Atrial fibrillation detection using heart sound morphology

Abstract

A system and method are disclosed for determining an indication of one of an atrial fibrillation S4 heart sound or a non-atrial fibrillation S4 heart sound for a S4 signal portion of cardiac acceleration information of a patient based on determined first and second correlations of a morphology of the S4 signal portion with an atrial fibrillation S4 template and a non-atrial fibrillation S4 template, respectively, and determining an atrial fibrillation event of the patient using cardiac electrical information of the patient and the determined indication for the S4 signal portion.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 421,834, filed on November 2, 2022, which is incorporated herein by reference in its entirety. Background of the Invention

[0003] The present invention generally relates to medical devices, and more particularly to atrial fibrillation detection using heart sound morphology. Background of the Invention

[0005] Heart failure (HF) is a decline in the heart's ability to deliver sufficient blood to meet the body's needs. Patients with heart failure typically present with an enlarged heart and weakened myocardium, resulting in reduced contractility and poor cardiac output. Signs of heart failure include pulmonary congestion, edema, dyspnea, etc. Heart failure is usually a chronic disease but can also occur suddenly, affecting the left side, right side, or both sides of the heart. Causes of heart failure include coronary artery disease, myocardial infarction, hypertension, atrial fibrillation, valvular heart disease, alcoholism, infection, cardiomyopathy, or one or more other conditions that reduce the heart's pumping efficiency.

[0006] An arrhythmia is an abnormal heart rhythm (e.g., too fast, too slow, irregular, etc.). Arrhythmias include bradycardia, tachycardia, premature beats, extra or skipped heartbeats, and atrial or ventricular fibrillation affecting one or more chambers of the heart. Atrial fibrillation (AF) is an abnormal heart rhythm characterized by rapid and irregular activity in the left or right atrium of the heart. Atrial fibrillation is usually associated with a reduction in cardiac output and an increased risk of heart failure, dementia, and stroke. Risk factors for atrial fibrillation include hypertension, heart failure, valvular heart disease, chronic obstructive pulmonary disease (COPD), obesity, and sleep apnea, among others.

[0007] An ambulatory medical device (AMD), including implantable, subcutaneous, wearable, or one or more other medical devices, etc., can monitor, detect, or treat various conditions, including heart failure, atrial fibrillation, etc. The ambulatory medical device can include a sensor for sensing physiological information from a patient, and one or more circuits for using the sensed physiological information to detect one or more physiological events or transmit the sensed physiological information or the detected physiological events to one or more remote devices. Frequent patient monitoring can provide early detection of patient deterioration, including deteriorating heart failure or atrial fibrillation. Accurate identification of patients or groups of patients at an elevated risk of future adverse events can control the mode or feature selection or resource management of one or more ambulatory medical devices, control notifications or messages to various users in a connected system associated with a particular patient or group of patients, organize or schedule doctor or patient contacts or treatments, or prevent or reduce patient hospitalizations. Correctly identifying and safely managing the risk of patient deterioration can avoid unnecessary medical interventions, extend the service life of ambulatory medical devices, and reduce medical costs. Summary of the Invention

[0008] A system and method are disclosed for determining an indication of either an atrial fibrillation S4 heart sound or a non-atrial fibrillation S4 heart sound for a S4 signal portion of a patient's cardiac acceleration information based on a first correlation and a second correlation respectively determined between the morphology of the S4 signal portion and an atrial fibrillation S4 template and a non-atrial fibrillation S4 template, and for using the patient's cardiac electrical information and the determined indication for the S4 signal portion to determine an atrial fibrillation event of the patient.

[0009] An example (e.g., "Example 1") of a subject matter (e.g., a medical device system) can include: a signal receiver circuit configured to receive (1) the patient's cardiac electrical information, including a timing metric between a first cardiac feature and a second cardiac feature of the patient; and (2) the patient's cardiac acceleration information, including a fourth heart sound (S4) signal portion occurring between the first cardiac feature and the second cardiac feature of the patient; an evaluation circuit configured to: determine a first correlation between the morphology of the S4 signal portion and a non-atrial fibrillation S4 template and a second correlation between the morphology of the S4 signal portion and an atrial fibrillation S4 template, and determine an indication of either an atrial fibrillation S4 heart sound or a non-atrial fibrillation S4 heart sound for the S4 signal portion based on the determined first correlation and second correlation; and an atrial fibrillation detection circuit configured to detect an atrial fibrillation event of the patient using the received timing metric and the determined indication for the S4 heart sound portion.

[0010] In Example 2, the subject matter according to Example 1 can optionally be configured to include: a heart sensor coupled to a signal receiver circuit, the heart sensor being configured to sense electrical heart information of a patient; and a heart sound sensor coupled to the signal receiver circuit, the heart sound sensor being configured to sense cardiac acceleration information of the patient.

[0011] In Example 3, the subject matter according to any one or more of Examples 1 to 2 can optionally be configured to include: an implantable medical device including an electrical sensor, a heart sound sensor, a signal receiver circuit, an evaluation circuit, and an atrial fibrillation detection circuit.

[0012] In Example 4, the subject matter according to any one or more of Examples 1 to 3 can optionally be configured such that the heart sensor includes a processing circuit configured to: determine a timing metric between a first cardiac feature and a second cardiac feature of a first cardiac interval of a patient or between a first cardiac feature and a second cardiac feature of corresponding consecutive first and second cardiac intervals of the patient, and the heart sound sensor includes a processing circuit configured to: determine an S4 signal portion in an S4 window of cardiac acceleration information of a corresponding first or second cardiac interval of the patient.

[0013] In Example 5, the subject matter according to any one or more of Examples 1 to 4 can optionally be configured such that the first cardiac feature and the second cardiac feature include equivalently detected features in consecutive first and second cardiac intervals.

[0014] In Example 6, the subject matter according to any one or more of Examples 1 to 5 can optionally be configured such that the first cardiac feature is an R wave of a first cardiac interval, and the second cardiac feature is an R wave of an ensuing second cardiac interval.

[0015] In Example 7, the subject matter according to any one or more of Examples 1 to 6 can optionally be configured such that the timing metric is a timing metric of a cardiac interval, and wherein the S4 signal portion is an S4 signal portion of a cardiac interval.

[0016] In Example 8, the subject matter according to any one or more of Examples 1 to 7 can optionally be configured such that an atrial fibrillation event includes a plurality of cardiac intervals, and the evaluation circuit is configured to determine an indication of either an atrial fibrillation S4 heart sound or a non - atrial fibrillation S4 heart sound for the S4 signal portion based on first and second correlations determined for each of the plurality of cardiac intervals.

[0017] In Example 9, the subject matter according to any one or more of Examples 1 to 8 may optionally be configured such that an atrial fibrillation event includes a plurality of cardiac intervals, and the evaluation circuit is configured to use a portion of the S4 signal that occurs within the plurality of cardiac intervals to determine a composite S4 signal portion. The evaluation circuit is configured to: determine a first correlation between the composite S4 signal portion and a non-atrial fibrillation S4 template and a second correlation between the composite S4 signal portion and an atrial fibrillation S4 sound, and the evaluation circuit is configured to: determine an indication of either an atrial fibrillation S4 sound or a non-atrial fibrillation S4 sound for the composite S4 signal portion based on the determined first correlation and second correlation.

[0018] In Example 10, the subject matter according to any one or more of Examples 1 to 9 may optionally be configured such that the evaluation circuit is configured to: determine an indication of either an atrial fibrillation S4 sound or a non-atrial fibrillation S4 sound for the S4 sound in the S4 signal portion based on the difference between the correlation of the S4 signal portion with a non-atrial fibrillation S4 template and the correlation of the S4 signal portion with an atrial fibrillation S4 template.

[0019] In Example 11, the subject matter according to any one or more of Examples 1 to 10 may optionally be configured such that the evaluation circuit is configured to: determine an indication of either an atrial fibrillation S4 sound or a non-atrial fibrillation S4 sound for the S4 sound in the S4 signal portion based on the difference between the correlation of the S4 signal portion with an atrial fibrillation S4 template and the correlation of the S4 signal portion with a non-atrial fibrillation S4 template.

[0020] An example (e.g., "Example 12") of the subject matter (e.g., a method) may include: at a signal receiver circuit, receiving cardiac electrical information of a patient, the cardiac electrical information including a timing metric between a first cardiac feature and a second cardiac feature of the patient; at the signal receiver circuit, receiving cardiac acceleration information of the patient, the cardiac acceleration information including a portion of a fourth heart sound (S4) signal that occurs between the first cardiac feature and the second cardiac feature of the patient; using an evaluation circuit, determining a first correlation between the morphology of the S4 signal portion and a non-atrial fibrillation S4 template and a second correlation between the morphology of the S4 signal portion and an atrial fibrillation S4 template; using the evaluation circuit, determining an indication of either an atrial fibrillation S4 sound or a non-atrial fibrillation S4 sound for the S4 signal portion based on the determined first correlation and second correlation; and using an atrial fibrillation detection circuit, detecting an atrial fibrillation event of the patient using the received timing metric and the determined indication for the S4 signal portion.

