Medical device and method for determining risk of cardiac event

Abstract

A medical device is configured to receive at most two cardiac electrical signals. For each of the plurality of cardiac cycles, the device may derive an at least two-dimensional T-wave loop using one or two of the at most two cardiac electrical signals. The medical device may determine a repolarization measurement representative of each T-wave loop, and determine a change in the repolarization measurement from a previously determined repolarization measurement. The apparatus may determine a measure of a change in the determined repolarization measurement.

Description

[0001] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 377,227, filed on September 27, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present disclosure generally relates to medical devices and methods for determining a measure of cardiac repolarization changes indicative of risk of a cardiac event. Background Art

[0003] Medical devices can sense electrophysiological signals from the heart, brain, nerves, muscles, or other tissues. Such devices can be implantable, wearable, or external devices that use implantable and / or surface (skin) electrodes to sense electrophysiological signals. In some cases, such devices can be configured to deliver therapy based on sensed electrophysiological signals. For example, implantable or external cardiac pacemakers, cardioverter-defibrillators, cardiac monitors, etc. sense cardiac electrical signals from the patient's heart. Medical devices can sense cardiac electrical signals from the heart chambers and deliver electrical stimulation therapy to the heart chambers using electrodes carried by medical electrical leads, which position electrodes in or on the patient's heart to promote normal heart rhythm.

[0004] During normal sinus rhythm (NSR), the heartbeat is regulated by electrical signals generated by the sinoatrial (SA) node located in the wall of the right atrium. Each depolarization signal generated by the SA node spreads in the atrium, causing depolarization and contraction of the atrium, and reaches the atrioventricular (AV) node. The AV node propagates the depolarization signal through the His bundle of the atrioventricular septum, and thereafter reaches the bundle branches and Purkinje muscle fibers of the right and left ventricles to respond, which is sometimes referred to as the "His-Purkinje system". The depolarization of atrial tissue can be observed in an electrocardiogram (ECG) as a P wave. The depolarization of ventricular tissue can be observed in an ECG as an R wave. The repolarization of the ventricular myocardium after depolarization is represented by the T wave in the cardiac electrical signal. Changes in the repolarization of the myocardium may be associated with changes in the activity of the sympathetic nervous system and have been considered to be associated with the risk of sudden cardiac death. Summary of the invention

[0005] In general, the present disclosure relates to a measure for sensing up to two cardiac electrical signals and determining a change in the repolarization of the heart for use in assessing a patient's risk of a cardiac event (such as an arrhythmia, myocardial infarction, or sudden cardiac death). The processing circuit of the medical device is configured to determine a repolarization measurement based on each of a plurality of cardiac cycles. The medical device may determine a repolarization measurement based on a T wave of a cardiac electrical signal or based on the T waves of two cardiac electrical signals. The repolarization measurement may be determined by deriving a two-dimensional or three-dimensional T wave loop from one or two cardiac electrical signals. The repolarization measurement may be determined by the processing circuit by determining a T wave vector representing the T wave loop. The processing circuit may determine the change between consecutive repolarization measurements (e.g., between consecutive T wave vectors), and determine a measure of the determined change as an indicator of the risk of a cardiac event.

[0006] In one example, the present disclosure provides a medical device comprising a processing circuit configured to receive at most two cardiac electrical signals. The processing circuit may be configured to: derive at least a two-dimensional T-wave loop for each of a plurality of cardiac cycles of a received cardiac electrical signal consisting of the at most two cardiac electrical signals; determine a repolarization measurement representing the T-wave loop; and determine a change in the repolarization measurement based on a previously determined repolarization measurement. The processing circuit may determine a measure of the determined change in the repolarization measurement and determine when the measure is greater than a risk threshold associated with a cardiac event. The medical device may include a telemetry circuit configured to send a risk notification in response to the measure being greater than the risk threshold.

[0007] In another example, the present disclosure provides a method performed by a medical device, the method comprising receiving at most two cardiac electrical signals. The method may include: for each cardiac cycle of a plurality of cardiac cycles of the received cardiac electrical signal consisting of the at most two cardiac electrical signals, deriving at least a two-dimensional T wave loop; determining a repolarization measurement representing the T wave loop; and determining a change in the repolarization measurement based on a previously determined repolarization measurement. The method may also include determining a measure of the determined change in the repolarization measurement and determining when the measure is greater than a risk threshold associated with a cardiac event. The method may also include sending a risk notification in response to the measure being greater than the risk threshold.

[0008] In yet another example, the present disclosure provides a non-transitory computer-readable medium storing a set of instructions that, when executed by a control circuit of a medical device, causes the medical device to: receive at most two cardiac electrical signals. The instructions further cause the medical device to: derive at least a two-dimensional T-wave loop for each of a plurality of cardiac cycles of the received cardiac electrical signal consisting of the at most two cardiac electrical signals; determine a repolarization measurement representing the T-wave loop; and determine a change in the repolarization measurement based on a previously determined repolarization measurement. The instructions may further cause the medical device to determine a measure of the determined change in the repolarization measurement and determine when the measure is greater than a risk threshold associated with a cardiac event. The instructions may cause the medical device to send a risk notification in response to the measure being greater than the risk threshold.

[0009] The present invention also discloses the following embodiments:

[0010] Embodiment 1. A medical device, the medical device comprising a processing circuit, the processing circuit being configured to: receive at most two cardiac electrical signals; and for each cardiac cycle of a plurality of cardiac cycles of the received cardiac electrical signals consisting of the at most two cardiac electrical signals, derive at least a two-dimensional T wave loop. The processing circuit may determine a repolarization measurement representing the T wave loop, and determine a change in the repolarization measurement based on a previously determined repolarization measurement. The processing circuit may determine a metric of the determined change in the repolarization measurement, and determine that the metric satisfies a risk threshold associated with a cardiac event. The medical device may include a telemetry circuit configured to send a risk notification in response to the metric satisfying the risk threshold.

[0011] Embodiment 2. A medical device according to embodiment 1, wherein the processing circuit is further configured to derive at least two dimensions of the T-wave loop from the first cardiac electrical signal of the at most two cardiac electrical signals by determining a first coordinate in the first dimension and a second coordinate in the second dimension for each of the multiple points of the T-wave loop by the following steps: determining the first coordinate as a first amplitude of a first sampling point of the first cardiac electrical signal; and determining the second coordinate as a second amplitude of a second sampling point of the first cardiac electrical signal, the second sampling point being offset from the first sampling point by a first time interval.

[0012] Embodiment 3. A medical device according to embodiment 2, wherein the processing circuit is further configured to derive the three-dimensional T wave loop from the first cardiac electrical signal by determining a third coordinate of each of the multiple points of the T wave loop in the third dimension as a third amplitude of a third sampling point of the first cardiac electrical signal, and the third sampling point is offset from the first sampling point by a second time interval.

[0013] Embodiment 4. The medical device of embodiment 3, wherein the processing circuit is further configured to determine the third amplitude of the third sampling point offset from the first sampling point by the second time interval, wherein the second time interval is different from the first time interval.

[0014] Embodiment 5. A medical device according to embodiment 2, wherein the processing circuit is further configured to derive the three-dimensional T-wave loop from the first cardiac electrical signal and the second cardiac electrical signal of the at most two cardiac electrical signals by determining the third coordinate of each point of the multiple points of the T-wave loop in the third dimension as the third amplitude of the third sampling point of the second cardiac electrical signal.

[0015] Embodiment 6. The medical device according to embodiment 5, wherein the processing circuit is further configured to identify the third sampling point of the second cardiac electrical signal at a common sampling time as one of the first sampling point of the first cardiac electrical signal or the second sampling point of the first cardiac electrical signal.

[0016] Example 7. A medical device according to Example 1, wherein the processing circuit is further configured to derive at least two dimensions of the T-wave loop from the first cardiac electrical signal and the second cardiac electrical signal of the at most two cardiac electrical signals by determining a first coordinate in the first dimension and a second coordinate in the second dimension for each of the multiple points of the T-wave loop by the following steps: determining the first coordinate as a first amplitude of a first sampling point of the first cardiac electrical signal; and determining the second coordinate as a second amplitude of a second sampling point of the second cardiac electrical signal.

[0017] Example 8. A medical device according to Example 7, wherein the processing circuit is further configured to determine a third coordinate of each of the multiple points of the T wave loop by determining a third amplitude based on a combination of the first amplitude and the second amplitude, and derive the three-dimensional T wave loop from the first cardiac electrical signal and the second cardiac electrical signal of the at most two cardiac electrical signals.

[0018] Embodiment 9. The medical device according to any one of embodiments 1 to 8, wherein the processing circuit is further configured to determine the repolarization measurement by determining the at least two-dimensional T wave vector based on the T wave loop.

[0019] Embodiment 10. The medical device of Embodiment 9, wherein the processing circuit is further configured to determine the change in the repolarization measurement by determining an angle between the T wave vector and a previously determined T wave vector.

[0020] Example 11. A medical device according to Example 9, wherein the processing circuit is further configured to: determine the angle between the T wave vector and the axis of the at least two-dimensional coordinate system corresponding to the T wave loop; and determine the change in the repolarization measurement by determining the difference between the angle and a previously determined angle, the previously determined angle being the angle between the previously determined T wave vector and the axis of the coordinate system.

[0021] Embodiment 12. A medical device according to any one of embodiments 1 to 8, wherein the processing circuit is further configured to determine the repolarization measurement by determining at least one of: the area of ​​the T wave loop; the area of ​​a two-dimensional projection of the T wave loop; the distance from a first point of the T wave loop to a second point of the T wave loop; the distance from the origin of the at least two-dimensional coordinate system corresponding to the T wave loop to the farthest point of the T wave loop; the center of mass of the T wave loop; or the length of the perimeter of the T wave loop.

[0022] Embodiment 13. The medical device of any one of Embodiments 1 to 12, wherein the processing circuit is further configured to determine the metric by spectral analysis of the frequency of the change in the repolarization measurement over time.

[0023] Embodiment 14. The medical device of any one of Embodiments 1 to 12, wherein the processing circuit is further configured to determine the metric by amplitude analysis of the change in the repolarization measurement over time.

[0024] Embodiment 15. The medical device of any one of Embodiments 1 to 14, further comprising a therapy delivery circuit configured to deliver or adjust cardiac electrical stimulation therapy in response to the metric satisfying the risk threshold.

[0025] Embodiment 16. A medical device according to any one of Embodiments 1 to 15, wherein the processing circuit is further configured to receive a first cardiac electrical signal of the at most two cardiac electrical signals from a first sensing electrode vector in a horizontal plane of the patient.

[0026] Embodiment 17. The medical device according to Embodiment 17, wherein the processing circuit is further configured to receive a second cardiac electrical signal of the at most two cardiac electrical signals from a second sensing electrode vector orthogonal to the first sensing electrode vector.

[0027] Embodiment 18. A method performed by a medical device, the method comprising:

[0028] Receiving at most two cardiac electrical signals by processing circuitry of the medical device; and for each cardiac cycle of a plurality of cardiac cycles of the received cardiac electrical signals consisting of the at most two cardiac electrical signals, deriving at least a two-dimensional T wave loop; determining a repolarization measurement representing the T wave loop; and determining a change in the repolarization measurement based on a previously determined repolarization measurement. The method also includes: determining a metric of the determined change in the repolarization measurement; determining that the metric satisfies a risk threshold associated with a cardiac event; and sending a risk notification in response to the metric satisfying the risk threshold.

[0029] Example 19. According to the method described in Example 18, the method also includes deriving at least two dimensions of the T wave loop from the first cardiac electrical signal of the at most two cardiac electrical signals by determining a first coordinate in the first dimension and a second coordinate in the second dimension for each of the multiple points of the T wave loop through the following steps: determining the first coordinate as a first amplitude of a first sampling point of the first cardiac electrical signal; and determining the second coordinate as a second amplitude of a second sampling point of the first cardiac electrical signal, the second sampling point being offset from the first sampling point by a first time interval.

[0030] Example 20. According to the method described in Example 19, the method also includes deriving the three-dimensional T wave loop from the first cardiac electrical signal by determining the third coordinate of each point of the multiple points of the T wave loop in the third dimension as the third amplitude of the third sampling point of the first cardiac electrical signal, and the third sampling point is offset from the first sampling point by a second time interval.

[0031] Embodiment 21. The method according to embodiment 20 further comprises determining the third amplitude of the third sampling point offset from the first sampling point by the second time interval, wherein the second time interval is different from the first time interval.

[0032] Example 22. According to the method described in Example 19, the method also includes deriving the three-dimensional T wave loop from the first cardiac electrical signal and the second cardiac electrical signal of the at most two cardiac electrical signals by determining the third coordinate of each point of the multiple points of the T wave loop in the third dimension as the third amplitude of the third sampling point of the second cardiac electrical signal.

[0033] Embodiment 23. The method according to embodiment 22 further comprises identifying the third sampling point of the second cardiac electrical signal at a common sampling time as one of the first sampling point of the first cardiac electrical signal or the second sampling point of the first cardiac electrical signal.

[0034] Example 24. According to the method described in Example 18, the method also includes deriving at least two dimensions of the T wave loop from the first cardiac electrical signal and the second cardiac electrical signal of the at most two cardiac electrical signals by determining the first coordinate of each of the multiple points of the T wave loop in the first dimension and the second coordinate of the second dimension through the following steps: determining the first coordinate as the first amplitude of the first sampling point of the first cardiac electrical signal; and determining the second coordinate as the second amplitude of the second sampling point of the second cardiac electrical signal.

[0035] Example 25. A method according to Example 24, wherein the processing circuit is further configured to determine a third coordinate of each of the multiple points of the T wave loop by determining a third amplitude based on a combination of the first amplitude and the second amplitude, and derive the three-dimensional T wave loop from the first cardiac electrical signal and the second cardiac electrical signal of the at most two cardiac electrical signals.

[0036] Embodiment 26. According to any one of the methods of embodiments 18 to 25, the method also includes determining the repolarization measurement by determining the at least two-dimensional T wave vector based on the T wave loop.

[0037] Embodiment 27. The method according to embodiment 26 also includes determining the change in the repolarization measurement by determining the angle between the T wave vector and a previously determined T wave vector.

[0038] Example 28. According to the method described in Example 26, the method also includes: determining the angle between the T wave vector and the axis of the at least two-dimensional coordinate system corresponding to the T wave loop; and determining the change in the repolarization measurement by determining the difference between the angle and a previously determined angle, wherein the previously determined angle is the angle between the previously determined T wave vector and the axis of the coordinate system.

[0039] Embodiment 29. According to the method described in any one of embodiments 18 to 25, the method also includes determining the repolarization measurement by determining at least one of the following: the area of ​​the T wave loop; the area of ​​the two-dimensional projection of the T wave loop; the distance from the first point of the T wave loop to the second point of the T wave loop; the distance from the origin of the at least two-dimensional coordinate system corresponding to the T wave loop to the farthest point of the T wave loop; the center of mass of the T wave loop; or the length of the perimeter of the T wave loop.

[0040] Embodiment 30. The method of any one of embodiments 18 to 29, further comprising determining the metric by spectral analysis of the frequency of the change in the repolarization measurement over time.

[0041] Embodiment 31. The method of any one of embodiments 18 to 29, further comprising determining the metric by amplitude analysis of the change in the repolarization measurement over time.

[0042] Example 32. A method according to any one of Examples 18 to 31, further comprising delivering or adjusting cardiac electrical stimulation therapy in response to the metric satisfying the risk threshold.

[0043] Embodiment 33. A method according to any one of Embodiments 18 to 32, the method further comprising receiving a first cardiac electrical signal of the at most two cardiac electrical signals from a first sensing electrode vector in a horizontal plane of the patient.

[0044] Embodiment 34. The method according to Embodiment 33 further comprises receiving a second cardiac electrical signal of the at most two cardiac electrical signals from a second sensing electrode vector orthogonal to the first sensing electrode vector.

[0045] Embodiment 35. A non-transitory computer readable medium storing a set of instructions that, when executed by control circuitry of a medical device, causes the medical device to:

[0046] Receive up to two cardiac electrical signals; and for each cardiac cycle of a plurality of cardiac electrical signals received consisting of the up to two cardiac electrical signals: derive a T wave loop of at least two dimensions; determine a repolarization measurement representing the T wave loop; and determine a change in the repolarization measurement based on a previously determined repolarization measurement. The instructions may further cause the medical device to: determine a metric of the determined change in the repolarization measurement; determine that the metric satisfies a risk threshold associated with a cardiac event; and send a risk notification in response to the metric satisfying the risk threshold.

