Systems and methods for detecting haemodynamically unstable heart rhythms

Abstract

A medical device system is configured to sense electroencephalogram activity and to sense cardiac electrical activity. The system may detect a concerned heart rate from cardiac electrical activity and determine that the concerned heart rate is a haemodynamically unstable heart rhythm based on sensed brain electrical activity. The medical device system may generate an output for providing a response to determining that the concerned heart rate is a haemodynamically unstable heart rhythm.

Description

Technical Field

[0001] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 381,126, filed Oct. 26, 2022, the entire content of which is incorporated herein by reference.

[0002] The present disclosure generally relates to medical device systems and methods for detecting hemodynamically unstable cardiac rhythms based on cardiac electrical activity and electroencephalographic activity. Background Art

[0003] Medical devices can sense electrophysiological signals from the heart, brain, nerves, muscles, or other tissues. Such devices can be implantable, partially 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 the sensed electrophysiological signals. For example, implantable or external cardiac pacemakers, cardioverter defibrillators, cardiac monitors, etc. sense cardiac electrical signals from a patient's heart. A cardiac pacemaker or cardioverter defibrillator can sense cardiac electrical signals from the heart and deliver electrical stimulation therapy to the heart using electrodes carried by transvenous medical electrical leads, non-transvenous medical electrical leads, and / or leadless electrodes directly coupled to the housing of the medical device.

[0004] Electrical stimulation therapy can include signals such as pacing pulses or cardioversion / defibrillation shocks. In some cases, a medical device can sense cardiac event signals accompanying the intrinsic or pacemaker-induced depolarization of the heart and control the delivery of stimulation signals to the heart based on the sensed cardiac event signals. When an abnormal rhythm such as bradycardia, tachycardia, or fibrillation is detected based on the sensed cardiac event signal (or its absence), one or more appropriate electrical stimulation signals can be delivered to restore or maintain a more normal rhythm of the heart. For example, an implantable cardioverter defibrillator (ICD) can deliver pacing pulses to a patient's heart when bradycardia or tachycardia is detected, or deliver cardioversion or defibrillation (CV / DF) shocks to the heart when tachycardia or fibrillation is detected. Summary of the Invention

[0005] Generally, the present disclosure relates to medical device systems and methods for differentiating hemodynamically unstable (HU) heart rhythms from hemodynamically stable (HS) heart rhythms. Medical device systems operating in accordance with the techniques disclosed herein sense electrophysiological signals, such as electroencephalographic activity and cardiac electrical activity. In some examples, the medical device system includes two or more implantable medical devices, each implantable medical device being configured to sense electrophysiological signals and communicate wirelessly to collaboratively detect a concerning heart rate and determine whether the concerning heart rate is HU. A concerning heart rate may be determined to be HU when one or more metrics determined from the sensed electroencephalographic activity meet cerebral ischemia criteria. The one or more metrics may represent the amplitude and / or frequency of the electroencephalographic activity and may be determined in the time domain and / or frequency domain.

[0006] A concerning heart rate may be a rapid heart rate associated with tachycardia or fibrillation, which may be hemodynamically stable or unstable. In some cases, a concerning heart rate may be a relatively slow or irregular heart rate, e.g., associated with bradycardia or an irregularly conducted cardiac rhythm. Based on whether the concerning heart rate is HU or HS, the medical device system may select a response, which may include delivering one or more cardiac electrical stimulation therapies, stopping cardiac electrical stimulation therapies, and / or sending an alert, notification, or other communication when the concerning heart rate is determined to be HU.

[0007] In one example, the present disclosure provides a medical device system that includes sensing circuitry configured to sense electroencephalographic activity and cardiac electrical activity. The medical device system includes processing circuitry configured to detect a concerning heart rate from the cardiac electrical activity and may determine that the concerning heart rate is a hemodynamically unstable heart rhythm based on the sensed electroencephalographic activity. The processing circuitry may generate an output for providing a response to determining that the concerning heart rate is a hemodynamically unstable heart rhythm. The medical device system may include a memory configured to store the output generated by the processing circuitry.

[0008] In another example, the present disclosure provides a method that includes sensing electroencephalographic activity, sensing cardiac electrical activity, and detecting a concerning heart rate from the cardiac electrical activity by processing circuitry of a medical device system. The method may include determining that the concerning heart rate is a hemodynamically unstable heart rhythm based on the sensed electroencephalographic activity and generating an output for providing a response to determining that the concerning heart rate is a hemodynamically unstable heart rhythm. The method may include storing the generated output in a memory of the processing circuitry.

[0009] In another example, the present disclosure provides a non-transitory computer-readable medium storing instructions that, when executed by a processing circuit of a medical device system, cause the system to sense electroencephalographic activity, sense cardiac electrical activity, detect a concerning heart rate from the cardiac electrical activity, and determine, based on the sensed electroencephalographic activity, that the concerning heart rate is a hemodynamically unstable cardiac rhythm. The instructions may also cause the medical device system to generate an output for providing a response to determining that the concerning heart rate is a hemodynamically unstable rhythm. The instructions may cause the system to store the generated output in a memory of the medical device system.

[0010] The subject matter of the following embodiments is also disclosed herein:

[0011] Embodiment 1. A medical device system comprising a sensing circuit configured to sense electroencephalographic activity and cardiac electrical activity, and comprising a processing circuit configured to detect a concerning heart rate from the sensed cardiac electrical activity. The processing circuit may also be configured to determine, based on the sensed electroencephalographic activity, that the concerning heart rate is a hemodynamically unstable cardiac rhythm, and to generate an output for providing a response to determining that the concerning heart rate is a hemodynamically unstable cardiac rhythm. The medical device system may include a memory configured to store the output generated by the processing circuit.

[0012] Embodiment 2. The medical device system according to Embodiment 1, further comprising a therapy delivery circuit configured to deliver an electrical stimulation therapy. The control circuit may also be configured to generate the output by generating a therapy control signal, and the therapy delivery circuit may be configured to deliver the electrical stimulation therapy according to the therapy control signal.

[0013] Embodiment 3. The medical device system according to any one of Embodiments 1 to 2, wherein the processing circuit is further configured to determine at least one amplitude metric from the electroencephalographic activity and compare the amplitude metric to a cerebral ischemia criterion. The processing circuit may determine that the concerning heart rate is a hemodynamically unstable cardiac rhythm in response to the amplitude metric meeting the cerebral ischemia criterion.

[0014] Embodiment 4. The medical device system according to any one of Embodiments 1 to 3, wherein the processing circuit is further configured to: determine at least one frequency metric from the electroencephalographic activity; compare the frequency metric to a cerebral ischemia criterion; and determine that the concerning heart rate is a hemodynamically unstable cardiac rhythm in response to the frequency metric meeting the cerebral ischemia criterion.

[0015] Example 5. The medical device system according to Example 4, wherein the processing circuit is further configured to determine the at least one frequency metric from the electroencephalogram activity by determining at least one of the following: the dominant frequency of the electroencephalogram activity; the number of oscillations of the electroencephalogram activity during a time interval; and / or the magnitude of the signal derivative of the electroencephalogram activity. The processing circuit may also determine that the frequency metric meets a cerebral ischemia criterion; and in response to the frequency metric meeting the cerebral ischemia criterion, determine that the concerning heart rate is a hemodynamically unstable cardiac rhythm.

[0016] Example 6. The medical device system according to any one of Examples 1 to 5, wherein the processing circuit is further configured to determine at least one metric of the electroencephalogram activity and determine a cerebral ischemia stage from a plurality of cerebral ischemia stages based on the at least one metric. The processing circuit may determine that the concerning heart rate is a hemodynamically unstable cardiac rhythm based on the determined cerebral ischemia stage.

[0017] Example 7. The medical device system according to any one of Examples 1 to 6, wherein the processing circuit is further configured to determine a metric from the electroencephalogram activity for each of a plurality of time intervals and determine that a change in the metric determined for each of the plurality of time intervals meets a cerebral ischemia criterion. The processing circuit may determine that the concerning heart rate is a hemodynamically unstable cardiac rhythm based on the change in the metric meeting the cerebral ischemia criterion.

[0018] Example 8. The medical device system according to Example 7, wherein the processing circuit is further configured to determine that the change in the metric meets the cerebral ischemia criterion by at least determining that the change in the metric is within a threshold time interval at the onset of the concerning heart rate.

[0019] Example 9. The medical device system according to any one of Examples 1 to 8, wherein the processing circuit is further configured to detect the concerning heart rate by detecting a heart rate faster than a threshold rate.

[0020] Example 10. The medical device system according to Example 9, the medical device system further comprising a therapy delivery circuit configured to deliver cardioversion / defibrillation shocks. The processing circuit may also be configured to determine that the sensed electroencephalogram activity meets a severe cerebral ischemia criterion and control the therapy delivery circuit to abort cardioversion / defibrillation shocks in response to determining that the sensed electroencephalogram activity meets the severe cerebral ischemia criterion.

[0021] Example 11. The medical device system according to any one of Examples 1 to 10, the medical device system further includes a therapy delivery circuit configured to generate cardiac electrical stimulation therapy. The processing circuit may also be configured to detect a monomorphic ventricular tachyarrhythmia associated with the concerning heart rate based on the sensed cardiac electrical activity, and control the therapy delivery circuit to deliver a first antitachycardia pacing therapy in response to detecting the monomorphic ventricular tachyarrhythmia. The processing circuit may be configured to determine that the monomorphic ventricular tachyarrhythmia is not terminated by the first antitachycardia pacing therapy, and in response to determining that the monomorphic ventricular tachyarrhythmia is not terminated, determine at least one metric from the sensed brain electrical activity. The processing circuit may also be configured to determine that the monomorphic ventricular tachyarrhythmia is a hemodynamically unstable rhythm based on the at least one metric, and determine that the concerning heart rate is a hemodynamically unstable rhythm based on the sensed brain electrical activity.

[0022] Example 12. The medical device system according to Example 11, wherein the processing circuit is further configured to generate the output for providing the response by generating a cardioversion / defibrillation shock therapy signal.

[0023] Example 13. The medical device system according to any one of Examples 2 to 12, wherein the processing circuit is further configured to detect polymorphic ventricular tachycardia or ventricular fibrillation associated with the concerning heart rate, and control the therapy delivery circuit to deliver cardioversion / defibrillation shock therapy in response to detecting the polymorphic ventricular tachycardia or ventricular fibrillation, without determining that the polymorphic ventricular tachycardia or the ventricular fibrillation is hemodynamically unstable based on the sensed brain activity.

[0024] Example 14. The medical device system according to any one of Examples 1 to 8, wherein the processing circuit is further configured to detect the concerning heart rate by detecting either a heart rate slower than a threshold rate or a heart rate that meets a variable heart rate criterion.

[0025] Example 15. The medical device system according to Example 14, wherein the processing circuit is further configured to generate the output by generating a cardiac pacing delivery signal.

[0026] Example 16. The medical device system according to any one of Examples 14 to 15, wherein the processing circuit is further configured to generate the output by increasing a lower pacing rate.

[0027] Example 17. The medical device system according to any one of Examples 1 to 16, wherein the processing circuit is further configured to detect a normal sinus rhythm from the cardiac electrical activity and establish a cerebral ischemia criterion based on the detected cerebral electrical activity during the detected normal sinus rhythm. The processing circuit is further configured to determine that the concerning heart rate is hemodynamically unstable based on the sensed cerebral electrical activity meeting the cerebral ischemia criterion.

[0028] Example 18. The medical device system according to any one of Examples 1 to 17, the medical device system further comprising a communication circuit. The processing circuit is further configured to generate the output for providing the response by generating an alert signal, and the communication circuit is configured to transmit the alert signal.

[0029] Example 19. The medical device system according to any one of Examples 1 to 18, the medical device system further comprising at least one sensor configured to sense a sensor signal received by the processing circuit. The processing circuit is further configured to detect sleep based on at least one of the time of day or the sensor signal, and in response to detecting the sleep, determine that it is indeterminable that the concerning heart rate is hemodynamically unstable based on the sensed cerebral electrical activity.

[0030] Example 20. The medical device system according to any one of Examples 1 to 18, the medical device system further comprising at least one sensor configured to sense a sensor signal received by the processing circuit. The processing circuit is further configured to detect sleep based on at least one of the time of day or the sensor signal, generate a wake-up signal, and detect cerebral ischemia based on the cerebral electrical activity sensed after the wake-up signal. The processing circuit is configured to determine that the concerning heart rate is a hemodynamically unstable heart rhythm based on detecting the cerebral ischemia based on the cerebral electrical activity sensed after the wake-up signal.

[0031] Example 21. The medical device system according to any one of Examples 1 to 20, wherein the processing circuit is further configured to detect the termination of the concerning heart rate. The processing circuit may determine that the sensed cerebral electrical activity still meets the cerebral ischemia criterion after detecting the termination of the concerning heart rate, and in response to determining that the sensed cerebral electrical activity still meets the cerebral ischemia criterion, adjust the control parameters for detecting the concerning heart rate from the sensed cardiac electrical activity.

[0032] Example 22. The medical device system according to any one of Examples 1 to 21, wherein the processing circuit is further configured to detect a hemodynamically stable heart rhythm based on the sensed cardiac electrical activity and the sensed brain electrical activity, and generate a second output in response to detecting the hemodynamically stable heart rhythm. The memory is configured to store the second output.

[0033] Example 23. The medical device system according to Example 22, the medical device system further includes a therapy delivery circuit configured to deliver cardioversion / defibrillation shock therapy. The processing circuit is further configured to generate the second output by generating a therapy control signal for stopping the cardioversion / defibrillation shock therapy.

[0034] Example 24. A method, the method includes: sensing brain electrical activity through a sensing circuit of a medical device system; sensing cardiac electrical activity through the sensing circuit of the medical device system; detecting a concerning heart rate from the sensed cardiac electrical activity through a processing circuit of the medical device system; and determining that the concerning heart rate is a hemodynamically unstable heart rhythm based on the sensed brain electrical activity. The method may further include generating, by the processing circuit, an output for providing a response to determining that the concerning heart rate is a hemodynamically unstable heart rhythm, and may include storing the generated output in a memory of the medical device system.

[0035] Example 25. The method according to Example 24, the method further includes: generating the output by generating a therapy control signal and delivering an electrical stimulation therapy according to the therapy control signal.

[0036] Example 26. The method according to any one of Examples 24 to 25, the method further includes: determining at least one amplitude metric from the brain electrical activity; comparing the amplitude metric with a cerebral ischemia criterion; and in response to the amplitude metric meeting the cerebral ischemia criterion, determining that the concerning heart rate is a hemodynamically unstable heart rhythm.