[0021] In Example 13, the subject matter according to Example 12 may optionally be configured to include: sensing cardiac electrical information of a patient using a cardiac sensor coupled to a signal receiver circuit; and sensing cardiac acceleration information of the patient using a heart sound sensor coupled to the signal receiver circuit.

[0022] In Example 14, the subject matter according to any one or more of Examples 12 to 13 may optionally be configured such that the electrical sensor, the heart sound sensor, the signal receiver circuit, the evaluation circuit, and the atrial fibrillation detection circuit are components of an implantable medical device.

[0023] In Example 15, the subject matter according to any one or more of Examples 12 to 14 may optionally be configured to include: using a processing circuit of the cardiac sensor to determine a timing metric between a first cardiac feature and a second cardiac feature of a first cardiac interval of the patient or between a first cardiac feature and a second cardiac feature of corresponding consecutive first and second cardiac intervals of the patient; and using a processing circuit of the heart sound sensor to determine an S4 signal portion in an S4 window of cardiac acceleration information of a corresponding first cardiac interval or second cardiac interval of the patient.

[0024] In Example 16, the subject matter according to any one or more of Examples 12 to 15 may optionally be configured such that the first cardiac feature and the second cardiac feature include equivalent detected features in consecutive first and second cardiac intervals.

[0025] In Example 17, the subject matter according to any one or more of Examples 12 to 16 may optionally be configured such that the timing metric is a timing metric of a cardiac interval, and wherein the S4 signal portion is the S4 signal portion of the first cardiac interval.

[0026] In Example 18, the subject matter according to any one or more of Examples 12 to 17 may optionally be configured such that an atrial fibrillation event includes a plurality of cardiac intervals, and determining an indication of one of an atrial fibrillation S4 heart sound or a non-atrial fibrillation S4 heart sound for the S4 signal portion includes based on a first correlation and a second correlation determined for each of the plurality of cardiac intervals.

[0027] In Example 19, the subject matter described in any one or more of Examples 12 to 17 may optionally be configured such that an atrial fibrillation event includes a plurality of cardiac intervals, wherein the method includes using a portion of the S4 signal occurring within the plurality of cardiac intervals to determine a composite S4 signal portion, wherein determining a first correlation includes determining a first correlation between the composite S4 signal portion and a non-atrial fibrillation S4 template, determining a second correlation includes determining a second correlation between the composite S4 signal portion and an atrial fibrillation S4 template, and determining an indication of either an atrial fibrillation S4 heart sound or a non-atrial fibrillation S4 heart sound includes determining an indication of either an atrial fibrillation S4 heart sound or a non-atrial fibrillation S4 heart sound for the composite S4 signal portion based on the determined first and second correlations.

[0028] In Example 20, the subject matter described in any one or more of Examples 12 to 19 may optionally be configured to determine an indication of either an atrial fibrillation S4 heart sound or a non-atrial fibrillation S4 heart sound for an S4 heart sound in an S4 signal portion based on a difference between a correlation of the S4 signal portion with a non-atrial fibrillation S4 template and a correlation of the S4 signal portion with an atrial fibrillation S4 template.

[0029] In Example 21, the subject matter (e.g., a system or device) may optionally combine any portion or any combination of any portion described in any one or more of Examples 1 to 20 to include a "device" or at least one "non-transitory machine-readable medium" for performing any portion of the functions or methods described in any one or more of Examples 1 to 20, the non-transitory machine-readable medium including instructions that, when executed by a machine, cause the machine to perform any portion of the functions or methods described in any one or more of Examples 1 to 20.

[0030] This summary is intended to provide an overview of the subject matter of this patent application. It is not intended to provide an exclusive or exhaustive explanation of the disclosure. The detailed description is included to provide further information about the patent application. Other aspects of the disclosure will be apparent to those of ordinary skill in the art upon reading and understanding the following detailed description and referring to the drawings that form a part thereof, each of which should not be construed as limiting. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In the drawings, which are not necessarily to scale, like numeral designations may describe similar components in different views. Like numeral designations with different letter suffixes may represent different instances of similar components. By way of example and not limitation, the drawings generally illustrate the various embodiments discussed in this document.

[0032] Figure 1Shows the relationship between the measured patient physiological information (including patient heart sound information and cardiac electrical information) and the cardiac cycle.

[0033] Figure 2 Generally shows exemplary performance differences for evaluating the fourth heart sound (S4) signal using different features.

[0034] Figure 3 Shows exemplary atrial fibrillation S4 signal templates and non - atrial fibrillation S4 signal templates.

[0035] Figures 4 to 6 Shows an exemplary pseudo - P wave determination made using cardiac electrical information.

[0036] Figure 7 Shows an exemplary aggregated cardiac electrical information composite signal.

[0037] Figure 8 Shows an exemplary aggregated fourth heart sound (S4) signal partial composite signal.

[0038] Figure 9 Shows an exemplary system for using heart sound morphology to determine atrial fibrillation events.

[0039] Figure 10 Shows an exemplary patient management system and a portion of the environment in which the patient management system may operate.

[0040] Figure 11 Shows an exemplary method for using heart sound morphology to determine atrial fibrillation events in a patient.

[0041] Figure 12 Shows a block diagram of an exemplary machine on which any one or more of the techniques discussed herein may be executed. Detailed Description

[0042] Implantable and ambulatory medical devices may include or be configured to receive cardiac electrical information from one or more electrodes located within, on, or near the heart (such as coupled to leads and located within one or more chambers of the heart or within the vasculature near one or more chambers of the heart). An ambulatory medical device may additionally include or be configured to receive mechanical acceleration information from one or more accelerometer sensors to determine and monitor patient acceleration information, such as cardiac vibration information (e.g., heart sounds, heart wall motion, etc.) associated with blood flow or movement in the heart or the patient's vasculature, patient body activity or position information (e.g., patient posture, activity, etc.), respiratory information (e.g., respiratory rate, phase, ventilation sounds, etc.), and the like.

[0043] Arrhythmia events (including potential arrhythmia events such as atrial fibrillation events or potential events) can be detected using sensed or received cardiac electrical information, which includes, for example, detected atrial or ventricular events (e.g., beats, r-waves, p-waves, etc.) or intervals occurring therebetween within a detection window, which is typically between 30 seconds and 2 minutes, although in some examples it can be longer or shorter. A mobile medical device can, for example, use timing information between events and, in some examples, in combination with one or more other detected events to determine whether atrial fibrillation is present in each detection window, and can additionally determine, based on that determination, what sensed or detected information to store or transmit, such as for transmission to a remote device. In some examples, a mobile medical device can aggregate information from multiple sensors, use the information from each sensor individually or in combination to detect various events, update a detection status based on that information, and transmit a message or alert to one or more remote devices that detection has occurred and that information has been stored or transmitted, such that one or more additional processes or systems can use the stored or transmitted detection or information for one or more other checks or processes.

[0044] Atrial fibrillation detection algorithms typically rely on electrocardiographic features, such as cardiac intervals between successive R waves, rate variance between beats, etc. Examples of atrial fibrillation detection algorithms, including various atrial fibrillation detection parameters and criteria, can be found in the following applications: for example, U.S. Patent Application No. 14 / 825,669, titled "Atrial Fibrillation Detection Using Ventricular Rate Variability" by Krueger et al., assigned to the same assignee (hereinafter referred to as "‘669"); U.S. Patent Application No. 15 / 082,440, titled "Atrial Fibrillation Detection" by Perschbacher et al. (hereinafter referred to as "‘440 Application"); U.S. Patent Application No. 15 / 341,565, titled "Method and Apparatus for Enhancing Ventricular Based Atrial Fibrillation Detection Using Atrial Activity" by Krueger et al. (hereinafter referred to as "‘565 Application"); and U.S. Patent Application No. 15 / 864,953, titled "Atrial Fibrillation Discrimination Using Heart Rate Clustering" by Perschbacher et al. (hereinafter referred to as "‘953 Application"), each of which is incorporated herein by reference in its entirety, including the disclosure of its atrial fibrillation detection and atrial fibrillation detection algorithms, including, for example: paired atrial fibrillation detection using ventricular information detected from the ventricles, including heart rate variation and heart rate variation characteristics, and determination of valid heartbeats or intervals using various characteristics (including threshold heart rate, intervals, morphological criteria, etc.), such as disclosed in the ‘669 Application; atrial fibrillation detection using the distribution of ventricular depolarization intervals, such as disclosed in the ‘440 Application; atrial fibrillation detection using atrial activity scores from an atrial detection window prior to detected ventricular polarization, such as disclosed in the ‘565 Application; atrial fibrillation discrimination using cluster depolarization information, such as disclosed in the ‘953 Application, etc.

