criteria for switching from the confirmation state 156 to the normal state 152 are met. If the criteria for returning to the normal state are not met, the control circuit 80 switches from the confirmation state 156 back to the power conservation state 154. Example operations performed during various normal states 152, power conservation states 154, and confirmation states 156 are described below in connection with the flowcharts of FIGS. 6-8. Figures 5-7

[0061] Figure 5 is described in connection with the flowchart of FIG. 5. Figure 4 ​FIG. 30 is a flow diagram of operations performed by an IMD for detecting atrial arrhythmias when operating in a normal state 152. At block 301, control circuit 80 enters the normal state for controlling processor 92 to perform an atrial arrhythmia detection algorithm in accordance with the normal state. At block 302, cardiac events are sensed for detecting atrial arrhythmias. The techniques disclosed herein involve sensing cardiac events from cardiac electrical signals received by sensing circuit 86, however, it is contemplated that cardiac mechanical signals can also be sensed for arrhythmia detection. In some examples, control circuit 80 wakes up processor 92 after receiving each atrial sensed event signal, e.g., a P-wave signal received from sensing circuit 86. Processor 92 analyzes PP intervals, P-wave morphology, and / or specified P-wave features in accordance with the implemented AT / AF detection algorithm along with stored P-wave data, e.g., previous PP intervals and / or P-wave morphology. For example, control circuit 80 can detect AT / AF in response to a predetermined number of PP intervals less than a detection time interval. When awakened in response to each P-wave sensed event signal, processor 92 determines whether the most recent PP interval satisfies a detection criterion, which can be N intervals out of the most recent N consecutive PP intervals or N intervals out of the most recent M consecutive PP intervals, where M is greater than N, such that the threshold number N of PP intervals less than the detection interval need not be consecutive. In other examples, processor 92 can determine whether a threshold number of RR intervals contain evidence of an atrial arrhythmia, e.g., multiple P-waves sensed by an atrial channel during a single RR interval. To illustrate, AT / AF can be detected if at least 40 consecutive RR intervals each contain two or more P-waves sensed during the RR interval.

[0062] At block 304, if AT / AF is detected in accordance with the detection criteria applied by processor 92, control circuit 80 can determine whether one or more conditions for switching to a power conservation state are satisfied. At block 306, control circuit 80 can determine whether the detected AT / AF episode has reached a threshold duration (“YES” branch of block 306) to warrant switching to the power conservation state at block 308. When a patient is experiencing a persistent AT / AF episode or chronic AT / AF, the AT / AF detection algorithm executed by processor 92 on each P-wave sensed event signal can consume processing power that does not detect changes in the patient’s atrial rhythm. Accordingly, control circuit 80 can switch to a power conservation state to reduce the power consumed in monitoring the patient’s atrial rhythm during a persistent AT / AF episode. For example, the AT / AF episode duration threshold that causes control circuit 80 to switch to the power conservation state can be 30 seconds, one minute, several minutes, one hour, several hours, one day, or several days.

[0063] At block 304, if no AT / AF is detected, or if a detected AT / AF episode has not yet reached a threshold duration (the "No" branch of block 306), control circuit 80 may apply other criteria to determine whether to maintain the normal state or switch to a power-saving state. For example, control circuit 80 may determine at block 310 whether no atrial event was sensed within the threshold duration, such as in relation to sustained atrial pacing for the threshold duration. The threshold number of pacing pulses delivered in the absence of atrial sensing events, or the threshold ratio of atrial pacing to atrial sensing events, may define the power-saving state switching criteria. In various illustrative examples, if at least 80%, 90%, or 100% of atrial events are paced atrial events over a minute, several minutes, an hour, several hours, a day, several days, or other selected time periods, control circuit 80 may switch to a power-saving state at block 308.

[0064] In some cases, continuous or intermittent atrial pacing may be delivered due to insufficient continuous or intermittent P wave sensing. Control circuitry 80 can identify episodes of 100% atrial pacing alternating with episodes of 100% sensing low-amplitude P waves. Processing atrial signals during intermittent pacing due to insufficient P wave sensing may consume current from power supply 98, and AT / AF cannot be reliably detected due to insufficient sensing. In such cases, switching to a power-saving state is guaranteed. At block 310, if control circuitry 80 identifies continuous atrial pacing without atrial sensing events, intermittent atrial pacing interrupted by episodes of low-amplitude P waves suggesting insufficient atrial sensing, or detects or meets other criteria based on atrial pacing and / or sensing frequency, control circuitry 80 may switch to a power-saving state at block 308.

[0065] Control circuit 80 can apply other criteria to detect situations where AT / AF detection is meaningless or has limited diagnostic value, allowing control circuit 80 to switch from a normal state for AT / AF detection to a power-saving state. For example, executing AT / AF detection instructions by processor 92 during certain pacing modes may have limited utility or be irrelevant. An example is the AOO pacing mode, during which atrial pacing is delivered without atrial sensing, which could be... Figure 2 The programmable pacing modes of the intracardiac pacemaker. During certain tests or device diagnostic functions (such as impedance measurement or battery testing), the IMD performing the techniques disclosed herein can switch to a temporary AOO pacing mode. AT / AF detection can be temporarily paused by control circuitry 80 during the temporary AOO pacing mode. After the device test is completed and the temporary AOO pacing mode terminates, control circuitry 80 can return to a power-saving state (or normal state) to continue any AT / AF detection processing.

[0066] As other examples, other criteria for switching from the normal state to the power conservation state can involve the remaining battery voltage of power source 98 being at or below a threshold voltage, no change in AT / AF burden over a monitoring period, or no AT / AF detections over a threshold time interval. IMD 14 can be configured to calculate the remaining life of power source 98 based on therapy delivery history (e.g., pacing frequency and shock delivery history), current battery voltage, and other factors. Control circuit 80 can switch to the power conservation state when the remaining life of power source 98 reaches a threshold of weeks or months, or a selective battery replacement indicator (ERI) flag is set. It is recognized that many criteria can be defined relating to the length or stable state of atrial rhythm, the current pacing or therapy delivery mode of operation of the IMD, and / or the state of power source 98 for switching to the power conservation state. Once one or more switching criteria are met, control circuit 80 switches to the power conservation state at block 308 by proceeding to block 402 Figure 6 ) and the normal state is maintained and control circuit 80 returns to block 301 if the criteria for switching the atrial arrhythmia detection operating state are not met.