[0037] Example 27. The method according to any one of Examples 24 to 26, the method further includes: determining at least one frequency metric from the brain electrical activity; comparing the frequency metric with a cerebral ischemia criterion; and in response to the frequency metric meeting the cerebral ischemia criterion, determining that the concerning heart rate is a hemodynamically unstable heart rhythm.

[0038] Example 28. The method according to Example 27, the method further comprising determining at least one frequency metric from the electroencephalogram activity by determining at least one of the following: the dominant frequency of the electroencephalogram activity, the number of oscillations of the electroencephalogram activity during a time interval, and / or the magnitude of the signal derivative of the electroencephalogram activity. The method may further comprise: determining that the frequency metric meets a cerebral ischemia criterion; and in response to the frequency metric meeting the cerebral ischemia criterion, determining that the concerning heart rate is a hemodynamically unstable cardiac rhythm.

[0039] Example 29. The method according to any one of Examples 24 to 28, the method further comprising: determining at least one metric of the electroencephalogram activity; determining a cerebral ischemia stage from a plurality of cerebral ischemia stages based on the at least one metric; and determining that the concerning heart rate is a hemodynamically unstable cardiac rhythm based on the determined cerebral ischemia stage.

[0040] Example 30. The method according to any one of Examples 24 to 29, the method further comprising: determining a metric from the electroencephalogram activity for each of a plurality of time intervals; determining that a change in the metric determined for each of the plurality of time intervals meets a cerebral ischemia criterion; and determining that the concerning heart rate is a hemodynamically unstable cardiac rhythm based on the change in the metric meeting the cerebral ischemia criterion.

[0041] Example 31. The method according to Example 30, the method further comprising determining that the change in the metric meets the cerebral ischemia criterion by at least determining that the change in the metric is within a threshold time interval at the onset of the concerning heart rate.

[0042] Example 32. The method according to any one of Examples 24 to 31, the method further comprising: detecting the concerning heart rate by detecting a heart rate faster than a threshold rate.

[0043] Example 33. The method according to Example 32, the method further comprising: determining that the sensed electroencephalogram activity meets a severe cerebral ischemia criterion, and aborting cardioversion / defibrillation shock in response to determining that the sensed electroencephalogram activity meets the severe cerebral ischemia criterion.

[0044] Example 34. The method according to any one of Examples 25 to 33 further includes: detecting a monomorphic ventricular tachyarrhythmia associated with the concerning heart rate based on the sensed cardiac electrical activity, and delivering a first antitachycardia pacing therapy in response to detecting the monomorphic ventricular tachyarrhythmia. The method may further include determining that the monomorphic ventricular tachyarrhythmia is not terminated by the first antitachycardia pacing therapy. In response to determining that the monomorphic ventricular tachyarrhythmia is not terminated, determining at least one metric from the sensed brain electrical activity, and determining that the monomorphic ventricular tachyarrhythmia is a hemodynamically unstable rhythm based on the at least one metric, and determining that the concerning heart rate is a hemodynamically unstable rhythm based on the sensed brain electrical activity.

[0045] Example 35. The method according to Example 34 further includes: generating the output for providing the response by generating a cardioversion / defibrillation shock therapy signal.

[0046] Example 36. The method according to any one of Examples 25 to 35 further includes: detecting polymorphic ventricular tachycardia or ventricular fibrillation associated with the concerning heart rate, and delivering a cardioversion / defibrillation shock therapy in response to detecting the polymorphic ventricular tachycardia or ventricular fibrillation, without determining that the polymorphic ventricular tachycardia or the ventricular fibrillation is hemodynamically unstable based on the sensed brain activity.

[0047] Example 37. The method according to any one of Examples 24 to 31 further includes: detecting the concerning heart rate by detecting either a heart rate slower than a threshold rate or a heart rate meeting a variable heart rate criterion.

[0048] Example 38. The method according to Example 37 further includes: generating the output by generating a cardiac pacing signal.

[0049] Example 39. The method according to any one of Examples 35 to 36 further includes: generating the output by increasing a lower pacing rate.

[0050] Example 40. The method according to any one of Examples 24 to 39 further includes: detecting normal sinus rhythm from the cardiac electrical activity, and establishing a cerebral ischemia criterion based on the sensed brain electrical activity during the detected normal sinus rhythm. The method further includes determining that the concerning heart rate is hemodynamically unstable based on the sensed brain electrical activity meeting the cerebral ischemia criterion.

[0051] Example 41. The method according to any one of Examples 24 to 40 further includes: generating the output for providing the response by generating an alarm signal and sending the alarm signal.

[0052] Example 42. The method according to any one of Examples 24 to 41 further comprises: receiving at least one sensor signal; detecting sleep based on the time of day or at least one of the sensor signals; and determining that the concerning heart rate is a hemodynamically unstable heart rate that cannot be determined based on the sensed electroencephalogram (EEG) activity in response to detecting the sleep.

[0053] Example 43. The method according to any one of Examples 24 to 41 further comprises: receiving at least one sensor signal; detecting sleep based on the time of day or at least one of the sensor signals; generating a wake-up signal; and detecting cerebral ischemia based on the EEG activity sensed after the wake-up signal. The method further comprises determining that the concerning heart rate is a hemodynamically unstable heart rhythm based on detecting the cerebral ischemia based on the EEG activity sensed after the wake-up signal.

[0054] Example 44. The method according to any one of Examples 24 to 43 further comprises: detecting the termination of the concerning heart rate; after detecting the termination of the concerning heart rate, determining that the sensed EEG activity still meets the cerebral ischemia criteria; and adjusting the control parameter for detecting the concerning heart rate from the sensed cardiac electrical activity in response to determining that the sensed EEG activity still meets the cerebral ischemia criteria.

[0055] Example 45. The method according to any one of Examples 24 to 44 further comprises: detecting a hemodynamically stable heart rhythm based on the sensed cardiac electrical activity and the sensed EEG activity, generating a second output in response to detecting the hemodynamically stable heart rhythm, and storing the second output in the memory.

[0056] Example 46. The method according to Example 45 further comprises: generating the second output by generating a therapy control signal for stopping cardioversion / defibrillation shock therapy.

[0057] Example 47. A non-transitory computer-readable storage medium storing instructions that, when executed by a processing circuit of a medical device system, cause the system to sense EEG activity, sense cardiac electrical activity, detect a concerning heart rate from the sensed cardiac electrical activity, and determine that the concerning heart rate is a hemodynamically unstable heart rhythm based on the sensed EEG activity. The instructions may further cause the medical device system to generate an output to provide a response to determining that the concerning heart rate is a hemodynamically unstable heart rhythm and store the generated output in the memory of the medical device system.

[0058] The present invention content aims to provide an overview of the subject matter described in this disclosure. It is not intended to provide an exclusive or exhaustive interpretation of the devices and methods described in the following figures and description. Further details of one or more examples are set forth in the following figures and description. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 is a conceptual diagram of a plurality of implantable medical devices (IMDs) that can be co-implanted into a medical device system configured to sense cardiac electrical activity and electroencephalogram (EEG) activity to distinguish HU rhythms from HS rhythms.

[0060] Figure 2 is a conceptual diagram of another medical device system configured to sense cardiac electrical activity and EEG activity to detect HU rhythms according to another example.

[0061] Figure 3 is a conceptual diagram of a medical device system configured to sense cardiac electrical activity and EEG activity to detect HU rhythms according to yet another example.

[0062] Figure 4 is a conceptual diagram of an IMD configured to sense cardiac electrical signals and deliver cardiac electrical stimulation therapy according to one example.

[0063] Figure 5 is a conceptual diagram of an electrocochleogram (ECoG) sensor according to one example.

[0064] Figure 6 is a flowchart of a method for distinguishing HU and HS rhythms that can be performed by a medical device system according to some examples.

[0065] Figure 7 is during different stages of cerebral ischemia that can be performed by Figure 5 the ECoG sensor senses various examples of ECoG signals.

[0066] Figure 8 is a flowchart of a method for detecting cerebral ischemia to classify rhythms as HU or HS according to some examples.

[0067] Figure 9 is a flowchart of a method for detecting tachyarrhythmia and selecting a therapy response based on determining whether the tachyarrhythmia is HU or HS that can be performed by a medical device system according to some examples.

[0068] Figure 10 is a flowchart of a method for detecting tachyarrhythmia and selecting a therapy response that can be performed by a medical device system according to another example.

[0069] Figure 11A flowchart of a method for detecting HU and HS heart rhythms according to another example. Detailed implementation

[0070] Generally speaking, the present disclosure describes medical device systems and techniques for detecting hemodynamically unstable (HU) heart rhythms based on the processing and analysis of cardiac electrical signals and electroencephalogram signals. A medical device can sense and analyze cardiac electrical activity to detect a concerning heart rate, which can be a rapid heart rate caused by tachycardia or fibrillation, or a slow heart rate caused by, for example, bradycardia or irregular conduction of cardiac beats that cause an irregular or variable heart rate. For some patients experiencing various types of syncope, hypotension, or other conditions, a slow or irregular heart rate may be a concern. In some cases, when cardiac event signals (e.g., the P wave associated with atrial depolarization or the R wave associated with ventricular depolarization) in the cardiac electrical signals are insufficiently sensed during tachycardia or fibrillation (which can be HU), a slow heart rate may be misdetected. The analysis of cardiac electrical signals can include differentiating the types of tachyarrhythmias, such as supraventricular tachycardia (SVT), ventricular tachycardia (VT), and ventricular fibrillation (VF).

[0071] When a concerning heart rate is detected, the difference between HS and HU heart rhythms can be determined based on the analysis of electroencephalogram activity (e.g., EEG), which can be sensed and analyzed by a second medical device in some medical device systems. Various examples of combinations of IMDs are described herein, which can be configured to process and analyze cardiac electrical signals that can be sensed by one IMD and electroencephalogram signals (e.g., EEG signals) that can be sensed by a second IMD, where the two IMDs communicate with each other (communicate directly or indirectly via one or more relay devices) for collaboratively detecting HU heart rhythms. Cardiac electrical activity can be sensed as an electrocardiogram (ECG) signal using electrodes implanted far from the heart and / or electrogram (EGM) signals sensed from electrodes implanted in or on the heart.

[0072] In some examples, at least one IMD configured to sense cardiac electrical activity may also be configured to deliver cardiac electrical stimulation therapy. Cardiac electrical stimulation therapy may be delivered to treat bradycardia (when a slow heart rate determined to be HU is detected) or treat tachyarrhythmia (when a fast heart rate is detected). According to the techniques disclosed herein, a therapy response to a detected heart rhythm may be selected based on whether the detected heart rhythm is HS or HU. Cardiac electrical stimulation therapy may include bradycardia pacing, anti-tachyarrhythmia pacing (ATP), and / or cardioversion / defibrillation (CV / DF) shocks. In some examples, the electrical stimulation therapy may include nerve stimulation therapy, such as spinal cord stimulation or vagus nerve stimulation, to alter autonomic tone and thereby promote or restore hemodynamic stability. In various examples, the medical device system may make a therapy delivery decision based on a determination of a HU or HS heart rhythm, e.g., whether to deliver therapy or select from a plurality of available therapies (e.g., ATP or CV / DF shocks).

[0073] In some illustrative examples presented herein, an IMD configured to sense cardiac electrical signals may be a pacemaker or implantable cardioverter defibrillator (ICD) configured to sense cardiac electrical signals and deliver cardiac electrical stimulation pulses for cardiac pacing and / or CV / DF shock delivery. The pacemaker or ICD may be coupled to one or more transvenous or non-transvenous leads for carrying electrodes that sense cardiac electrical activity and deliver electrical stimulation therapy. For example, the pacemaker or ICD may be coupled to an "extracardiovascular" lead, which refers to a lead that positions electrodes outside the blood vessels, heart, and pericardium surrounding the patient's heart. The extracardiovascular lead may also be referred to as a "non-transvenous" lead. For example, implantable electrodes carried by an extracardiovascular lead may be positioned outside the thorax (outside the chest cavity and sternum, e.g., subcutaneously or submuscularly) or inside the thorax (e.g., below the chest cavity or sternum, sometimes referred to as a "sub-sternal" position). Electrodes for sensing cardiac electrical activity and / or for delivering cardiac electrical stimulation therapy may or may not be in intimate contact with myocardial tissue. For example, electrodes carried by one or more non-transvenous leads may be implanted within the pericardium and coupled to an IMD in a medical device system configured to operate according to the techniques disclosed herein.

[0074] In other examples, a pacemaker or ICD may be coupled to a transvenous lead that positions electrodes within a blood vessel, and the transvenous lead may be maintained in an "extra-cardiac" position outside of the heart or advanced to position the electrodes within a heart chamber, such as endocardially or along the endocardium. In some cases, by way of example, a transvenous medical lead may be advanced along a venous pathway to position the electrodes in an extra-cardiac position within the internal thoracic vein (ITV), intercostal vein, superior epigastric vein, or azygos, hemiazygos, or accessory hemiazygos vein. In still other examples, one or more transvenous leads may be advanced to position the electrodes within the heart, such as within a heart chamber of the atrium and / or ventricle.

[0075] In some examples, two or more IMDs may be co-implanted in a patient within a medical device system capable of sensing at least one cardiac electrical signal (for sensing cardiac electrical activity) and at least one EEG signal (for sensing brain electrical activity). At least one implanted device configured to sense cardiac electrical signals may be capable of wireless communication with a second implanted device configured to sense EEG signals to collaboratively determine whether the heart rhythm is a HU rhythm or a HS rhythm. The two devices may be monitoring-only devices without therapy delivery capabilities. In other examples, at least one device may be capable of delivering a therapy for treating a patient condition. For example, at least one IMD configured to sense cardiac electrical signals may be capable of delivering a therapy in response to detecting a tachyarrhythmia. The techniques disclosed herein may be used to select the therapy to be delivered based on whether the detected tachyarrhythmia is HU or HS. In some examples, one or more of the co-implanted devices may be capable of delivering other therapies for treating other patient conditions. For example, an IMD configured to sense EEG signals may be configured to deliver a nerve stimulation therapy, deep brain stimulation, drug delivery, or other therapies for treating a patient condition other than an arrhythmia. Although in some cases, an IMD configured to sense brain electrical activity may be positioned to deliver a vagus nerve stimulation, spinal cord stimulation, or other nerve stimulation to alter the patient's autonomic tone, which in some examples may be delivered as a therapy response to a detected HU rhythm.