[0045] Heart sounds are recurrent mechanical signals associated with heart vibrations or accelerations caused by blood flowing through the heart or other cardiac movements during each cardiac cycle or interval, and can be separated and classified based on activities associated with such vibrations, accelerations, movements, pressure waves, or blood flow. Heart sounds include four main features: the first heart sound through the fourth heart sound (S1 to S4, respectively). The first heart sound (S1) is a vibratory sound emitted by the heart at the start of systole (or ventricular contraction) during the closure of the atrioventricular (AV) valves (mitral and tricuspid valves) and the opening of the aortic valve. The second heart sound (S2) is a vibratory sound emitted by the heart during the closure of the aortic and pulmonary valves at the start of diastole (or ventricular relaxation). The third heart sound (S3) and the fourth heart sound (S4) are related to the filling pressure of the left ventricle during diastole. A sudden stop in early diastolic filling can cause the third heart sound (S3). Vibrations caused by the late atrial kick can cause the fourth heart sound (S4). Valve closures, blood movements, and pressure changes in the heart can cause accelerations, vibrations, or movements of the heart wall, which can be detected using accelerometers or microphones to provide an output herein referred to as "heart acceleration information".

[0046] The S4 heart sound, which reflects atrial contraction during sinus rhythm, is typically absent during atrial fibrillation. Thus, in some examples, the determination of the presence or absence of the S4 heart sound can be used to improve the determination of atrial fibrillation. For example, the S4 morphology can be used to determine the presence of the S4 heart sound within an S4 window during a particular cardiac cycle, such as disclosed in the co-owned U.S. Patent Application No. 16 / 215,230 to Thakur et al. titled "Systems And Methods For Detecting Atrial Tachyarrhythmia Using Heart Sounds" (hereinafter referred to as the "‘230 application"), which is incorporated herein by reference in its entirety, the disclosure of which includes comparing a fourth heart sound (S4) signal portion to an S4 template and determining whether a match score exceeds a threshold, and using the determined score to improve the determination of atrial fibrillation.

[0047] The present inventor has recognized, among other things, additional improvements in determining atrial fibrillation using the S4 morphology. For example, in some patients, during atrial fibrillation, there are at least some heart sound signals in the S4 window (which includes at least some S4 signal portions in some examples), such that their presence or absence alone may not provide the most accurate determination of atrial fibrillation. Thus, to improve the sensitivity and specificity of atrial fibrillation detection, a separate and specific atrial fibrillation S4 signal template and a non-atrial fibrillation S4 signal template can be determined, and the S4 signal portion of the heart sound signal can be compared to the separate and specific atrial fibrillation S4 signal template and non-atrial fibrillation S4 signal template, and an atrial fibrillation determination can be made based on these two comparisons, such as, for example:

[0048] score = corr(data(t), nonAF_model) - corr(data(t), AF_model) (1)

[0049] Compared to a crude determination of presence or absence alone, the score can include a determination of whether the S4 signal portion more accurately represents the S4 signal portion during non-atrial fibrillation (e.g., normal sinus rhythm) or during atrial fibrillation. For example, a positive score can indicate a non-atrial fibrillation S4 heart sound and a negative score can indicate an atrial fibrillation S4 heart sound. The term "corr" can be a correlation function configured to determine the similarity between two signals, "data(t)" can be the S4 signal portion of the heart sound signal, "nonAF_model" can be the non-atrial fibrillation S4 signal template, and "AF_model" can be the atrial fibrillation S4 signal template.

[0050] In other examples, the determination can additionally include other fiducial points or patterns or spectral components of the S4 signal portion, such as those described herein. The improved sensitivity and specificity of the atrial fibrillation determination can improve the detection of false positive atrial fibrillation episodes, more accurately control the active sensing or data storage mode (e.g., sampling time, sampling frequency, length of stored episode, etc.) of a mobile medical device or sensor associated with such determination, reduce the storage of false positive atrial fibrillation episodes, reduce the data transmission of the stored episodes to one or more remote devices, reduce the manual review of such transmitted and determined events or episodes, or provide or change one or more treatment parameters to a patient based on the detected event or determination. In some examples, an initial detection of an atrial fibrillation event can be rejected or confirmed based on positive and negative scores, respectively. In other examples, based on the determined positive and negative scores, etc., data can be relabeled, triggered storage can be revoked, mode transitions can be revoked, etc.

[0051] In atrial fibrillation detection based solely on cardiac electrical information (such as ECG), for example, in the absence of heart sound or P-wave confirmation, P-waves were detected in only 30 - 35% of false atrial fibrillation detections. Although P-wave confirmation can improve false positive atrial fibrillation detection compared to detection based solely on cardiac electrical information, and the presence of the S4 heart sound can provide a separate indication of the presence of P-waves based on false detections (such as those caused by artifacts, noise, vector or lead placement, or specific patient anatomy), the inventors have recognized that determining separate correlations with a separate template for atrial fibrillation S4 signals and a separate template for non-atrial fibrillation S4 signals can further improve the performance of atrial fibrillation detection. Specifically, in one example, 140 out of 163 clinically determined ECG-based false positive results were corrected by the techniques described herein.

[0052] There is a technical problem in medical devices in that, in a low-power monitoring mode, a mobile medical device powered by one or more rechargeable or non-rechargeable batteries must make certain trade-offs between battery life (or in the case of an implantable medical device with a non-rechargeable battery, the device replacement period, which typically includes surgery) and sampling resolution, sampling period, and the processing, storage, and transmission of the sensed physiological information. The medical device may include a higher-power monitoring mode. Physiological information (such as physiological information indicating a potential adverse physiological event) can be used to transition from a low-power monitoring mode (such as a low-power mode) to a higher-power or higher-resolution monitoring mode (such as a high-power mode). In some examples, the low-power mode may include a low-resource mode, which is characterized by requiring less power, processing time, memory, or communication time or bandwidth (such as transmitting less data, etc.) compared to the corresponding high-power mode. The high-power mode may include a relatively high-resource mode, which is characterized by requiring more power, processing time, memory, or communication time or bandwidth compared to the corresponding low-power mode. However, when physiological information detected in the low-power mode indicates a possible event, valuable information has been lost and cannot be recorded in the high-power mode.

[0053] Conversely, an incorrect or inaccurate determination of an error that triggers a high-power mode unnecessarily and overly limits the useful life of certain mobile medical devices. A change in mode can enable higher-resolution sampling, or increase the sampling frequency, or increase the number or type of sensors used to sense physiological information before and during a potential event. For example, heart sounds and patient activity are typically detected using non-overlapping time periods of the same single-axis or multi-axis accelerometer at different sampling frequencies and power costs. In one example, the transition to a high-power mode can include: using the accelerometer to always detect heart sounds throughout the high-power mode, or detecting heart sounds for a greater percentage of time during the high-power mode than during the corresponding low-power mode. Additionally, waveforms for medical events are often recorded, stored in long-term memory, and often transmitted to a remote device for clinician review. In some examples, only a notification that the event has been stored or summary information about the event is transmitted. In response, the full event can be requested for subsequent transmission and review. However, even in cases where the event is stored instead of transmitted, the resources for storing and processing the event are still provided by the medical device. Thus, for many reasons, it is advantageous to accurately detect and determine physiological events (including reducing false-positive device detections) to appropriately manage and utilize medical device resources.

[0054] Figure 1 Shows the relationship 100 between the measured patient physiological information (including patient heart sound information 101 (including first heart sound (S1) 103, second heart sound (S2) 104, third heart sound (S3) 105, fourth heart sound (S4) 106, ejection sound 107, systolic murmur 108, opening sound between S2 and S3, and diastolic murmur 109)) and cardiac electrical information 102 (including P wave 112, Q wave 113, R wave 114, S wave 115, and T wave 116 of an electrocardiogram signal) and the cardiac cycle (including the periods of systole 110 and diastole 111).

[0055] Figure 2 Generally shows an example performance difference 200 for evaluating an S4 signal using different features: These features include: (A) ECG-based detection 201 and corresponding sensitivity 201A and specificity 201B; (B) root mean square (RMS) determination of heart sound energy in the S4 detection window 202 and corresponding sensitivity 202A and specificity 202B; (C) raw heart sound signal correlation for a single cardiac interval 203 and corresponding sensitivity 203A and specificity 203B; and (D) filtered and denoised correlation for a portion of the S4 signal 204 and corresponding sensitivity 204A and specificity 204B.

[0056] Figure 3Illustrates an example heart sound template 300 in the S4 heart sound window, which includes an atrial fibrillation S4 signal template 301 and a non - atrial fibrillation S4 signal template 302 (e.g., an S4 signal template in normal sinus rhythm). In some examples, the atrial fibrillation and non - atrial fibrillation S4 signal templates 301, 302 can be population templates determined respectively based on clinical determination of the S4 signal portions of the heart sound waveforms of patients exhibiting atrial fibrillation and non - atrial fibrillation (e.g., normal sinus rhythm). The atrial fibrillation and non - atrial fibrillation signal templates 301, 302 can be generated as the mean or median value of a plurality of pre - labeled (e.g., clinically labeled or determined to be an atrial fibrillation signal portion or a non - atrial fibrillation signal portion, such as by a clinician, a separate detection algorithm, etc.). In some examples, the labeling can include an atrial fibrillation detection algorithm based on cardiac electrical information, which is collected and reviewed over time, such as from a patient or a patient population. In some examples, the corresponding signal templates can be updated as more determinations are collected and become available.