[0067] Figure 6 is a flowchart 400 of operations performed by an IMD in a power conservation state of atrial arrhythmia monitoring according to one example. At block 402, control circuit 80 enters the power conservation state from the normal state. At block 404, control circuit 80 can adjust the processor wake-up criteria that need to be met before the processor 92 is woken up to process atrial signal data for AT / AF detection. The wake-up criteria are adjusted to reduce the frequency or rate at which the processor 92 is woken up to detect AT / AF. For example, control circuit 80 can increase the threshold number of sensed P-waves required to wake up the processor 92. In some examples, control circuit 80 includes a counter for counting the number of P-wave sense event signals received from sensing circuit 86. Upon switching to the power conservation state, control circuit 80 can enable the P-wave sense event counter to count P-waves sensed by sensing circuit 86 and set a counter threshold at which the processor 92 is woken up to process atrial signal data for AT / AF detection. During the normal state for monitoring atrial arrhythmias, the processor 92 can be powered up to process atrial signal data each time a P-wave sense event signal is received from sensing circuit 86. This rate at which the processor is woken up for data processing (equal to the rate of sensed P-waves) is high when a rapid atrial rate occurs (e.g., during persistent or chronic AT / AF). By reducing the rate at which the processor 92 is woken up for atrial signal processing during the power conservation state, the current drain of power source 98 is reduced.

[0068] Accordingly, at block 404, the P-wave sensed event counter must reach a value, referred to herein as a "wake-up count," prior to waking up the processor 92 for atrial signal processing, which can be adjusted by the control circuit 80. The counter value can be reset to zero when the processor 92 is woken up to process atrial signal data. The wake-up count can be adjusted to be twice, three times, four times, or other multiple of the wake-up count required in the normal state. In one example, during the power conservation state, the processor 92 is woken up after receiving every eight P-wave sensed event signals from the sensing circuit 86.

[0069] By reducing the rate at which the processor is woken up, power used for detecting AT / AF can be reduced without disabling AT / AF detection or monitoring ongoing AT / AF episodes during the power conservation state. Accordingly, the control circuit 80 can be configured to perform detection of AT / AF, re-detection of AT / AF persistent episodes, detection of non-AT / AF rhythms, and / or termination of detection of AT / AF episodes during the power conservation state. Depending on the adjusted wake-up count, the time at which AT / AF or termination of an AT / AF episode is detected can be delayed from the actual start or end time of the AT / AF episode. However, the processor 92 can still identify the actual time of the start or termination of an AT / AF episode or cardiac cycle from analysis of the atrial signal data.

[0070] The adjustment of the wake-up count at block 404 can be performed independently of processor wake-ups scheduled for other signal processing purposes. For example, the processor 92 can be woken up at other time intervals or sensed event counts to process ventricular signal data, activity sensor signal data, or other sensor signal data in order to detect other conditions of the patient, such as detecting ventricular arrhythmias, determining a measure of patient physical activity, or determining patient posture, as a few examples. Accordingly, the adjustment of the wake-up count at block 404 can be performed to conserve power used for detecting AT / AF without changing other operations performed by the processor 92 for controlling therapy delivery and / or detecting other patient conditions.

[0071] In other examples, adjusting the wake-up criteria at block 404 reduces the rate of processor wake-ups for AT / AF detection by scheduling the wake-up of the processor 92 for atrial arrhythmia detection to coincide with another scheduled wake-up of the processor 92. For example, if the power conservation state is entered due to detection of an AT / AF episode that exceeds a threshold duration, a number of P-wave sense event signals can be received between every two consecutive R-wave sense event signals. In response to receiving each R-wave sense event signal from the sensing circuit 86, the processor 92 can be woken up to detect a tachyarrhythmia. During the power conservation state, the processor wake-up for AT / AF detection can be scheduled to coincide with the processor wake-up triggered by each R-wave sense event signal. In other examples, the atrial signal processing for AT / AF detection can be scheduled to occur when the processor 92 is woken up to process signals from the activity sensor 96. For example, the processor 92 can be woken up at two-second intervals or another predetermined time interval to process signals received from the activity sensor 96 to determine a measure of patient physical activity. The atrial signal processing can be performed by the processor 92 at the scheduled activity sensor signal processing wake-up intervals. In this way, the AT / AF detection algorithm rides on other scheduled processor wake-up times rather than waking up the processor solely for the purpose of detecting AT / AF.

[0072] In other examples, the processor wake-up criteria can be adjusted based on changes in the rate of P-wave sense event signals counted between processor wake-ups. For example, the hardware of the sensing circuit 86 and control circuit 80 can be configured to count P-wave sense event signals within a specified time interval or between R-wave sense event signals. The count of P-wave sense event signals within a limited time interval can be used as an indication of the atrial rate without the need to wake up the processor 92. The count of P-wave sense event signals can be compared to a threshold or to a previous count to determine whether the indicated atrial rate has changed. This process of detecting changes in the indicated atrial rate based on P-wave sense event counts can be implemented in hardware without the need to wake up the processor 92. If the sensed P-wave count or PP interval timed by the timing circuit 94 indicates a change in the atrial rate, the control circuit 80 can wake up the processor 92 to process atrial signal data for AT / AF detection. In this way, if the atrial rate indicated by the count of P-wave sense events or PP intervals determined by the timing circuit 94 remains relatively constant, the processor 92 is not woken up to process atrial signal data for AT / AF detection. The atrial rhythm can be deemed unchanged (indicating a persistent AT / AF episode or a persistent normal sinus rhythm), which makes it less of a priority for the processor 92 to repeatedly execute the AT / AF detection algorithm and for power usage.

[0073] In addition to the adjustment of the wake-up criteria at block 404 or in lieu of the adjustment, the control circuit 80 can adjust P-wave sensing control parameters at block 406 to reduce power consumption during the power conservation state. For example, the atrial sensing channel 87 can be disabled for a time interval or a predetermined number of ventricular cycles to conserve power. For example, the sense amplifiers, ADCs, and / or other circuitry included in the atrial sensing channel 87 for sensing P-waves and producing an atrial EGM signal that is passed to the control circuit 80 can be powered down for alternating time periods and then powered up. The time periods can be set to 2 seconds, 5 seconds, 10 seconds, one minute, or other time periods greater than or less than one minute to reduce power consumed in sensing atrial events. Alternatively, the time periods can be variable and set, for example, according to a count of R-wave sense event signals.

[0074] In other examples, the atrial sensing channel 87 can remain enabled, but the P-wave sensing threshold can be temporarily increased to intentionally cause P-wave undersensing. In this way, the absence of P-wave sense event signals will preclude P-wave triggered wake-up of the processor 92 for atrial signal processing. The P-wave sensing threshold can be temporarily increased for a predetermined or variable time interval as described above and then returned to the programmed P-wave sensing threshold for another predetermined or variable time interval to enable P-wave triggered wake-up of the processor 92 for atrial signal processing.