[0076] In addition, it should be recognized that one or more IMDs may be configured to monitor cardiac electrical activity and brain electrical activity to detect and distinguish between HS rhythms and HU rhythms, and one or more IMDs configured to detect HS rhythms and HU rhythms may communicate with a third IMD configured to deliver a therapy. The determination of the HS or HU rhythm may be sent to the third IMD, which is configured to select and deliver an appropriate therapy based on the determination of the HS or HU rhythm.

[0077] In combination with the following Figures 1 to 3The illustrated and described IMDs are illustrative examples of IMDs that can be co-implanted within a patient and configured to perform the techniques disclosed herein, but are not intended to be limiting. It should be understood that the techniques disclosed herein are not limited to implementation in a medical device system that includes only implantable devices configured to detect HU and HS heart rhythms. For example, a device for sensing EEG signals and cardiac electrical signals to distinguish between HU and HS heart rhythms can include an external medical device. One or more medical devices included in a medical device system configured to perform the techniques disclosed herein can be external devices, such as wearable devices having electrodes for sensing electroencephalographic activity and / or cardiac electrical activity, such as an external EEG monitor, an external ECG monitor, a smartwatch, a fitness tracker, and the like. In some examples, a medical device system configured to perform the techniques disclosed herein can include a partially implantable device that can include one or more implantable components (e.g., electrodes carried by percutaneous leads or conductors) that are coupled to one or more external components (e.g., an external housing that encloses a circuit coupled to the implanted electrodes).

[0078] Figure 1 is a conceptual diagram of multiple IMDs that can be co-implanted in medical device system 10, which is configured to sense cardiac electrical activity and electroencephalographic activity to detect and distinguish between HU heart rhythm and HS heart rhythm. In this example, patient 12 is shown as implanted with an ICD 14 that is connected to a non-transvenous, extracardiac electrical stimulation and sensing lead 16. ICD 14 can be configured to sense at least one cardiac electrical signal (e.g., an ECG signal) for detecting a concerning heart rate. When a rapid heart rate is detected, ICD 14 can optionally detect and distinguish between different types of tachyarrhythmias, such as SVT, VT, and VF. Additionally or alternatively, patient 12 can be implanted with a cardiac monitor 44 for sensing cardiac electrical signals using housing-based electrodes 46a and 46b (collectively referred to as electrodes 46) to detect a concerning heart rate. Patient 12 can also be implanted with an EEG sensor 40 that can include housing-based electrodes 42a and 42b (collectively referred to as electrodes 42) for sensing electroencephalographic activity (e.g., an EEG signal).

[0079] In some examples, patient 12 may be implanted with a cardiac monitor 44 and an EEG sensor 40 for detecting HU and HS heart rhythms without necessarily having the ability to deliver an automated therapy for treating or terminating tachyarrhythmias. Additionally, depending on the implantation location of the EEG sensor 40 or the cardiac monitor 44, a single implanted device (e.g., the EEG sensor 40 or the cardiac monitor 44) may be configured to sense both electroencephalographic activity and cardiac electrical activity using the respective electrodes 42 or 46 to detect HU and HS heart rhythms using the techniques disclosed herein. For example, when the EEG sensor 40 is implanted near the base of the patient's skull or behind the neck, the electrical signals sensed using the electrode 42 may be processed and analyzed by the EEG sensor 40 to determine both electroencephalographic activity and cardiac electrical activity. The EEG sensor 40 may correspond to an implantable medical device generally disclosed in U.S. Publication No. 2022 / 0061743 (Christensen et al.), the disclosure of which is incorporated herein by reference in its entirety. In some examples, a single medical device including one or more electrodes on the housing of the medical device and / or one or more electrodes carried by leads extending from the medical device may be positioned to sense cardiac electrical activity and electroencephalographic activity to detect HU and HS heart rhythms in accordance with the techniques disclosed herein.

[0080] In other examples, patient 12 may be implanted with an ICD 14 (without the cardiac monitor 44) in combination with the EEG sensor 40 for detecting a concerning heart rate and delivering a cardiac electrical stimulation therapy selected based on determining whether the concerning heart rate is HS or HU. In other examples, patient 12 may be implanted with all three devices, the ICD 14, the cardiac monitor 44, and the EEG sensor 40, for sensing cardiac electrical signals, sensing EEG signals, detecting a concerning heart rate, determining whether the rhythm associated with the concerning heart rate is a HU rhythm or an HS rhythm, and selecting a therapy delivery response based on the HU or HS determination.

[0081] The ICD 14 includes a housing 15 that forms an airtight seal protecting the internal components of the ICD 14. The housing 15 of the ICD 14 may be formed of a conductive material such as titanium or a titanium alloy. The housing 15 may act as an electrode (sometimes referred to as a "can" electrode). The housing 15 may be used as an active can electrode for delivering CV / DF shocks or other relatively high voltage pulses delivered using a high voltage therapy delivery circuit. In other examples, the housing 15 may be used to deliver single low voltage cardiac pacing pulses and / or for sensing cardiac electrical signals in combination with electrodes carried by the lead 16. In other instances, the housing 15 of the ICD 14 may include multiple electrodes on an external portion of the housing. One or more external portions of the housing 15 that act as one or more electrodes may be coated with a material such as titanium nitride, for example, to reduce post-stimulation polarization artifacts.

[0082] The ICD 14 includes a connector assembly 17 (also referred to as a connector block or header), which includes electrical feedthroughs passing through the housing 15 to provide an electrical connection between conductors extending within the lead body 18 of the lead 16 and electronic components included within the housing 15 of the ICD 14. As will be described in further detail herein, the housing 15 may house one or more processors, memories, transceivers, cardiac electrical signal sensing circuits, therapy delivery circuits, power supplies, and other components for sensing cardiac electrical signals, detecting cardiac rhythms, and controlling and delivering electrical stimulation pulses to treat abnormal cardiac rhythms.

[0083] The lead 16 is shown in this example as an epicardial, non-transvenous lead implanted beneath the sternum 22. The lead 16 includes an elongated lead body 18 having: a proximal end 27 that includes a lead connector (not shown) configured to connect to the ICD connector assembly 17; and a distal portion that includes one or more electrodes. Figure 1 In the example shown, the distal portion of the lead body 18 includes defibrillation electrodes 24 and 26 and pacing / sensing electrodes 28 and 30. In some cases, defibrillation electrodes 24 and 26 may together form a defibrillation electrode in that they may be configured to be activated simultaneously. Alternatively, defibrillation electrodes 24 and 26 may form separate defibrillation electrodes, in which case each of electrodes 24 and 26 may be independently activated.

[0084] Electrodes 24 and 26 (and in some examples, the housing 15) may be referred to as defibrillation electrodes because they are used, either singly or jointly, to deliver high voltage stimulation therapy (e.g., cardioversion or defibrillation shocks). Electrodes 24 and 26 may be elongated coil electrodes and typically have a relatively high surface area for delivering high voltage electrical stimulation pulses as compared to pacing electrodes 28 and sensing electrodes 30. However, in addition to or instead of high voltage stimulation therapy, electrodes 24 and 26 and the housing 15 may also be used to provide a pacing function, a sensing function, or both a pacing function and a sensing function. In this sense, the use of the term "defibrillation electrode" herein should not be construed as limiting electrodes 24 and 26 to only high voltage cardioversion / defibrillation shock therapy applications. For example, either of electrodes 24 and 26 may be used as a sensing electrode in a sensing electrode vector for sensing cardiac electrical signals to detect and discriminate cardiac rhythms and determine the need for electrical stimulation therapy.

[0085] Electrodes 28 and 30 are electrodes that are available for sensing electrode vectors for sensing cardiac electrical signals and have a relatively small surface area, and in some configurations can be used to deliver relatively low-voltage pacing pulses. Electrodes 28 and 30 are referred to herein as pacing "electrode / sensing electrodes" because they are typically configured for low-voltage applications, e.g., as opposed to delivering high-voltage CV / DF shocks, serving as a cathode or anode for delivering pacing pulses and / or sensing cardiac electrical signals. In some cases, electrodes 28 and 30 may provide only pacing functionality, only sensing functionality, or both.

[0086] The ICD 14 can sense cardiac electrical signals corresponding to the electrical activity of the heart 8 via one or more sensing electrode vectors, which include combinations of electrodes 24, 26, 28, and / or 30. In some examples, the housing 15 of the ICD 14 is used in combination with one or more of the electrodes 24, 26, 28, and / or 30 in the sensing electrode vector. In Figure 1 A and Figure 1 In the examples illustrated in B, electrode 28 is proximal to the defibrillation electrode 24, and electrode 30 is between the defibrillation electrodes 24 and 26. One, two, or more pacing / sensing electrodes may be carried by the lead body 18. For example, in some examples, a third pacing / sensing electrode may be distal to the defibrillation electrode 26. In some cases, the lead body 18 may carry only the relatively large-surface-area defibrillation electrodes and not the smaller pacing / sensing electrodes.

[0087] Electrodes 28 and 30 are shown as annular electrodes; however, electrodes 28 and 30 can include any of a variety of different types of electrodes, including annular electrodes, short coil electrodes, hemispherical electrodes, directional electrodes, or segmented electrodes, etc. Electrodes 28 and 30 can be positioned at other locations along the lead body 18 and are not limited to the locations shown. In other examples, the lead 16 can include fewer or more pacing / sensing electrodes and / or defibrillation electrodes than the examples shown herein.

[0088] The lead 16 extends subcutaneously or submuscularly from the connector assembly 27 of the ICD 14 inwardly and toward the center of the patient 12's torso (e.g., toward the xiphoid process 20 of the patient 12) throughout the thoracic cavity 32. In Figure 1In the example, lead 16 is at least partially implanted beneath the sternum 22 of patient 12. At a location near the xiphoid process 20, lead 16 can be bent upward or rotated and extend upward in a sub-sternal location (e.g., within the anterior mediastinum). The anterior mediastinum can be bounded laterally by the pleura, posteriorly by the pericardium, and anteriorly by the sternum 22. The distal portion 25 of lead 16 can extend substantially along the posterior side of the sternum 22 within the loose connective tissue and / or sub-sternal muscle tissue of the anterior mediastinum. A lead implanted such that its distal portion 25 is substantially within the anterior mediastinum or within the pleural cavity or more generally within the thoracic cavity can be referred to as a "sub-sternal lead".

[0089] In Figure 1 In the example shown, lead 16 is positioned to be substantially centered beneath the sternum 22. However, in other cases, lead 16 is implanted such that it is laterally offset from the center of the sternum 22. In some cases, lead 16 can extend laterally such that, in addition to or instead of the sternum 22, the distal portion 25 of lead 16 is beneath / below the thoracic cavity 32. In other examples, the distal portion 25 of lead 16 can be implanted in other extra-cardiac intrathoracic locations, including the pleural cavity or the periphery of the pericardium 38 around the heart 8 and adjacent to or within the pericardium 38 of the heart 8. In various examples, electrodes for sensing cardiac electrical signals are carried by a lead that can be advanced to a supra-diaphragmatic location, which can be within the thoracic cavity or outside the thoracic cage in various examples.

[0090] For example, lead 16 can be bent or rotated near the xiphoid process 20 to extend above the thoracic cavity and / or the sternum, subcutaneously or sub-muscularly, substantially parallel to the sternum 22, offset to the right or left of the sternum 22, laterally inclined away from the sternum 22 toward the left or right, etc. Alternatively, lead 16 can be placed along other subcutaneous or sub-muscular paths. The path of lead 16 can depend on the location of the ICD 14, the arrangement and location of the electrodes carried by the lead body 18, and / or other factors. The techniques disclosed herein are not limited to a particular path of lead 16 or the final location of the electrodes 24, 26, 28, and 30 for sensing cardiac electrical signals and delivering cardiac pacing therapy and / or CV / DF shocks.

[0091] An electrical conductor (not shown) extends from the lead connector at the proximal lead end 27 through one or more lumens of the elongated lead body 18 of the lead 16 to electrodes 24, 26, 28, and 30 positioned along the 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. Via the connectors in the connector assembly 17, including associated electrical feedthroughs through the housing 15, the respective conductors electrically couple the electrodes 24, 26, 28, and 30 to the circuitry of the ICD 14, such as a therapy delivery circuit and / or one or more cardiac electrical signal sensing circuits. The electrical conductors send therapy from the therapy delivery circuit within the ICD 14 to one or more of the defibrillation electrodes 24 and 26 and / or pacing / sensing electrodes 28 and 30, and send cardiac electrical sensing signals from the patient's heart 8 from one or more of the defibrillation electrodes 24 and 26 and / or pacing / sensing electrodes 28 and 30 to the sensing circuit within the ICD 14.

[0092] The lead body 18 of the lead 16 may be formed of a non-conductive material (including silicone, polyurethane, fluoropolymer, mixtures thereof, and / or other suitable materials) and shaped to form one or more lumens within which one or more conductors extend. The lead body 18 may be tubular or cylindrical in shape. In other examples, the distal portion 25 (or all) of the elongated lead body 18 may have a flat, ribbon, or paddle shape. The lead body 18 may be formed to have a preformed distal portion 25 that is generally straight, curved, kinked, serpentine, wavy, or zigzag.

[0093] In the example shown, the lead body 18 includes a curved distal portion 25 having two "C" - shaped curves that together may resemble the Greek letter epsilon "ε". The defibrillation electrodes 24 and 26 are each carried by one of two respective C - shaped portions of the distal portion 25 of the lead body. The two C - shaped curves extend or curve 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 generally 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. Other examples of leads including one or more defibrillation electrodes and one or more pacing and sensing electrodes may include curved, serpentine, wavy, or zigzag distal portions of the lead body 18. However, the techniques disclosed herein are not limited to any particular lead body design. In other examples, the lead body 18 is a flexible elongated lead body without any preformed shape, kinks, or bends.