[0057] Figures 4 to 6 Illustrates an example spurious P - wave determination, demonstrating the challenges in accurately detecting P - waves across various patients using cardiac electrical information. Figure 4 Illustrates an example atrial flutter rhythm 400 detected as a spurious P - wave detection. Figure 5 Illustrates an example rhythm 500 including an artifact (e.g., noise) that obscures P - wave detection. Figure 6 Illustrates an exemplary inherently low P - wave 600 caused by a patient detection vector or anatomical structure that obscures the P - wave detection direction.

[0058] Figure 7 Illustrates an example aggregated cardiac electrical information composite signal 700, including a true - positive P - wave detection 701 and a false - positive P - wave detection 702. The composite signal generally includes a combination of multiple signals (e.g., mean or median representation, in some examples, a filtered mean and median, etc.). The similarity between the true - positive composite signal and the false - positive composite signal demonstrates the difficulty in differentiating different events across patient populations.

[0059] Figure 8 Illustrates an example aggregated S4 signal portion composite signal 800, including a true - negative atrial fibrillation detection 801, a false - positive atrial fibrillation detection 802 (e.g., from an atrial fibrillation detection based on cardiac electrical information), and a positive atrial fibrillation detection 803. The positive atrial fibrillation detection 803 shows a substantial difference from the true - negative atrial fibrillation detection 801 and the false - positive atrial fibrillation detection 802. However, the true - negative atrial fibrillation detection 801 and the false - positive atrial fibrillation detection 802 are more similar, demonstrating more subtle changes in the cardiac mechanical signals.

[0060] Figure 9 An example system 900 for detecting atrial fibrillation events using heart sound morphology is shown, such as determining an indication of either an atrial fibrillation S4 heart sound or a non-atrial fibrillation S4 heart sound for an S4 signal portion of a patient's cardiac acceleration information based on a first correlation and a second correlation respectively determined between the morphology of the S4 signal portion and an atrial fibrillation S4 template and a non-atrial fibrillation S4 template, and using the patient's cardiac electrical information and the determined indication for the S4 signal portion to determine an atrial fibrillation event for the patient.

[0061] The example system 900 may include a medical device system, a cardiac rhythm management (CRM) device, etc. In an example, one or more aspects of the example system 900 may be components of a mobile medical device (AMD), an implantable cardiac monitor, etc., or communicatively coupled to a mobile medical device (AMD), an implantable cardiac monitor, etc. The system 900 may be configured to monitor, detect, or treat various physiological conditions of the body, such as cardiac conditions associated with a decreased ability of the heart to deliver blood to the body, including heart failure, arrhythmia, cardiac dyssynchrony, etc., or one or more other physiological conditions, and in certain examples, may be configured to provide electrical stimulation or one or more other therapies or treatments to a patient.

[0062] The system 900 may include a single medical device or multiple medical devices implanted in a patient or otherwise positioned on or around the patient to monitor the patient's physiological information using one or more sensors, such as sensor 901. In an example, sensor 901 may include one or more of the following: a respiratory sensor configured to receive respiratory information (e.g., respiratory rate, respiratory volume (tidal volume), etc.); an acceleration sensor (e.g., an accelerometer, a microphone, etc.) configured to receive cardiac acceleration information (e.g., cardiac vibration information, pressure waveform information, heart sound information, endocardial acceleration information, acceleration information, activity information, position information, etc.); an impedance sensor (e.g., an intrathoracic impedance sensor, a transthoracic impedance sensor, etc.) configured to receive impedance information; a cardiac sensor configured to receive cardiac electrical information; an activity sensor configured to receive information about body movement (e.g., activity, steps, etc.); a position sensor configured to receive position or location information; a pressure sensor configured to receive pressure information; a plethysmograph sensor (e.g., a photoplethysmograph sensor, etc.); a chemical sensor (e.g., an electrolyte sensor, a pH sensor, an anion gap sensor, etc.); a temperature sensor; a skin elasticity sensor; or one or more other sensors configured to receive the patient's physiological information.

[0063] Example system 900 may include signal receiver circuit 902 and evaluation circuit 903. Signal receiver circuit 902 may be configured to receive physiological information of a patient (or group of patients) from sensor 901. Evaluation circuit 903 may be configured to receive information from signal receiver circuit 902 and use the received physiological information to determine one or more parameters (e.g., physiological parameters, stratification factors, etc.) or an existing or changing patient condition (e.g., an indication of patient dehydration, respiratory condition, cardiac condition (e.g., heart failure, arrhythmia), sleep apnea, etc.), such as described herein. Among other aspects, the physiological information may include cardiac electrical information, impedance information, respiratory information, heart sound information, activity information, position information, temperature information, or one or more other types of physiological information.

[0064] In some examples, evaluation circuit 903 may aggregate information from multiple sensors or devices, detect various events using the information from each sensor or device alone or in combination, update the detection status for one or more patients based on the information, and transmit a message or alert that a detection has been made or information has been stored or transmitted for one or more patients to one or more remote devices such that one or more additional processes or systems may use the stored or transmitted detection or information for one or more other examinations or processes.

[0065] Evaluation circuit 903 may be configured to provide an output to a user, such as to a display or one or more other user interfaces, the output including a score, trend, alert, or other indication. In other examples, evaluation circuit 903 may be configured to provide an output to another circuit, machine, or process, such as treatment circuit 904 (e.g., cardiac resynchronization therapy (CRT) circuit, chemotherapy circuit, etc.) to control, adjust, or stop the treatment of a medical device, drug delivery system, etc., or otherwise change one or more processes or functions of one or more other aspects of a medical device system, such as one or more cardiac resynchronization therapy parameters, drug delivery, dose determination or recommendation, etc. In an example, treatment circuit 904 may include one or more of a stimulation control circuit, a cardiac stimulation circuit, a nerve stimulation circuit, a dose determination or control circuit, etc. In other examples, treatment circuit 904 may be controlled by evaluation circuit 903 or one or more other circuits, etc.

[0066] In some examples, among other things, the assessment circuit 903 can include an atrial fibrillation detection circuit 905 and a morphology circuit 906. The atrial fibrillation detection circuit 905 can be configured to perform one or more atrial fibrillation detection algorithms or otherwise determine one or more indicators of atrial fibrillation in one or more cardiac cycles or in a time window including multiple cardiac cycles, such as to determine one or more measures and compare the one or more measures to a patient-specific threshold or a population threshold. The morphology circuit 906 can be configured to determine the correlation (e.g., cross-correlation, correlation coefficient, correlation waveform analysis, etc.) between the shape of one or more signal features (such as the S4 signal portion of a heart sound signal of one or more cardiac cycles) and one or more templates (such as those described herein), such as to determine one or more measures and compare the one or more measures to a patient-specific threshold or a population threshold. In some examples, one or more templates can be patient-specific templates or population templates. An indication of either an atrial fibrillation S4 heart sound or a non-atrial fibrillation S4 heart sound in the S4 signal portion can be determined based on a difference between the determined correlations between the S4 signal portion of the heart sound signal and a non-atrial fibrillation S4 template and an atrial fibrillation S4 template.

[0067] In other examples, the determination can additionally include other fiducial points or patterns or spectral components of the S4 signal portion. For example, the magnitude of the frequency components in the S4 window can be used to determine an indication of either an atrial fibrillation S4 heart sound or a non-atrial fibrillation S4 heart sound. Generally, the atrial fibrillation S4 heart sound has fewer frequency components in the S4 window than the non-atrial fibrillation S4 heart sound. Thus, template frequency components can be determined for each of the atrial fibrillation S4 heart sound and the non-atrial fibrillation S4 heart sound, which is a population template or a patient-specific template, and such templates can be used as additional features in the determination described herein.

[0068] The change over time of the S4 signal portion can indicate a change in ventricular sclerosis. In an example, an increase over time of the S4 signal portion can be used to detect a worsening of a cardiac condition. A relative change above a threshold can trigger an alert, notification, mode switch, or one or more other medical device changes or actions, such as those described herein.

[0069] Figure 10 An exemplary patient management system 1000 and a portion of the environment in which the patient management system 1000 can operate are shown. The patient management system 1000 can perform a series of activities, including remote patient monitoring and disease condition diagnosis. Such activities can be performed proximal to the patient 1001, such as in the patient's home or office, by a central server, such as in a hospital, clinic, or doctor's office, or by a remote workstation, such as a secure wireless mobile computing device.

[0070] The patient management system 1000 may include one or more mobile medical devices, an external system 1005, and a communication link 1011 that provides for communication between the one or more mobile medical devices and the external system 1005. The one or more mobile medical devices may include an implantable medical device (IMD) 1002, a wearable medical device 1003, or one or more other implantable, leadless, subcutaneous, external, wearable, or mobile medical devices configured to monitor, sense, or detect information from a patient 1001, determine physiological information about the patient 1001, or provide one or more therapies to treat various conditions of the patient 1001, such as one or more cardiac or non-cardiac conditions (e.g., dehydration, sleep apnea, etc.).