[0047] The present disclosure is intended to provide an overview of the subject matter described in the present disclosure. It is not intended to provide an exclusive or exhaustive explanation of the devices and methods described in detail in the following figures and descriptions. Further details of one or more examples are set forth in the following figures and descriptions. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1A and Figure 1B is a conceptual diagram of one example of a medical device system that may be configured to sense cardiac electrical signals and determine a measure of changes in repolarization of the myocardium for use in assessing the risk of a cardiac event in accordance with the techniques disclosed herein.

[0049] FIG. 2A to FIG. 2C Is implanted in Figure 1A to Figure 1B Conceptual illustration of a patient with a medical device system arranged in different implant configurations is shown.

[0050] Figure 3 is a conceptual diagram of another example of a medical device system that may be configured to perform the techniques disclosed herein.

[0051] Figure 4 is a conceptual diagram of one example of a leadless medical device that may be configured to sense at least one cardiac electrical signal and determine a measure of repolarization changes in accordance with the techniques disclosed herein.

[0052] Figure 5A and Figure 5B is a conceptual diagram of other examples of leadless medical devices that may be configured to sense at least one cardiac electrical signal and determine a measure of repolarization changes in accordance with the techniques disclosed herein.

[0053] Figure 6 is a conceptual diagram of a medical device configured to perform the techniques disclosed herein, according to some examples.

[0054] Figure 7 is a flow chart of a method performed by a medical device for determining a measure of cardiac repolarization variation to predict risk of a cardiac event, such as sudden cardiac death.

[0055] Figure 8 is a flow chart of a method for deriving a repolarization measurement from a single cardiac electrical signal received by processing circuitry of a medical device or computing device.

[0056] Fig.9A is a diagram of a T wave that may be sensed during a T wave window.

[0057] Fig. 9B is a diagram of a T wave loop that may be generated by processing circuitry from a single cardiac electrical signal.

[0058] Fig.10 is an illustrative graph of determined measured changes in repolarization (ΔRM) that may be accumulated in a memory of a medical device over a specified period of time or a number of cardiac cycles.

[0059] Fig.11 is an illustration of an example 3D T-wave loop that can be generated from a single cardiac electrical signal.

[0060] Fig.12 is a diagram of two T wave vectors, each T wave vector representing a T wave loop determined from a single cardiac cycle, which may be determined by processing circuitry of a medical device according to some examples.

[0061] Fig.13 is a flow chart of a method for determining a measure of repolarization variation to predict risk of a cardiac event according to another example.

[0062] Fig.14is a diagram of two cardiac electrical signals that may be received by medical device processing circuitry for use in determining measures of T wave looping and repolarization changes. DETAILED DESCRIPTION

[0063] In general, the present disclosure describes medical devices and techniques for determining a metric indicating a patient's risk of a serious cardiac event, such as a tachyarrhythmia or sudden cardiac death. In various examples, a medical device that performs the techniques disclosed herein includes a processing circuit for receiving up to two cardiac electrical signals and determining a repolarization measurement based on T waves of multiple cardiac cycles of one received cardiac electrical signal or two received cardiac electrical signals. In the various examples described herein, the repolarization measurement can be determined by the processing circuit by deriving a two-dimensional (2D) or three-dimensional (3D) T wave loop from the cardiac electrical signal received during the T wave window and determining a repolarization measurement representing the T wave loop. Changes in the repolarization measurement can be quantified by determining a metric indicating a patient's risk of a serious cardiac event based on changes over time.

[0064] Medical devices and techniques disclosed herein provide various improvements to medical devices configured to predict cardiac events or identify patients at risk of serious cardiac events to enable early or preventive treatment to prevent or reduce the severity of the event. The techniques disclosed herein improve the functionality of a medical device in providing an indication of the risk of a cardiac event by reducing the number of cardiac electrical signals required to determine a metric of changes in repolarization of the myocardium that are indicative of the risk of a cardiac event. By reducing the number of cardiac electrical signals required to determine a metric, the processing time and power required to determine the metric can be reduced, thereby allowing the techniques for assessing patient risk to be implemented in various medical devices or computing devices configured to sense or receive at least one cardiac electrical signal.

[0065] Therefore, the technology disclosed herein provides improvements in the computer-related fields of cardiac monitoring and cardiac therapy delivery. By providing a medical device system capable of determining a measure of repolarization changes according to the technology herein, the complexity and possibility of human error in identifying patients who may benefit from various treatments (e.g., pharmacology and / or implantable medical devices such as pacemakers or implantable cardioverter-defibrillators) can be reduced. Life-saving treatment can be provided for patients who can be identified as having a risk of cardiac events. The technology disclosed herein can reduce the time burden and expertise required by clinicians when interpreting cardiac electrical signals to identify patients at risk of serious cardiac events. When risks are identified in a simplified, flexible and patient-specific manner with a relatively high degree of confidence, the technology disclosed herein can enable risk notifications to be sent or displayed by a medical device and / or can deliver therapy to reduce the possibility of cardiac events or prevent cardiac events.

[0066] Figure 1A and Figure 1B is a conceptual diagram of one example of a medical device system 10 that may be configured to sense cardiac electrical signals and determine a measure of changes in repolarization of the myocardium for use in assessing the risk of a cardiac event in accordance with the techniques disclosed herein. Figure 1A is a front view of medical system 10 implanted in patient 12. Figure 1B 1 is a side view of a medical device system 10 implanted in a patient 12. The medical device system 10 includes an implantable medical device (IMD) 14 connected to at least one medical lead 16. When the IMD 14 is capable of delivering electrical stimulation therapy (such as cardiac pacing, CV / DF shock, or neural stimulation therapy), the medical lead 16 can be used to sense at least one cardiac electrical signal and can be used to deliver the electrical stimulation therapy. For purposes of illustration, Figure 1A and Figure 1B IMD 14 is described in the context of an implantable cardioverter-defibrillator (ICD) capable of providing high-voltage CV / DF shocks and / or cardiac pacing pulses in response to detection of an arrhythmia based on processing of sensed cardiac electrical signals.

[0067] However, the technology disclosed herein for determining a measure of changes in the repolarization of the myocardium may be implemented in a cardiac monitoring device that does not necessarily include a therapy delivery capability. In other examples, the technology disclosed herein may be implemented in a device capable of delivering one or more therapies other than cardiac electrical stimulation therapy (such as neural stimulation therapy and / or drug delivery). For example, the technology disclosed herein may be implemented in a medical device configured to deliver neural stimulation to the vagus nerve or another nervous system site to change the autonomic nerve tone. The technology disclosed herein may be implemented in a medical device including a drug pump that is configured to deliver a pharmacological agent that can reduce the likelihood of myocardial infarction, reduce the likelihood of arrhythmia, or otherwise reduce the likelihood of a serious or life-threatening cardiac event. The technology disclosed herein for sensing at least one cardiac electrical signal and determining a measure indicating the risk of a cardiac event may be implemented in a variety of medical devices, including external or implantable medical devices or computing devices, including handheld or wearable devices, such as fitness trackers, tablets, smart phones, or other devices.

[0068] IMD 14 includes a housing 15 that forms an airtight seal that protects the internal components of IMD 14. Housing 15 of IMD 14 may be formed of a conductive material such as titanium or a titanium alloy. Housing 15 may act as an electrode (sometimes referred to as a "can" electrode). Housing 15 may be used as an active can electrode for delivering CV / DF shocks or other high voltage pulses delivered using a high voltage therapy circuit. In other examples, housing 15 may be used to deliver unipolar, relatively low voltage cardiac pacing pulses and / or for sensing cardiac electrical signals in conjunction with electrodes carried by lead 16. In other cases, housing 15 of IMD 14 may include a plurality of electrodes on an external portion of the housing. One or more external portions of housing 15 that act as one or more electrodes may be coated with a material such as titanium nitride, for example, to reduce post-stimulation polarization artifacts.

[0069] The IMD 14 includes a connector assembly 17 (also referred to as a connector block or header) that includes electrical feedthroughs that pass through the housing 15 to provide electrical connections between conductors extending within lead bodies 18 of leads 16 and electronic components included within the housing 15 of the IMD 14. As will be described in further detail herein, the housing 15 may house one or more processing circuits for analyzing cardiac signals and controlling IMD functions, memory, transceivers, cardiac electrical signal sensing circuitry, therapy delivery circuitry, power supplies, and / or other components for sensing cardiac electrical signals, detecting cardiac rhythms, and controlling and delivering electrical stimulation pulses to treat abnormal cardiac rhythms and / or reduce the likelihood of a serious cardiac event predicted based on a measure of repolarization changes determined according to the techniques disclosed herein.

[0070] Lead 16 includes an elongated lead body 18 having a proximal end 27 including a lead connector (not shown) configured to connect to IMD connector assembly 17 and a distal portion 25 including one or more electrodes. Figure 1A and Figure 1B In the example illustrated in , the distal portion 25 of the lead body 18 includes defibrillation electrodes 24 and 26 and pacing / sensing electrodes 28 and 30. In some cases, the defibrillation electrodes 24 and 26 may together form a defibrillation electrode because they may be configured to be activated simultaneously. Alternatively, the defibrillation electrodes 24 and 26 may form separate defibrillation electrodes, in which case each of the electrodes 24 and 26 may be independently activated.

[0071] Electrodes 24 and 26 (and in some examples, housing 15) are referred to herein as defibrillation electrodes because they are used, individually or collectively, to deliver high voltage stimulation therapy (e.g., CV / DF shock) to terminate tachyarrhythmias. Electrodes 24 and 26 may be elongated coil electrodes and typically have a relatively high surface area for delivering high voltage electrical stimulation pulses compared to pacing electrode 28 and sensing electrode 30. However, electrodes 24 and 26 and housing 15 may be used to provide pacing functionality, sensing functionality, or both pacing functionality and sensing functionality in addition to or in lieu of high voltage stimulation therapy. In this sense, the use of the term "defibrillation electrodes" herein should not be construed as limiting electrodes 24 and 26 to be used only in the delivery of high voltage CV / DF shock therapy. For example, either or both electrodes 24 and 26 may be used as sensing electrodes in a sensing electrode vector for sensing at least one cardiac electrical signal used to determine a measure of repolarization change used in assessing a patient's risk of future cardiac events.

[0072] Electrodes 28 and 30 are relatively small surface area electrodes that can be used in a sensing electrode vector for sensing cardiac electrical signals, and in some configurations can be used to deliver relatively low voltage pacing pulses. Electrodes 28 and 30 are referred to as pacing electrodes / sensing electrodes because they are typically configured for use in low voltage applications, e.g., as cathodes or anodes for delivering pacing pulses and / or sensing cardiac electrical signals, as opposed to delivering high voltage CV / DF shocks. In some cases, electrodes 28 and 30 may provide only pacing functionality, only sensing functionality, or both.

[0073] IMD 14 may obtain cardiac electrical signals corresponding to the electrical activity of heart 8 via a combination of sensing electrode vectors including a combination of electrodes 24, 26, 28, and / or 30. In some examples, housing 15 of IMD 14 is used in combination with one or more of electrodes 24, 26, 28, and / or 30 in at least one sensing electrode vector. Various sensing electrode vectors utilizing a combination of electrodes 24, 26, 28, and 30 and housing 15 are described below for sensing one or more cardiac electrical signals that may be used to acquire up to two cardiac electrical signals that may be used to determine a measure of a change in repolarization of the myocardium. Each cardiac electrical signal sensed by IMD 14 may be sensed using a different sensing electrode vector that may be selected by a sensing circuit included in IMD 14. In some examples, the cardiac electrical signals received via the selected sensing electrode vector may be used by IMD 14 to sense an R wave associated with ventricular depolarization and / or a P wave associated with atrial depolarization. The R and P waves may be referred to herein as "depolarization signals" or "cardiac depolarization signals." The sensed R and / or P waves may be used by the IMD processing circuitry to determine heart rate and determine the need for cardiac pacing, e.g., to treat bradycardia or asystole to prevent long ventricular pauses, or to determine the need for tachyarrhythmia therapy, such as antitachycardia pacing (ATP) or CV / DF shocks.

[0074] At least one cardiac electrical signal may be sensed by the IMD 14 using a sensing electrode vector selected from the available electrodes 24, 26, 28, 30 and the housing 15 to obtain a T wave signal associated with myocardial repolarization. The T wave signal (which may also be referred to herein as a "repolarization signal") may be used by the processing circuitry of the IMD 14 to determine a repolarization measurement based on each of a plurality of cardiac cycles. As described in more detail below, changes in the repolarization measurement determined based on one or at most two consecutive T waves of the ECG may be quantified for use in determining a patient's risk of a severe or life-threatening cardiac event (such as sudden cardiac death).

[0075] exist Figure 1A and Figure 1BIn the example illustrated in , electrode 28 is located proximal to defibrillation electrode 24, and electrode 30 is located between defibrillation electrodes 24 and 26. One, two or more pacing / sensing electrodes may be carried by lead body 18. For example, in some examples, a third pacing / sensing electrode may be located distal to defibrillation electrode 26. Electrodes 28 and 30 are shown as ring electrodes; however, electrodes 28 and 30 may include any of a variety of different types of electrodes, including ring electrodes, short coil electrodes, hemispherical electrodes, directional electrodes, or segmented electrodes, etc. Electrodes 28 and 30 may be positioned at other locations along lead body 18 and are not limited to the locations shown. In other examples, lead 16 may include fewer or more pacing / sensing electrodes and / or defibrillation electrodes than the examples shown here.

[0076] In the example shown, lead 16 is a non-transvenous lead that can extend from connector assembly 27 of IMD 14 toward the center of the torso of patient 12 (e.g., toward xiphoid process 20 of patient 12) in the middle of thorax 32, subcutaneously or submuscularly. At a location near xiphoid process 20, lead 16 bends or turns and extends upward, subcutaneously or submuscularly, above the thorax and / or sternum, substantially parallel to sternum 22. Although in Figure 1A 2 is shown as being laterally offset from and extending substantially parallel to the sternum 22, but the distal portion 25 of the lead 16 may be implanted in other locations, such as above the sternum 22, offset to the right or left side of the sternum 22, or angled laterally from the sternum 22 to the left or right side. Alternatively, the lead 16 may be placed along other subcutaneous or submuscular paths. The path of the lead 16 may depend on the location of the IMD 14, the arrangement and location of the electrodes carried by the lead body 18, and / or other factors. The technology disclosed herein is not necessarily limited to a particular path of the lead 16 or the final location of the electrodes 24, 26, 28 and 30. However, it should be recognized that some sensing electrode vectors for sensing up to two cardiac electrical signals used in assessing the risk of a patient having a cardiac event may provide greater confidence in predicting a cardiac event than other sensing electrode vectors. For example, T waves associated with myocardial repolarization may have greater signal strength along some sensing electrode vectors than other sensing electrode vectors, and / or periodic variations in the T wave may be more pronounced along some sensing electrode vectors than along other sensing electrode vectors.

[0077] Electrical conductors (not shown) extend from a lead connector at a proximal lead end 27 through one or more lumens of the elongated lead body 18 of lead 16 to electrodes 24, 26, 28, and 30 located along a distal portion 25 of the lead body 18. The elongated electrical conductors contained within the lead body 18 (which may be separate respective insulated conductors within the lead body 18) are each electrically coupled to respective defibrillation electrodes 24 and 26 and pacing / sensing electrodes 28 and 30. The respective conductors electrically couple the electrodes 24, 26, 28, and 30 to circuitry (such as therapy delivery circuitry and / or sensing circuitry) of the IMD 14 via connections in the connector assembly 17 (including associated electrical feedthroughs that pass through the housing 15). The electrical conductors transmit electrical stimulation pulses from therapy delivery circuitry within the IMD 14 to one or more of the defibrillation electrodes 24 and 26 and / or the pacing / sensing electrodes 28 and 30, and transmit electrical signals generated by the patient's heart 8 from the defibrillation electrodes 24 and 26 and / or the pacing / sensing electrodes 28 and 30 to sensing circuitry within the IMD 14.