[0075] The time interval during which the P-wave sensing threshold is increased to intentionally cause P-wave undersensing and the time interval during which the P-wave sensing threshold is not increased to promote reliable P-wave sensing can be equal or different. For example, the P-wave sensing threshold can be increased by increasing the atrial sensing channel sensitivity setting in millivolts for an n second interval or n R-wave sense event signals. The P-wave sensing threshold can be decreased by decreasing the atrial sensing channel sensitivity setting in millivolts for a multiple (or fraction) of n seconds or n R-wave sense event signals. The time interval during which the P-wave sensing threshold is set to its normal level for reliably sensing P-waves can depend at least in part on the minimum number of atrial cycles required to satisfy the AT / AF detection criteria. For example, if at least 18 of 24 atrial cycles are required to satisfy the interval and / or morphology criteria for detecting AT / AF, the atrial channel sensitivity can be set to the programmed sensitivity until at least 24 P-wave sense event signals have been received.

[0076] Adjustment of the atrial sensing control parameters at block 406 can be performed with or without adjustment of the processor wake-up criteria at block 404. Since the adjustment of the atrial sensing control parameters can effectively reduce the rate at which the processor 92 is woken up compared to the normal state without adjustment of the wake-up criteria at block 404, the power used to detect AT / AF will be reduced. In addition, the power used to sense P-waves by the sensing circuit 86 and / or to generate an atrial EGM signal is also reduced.

[0077] However, depending on other operational modes of the IMD, adjustment of the atrial sensing control parameters can not always be feasible. For example, if CRT or bi-ventricular pacing is being delivered, P-wave sensing can be needed to control atrial-synchronized ventricular pacing. In other examples, the atrial rate can be determined from PP intervals and used to distinguish supraventricular tachycardia from ventricular tachycardia in a ventricular tachycardia detection algorithm performed by the control circuit 80. Thus, at block 406, the control circuit 80 can first determine whether P-wave sensing is needed for controlling ventricular pacing or for other IMD operations. When P-wave sensing is used for controlling ventricular pacing or for other IMD operations, such as ventricular rhythm detection and discrimination during a power conservation state, adjustment of the atrial sensing control parameters at block 406 is inhibited. Power conservation is achieved by adjusting the wake-up count or other wake-up criteria at block 404 to reduce the rate at which the processor 92 is woken up to perform atrial signal processing for AT / AF detection and thereby conserve power.

[0078] At block 408, atrial event sensing by the sensing circuit 86 is performed according to any adjustments made at block 406. When a wake-up count is reached at block 410, the processor 92 is awakened at block 412. The wake-up count can be based on a count of sensed P-waves, sensed R-waves, a number of activity count time intervals, or other counted events established at block 404. At block 414, the processor 92 analyzes the atrial signal and data extracted therefrom, e.g., PP intervals, P-wave morphology, P-R intervals, R-P intervals, and / or other atrial signal related data, for determining the atrial rhythm at block 414. The control circuit 80 can include hardware, such as a timing circuit 94, that determines cardiac event intervals between successive received sensed event signals from the sensing circuit 86, so that a circular buffer in the memory 82 can be filled with event intervals between processor wake-ups. In some examples, segments of the digital atrial EGM signal received from the atrial channel 87 can be buffered in the memory 82 between processor wake-ups. A count of the number of atrial events sensed during each ventricular event interval can be buffered for each ventricular cycle. The processor 92 can analyze the filled buffers of cardiac event intervals, P-wave signal segments, sensed event counts, etc. when awakened. In this way, data can be accumulated while the processor 92 is asleep and can be processed during less frequent wake-ups. In other examples, P-wave signals and / or cardiac event intervals can be accumulated at processor wake-ups and analyzed as events are sensed to determine the current AT / AF status.

[0079] The processor 92 can be configured to perform an analysis of the atrial signal and data derived therefrom that is a subset of the analysis performed by the processor 92 for determining the presence of AT / AF during the power conservation state. For example, fewer steps, comparisons, or criteria can be applied to detect AT / AF or to detect termination of a persistent AT / AF event that triggered entry into the power conservation state. The atrial signal analysis performed by the processor 92 at each wake-up can require less power from the power source 98 than the atrial signal analysis performed at each wake-up during the normal state.

[0080] An indicator of the atrial rhythm determined at block 414, e.g., indicating AT / AF detection or non-AT / AF detection (e.g., normal sinus rhythm), can be set in memory 82. In response to detecting AT / AF, atrial EGM signal segments can be stored in memory 82. AT / AF burden can be determined and updated in memory 82 and / or other AT / AF metrics can be updated in memory 82 to provide atrial rhythm information to a clinician when IMD 14 is interrogated. The response to AT / AF detection during the power conservation state can be the same as provided during the normal state, even though the rate of AT / AF detection is reduced. In other examples, the response to AT / AF detection, such as storing EGM signal segments, PP intervals, or other AT / AF episode data, can be performed during the normal state and not performed during the power conservation state.

[0081] At block 416, control circuit 80 determines whether an AT / AF detection state switch criterion is met. In some examples, control circuit 80 operates in the power conservation state for a fixed time interval. Control circuit 80 can set a timer for a predetermined time interval, e.g., 1 minute, 10 minutes, 30 minutes, one hour, four hours, eight hours, 24 hours, or other time intervals from a few minutes to a few hours or even days. After operating in the power conservation state for the fixed time interval, control circuit 80 can switch from the power conservation state to the normal state. In other examples, control circuit 80 can include a clock to schedule the switch back to the normal power conservation state at a specified time of day. For example, AT / AF detection according to the power conservation state can be performed during the day, at night, or at various time intervals throughout a 24 hour period. Control circuit 80 can determine that the switch criterion is met at block 416 according to a predetermined time of day and switch back to the normal state at block 418.

[0082] In other examples, the criterion that can be met at block 416 for switching back to the normal state can be the inverse of the condition that caused control circuit 80 to switch from the normal state to the power conservation state. In this case, control circuit 80 can set the criterion for switching from the power conservation state to the normal state applied at block 416 based on the switch criterion that triggered entry into the power conservation state. Control circuit 80 sets the criterion and monitors the parameters required for determining when the switch criterion is met at block 416. For example, if an AT / AF episode lasting more than a threshold duration caused control circuit 80 to switch to the power conservation state (e.g., at block 412), then control circuit 80 can set the criterion for switching from the power conservation state to the normal state as an AT / AF episode lasting less than the threshold duration. Control circuit 80 monitors the duration of AT / AF episodes and switches from the power conservation state to the normal state at block 418 when an AT / AF episode lasting less than the threshold duration is detected. Figure 5If the atrial pacing frequency results in a switch to the power save state, the switch criteria can be met at block 416 when the atrial pacing frequency is reduced, resulting in a switch back to the normal state at block 418. In these examples, the control circuit 80 can only monitor parameters, e.g., atrial rate, atrial pacing frequency or duration, that resulted in a switch to the power save state in order to detect that the power save state exit criteria are met at block 416.