[0071] In an example, the implantable medical device 1002 may include one or more conventional cardiac rhythm management devices implanted in a patient's chest, having a lead system that includes one or more transvenous, subcutaneous, or non-invasive leads or catheters to position one or more electrodes or other sensors (e.g., heart sound sensors) within, on, or around the heart, or at one or more other locations in the patient 1001's chest, abdomen, or neck. In another example, the implantable medical device 1002 may include, for example, a monitor subcutaneously implanted in the patient 1001's chest, the implantable medical device 1002 including a housing containing circuitry and, in some examples, including one or more sensors, such as a temperature sensor, etc.

[0072] Conventional cardiac rhythm management devices (such as insertable cardiac monitors, pacemakers, defibrillators, or cardiac resynchronizers) include implantable or subcutaneous devices having an airtight sealed housing configured to be implanted in a patient's chest. The cardiac rhythm management device may include one or more leads to position one or more electrodes or other sensors at various locations within or near the heart, such as at one or more locations in the atria or ventricles of the heart, etc. Thus, the cardiac rhythm management device may include aspects that are subcutaneous, although near the patient's distal skin, and aspects that are near one or more organs of the patient, such as leads or electrodes. Separate from or in addition to the one or more electrodes or other sensors of the leads, the cardiac rhythm management device may include one or more electrodes or other sensors (e.g., pressure sensors, accelerometers, gyroscopes, microphones, etc.) powered by a power source within the cardiac rhythm management device. The one or more electrodes or other sensors of the leads, the cardiac rhythm management device, or a combination thereof may be configured to detect physiological information from the patient, or to provide one or more treatments or stimuli to the patient.

[0073] An implantable device may additionally or alternatively include a leadless cardiac pacemaker (LCP), which is a small (e.g., smaller than traditional implantable cardiac rhythm management devices, having a volume of about 1 cc in some examples, etc.) self - contained device that includes one or more sensors, circuitry, or electrodes configured to monitor physiological information from the heart (e.g., heart rate, etc.), detect physiological conditions associated with the heart (e.g., tachycardia), or provide one or more therapies or stimuli to the heart without the complications associated with traditional leads or implantable cardiac rhythm management devices (e.g., the required incisions and pockets, complications associated with lead placement, breakage, or displacement, etc.). In some examples, a leadless cardiac pacemaker may have more limited power and processing capabilities than traditional cardiac rhythm management devices; however, multiple leadless cardiac pacemakers may be implanted in or around the heart to detect physiological information from one or more chambers of the heart or provide one or more therapies or stimuli to one or more chambers of the heart. Multiple leadless cardiac pacemakers may communicate with each other, or with one or more other implanted devices or external devices.

[0074] The implantable medical device 1002 may include an evaluation circuit configured to detect or determine specific physiological information of a patient 1001, or determine one or more conditions, or provide information or alerts to a user (such as the patient 1001 (e.g., the patient), a clinician, or one or more other caregivers or processes) as described herein. The implantable medical device 1002 may alternatively or additionally be configured as a treatment device configured to treat one or more medical conditions of the patient 1001. The treatment may be delivered to the patient 1001 via a lead system and associated electrodes or using one or more other delivery mechanisms. The treatment may include delivering one or more drugs to the patient 1001, such as using the implantable medical device 1002 or one or more other mobile medical devices, etc. In some examples, the treatment may include cardiac resynchronization therapy for correcting asynchrony and improving the heart function of patients with heart failure. In other examples, the implantable medical device 1002 may include a drug delivery system, such as a drug infusion pump for delivering drugs to the patient for managing arrhythmias or complications caused by arrhythmias, hypertension, hypotension, or one or more other physiological conditions. In other examples, the implantable medical device 1002 may include one or more electrodes configured to stimulate the patient's nervous system or provide stimulation to the muscles of the patient's airway, etc.

[0075] The wearable medical device 1003 may include one or more wearable or external medical sensors or devices (e.g., an automated external defibrillator (AED), a Holter monitor, a patch - based device, a smartwatch, a smart accessory, a wrist - worn or finger - worn medical device, such as a finger - based photoplethysmography sensor, etc.).

[0076] The external system 1005 can include a dedicated hardware / software system, such as a programmer, a remote server-based patient management system, or alternatively a system defined primarily by software running on a standard personal computer. The external system 1005 can manage the patient 1001 via the implantable medical device 1002 or one or more other ambulatory medical devices connected to the external system 1005 via a communication link 1011. In other examples, the implantable medical device 1002 can be connected to a wearable medical device 1003, or the wearable medical device 1003 can be connected to the external system 1005 via the communication link 1011. For example, this can include programming the implantable medical device 1002 to perform one or more of acquiring physiological data, performing at least one self-diagnostic test (such as a self-diagnostic test for the device operating state), analyzing physiological data, or optionally delivering or adjusting treatment for the patient 1001. Additionally, the external system 1005 can send information to or receive information from the implantable medical device 1002 or the wearable medical device 1003 via the communication link 1011. Examples of information can include real-time or stored physiological data from the patient 1001, diagnostic data (such as detection of the patient's hydration status, hospitalization, response to treatment delivered to the patient 1001), or the device operating state of the implantable medical device 1002 or the wearable medical device 1003 (e.g., battery status, lead impedance, etc.). The communication link 1011 can be an inductive telemetry link, a capacitive telemetry link, or a radio-frequency (RF) telemetry link, or a wireless telemetry based on, for example, the "strong" Bluetooth or IEEE 602.11 wireless fidelity "Wi-Fi" interface standards. Other configurations and combinations of patient data source interfaces are possible.

[0077] The external system 1005 can include an external device 1006 near one or more mobile medical devices and a remote device 1008 at a relatively far location from the one or more mobile medical devices, which communicates with the external device 1006 via a communication network 1007. Examples of the external device 1006 can include a medical device programmer. Among other possible functions, the remote device 1008 can be configured to evaluate the collected patient or patient information and provide alert notifications. In an example, the remote device 1008 can include a centralized server that acts as a central hub for storing and analyzing data collected from multiple different sources. The combination of information from multiple sources can be used to make determinations and update individual patient status, or to adjust one or more alerts or determinations for one or more other patients. The server can be configured as a single, multiple, or distributed computing and processing system. The remote device 1008 can receive data from multiple patients. The data can be collected by one or more mobile medical devices other than the other data acquisition sensors or devices associated with the patient 1001. The server can include a memory device to store the data in a patient database. The server can include an alert analyzer circuit to evaluate the collected data to determine whether specific alert conditions are met. The satisfaction of the alert conditions can trigger the generation of an alert notification, such as an alert notification to be provided by one or more human-perceivable user interfaces. In some examples, the alert conditions can alternatively or additionally be evaluated by one or more mobile medical devices (such as implantable medical devices). For example, the alert notification can include a web page update, a phone call or pager, an email, an SMS, a text or "instant" message, and a message to the patient and a direct notification to emergency services and clinicians simultaneously. Other alert notifications are possible. The server can include an alert priority sorter circuit configured to prioritize the alert notifications. For example, alerts for detected medical events can be prioritized using a similarity metric between the physiological data associated with the detected medical event and the physiological data associated with historical alerts.

[0078] Additionally, the remote device 1008 may include one or more locally configured clients or remote clients securely connected to the server via the communication network 1007. Examples of clients may include personal desktop computers, laptop computers, mobile devices, or other computing devices. System users (such as clinicians or other qualified medical professionals) may use the clients to securely access the stored patient data compiled in the database in the server, and select patients and alerts and prioritize them for healthcare delivery. In addition to generating alert notifications, the remote device 1008 (including the server and interconnected clients) may also execute a follow-up program by sending a follow-up request to one or more mobile medical devices, or by sending a message or other communication to the patient 1001 (such as the patient), clinician, or authorized third party as a compliance notification.

[0079] The communication network 1007 may provide wired or wireless interconnectivity. In an example, the communication network 1007 may be based on Transmission Control Protocol / Internet Protocol (TCP / IP) network communication specifications, although other types or combinations of networking implementations are possible. Similarly, other network topologies and arrangements are possible.

[0080] One or more of the external device 1006 or the remote device 1008 may output a detected medical event to a system user (such as a patient or clinician) or to a process (such as an instance of a computer program executable in a microprocessor). In an example, the process may include the automatic generation of recommendations for antiarrhythmic therapy or recommendations for further diagnostic tests or treatments. In an example, the external device 1006 or the remote device 1008 may include a corresponding display unit for displaying physiological or functional signals, or issuing a warning, alert, emergency call, or other form of warning indicating the detection of an arrhythmia. In some examples, the external system 1005 may include an external data processor configured to analyze physiological or functional signals received by one or more mobile medical devices and confirm or reject the detection of an arrhythmia. Computationally intensive algorithms (such as machine learning algorithms) may be implemented in the external data processor for retrospectively processing data to detect arrhythmias.