[0078] The lead body 18 of the lead 16 can be formed of a non-conductive material (including silicone, polyurethane, fluoropolymer, mixtures thereof, and / or other suitable materials) and is shaped to form one or more lumens in which one or more conductors extend. The lead body 18 can be tubular or cylindrical in shape. In other examples, the distal portion 25 (or all) of the elongated lead body 18 can have a flat, ribbon-like or paddle-like shape. The lead body 18 can be formed to have a preformed distal portion 25 that is typically straight, curved, bent, serpentine, wavy or zigzag.

[0079] In the example shown, the lead body 18 includes a curved distal portion 25 having two "C"-shaped curves, which together may resemble the Greek letter epsilon "ε". The defibrillation electrodes 24 and 26 are each carried by a portion of one of the two corresponding C-shaped portions of the lead body distal portion 25. The two C-shaped curves extend or bend in the same direction away from the central axis of the lead body 18, along which the pacing / sensing electrodes 28 and 30 are positioned. In some cases, the pacing / sensing electrodes 28 and 30 may be substantially aligned with the central axis of the straight proximal portion of the lead body 18, such that the midpoints of the defibrillation electrodes 24 and 26 are laterally offset from the pacing / sensing electrodes 28 and 30.

[0080] Other examples of cardiovascular external leads may include one or more defibrillation electrodes and / or one or more pacing and sensing electrodes carried by a curved, serpentine, wavy, or zigzag distal portion of lead body 18. However, the technology disclosed herein is not limited to any particular lead body design. In other examples, lead body 18 is a flexible, elongated lead body that does not have any preformed shape, bends, or bends.

[0081] IMD 14 can be configured to analyze cardiac electrical signals received from one or more sensing electrode vectors to monitor abnormal rhythms, such as cardiac arrest, bradycardia, ventricular tachycardia (VT) or ventricular fibrillation (VF). IMD 14 can analyze the morphology of heart rate and / or cardiac electrical signals to monitor tachyarrhythmias based on tachyarrhythmia detection technology. IMD 14 can generate and deliver electrical stimulation therapy in response to detecting tachyarrhythmias (e.g., VT or VF (VT / VF)) using a therapy delivery electrode vector that can be selected from any of the available electrodes 24, 26, 28, 30 and / or housing 15. IMD 14 can deliver ATP in response to VT detection, and in some cases can deliver ATP before CV / DF shock or during charging of the high voltage capacitor to try to avoid the need to deliver CV / DF shock. If ATP does not successfully terminate VT or when VF is detected, IMD 14 may deliver one or more CV / DF shocks via one or both of defibrillation electrodes 24 and 26 and / or housing 15 .

[0082] In the absence of a sensed R wave, when asystole is detected or when a pacing escape interval expires before a ventricular event signal is sensed (e.g., when AV block is present), IMD 14 may generate and deliver a cardiac pacing pulse, such as a post-shock pacing pulse or a bradycardia pacing pulse. The cardiac pacing pulse may be delivered using a pacing electrode vector including one or more of electrodes 24, 26, 28, and 30 and housing 15 of IMD 14.

[0083] As described below, at least one sensing electrode vector may be selected for sensing cardiac electrical signals during multiple T wave windows. The cardiac electrical signals sensed during the T wave windows of multiple cardiac cycles may be received by processing circuitry of IMD 14 and analyzed to determine a metric of repolarization change that may be compared to a risk threshold. Electrodes 24, 26, 28, 30 and / or housing 15 may be selected in one or more therapy delivery electrode vectors for delivering electrical stimulation therapy to reduce the likelihood of a cardiac event associated with a risk threshold when the metric meets (e.g., exceeds) the risk threshold.

[0084] IMD 14 is shown as being implanted subcutaneously on the left side of patient 12 along thorax 32. In some cases, IMD 14 may be implanted between the left posterior axillary line and the left anterior axillary line of patient 12. However, IMD 14 may be implanted at other subcutaneous or submuscular locations in patient 12. For example, IMD 14 may be implanted in a subcutaneous pocket in the pectoralis region. In this case, lead 16 may extend from IMD 14 subcutaneously or submuscularly toward the manubrium of sternum 22 and bend or turn downward from the manubrium and extend to a desired location subcutaneously or submuscularly. In yet another example, IMD 14 may be placed in the abdomen. Lead 16 may also be implanted in other extracardiac locations. For example, as described with respect to FIG. 2A to FIG. 2C As described, the distal portion 25 of the lead 16 may be implanted beneath the sternum / thoracic cavity in the substernal space. Figure 1A and Figure 1B It is illustrative in nature and should not be construed as limiting the practice of the technology disclosed herein.

[0085] In various examples, a medical device operating according to the techniques disclosed herein may be coupled to a transvenous or non-transvenous lead for carrying electrodes for sensing cardiac electrical signals and, in some examples, delivering electrical stimulation therapy. For example, a medical device such as IMD 14 may be coupled to a cardiovascular external lead as shown in the accompanying drawings, which refers to a lead that positions electrodes outside of a patient's blood vessels, heart, and pericardium surrounding the heart. The implantable electrodes carried by the cardiovascular external lead may be positioned outside the thorax (outside the chest and sternum), subcutaneously, or under the muscle, or inside the thorax (below the chest or sternum, sometimes referred to as a sub-sternal position), and may not necessarily be in close contact with the myocardial tissue. Cardiovascular external leads may also be referred to as "non-transvenous" leads.

[0086] In other examples, the medical device may be coupled to a transvenous lead that positions the electrode within a blood vessel, which may remain in an "extracardiac" position outside the heart or be advanced to position the electrode within a cardiac chamber. For example, as an example, a transvenous medical lead may be advanced along a venous pathway to position the electrode in an extracardiac position within an internal thoracic vein (ITV), an intercostal vein, an epigastric vein, or an azygos, hemiazygos, or para-hemiazygos vein. In yet other examples, the transvenous lead may be advanced to position the electrode within the heart, for example, within a cardiac chamber of the atria and / or ventricles or within a cardiac vein.

[0087] exist Figure 1A, external device 40 is shown in telemetric communication with IMD 14 via wireless communication link 42. External device 40 may include processor 52, memory 53, display 54, user interface 56, and telemetry unit 58. Processor 52 controls external device operation and processes data and signals received from IMD 14. Display unit 54, which may include a graphical user interface, displays data and other information to a user to view IMD operation and programmed parameters as well as cardiac electrical signals retrieved from IMD 14.

[0088] User interface 56 may include a mouse, touch screen, keypad, etc. to enable a user to interact with external device 40 to initiate a telemetry session with IMD 14 to retrieve data from and / or send data to IMD 14, including programmable parameters for controlling cardiac event signal sensing, arrhythmia detection, and therapy delivery. Telemetry unit 58 includes a transceiver and antenna configured for bidirectional communication with telemetry circuitry included in IMD 14 and configured to operate in conjunction with processor 52 to send and receive data related to IMD functionality via communication link 42.

[0089] You can use A radio frequency (RF) link, such as Wi-Fi or Medical Implant Communications Service (MICS), or other RF or communications frequency bandwidth or communications protocol, establishes a communications link 42 between the IMD 14 and the external device 40. Data stored or acquired by the IMD 14, including physiological signals or associated data derived therefrom, results of device diagnostics, battery status, and a history of detected rhythm episodes and delivered therapies, etc., can be retrieved from the IMD 14 by the external device 40 following an interrogation command.

[0090] External device 40 may be embodied as a programmer used in a hospital, clinic, or physician's office to retrieve data from IMD 14 and program operating parameters and algorithms in IMD 14 to control ICD functions. External device 40 may alternatively be embodied as a home monitor or handheld device. External device 40 may be used to program cardiac signal sensing parameters, cardiac rhythm detection parameters, and therapy control parameters used by IMD 14. In some examples, external device 40 may be used to program at least some of the control parameters used in sensing cardiac event signals and detecting arrhythmias according to the techniques disclosed herein, as well as therapy delivery, into IMD 14.

[0091] As described herein, the IMD 14 may send a notification in response to determining that a measure of a change in a repolarization measurement determined from a T wave of one cardiac electrical signal or up to two cardiac electrical signals satisfies a risk threshold. The display unit 54 may display a warning or alarm in response to the external device 40 receiving the notification. The external device 40 may be used to program the risk threshold and / or other control parameters for determining the measure of the change in the repolarization measurement. Such control parameters may include a sensing electrode vector, a number of cardiac electrical signals used to determine the measure, control parameters for calculating the measure, and the like. The IMD 14 may be programmed by a clinician using the external device 40 to respond to a measure that satisfies a risk threshold by adjusting therapy. As used herein, "adjusting therapy" may refer to starting therapy, stopping therapy, and / or changing the therapy being delivered, for example, by changing the rate, dose, or other therapy control parameters.

[0092] FIG. 2A to FIG. 2C is different from Figure 1A to Figure 1B Conceptual illustration of patient 12 having medical device system 10 implanted in an implant configuration arranged as shown. Figure 2A is a front view of a patient 12 having a medical device system 10 implanted therein. Figure 2B is a side view of a patient 12 having a medical device system 10 implanted therein. Figure 2C 1 is a lateral view of a patient 12 having a medical device system 10 implanted therein. In this arrangement, the leads 16 of the system 10 are at least partially implanted beneath the sternum 22 of the patient 12. The leads 16 may extend subcutaneously or submuscularly from the IMD 14 toward the xiphoid process 20 and, at a location near the xiphoid process 20, bend or turn within the anterior mediastinum 36 in a substernal position and extend upward (see FIG. Figure 2C ).

[0093] The anterior mediastinum 36 can be considered to be bounded laterally by the pleura 39, posteriorly by the pericardium 38, and anteriorly by the sternum 22 (see Figure 2C ). The distal portion 25 of the lead 16 may extend substantially along the posterior side of the sternum 22 within the loose connective tissue and / or substernal musculature of the anterior mediastinum 36. A lead implanted so that the distal portion 25 is substantially within the anterior mediastinum 36 may be referred to as a "substernal lead."

[0094] exist FIG. 2A to FIG. 2C In the example shown, lead 16 is positioned to be substantially centered beneath sternum 22. However, in other cases, lead 16 is implanted such that it is laterally offset from the center of sternum 22. In some cases, lead 16 may extend laterally such that distal portion 25 of lead 16 is below / under thoracic cavity 32 in addition to or in lieu of sternum 22. In other examples, distal portion 25 of lead 16 may be implanted in other extracardiac intrathoracic locations, including in the pleural cavity or around the periphery of pericardium 38 of heart 8 and adjacent to the pericardium of the heart.

[0095] Figure 3 1 is a conceptual diagram of another example of a medical device system 100 that can be configured to perform the techniques disclosed herein. The medical device system 100 includes an IMD 14 coupled to transvenous leads 116, 117, and 118 for sensing cardiac electrical signals and delivering cardiac electrical stimulation therapy in each of the right atrium (RA), right ventricle (RV), and left ventricle (LV) of the heart 8. In this example, the IMD 14 can be configured as a multi-chamber pacemaker and defibrillator capable of providing cardiac resynchronization therapy (CRT). CRT includes delivering pacing pulses in the LV, RV, and / or RA to improve mechanical synchronization of the left and right ventricles with each other and / or with the atria, which can promote more efficient pumping of the heart 8. Therefore, the IMD 14 is coupled to three leads 116, 117, and 118 in this example to provide multi-chamber sensing and pacing. The IMD 14 can additionally be capable of delivering high-voltage cardioversion or defibrillation (CV / DF) shocks to treat cardiac tachyarrhythmias.

[0096] However, in other examples, the techniques disclosed herein may be implemented in single-chamber, dual-chamber, or multi-chamber cardiac pacemakers with or without CV / DF capabilities. Furthermore, it should be understood that any IMD capable of sensing cardiac electrical signals including T-wave signals accompanying ventricular myocardial repolarization may be adapted to perform the techniques disclosed herein. When coupled to multiple transvenous leads, the multi-chamber cardiac sensing and cardiac pacing therapy capabilities described for IMD 14 need not be incorporated to practice the presently disclosed techniques for monitoring T-wave signals to determine a metric of changes in repolarization measurements that indicate a patient's risk of experiencing a cardiac event.

[0097] As described above, IMD 14 may include connector assembly 17 coupled to housing 15 that encloses circuitry configured to perform IMD functions, such as in the following combination: Figure 6 A connector assembly 17, sometimes referred to as a "header," is hermetically sealed to the housing 15 and includes, in this example, three connector apertures for receiving proximal lead connectors 140, 142, and 144 of each of the respective leads 116, 117, and 118 to provide electrical communication between the electrodes carried by the distal portion of each lead and the sensing and therapy delivery circuitry enclosed by the housing 15.

[0098] Leads coupled to IMD 14 may include RA lead 116, RV lead 117, and coronary sinus (CS) lead 118. RA lead 116 may carry a distal tip electrode 120 and a ring electrode 122 proximally spaced from tip electrode 120 for sensing atrial electrical signals (e.g., P waves) and delivering RA pacing pulses. RA lead 116 may be positioned so that its distal end is located near the RA and superior vena cava, and includes an insulated electrical conductor extending from each of electrodes 120 and 122 through an elongated lead body to a proximal lead connector 140.

[0099] RV lead 117 includes pacing electrodes 128 and sensing electrodes 130, both of which are shown as tip electrodes 128 and ring electrodes 130 that are spaced proximally from tip electrodes 128. Electrodes 128 and 130 provide sensing and pacing in the RV, and each electrode is connected to a corresponding insulated conductor within the body of RV lead 117. Each insulated conductor is coupled to a proximal lead connector 142 at its proximal end. RV lead 117 is positioned so that its distal end is used in the RV to sense RV electrical signals, such as the R wave accompanying ventricular depolarization and the T wave accompanying ventricular repolarization, and to deliver pacing pulses in the RV. In some examples, IMD 14 is capable of delivering high voltage pulses for cardioversion or defibrillation of heart 8 in response to detecting a tachyarrhythmia. In this case, RV lead 117 may include defibrillation electrodes 124 and 126, both of which may be elongated coil electrodes for delivering high voltage CV / DF therapy, also referred to as "shock" or "shock pulses".

[0100] The defibrillation electrode 124 may be referred to as a "RV defibrillation electrode" or "RV coil electrode" because it is carried along the body of the RV lead 117 so that it is substantially positioned within the RV when the distal pacing electrode 128 and the sensing electrode 130 are positioned for pacing and sensing in the RV. For example, the electrode 128 may be positioned at an endocardial location at the RV apex or along the atrioventricular septum. The defibrillation electrode 126 may be referred to as a "superior vena cava (SVC) defibrillation electrode" or "SVC coil electrode" because it is carried along the body of the RV lead 117 so that it is at least partially positioned along the SVC when the distal end of the RV lead 117 is advanced within the RV. The IMD housing 15 may serve as a subcutaneous defibrillation electrode in combination with one or both of the RV coil electrode 124 and the SVC coil electrode 126 for delivering CV / DF shocks to the heart 8. Although electrodes 124 and 126 are referred to herein as defibrillation electrodes, it should be understood that electrodes 124 and 126 can be used to sense cardiac electrical signals, deliver cardiac pacing pulses, or deliver anti-tachycardia pacing (ATP) therapy, and are not necessarily limited to being used to deliver high voltage CV / DV shock pulses. In some examples, according to the techniques disclosed herein, any of electrodes 124, 126, 128, and 130 of RV lead 117 can be used to sense T wave signals for deriving T wave loops and determining a metric indicating the risk of a cardiac event. Each of electrodes 124, 126, 128, and 130 is connected to a corresponding insulated conductor extending within the body of lead 117. The proximal end of the insulated conductor is coupled to a corresponding connector (e.g., a DF-4 connector) carried by proximal lead connector 142, which is located at the proximal end of lead 117 for providing an electrical connection with IMD 14.

[0101] CS lead 118 may be advanced within the vasculature of the left side of the heart via the coronary sinus and cardiac vein (CV). CS lead 118 may include one or more electrodes for sensing cardiac electrical signals and delivering pacing pulses to the LV. CS lead 118 is shown as a quadripolar lead having four electrodes 138a, 138b, 138c, and 138d (collectively referred to as "electrodes 138"), which may be selected in various bipolar or unipolar electrode vectors for sensing cardiac electrical signals from the LV and delivering cardiac pacing pulses to the LV (e.g., during CRT delivery). Electrodes 138 are each coupled to corresponding insulated conductors within the body of CS lead 118, which provide electrical connections to proximal lead connector 144, which is coupled to IMD connector assembly 17.