[0083] In still other examples, a change in pacing mode, a detected ventricular tachyarrhythmia, a change in ventricular rate, a change in user programmed parameters, or other events that warrant more frequent analysis of atrial signal processing to detect AT / AF can satisfy the criteria at block 416 to switch back to the normal state at block 418. The control circuit 80 need not wait until each processor wakes up and determines the atrial rhythm during the power save state before determining whether the switch criteria are met, as generally indicated by the flow of flow diagram 400. It will be appreciated that the switch criteria can be met at any time between processor wake-ups during the power save state, and the control circuit 80 can switch back to the normal state at block 418. The control circuit 80 returns to the normal state by proceeding to block 301 of flow diagram 300. Figure 5

[0084] Figure 7 Flow diagram 500 is a method for controlling operational states of arrhythmia monitoring and detection, e.g., AT / AF monitoring and detection, by an IMD according to another example. At block 402, the control circuit 80 enters a power save state for AT / AF monitoring and detection, e.g., from block 308 of flow diagram 300. Figure 5 At block 504, control parameters for sensing atrial signals and / or waking up the processor 92 for processing atrial signals are adjusted according to the power save state, e.g., according to any of the above examples. During the power save state, the control circuit 80 can determine when to switch to a confirmation state to confirm that the power save state is still an appropriate operational state at block 506.

[0085] ​The criteria applied at block 506 for determining whether to switch to a confirmed state at block 512 can include a predetermined duration in the power conservation state, a detected change in ventricular rhythm (e.g., a change in intrinsic ventricular rate, intrinsic ventricular rate stability, or a ventricular tachyarrhythmia detection), a change in atrial pacing rate, or a change in patient activity or posture. In some examples, the factors or conditions that can trigger a switch to a confirmed state at block 506 can be conditions that can be detected by hardware functionality of the control circuit 80. For example, hardware included in the sensing circuit 86 and control circuit 80 can determine a count of P-wave sense events during a ventricular cycle or other predetermined time interval and detect a change in the number of P-waves counted that indicates a potential change in atrial rate that meets criteria for switching to a confirmed state. In other examples, hardware included in the control circuit 80 and therapy delivery circuit 84 can determine a change in ventricular or atrial pacing rate. In other examples, the criteria for switching to a confirmed state can be determined by processor functionality that performs ventricular rhythm analysis, patient activity analysis, or other processing functionality that does not include atrial signal analysis for AT / AF detection when the processor 92 is awakened.

[0086] As long as the confirmed state criteria are not met at block 506, atrial events are sensed in accordance with the power conservation state at block 508. When processor wake-up criteria are met at block 518, e.g., based on a P-wave sense event count reaching a threshold, the processor 92 is powered on at block 520 to perform atrial signal analysis to determine an atrial rhythm at block 522, e.g., to detect AT / AF when detection criteria are met. At block 524, the control circuit 80 can determine that switch criteria are met for switching directly to a normal state at block 526. The criteria applied at block 524 for directly switching back to a normal state can correspond to any of the examples described above in connection with block 524. Figure 6

[0087] ​If the switch criteria are not met at block 524, the control circuit 80 remains in the power conservation state by returning to block 504. In this example, the control circuit 80 can adjust the power conservation state control parameters at block 504 after being in the power conservation state for a period of time. The power conservation state control parameters can be adjusted according to the atrial rhythm determination made at block 522 and / or the duration of time the control circuit 80 has been operating in the power conservation state. For example, if the atrial rhythm determined at block 522 has not changed since entering the power conservation state, the rate at which the processor 92 is awakened to process atrial signals for AT / AF detection can be decreased. To illustrate, if the power conservation state was entered at block 402 due to detection of AT / AF for a threshold duration of time, the rate at which the processor 92 is awakened can initially be set to every eighth sensed P-wave (compared to every sensed P-wave during the normal state) upon entering the power conservation state. If AT / AF episodes continue to be detected during the power conservation state, the wake-up count can be further increased at block 504. For example, if AT / AF episodes have been re-detected a threshold number of times, e.g., every n consecutive times the processor 92 is awakened, the control circuit 80 can incrementally or exponentially increase the wake-up count at block 504. For example, the wake-up count can be doubled from a P-wave sensed event count of 8 to a P-wave sensed event count of 16. The wake-up count can continue to increase as the duration of time operating in the power conservation state increases, and no change in AT / AF rhythm is detected.

[0088] In other examples, other control parameters can be adjusted at block 504 to decrease the rate or frequency of processor wake-up for AT / AF detection, including the wake-up criteria and / or the atrial sensing control parameters. For example, the time interval for which the sensitivity of the atrial sensing channel 87 is reduced can be increased to further decrease the rate or frequency of processor wake-up. In this way, the battery current saved during the power conservation state can be incrementally increased with each adjustment of the power conservation state control parameters made at block 504.

[0089] Any time the criteria for switching to the confirmed state is met at block 506, the control circuit 512 switches to the confirmed state at block 512. The confirmed state can be different than the normal state because the criteria for switching back to the power save state can be different. For example, any timers or counters used to monitor the switching criteria can be reset when the control circuit 80 switches from the power save state to the normal state. Thus, when switching from the power save state or the confirmed state to the normal state, the timer used to track the duration of a persistent AT / AF episode can be reset to zero. Before switching back to the power save state, the threshold duration of an AT / AF episode needs to be reached again. However, in the confirmed state, an analysis of the atrial signals at block 514 (the "yes" branch of block 516) that results in a determination that the atrial rhythm has not changed results in a direct return to the power save state. The return to the power save state can resume from where it stopped at block 518 when the processor wake-up criteria was met according to the power save state control parameters currently set. For example, the P-wave sensed event counter can not be reset when switching to the confirmed state and returning to the power save state.

[0090] In other examples, the control circuit 80 can switch from the confirmed state back to the power save state with any P-wave sensed event counter or other counter, timer, or criteria monitored to schedule the next processor wake-up reset to the starting point at block 520. In still other examples, the control circuit 80 can determine the atrial rate at block 514 during the confirmed state, and if the atrial rate has changed, the control circuit 80 can directly return to the power save state to block 520 to wake up the processor 92 to perform the full AT / AF detection algorithm for determining the atrial rhythm. Whether the switching criteria for switching to the normal state is met can then be determined at block 524 based on the results of the AT / AF detection algorithm determined at block 522.