[0081] Portions of one or more mobile medical devices or external systems 1005 may be implemented using hardware, software, firmware, or combinations thereof. Portions of one or more mobile medical devices or external systems 1005 may be implemented using dedicated circuitry that may be constructed or configured to perform one or more functions, or may be implemented using general-purpose circuitry that may be programmed or otherwise configured to perform one or more functions. Such general-purpose circuitry may include a microprocessor or a portion thereof, a microcontroller or a portion thereof, or programmable logic circuitry, memory circuitry, network interfaces, and various components for interconnecting these components. For example, among other things, a "comparator" may include an electronic circuit comparator that may be configured to perform a specific function of comparing two signals, or the comparator may be implemented as part of a general-purpose circuit that may be driven by code that instructs the portion of the general-purpose circuit to perform a comparison between two signals. A "sensor" may include an electronic circuit configured to receive information and provide an electronic output representative of the received information.

[0082] Treatment device 1010 may be configured to send information to or receive information from one or more mobile medical devices or external systems 1005 using communication link 1011. In an example, one or more mobile medical devices, external device 1006, or remote device 1008 may be configured to control one or more parameters of treatment device 1010. External system 1005 may allow programming of one or more mobile medical devices and may receive information about one or more signals acquired by one or more mobile medical devices, such as information that may be received via communication link 1011. External system 1005 may include a local external implantable medical device programmer. External system 1005 may include a remote patient management system that may monitor patient status or adjust one or more treatments, such as from a remote location.

[0083] Figure 11 An example method 1100 for using heart sound morphology to determine an atrial fibrillation event in a patient is shown, such as by determining an indication of either an atrial fibrillation S4 heart sound or a non-atrial fibrillation S4 heart sound for an S4 signal portion of the patient's cardiac acceleration information based on a first correlation and a second correlation respectively determined between the morphology of the S4 signal portion and an atrial fibrillation S4 template and a non-atrial fibrillation S4 template, and using the patient's cardiac electrical information and the determined indication for the S4 signal portion to determine the atrial fibrillation event in the patient.

[0084] At 1101, physiological information of a patient can be sensed, such as by one or more sensors located within the patient, on the patient's body surface, or near the patient, such as a cardiac sensor, a heart sound sensor, or one or more other sensors described herein. For example, a cardiac sensor can be used to sense the cardiac electrical information of the patient. In other examples, a heart sound sensor can be used to sense the cardiac acceleration information of the patient. The cardiac sensor and the heart sound sensor can be components of one or more (e.g., the same or different) medical devices (e.g., implantable medical devices, mobile medical devices, etc.).

[0085] At 1102, such as by the processing circuit of the cardiac sensor or one or more other medical devices or medical device components, etc., a timing metric between a first cardiac feature and a second cardiac feature can be determined. In some examples, the timing metric can include: the interval or metric between the first cardiac feature and the second cardiac feature of a first cardiac interval of the patient (e.g., the duration of a cardiac cycle or interval, QRS width, etc.), or the interval or metric between the first cardiac feature and the second cardiac feature of corresponding consecutive first cardiac intervals and second cardiac intervals of the patient. In an example, the first cardiac feature and the second cardiac feature include equivalent detected features in consecutive first cardiac intervals and second cardiac intervals, such as consecutive R waves (e.g., R-R interval, etc.) or one or more other features of the cardiac electrical signal, etc.

[0086] At 1103, such as by the processing circuit of the heart sound sensor or one or more other medical devices or medical device components, etc., an S4 signal portion can be determined. In some examples, the S4 signal portion can include a filtered signal from an S4 window of a cardiac interval. In an example, the S4 interval can be determined as a set time period within a cardiac interval relative to one or more other cardiac electrical or mechanical features, such as a set time period forward from one or more features of an R wave, a T wave, or a heart sound waveform (such as the first heart sound, the second heart sound, or the third heart sound (S1, S2, S3)), or a set time period backward from a detected S1 of a subsequent R wave or a subsequent cardiac interval. In some examples, the length of the S4 window can depend on the heart rate or one or more other factors. In an example, the timing metric of the cardiac electrical information can be the timing metric of a first cardiac interval, and the S4 signal portion can be the S4 signal portion of the same first cardiac interval.

[0087] In an example, the cardiac electrical information of the patient can be received, such as using the signal receiver circuit of a medical device, from a cardiac sensor (e.g., one or more electrodes, etc.) or a cardiac sensor circuit (e.g., including one or more amplifier or filter circuits, etc.). In an example, the received cardiac electrical information can include the timing metric between the first cardiac feature and the second cardiac feature of the patient.

[0088] In an example, cardiac acceleration information of a patient can be received from a heart sound sensor (such as an accelerometer, etc.) or a heart sound sensor circuit (such as including one or more amplifier or filter circuits, etc.) using the same or different signal receiver circuits of a medical device. In an example, the received cardiac acceleration information can include an S4 signal portion occurring between a first cardiac feature and a second cardiac feature of the patient. In some examples, additional physiological information, such as one or more of heart rate information, activity information of the patient, or body position information of the patient, can be received from one or more other sensors or sensor circuits.

[0089] At 1104, a first correlation and a second correlation of the morphology or shape of the S4 signal portion with a corresponding non - atrial fibrillation S4 template and an atrial fibrillation S4 template can be determined—such as using an evaluation circuit to determine a similarity metric between different signals. At 1105, an indication of either an atrial fibrillation S4 heart sound or a non - atrial fibrillation S4 heart sound for the S4 signal portion can be determined based on the determined first correlation and second correlation—such as using an evaluation circuit or one or more other processing circuits to determine the difference between the determined first correlation and second correlation.

[0090] At 1106, the received timing metric and the determined indication for the S4 signal portion (such as using an atrial fibrillation detection circuit) can be used to determine an atrial fibrillation event of the patient. In an example, an initial determination of atrial fibrillation can be made using only cardiac electrical information, such as based on the heart rate or the timing of consecutive cardiac cycles or intervals or the inter - beat timing between groups of cardiac cycles. The initial determination of atrial fibrillation based on cardiac electrical information can trigger the determination of the S4 signal portion of the cardiac acceleration information, the sensing of the cardiac acceleration information (such as within an S4 window of one or more cardiac intervals), or the determination of the first correlation or the second correlation, or the determination of an indication of either an atrial fibrillation S4 heart sound or a non - atrial fibrillation S4 heart sound for the S4 signal portion based on the determined first correlation and second correlation.

[0091] In some examples, the determined atrial fibrillation event can include multiple cardiac intervals, and in some examples, these cardiac intervals occur within a specific time interval (e.g., a threshold inter - beat timing or rate change or pattern, etc. within a 2 - minute time window). In an example, an indication of either an atrial fibrillation S4 heart sound or a non - atrial fibrillation S4 heart sound for the S4 signal portion can be determined based on the determined first correlation and second correlation for each of the multiple cardiac intervals.

[0092] In an example, a portion of the S4 signal that occurs over multiple cardiac intervals can be used to determine a composite S4 signal portion (e.g., combining multiple signal portions into a representative composite signal), and a first correlation between the composite S4 signal portion and a non-atrial fibrillation S4 template and a second correlation between the composite S4 signal portion and an atrial fibrillation S4 heart sound can be determined separately. Based on the determined first and second correlations, an indication of either the atrial fibrillation S4 heart sound or the non-atrial fibrillation S4 heart sound can be determined for the composite S4 signal portion.

[0093] In an example, an indication of either the atrial fibrillation S4 heart sound or the non-atrial fibrillation S4 heart sound for an S4 heart sound in an S4 signal portion can be determined based on a difference between a correlation of the S4 signal portion with a non-atrial fibrillation S4 template and a correlation of the S4 signal portion with an atrial fibrillation S4 template. In other examples, an indication of either the atrial fibrillation S4 heart sound or the non-atrial fibrillation S4 heart sound for an S4 heart sound in an S4 signal portion can be determined based on a distinction of a correlation of the S4 signal portion with an atrial fibrillation S4 template from a correlation of the S4 signal portion with a non-atrial fibrillation S4 template.

[0094] In an example, an indication of either the atrial fibrillation S4 heart sound or the non-atrial fibrillation S4 heart sound for an S4 heart sound in an S4 signal portion can additionally be determined based on one or more heart sound parameters. In an example, the heart sound parameters can include one or more of an S1 value, an S2 value, an S3 value, or an S4 value, such as an amplitude value or an energy value (e.g., an energy value in a heart sound window defined by cardiac signal characteristics, one or more other heart sounds, or a combination thereof over one or more cardiac cycles, among other things). In an example, the heart sound parameters can include information regarding multiple identical heart sound parameters or different combinations of heart sound parameters over one or more cardiac cycles or a specified time period (e.g., 1 minute, 1 hour, 1 day, 1 week, etc.). For example, the heart sound parameters can include a composite S1 parameter representative of multiple S1 parameters over a certain time period (e.g., multiple cardiac cycles, a representative time period, etc.).