[0102] According to the techniques disclosed herein, various electrodes 120, 122, 124, 126, 128, 130, 138 and housing 15 may be selected in various unipolar and / or bipolar sensing electrode vectors for sensing T wave signals to determine a measure of repolarization changes for use in assessing a patient's risk of a cardiac event. It should be appreciated that a number of sensing and electrical stimulation electrode vectors may be obtained using various electrodes carried by one or more of leads 116, 117, and 118. Alternative transvenous lead systems may be substituted Figure 3 For example, a medical device implementing the techniques disclosed herein may be coupled to one or more transvenous leads, such as leads 116, 117, and 118 and / or one or more extracardiac leads extending subcutaneously, submuscularly, or substernally.

[0103] Figure 4 is a conceptual diagram of an example of a leadless medical device that can be configured to sense at least one cardiac electrical signal and determine a measure of repolarization change according to the techniques disclosed herein. Figures 1A to 3 In the depicted example, IMD 14 is shown coupled to medical electrical leads carrying electrodes for sensing at least one cardiac electrical signal. In other examples, an IMD configured to perform the techniques disclosed herein may be a lead medical device carrying electrodes on a housing of the IMD. Figure 4 The illustrated IMD 114 includes electrodes 162 and 164 spaced apart along a housing 150 of the IMD 114 for sensing cardiac electrical signals. The IMD 114 can be configured as a leadless pacemaker configured to sense cardiac electrical signals and deliver cardiac pacing pulses from the electrodes 162 and 164. The IMD 114 can be configured to be implanted entirely within a cardiac chamber, such as an atrial or ventricular cardiac chamber. The housing 150 can be generally cylindrical to facilitate delivery via a delivery device, such as a transvenous catheter.

[0104] Electrode 164 is shown as a tip electrode extending from distal end 102 of IMD 114, and electrode 162 is shown as a ring electrode along a mid-portion of housing 150 (e.g., adjacent proximal end 104). Distal end 102 is referred to as "distal" because it is intended to be the leading end when IMD 114 is advanced through a delivery tool (such as a catheter) and placed against a target pacing site.

[0105] Electrodes 162 and 164 form an anode and cathode pair for bipolar cardiac pacing and sensing. In other examples, IMD 114 may include two or more ring electrodes, two tip electrodes, and / or other types of electrodes exposed along housing 150 for delivering electrical stimulation to the patient's heart and sensing at least one cardiac electrical signal. Tip electrode 164 is shown as a relatively flat button electrode. In other examples, tip electrode 164 may be a tissue piercing electrode having a spiral or straight axis configured to be advanced into cardiac tissue, for example. Electrode 164 may be positioned against or operably adjacent to the ventricular myocardium for sensing ventricular electrical signals including a T wave signal for determining a measure of repolarization changes. In other examples, tip electrode 164 may be a tissue piercing electrode that may be advanced into cardiac tissue near the ventricular conduction system to deliver conduction system pacing. Electrodes 162 and 164 may be, but are not limited to, titanium, platinum, iridium, or alloys thereof, and may include a low polarization coating such as titanium nitride, iridium oxide, ruthenium oxide, platinum black, and the like. Electrodes 162 and 164 may be positioned at locations along IMD 114 other than those shown.

[0106] Housing 150 is formed of a biocompatible material such as stainless steel or a titanium alloy. In some examples, housing 150 may include an insulating coating. Examples of insulating coatings include polyparaxylene, urethane, PEEK, or polyimide, etc. The entire housing 150 may be insulated, but only electrodes 162 and 164 are non-insulated. Electrode 164 may act as a cathode electrode and be coupled to an internal circuit encapsulated by housing 150, such as a pacing pulse generator and a cardiac electrical signal sensing circuit, via an electrical feedthrough across housing 150. Electrode 162 may be formed as a portion of housing 150 as defined by the present invention. Figure 4 164 is a conductive portion of a ring electrode generally shown in FIG. 16A that is electrically isolated from the rest of the housing 150. In other examples, instead of providing a localized ring electrode, such as anode electrode 162, the entire perimeter of the housing 150 may serve as an electrode that is electrically isolated from the tip electrode 164. Electrode 162 formed along the conductive portion of the housing 150 serves as a return anode during pacing and sensing.

[0107] Housing 150 includes a control electronics subassembly 152 that houses electronics for sensing cardiac signals, generating pacing pulses, and controlling therapy delivery and other functions of IMD 114 as described herein. Housing 150 also includes a battery subassembly 160 that provides power to control electronics subassembly 152. Battery subassembly 160 may include one or more rechargeable or non-rechargeable batteries.

[0108] The IMD 114 may include a set of fixation forks 166 to fix the IMD 114 to the patient tissue, for example, by actively engaging the ventricular endocardium and / or interacting with the ventricular trabeculae. The fixation forks 166 are configured to anchor the IMD 114 to position the electrodes 164 operably close to the target tissue for sensing cardiac electrical signals and delivering therapeutic electrical stimulation pulses. Various types of active and / or passive fixation members may be used to anchor or stabilize the pacemaker 14 in an implantation position. The IMD 114 may optionally include a delivery tool interface 158. The delivery tool interface 158 may be positioned at the proximal end 104 of the IMD 114 and is configured to be connected to a delivery device, such as a catheter, for positioning the IMD 114 at the implantation position (e.g., within a heart chamber) during an implantation procedure.

[0109] Figure 5A and Figure 5B is a conceptual diagram of other examples of leadless medical devices that may be configured to sense at least one cardiac electrical signal and determine a measure of repolarization changes in accordance with the techniques disclosed herein. Figure 5A is a conceptual diagram of a sensing device 180. The sensing device 180 may be a cardiac monitoring device configured to sense at least one cardiac electrical signal that may be used to determine a measure of changes in repolarization of the myocardium to assess a patient's risk of a cardiac event. The sensing device 180 includes a housing 182 that forms an airtight seal to protect components within the sensing device 180. The housing 182 may be formed of a conductive material, such as stainless steel or a titanium alloy or other biocompatible conductive material or a combination of conductive and non-conductive materials. The housing 182 encloses one or more components that may include one or more processors, memory, a transceiver, and a sensing circuit.

[0110] The head 184 is coupled to the housing 182 for carrying the electrode 186 and insulating the electrical connection between the electrode 186 and the sensing circuit enclosed in the housing 182. The electrode 186 may be exposed on the surface of the head 184. The head 184 encloses or packages an electrical feedthrough 185, which extends from the electrode 186 across the housing 182 and electrically couples the electrode 186 to the sensing circuit enclosed by the housing 182. The second electrode 188 may be formed as a non-insulated portion of the housing 182 and serve as a ground electrode or a reference electrode. In some examples, the housing 182 may include an insulating coating. The entire housing 182 may be insulated, but only the electrode 188 is non-insulated. Examples of insulating coatings include polyparaxylene, urethane, PEEK, or polyimide, among others. In other examples, an insulating coating for the housing 182 is not provided, and the entire housing 182 may serve as the electrode 188. The electrodes 186 and 188 may be, but are not limited to, titanium, platinum, iridium, or alloys thereof. In Figure 5AIn the embodiment of the present invention, the housing 182 is generally rectangular, and the electrodes 186 and 188 are positioned near opposite ends of the housing 182. In some examples, the electrodes 186 and 188 may be positioned to be approximately cm2 to 5 cm apart for acquiring cardiac electrical signals received by the sensing circuit within the housing 182. The cardiac electrical signals may be transmitted to the processing circuit enclosed by the housing 182 for processing and analysis according to the techniques disclosed herein to determine a metric of changes in repolarization measurements that indicates the risk of a cardiac event in the patient. The sensing device may include communication or telemetry circuitry for sending a signal, for example, via a radio frequency signal, tissue conduction communication (TCC), or other communication protocol in response to determining that the metric meets a risk threshold associated with a cardiac event.

[0111] Figure 5B 1 is a conceptual diagram of an alternative example of a sensing device 180. In this example, the housing 182' can be a nonlinear, angled housing including a curve or bend 183. The housing 182' can carry three electrodes 186, 187, and 188 to provide multiple sensing electrode vectors. Electrodes 186 and 188 can be carried at or near opposite ends of the housing 182', and a third electrode 187 can be located between electrodes 186 and 188. Electrode 187 can be located at the housing bend 183 so that one sensing electrode vector between electrodes 188 and 187 is approximately horizontal (or extends in one direction) and another sensing electrode vector between electrodes 186 and 187 is approximately vertical (or extends in a second direction approximately orthogonal to the first direction). Electrodes 186, 187, and 188 can be equally spaced, for example, 2 cm to 8 cm apart (without intending to be limiting). The electrode spacing between electrodes 186, 187, and 188 can vary between examples. For example, without any limitation, electrodes 186 and 188 may be spaced apart by about 1 inch to about 6 inches. In one example, the spacing between electrodes 186 and 188 is at least about 4 centimeters and up to about 10 centimeters, with electrode 187 positioned between electrodes 186 and 188. In other examples, electrodes 186, 187, and 188 may be unequally spaced from one another, such that one sensing electrode vector between electrode 187 and one of electrodes 188 or 186 has a greater inter-electrode distance than another sensing electrode vector between electrode 187 and another of electrodes 186 and 188.

[0112] Electrodes 186 and 188 may be electrically isolated from housing 182' and electrically coupled to a circuit enclosed by housing 182' via an electrical feedthrough that passes through the wall of housing 182'. Electrode 187 may be electrically coupled to housing 182' and serve as a ground electrode or return electrode coupled to a sensing circuit enclosed by housing 182'. Housing 182' may be a conductive housing with an insulating coating, wherein electrode 187 is an uninsulated exposed portion of conductive housing 182'. Angular housing 182' and electrodes 186, 187, and 188 are one example of a sensing device 180 that includes multiple sensing vectors. Other housing and electrode arrangements are envisioned that would provide multiple sensing vectors to enable processing circuitry to receive one cardiac electrical signal or two cardiac electrical signals that can be used to determine a measure of repolarization changes in the myocardium as described herein.

[0113] Figure 5B The sensing device 180 may use the sensing electrode vectors between electrodes 186 and 187 and between electrodes 188 and 187 to obtain cardiac electrical signals. In other examples, the sensing device 180 may be configured to select a sensing electrode vector to sense T waves to analyze changes in myocardial repolarization. Another electrode pair may be used for communication (e.g., sending TCC signals to / receiving TCC signals from another medical device). Figure 5A A cardiac electrical signal as shown or Figure 5B The sensing device 180 of the plurality of cardiac electrical signals shown may obtain a T wave signal that is analyzed by the sensing device 180. When it is determined based on processing and analysis of the T wave signal from one cardiac electrical signal or at most two cardiac electrical signals that the measure of the repolarization change meets the risk threshold, the sensing device 180 may send a signal that may be transmitted by another medical device (e.g., IMD 14 or external device 40 ( Figure 1A In some examples, sensing device 180 obtains T wave signals, which can be sent to another device (e.g., Figure 1A The external device 40 or IMD 14 shown is used to perform processing and analysis of T wave signals required to determine a measure of repolarization changes to assess the patient's risk of a cardiac event. The processing and analysis of up to two cardiac electrical signals according to the techniques disclosed herein can be performed collaboratively between the sensing device 180 or other cardiac monitoring device (such as the LINQ™ insertable cardiac monitor (Medtronic, Inc., Dublin, Ireland)) and processing circuitry of another implanted or external device (such as the CARELINK SMARTSYNC™ patient monitor (Medtronic, Inc., Dublin, Ireland)) or other remote or clinic-based patient monitoring system.

[0114] Figure 6 is a conceptual diagram of a medical device configured to perform the techniques disclosed herein. Figures 1A to 2C IMD 14 is used to describe Figure 6 However, it should be understood that the various components and circuits described for performing the functionality disclosed herein may be implemented in other implantable or external devices (e.g., wearable or bedside devices) configured to use up to two cardiac electrical signals to determine a measure of repolarization changes. The electronic circuitry enclosed within IMD housing 15 (in Figure 6 The IMD 14 may be coupled to leads (such as lead 16 carrying electrodes 24, 26, 28, and 30) for sensing cardiac electrical signals and delivering electrical stimulation pulses to the patient's heart. As described above, in other examples, the electrodes for receiving cardiac electrical signals may include housing-based electrodes or simply housing-based electrodes, such as Figure 4 , Figure 5A and Figure 5B shown.

[0115] IMD 14 includes control circuitry 80, memory 82, therapy delivery circuitry 84, cardiac electrical signal sensing circuitry 86, and telemetry circuitry 88. Power supply 98 provides power to the circuitry of IMD 14, including each of components 80, 82, 84, 86, and 88 as required. Power supply 98 may include one or more energy storage devices, such as one or more rechargeable or non-rechargeable batteries. Connections between power supply 98 and each of components 80, 82, 84, 86, and 88 will be from Figure 6 80 , but are not shown for clarity. For example, the power supply 98 may be coupled to one or more charging circuits included in the therapy delivery circuit 84 for charging the holding capacitors included in the therapy delivery circuit 84, which are discharged at appropriate times under the control of the control circuit 80 to generate electrical pulses according to the therapy protocol. The power supply 98 is also coupled to components of the cardiac electrical signal sensing circuit 86 as needed, such as sense amplifiers, analog-to-digital converters, switching circuits, etc.

[0116] Figure 6The circuits shown are representative of functionality included in IMD 14 and may include any discrete and / or integrated electronic circuit components that implement analog circuits and / or digital circuits capable of producing the functions attributed to IMD 14 herein. The functionality associated with one or more circuits may be performed by separate hardware components, firmware components, and / or software components, or integrated within common hardware components, firmware components, and / or software components. For example, cardiac electrical signal sensing and analysis for detecting arrhythmias may be performed collaboratively by sensing circuit 86 and control circuit 80, and may include operations implemented in other signal processing circuits included in a processor or control circuit 80 that executes instructions and control signals stored in memory 82, such as blanking intervals and timing periods and sensing threshold amplitude signals sent from control circuit 80 to sensing circuit 86.

[0117] The control circuit 80 may include hardware configured to perform subroutines of the signal processing and analysis techniques disclosed herein to reduce the processing burden associated with the firmware and / or software execution of the processing routines. For example, hardware subroutines (HSRs) may be implemented in the control circuit 80 to perform specific processing functions, such as dedicated mathematical operations, which may include any of sums, absolute values, differences, extreme values, histogram counts, signal filtering (e.g., biquad filters, differential filters, or other filters), etc. The control circuit firmware may call these HSRs when processing and analyzing cardiac signals to detect arrhythmias and / or determine T-wave loops, repolarization measurements, changes in repolarization measurements, and metrics of changes in repolarization measurements. These HSRs may offload the processing burden associated with the firmware and / or software processing to reduce the current drain of the power supply 98 and thereby extend the useful life of the IMD 14.

[0118] The various circuits of the IMD 14 may include application specific integrated circuits (ASICs), electronic circuits, (shared, dedicated, or group) processors and memories executing one or more software or firmware programs, combinational logic circuits, state machines, HSRs, or other suitable components or combinations of components that provide the described functionality. The specific form of software, hardware, and / or firmware used to implement the functionality disclosed herein will be determined primarily by the specific system architecture employed in the medical device and the specific sensing and therapy delivery methods employed by the medical device. Given the disclosure herein, it is within the capabilities of those skilled in the art to provide software, hardware, and / or firmware to implement the described functionality in the context of any modern medical device system.

[0119] Memory 82 may include any volatile, nonvolatile, magnetic, or electrically non-transitory computer-readable storage medium, such as random access memory (RAM), read-only memory (ROM), nonvolatile RAM (NVRAM), electrically erasable programmable ROM (EEPROM), flash memory, or any other memory device. In addition, memory 82 may include a non-transitory computer-readable medium storing instructions that, when executed by one or more processing circuits, cause control circuitry 80 and / or other medical device components to perform various functions attributed to IMD 14 or those IMD components. The non-transitory computer-readable medium storing instructions may include any of the media listed above.