[0094] The ICD 14 analyzes cardiac electrical signals received from one or more sensing electrode vectors to monitor abnormal rhythms, such as bradycardia, ventricular tachycardia (VT), or ventricular fibrillation (VF). The ICD 14 can analyze the rate and morphology of sensed cardiac events to monitor tachyarrhythmias according to any one of a variety of tachyarrhythmia detection techniques. In response to detecting a tachyarrhythmia (e.g., VT or VF), the ICD 14 can generate and deliver an electrical stimulation therapy using a therapy delivery electrode vector that can be selected from any one of the available electrodes 24, 26, 28, 30 and / or the housing 15. The ICD 14 can deliver antitachycardia pacing (ATP) in response to VT detection, particularly HS VT, and in some cases can deliver ATP prior to a CV / DF shock or during the charging of a high-voltage capacitor in an attempt to avoid the need to deliver a CV / DF shock. If ATP does not successfully terminate VT or when VF is detected or when HU VT is detected based on EEG signal analysis in combination with cardiac electrical signal analysis, the ICD 14 can deliver one or more CV / DF shocks via one or both of the defibrillation electrodes 24 and 26 and / or the housing 15. The ICD 14 can use the electrodes 24 and 26 alone or together as the cathode (or anode) and the housing 15 as the anode (or cathode) to deliver CV / DF shocks. As described below, the control circuit of the ICD 14 can be configured to select, deliver, or stop an electrical stimulation therapy based on determining whether the detected tachyarrhythmia is HU or HS according to an analysis of electroencephalogram (EEG) activity that can be sensed by the EEG sensor 40. The ICD 14 can use a pacing electrode vector that includes one or more of the electrodes 24, 26, 28, and 30 and the housing 15 of the ICD 14 to generate and deliver other types of electrical stimulation pulses, such as post-shock pacing pulses, asystole pacing pulses, or bradycardia pacing pulses. In some cases, the ICD 14 can detect a slow heart rate determined to be HU and deliver a bradycardia pacing pulse that can be delivered at a pacing rate faster than a programmed lower rate to promote improved cerebral blood flow and hemodynamic stability.

[0095] The ICD 14 is shown implanted subcutaneously along the thorax 32 on the left side of the patient 12. In some cases, the ICD 14 may be implanted between the patient 12's left posterior axillary line and left anterior axillary line. However, the ICD 14 may be implanted at other subcutaneous or submuscular locations in the patient 12. For example, the ICD 14 may be implanted in a subcutaneous pocket in the pectoral muscle region. In such a case, the lead 16 may extend subcutaneously or submuscularly from the ICD 14 toward the manubrium of the sternum 22, and bend or turn downward from the manubrium and extend to a desired location subcutaneously, submuscularly, sub-sternally, within the thorax 32. In yet another example, the ICD 14 may be placed in the abdomen. The ICD 14 may be communicatively coupled to an external device 50, and to an EEG sensor 40 and / or a heart monitor 44, for example via a wireless link 60, as further described below.

[0096] The heart monitor 44 may be implanted subcutaneously or submuscularly for sensing cardiac electrical signals via electrodes 46. In Figure 1 one example, the heart monitor 44 is implanted below the collarbone and may be implanted in the chest, on the sternum, or other chest locations capable of sensing cardiac electrical signals via electrodes 46. The heart monitor 44 includes a housing 45 that encloses a sensing circuit, a communication circuit, a memory, and a processing circuit for analyzing the sensed cardiac electrical signals and controlling the heart monitor functions. The housing 45 may be formed of the types of materials listed above for the ICD housing 15. One of the electrodes 46a may be carried on a head 47 coupled to the housing 45 and is electrically coupled to the internal device circuitry via an electrical feedthrough extending through the head 47 into the hermetically sealed housing 45. The other electrode 46b may be a conductive portion (or all) of the outer surface of the housing 45 and is electrically insulated from the electrode 46a. The electrodes 46a and 46b may be formed of the exemplary electrode materials listed above and form a sensing electrode pair for receiving cardiac electrical signals (e.g., ECG signals) that may be analyzed for detecting rapid heart rates and for detecting and differentiating between different types of arrhythmias. The heart monitor 44 may be implemented as an insertable cardiac signal monitor that is configured to store cardiac signal episodes and detect various arrhythmias and generally may correspond to the insertable Reveal LinQ TM heart monitor (which is adapted to operate in the IMD system 10 in accordance with the techniques disclosed herein). The heart monitor 44 may be configured to communicate with the external device 50, for example by establishing a wireless link 64.

[0097] In some examples, it is contemplated that the cardiac monitor 44 may include neurostimulation capabilities. In some examples, the cardiac monitor 44 may be implanted in a location for delivering electrical stimulation pulses via the electrodes 46 to the patient's nervous system (e.g., to the spinal cord, vagus nerve, or other nervous system tissue) in response to detecting a HU rhythm to alter the patient's autonomic tone. Electrical nerve stimulation may be delivered to increase sympathetic activity, thereby promoting or restoring hemodynamic stability.

[0098] The EEG sensor 40 may be a relatively small device and may be placed (e.g., inserted) under or over the skin at a cranial location or along the patient's neck or base of the skull in various examples. Other target sites where the EEG sensor 40 may be positioned include other locations on the head, such as above the temporal bone. As described in more detail below, the EEG sensor 40 may sense electroencephalographic activity corresponding to one or more regions of the patient's brain, such as one or more EEG signals. The EEG sensor 40 may be configured to communicate with an external device 50, for example, by establishing a wireless link 62.

[0099] As described below, the EEG sensor 40 may be configured to detect changes in electroencephalographic activity associated with cerebral ischemia, which may indicate HU tachyarrhythmia. Thus, the EEG sensor 40 may include a plurality of electrodes for sensing the electrical activity of the patient's brain. In the example shown, the EEG sensor 40 includes two electrodes 42a and 42b (collectively referred to as electrodes 42) for sensing electroencephalographic activity, but may include more than two electrodes in other examples. In various embodiments, the number and configuration of the electrodes 42 may vary. For example, the EEG sensor 40 may include at least 2, at least 3, at least 4, at least 5, or more electrodes in an electrode array. In some embodiments, the EEG sensor 40 includes fewer than 6, fewer than 5, fewer than 4, or fewer than 3 electrodes.

[0100] The electrodes 42 may be any suitable one or more conductive materials, such as any of the materials listed above for the electrodes carried by the ICD lead 16, such that the EEG sensor 40 can receive electrical signals via the electrodes 42. In some examples, the EEG sensor 40 may be configured to analyze data from the electrodes 42 to extract both electroencephalographic activity data (e.g., EEG signals) and cardiac electrical activity data (e.g., ECG signals). The electroencephalographic activity data may be evaluated to determine cerebral ischemia, while the cardiac electrical activity data may be evaluated to detect a rapid heart rate that may be identified as a HU or HS rhythm based on the analysis of the electroencephalographic activity data.

[0101] In some examples, the EEG sensor 40 is configured to analyze data from the electrodes 42 to extract brain activity data and discard or reduce any contribution from cardiac or muscular activity. For example, filtering, blind source separation, or other techniques may be performed by the EEG sensor 40 to remove cardiac, skeletal muscle, or other electrical signals from the EEG signal before determining EEG signal features or changes indicative of cerebral ischemia. The EEG sensor 40 may optionally include other sensors, such as an accelerometer, a gyroscope, a pulse oximeter, a temperature sensor, or any other sensor for monitoring a patient's physiological condition.

[0102] The housing 41 may include a head 43 that is hermetically sealed to a housing case or canister, the head defining an enclosed lumen that contains the internal circuitry of the EEG sensor 40. The housing 41 is shown in Figure 1 as being generally rectangular or prismatic in shape. The EEG sensor housing 41 may be generally cylindrical, spherical, angular, or other shapes to accommodate a desired number of electrodes and electrode sensing vectors and to accommodate a desired implantation location. The electrodes 42 may all be housing-based electrodes. For example, one or more of the electrodes 42a may be carried by the head 43 that is hermetically sealed to the EEG sensor housing 41. The electrode 42a may be electrically coupled to the sensing circuitry within the housing 41 via an electrical feedthrough. One or more of the electrodes 42b may be carried on the housing 41, for example as part of the outer surface of a conductive material (e.g., any of the exemplary housing materials listed above) that forms the housing 41. Portions of the housing 41 may be electrically insulated, for example by an insulating coating, to define one or more housing-based electrodes. In some examples, the EEG sensor head 43 may be configured to receive removable leads or be fixedly coupled to non-removable leads that extend away from the housing 41 to carry one or more electrodes for sensing electrical signals to monitor electroencephalographic activity (and in some cases cardiac electrical activity). In such a configuration, a portion of the plurality of electrodes 42 for sensing electroencephalographic activity by the EEG sensor 40 may be located at a position spaced apart from the housing 41.

[0103] The EEG sensor 40 may be configured to be a monitoring-only device and implanted at a location for sensing electroencephalographic activity and in some examples cardiac electrical activity. However, it is contemplated that in some examples, the EEG sensor 40 includes neurostimulation capabilities. The EEG sensor 40 may be positioned to deliver electrical stimulation pulses to a patient's nervous system via the electrodes 42, such as to the brain, spinal cord, vagus nerve, or other nervous system tissue, for example to alter autonomic tone in some examples. In some examples, electrical stimulation may be delivered to increase sympathetic nerve activity, thereby promoting or restoring hemodynamic stability.

[0104] Two or more co-implanted devices in the medical device system 10 can be configured to communicate wirelessly, such as represented by wireless communication links 72, 74, and 76, to coordinate the detection and response to HU and HS heart rhythms. The ICD 14, EEG sensor 40, and / or cardiac monitor 44 can communicate via radio frequency communication, tissue conduction communication, or other communication methods. As described below, an implanted medical device (e.g., cardiac monitor 44 or ICD 14) can detect a concerning heart rate and send a request to the EEG sensor 40 to determine the stage of cerebral ischemia. The EEG sensor 40 can analyze the sensed brain electrical activity and send an indication of the stage of cerebral ischemia using the techniques described below. The requesting device can receive the sent cerebral ischemia indication to determine whether the concerning heart rate is HU or HS. When a HU heart rhythm is detected, the medical device system 10 can respond by sending an alert or notification to an external device or communication network to alert a medical responder or caregiver. When the implanted medical device of the system 10 is capable of delivering therapy (e.g., ICD 14), therapy can be delivered or stopped based on the determination of whether the heart rhythm is HU or HS.

[0105] The external device 50 is shown communicating telemetrically with the ICD 14, EEG sensor 40, and cardiac monitor 44 via wireless communication link 60, wireless communication link 62, and wireless communication link 64, respectively. The external device 50 can include a processor 52, a memory 53, a display unit 54, a user interface 56, and a telemetry unit 58. The processor 52 controls the operation of the external device and can be configured to process data and signals received from the ICD 14, EEG sensor 40, and cardiac monitor 44.

[0106] The external device 50 can be used to program the sensing control parameters, heart rhythm detection parameters, and therapy delivery control parameters used by the ICD 14. The external device 50 can be embodied as a programmer used in a hospital, clinic, or doctor's office to retrieve data from the ICD 14, EEG sensor 40, and cardiac monitor 44, and to program the operating parameters and algorithms in each of the ICD 14, EEG sensor 40, and cardiac monitor 44 used by the respective devices for sensing physiological signals and, at least in the case of the ICD 14, delivering therapy. The external device 50 can alternatively be embodied as a home monitor or a handheld device, which can be a tablet computer, a cellular phone, or other personal device. Although Figure 1A single external device 50 is shown, but it should be understood that each of the ICD 14, EEG sensor 40, and cardiac monitor 44 can be configured to communicate with one or more external devices, such as a system analyzer, programmer, computer, home monitor, communication relay device, cellular phone, tablet computer, or other personal device, and any one of these devices can further communicate with a patient remote monitoring network or database (e.g., CARELINK available from Medtronic, Inc. of Minneapolis, Minnesota, USA). TM A remote monitoring network). An example IMD programmer that can be configured to communicate with an IMD implementing the techniques disclosed herein is CARELINK TM Programmer, which is commercially available from Medtronic, Inc. of Minneapolis, Minnesota, USA.

[0107] The processor 52 executes instructions stored in the memory 53. The processor 52 can include any one or more of the following: a microprocessor, a controller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or equivalent discrete or analog logic circuitry. In some examples, the processor 52 can include multiple components (such as any combination of one or more microprocessors, one or more controllers, one or more DSPs, one or more ASICs, or one or more FPGAs) and other discrete or integrated logic circuitry. The functions attributed to the processor 52 herein can be embodied as software, firmware, hardware, or any combination thereof.

[0108] A display 54, which can include a graphical user interface, displays data and other information to a user for viewing IMD (e.g., ICD 14, EEG sensor 40, or cardiac monitor 44) operation and programmed parameters, as well as cardiac electrical signals and / or EEG signals retrieved from the IMD.

[0109] The memory 53 can include any volatile medium, non-volatile medium, magnetic medium, optical medium, or dielectric medium, such as random access memory (RAM), read only memory (ROM), non-volatile RAM (NVRAM), electrically erasable programmable ROM (EEPROM), flash memory, or any other digital or analog medium. The memory 53 can be configured to store sensing and / or therapy delivery control parameters corresponding to a given IMD and associated programmable settings.

[0110] The user interface 56 may include a mouse, a touch screen, a keypad, etc., to enable a user to interact with the external device 50 to initiate a telemetry session with the IMD implanted in the patient 12, in order to retrieve data from and / or send data to the IMD, including programmable parameters for controlling tachyarrhythmia detection, determining HU tachyarrhythmia, and / or therapy delivery. A clinician may use the user interface 56 to transmit and receive commands to and from the IMD implanted in the patient 12 via the external device 50. Generally, the user interface 56 includes one or more input devices and one or more output devices, including the display unit 54. The input devices of the user interface 56 may include communication devices such as network interfaces, keyboards, pointing devices, voice response systems, cameras, biometric detection / response systems, buttons, sensors, mobile devices, control panels, microphones, presence-sensitive screens, touch-sensitive screens (which may be included in the display unit 54), networks, or any other type of device for detecting input from a person or a machine.

[0111] One or more output devices of the user interface 56 may include communication units such as network interfaces, displays, sound cards, video graphics adapter cards, speakers, presence-sensitive screens, one or more USB interfaces, video and / or audio output interfaces, or any other type of device capable of generating tactile, audio, video, or other output. The display unit 54 may be used as an input and / or output device using technologies including liquid crystal displays (LCDs), quantum dot displays, dot matrix displays, light-emitting diode (LED) displays, organic light-emitting diode (OLED) displays, cathode ray tube (CRT) displays, electronic ink, or monochromatic, color, or any other type of display capable of generating tactile, audio, and / or visual output. In other examples, the user interface 56 may generate output to the user in another way, such as via a sound card, a video graphics adapter card, a speaker, a presence-sensitive screen, a touch-sensitive screen, one or more USB interfaces, a video and / or audio output interface, or any other type of device capable of generating tactile, audio, video, or other output. In some examples, the display unit 54 is a presence-sensitive display that can be used as a user interface device, and the presence-sensitive display operates as one or more input devices and one or more output devices.