[0095] In an example, the heart sound parameters can include an ensemble average of a particular heart sound on a heart sound waveform, such as disclosed in U.S. Patent No. 7,115,096 to Siejko et al. entitled “THIRD HEART SOUND ACTIVITY INDEX FOR HEART FAILURE MONITORING” and assigned herewith, or in U.S. Patent No. 7,853,327 to Patangay et al. entitled “HEART SOUND TRACKING SYSTEM AND METHOD” and assigned herewith, each of which is incorporated herein by reference in its entirety, including their disclosure of ensemble averaging acoustic signals and determining a particular heart sound of a heart sound waveform.

[0096] In an example, one or more of the following operations of a medical device, such as initial atrial fibrillation detection using cardiac electrical information, confirmed atrial fibrillation detection using the determined indication of atrial fibrillation S4 heart sound for the S4 signal portion based on the determined first and second correlations, or composite detection using cardiac electrical information and the determined indication of atrial fibrillation S4 heart sound for the S4 signal portion based on the determined first and second correlations, can transition the operation of the medical device, such as from a low-power mode to a high-power mode. In some examples, the high-power mode can be the opposite of the low-power mode and can include one or more of the following: enabling one or more additional sensors, transitioning from a low-power sensor or set of sensors to a higher-power sensor or set of sensors, triggering additional sensing from one or more additional sensors or the medical device, increasing the sensing frequency or sensing or storage resolution, increasing the amount of data to be collected, communicated (e.g., from a first medical device to a second medical device, etc.) or stored, triggering storage of current available information from a loop recorder in a long-term storage device, or increasing the storage capacity or time period of the loop recorder, or otherwise changing the device behavior to capture additional or higher-resolution physiological information or perform more processing, etc.

[0097] In contrast, the determined indication of non-atrial fibrillation S4 heart sound (such as the S4 signal template in normal sinus rhythm, etc.) can be used to reject the initial atrial fibrillation detection.

[0098] Additionally or alternatively, an event storage can be triggered, such as in response to the detected or confirmed atrial fibrillation detection. Information sensed or recorded in the high-power mode can be transferred from a short-term storage device (such as in a loop recorder) to a long-term or non-volatile memory, or in some examples, be made ready for communication to an external device separate from the medical device. In an example, the cardiac electrical or cardiac mechanical information that led to the detected atrial fibrillation event can be stored, and in some examples, includes the cardiac electrical or cardiac mechanical information of the detected atrial fibrillation event, such as to increase the specificity of the detection. In an example, multiple loop recorder windows (such as 2-minute windows) can be stored sequentially. In a system without early detection, to record this information, a loop recorder with a longer time period would be required, which would require a significant additional cost (such as power, processing resources, component cost, storage capacity, etc.). Storing multiple windows using such early detection before a single event can provide a complete event evaluation while saving power and cost compared to a longer loop recorder window. Additionally, early detection can trigger additional parameter calculations or storage at different resolutions or sampling frequencies without overly consuming limited system resources.

[0099] In some examples, one or more alerts may be provided, such as to a patient, a physician, or one or more other caregivers (e.g., using a patient smartwatch, cellular or smart phone, computer, etc.), such as in response to a transition to a high power mode, in response to a detected event or condition, or after updating information or transferring information from a first device to a remote device. In other examples, the medical device itself may provide an audible or tactile alert to alert the patient of the detected condition. For example, an alert may be issued to the patient in response to the detected condition such that they may perform a corrective action, such as sitting down, etc.

[0100] In some examples, treatment may be provided in response to the detected condition. For example, pacing therapy may be provided, enabled, or adjusted, such as to interrupt or reduce the effects of the detected atrial fibrillation event. In other examples, delivery of one or more drugs (e.g., vasoconstrictors, pressor drugs, etc.) may be triggered, provided, or adjusted (such as using a drug pump), either alone or in combination with pacing therapy (such as the pacing therapy described above), in response to the detected condition, such as to increase arterial pressure, maintain cardiac output, and interrupt or reduce the effects of the detected atrial fibrillation event.

[0101] Figure 12 A block diagram of an example machine 1200 is shown on which any one or more of the techniques (e.g., methods) discussed herein may be performed. Portions of the description may apply to the computing framework of one or more of the medical devices (such as wearable medical devices, external programmers, etc.) described herein. Additionally, as described herein with respect to medical device components, systems, or machines, such regulatory compliance may be required that may not be achievable by a general-purpose computer, component, or machine.

[0102] As described herein, an example can include or be operated by logic or multiple components or mechanisms in a machine 1200. A circuit system (e.g., a processing circuit system, an evaluation circuit, etc.) is a collection of circuits implemented in a tangible entity that includes hardware (e.g., simple circuits, gates, logic, etc.). Circuit system members can be flexible over time. A circuit system includes members that can perform specified operations individually or in combination when operated. In an example, the hardware of a circuit system can be immutably designed to perform a particular operation (e.g., hardwired). In an example, the hardware of a circuit system can include physically components that are variably connected (e.g., execution units, transistors, simple circuits, etc.), which include a computer-readable medium that is physically modified (e.g., magnetically, electrically, movable placement of immutably aggregated particles, etc.) to encode instructions for a particular operation. When connecting the physical components, the underlying electrical properties of the hardware composition change, such as from an insulator to a conductor, or vice versa. The instructions enable the embedded hardware (e.g., an execution unit or a loading mechanism) to create members of the circuit system in the hardware via variable connections to perform portions of a particular operation when operated. Thus, in an example, the computer-readable medium element is part of the circuit system or communicatively coupled to other components of the circuit system when the device is operated. In an example, any of the physical components can be used in more than one member of more than one circuit system. For example, in operation, an execution unit can be used in a first circuit of a first circuit system at one point in time and reused by a second circuit in the first circuit system or a third circuit in a second circuit system at a different time. The following are additional examples of these components with respect to the machine 1200.

[0103] In an alternative embodiment, the machine 1200 can operate as a stand-alone device or can be connected (e.g., networked) to other machines. In a networked deployment, the machine 1200 can operate as a server machine, a client machine, or both, in a server-client network environment. In an example, the machine 1200 can act as a peer machine in a peer-to-peer (P2P) (or other distributed) network environment. The machine 1200 can be a personal computer (PC), a tablet PC, a set-top box (STB), a personal digital assistant (PDA), a mobile phone, a network appliance, a network router, a switch or bridge, or any machine capable of executing instructions (sequentially or otherwise) that specify actions to be taken by that machine. Moreover, although only a single machine is shown, the term "machine" shall also be taken to include any collection of such machines that individually or jointly execute a set of one (or more) instructions to perform any one or more of the methods discussed herein, such as cloud computing, software as a service (SaaS), other computer cluster configurations.

[0104] A machine (e.g., a computer system) 1200 may include a hardware processor 1202 (e.g., a central processing unit (CPU), a graphics processing unit (GPU), a hardware processor core, or any combination thereof), a main memory 1204, a static memory 1206 (e.g., a memory or storage device for firmware, microcode, basic input / output (BIOS), unified extensible firmware interface (UEFI), etc.), and a mass storage device 1208 (e.g., a hard disk drive, a tape drive, a flash storage device, or other block device), some or all of which may communicate with each other via an interconnect link 1230 (e.g., a bus). The machine 1200 may also include a display unit 1210, an input device 1212 (e.g., a keyboard), and a user interface (UI) navigation device 1214 (e.g., a mouse). In an example, the display unit 1210, the input device 1212, and the UI navigation device 1214 may be a touchscreen display. The machine 1200 may also additionally include a signal generation device 1218 (e.g., a speaker), a network interface device 1220; and one or more sensors 1216, such as a global positioning system (GPS) sensor, a compass, an accelerometer, or one or more other sensors. The machine 1200 may include an output controller 1228, such as a serial connection (e.g., a universal serial bus (USB)), a parallel connection, or other wired or wireless (e.g., infrared (IR), near field communication (NFC), etc.) connection, to communicate with or control one or more peripheral devices (e.g., a printer, a card reader, etc.).

[0105] Registers of the hardware processor 1202, the main memory 1204, the static memory 1206, or the mass storage device 1208 may be or include a machine-readable medium 1222, on which one or more sets of data structures or instructions 1224 (e.g., software) are stored, which data structures or instructions embody any one or more of the techniques or functions described herein or are utilized thereby. The instructions 1224 may also reside, completely or at least partially, within any one of the registers of the hardware processor 1202, the main memory 1204, the static memory 1206, or the mass storage device 1208 during execution thereof by the machine 1200. In an example, the hardware processor 1202, the main memory 1204, the static memory 1206, or any combination of the mass storage device 1208 may constitute a machine-readable medium. Although the machine-readable medium 1222 is shown as a single medium, the term "machine-readable medium" may include a single medium or multiple media (e.g., a centralized database or a distributed database, and / or associated caches and servers) configured to store one or more instructions 1224.