[0120] The control circuit 80 communicates with the therapy delivery circuit 84 and the sensing circuit 86, for example, via a data bus, for sensing cardiac electrical signals, detecting cardiac rhythms, and controlling the delivery of cardiac electrical stimulation therapy in response to the sensed cardiac signals. To provide cardiac signal sensing and optional therapy delivery, the therapy delivery circuit 84 and the sensing circuit 86 are electrically coupled to the electrodes 24, 26, 28, 30 carried by the lead 16 and the housing 15, which can act as a common or ground electrode or as an active can electrode for delivering CV / DF shock pulses or cardiac pacing pulses.

[0121] The cardiac electrical signal sensing circuit 86 (also referred to herein as "sensing circuit" 86) may be selectively coupled to the electrodes 28, 30 and / or the housing 15 to monitor the electrical activity of the patient's heart. The sensing circuit 86 may additionally be selectively coupled to the defibrillation electrodes 24 and / or 26 for use in a sensing electrode vector together or in combination with one or more of the electrodes 28, 30 and / or the housing 15. In some examples, the sensing circuit 86 may be enabled to receive cardiac electrical signals from at least one sensing electrode vector selected from the available electrodes 24, 26, 28, 30 and the housing 15. In some examples, at least two, three or more cardiac electrical signals from two, three or more different sensing electrode vectors may be simultaneously received by the sensing circuit 86 for determining heart rate, detecting arrhythmias, and performing T wave analysis for cardiac event risk assessment. The sensing circuit 86 may monitor one or more cardiac electrical signals for sensing R waves associated with intrinsic ventricular myocardial depolarization, T waves associated with ventricular myocardial depolarization, and P waves associated with atrial myocardial depolarization in some examples. In some examples, sensing circuit 86 may be configured to sense two cardiac electrical signals simultaneously to provide up to two cardiac electrical signals to control circuit 80 for T wave analysis, as described below in conjunction with the accompanying flow charts and diagrams.

[0122] Thus, the sensing circuit 86 may include one or more sensing channels, which may each be selectively coupled to a sensing electrode vector via a switching circuit included in the sensing circuit 86. Each sensing channel may include dedicated and / or shared sensing channel components that are configured to amplify, filter and digitize cardiac electrical signals received from selected electrodes coupled to the corresponding sensing channel to improve the signal quality for sensing cardiac depolarization and repolarization signals (e.g., R waves and T waves). The sensing channel may include a pre-filter and amplifier circuit 83. The pre-filter and amplifier circuit 83 may include a high-pass filter to remove DC offset, such as a high-pass filter of 2.5 Hz to 5 Hz, or a wideband filter with a bandpass of 2.5 Hz to 100 Hz or narrower to remove DC offset and high-frequency noise. The pre-filter and amplifier circuit 83 may also include an amplifier to amplify the "raw" cardiac electrical signal passed to an analog-to-digital converter (ADC) 85. The ADC 85 may pass a multi-bit digital ECG signal (or an electrogram (EGM) signal when the sensing electrodes are implanted inside the heart) to the control circuit 80 for processing and analysis. The digital cardiac electrical signals received from ADC 85 may be buffered in memory 82 for subsequent processing and analysis. In some examples, segments of the digital cardiac electrical signals sensed during the T wave window are buffered for processing and analysis as described below.

[0123] The digital signal from the ADC 85 may be passed to a rectifier and amplifier circuit 87, which may include a rectifier, a bandpass filter, and an amplifier, to pass the cardiac signal to a signal detector 89. The signal detector 89 may include a sense amplifier or other detection circuit that compares the incoming rectified cardiac electrical signal to a sensing threshold (which may be an automatically adjusted threshold). For example, when the input signal crosses the R wave sensing threshold, the signal detector 89 may generate a ventricular sensing signal (Vsense) that is passed to the control circuit 80 to mark the timing of the sensed R wave. The control circuit 80 may use the Vsense signal to apply a T wave window to the incoming digitized cardiac electrical signal received from the ADC 85 to obtain a T wave for analysis as described below. In various examples, the signal detector 89 may receive the digital output of the ADC 85 for sensing R waves, P waves, and / or T waves through a comparator, morphological signal analysis of the digital signal, or other signal detection techniques. The Vsense signal passed from signal detector 89 to control circuit 80 may also be used to schedule ventricular pacing pulses delivered by therapy delivery circuit 84, determine heart rate, and detect arrhythmias. Control circuit 80 may provide sensing control signals to sensing circuit 86, such as sensing threshold adjustment parameters, sensitivity, and various blanking and refractory periods applied to the cardiac electrical signals for controlling the sensing of R waves, P waves, and / or T waves.

[0124] Control circuitry 80 may include timing circuitry configured to control various timers and / or counters used to set various intervals and windows used in sensing cardiac signals, determine time intervals between received Vsense signals, perform cardiac signal analysis, and control the timing of electrical stimulation pulses (e.g., cardiac pacing pulses and / or CV / DF shocks) generated by therapy delivery circuitry 84. The timing circuitry may initiate a timer in response to receiving a Vsense signal from sensing circuitry 86 to time the RRI between consecutive received Vsense signals, initiate a T wave window, a pacing escape interval, and / or other timing control intervals.

[0125] The control circuit 80 may include an arrhythmia detection circuit that is configured to analyze the RRI received from the timing circuit and the cardiac electrical signal received from the sensing circuit 86 to detect arrhythmias. The control circuit 80 may be configured to detect cardiac arrest, long ventricular pause, tachyarrhythmia and / or other arrhythmias based on the sensed cardiac electrical signal satisfying the corresponding cardiac arrest, long pause, tachyarrhythmia detection or other criteria. For example, when a threshold number of ventricular sensing event signals from one sensing channel 83 or 85 each occur with a sensing event interval (RRI) that is less than the tachyarrhythmia detection interval, the control circuit 80 may detect VT / VF. An RRI that is less than the tachyarrhythmia detection interval is referred to as a "tachyarrhythmia interval." In some examples, a tachyarrhythmia detection based on reaching a threshold number of tachyarrhythmia intervals (NIDs) may be confirmed or rejected based on a morphological analysis of the cardiac electrical signal.

[0126] For example, the NID for detecting VT may require the VT interval counter to reach 18 VT intervals, 24 VT intervals, 32 VT intervals, or other selected NIDs. In some examples, the VT intervals may need to be continuous intervals, such as 18 of 18, 24 of 24, or 32 of 32, or 100 of the last 100 consecutive RRIs. The NID required for detecting VF can be programmed as a threshold number of X VF intervals in Y consecutive RRIs. For example, as an example, the NID required for detecting VF can be 18 VF intervals in the last 24 consecutive RRIs, 30 VF intervals in 40 consecutive RRIs, or up to 120 VF intervals in 160 consecutive RRIs. When the VT or VF interval counter reaches the corresponding NID, the control circuit 80 can detect ventricular tachyarrhythmia. The NID is programmable and ranges from as low as 12 VF intervals to as high as 120 VF intervals without any restrictions. When VT and / or VF intervals are detected continuously or non-continuously from a specified number of recent RRIs, the VT or VF interval may reach a corresponding NID. In some cases, a combined VT / VF interval counter may count both VT and VF intervals and detect a tachyarrhythmia episode based on the fastest interval detected when the specified NID is reached.

[0127] The control circuit 80 may be configured to perform other signal analyses to determine whether other detection criteria, such as R-wave morphology criteria, onset criteria, stability criteria, and noise and oversensing rejection criteria, are met prior to detecting VT or VF based on reaching the NID. To support these additional analyses, the sensing circuit 86 may transmit digitized cardiac electrical signals to the control circuit 80 for use in detecting and distinguishing cardiac rhythms.

[0128] In some examples, the control circuit 80 may adjust the tachyarrhythmia detection algorithm or control parameters in response to the measure of the change in repolarization measurement meeting the risk threshold. When the patient is considered to be at risk of a cardiac event based on the analysis of the T wave as described herein, the control circuit 80 may turn on VT and / or VF detection, reduce NID, adjust the tachyarrhythmia threshold interval, or otherwise enable tachyarrhythmia detection to be more sensitive and / or faster. In this way, ATP and / or CV / DF shocks can be delivered immediately when the patient is expected to have a higher risk of a cardiac event (such as sudden cardiac death).

[0129] The therapy delivery circuit 84 includes at least one charging circuit 94 including one or more charge storage devices, such as one or more high voltage capacitors for generating high voltage shock pulses for treating VT / VF. The charging circuit 94 may include one or more low voltage capacitors for generating relatively low voltage pulses, such as for cardiac pacing therapy. The therapy delivery circuit 84 may include a switch circuit 95 that controls when the charge storage device is discharged across a selected pacing electrode vector or CV / DF shock vector via an output circuit 96.

[0130] In response to detecting VT / VF, the control circuit 80 may schedule therapy and control the therapy delivery circuit 84 to generate and deliver therapy, such as ATP and / or CV / DF shocks. Therapy may be generated by initiating charging of a high voltage capacitor of a charging circuit 94. Charging is controlled by the control circuit 80, which monitors the voltage on the high voltage capacitor, which is transmitted to the control circuit 80 via a charging control line. When the voltage reaches a predetermined value set by the control circuit 80, a logic signal is generated across the capacitor line and transmitted to the therapy delivery circuit 84, thereby terminating charging. The CV / DF pulses are delivered to the heart via a control bus through an output circuit 96 of the therapy delivery circuit 84 under the control of the control circuit 80. The output circuit 96 may include an output capacitor through which the charged high voltage capacitor is discharged via a switching circuit (e.g., an H-bridge) that determines the electrodes used to deliver the cardioversion or defibrillation pulse and pulse waveform. The therapy delivery circuit 84 may be configured to: receive a signal from an external device 40 ( Figure 1A ) when a programmed command is given by the device to deliver electrical stimulation pulses to induce a tachyarrhythmia (e.g., a T wave shock or an induction pulse train).

[0131] In some examples, a high voltage therapy circuit configured to deliver CV / DF shock pulses may be controlled by the control circuit 80 to deliver pacing pulses, for example, for delivering ATP, post-shock pacing pulses, bradycardia pacing pulses, or asystole pacing pulses. The therapy delivery circuit 84 may be configured to generate and deliver cardiac pacing pulses using a high voltage capacitor that is chargeable to a shock voltage amplitude by charging the high voltage capacitor to a relatively low voltage corresponding to a cardiac pacing pulse amplitude for capturing and pacing ventricular myocardium. The therapy delivery circuit 84 may include a low voltage therapy circuit that includes one or more separate or shared charging circuits, switching circuits, and output circuits for generating and delivering relatively low voltage pacing pulses for a variety of pacing needs. The therapy delivery circuit 84 may perform the following operations according to a control signal received from the control circuit 80 for delivering cardiac pacing pulses: charging the capacitor to a programmed pulse amplitude, and discharging the capacitor for a programmed pulse width. As described above, the timing circuits included in the control circuit 80 may include various timers or counters that control when cardiac pacing pulses are delivered. The microprocessor of the control circuit 80 may set the amplitude, pulse width, polarity, or other characteristics of the cardiac pacing pulses that may be based on programmed values ​​stored in the memory 82.

[0132] When the control circuit 80 determines that the measure of the repolarization measurement change meets the risk threshold based on the T wave signal analysis described below, the control circuit 80 can control the therapy delivery circuit to adjust the therapy. Ventricular pacing (e.g., high-speed pacing), CRT, or other pacing therapies can be delivered or adjusted to reduce the likelihood of a tachyarrhythmia or other life-threatening cardiac event. In other examples, depending on the therapy delivery capabilities of the medical device system that implements the technology disclosed herein, vagus nerve stimulation, drug delivery, or other therapies can be delivered. In some cases, the telemetry circuit 88 can send a signal to another implanted or external device in response to a detected repolarization measurement change to trigger therapy delivery or instruct the patient to take medication or seek medical attention.

[0133] The control parameters used by control circuit 80 to sense cardiac event signals, detect arrhythmias and control therapy delivery may be programmed into memory 82 via telemetry circuit 88. Telemetry circuit 88 includes a transceiver and antenna for communicating with external device 40 (in the case of a cellular telephone) using RF communications or other communications protocols as described above. Figure 1A ) communications. Under control of the control circuitry 80, the telemetry circuitry 88 may receive downlink telemetry from the external device 40 and send uplink telemetry to the external device. The telemetry circuitry 88 may send a notification in response to the control circuitry 80 determining that the measure of repolarization change meets a risk threshold, so as to notify the patient or clinician that medical attention or intervention may be required.

[0134] Figure 7 Flowchart 200 of a method performed by a medical device for determining a measure of cardiac repolarization variation (also referred to herein as a "measure of repolarization variation") to predict the risk of a cardiac event, such as sudden cardiac death. For purposes of illustration, the processes of flowchart 200 and other flowcharts and diagrams presented herein are described as being performed by processing circuitry included in an IMD (e.g., by control circuitry 80 of IMD 14). However, it should be understood that these techniques may be performed by processing circuitry of an external device (e.g., processor 52 of external device 40) or other computing devices or processing circuitry of multiple devices (e.g., IMD 14 and external device 40) configured to operate cooperatively to perform the methods disclosed herein.

[0135] At box 202, the control circuit 80 receives up to two cardiac electrical signals for T wave signal analysis. The cardiac electrical signals received at box 202 for T wave signal analysis may include one or two ECG signals sensed from electrodes implanted outside the heart (e.g., subcutaneously, submuscularly, or substernally). Additionally or alternatively, the cardiac electrical signals received at box 202 may include one or two EGM signals sensed from electrodes implanted in or on the patient's heart. In other examples, the processing circuit that receives the cardiac electrical signals for T wave analysis at box 202 may receive ECG signals from surface electrodes placed on the patient's body.

[0136] It should be appreciated that the processing circuitry configured to receive up to two cardiac electrical signals to perform T wave analysis and determine a measure of repolarization change may receive additional cardiac electrical signals for other medical device functions. For example, the processing circuitry configured to perform the techniques disclosed herein may receive atrial EGM signals and / or other ECG or EGM signals for sensing R waves, P waves, detecting arrhythmias, determining heart rate, etc. However, the cardiac electrical signals received by the processing circuitry (e.g., control circuitry 80) for performing T wave analysis to determine a measure of repolarization change consist of up to two cardiac electrical signals.

[0137] At least one cardiac electrical signal received at block 202 may be sensed from a sensing electrode vector in a substantially horizontal plane of the patient. A “substantially horizontal plane” may be a plane of the patient that is less than 45 degrees from a horizontal plane of the patient. For example, referring to Figure 1A , the sensing electrode vector between the pacing / sensing electrode 28 or the pacing / sensing electrode 30 and the housing 15 can be used to sense the first cardiac electrical signal. Figure 3At block 202, a first cardiac electrical signal may be received from a sensing electrode vector between any of the electrodes 124, 126, 128, or 130 carried by the RV lead 117 and any of the electrodes 138 of the CS lead 118 or the housing 15. Depending on the implantation locations of the electrodes available for sensing, when a single cardiac electrical signal is received, the sensing electrode vector may be a substantially sagittal sensing electrode vector extending substantially in the horizontal plane of the patient between a relatively more posterior electrode and a relatively more anterior electrode.

[0138] In some examples, a second cardiac electrical signal is received from a second sensing vector that may extend in a substantially frontal plane or in a substantially horizontal plane. The second sensing electrode vector may extend approximately orthogonal to the first cardiac electrical signal, for example greater than 45 degrees relative to the first sensing electrode vector. For example, when the first sensing electrode vector extends between a relatively more posterior electrode and a relatively more anterior electrode, the second cardiac electrical signal may be received from a second sensing electrode vector that is a relatively lateral sensing electrode vector extending between a relatively left electrode and a relatively right electrode in a horizontal plane of the patient. In other cases, the second cardiac electrical signal may be received from a second sensing electrode vector that extends between a relatively upper electrode and a relatively lower electrode in a substantially frontal plane of the patient. For example, with reference to Figure 1A The sensing electrode vector between the sensing electrode 28 and the CV / DF electrode 24 or the CV / DF electrode 26 can be used to sense the second cardiac electrical signal. Figure 3 , the second sensing electrode vector may extend between the tip electrode 128 and either of the CV / DF coil electrodes 124 or 126. The example sensing electrode vectors described herein are illustrative in nature and are not intended to be limiting. The sensing electrode vector used to receive one or both cardiac electrical signals at block 202 will depend on a number of factors, including the number and location of electrodes available for sensing ECG or EGM signals.