[0091] The steps or processes performed at block 514 to confirm the atrial rhythm can include a full analysis of the atrial signals, e.g., interval and / or morphology analysis, as performed by the processor 92 at block 522. In other examples, different criteria and / or fewer comparisons, fewer atrial cycles or sensed P-waves, or other parameters or functions performed can be scaled back or reduced during the confirmed state, enabling a relatively quick verification of the atrial rhythm to confirm that it is appropriate to remain in the power save state. Limited processing of a subset of the atrial signals and / or AT / AF detection algorithm steps can be performed to confirm an unchanging atrial rhythm or to detect a changing atrial rhythm. For example, the atrial rate can be determined at block 514 based on a limited, predetermined number of P-wave sensed event intervals to verify that the atrial rate has not changed from a previously detected atrial rate during an AT / AF rhythm.

[0092] At block 514, one or more conditions can be determined during the confirmation state to determine whether it is appropriate to return directly to the power save state or whether a switch to the normal state is required. For example, control circuit 80 can verify that the atrial rhythm has not changed, that a P-wave sensed event has not been received within a threshold time interval, or that the pacing mode or other IMD operating mode makes the determination of the atrial rhythm meaningless based on the PP interval. One of these conditions can prove that it is reasonable to remain in the power save state ("NO" branch of block 516). Thus, even if the atrial rhythm or heart rate has changed, another condition can be met at block 516 that proves it is reasonable to remain in the power save state.

[0093] Control circuit 80 can additionally check conditions or criteria that warrant a switch to the normal state at blocks 514 and 516. For example, in addition to checking the criteria corresponding to the power save state conditions at block 516 (e.g., that the atrial rate has not changed), control circuit 80 can check one or more normal state conditions at block 516. Such conditions can include a change in ventricular rhythm or a change in the pacing mode or other operating state that requires normal atrial P-wave sensing for proper system operation. If one or more normal state conditions are met at block 516, control circuit 80 can switch from the confirmation state directly to the normal state at block 526. By proceeding to block 301 of the normal state, the AT / AF monitoring and detection operations are resumed. Figure 5

[0094] Thus, in some examples, the confirmation state is entered only from the power save state, but can transition to either the power save state or the normal state depending on confirmation of one or more conditions that warrant remaining in the power save state. If such conditions are not confirmed, control circuit 80 can switch to the normal state. The confirmation state can differ from the power save state in that conditions other than the atrial rhythm state can be checked to verify the appropriateness of remaining in the power save state.

[0095] Operation in the power save state reduces the current consumption associated with AT / AF monitoring and detection, which can translate into extending the useful life of the IMD from weeks to months or even years. For example, in some patients experiencing a relatively high AT / AF burden or chronic AT / AF, the current due to atrial signal processing and atrial EGM storage in IMD memory 82 can reduce the useful life of the IMD by months or even up to two years or more in some cases. Thus, by selectively switching between the normal state and the power save state to extend the useful life of the IMD power source while still providing AT / AF detection capabilities during the power save state, the overall IMD performance in providing chronic rhythm monitoring and therapy delivery is improved.

[0096] Figure 8 ​is a flowchart 700 of a method for controlling an atrial arrhythmia detection state by an IMD according to another example. At block 702, the control circuit 80 operates in a normal state during which the processor 92 analyzes the atrial signal and data derived therefrom according to normal state processor wake-up schedule and normal atrial event sensing control parameters. In one example, the processor 92 is woken up at every eighth P-wave sensed from the cardiac electrical signal received by the sensing circuit 86 to determine an atrial arrhythmia state. In some examples, the hardware of the control circuit 80, including the timing circuit 94, is configured to detect AT / AF. Each P-wave sensed event signal can cause a PP interval timeout by the timing circuit 94 and is buffered in the memory 82 in a circular buffer that stores a required number of PP intervals required to detect AT / AF. In other examples, the timing circuit 94 times out RR intervals, which can be paced or sensed RR intervals, and a counter included in the control circuit 80 counts the number of P-waves sensed by the sensing circuit 86 during each RR interval. The P-wave count for a predetermined number of RR intervals can be buffered in the memory 82 for detection of AT / AF. P-wave signal segments can additionally be stored in the memory 82 to enable waveform morphology analysis or determination of other P-wave features for detection of AT / AF. The P-wave sensed event data can be stored in a circular buffer and analyzed by the processor 92 in response to being woken up at every nth P-wave sensed event signal according to the normal state processor wake-up count.

[0097] At block 704, the control circuit 80 detects AT / AF. In some examples, the AT / AF is detected based on analysis performed by the processor 92. In other examples, the hardware included in the control circuit 80 and the sensing circuit 86 can be configured to detect AT / AF without waking up the processor 92. For example, the AT / AF can be detected at block 706 based on a required number of PP intervals being less than an AT / AF detection interval or a required number of consecutive RR intervals including a number of sensed P-waves. In one example, the AT / AF onset is detected in response to 18 of 24 PP intervals being less than or equal to an AT / AF detection interval of 350 ms or less, as an example. The AT / AF detection interval can correspond to an atrial rate greater than 180 beats per minute (e.g., a PP interval of 333 milliseconds), and can be programmed according to the needs of the individual patient.

[0098] At block 705, control circuit 80 can set an AT / AF onset flag in response to detecting AT / AF (e.g., in response to satisfying a hardware-based detection criterion, such as N of M PP intervals being equal to or less than an AT / AF detection interval). In response to the AT / AF onset flag being set, control circuit 80 can switch to a power conservation state at block 708 during which the rate at which processor 92 is awakened is reduced compared to the normal state. However, in some instances, control circuit 80 can remain in the normal state after setting the AT / AF onset flag until a power conservation state switch criterion is satisfied at block 707.

[0099] For example, the detected AT / AF episode can need to last a threshold time interval prior to switching to the power conservation state, which can be any of the threshold duration examples given above. Meanwhile, after the AT / AF flag is set, processor 92 can be awakened according to a normal state wake-up count at block 706 to determine the status of the detected AT / AF episode. For example, processor 92 can be awakened upon receiving every 8th P-wave sense event signal from sensing circuit 86 to determine an updated AT / AF episode duration to determine whether the switch criterion is satisfied at block 707. In one example, the AT / AF episode needs to last at least six minutes prior to switching to the power conservation state at block 708. Processor 92 can be awakened to process event intervals, signal waveforms, and / or other episode data (which can include historical AT / AF episode data) to determine the status of the atrial arrhythmia until the switch criterion is satisfied. The determination of the status of the atrial arrhythmia can include one or more of detecting an atrial arrhythmia, detecting termination of an atrial arrhythmia, determining a duration of the detected AT / AF episode, determining a rate of the AT / AF episode, determining an updated AT / AF burden, or determining other detected AT / AF episode information that requires processor 92 to execute firmware or software.