[0112] The telemetry unit 58 includes a transceiver and an antenna configured to communicate bidirectionally with the telemetry circuit included in the IMD implanted in the patient 12, and is configured to operate in conjunction with the processor 52 to transmit and receive data related to IMD functions via a communication link (e.g., any one of the corresponding communication links 60, 62, or 64). Can be used such as An RF link, such as Wi-Fi or Medical Implant Communication Service (MICS) or other RF or communication frequency bandwidths or communication protocols, establishes a communication link between the IMD and the external device 50. As Figure 1 shown, the various medical devices of the system 10 (which may include the ICD 14, the EEG sensor 40, the cardiac monitor 44, and / or other example implantable, partially implantable, or wearable medical devices listed herein) can communicate directly with each other (e.g., as shown by the communication links 72, 74, and 76) and / or indirectly with each other via the external device 50. For example, at least one of the ICD 14, the EEG sensor 40, or the cardiac monitor 44 can communicate with the external device 50 and act as a relay device for sending and receiving data from one or more other co-implanted devices. Data stored or acquired by the ICD 14, the EEG sensor 40, and / or the cardiac monitor 44 (including cardiac electrical signals or related data derived therefrom and / or EEG signals or related data derived therefrom), the results of device diagnostics, the history of detected cardiac rhythm episodes, the history of detected cerebral ischemia, and any delivered therapies can be retrieved by the external device 50 from the ICD 14, the EEG sensor 40, and / or the cardiac monitor 44 in accordance with an interrogation command. In some examples, the IMD system 10 is configured to detect HU rhythms and generate a response by sending an alert signal or notification to the external device 50 or another external device. In some examples, the alert signal can be a phone call to the Emergency Medical Services (EMS). The IMD system 10 can be configured to make an emergency phone call via a communication network to alert the EMS or other medical responders of the detected HU rhythm.

[0113] Figure 2 is a conceptual diagram of the EEG sensor 40 and the ICD 114 in a co-implantable medical device system 100 according to another example, the medical device system being configured to sense at least one cardiac electrical signal and at least one EEG signal to detect HU and HS rhythms. In this example, the ICD 114 is shown connected to transvenous, therapy delivery, and sensing leads 116 and 118. The ICD 14 can be a dual-chamber cardiac pacemaker including high voltage CV / DF capabilities. Thus, the ICD 14 is connected to the transvenous leads 116 and 118 that communicate with the right atrium (RA) and the right ventricle (RV) of the heart 8, respectively. For example, as described generally below in connection with Figure 4 the ICD 114 includes a housing 115 enclosing circuits such as a processing circuit, a telemetry circuit, a sensing circuit, and a therapy delivery circuit. The ICD 114 includes a connector assembly 117 having connector holes for receiving the proximal connectors of the RA lead 116 and the RV lead 118 and providing an electrical connection between the electrodes carried by the leads 116 and 118 and the internal ICD circuits.

[0114] The RA lead 116 can carry the distal tip electrode 120 and the annular electrode 122 for sensing atrial electrical signals and generating atrial intracardiac electrogram (EGM) signals. The RA electrodes 120 and 122 can be used to deliver RA pacing pulses. The RV lead 118 can carry pacing and sensing electrodes 132 and 134 for sensing ventricular electrical signals and generating RV EGM signals. The RV electrodes 132 and 134 can be used to deliver RV pacing pulses. The RV lead 118 can also carry the RV defibrillation electrode 124 and the superior vena cava (SVC) defibrillation electrode 126. The defibrillation electrodes 124 and 126 are shown as coil electrodes proximally spaced from the distal pacing electrode 132 and the sensing electrode 134. Although both the RA lead 116 and the RV lead 118 are shown as advancing within the respective heart chambers, in some examples, transvenous leads coupled to the ICD 114 can be advanced to position the electrodes within venous locations external to the heart 8, such as any of the transvenous, extra-cardiac locations listed above.

[0115] The ICD 114 can be configured to provide dual-chamber sensing and pacing therapy and high-voltage CV / DF shock therapy in response to detecting VT or VF. In other examples, the ICD 114 can be configured to provide multi-chamber sensing and pacing therapy, including cardiac resynchronization therapy (CRT), in which case a coronary sinus lead can be advanced along a cardiac vein to position electrodes for sensing and pacing the left ventricle of the heart 8. In other examples, the ICD 114 can be a single-chamber device coupled to a single lead (e.g., lead 116 or lead 118) for sensing cardiac electrical signals and delivering electrostimulation therapy. For example, the ICD 114 can be a single-chamber device coupled to the RV lead 118 for sensing ventricular EGM signals, detecting and differentiating cardiac tachyarrhythmias, and delivering ventricular pacing, ATP, and CV / DF shocks. Although the RV lead 118 is shown as having a tip electrode 132 positioned at the RV apex, the positions of the leads and electrodes shown are illustrative in nature and are not intended to be restrictive. The electrodes can be positioned at other locations. For example, the RV lead tip electrode 132 can be positioned in the interventricular septum and can be positioned near the His-Purkinje conduction system for delivering conduction system pacing, such as in the region of the His bundle, left bundle branch, or right bundle branch.

[0116] The ICD 114 can be configured to sense at least one cardiac electrical signal to detect a concerning heart rate. In accordance with the techniques disclosed herein, the cardiac electrical signal can be processed and analyzed according to a tachycardia detection algorithm for detecting supraventricular tachycardia (SVT) and determining HU SVT or HS SVT in combination with data or information from the EEG sensor 40. The ICD 114 and the EEG sensor 40 can be configured to communicate wirelessly, as shown by the communication link 172, for collaboratively detecting HU and HS heart rhythms. Each of the EEG sensor 40 and the ICD 114 can be capable of two-way wireless communication with an external device 50 via respective communication links 62 and 160 to send signals or data related to heart rhythm, cerebral ischemia and to send an alert signal or notification, which in some examples can include making an EMS call and / or calling, texting or emailing a family member or other caregiver or first responder in response to detecting a HU heart rhythm.

[0117] Figure 3 is a conceptual diagram of a medical device system 110 that includes an EEG sensor 40 and a leadless pacemaker 150. The leadless pacemaker 150 can be configured to sense cardiac electrical signals to detect a concerning heart rate and communicate wirelessly with the EEG sensor 40 (as shown by the communication link 78) for collaboratively detecting HU and HS heart rhythms. As Figure 3 shown, the pacemaker 150 can also be configured to communicate bidirectionally with an external device 50 via the communication link 68.

[0118] In some examples, the leadless pacemaker 150 can be configured to deliver a cardiac electrical stimulation therapy that can be selected in response to determining whether the concerning heart rate is HU or HS. When a slow heart rate is detected and determined to be HU, the leadless pacemaker 150 can deliver a bradycardia pacing pulse at a rate faster than the sensed intrinsic rate. The leadless pacemaker 150 can be configured to deliver ATP when a tachycardia is detected or when a rapid heart rate is determined to be HU. The leadless pacemaker 150 can deliver ATP based on whether the detected tachycardia is HS or HU. The leadless pacemaker 150 can deliver ATP in response to detecting an HS tachycardia and, if the detected tachycardia is determined to become HU, the leadless pacemaker 150 can continue to deliver ATP. The medical device system 110 can send an alert or make an EMS call in response to detecting a HU heart rhythm. In some examples, the leadless pacemaker 150 can collaboratively detect a HU heart rhythm with the EEG sensor 40 to issue an alert or an EMS phone call without being configured to deliver an ATP therapy in response to a HU heart rhythm.

[0119] While in Figure 3The ICD is not shown in the example of, but it should be understood that the leadless pacemaker 150 can be co-implanted with the EEG sensor 40 and an ICD (e.g., Figure 1 the ICD 14 shown). The leadless pacemaker 150 can be configured to deliver ATP when the ICD is co-implanted in a patient such that if the tachyarrhythmia is not terminated by the ATP delivered by the pacemaker 150, the co-implanted ICD can deliver a CV / DF shock to treat and terminate the tachyarrhythmia. For example, if an ICD is co-implanted to deliver a CV / DF shock to terminate a HU tachyarrhythmia, the pacemaker 150 can deliver ATP when the detected tachyarrhythmia is determined to be HS and stop delivering ATP when the detected tachyarrhythmia is determined to be HU.

[0120] In other examples, the pacemaker 150 can be co-implanted with the cardiac monitor 44 ( Figure 1 shown in). The cardiac monitor 44 can be configured to monitor a heart rate of concern and / or perform a tachyarrhythmia detection algorithm and, in cooperation with the EEG sensor 40, determine when the heart rhythm is HU. The cardiac monitor 44 can send a communication signal to the pacemaker 150 to trigger the delivery of a therapy (e.g., bradycardia pacing or ATP) of the pacemaker 150 based on whether the heart rhythm is HU or HS. When an ICD is not present, the pacemaker 150 can be triggered to deliver ATP when the detected tachyarrhythmia is HU to attempt to restore hemodynamic stability. When an ICD is also co-implanted with the pacemaker 150, the pacemaker 150 can be triggered to deliver ATP as long as the detected tachyarrhythmia is HS. When a HU tachyarrhythmia is detected and an ICD is co-implanted, the pacemaker 150 can be prohibited from delivering ATP and the ICD can deliver a CV / DF shock to terminate the HU tachyarrhythmia.

[0121] The pacemaker 150 is shown positioned in the RV along the endocardial wall, e.g., near the RV apex, but other positions are possible, e.g., along the ventricular septum. The techniques disclosed herein are not limited to Figure 3 the pacemaker positions shown in the examples of. For example, the pacemaker 150 can be positioned in the RA and configured to sense cardiac electrical signals and deliver atrial and / or ventricular pacing from the right atrial position. In some examples, the pacemaker 150 can be coupled to a lead for carrying one or more electrodes. In some examples, the pacemaker 150 can be co-implanted with a second endocardial pacemaker in a dual-chamber pacing system.

[0122] The pacemaker 150 is capable of generating electrical stimulation pulses, such as pacing pulses that are delivered to the heart 8 via electrodes 154 and 156 on the outer housing 152 of the pacemaker. In the illustrated position, the pacemaker 150 is configured to deliver RV pacing pulses and sense RV cardiac electrical signals using the housing-based electrodes 154 and 156 for generating an EGM signal. The EGM signal can be sensed using the housing-based electrodes 154 and 156 that are also used to deliver pacing pulses to the heart 8.

[0123] Electrode 154 is shown as a tip electrode positioned on the distal end 151 of the pacemaker 150. Electrode 156 is shown as an annular electrode surrounding the lateral sidewall 155 of the housing 152 (e.g., adjacent the proximal end 153 of the housing 152). The distal end 151 is referred to as "distal" because it is expected to be the front end when advancing the pacemaker 150 through a delivery tool, such as a catheter, and placing it against the targeted pacing site. The housing 152 can be generally cylindrical in shape to facilitate advancement via a catheter or other delivery tool through a transvenous access to the implantation site. In other examples, the housing 152 can be generally oval or prismatic in shape. The housing 152 can include a longitudinal sidewall 155 extending from the distal end 151 of the housing to the proximal end 153 of the housing to define a lumen for housing the pacemaker electronics.

[0124] Electrodes 154 and 156 can be used as a cathode and anode pair for bipolar cardiac pacing and sensing. Electrodes 154 and 156 can be positioned at locations other than the illustrated position along the pacemaker 150. In other examples, the pacemaker 150 can include two or more annular electrodes, two or more tip electrodes, and / or other types of electrodes, such as button electrodes, segmented electrodes, screw electrodes, fishhook electrodes, etc., that are exposed along the pacemaker housing 152 for delivering electrical stimulation to the heart 8 and sensing cardiac electrical signals. In some examples, the tip electrode 154 is provided as a tissue piercing electrode. The tip electrode 154 can be configured as a tissue piercing electrode for delivering cardiac pacing pulses (including ATP pulses) into a portion of the His-Purkinje conduction system, such as the region of the His bundle, left bundle branch, or right bundle branch, or Purkinje fibers. Electrodes 154 and 156 can be, but are not limited to, titanium, platinum, iridium, or alloys thereof, and can include low polarization coatings, such as titanium nitride, iridium oxide, ruthenium oxide, platinum black, etc.

[0125] The housing 152 is formed of a biocompatible material such as stainless steel or a titanium alloy. In some examples, the housing 152 may include an insulating coating. Examples of insulating coatings include parylene, urethane, PEEK, or polyimide, among others. The entire housing 152 may be insulating, but only the electrodes 154 and 156 are non-insulating. The electrode 154 may act as a cathode electrode and is coupled via an electrical feedthrough across the housing 152 to an internal circuit enclosed by the housing 152, such as a pacing pulse generator and a cardiac electrical signal sensing circuit. The electrode 156 may be formed as a conductive portion of the housing 152 that defines an annular electrode that is electrically isolated from the other parts of the housing 152 as generally shown in Figure 3 In other examples, instead of providing a local annular electrode such as the anode electrode 156, the entire perimeter of the housing 152 may act as an electrode that is electrically isolated from the tip electrode 154. The electrode 156 formed along the conductive portion of the housing 152 acts as a return anode during pacing and sensing.

[0126] The pacemaker 150 may include a set of fixation tines 158 to fix the pacemaker 150 to cardiac tissue, for example, by actively engaging with the ventricular endocardium and / or interacting with the ventricular trabeculae. In the RA position, the fixation tines 158 may be inserted into the atrial endocardium to anchor the pacemaker 150 at the implantation site. The fixation tines 158 are configured to anchor the pacemaker 150 to position the electrode 154 operatively close to the target tissue to deliver therapeutic electrical stimulation pulses. A variety of types of active and / or passive fixation members may be employed to anchor or stabilize the pacemaker 150 in the implantation position.

[0127] The pacemaker 150 may optionally include a delivery tool interface 159. The delivery tool interface 159 may be located at the proximal end 153 of the pacemaker 150 and is configured to connect to a delivery device such as a catheter for positioning the pacemaker 150 at the implantation position (e.g., within a cardiac chamber) during an implantation procedure.

[0128] Figure 4 is a conceptual diagram of an IMD configured to sense cardiac electrical signals and deliver cardiac electrical stimulation therapy. In conjunction with Figure 1 the ICD 14 described Figure 4 includes relatively low voltage cardiac pacing therapy delivery capabilities and relatively high voltage CV / DF therapy delivery capabilities. However, it should be understood that the circuits described in conjunction with Figure 4 and the functionality attributed to those circuits may be included, in whole or in part, in any of the example IMDs described or listed herein that are configured to sense at least one cardiac electrical signal and detect a concerning heart rate, such as the cardiac monitor 44, the ICD 114, or the pacemaker 150.

[0129] In some examples, since the housing of the ICD 14 can serve as an electrode in a sensing electrode vector for cardiac signal sensing and / or therapy delivery, the ICD housing 15 is schematically shown as an electrode in Figure 4 The electronic circuitry enclosed within the housing 15 includes software, firmware, and hardware that cooperate to monitor cardiac electrical signals, determine when electrical stimulation therapy is needed, and deliver therapy as needed in accordance with a programmed therapy delivery algorithm and control parameters.