[0139] At box 204, the control circuit 80 derives a 2D or 3D T wave loop for each of the multiple cardiac cycles of one or two cardiac electrical signals received at box 202. T wave loops may be derived from multiple continuous or non-continuous cardiac cycles. As an example, the T wave loop may be derived from multiple continuous cardiac cycles within 10 seconds, 30 seconds, 1 minute, 2 minutes, 5 minutes, 10 minutes, 30 minutes, or one hour. In some examples, a T wave loop is derived for each continuous cardiac cycle during a specified number of cardiac cycles or within a specified time interval (e.g., at least one minute). In other examples, as an example, a T wave loop may be derived for every n cardiac cycles (e.g., every other cardiac cycle, every three cardiac cycles, or every four cardiac cycles). The cardiac cycle may be a non-paced cardiac cycle so that repolarization changes may be evaluated during an intrinsic cardiac rhythm. However, in some cases, the rhythm may be a paced rhythm. For example, atrial pacing may be delivered in a patient with sinus node dysfunction. In other examples, ventricular pacing may be delivered in patients with atrioventricular block or other conduction abnormalities. However, it should be recognized that changes in myocardial repolarization during pacing may differ from those during intrinsic rhythm.

[0140] In some examples, each T wave loop can be derived from a single cardiac electrical signal. Figure 8 Methods for deriving 2D or 3D T wave loops from a single cardiac electrical signal are described. In other examples, each T wave loop may be derived from a sensed cardiac electrical signal composed of two cardiac electrical signals and may be a 2D or 3D T wave loop. Fig.13 A method for deriving a 2D or 3D T wave loop from two cardiac electrical signals is described. Thus, a T wave loop can be derived in 2D or 3D for use in determining a measure of repolarization variation based on fewer than three cardiac electrical signals. In some cases, the T wave loop is derived from a cardiac signal having fewer dimensions than the T wave loop. For example, the cardiac electrical signal analyzed by the control circuit 80 may consist of two cardiac electrical signals used to derive a 3D T wave loop, or one cardiac electrical signal may be analyzed by the control circuit 80 to derive a 2D or 3D T wave loop. In some examples, two cardiac electrical signals may be used to derive a 2D T wave loop. In each of these examples, the processing circuit receives fewer than three cardiac electrical signals for the purpose of determining a measure of repolarization variation.

[0141] At box 206, the control circuit 80 may determine a repolarization measurement representing each T wave loop. As described below, the control circuit 80 may determine a T wave vector representing a T wave loop. The T wave vector may be determined based on one or two cardiac electrical signals defined by magnitude and angle in a 2D or 3D polar coordinate system. The repolarization measurement may be determined based on the T wave vector representing the T wave loop. For example, the repolarization measurement may be an angle relative to a coordinate system axis or plane that defines the position of the T wave vector in the polar coordinate system. An example of a repolarization measurement determined based on a T wave loop is described below.

[0142] At box 208, the control circuit 80 determines the change between the repolarization measurements, each repolarization measurement corresponding to a corresponding cardiac cycle. For example, the control circuit 80 may determine the change between the T wave vector and the previous T wave vector. The T wave vector may be derived in polar coordinates so that each T wave vector is defined by at least one angle. In some examples, the change between two repolarization measurements is the change between the angle of a T wave vector relative to the polar coordinate axis (in 2D) or plane (in 3D) and the angle of the previous T wave vector. In some examples, the angle of the T wave vector may be determined as a weighted angle as described below. The change between the two determined T wave vectors may be determined as the angle between a three-dimensional T wave vector derived from a first cardiac cycle of one or two cardiac electrical signals and a three-dimensional second T wave vector derived from a second cardiac cycle (before or after the first cardiac cycle) of one or two cardiac electrical signals.

[0143] The determined changes between consecutive repolarization measurements may be stored in the memory 82. When a particular number of repolarization measurements have been determined or a T wave vector has been derived for a plurality of cardiac cycles for a particular time interval, the control circuit 80 may determine a measure of repolarization change based on the repolarization measurements at box 210. The measure of repolarization change may be determined as a quantitative measure of the change in amplitude, frequency, or other component of the determined change over time. The measure may be determined in the time domain or the frequency domain. In some examples, the measure may be determined by performing a wavelet analysis of a time-based graph of the repolarization change. The measure of repolarization change may represent periodic changes that occur in the T wave loop. The periodic changes may be associated with sympathetic nerve activity and indicate a risk of a cardiac event.

[0144] At block 212, the control circuit 80 may compare the measure of the repolarization change to a risk threshold. When the measure satisfies the risk threshold (e.g., is greater than the risk threshold), the control circuit 80 may generate a notification indicating a predicted risk of a cardiac event (such as sudden cardiac death) at block 214. The telemetry circuit 88 may send the risk notification to a receiving device, which may be a personal device, a medical device programmer, a remote patient monitoring system, another implanted medical device capable of delivering therapy, etc.

[0145] Figure 8 300 is a method for deriving a repolarization measurement from a single cardiac electrical signal received by a processing circuit of a medical device or computing device. For purposes of illustration, the process of flowchart 300 is described with reference to an IMD 14 including a control circuit 80. At box 302, the control circuit 80 receives a cardiac electrical signal (e.g., an ECG or EGM signal) for processing and analysis to determine a measure of repolarization change. In some examples, the cardiac electrical signal may be received from a sensing electrode vector extending along a horizontal plane of the patient, and in some examples may be a sagittal or transverse sensing electrode vector. However, the location of the sensing electrodes used to sense a cardiac electrical signal is not limited to a particular location or orientation.

[0146] At block 304, the control circuit 80 may derive a 2D T wave loop for a corresponding cardiac cycle of the cardiac electrical signal from the received cardiac electrical signal. The two-dimensional T wave loop may be derived from the received cardiac electrical signal by determining ordered pairs from sampling points of the received cardiac electrical signal using the lag time between the x-value and the y-value in the ordered pairs.

[0147] Fig.9A 350 is a diagram of a T wave 352 that may be sensed from a cardiac electrical signal during a T wave window 354. As an example, the duration of the T wave window 354 may be 150 ms to 400 ms or the duration of the T wave window may be approximately 200 ms to 300 ms. The T wave window 354 may have a start time 356 of 200 ms to 400 ms or approximately 250 to 300 ms after a ventricular depolarization event (e.g., after a Vsense signal, the start of a QRS waveform, an R wave peak, a ventricular pacing pulse, or other reference point of a QRS waveform). In some examples, the T wave window 354 may have a start time 356 that is applied at a selected time interval after an atrial pacing pulse that may be known to be conducted to the ventricles. In other examples, the T wave 352 may be detected by the control circuit 80, for example, based on a threshold crossing, a maximum peak amplitude of the T wave 352, or other waveform morphology analysis. A T wave window 354 can be applied to a received cardiac electrical signal having a start time 356 relative to a detected T wave (e.g., relative to a threshold crossing or maximum peak amplitude or other reference point of the T wave 352). The T wave 352 can be sampled to obtain sampling points X1 to Xn over the T wave window 354 at a desired sampling rate.

[0148] Fig. 9B FIG. 3 is a diagram 360 of a T wave loop 362 that may be generated by control circuit 80 from a single cardiac electrical signal. Figure 7 , Figure 8 A and Figure 8B, at block 302, the control circuit 80 may receive a T wave signal 352 in a cardiac electrical signal sensed from a sensing electrode vector during a cardiac cycle. Figure 8 At block 304, control circuit 80 may derive 2D T wave loop 362 from T wave signal 352. In some examples, T wave loop 362 may be derived from T wave signal 352 using attractor theory.

[0149] In the example shown, the control circuit 80 can generate the T wave loop 362 by obtaining ordered (x, y) pairs from the received T wave signal 352. The x coordinate of each ordered pair can be the amplitude of the i-th point of the T wave 352, and the y coordinate can be the amplitude of the i+1-th point of the T wave 352, wherein each i-th point and i+1-th point can be separated by a selected sample time difference (e.g., 0.5ms, 1ms, 2ms, 4ms, 5ms, 8ms, 10ms, 16ms, 20ms, 32ms or other selected time sample time differences). Fig.9A As shown, the amplitude of the consecutive sampling points of the T wave 352 defines Fig. 9B Each of the X(1) to X(n-1) values ​​of the x-coordinate of the T wave loop 362 is shown. Each Y(1) to Y(n-1) amplitude corresponding to the X(n+1) to X(n) sample points of the T wave 352 defines the y-coordinate of the T wave loop 362 in each corresponding (x, y) ordered pair. Thus, each point on the T wave loop 362 can be defined by an (X(i), X(i+n ms)) ordered pair 366, where X(i) is the amplitude of the i-th sample point of the T wave 312 (defining the x-coordinate of the point on the T wave loop 362), and X(i+n ms) is the amplitude of the sample point n ms after the i-th sample point (defining the y-coordinate of the point on the T wave loop 362).

[0150] It should be understood that the cardiac electrical signals may be sampled at the same or different sensing sampling rate than the sampling rate corresponding to the time lag between T wave sampling points used to obtain (X, Y) coordinate pairs from the T wave 352 to generate the T wave loop 362. For example, a sampling rate of 128 Hz to 1024 Hz may be used to sense the cardiac electrical signals. Fig. 9BThe n ms time lag between points of the T wave loop 362 of the sensed cardiac electrical signal may be greater than, equal to, or less than the sampling time between sampling points of the sensed cardiac electrical signal. For example, if the received cardiac electrical signal is sampled at 256 Hz (with approximately 4 ms between sampling points), the T wave loop 362 may be generated using each sampling point (4 ms time lag between X and Y coordinate amplitudes), every other sampling point (8 ms time lag between X and Y coordinate amplitudes), every third sampling point (12 ms time lag between X and Y coordinate amplitudes), etc. In some examples, the X and Y coordinate amplitudes may be the sampling points of the sensed cardiac electrical signal or interpolated between the sampling points of the sensed cardiac electrical signal. For example, when the cardiac electrical signal is sampled at 256 Hz, the X and Y coordinate amplitudes of a given point on the T wave loop 362 may be spaced 2 ms apart on the T wave 352, where the amplitudes of the x and y coordinates are interpolated at 2 ms intervals between the sampling points of the T wave 352, for example, by averaging or other interpolation methods.

[0151] Reference again Figure 7 , the control circuit 80 may determine a repolarization measurement based on the T wave loop at block 308. The repolarization measurement may be a T wave loop (e.g., Fig. 9B Quantitative representation of the T wave loop 362 shown. T wave vector 372 ( Fig. 9B ) can be found in Figure 8 The control circuit 206 may determine a T wave vector 372 from the 2D T wave loop 362 as a vector extending from an origin 376 of a Cartesian coordinate system to a point 374 on the T wave loop 362 that is a maximum distance R from the origin 376. The control circuit 80 may determine the T wave vector 372 in polar coordinates, which is defined by an angle A 380 from the x-axis and has a magnitude R. In other examples, the angle A 380 may be measured relative to the y-axis rather than the x-axis. Zero degrees may be defined as being aligned with the positive x-axis, where the angle increases in a clockwise direction, as shown in the illustrated example. In other examples, zero degrees may be defined as being aligned with the negative x-axis, the positive y-axis, or the negative y-axis, where the angle increases in a clockwise or counterclockwise direction. When a cardiac electrical signal is sensed using a sensing electrode vector extending substantially horizontally in a sagittal plane, the y-axis may correspond to the sagittal plane, and the x-axis may correspond to a horizontal plane. In various examples, repolarization measurements of the cardiac cycle including the T wave 352 may be determined by the control circuit 80 and buffered in the memory 82 as an angle A 380, a magnitude R 374, and / or a product of the angle and the magnitude A*R calculated relative to the x-axis or y-axis according to any of the examples given above.

[0152] In other examples, the control circuit 80 may determine a complex polarization measurement from the T wave loop 362 by calculating a weighted angle measurement using the (X(i), X(i+nms)) points of the T wave loop 362. The control circuit 80 may convert each point of the T wave loop 362 into a polar coordinate defined by an angle "a" (e.g., an angle with the x-axis) and having a magnitude "r" in a polar coordinate system. The control circuit 80 may calculate a weighted angle measurement (WAM) by summing the product of each angle and magnitude of the T wave loop point (WAM=Σa(i)*r(i), where i=1 to n-1 when a total of n-1 points define the T wave loop 362 based on n sampling points of the T wave 352). In some examples, the WAM may be normalized by the sum of the magnitude "r" of each T wave loop point (WAM={Σa(i)*r(i)} / {Σr(i)}, where i=1 to n-1). The WAM may be buffered in memory 82 as a measure of repolarization for a given cardiac cycle.

[0153] Other examples of repolarization measurements that the control circuit 80 may calculate based on the T wave loop may include the area of ​​the T wave loop, the area of ​​the T wave loop projected in a 2D plane (when determining a 3D T wave loop), the total length of the perimeter of the T wave loop, or the center of mass of the T wave loop. One or more repolarization measurements may be determined. In some examples, a combination of repolarization measurements may be determined. A combination of multiple repolarization measurements may be determined, which may be a sum, a weighted sum, a product, a difference and / or a ratio or any other combination. In some examples, one repolarization measurement (or a combination of multiple repolarization measurements) may be normalized by another repolarization measurement (or a combination of multiple repolarization measurements) to obtain a repolarization measurement representing the T wave loop.

[0154] At box 310, the control circuit 80 may determine a change in the repolarization measurement relative to a previous repolarization measurement. The change may be a difference between the repolarization measurement and a previous repolarization measurement, such as a difference in WAM, a difference in A, a difference in R, or a difference in A*R, and the previous repolarization measurement may be the most recent previous repolarization measurement. At box 312, the control circuit 80 may determine whether another cardiac cycle can be used to determine the repolarization measurement of the next T wave. The repolarization measurement and the corresponding change relative to the previous repolarization measurement may be determined for a specified number of T waves or for all T waves occurring during a specified time period (or every other T wave, every third T wave, etc.) to evaluate the repolarization change. When multiple repolarization measurements are determined based on each T wave loop, the change in the repolarization measurement may be determined for each repolarization measurement. In some examples, the change in each repolarization measurement in the multiple repolarization measurements may be mathematically combined as a sum, ratio, product, or other combination to obtain a change in the repolarization measurement between two cardiac cycles.

[0155] When another cardiac cycle is available, the control circuit 80 may return to block 304 to determine the 2D T wave loop point coordinates of the next T wave based on the received cardiac signal. When a specified number of T waves or a specified time period of cardiac signals have been evaluated, the control circuit 80 may advance to block 314 to determine a measure of the determined change in repolarization measurement.

[0156] Fig.10 is an exemplary graph 400 of determined changes in repolarization measurements (ΔRM) that may be accumulated in memory 82 over a specified period of time or a plurality of cardiac cycles. Due to the cyclical nature of sympathetic nerve activity, the repolarization measurements may have a cyclical behavior. For patients at risk for clinically significant or life-threatening cardiac events, the changes in repolarization measurements over consecutive cardiac cycles may increase. The control circuit 80 may be configured to Figure 8 A quantitative measure of the periodic variation of the repolarization measurement is determined at block 314 of . The measure may be determined in the time domain or the frequency domain. The measure may be a representative amplitude, such as an average peak amplitude, a sum of sample points greater than a threshold, or other value determined based on the amplitude of the variation of the repolarization measurement.

[0157] In other examples, the measure of the change in repolarization may be determined as an average frequency, a center frequency, or a main frequency of the change in the repolarization measure. In some examples, a wavelet transform of a graph of the change in the repolarization measure over time may be performed by the control circuit 206, and a maximum wavelet coefficient may be determined as a measure of the change in repolarization. In other examples, an average of the phase-rectified signal may be applied to the change in the repolarization measure over time to obtain a maximum frequency or a center frequency after the phase-rectified signal is averaged. In some examples, a wavelet transform of the change in the repolarization measure over time may be performed, and the average wavelet coefficient for frequencies in a low frequency range (e.g., less than 0.5 Hz, less than 0.3 Hz, less than 0.2 Hz, or less than 0.1 Hz) may be determined as a measure at box 314.

[0158] In another example, a measure of repolarization variation may be determined by determining the variability of an average beat-to-beat difference in repolarization measures determined over a specified number of consecutive cardiac cycles. For example, the difference between two consecutive repolarization measurements may be determined for each of 3, 5, 6, 8, 10, 20, or other specified number of cardiac cycles and averaged to determine an average beat-to-beat difference. The process may be repeated for the next specified number of cardiac cycles to determine the next average beat-to-beat difference. The variability of the consecutive average beat-to-beat differences may be determined as a measure of repolarization variation. The variability of the consecutive average beat-to-beat differences may reflect high variability or confusion in repolarization that indicates risk of a cardiac event.