[0100] In some cases, termination of the AT / AF episode can be detected at block 709 prior to the switch criteria being met at block 707. Control circuit 80 can detect AT / AF episode termination according to a hardware-implemented criterion (e.g., P of Q consecutive PP intervals greater than the AT / AF detection interval). In other examples, AT / AF termination can be detected by processor 92 based on analysis of the atrial signal upon waking. If termination is detected, control circuit 80 remains in the normal state and returns to block 702 to await the next AT / AF detection. If termination is not detected, processor 92 continues to be woken up according to the normal state wake-up count to update the state of the detected AT / AF episode, e.g., episode duration, until the switch criteria are met at block 708. Processor 92 can store the EGM signal representative of the AT / AF episode, e.g., when the AT / AF episode reaches a threshold duration, control circuit 80 switches to the power conservation state at block 708.

[0101] During the power conservation state, control circuit 80 can reduce the rate at which processor 92 is woken up by suppressing processor wake-up during the power conservation state. Control circuit 80 can suppress processor wake-up until termination of the AT / AF is detected. Termination of the AT / AF can be detected by detecting a threshold number of sensed atrial events occurring at a rate slower than the tachyarrhythmia detection rate. In some examples, processor 92 can be woken up by control circuit 80 to perform other required device functions, however processor 92 is not woken up during the power conservation state to determine the state of the detected tachyarrhythmia. Control circuit 80 can suppress processor wake-up by disabling a counter contained in control circuit 80 that counts the number of P-wave sensed events until the wake-up count.

[0102] Control circuit 80 can continue to count P-waves and determine PP intervals at block 710 by timing circuit 94 to detect termination of a persistent AT / AF episode during the power conservation state based on a hardware-implemented termination detection criterion. Termination of AT / AF can be detected by detecting a threshold number of sensed atrial events occurring at a rate slower than the tachyarrhythmia detection rate. Control circuit 80 can count PP intervals that are greater than the tachyarrhythmia detection interval. AT / AF termination is detected at block 712 when P intervals out of Q consecutive PP intervals are greater than the tachyarrhythmia detection interval. In one example, AT / AF termination is detected in response to at least 10 intervals out of 20 PP intervals being greater than the AT / AF detection interval (e.g., 330 to 350 ms). In another example, the threshold number of sensed atrial events occurring at a rate slower than the AT / AF detection rate can be detected based on a single P-wave sensed during each of a predetermined number of RR intervals. In these examples, the wake-up criterion adjusted to reduce the processor wake-up rate can be defined as the detection of AT / AF termination. From the time the switching criterion is met at block 707 until control circuit 80 detects AT / AF termination based on sensed atrial event signals monitored by hardware included in control circuit 80, processor wake-up can be inhibited.

[0103] Upon detecting AT / AF termination, control circuit 80 can set an AT / AF termination flag at block 715. In response to the termination flag being set, control circuit 80 switches to the normal state at block 722. In response to control circuit 80 switching back to the normal state, processor 92 is woken up at the next wake-up count at block 724. At block 724, processor 92 can update AT / AF episode information at block 724. For example, processor 92 can determine a total episode duration based on the time the onset flag was set and the time the termination flag was set. Processor 92 can determine other AT / AF episode information, such as an updated AT / AF burden. The updated status of the AT / AF episode can be stored in memory 82.

[0104] In some examples, upon being awakened, the processor 92 can analyze the PP intervals and / or P-wave signal segments to verify AT / AF termination. In other examples, the control circuit 80 can awaken the processor 92 upon setting the AT / AF flag prior to switching back to the normal state. The processor 92 can analyze the atrial signals to detect termination of the AT / AF episode, thereby confirming the hardware-based detection. If the analysis performed by the processor 92 after setting the AT / AF offset detection flag does not confirm termination, the control circuit 80 can remain in the power conservation state. The control circuit 80 can again awaken the processor 92 the next time the AT / AF termination detection criteria are met, which can include resetting all PP interval counters to again count P intervals greater than the AT / AF detection interval out of Q consecutive PP intervals from zero.

[0105] It is recognized that medical therapy can perform device diagnostics or other testing during the power conservation state, or the device can enter into a telemetry session with another medical device, such as when a user interrogates the IMD using the external device 50 Figure 1 ). In these cases, a temporary pacing mode and / or acquisition and transmission of EGM signals can be performed. Such operations can require suspension or termination of the power conservation state. For example, if a temporary AOO pacing mode is enabled to perform impedance measurements or other testing, the determination of PP intervals for detecting AT / AF termination can be excluded. If AT / AF termination has not been detected at block 712 during the power conservation state, the control circuit 80 can determine whether a suspension event is detected at block 714. Suspension events can include switching to an AOO pacing mode or other device diagnostic testing, impedance measurements, etc., which can interfere with counting PP intervals to detect termination criteria. When a suspension event is detected, the control circuit 80 disables termination detection at block 716 and waits for the suspension event to complete at block 718. For example, the suspension event completes when the temporary AOO pacing mode terminates or the device testing or measurements are complete.

[0106] When the suspension event completes, the control circuit 80 resumes AT / AF termination detection, such as by resuming counting PP intervals greater than the AT / AF detection interval. When a suspension event is detected, the PP interval counters can be reset so that termination detection resumes at block 720 from the existing count of PP intervals, rather than resuming from the existing count of PP intervals at the time the suspension event was detected. In other examples, AT / AF termination detection can resume from the existing state (e.g., the existing PP interval counter values) at the time the suspension event was detected. In this way, AT / AF termination detection can be suspended during the power conservation state, particularly when such determinations can be confused by temporary medical device operations.

[0107] At block 726, the control circuit 80 can detect a telemetry session into which the telemetry circuit 88 has entered. When a user, for example, interrogates the IMD using the external device 50Figure 1 ) Upon transmission of the interrogation request, telemetry circuit 88 can enter a telemetry session, which can happen to coincide with the power save state being in effect. Another medical device, such as a home monitor or patient hand-held device, can request data from the medical device executing the process of flowchart 700 according to a regularly scheduled interrogation session. When the regularly scheduled interrogation session happens to fall during the power save state, control circuit 80 can detect the telemetry session at block 726. In other examples, telemetry circuit 88 can initiate a telemetry session with another device according to a regularly scheduled data transmission time or in response to a triggering event.