[0130] The control circuit 80 communicates with the therapy delivery circuit 84 and the sensing circuit 86 via a data bus, for example, to sense cardiac event signals, detect heart rhythms, and control the delivery of cardiac electrical stimulation therapy in response to sensed cardiac event signals. The therapy delivery circuit 84 and the sensing circuit 86 are electrically coupled to electrodes 24, 26, 28, 30 and the housing 15 (e.g., carried by a lead 16 as shown in Figure 1 ), and the housing can serve as a common or ground electrode or as an active can electrode for delivering CV / DF shock pulses or cardiac pacing pulses. As described above, Figure 4 the electrodes 24, 26, 28, and 30 shown in can be carried by an advancing non-transvenous lead to position the electrodes sub-sternally, subcutaneously, or sub-muscularly, outside the heart (e.g., as shown in Figure 1 ). In other examples, the electrodes coupled to the sensing circuit 86 and / or the therapy delivery circuit 84 can be carried by a transvenous lead to position the electrodes intravascularly or intracardially (e.g., the electrodes 120, 122, 124, 126, 132, and 134 shown in Figure 2 ). Additionally, in some examples, the electrodes coupled to the ICD (or a pacemaker, such as the pacemaker 150) can include multiple housing-based electrodes that are not carried by leads.

[0131] As Figure 4 shown, the ICD 14 includes a control circuit 80, a memory 82, a therapy delivery circuit 84, a cardiac electrical signal sensing circuit 86, a communication circuit 88, and optionally one or more physiological sensors 89. A power source 98 powers the circuits of the ICD 14, including each of the required components 80, 82, 84, 86, and 88. The power source 98 can include one or more energy storage devices, such as one or more rechargeable or non-rechargeable batteries. The connections between the power source 98 and each of the other components 80, 82, 84, 86, and 88 will be from Figure 4It can be understood from the overall block diagram, but is not shown for clarity. For example, a power source 98 may be coupled to one or more charging circuits included in the therapy delivery circuit 84 to charge a holding capacitor or other charge storage device included in the therapy delivery circuit 84. The holding capacitor or other charge storage device discharges at an appropriate time under the control of the control circuit 80 to generate electrical pulses according to a therapy protocol. In other examples, the power source 98 may be used as a voltage or current source for the therapy delivery circuit 84 without the need for a charge storage device. The power source 98 is also coupled to components of the cardiac electrical signal sensing circuit 86 as needed, such as a sensing amplifier, an analog-to-digital converter, a switching circuit, and the like.

[0132] Figure 4 The circuit representations shown include the functionality included in the ICD 14 and other medical devices operating in accordance with the techniques disclosed herein, and may include any discrete and / or integrated electronic circuit components that implement analog and / or digital circuits capable of performing the functions attributed to the ICD 14 herein. The functionality associated with one or more circuits may be performed by separate hardware components, firmware components, or software components, or integrated within a common hardware component, firmware component, or software component. For example, cardiac event sensing and determining the sensed cardiac event intervals to detect a concerning heart rate and / or tachyarrhythmia detection may be performed in cooperation by the sensing circuit 86 and the control circuit 80, and may include operations implemented in a processor or other signal processing circuits included in the control circuit 80 that execute instructions stored in the memory 82. Control signals such as blanking and timing intervals associated with cardiac event signal sensing (e.g., R-wave sensing and / or P-wave sensing) may be transmitted from the control circuit 80 to the sensing circuit 86 according to programmed sensing control parameter settings.

[0133] The various circuits of the ICD 14 may include application-specific integrated circuits (ASICs), electronic circuits, (shared, dedicated, or group) processors and memories that execute one or more software or firmware programs, combinational logic circuits, state machines, or other suitable components or combinations of components that provide the functionality. The specific form of the software, hardware, and / or firmware used to implement the functionality disclosed herein will be determined primarily by the particular system architecture employed in the medical device system and the particular detection and therapy delivery methods employed by the medical device system. Given the disclosure herein, it is within the ability of those skilled in the art to provide software, hardware, and / or firmware to perform the functionality described in the context of any modern medical device.

[0134] Memory 82 may include any volatile, non-volatile, magnetic, or electrical non-transitory computer-readable storage medium, such as random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically erasable programmable ROM (EEPROM), flash memory, or any other memory device. Additionally, memory 82 may include a non-transitory computer-readable medium storing instructions that, when executed by one or more processing circuits, cause control circuit 80 and / or other ICD components to perform the various functions attributed to ICD 14 or those ICD components. The non-transitory computer-readable medium storing instructions may include any of the media enumerated above.

[0135] The cardiac electrical signal sensing circuit 86 (also referred to herein as “sensing circuit” 86) may be selectively coupled to electrodes 28, 30, and / or housing 15 to sense the electrical activity of a patient's heart. Sensing circuit 86 may additionally be selectively coupled to defibrillation electrodes 24 and / or 26 for use in a sensing electrode vector with one or more of electrodes 28, 30, and / or housing 15. In some examples, sensing circuit 86 may be enabled to selectively receive cardiac electrical signals from one or more different sensing electrode vectors from available electrodes 24, 26, 28, 30, and housing 15. Sensing circuit 86 may monitor one or more cardiac electrical signals for sensing cardiac event signals associated with myocardial depolarization and / or for generating digitized cardiac electrical signals for transmission to control circuit 80 for processing and analysis and / or for further transmission via telemetry circuit 88 to an external device 50. For example, sensing circuit 86 may include a switching circuit for selecting which of electrodes 24, 26, 28, 30, and housing 15 are coupled to one or more sensing channels of sensing circuit 86.

[0136] Sensing circuit 86 may be configured to amplify, filter, rectify, and digitize or otherwise process the cardiac electrical signals received from each selected sensing electrode vector to improve the signal quality for sensing cardiac electrical event signals, such as the R wave associated with ventricular myocardial depolarization and the P wave associated with atrial myocardial depolarization. The cardiac event detection circuit included within sensing circuit 86 may include one or more sensing amplifiers, filters, rectifiers, threshold detectors, comparators, analog-to-digital converters (ADCs), timers, or other analog or digital components configured to sense cardiac event signals.

[0137] The sensing circuit 86 can control the amplitude of the automatically adjusted cardiac event sensing threshold within each cardiac cycle. In response to the received cardiac electrical signal exceeding the sensing threshold, the sensing circuit 86 can sense a cardiac event signal. The sensing circuit 86 can generate a cardiac sensing event signal, for example, an atrial sensing event signal in response to the P-wave sensing threshold being exceeded or a ventricular sensing event signal in response to the R-wave sensing threshold being exceeded. The cardiac sensing event signal can be transmitted to the control circuit 80 to indicate the timing of the sensing threshold being exceeded. The sensing circuit 86 can use various sensing threshold control parameters to set and adjust the cardiac event sensing threshold during each cardiac cycle. These sensing threshold control parameters can be stored in the memory 82 and transmitted from the control circuit 80 to the sensing circuit 86 for use by the hardware, firmware, and / or software of the control circuit 80 and / or the sensing circuit 86 to control the amplitude of the cardiac event sensing threshold according to one or more blanking periods, refractory periods, sensing delay times, fall time intervals, decay time intervals, sensitivities, or other sensing threshold control parameters.

[0138] The control circuit 80 can receive the cardiac sensing event signal from the sensing circuit 86 to determine the sensed event intervals, such as the RR interval (RRI) and / or the PP interval (PPI), through the timing circuit 90. The RRI is the time interval between consecutively sensed R waves and can be determined between consecutive R-wave sensing event signals received by the control circuit 80 from the sensing circuit 86. The PPI is the time interval between consecutively sensed P waves and can be determined by the control circuit 80 between consecutive R-wave sensing event signals received from the sensing circuit 86. Depending on the programmed therapy, the timing circuit 90 can trigger the therapy delivery circuit 84 to: generate and deliver an electrical stimulation pulse in response to the sensed event signal; and / or start a pacing escape interval timer in response to the sensed event signal and restart the escape interval timer in response to the next sensed event signal. The value of the escape interval timer at the next sensed event signal can be cached in the memory 82 as the sensed event interval associated with the sensed event signal. In this way, the memory 82 can store a series of cardiac sensing event intervals, such as the RRI, to determine the sensed heart rate and detect a concerning heart rate.

[0139] As further described below, in some examples, the ICD 14 can request the EEG sensor 40 to analyze the brain electrical activity when a concerning heart rate is detected. The ICD 14 can detect a concerning heart rate when the RRI (or PPI) meets a fast heart rate criterion. Additionally or alternatively, the ICD 14 can detect a concerning heart rate when the RRI (or PPI) meets a slow heart rate criterion. The criteria for detecting a concerning heart rate can be programmed by the user and can be customized for an individual patient according to the patient's needs.

[0140] For example, a rapid heart rate can be detected when the median or average RRI of a threshold number of RRIs or the most recent specified number of RRIs is less than a rapid rate threshold interval. Detection of a rapid heart rate can meet or not meet tachyarrhythmia detection requirements, such as VT or VF detection requirements. When a rapid heart rate is detected, the medical device system can determine whether the heart rhythm is HU or HS. The HU or HS determination can be made before or after detection of a tachyarrhythmia, or when tachyarrhythmia detection is made at a relatively low confidence level or low probability level.

[0141] The ICD 14 can be configured to detect a slow heart rate when the median or average RRI (or PPI) of a threshold number of RRIs (or PPIs) or the most recent specified number of RRIs is greater than a slow rate threshold interval. Detection of a slow heart rate can be a heart rate slower or faster than a programmed lower pacing rate. When the heart rate decreases, but may still be faster than a programmed lower pacing rate, especially in combination with a drop in blood pressure, some patients may experience reduced cerebral perfusion. Thus, a slow heart rate threshold for detecting a concerning heart rate by the control circuit 80 can be defined based on sensed event signals received from the sensing circuit 86. Based on analysis of sensed brain electrical activity, the slow heart rate can be determined as HU or HS.

[0142] The timing circuit 90 can include various timers and / or counters for controlling the timing of therapy delivery by the therapy delivery circuit 84. In response to expiration of an escape interval timer without receipt of a cardiac sensed event signal, the control circuit 80 can control the therapy delivery circuit 84 to generate and deliver a pacing pulse. The timing circuit 90 can additionally be designed to time windows such as a morphology template window, a morphology analysis window, or perform other timing-related functions of the ICD 14, including synchronizing CV / DF shocks or other therapies delivered by the therapy delivery circuit 84 with sensed cardiac events.

[0143] The control circuit 80 may include a tachyarrhythmia detection circuit 92 configured to analyze signals received from the sensing circuit 86 to detect tachyarrhythmias. The tachyarrhythmia detection circuit 92 may detect tachyarrhythmias based on cardiac events sensed by the sensing circuit 86 that meet tachyarrhythmia detection criteria, such as a threshold number of sensed cardiac event signals occurring within sensed event intervals that fall within tachyarrhythmia interval ranges. The tachyarrhythmia detection circuit 92 may be implemented in the control circuit 80 as hardware, software, and / or firmware that processes and analyzes signals received from the sensing circuit 86 for the detection of tachyarrhythmias, such as supraventricular tachycardia (SVT), VT, and / or VF. The tachyarrhythmia detection circuit 92 may include a comparator and a counter that are used to count cardiac event intervals (such as PPI and / or RRI) determined by the timing circuit 90 that fall into various rate detection zones for determining atrial rate and / or ventricular rate or performing other rate or interval-based evaluations of cardiac sensed event signals for the detection and differentiation of tachyarrhythmias.

[0144] For example, the tachyarrhythmia detection circuit 92 may compare the RRI determined by the timing circuit 90 with one or more tachyarrhythmia detection interval zones, such as a tachycardia detection interval zone and a fibrillation detection interval zone. RRIs that fall into the detection interval zones are counted by corresponding VT interval counters or VF interval counters and, in some cases, in a combined VT / VF interval counter included in the tachyarrhythmia detection circuit 92. For example, the VF detection interval threshold may be set to 300 milliseconds (ms) to 350 ms. For example, if the VF detection interval is set to 320 ms, the VF interval counter will count RRIs that are less than 320 ms. When VT detection is enabled, the VT detection interval may be programmed to be in the range of 350 ms to 420 ms, or 400 ms for example. RRIs that are less than the VT detection interval but greater than or equal to the VF detection interval may be counted by the VT interval counter. To detect VT or VF, the corresponding VT or VF interval counter needs to reach a threshold "number of detection intervals" or "NID".

[0145] 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 consecutive intervals, such as 18 out of 18, 24 out of 24, or 32 out of the most recent 32 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, by way of example, the NID required for detecting VF can be 18 VF intervals in the most recent 24 consecutive RRIs or 30 VF intervals in 40 consecutive RRIs. When the VT or VF interval counter reaches the NID, the tachyarrhythmia detection circuit 92 can detect ventricular tachyarrhythmia. The NID can be programmable and can range from as low as 12 VF intervals to as high as 100 VF intervals, without any limitation. The VT or VF intervals can be detected from the most recent specified number of RRIs either continuously or discontinuously. In some cases, a combined VT / VF interval counter can count both VT intervals and VF intervals and detect the onset of tachyarrhythmia based on the fastest interval detected when the specified NID is reached.

[0146] The tachyarrhythmia detection circuit 92 can be configured to perform additional signal analysis to determine whether other detection criteria, such as R-wave morphology criteria and onset criteria, are met before detecting VT or VF. To support additional cardiac signal analysis, the sensing circuit 86 can transfer digitized cardiac electrical signals (e.g., an electrocardiogram (ECG) signal when sensing with electrodes external to the heart or an EGM signal when sensing with intracardiac electrodes) to the control circuit 80 for morphology analysis by the tachyarrhythmia detection circuit 92 to detect and distinguish heart rhythms. The cardiac electrical signals from the selected sensing electrode vectors can pass through filters and amplifiers, be provided to a multiplexer, and then be converted into a multi-bit digital signal by an analog-to-digital converter, all included in the sensing circuit 86 for storage in the memory 82 and / or for real-time transmission via the telemetry circuit 88. The memory 82 can include one or more circular buffers to temporarily store digital cardiac electrical signal segments (or episodes) for analysis by the control circuit 80 and / or by an external device processor 52 after transmission via the telemetry circuit 88. The control circuit 80 can be a microprocessor-based controller that employs digital signal analysis techniques to characterize the digitized signals stored in the memory 82 to identify and classify the patient's heart rhythm using any one of a variety of signal processing methods for analyzing cardiac electrical signals and cardiac event waveforms (e.g., R-waves).