[0159] In yet another example, the measure of repolarization change may be determined as the maximum slope of repolarization change plotted over time, the minimum slope of repolarization change plotted over time, or the difference between the maximum slope and the minimum slope of repolarization change plotted over time. Patients with less compensatory mechanisms (vagal compensation) may have steeper transitions between repolarization measures than patients with a lower risk of a cardiac event.

[0160] exist Fig.9A , Fig. 9B and Fig.10 In the example, a two-dimensional T wave loop is determined from the cardiac electrical signal using an ordered pair of (X(i), X(i+nms)) determined from a single cardiac electrical signal. A measure of repolarization change is determined based on a measured change in repolarization in the 2D T wave loop. In other examples, a 3D T wave loop can be derived from a single cardiac electrical signal for each of a plurality of cardiac cycles. To derive the 3D T wave loop, three-dimensional Cartesian coordinates can be determined as (X(i), X(i+nms), X(i+mm ms)) to define each T wave loop point that can be plotted along the x-axis, y-axis, and z-axis of a Cartesian coordinate system. The third dimension of the Cartesian coordinate, X(i+mm ms), can be determined at mms from the X(i) point of the T wave signal (see Fig.9A ), where m may be equal to 2n (twice the time lag of point X(i) relative to point X(i+mm ms)). However, m may be any value different from or equal to n for extracting 3D Cartesian coordinates from a single cardiac electrical signal to generate a 3D T wave loop for a corresponding cardiac cycle of the single cardiac electrical signal.

[0161] Fig.11 4 is a diagram 400 of an example 3D T wave loop 402 that can be generated from a single cardiac electrical signal. Each point of the 3D T wave loop 402 can be defined by Cartesian coordinates determined from the signal cardiac electrical signal as (X(i), X(i+n ms), X(i+mms)), as described above. A repolarization measure can be determined from the T wave loop 402. The points of the T wave loop 402 can be converted to a polar coordinate system, and a repolarization measure can be determined from the T wave loop 402. In some examples, one or more points of the T wave loop can be converted to a polar coordinate system to determine a repolarization measure.

[0162] For example, a representative T-wave vector 410 may be determined. The T-wave vector 410 may be determined as a vector extending from the origin 401 to a point on the T-wave loop 402 that is the farthest away from the origin 402. A repolarization measurement may be determined from the T-wave vector 410 as an azimuth angle (AA) of the x-axis (or y-axis) relative to a projection 412 of the T-wave vector 410 in the xy plane. A repolarization measurement may be determined from the T-wave vector 410 as an elevation angle (AE) 408 between the z-axis and the T-wave vector 410 (or between the xy plane and the T-wave vector 410). The repolarization measurement can be determined as the magnitude R of the T wave vector 410, the weighted AA (AA*R), the weighted AE (AE*R), the area of ​​the T wave loop 410, the distance from the point on the T wave loop 402 closest to the origin 401 to the point on the T wave loop 402 farthest from the origin 401, or the maximum distance between any two points of the T wave loop 402 can be determined as various examples of repolarization measurements representing the T wave loop 402.

[0163] In some examples, the T wave vector 404 is determined as a unit vector defined by weighted AA (WAA) and weighted AE (WAE) from points of the T wave loop 402 converted to polar coordinates. WAA can be calculated as the sum WAA = {Σaa (i) * r (i)} / {Σr (i)}, where for n T wave sampling points, i = 1 to n-2, aa (i) is the azimuth of the i-th point on the T wave loop 402, and r (i) is the magnitude of the i-th point on the T wave loop 402 in polar coordinates. WAE can be calculated as the sum WAA = {Σaa (i) * r (i)} / {Σr (i)}, where i = 1 to n-2, ae (i) is the elevation of the i-th point on the T wave loop 402, and r (i) is the magnitude of the i-th point on the T wave loop 402 in polar coordinates. When T-wave vector 404 is determined as a unit vector defined by WAA and WAE, changes in repolarization measurements from one T-wave to another can be determined as changes in WAA, changes in WAE, or changes in the angle between one T-wave vector and the next in three dimensions.

[0164] Fig.12 4 is a diagram of two T wave vectors, each T wave vector representing a T wave loop determined from a single cardiac cycle, which may be determined by processing circuitry of a medical device according to some examples. Diagram 420 includes Fig.119 , which can be determined as a unit vector defined by WAA and WAE. A second T wave vector 414 can be determined by the control circuit 80 for a subsequent cardiac cycle. The angle ΔT 422 between the two T wave vectors 404 and 414 can be determined as a measured change in repolarization between the two cardiac cycles. The angle ΔT 422 can be determined by calculating the dot product of the T wave vectors 404 and 414. The angle ΔT or any other change determined between the 3D T wave vectors 404 and 414 can be stored over time for multiple cardiac cycles to obtain a time-based ΔT signal, such as a time-based ΔRM signal similar to that shown in FIG. 9 . A quantitative measure of the time-based ΔT (or more generally, a ΔRM signal of any aspect of the change between consecutive 3D T wave vectors) can be determined according to any of the examples given herein.

[0165] return Figure 8 At box 316, the control circuit 80 may compare the measure of the repolarization change determined from the 2D or 3D T wave loop with a risk criterion (e.g., a risk threshold). The risk threshold may be established based on empirical data from a patient population. The risk threshold may be established based on a patient population known to have no history of cardiac events. The risk threshold may be established based on a patient population known to be survivors of cardiac events (e.g., myocardial infarction). The risk threshold may be established based on a patient population known to be non-survivors of cardiac events. The risk threshold may be established between the average measure from a patient population known to be cardiac survivors and the average measure from a patient population known to be non-survivors of cardiac events. In other examples, the risk threshold may be established based on empirical data from a patient population without a history of cardiac events and / or a patient population with a known history of cardiac events.

[0166] In other examples, the risk threshold can be customized for the patient. A baseline metric can be determined based on the patient using a baseline cardiac electrical signal recorded from the patient. A metric of repolarization change determined at a later time point can be compared to the baseline metric or a risk threshold established based on the baseline metric. For example, a metric of repolarization change can be determined to be greater than a risk threshold when the metric increases by more than, for example, 10%, 20%, 30%, or other threshold percentage increase from the baseline metric.

[0167] In yet other examples, the measure of repolarization change may meet the risk criteria when the measure of repolarization change is the nth measure of n continuously increasing measures of repolarization change. For example, if the most recent three, five, eight, or other threshold number of measures of repolarization change each represent an increase relative to the previous measure of repolarization change, the control circuit 80 may determine that the risk threshold is met. In another example, the control circuit 80 may determine that the risk criteria are met when at least x depolarization measures represent an increase relative to the previous measure of repolarization change within a given time period (e.g., within one hour, 24 hours, 48 ​​hours, 72 hours, or other time period). In another example, the control circuit 80 may sum the continuous differences between the measures of repolarization change and compare the sum of the continuous differences with the risk threshold. When the sum of the continuous differences meets the risk threshold, the continuously increasing measure of repolarization change may indicate that the patient is at risk of a serious cardiac event.

[0168] When the repolarization variation metric does not meet the risk criteria ("NO" branch of block 316), the control circuit 80 may return to block 302 to receive cardiac electrical signals the next time monitoring for risk of a cardiac event is to be performed. Figure 8 The process of flowchart 300 may be performed continuously, once a day, once a week, or at other predetermined frequencies. The process of flowchart 300 may be triggered in response to detecting an arrhythmia, an increase in tachyarrhythmia burden, an increase in the occurrence of non-sustained tachyarrhythmias, or other changes in cardiac rhythm, which may be determined by control circuitry 80 based on one or more cardiac electrical signals received from sensing circuitry 82.

[0169] When the measure of the repolarization change meets the risk criteria (the "yes" branch of box 316), the control circuit 80 may execute a response to determine that the risk threshold is met (box 318). The response may include generating a risk notification that can be sent by the telemetry circuit 88. The response may include delivering or adjusting therapy. For example, the control circuit 80 may control the therapy delivery circuit 84 to deliver cardiac pacing at a pacing rate greater than the intrinsic ventricular rate and / or according to a pacing mode to promote a stable cardiac rhythm. The response may include adjusting a tachyarrhythmia detection method or control parameter. For example, the control circuit 80 may turn on VT and / or VF detection, adjust one or more parameters for detecting tachycardia or fibrillation to reduce the time required to detect tachyarrhythmias, and / or adjust one or more detection control parameters to increase the sensitivity of detecting tachyarrhythmias so that ATP and / or CV / DF shocks can be delivered in a time-efficient manner when a tachyarrhythmia is detected.

[0170] Fig.13 500 is a flow chart of a method for determining a measure of repolarization variation to predict the risk of a cardiac event according to another example. Figures 7 to 11The described techniques do not require receiving more than one cardiac electrical signal to determine a measure of repolarization change. In other examples, the processing circuitry that calculates the measure of repolarization change may receive up to two cardiac electrical signals. For illustration purposes, Fig.13 The processes are described as being performed by control circuitry 80 of IMD 14. However, it should be appreciated that these techniques may be performed by different implantable devices, external computing devices, or cooperatively performed by processing circuitry of more than one implantable device and / or external device.

[0171] At box 502, the control circuit 80 receives two cardiac electrical signals. The cardiac electrical signals may be received from two sensing electrode vectors, which in some examples may be approximately orthogonal to each other. The two sensing electrode vectors may correspond to a horizontal plane of the patient and may be composed of a sagittal sensing electrode vector and a transverse sensing electrode vector. The two sensing electrode vectors may include a sensing electrode vector in a substantially horizontal plane (radial or transverse) and a sensing electrode vector in a substantially vertical plane (e.g., in a frontal plane or a sagittal plane). It should be appreciated that, depending on the number and position of implanted electrodes and / or external electrodes used in the two sensing electrode vectors, the sensing electrode vectors may extend in a non-orthogonal relationship and may extend diagonally relative to each other, rather than substantially in the vertical or horizontal plane of the patient.

[0172] At block 504, the control circuit 80 determines a T wave loop from the cardiac cycles of the two cardiac signals. In some examples, the 2DT wave loop is derived from the two cardiac signals by obtaining time-aligned pairs of sampling points from the two cardiac electrical signals over a T wave window. Each pair of time-aligned sampling points from the two cardiac electrical signals can define an ordered pair in a Cartesian coordinate system.

[0173] Fig.14 600 is a diagram of two cardiac electrical signals 602 and 612 that can be received by the control circuit 80 for determining a T wave loop and a measure of repolarization changes from the T wave loop. Points from each T wave 604 and 614 can be sampled on a T wave window 610 to obtain X and Y pairs of sample point amplitudes from the corresponding T waves 604 and 614. Each (X1, Y1), (X2, Y2) to (XN, YN) time-aligned sample point pair defines the x-coordinate and y-coordinate of a point on the 2D T wave loop. As described above, the T wave window 610 can have a start time set relative to the previous R wave 603 or 613 (e.g., the time of the R wave sensing threshold crossing, the R wave maximum peak, etc.). In other examples, the T wave 604 or 614 may be identified based on a threshold crossing, peak amplitude, or other identifiable feature of the T wave 604 or 614 to enable the control circuit 80 to set a T wave window 610 applied to both cardiac electrical signals 602 and 612 for obtaining ordered (X, Y) pairs from the amplitudes of the sampling points of the T waves 604 and 614.

[0174] In other examples, the control circuit 80 may derive a 3D T wave loop from two received cardiac electrical signals. The position of the T wave loop point along the third axis of the 3D coordinate system may be determined based on one or both of the received cardiac electrical signals 602 and 612. For example, a T wave loop point defined by (X, Y, Z) coordinates may be determined to have an x ​​coordinate of the T wave 604 from the first received cardiac electrical signal 602, a y coordinate of the T wave 614 from the second received cardiac electrical signal 612, and a z coordinate determined based on a combination of the two cardiac electrical signals 602 and 612. For example, each z coordinate may be the sum, difference, product, quotient, or other combination of time-aligned sampling points of the first cardiac electrical signal 602 and the second cardiac electrical signal 612. The z coordinate may be determined based on time-aligned sampling points of the T waves 604 and 614, or based on a sampling point of the T wave 604 that is temporally offset (e.g., an advance time interval or a lag time interval) from a sampling point of the T wave 614. In various examples, the lead time or lag time interval may be between 0.5 ms and 20 ms. For example, each T wave loop point (X, Y, Z) may be defined in a three-dimensional Cartesian coordinate system as (X(i), Y(i), Z(i)), where Z(i) may be determined as w1*X(i+n ms)+w2*Y(i+m ms), where w1 and w2 may be weighted values ​​that may be equal to 1 or any other fractional or integer value, n may be between -20 ms and +20 ms and may be equal to zero, and m may be between -20 ms and +20 ms and may be equal to zero.

[0175] Thus, in some examples, the third coordinate of each T wave loop point may be determined based on either the first cardiac electrical signal 602 or the second cardiac electrical signal 612 (when the weighting factor w1 or w2 is zero). For example, the third coordinate may be determined as a sampling point amplitude from the T wave 604 or the T wave 614 that leads or lags the time-aligned x and y coordinate sampling point lead time or lag time interval. For example, as an example, each T wave loop point (X, Y, Z) may be defined in a three-dimensional Cartesian coordinate system as (X(i), Y(i), X(i+n ms). Given the illustrative examples presented herein, various methods for deriving third coordinate values ​​from the two T wave signals 604 and 614 may be envisioned.

[0176] Return to Fig.13, after determining a two-dimensional or three-dimensional T-wave loop based on the received cardiac electrical signal composed of two cardiac electrical signals, the control circuit 80 may determine a repolarization measurement based on the T-wave loop at box 508 according to any of the examples given herein. At box 510, the control circuit 80 may determine a change in the repolarization measurement based on the previously determined repolarization measurement. The process of determining the T-wave loop, determining the repolarization measurement based on the T-wave loop, and determining the change in the repolarization measurement based on the previous repolarization measurement may be repeated for each cardiac cycle in a plurality of cardiac cycles. When all cardiac cycles have been analyzed as needed to determine a measure of repolarization change, as determined at box 512, the measure of repolarization change may be determined by the control circuit 80 at box 514 according to any of the examples described herein.

[0177] At box 516, the measure of repolarization change can be compared to the risk threshold by the control circuit 80 to provide a risk response when the measure of repolarization change meets the risk threshold at box 518. As described above, a warning can be sent by the telemetry circuit 88 and / or cardiac electrical stimulation therapy can be delivered or adjusted in response to the measure of repolarization change meeting the risk threshold. Additionally or alternatively, a tachyarrhythmia detection function can be turned on or adjusted to provide earlier and / or more sensitive tachyarrhythmia detection.

[0178] It should be understood that, depending on the example, certain actions or events of any of the methods described herein may be performed in a different order, may be added, combined, or omitted entirely (e.g., not all of the actions or events described are necessary to practice the method). In addition, in some examples, actions or events may be performed simultaneously, for example, through multi-threaded processing, interrupt processing, or multiple processors, rather than sequentially. In addition, for the purpose of clarity, although certain aspects of the present disclosure are described as being performed by a single circuit or unit, it should be understood that the techniques of the present disclosure may be performed by a combination of units or circuits associated with, for example, a medical device.

[0179] In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored as one or more instructions or codes on a computer-readable medium and executed by a hardware-based processing unit. A computer-readable medium may include a computer-readable storage medium, which corresponds to a tangible medium, such as a data storage medium (e.g., RAM, ROM, EEPROM, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and can be accessed by a computer).

[0180] Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPLAs), or other equivalent integrated or discrete logic circuits. Thus, the term "processor" as used herein may refer to any of the foregoing structures or any other structure suitable for implementing the techniques described herein. Additionally, these techniques may be fully implemented in one or more circuits or logic elements.

[0181] The following examples are a non-limiting list of clauses in accordance with one or more techniques of the present disclosure.