[0108] In response to determining that telemetry circuit 88 is communicating with (or about to communicate with) another device, control circuit 80 switches from the power save state to the normal state by proceeding to block 702. During the normal state, processor 92 can be awakened according to the wake-up criteria for processing data and EGM signals generated by sensing circuit 86, which can then be available for transmission by telemetry circuit 88. Control circuit 80 can refrain from switching back to the power save state until the telemetry session is complete and any other power save state switching criteria are again met.

[0109] If the detected AT / AF episode prior to switching to the power save state is still ongoing at the time of the switch back to the normal state at block 702, then in response to detecting the telemetry session at block 726, it is recognized that the ongoing AT / AF episode is not detected as a new episode at block 704. Upon re-entering the normal state, the AT / AF onset flag that was previously set upon detecting the ongoing AT / AF episode is unset at block 705. Upon re-entering the normal state in response to detecting the telemetry session at block 726, blocks 704 and 706 can be skipped. Control circuit 80 can awaken processor 92 to determine the status of the ongoing AT / AF episode at block 706 according to the normal state processor wake-up criteria. Control circuit 80 monitors for termination of the ongoing AT / AF episode at block 709. If the telemetry session ends and the AT / AF episode is still ongoing, the switching criteria are met at block 707, then control circuit 80 can switch back to the power save state at block 708.

[0110] It should be understood that, in accordance with examples, certain acts or events of any of the methods described herein can be performed in a different sequence, can be added, merged, or eliminated altogether (e.g., not all described acts or events are necessary for the practice of these methods). In addition, in certain examples, acts or events can be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors, rather than sequentially. Additionally, although certain aspects of the disclosure are described as being performed by a single circuit or component for purposes of clarity, it should be understood that these techniques can be performed by a combination of components associated with, for example, a medical device.

[0111] In one or more examples, the functions described can be implemented in hardware, software, firmware, or any combination thereof. If implemented in software or firmware, the functions can be stored as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media can include computer-readable storage media, which corresponds to a tangible medium such as data storage media (e.g., RAM, ROM, EEPROM, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer).

[0112] Instructions can be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, as used herein the term "processor" can refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. Also, the techniques could be fully implemented in one or more circuits or logic elements.

[0113] Accordingly, medical devices have been presented in the foregoing description with reference to specific examples. It is contemplated that various aspects disclosed herein can be combined in different combinations than the specific combinations presented in the accompanying drawings. It is also contemplated that various modifications might be made by persons skilled in the art to the preceding realizations, without departing from the scope of the disclosure and the following claims and examples.

[0114] Example 1. A method comprising: sensing a cardiac signal; operating in a normal state by waking up a processor to analyze the cardiac signal to determine a status of a cardiac arrhythmia at a first rate; and switching from the normal state to a power saving state that uses less power than the normal state in determining the status of the cardiac arrhythmia; operating in the power saving state by waking up the processor to analyze the cardiac signal to determine the status of the cardiac arrhythmia at a second rate, the second rate being less than the first rate.

[0115] Example 2. The method of example 14, further comprising: determining that the power saving state has been in effect for a threshold duration; and adjusting the second rate at which the processor is woken up in the power saving state to a third rate in response to the power saving state being in effect for the threshold duration, the third rate being less than the second rate.

[0116] Example 3. The method of Example 1, further comprising: sensing atrial events from the cardiac signal; waking the processor at the first rate during the normal state by waking the processor each time a first predetermined number of atrial events are sensed by the sensing circuit; and waking the processor at the second rate during the power conservation state by waking the processor each time a second predetermined number of atrial events are sensed, the second predetermined number of atrial events being greater than the first predetermined number of atrial events.

[0117] Example 4. The method of any one of Examples 1-2, further comprising: sensing atrial events in response to the cardiac signal exceeding an atrial event sensing threshold; waking the processor at the first rate during the normal state in response to the sensing circuit sensing a predetermined number of atrial events; and waking the processor at the second rate during the power conservation state by: disabling sensing of atrial events by the sensing circuit for a first time interval during the power conservation state; after expiration of the first time interval, enabling sensing of atrial events by the sensing circuit during a second time interval during the power conservation state; and waking the processor during the power conservation state in response to the sensing circuit sensing a second predetermined number of atrial events during the second time interval.

[0118] Example 5. The method of Example 4, wherein disabling sensing of atrial events for the first time interval comprises at least one of: increasing an atrial event sensing threshold from a first sensing threshold magnitude used to sense the atrial events during the normal state to a second sensing threshold magnitude that is higher than the first sensing threshold magnitude to cause under-sensing of atrial events during the first time period; and suppressing power required to sense atrial events during the first time interval.

[0119] Example 6. The method of any one of Examples 1-5, further comprising: performing a first analysis on the cardiac signal to determine whether the cardiac arrhythmia is present during the normal state; and performing a second analysis to determine whether the cardiac arrhythmia is present during the power conservation state, the second analysis being a subset of the first analysis and requiring less power than the first analysis.

[0120] Example 7. The method of any one of examples 1-6, further comprising: determining whether a switching criterion is met; and switching from the normal state to the power conservation state in response to the switching criterion being met, wherein determining whether a switching criterion is met comprises at least one of: operating in the normal state for a predetermined duration; determining that a detected cardiac arrhythmia persists for a predetermined period of time; determining that a frequency of a cardiac signal sensed in conjunction with cardiac muscle depolarization is less than a threshold frequency; or detecting a change in a therapy delivery pattern.

[0121] Example 8. The method of any one of examples 1-7, further comprising: switching from the power conservation state to a confirmation state; operating in the confirmation state by determining whether a criterion for operating in the power conservation state is met; switching back to the power conservation state in response to the criterion being met; and switching to the normal state in response to the criterion not being met.

[0122] Example 9. The method of any one of examples 1-8, further comprising: generating cardiac electrical stimulation pulses in accordance with a therapy regimen that is invariant during the normal state and the power conservation state.

[0123] Example 10. The method of any one of examples 1-9, further comprising: detecting termination of the cardiac arrhythmia without waking up the processor; wherein waking up the processor at the second rate comprises refraining from waking up the processor to determine a status of a detected atrial arrhythmia until termination of the cardiac arrhythmia is detected.

[0124] Example 11. The method of example 10, further comprising: sensing atrial events from the cardiac signal; detecting an atrial arrhythmia based on sensed atrial events during the normal state; waking up the processor at the first rate during the normal state to determine a status of the detected atrial arrhythmia by waking up the processor each time the sensing circuitry senses a first predetermined number of atrial events; switching to the power conservation state in response to detecting the atrial arrhythmia for a threshold duration; detecting the termination of the atrial arrhythmia during the power conservation state in response to detecting a second threshold number of sensed atrial events occurring slower than an atrial arrhythmia detection rate; and switching back to the normal state of waking up the processor at the first rate in response to detecting the termination of the atrial arrhythmia.