[0147] In some examples, control circuit 80 can establish an R-wave morphology template that is stored in memory 82 and compared to the sensed cardiac electrical signal waveform to determine a morphology match score. In some examples, wavelet transform techniques can be used to determine the morphology match score. The morphology match score can be determined by the tachyarrhythmia detection circuit 92 for differentiating rapid heart rhythms such as SVT, monomorphic VT, polymorphic VT, or VF.

[0148] 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 and / or low-voltage capacitors) and a switch circuit 95 that controls when the charge storage device discharges across a selected pacing electrode vector or CV / DF shock vector via output circuit 96. The following operations can be performed by therapy delivery circuit 84 in accordance with control signals received from 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, timing circuit 90 can include various timers or counters that control when cardiac pacing pulses are delivered. The microprocessor of control circuit 80 can set the amplitude, pulse width, polarity, or other characteristics of the cardiac pacing pulses based on programmed values stored in memory 82.

[0149] In response to detecting VT or VF, control circuit 80 can arrange for and control therapy delivery circuit 84 to generate and deliver therapies such as ATP and / or CV / DF therapy. The therapy can be selected based on determining HS tachyarrhythmia or HU tachyarrhythmia using EEG signals sensed by EEG sensor 40, as further described below. The therapy can be generated by initiating charging of the high-voltage capacitor in charging circuit 94. The charging is controlled by control circuit 80, which monitors the voltage on the high-voltage capacitor that is transmitted to control circuit 80 via a charging control line. When the voltage reaches a predetermined value set by control circuit 80, a logic signal is generated on the capacitor full line and transmitted to therapy delivery circuit 84 to terminate charging. Relatively high-voltage pacing pulses or CV / DF pulses can be delivered to the heart via output circuit 96 of therapy delivery circuit 84 under the control of timing circuit 90, for example, using electrodes 24, 26, and / or can 15 via a control bus. The output circuit can include an output capacitor through which the charged high-voltage capacitor discharges via a switch circuit (e.g., an H-bridge) that determines the electrodes for delivering CV / DF shock pulses and pulse waveforms.

[0150] In some examples, a high voltage therapy circuit configured to deliver CV / DF shock pulses can be controlled by control circuit 80 to deliver pacing pulses, e.g., for delivering ATP, post-shock pacing pulses, or other ventricular pacing pulses. In other examples, therapy delivery circuit 84 can include a low voltage therapy circuit that generates and delivers pacing pulses for a variety of pacing needs. When the medical device system is configured to determine when a slow heart rate is HU, the therapy delivery circuit can be controlled by control circuit 80 to deliver bradycardia pacing pulses at a rate faster than the sensed slow heart rate to improve or restore hemodynamic stability.

[0151] It should be appreciated that the methods for processing and analyzing cardiac electrical signals and EEG signals disclosed herein can be implemented in a medical device system that includes a cardiac monitor 44 for monitoring cardiac electrical signals via sensing circuit 86 and control circuit 80( Figure 1 ), without necessarily having therapy delivery capabilities (e.g., without therapy delivery circuit 84), or in a medical device system that includes a pacemaker (e.g., pacemaker 150( Figure 3 )) without high voltage therapy capabilities such as CV / DF shock capabilities, where the pacemaker monitors cardiac electrical signals and delivers cardiac pacing therapy via therapy delivery circuit 84.

[0152] Sensor 89 can include one or more of an accelerometer, gyroscope, pressure sensor, temperature sensor, oxygen sensor, impedance sensor, or other physiological sensors for sensing signals responsive to changes in a patient's physiological condition. For example, sensor 89 can include an accelerometer for sensing patient body movement and / or patient posture. In some examples, body movement and / or patient posture can be used to detect patient sleep. EEG signals during sleep can be similar to EEG signals during cerebral ischemia. As described below, in some examples, when EEG signal analysis indicates reduced cerebral perfusion and a possible HU rhythm, the medical device system can determine whether the patient is likely asleep. If the patient is asleep, the determination of cerebral ischemia may be indeterminate or of low confidence. Sleep can be detected based on a horizontal or reclined posture (e.g., a non-upright posture) and / or a non-rest level of patient body movement, and control circuit 80 can determine one or both of a horizontal or reclined posture and / or a non-rest level based on accelerometer signals received from sensor 89. Reduced body temperature and / or respiratory rate are other examples that can be determined based on sensor signals received by control circuit 80 from sensor 89 for detecting sleep to distinguish changes in brain electrical activity due to cerebral ischemia from sleep or other physiological conditions.

[0153] In other examples, when cerebral ischemia is detected based on EEG signal analysis, other physiological signals can be analyzed to confirm or verify the likelihood of cerebral ischemia and HU arrhythmia. For example, a decrease in oxygen saturation and / or blood pressure can be detected based on sensor signals received by control circuit 80 from sensor 89. The decrease in oxygen saturation and / or blood pressure can be used by control circuit 80 to confirm the cerebral ischemia detected from the brain electrical activity, thereby indicating HU arrhythmia. Although sensor 89 is shown in Figure 4 as being included in ICD 14, it should be understood that any of the example sensors listed herein can be included in one or more of the medical devices included in a medical device system that performs the methods disclosed herein. For example, any one of EEG sensor 40, cardiac monitor 44, ICD 114, and / or pacemaker 150 can include one or more of the sensors listed above for detecting sleep that can cause the cerebral ischemia condition to be indeterminate and / or for detecting physiological signal changes that can be used to confirm the cerebral ischemia detection and the corresponding HU arrhythmia.

[0154] The control parameters used by control circuit 80 to sense cardiac event signals, detect tachyarrhythmias, and control therapy delivery can be programmed into memory 82 via communication circuit 88. Communication circuit 88 includes a transceiver and an antenna that are used to communicate with an external device 50 (shown in Figure 1 ) using RF communication (such as Bluetooth) or other communication protocols as described above. Under the control of control circuit 80, communication circuit 88 can receive downlink telemetry from external device 50 and transmit uplink telemetry to the external device. Communication circuit 88 can send the sensed cardiac electrical signals (and in some cases, sensed cardiac event markers and associated sensed event intervals) to another medical device (e.g., external device 50) for processing, analysis, and / or display by the external device 50.

[0155] The communication circuit 88 can be configured to transmit and receive data to and from a co-implanted IMD using RF telemetry techniques such as Bluetooth or other wireless RF transmission protocols. However, in some examples, the ICD 14, EEG sensor 40, cardiac monitor 44, ICD 114, and / or pacemaker 150 can communicate using tissue conduction communication (TCC) when co-implanted with one or more other IMDs in a medical device system implementing the techniques disclosed herein. Examples of TCC devices and methods that can be implemented in IMD systems configured to distinguish HS and HU heart rhythms are generally disclosed in U.S. Patent No. 9,636,511 (Carney et al.), U.S. Patent No. 11,213,684 (Peichel et al.), U.S. Patent No. 11,235,162 (Reinke et al.), U.S. Patent No. 11,045,654 (Peichel et al.), and U.S. Patent No. 11,110,279 (Roberts et al.). For example, upon detection of a concerning heart rate or when a tachyarrhythmia detection criterion is met, the ICD 14 can transmit a TCC signal via the communication circuit 88, using, for example, electrodes 28 and 30 or other electrodes coupled to the ICD 14, to request the EEG sensor 40 to analyze the electroencephalogram activity to determine whether the heart rhythm is HU or HS. The communication circuit 88 can receive an RF signal or a TCC signal transmitted by the EEG sensor 40 to indicate whether cerebral ischemia is detected at a level or stage indicative of a HU heart rhythm.

[0156] Figure 5is a conceptual diagram of an electronic circuit that may be included in the EEG sensor 40 according to an example. The EEG sensor 40 may include a processing circuit 200, a memory 202, an EEG sensing circuit 204, a communication circuit 208, and a power supply 210. As described above, the EEG sensor 40 may include one or more sensors 209 for sensing signals responsive to changes in a patient's physiological condition for detecting cerebral ischemia. Any of the example sensors listed herein may be included in the sensor 209. When the EEG sensor 40 includes a nerve stimulation capability, the EEG sensor 40 may optionally include a pulse generator 205. As described above, an IMD included in a medical device system implementing the techniques disclosed herein may be configured to deliver nerve stimulation to alter a patient's autonomic tone in response to detecting a HU rhythm. The pulse generator 205 may be included in the EEG sensor 40 (or in a cardiac monitor 44 in other examples) for delivering nerve stimulation pulses via electrodes 42 in response to a generated therapy control signal to provide a response to HU rhythm detection. The power supply 210 powers the circuits of the EEG sensor 40 as needed, the circuits including each of the circuits 200, 202, 204, 205, 206, and 208. The power supply 210 may include one or more energy storage devices, such as one or more rechargeable or non-rechargeable batteries.

[0157] Figure 5 The functional blocks shown therein represent the functionality included in the EEG sensor 40, which functionality is implemented as one or more discrete and / or integrated electronic circuit components that implement analog and / or digital circuits capable of performing the functions attributed to the EEG sensor 40 herein. The processing circuit 200 may include one or more central processors, ASICs, digital signal processing circuits, or any other suitable electrical components configured to process and analyze data from the EEG sensing circuit 204 and control the operation of the EEG sensor 40. The processing circuit 200 may include hardware particularly suitable for artificial intelligence (AI) and / or machine learning applications, for example, a tensor processing unit (TPU) or other such hardware.

[0158] The memory 202 may include any volatile, non-volatile, magnetic, or electrically non-transitory computer-readable storage medium, such as any of the examples listed above. Additionally, the memory 202 may include a non-transitory computer-readable medium storing instructions that, when executed by the processing circuit 200 (and / or other processing circuits included in the EEG sensing circuit 204 and / or the communication circuit 208), cause the processing circuit 200 to perform the various functions attributed to the EEG sensor 40. The non-transitory computer-readable medium storing instructions may include any of the media listed above.

[0159] The EEG sensor 40 can be configured to sense an electrophysiological signal corresponding to brain electrical activity and analyze the signal to detect a change in the brain electrical activity indicative of cerebral ischemia that may be associated with the HU heart rhythm. The electrophysiological signal is received by the EEG sensing circuit 204 via the electrodes 42. Although only two electrodes are shown in Figure 5 , it is contemplated that three or more electrodes may be coupled to the EEG sensor 40 to sense the electrophysiological signal to monitor the brain electrical activity, which may include separating or extracting the EEG signal from other electrophysiological signals and / or non-physiological noise.

[0160] The EEG sensor 40 can be implanted at a location to detect the electrical activity (e.g., EEG data) corresponding to brain activity, but depending on the implantation location, it may receive cardiac electrical signals and / or skeletal muscle electrical signals and / or other electrophysiological signals. The EEG sensing circuit 204 can be configured to filter, amplify, and digitize the incoming electrophysiological signals to remove electrical noise, cardiac electrical signals, skeletal muscle signals, or other non-EEG signals to pass the EEG signal to the processing circuit 200. The EEG sensing circuit 204 can include one or more filters, amplifiers, analog-to-digital converters (ADCs), rectifiers, comparators, or other circuits for receiving signals from the electrodes 42 and passing the EEG signal representative of the brain electrical activity to the processing circuit 200. For example, the EEG sensing circuit 204 can include one or more input protection circuits to filter the electrical signals sensed via the electrodes 42, and can include an amplifier / filter circuit to remove DC and high-frequency components or any other suitable components.

[0161] In some examples, processing circuitry 200 may also be configured to process incoming EEG signals to remove cardiac electrical signals or other non-EEG signal content from the EEG signals, for example, using blind source separation or other techniques. The processing circuitry 200 may be configured to analyze the EEG signals to determine one or more EEG metrics for detecting cerebral ischemia. In some examples, as further described below, changes in EEG frequency content and / or amplitude may be detected by the processing circuitry 200 to identify two or more stages of cerebral ischemia (which may also be referred to as levels or degrees of cerebral ischemia). However, it should be understood that in some examples, the processing circuitry 200 may control the communication circuitry 208 to transmit an EEG signal episode to another co-implanted device (or external device 50) included in the medical device system for processing and analysis to detect cerebral ischemia indicative of reduced cerebral blood flow, which may be caused by HU tachyarrhythmia. One or more co-implanted IMDs (e.g., ICD 14, cardiac monitor 44, ICD 114, and / or pacemaker 150) may use the detected stages of cerebral ischemia to generate a response to the HU rhythm, which may include selecting a cardiac electrical stimulation therapy response (which may include stopping, delaying, and / or delivering cardiac electrical stimulation therapy) and / or generating an alert to notify the patient, clinician, first responder, or other caregiver of the HU rhythm, which may include calling EMS via a communication network.

[0162] In some examples, processing circuitry 200 can be configured to analyze sensed signals received from sensing circuitry 204 to extract both EEG signals and cardiac electrical signals (e.g., ECG signals). The EEG signals can be analyzed by processing circuitry 200 to detect cerebral ischemia. The ECG signals can be analyzed by processing circuitry 200 to detect a concerning heart rate (e.g., less than a slow heart rate threshold and / or faster than a fast heart rate threshold) and / or to detect and distinguish tachyarrhythmias, such as atrial fibrillation, sinus tachycardia, or other SVT, monomorphic VT, polymorphic VT, and / or VF. In this way, EEG sensor 40 can perform the techniques disclosed herein for detecting HU and HS heart rhythms and generating an alert or notification of HU tachyarrhythmia without the need for another co-implanted IMD. In other examples, EEG sensor 40 can be co-implanted with an IMD (such as ICD 14, ICD 114, or pacemaker 150) that is capable of delivering an electrical stimulation therapy selected based on whether the heart rhythm is determined to be HU or HS. For example, in response to detecting HU tachyarrhythmia, processing circuitry 200 can control communication circuitry 208 to send a communication signal indicating the detected cerebral ischemia or HU heart rhythm to a co-implanted IMD capable of delivering cardiac pacing, ATP, CV / DF shock, vagus nerve stimulation, spinal cord stimulation, or other nerve stimulation. When cerebral ischemia is not detected or the cerebral ischemia is less than a threshold phase of cerebral ischemia, communication circuitry 208 can send a communication signal to the co-implanted IMD indicating that no cerebral ischemia or HS heart rhythm has been detected. When an HS heart rhythm is detected, the co-implanted IMD may or may not deliver a therapy. For example, a slow heart rate as an HS may not require any therapy delivery. However, for example, a fast heart rate detected as VT may require delivery of ATP to terminate HS ventricular tachycardia before it becomes HU.