[0182] Embodiment 1. A medical device, comprising: a processing circuit configured to: receive at most two cardiac electrical signals; for each cardiac cycle of a plurality of cardiac electrical signals received consisting of the at most two cardiac electrical signals: derive at least a two-dimensional T wave loop; determine a repolarization measurement representing the T wave loop; and determine a change in the repolarization measurement based on a previously determined repolarization measurement; determine a measure of the determined change in the repolarization measurement; and determine that the measure satisfies a risk threshold associated with a cardiac event; and a telemetry circuit configured to send a risk notification in response to the measure satisfying the risk threshold.

[0183] Embodiment 2. A medical device according to embodiment 1, wherein the processing circuit is further configured to derive at least two dimensions of the T-wave loop from the first cardiac electrical signal of the at most two cardiac electrical signals by determining a first coordinate in the first dimension and a second coordinate in the second dimension for each of the multiple points of the T-wave loop by the following steps: determining the first coordinate as a first amplitude of a first sampling point of the first cardiac electrical signal; and determining the second coordinate as a second amplitude of a second sampling point of the first cardiac electrical signal, the second sampling point being offset from the first sampling point by a first time interval.

[0184] Embodiment 3. A medical device according to embodiment 2, wherein the processing circuit is further configured to derive the three-dimensional T wave loop from the first cardiac electrical signal by determining a third coordinate of each of the multiple points of the T wave loop in the third dimension as a third amplitude of a third sampling point of the first cardiac electrical signal, and the third sampling point is offset from the first sampling point by a second time interval.

[0185] Embodiment 4. The medical device of embodiment 3, wherein the processing circuit is further configured to determine the third amplitude of the third sampling point offset from the first sampling point by the second time interval, wherein the second time interval is different from the first time interval.

[0186] Embodiment 5. A medical device according to any one of Embodiments 2 to 4, wherein the processing circuit is further configured to derive the three-dimensional T-wave loop from the first and second cardiac electrical signals of the at most two cardiac electrical signals by determining the third coordinate of each point of the multiple points of the T-wave loop in the third dimension as the third amplitude of the third sampling point of the second cardiac electrical signal.

[0187] Embodiment 6. The medical device according to embodiment 5, wherein the processing circuit is further configured to identify the third sampling point of the second cardiac electrical signal at a common sampling time as one of the first sampling point of the first cardiac electrical signal or the second sampling point of the first cardiac electrical signal.

[0188] Embodiment 7. A medical device according to any one of Embodiments 1 to 6, wherein the processing circuit is further configured to derive at least two dimensions of the T-wave loop from a first cardiac electrical signal and a second cardiac electrical signal of the at most two cardiac electrical signals by determining a first coordinate in a first dimension and a second coordinate in a second dimension for each of a plurality of points of the T-wave loop by the following steps: determining the first coordinate as a first amplitude of a first sampling point of the first cardiac electrical signal; and determining the second coordinate as a second amplitude of a second sampling point of the second cardiac electrical signal.

[0189] Example 8. A medical device according to Example 7, wherein the processing circuit is further configured to determine a third coordinate of each of the multiple points of the T wave loop by determining a third amplitude based on a combination of the first amplitude and the second amplitude, and derive the three-dimensional T wave loop from the first cardiac electrical signal and the second cardiac electrical signal of the at most two cardiac electrical signals.

[0190] Embodiment 9. The medical device according to any one of embodiments 1 to 8, wherein the processing circuit is further configured to determine the repolarization measurement by determining the at least two-dimensional T wave vector based on the T wave loop.

[0191] Embodiment 10. The medical device of Embodiment 9, wherein the processing circuit is further configured to determine the change in the repolarization measurement by determining an angle between the T wave vector and a previously determined T wave vector.

[0192] Example 11. A medical device according to any one of Examples 9 or 10, wherein the processing circuit is further configured to: determine the angle between the T wave vector and the axis of the at least two-dimensional coordinate system corresponding to the T wave loop; and determine the change in the repolarization measurement by determining the difference between the angle and a previously determined angle, the previously determined angle being the angle between the previously determined T wave vector and the axis of the coordinate system.

[0193] Example 12. A medical device according to any one of claims 1 to 11, wherein the processing circuit is further configured to determine the repolarization measurement by determining at least one of: the area of ​​the T wave loop; the area of ​​a two-dimensional projection of the T wave loop; the distance from a first point of the T wave loop to a second point of the T wave loop; the distance from the origin of the at least two-dimensional coordinate system corresponding to the T wave loop to the farthest point of the T wave loop; the center of mass of the T wave loop; or the length of the perimeter of the T wave loop.

[0194] Embodiment 13. The medical device of any one of Embodiments 1 to 12, wherein the processing circuit is further configured to determine the metric by spectral analysis of the frequency of the change in the repolarization measurement over time.

[0195] Embodiment 14. The medical device of any one of Embodiments 1 to 12, wherein the processing circuit is further configured to determine the metric by amplitude analysis of the change in the repolarization measurement over time.

[0196] Embodiment 15. The medical device of any one of Embodiments 1 to 14, further comprising a therapy delivery circuit configured to deliver or adjust cardiac electrical stimulation therapy in response to the metric satisfying the risk threshold.

[0197] Embodiment 16. A medical device according to any one of Embodiments 1 to 15, wherein the processing circuit is further configured to receive a first cardiac electrical signal of the at most two cardiac electrical signals from a first sensing electrode vector in a horizontal plane of the patient.

[0198] Embodiment 17. A medical device according to any one of Embodiments 1 to 16, wherein the processing circuit is further configured to receive a second cardiac electrical signal of the at most two cardiac electrical signals from a second sensing electrode vector orthogonal to the first sensing electrode vector.

[0199] Embodiment 18. A method performed by a medical device, the method comprising: receiving, by a processing circuit of the medical device, at most two cardiac electrical signals; for each cardiac cycle of a plurality of received cardiac electrical signals consisting of the at most two cardiac electrical signals: deriving a T wave loop of at least two dimensions; determining a repolarization measurement representing the T wave loop; and determining a change in the repolarization measurement based on a previously determined repolarization measurement; determining a measure of the determined change in the repolarization measurement; determining that the measure satisfies a risk threshold associated with a cardiac event; and sending a risk notification in response to the measure satisfying the risk threshold.

[0200] Example 19. According to the method described in Example 18, the method also includes: deriving at least two dimensions of the T wave loop from the first cardiac electrical signal of the at most two cardiac electrical signals by determining a first coordinate in the first dimension and a second coordinate in the second dimension for each of the multiple points of the T wave loop through the following steps: determining the first coordinate as a first amplitude of a first sampling point of the first cardiac electrical signal; and determining the second coordinate as a second amplitude of a second sampling point of the first cardiac electrical signal, the second sampling point being offset from the first sampling point by a first time interval.

[0201] Example 20. According to the method described in Example 19, the method also includes deriving the three-dimensional T wave loop from the first cardiac electrical signal by determining the third coordinate of each point of the multiple points of the T wave loop in the third dimension as the third amplitude of the third sampling point of the first cardiac electrical signal, and the third sampling point is offset from the first sampling point by a second time interval.

[0202] Embodiment 21. The method according to embodiment 20 further comprises determining the third amplitude of the third sampling point offset from the first sampling point by the second time interval, wherein the second time interval is different from the first time interval.

[0203] Example 22. A method according to any one of Examples 19 to 21, further comprising deriving the three-dimensional T wave loop from the first and second cardiac electrical signals of the at most two cardiac electrical signals by determining the third coordinate of each of the multiple points of the T wave loop in the third dimension as the third amplitude of the third sampling point of the second cardiac electrical signal.

[0204] Embodiment 23. The method according to embodiment 22 further comprises identifying the third sampling point of the second cardiac electrical signal at a common sampling time as one of the first sampling point of the first cardiac electrical signal or the second sampling point of the first cardiac electrical signal.

[0205] Example 24. A method according to any one of Examples 18 to 23, the method further comprising deriving at least two dimensions of the T-wave loop from a first cardiac electrical signal and a second cardiac electrical signal of the at most two cardiac electrical signals by determining a first coordinate in the first dimension and a second coordinate in the second dimension for each of the multiple points of the T-wave loop by the following steps: determining the first coordinate as a first amplitude of a first sampling point of the first cardiac electrical signal; and determining the second coordinate as a second amplitude of a second sampling point of the second cardiac electrical signal.

[0206] Example 25. A method according to Example 24, wherein the processing circuit is further configured to determine a third coordinate of each of the multiple points of the T wave loop by determining a third amplitude based on a combination of the first amplitude and the second amplitude, and derive the three-dimensional T wave loop from the first cardiac electrical signal and the second cardiac electrical signal of the at most two cardiac electrical signals.

[0207] Embodiment 26. According to any one of the methods of embodiments 18 to 25, the method also includes determining the repolarization measurement by determining the at least two-dimensional T wave vector based on the T wave loop.

[0208] Embodiment 27. The method according to embodiment 26 also includes determining the change in the repolarization measurement by determining the angle between the T wave vector and a previously determined T wave vector.

[0209] Embodiment 28. The method according to any one of embodiments 26 or 27, further comprising:

[0210] determining an angle between the T wave vector and an axis of the at least two-dimensional coordinate system corresponding to the T wave loop; and determining the change in the repolarization measurement by determining a difference between the angle and a previously determined angle, the previously determined angle being the angle between the previously determined T wave vector and the axis of the coordinate system.

[0211] Embodiment 29. According to the method described in any one of embodiments 18 to 28, the method also includes determining the repolarization measurement by determining at least one of the following: the area of ​​the T wave loop; the area of ​​the two-dimensional projection of the T wave loop; the distance from the first point of the T wave loop to the second point of the T wave loop; the distance from the origin of the at least two-dimensional coordinate system corresponding to the T wave loop to the farthest point of the T wave loop; the center of mass of the T wave loop; or the length of the perimeter of the T wave loop.

[0212] Embodiment 30. The method of any one of embodiments 18 to 29, further comprising determining the metric by spectral analysis of the frequency of the change in the repolarization measurement over time.

[0213] Embodiment 31. The method of any one of embodiments 18 to 30, further comprising determining the metric by amplitude analysis of the change in the repolarization measurement over time.

[0214] Example 32. A method according to any one of Examples 18 to 31, further comprising delivering or adjusting cardiac electrical stimulation therapy in response to the metric satisfying the risk threshold.

[0215] Embodiment 33. A method according to any one of Embodiments 18 to 32, the method further comprising receiving a first cardiac electrical signal of the at most two cardiac electrical signals from a first sensing electrode vector in a horizontal plane of the patient.

[0216] Embodiment 34. According to the method described in any one of Embodiments 18 to 33, the method also includes receiving a second cardiac electrical signal of the at most two cardiac electrical signals from a second sensing electrode vector orthogonal to the first sensing electrode vector.

[0217] Embodiment 35. A non-transitory computer-readable medium storing a set of instructions which, when executed by a control circuit of a medical device, causes the medical device to: receive at most two cardiac electrical signals; for each cardiac cycle of a plurality of received cardiac electrical signals consisting of the at most two cardiac electrical signals: derive at least a two-dimensional T wave loop; determine a repolarization measurement representing the T wave loop; and determine a change in the repolarization measurement based on a previously determined repolarization measurement; determine a measure of the determined change in the repolarization measurement; determine that the measure satisfies a risk threshold associated with a cardiac event; and send a risk notification in response to the measure satisfying the risk threshold.

[0218] Thus, the medical devices have been presented in the foregoing description with reference to specific embodiments. It should be understood that the various aspects disclosed herein may be combined in combinations different from the specific combinations presented in the drawings. It should be understood that various modifications may be made to the referenced embodiments without departing from the scope of the present disclosure and the following claims.

Claims

1. A medical device, comprising: A processing circuit, the processing circuit being configured to: receiving up to two cardiac electrical signals; For each cardiac cycle of a plurality of cardiac cycles of the received cardiac electrical signal consisting of the at most two cardiac electrical signals: deriving at least two-dimensional T wave loops; determining a repolarization measure representative of the T wave loop; and determining a change in the repolarization measure based on a previously determined repolarization measure; determining a measure of the determined change in the repolarization measurement; as well as determining that the metric satisfies a risk threshold associated with a cardiac event; and Telemetry circuitry configured to send a risk notification in response to the metric satisfying the risk threshold.

2. The medical device of claim 1 , wherein the processing circuit is further configured to derive the T wave loop in at least two dimensions from a first cardiac electrical signal of the at most two cardiac electrical signals by determining a first coordinate in a first dimension and a second coordinate in a second dimension for each of a plurality of points of the T wave loop by: determining the first coordinate as a first amplitude of a first sampling point of the first cardiac electrical signal; and The second coordinate is determined as a second amplitude of a second sampling point of the first cardiac electrical signal, the second sampling point being offset from the first sampling point by a first time interval.

3. The medical device according to claim 2, wherein the processing circuit is further configured to derive the three-dimensional T wave loop from the first cardiac electrical signal by determining a third coordinate of each of the multiple points of the T wave loop in the third dimension as a third amplitude of a third sampling point of the first cardiac electrical signal, and the third sampling point is offset from the first sampling point by a second time interval. 4 . The medical device of claim 3 , wherein the processing circuit is further configured to determine the third amplitude at the third sampling point offset from the first sampling point by the second time interval, wherein the second time interval is different from the first time interval.

5. A medical device according to any one of claims 2 to 4, wherein the processing circuit is further configured to derive the three-dimensional T wave loop from the first and second cardiac electrical signals of the at most two cardiac electrical signals by determining a third coordinate of each of the multiple points of the T wave loop in the third dimension as a third amplitude of a third sampling point of the second cardiac electrical signal.

6. The medical device according to claim 5, wherein the processing circuit is further configured to identify the third sampling point of the second cardiac electrical signal at a common sampling time as one of the first sampling point of the first cardiac electrical signal or the second sampling point of the first cardiac electrical signal.

7. The medical device according to any one of claims 1 to 6, wherein the processing circuit is further configured to derive the at least two-dimensional T-wave loop from the first and second cardiac electrical signals of the at most two cardiac electrical signals by determining a first coordinate in a first dimension and a second coordinate in a second dimension for each of a plurality of points of the T-wave loop by the following steps: determining the first coordinate as a first amplitude of a first sampling point of the first cardiac electrical signal; and The second coordinate is determined as a second amplitude of a second sampling point of the second cardiac electrical signal.

8. The medical device according to claim 7, wherein the processing circuit is further configured to determine a third coordinate of each of the multiple points of the T wave loop by determining a third amplitude based on a combination of the first amplitude and the second amplitude, and derive the three-dimensional T wave loop from the first cardiac electrical signal and the second cardiac electrical signal of the at most two cardiac electrical signals.

9. The medical device of any one of claims 1 to 8, wherein the processing circuit is further configured to determine the repolarization measurement by determining the at least two-dimensional T-wave vector from the T-wave loop.

10. The medical device of claim 9, wherein the processing circuit is further configured to determine the change in the repolarization measurement by determining an angle between the T wave vector and a previously determined T wave vector.

11. The medical device of claim 9, wherein the processing circuit is further configured to: determining an angle between the T-wave vector and an axis of the at least two-dimensional coordinate system corresponding to the T-wave loop; and The change in the repolarization measurement is determined by determining a difference between the angle and a previously determined angle between a previously determined T-wave vector and the axis of the coordinate system.

12. The medical device of any one of claims 1 to 11, wherein the processing circuit is further configured to determine the repolarization measurement by determining at least one of: The area of ​​the T wave loop; The area of ​​the two-dimensional projection of the T wave loop; a distance from a first point of the T wave loop to a second point of the T wave loop; a distance from the origin of the at least two-dimensional coordinate system corresponding to the T wave loop to the farthest point of the T wave loop; the centroid of the T wave loop; or The length of the circumference of the T wave loop.

13. A medical device according to any one of claims 1 to 12, wherein the processing circuit is further configured to determine the metric by one or more of a spectral analysis of the frequency of the change in the repolarization measurement over time or an amplitude analysis of the change in the repolarization measurement over time.

14. The medical device of any one of claims 1 to 13, further comprising a therapy delivery circuit configured to deliver or adjust cardiac electrical stimulation therapy in response to the metric satisfying the risk threshold.

15. A medical device according to any one of claims 1 to 14, wherein the processing circuit is further configured to receive a first cardiac electrical signal of the at most two cardiac electrical signals from a first sensing electrode vector in a horizontal plane of the patient, and to receive a second cardiac electrical signal of the at most two cardiac electrical signals from a second sensing electrode vector orthogonal to the first sensing electrode vector.

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