[0125] Example 12. The method of Example 11, further comprising: detecting a pause event during the power saving state; in response to detecting the pause event, suspending detection of the termination of the atrial arrhythmia; detecting completion of the pause event; and in response to detecting the completion of the pause event, resuming detection of termination of the atrial arrhythmia during the power saving state.

[0126] Example 13. The method of any one of Examples 1-12, further comprising: communicating with another device; and switching from the power saving state to the normal state in response to communicating with another device.

[0127] Example 14. A non-transitory computer-readable storage medium comprising a set of instructions, which when executed by control circuitry of a medical device, cause the medical device to: sense a cardiac signal; operate in a normal state by waking up a processor to analyze the cardiac signal to determine a status of an arrhythmia at a first rate; switch from the normal state to a power saving state that uses less power from a power source of the medical device than the normal state in determining the status of the arrhythmia; and operate in the power saving state by waking up the processor to analyze the cardiac signal to determine the status of the arrhythmia at a second rate that is less than the first rate.

Claims

1. A medical device comprising: sensing circuitry configured to sense a cardiac signal; a power source; and control circuitry comprising a processor powered by the power source, wherein the control circuitry is configured to: operate in a normal state by waking up the processor at a first rate to analyze the cardiac signal to determine a status of a cardiac arrhythmia; switch from the normal state to a power conservation state that uses less power from the power source than the normal state in determining the status of the cardiac arrhythmia; and operate in the power conservation state by waking up the processor at a second rate to analyze the cardiac signal to determine the status of the cardiac arrhythmia, the second rate being less than the first rate.

2. The medical device of claim 1, wherein the control circuitry is further configured to operate in the power conservation state by: determining that the power conservation state has been in effect for a threshold duration; and adjusting the second rate at which the processor is to be woken up in the power conservation state to a third rate in response to the power conservation state being in effect for the threshold duration, the third rate being less than the second rate.

3. The medical device of any one of claims 1-2, wherein: the sensing circuitry is configured to sense atrial events from the cardiac signal; the control circuitry is configured to: wake up the processor at the first rate during the normal state by waking up the processor each time a first predetermined number of atrial events are sensed by the sensing circuitry; and wake up the processor at the second rate during the power conservation state by waking up the processor each time a second predetermined number of atrial events are sensed by the sensing circuitry, the second predetermined number of atrial events being greater than the first predetermined number of atrial events.

4. The medical device of any one of claims 1-2, wherein: the sensing circuitry is configured to sense atrial events in response to the cardiac signal exceeding an atrial event sensing threshold; the control circuitry is configured to: wake up the processor at the first rate during the normal state in response to a first predetermined number of atrial events being sensed by the sensing circuitry; wake up the processor at the second rate during the power conservation state by: disabling sensing of atrial events by the sensing circuitry for a first time interval during the power conservation state; after the first time interval expires, enabling sensing of atrial events by the sensing circuitry during a second time interval during the power conservation state; and wake up the processor in response to a second predetermined number of atrial events being sensed by the sensing circuitry during the second time interval.

5. The medical device of claim 4, wherein the control circuitry is configured to disable sensing of atrial events by the sensing circuitry for the first time interval by at least one of: ​ ​ ​ ​ increasing an atrial event sensing threshold from the sensing circuit used to sense the atrial events during the normal state from a first sensing threshold amplitude to a second sensing threshold amplitude that is higher than the first sensing threshold amplitude to cause atrial event undersensing during the first time interval; and inhibiting power from the power source to the sensing circuit during the first time interval.

6. The medical device of any one of claims 1-2, wherein: the processor is configured to perform a first analysis on the cardiac signal to determine whether the cardiac arrhythmia is present during the normal state; and the processor is configured to perform a second analysis as a subset of the first analysis to determine whether the cardiac arrhythmia is present during the power conservation state, the second analysis requiring less power from the power source than the first analysis.

7. The medical device of any one of claims 1-2, wherein the control circuit is configured to switch from the normal state to the power conservation state in response to at least one of: expiration of a predetermined duration of operation in the normal state; determination that a detected cardiac arrhythmia persists for a predetermined period of time; determination that a frequency of a sensed cardiac signal is less than a threshold frequency; or detection of a change in a therapy delivery mode of the medical device.

8. The medical device of any one of claims 1-2, wherein the control circuit is further configured to: switch from the power conservation state to a validation state; operate in the validation state by determining whether criteria for operating in the power conservation state are met; switch back to the power conservation state in response to the criteria being met; and switch to the normal state in response to the criteria not being met.

9. The medical device of any one of claims 1-2, further comprising: a therapy delivery circuit configured to generate cardiac electrical stimulation pulses according to a therapy program that is invariant during the normal state and the power conservation state.

10. The medical device of any one of claims 1-2, wherein the control circuit is configured to: detect termination of the cardiac arrhythmia without waking up the processor; and wake up the processor at the second rate by inhibiting waking up the processor to determine the status of the detected cardiac arrhythmia until the termination of the cardiac arrhythmia is detected.

11. The medical device of claim 10, wherein: the sensing circuit is configured to sense atrial events from the cardiac signal; the control circuit is configured to: detect an atrial arrhythmia based on sensed atrial events during the normal state; wake up the processor at the first rate during the normal state to determine a status of a detected atrial arrhythmia by waking up the processor each time the sensing circuit senses a first predetermined number of atrial events; switch to the power conservation state in response to detecting the atrial arrhythmia for a threshold duration of time; in response to detecting a second threshold number of sensed atrial events occurring slower than an atrial tachyarrhythmia detection rate, detecting the termination of the atrial tachyarrhythmia during the power conservation state; and switching back to the normal state of waking up the processor at the first rate in response to detecting the termination of the atrial tachyarrhythmia.

12. The medical device of claim 11, wherein the control circuit is further configured to: detect a pause event during the power conservation state; in response to detecting the pause event, suspend detecting the termination of the atrial tachyarrhythmia; detect a completion of the pause event; and in response to detecting the completion of the pause event, resume detecting the termination of the atrial tachyarrhythmia during the power conservation state.

13. The medical device of any of claims 1-2, further comprising a telemetry circuit configured to communicate with another device; wherein in response to the telemetry circuit communicating with another device during the power conservation state, the control circuit is configured to switch from the power conservation state to the normal state.

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