[0106] The term "machine-readable medium" can include any medium that can store, encode, or carry instructions for execution by machine 1200 and cause machine 1200 to execute any one or more of the techniques in this disclosure, or can store, encode, or carry data structures used by or associated with such instructions. Non-limiting examples of machine-readable media can include solid-state memory, optical media, magnetic media, and signals (such as radio frequency signals, other photon-based signals, sound signals, etc.). In an example, a non-transitory machine-readable medium includes a machine-readable medium having a plurality of particles that have invariant (e.g., rest) mass and are thus a composition of matter. Thus, a non-transitory machine-readable medium is a machine-readable medium that does not include transitory propagated signals. Specific examples of non-transitory machine-readable media can include non-volatile memory, such as semiconductor memory devices (e.g., electrically programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM)), and flash memory devices; magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks.

[0107] Instruction 1224 can also be transmitted or received via a transmission medium through a communication network 1226 by a network interface device 1220 that utilizes any one of a variety of transmission protocols (e.g., Frame Relay, Internet Protocol (IP), Transmission Control Protocol (TCP), User Datagram Protocol (UDP), Hypertext Transfer Protocol (HTTP), etc.). Example communication networks can include local area networks (LANs), wide area networks (WANs), packet data networks (e.g., the Internet), mobile phone networks (e.g., cellular networks), plain old telephone (POTS) networks, and wireless data networks (e.g., the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard series, known as the IEEE 802.11 standard series, the IEEE 802.16 standard series, known as the IEEE 802.16 standard series), the IEEE 802.15.4 standard series, peer-to-peer (P2P) networks, etc. In an example, network interface device 1220 can include one or more physical jacks (e.g., Ethernet jacks, coaxial jacks, or telephone jacks) or one or more antennas to connect to communication network 1226. In an example, network interface device 1220 can include multiple antennas to perform wireless communication using at least one of single-input multiple-output (SIMO), multiple-input multiple-output (MIMO), or multiple-input single-output (MISO) techniques. The term "transmission medium" should be regarded as including any intangible medium that can store, encode, or carry instructions for execution by machine 1200, and includes digital or analog communication signals or other intangible media to facilitate the communication of such software. A transmission medium is a machine-readable medium.

[0108] Various embodiments are shown in the above figures. One or more features from one or more of these embodiments can be combined to form other embodiments. The method examples described herein can be at least partially machine or computer-implemented. Some examples can include a computer-readable medium or a machine-readable medium encoded with instructions that are operable to configure an electronic device or system to perform the methods described as above in the examples. Implementations of such methods can include code, such as microcode, assembly language code, or high-level language code, etc. Such code can include computer-readable instructions for performing various methods. The code can form part of a computer program product. Further, the code can be tangibly stored on one or more volatile or non-volatile computer-readable media during execution or at other times.

[0109] The above detailed description is intended to be illustrative and not restrictive. Accordingly, the scope of the present disclosure should be determined with reference to the appended claims together with the full scope of equivalents to which such claims are entitled under the law.

Claims

1. A medical device system, comprising: A device for receiving cardiac electrical information of a patient and cardiac acceleration information of the patient, wherein the cardiac electrical information includes a timing metric between a first cardiac feature and a second cardiac feature of the patient, and the cardiac acceleration information includes a portion of a fourth heart sound (S4) signal occurring between the first cardiac feature and the second cardiac feature of the patient; A device for determining a first correlation of the morphology of the S4 signal portion with a non-atrial fibrillation S4 template, determining a second correlation of the morphology of the S4 signal portion with an atrial fibrillation S4 template, and determining an indication of either an atrial fibrillation S4 heart sound or a non-atrial fibrillation S4 heart sound for the S4 signal portion based on the determined first correlation and second correlation; And A device for detecting an atrial fibrillation event in a patient using the received timing metric and the determined indication for the S4 heart sound portion.

2. The medical device system according to claim 1, wherein, The device for receiving includes a signal receiver circuit, wherein the device for determining includes an evaluation circuit, and wherein the device for detecting the atrial fibrillation event includes an atrial fibrillation detection circuit.

3. The medical device system according to claim 2, comprising: A cardiac sensor coupled to the signal receiver circuit, the cardiac sensor being configured to sense the cardiac electrical information of the patient; And A heart sound sensor coupled to the signal receiver circuit, the heart sound sensor being configured to sense the cardiac acceleration information of the patient.

4. The medical device system according to claim 3, comprising: An implantable medical device, the implantable medical device including the electrical sensor, the heart sound sensor, the signal receiver circuit, the evaluation circuit, and the atrial fibrillation detection circuit.

5. The medical device system according to claim 3, wherein, The cardiac sensor includes a processing circuit configured to: determine the timing metric between a first cardiac feature and a second cardiac feature of a first cardiac interval of the patient or between a first cardiac feature and a second cardiac feature of corresponding consecutive first and second cardiac intervals of the patient, and wherein the heart sound sensor includes a processing circuit configured to: determine the portion of the S4 signal in an S4 window of the cardiac acceleration information of a corresponding first cardiac interval or second cardiac interval of the patient.

6. The medical device system according to any one of claims 1 to 5, wherein, The first cardiac feature and the second cardiac feature include equivalently detected features in consecutive first and second cardiac intervals.

7. The medical device system according to claim 6, wherein, The first cardiac feature is an R wave of a first cardiac interval, and wherein the second cardiac feature is an R wave of a second cardiac interval that follows.

8. The medical device system according to any one of claims 1 to 7, wherein, The timing metric is a timing metric of a cardiac interval, and wherein the portion of the S4 signal is a portion of the S4 signal of the cardiac interval.

9. The medical device system according to any one of claims 1 to 8, wherein, The atrial fibrillation event includes a plurality of cardiac intervals, and wherein the device for determining an indication of either an atrial fibrillation S4 heart sound or a non-atrial fibrillation S4 heart sound for the S4 signal portion includes based on the determined first correlation and second correlation for each of the plurality of cardiac intervals.

10. The medical device system according to any one of claims 1 to 8, wherein, The atrial fibrillation event includes a plurality of cardiac intervals, wherein the system includes: a device for determining a composite S4 signal portion using the portions of the S4 signal occurring over the plurality of cardiac intervals, Among them, the device for determining the first correlation and the second correlation includes: a device for determining the first correlation between the composite S4 signal portion and the non-atrial fibrillation S4 template, and a device for determining the second correlation between the composite S4 signal portion and the atrial fibrillation S4 heart sound, and Among them, the device for determining an indication of one of the atrial fibrillation S4 heart sound or the non-atrial fibrillation S4 heart sound includes: a device for determining an indication of one of the atrial fibrillation S4 heart sound or the non-atrial fibrillation S4 heart sound for the composite S4 signal portion based on the determined first correlation and second correlation.

11. The medical device system according to any one of claims 1 to 8, wherein, The device for determining an indication of one of the atrial fibrillation S4 heart sound or the non-atrial fibrillation S4 heart sound for the S4 heart sound in the S4 signal portion includes: a device for determining an indication of one of the atrial fibrillation S4 heart sound or the non-atrial fibrillation S4 heart sound for the S4 heart sound in the S4 signal portion based on the difference between the correlation of the S4 signal portion and the non-atrial fibrillation S4 template and the correlation of the S4 signal portion and the atrial fibrillation S4 template.

12. The medical device system according to claim 11, wherein, The device for determining an indication of one of the atrial fibrillation S4 heart sound or the non-atrial fibrillation S4 heart sound for the S4 heart sound in the S4 signal portion includes: a device for determining an indication of one of the atrial fibrillation S4 heart sound or the non-atrial fibrillation S4 heart sound based on the difference between the correlation of the S4 signal portion and the atrial fibrillation S4 template and the correlation of the S4 signal portion and the non-atrial fibrillation S4 template.

13. A method, comprising: At a signal receiver circuit, cardiac electrical information of a patient is received, the cardiac electrical information including a timing metric between a first cardiac feature and a second cardiac feature of the patient; At a signal receiver circuit, cardiac acceleration information of the patient is received, the cardiac acceleration information including a portion of a fourth heart sound (S4) signal occurring between a first cardiac feature and a second cardiac feature of the patient; Using an evaluation circuit, determine a first correlation between the morphology of the S4 signal portion and a non-atrial fibrillation S4 template and a second correlation between the morphology of the S4 signal portion and an atrial fibrillation S4 template; Using an evaluation circuit, determine an indication of one of the atrial fibrillation S4 heart sound or the non-atrial fibrillation S4 heart sound for the S4 signal portion based on the determined first correlation and second correlation; And Using an atrial fibrillation detection circuit, use the received timing metric and the determined indication for the S4 signal portion to detect an atrial fibrillation event of the patient.

14. The method according to claim 13, comprising: Use a cardiac sensor coupled to the signal receiver circuit to sense the cardiac electrical information of the patient; And Use a heart sound sensor coupled to the signal receiver circuit to sense the cardiac acceleration information of the patient.

15. The method according to claim 14, comprising: Using a processing circuit of the cardiac sensor, determine the timing metric between a first cardiac feature and a second cardiac feature of a first cardiac interval of the patient or between a first cardiac feature and a second cardiac feature of corresponding consecutive first and second cardiac intervals of the patient; And Using the processing circuit of the heart sound sensor, determine the S4 signal portion in the S4 window of the cardiac acceleration information of the corresponding first cardiac interval or second cardiac interval of the patient.

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