[0163] In other examples, processing circuitry 200 is configured to analyze signals sensed by electrodes 42 and received from EEG sensing circuitry 204 to extract EEG signal data and discard or reduce any contribution from cardiac or muscular activity. Processing circuitry 200 can be configured to determine one or more EEG metrics that can be sent via communication circuitry 208 for receipt by a co-implanted IMD (or sent to external device 50). The EEG metrics can be sent when cerebral ischemia is detected or in response to a request from a co-implanted IMD that may be detecting a concerning heart rate. The receiving IMD (or external device 50) can determine the phase of cerebral ischemia based on the EEG metrics and perform an appropriate response, such as generating an alert signal ( For example, for calling EMS or notifying a clinician, first responder, family member, or other caregiver), delivering, delaying, or stopping therapy, performing continuous monitoring of EEG signals, or other responses as described herein. In other examples, the processing circuit 200 determines EEG metrics and determines the stage of cerebral ischemia based on the EEG metrics. The communication circuit 208 may send an indication of the stage of cerebral ischemia to a co-implanted IMD (or external device 50), which uses the cerebral ischemia determination to distinguish between HS and HU heart rhythms and select an appropriate response.

[0164] In some examples, the communication circuit 208 may include an antenna and an RF transceiver for sending and receiving data to collaboratively detect HU heart rhythms in conjunction with one or more co-implanted IMDs (and / or external devices). The communication circuit 208 may also be configured to send an alert when cerebral ischemia is detected based on electroencephalographic activity. Additionally or alternatively, the communication circuit 208 may be configured to transmit and receive TCC signals via the electrode 42. For example, the communication circuit 208 may be configured to receive and demodulate a TCC signal received via the electrode 42, which triggers the processing circuit 200 to analyze the incoming EEG signal to determine one or more EEG metrics and determine the stage of cerebral ischemia. The communication circuit 208 may send a TCC signal via the electrode 42 to another co-implanted IMD (such as ICD 14, cardiac monitor 44, ICD 114, and / or pacemaker 150) to indicate the detection of cerebral ischemia and / or convey the stage (or level or degree) of cerebral ischemia. The communication circuit 208 may include an oscillator that generates a carrier signal that is modulated to produce a TCC signal, which in some examples may have a frequency of 10 kHz to 100 kHz and an amplitude amplified to 50 millivolts to 500 millivolts. Examples of TCC communication circuits and techniques that may be implemented in an IMD system for performing the methods disclosed herein are generally disclosed in U.S. Patent No. 9,636,511 (Carney et al.), U.S. Patent No. 11,213,684 (Peichel et al.), U.S. Patent No. 11,235,162 (Reinke et al.), U.S. Patent No. 11,045,654 (Peichel et al.), and U.S. Patent No. 11,110,279 (Roberts et al.), which are incorporated above.

[0165] Figure 6 is a flowchart 300 of a method for distinguishing between HU and HS heart rhythms that may be performed by a medical device according to some examples. Figure 6 The process may be performed by a processing circuit included in one or more IMDs (such as one or more of ICD 14, ICD 114, cardiac monitor 44, and / or pacemaker 150) and the EEG sensor 40. For illustration, in conjunction with including Figure 1The process will be described with respect to the co-implanted EEG sensor 40 and IMD system of the ICD 14 shown. Figure 6 However, it should be understood that different combinations of medical devices, which may include one or more wearable or other external devices, can be configured to collaboratively detect a concerning heart rate and identify the heart rhythm as HU or HS. Additionally, in some examples, a single device can sense both cardiac electrical activity and electroencephalographic activity to detect a HU rhythm and generate an alert or an EMS call and / or deliver therapy to promote or restore hemodynamic stability.

[0166] At block 302, a concerning heart rate can be detected from the ECG signal sensed by the ICD 14. For example, the concerning heart rate can be a rapid heart rate detected based on RRI determined from ventricular sensed event signals received by the control circuit 80 from the sensing circuit 86. The rapid heart rate can be detected based on a threshold number of RRIs among the most recent number of RRIs that are shorter than a rapid rate threshold. For example, a rapid heart rate can be detected when the NID for detecting VT is reached. In other examples, a rapid heart rate can be detected when the number of VT intervals counted by the control circuit 80 is less than the NID required to detect VT. In other examples, a rapid heart rate can be detected when a threshold number of rapid VT or VF intervals are reached, where the rapid VT or VF detection intervals are shorter than the VT detection intervals. Thus, in some examples, the detection of a rapid heart rate can be the detection of VT or VF associated with the rapid heart rate according to a tachyarrhythmia detection algorithm. However, in other examples, detecting a rapid heart rate as a concerning heart rate at block 302 may not correspond to meeting VT or VF detection criteria and can be based on an interval / rate-based criterion different from the VT or VF detection criteria.

[0167] Without limitation, when the threshold number of intervals is shorter than 400 ms, 380 ms, 360 ms, 340 ms, 320 ms, 300 ms, 280 ms, or 260 ms, the control circuit 80 may detect a rapid heart rate at block 302. As an example, the threshold number may be between 3 RRIs and 100 RRIs. In some examples, the threshold number of intervals is between 12 RRIs and 80 RRIs. In some examples, a relatively high threshold number of RRIs may be applied to detect a rapid heart rate and initiate EEG signal analysis because changes in the EEG signal due to cerebral ischemia caused by HU arrhythmia may delay the onset of the rapid heart rate. In other examples, EEG signal analysis may begin after a relatively small threshold number of RRIs that is less than the rapid rate threshold interval. Initiating EEG signal monitoring early at the onset of a rapid heart rate may enable tracking of the start time and the time interval during which the electroencephalogram activity changes. The start time and the time at which the electroencephalogram activity changes may enable the medical device system to distinguish cerebral ischemia due to HU arrhythmia from other conditions that may cause similar EEG signal changes, such as sleep, drug effects, stroke, and the like. Thus, in various examples, the threshold number of RRIs that are less than the rapid interval threshold may be less than, equal to, or greater than the NID used by the control circuit 80 to detect VT or VF. In other examples, a mean, median, or other representative RRI may be determined based on a specified number of RRIs (e.g., 8 to 100 RRIs) and compared to the rapid interval threshold for detecting a rapid heart rate.

[0168] In response to meeting the rapid heart rate criteria, an analysis of the EEG signal may be performed to distinguish whether the heart rhythm is HS or HU. In other examples described below, in addition to or as an alternative to the interval-based rate criteria, before analyzing the EEG signal to distinguish HS and HU heart rhythms upon detection of a rapid heart rate, the ICD control circuit 80 may also detect tachyarrhythmia based on morphological analysis of one or more sensed ECG (or EGM) signals and based on meeting VT or VF detection criteria.

[0169] In some cases, a concerning heart rate detected at block 302 can be a slow or irregular heart rate detected based on the RRI determined from ventricular sensing event signals received by the ICD control circuitry 80 from the sensing circuitry 86. A slow heart rate can be detected based on a threshold number of RRIs in the most recent number of RRIs that are longer than a slow rate threshold interval. A slow heart rate can be detected when the mean, median, or other representative RRI is longer than the slow rate threshold interval. In other examples, an irregular heart rate can be detected as a concerning heart rate, such as based on RRI variability. The slow heart rate can be equal to or faster than a programmed lower pacing rate. For example, the programmed lower pacing rate can be 30, 40, or 50 beats per minute (bpm). For example, a concerning heart rate can be detected in a particular patient when the RRI corresponds to a heart rate less than 60 bpm, 55 bpm, 50 bpm, 45 bpm, 40 bpm, 35 bpm, or 30 bpm. Some patients may experience various forms of syncope that can occur at relatively slow heart rates that can be faster than the programmed lower pacing rate (and in some cases, the implanted device of the medical device system may not be configured to deliver bradycardia pacing). Thus, the medical device system can be configured to detect a concerning heart rate based on fast heart criteria and / or slow heart criteria according to the individual needs of a particular patient.

[0170] In some examples, when a concerning heart rate is detected at block 302, the control circuitry 80 can cause the communication circuitry 88 to send a signal requesting cerebral ischemia data to the EEG sensor 40. In other examples, the EEG sensor 40 can be configured to detect a concerning heart rate using any of the above criteria such that a request for cerebral ischemia data from the ICD 14 is not required to trigger the EEG sensor 40 to analyze the electroencephalogram activity. As described above, the EEG sensor 40 can be configured to extract cardiac electrical activity from the electrical signals received via the electrodes 42. For example, the EEG sensor 40 can filter the electrical signals, use blind source separation or other techniques to obtain an ECG signal (or more generally, cardiac electrical activity) from which a concerning heart rate can be detected at block 302.

[0171] When the EEG sensor 40 detects a concerning heart rate, the EEG sensor 40 can analyze the sensed EEG signal at block 304 to determine an EEG metric without requiring a request received from the ICD 14. Thus, in some examples, both the EEG sensor 40 and the ICD 14 can be configured to detect a concerning heart rate from the electrical signals sensed by the respective devices at block 302. In other examples, only the EEG sensor 40 can detect a concerning heart rate at block 302 based on RRI data determined from an ECG signal that is filtered from the electrical signals sensed by the EEG sensor 40. The ICD 14 can perform a VT / VF or other arrhythmia detection algorithm, which may or may not include detecting a concerning heart rate according to the same interval - or rate - based criteria and thresholds used by the EEG sensor 40. In such a case, if the ICD 14 requires it, e.g., when VT detection criteria are met, the EEG sensor 40 can send data to the ICD 14 for determining the HU heart rhythm.

[0172] At block 304, the processing circuitry 200 of the EEG sensor 40 can determine one or more EEG metrics from the sensed EEG signal. The EEG metrics can be determined in response to the EEG sensor 40 detecting a concerning heart rate or in response to a communication signal received from the ICD 14. At block 306, the EEG sensor processing circuitry 200 can determine whether the EEG metrics meet the cerebral ischemia criteria. When the cerebral ischemia criteria are not met, the medical device system can detect an HS heart rhythm at block 308. For example, the EEG sensor 40 can send a signal at block 308 indicating that no cerebral ischemia or "normal" EEG metrics and / or HS heart rhythm indicators have been detected. The processing circuitry of the medical device system can generate an output at block 310 in response to detecting the HS heart rhythm. The output can be used to control the response to the HS heart rhythm detection. For example, in response to receiving a signal from the EEG sensor 40 indicating no cerebral ischemia, the ICD control circuitry 80 can generate an output that can be stored in the memory 82, which can include a therapy selection and / or therapy control signal for selecting and controlling a therapy response at block 310. The therapy response can include delivering, stopping, or delaying therapy according to the detected heart rate or detected arrhythmia and the available programmed therapies. The output generated at block 310 can be used to control the therapy delivery circuitry 84 to deliver, stop, or delay therapy according to the detected heart rate and rhythm. In other examples, the output generated at block 310 can be used to send a therapy control signal to another medical device, such as a pacemaker 150 or a nerve stimulation device.

[0173] When a concerning heart rate is detected as a rapid heart rate, the ICD control circuit 80 may generate a therapy control signal output at block 310 to stop all ATP and CV / DF therapies because the rapid heart rate is determined to be HS (the cerebral ischemia criteria are not met at block 306). In other examples, when the control circuit 80 detects VT but the rapid heart rate associated with the VT is determined to be an HS rhythm, the control circuit 80 may select a therapy response by delivering ATP via the therapy delivery circuit 84 at block 310. If the VT is HS, the control circuit 80 may stop or delay any CV / DF shock therapies that may be programmed in the therapy menu when the VT is detected. In other examples, when a pacemaker 150 is present, a communication signal may be sent from the EEG sensor 40 or from the ICD 14 to trigger the pacemaker 150 to deliver ATP in response to the detected rapid heart rate that is determined to be HS. The ICD control circuit 80 may stop or delay CV / DF shocks in response to detecting VT that is determined to be HS.

[0174] When the concerning heart rate is a slow heart rate that is determined to be HS, the therapy delivery circuit 84 of the ICD 14 (or the pacemaker 150, if present) may be controlled (based on the output generated at block 310) to stop cardiac pacing. However, if the slow heart rate drops below a programmed lower pacing rate, the therapy delivery circuit 84 (or the pacemaker 150) may deliver cardiac pacing at the lower rate to treat bradycardia and prevent cardiac arrest or prolonged ventricular pauses.

[0175] The output generated at block 310 may include storing the onset of the EEG signal and / or the onset of the ECG signal and / or the onset of other sensor signals that may be available. The output may include EEG metrics and / or the cerebral ischemia stage determined from the EEG metrics. Data stored in the memory of the medical device system in conjunction with the HS rhythm determination may be sent to an external device 50 for use by a clinician in monitoring and managing the patient.

[0176] The ICD control circuit 80 and / or the EEG sensor processing circuit 200 may be configured to detect the termination of a concerning heart rate at block 312. For example, the termination of a rapid heart rate may be detected based on a threshold number of slow RRIs that are longer than a rapid rate interval or longer than the rapid rate interval plus an offset. The threshold number of slow RRIs required to detect termination may be equal to, less than, or greater than the threshold number of rapid RRIs required to detect a rapid heart rate at block 302. The ICD 14 may be configured to detect the termination of VT at block 312 according to multiple termination detection algorithms and criteria. When a concerning heart rate is detected as a slow heart rate, termination may be detected at block 312 when the heart rate is greater than a slow heart rate threshold (e.g., based on a threshold number of RRIs or a mean or median RRI that is shorter than a slow rate RRI threshold). When the termination of a concerning heart rate is detected, the process of flowchart 300 may return to block 302 to wait until the concerning heart rate criteria are met again. If termination is not detected, the EEG sensor processing circuit 200 may re-determine the EEG metric at block 304 for comparison with the cerebral ischemia criteria at block 306.

[0177] When the EEG metric meets the cerebral ischemia criteria indicating a HU heart rhythm at block 306, the medical device system detects a HU heart rhythm at block 320. Examples of EEG metrics and criteria for detecting cerebral ischemia and optionally differentiating different stages of cerebral ischemia are described below in connection with Figure 7 and Figure 8 The HU heart rhythm may be detected at block 320 by the ICD control circuit 80 in response to a communication signal received from the EEG sensor 40, which is sent when the EEG metric meets the cerebral ischemia criteria determined by the EEG sensor processing circuit 200. In these examples, the EEG sensor processing circuit 200 determines when the EEG metric meets the cerebral ischemia criteria and controls the EEG sensor communication circuit 208 to send a signal indicating the detection (or non-detection) of cerebral ischemia. It should be understood that in other examples, the EEG sensor 40 may be configured to send the determined EEG metric to the ICD 14. The ICD control circuit 80 may analyze the EEG metric to determine when cerebral ischemia is detected, which may include determining the stage of cerebral ischemia, as further described below. In other examples, the EEG sensor 40 may send an EEG signal onset to the ICD 14 to determine the EEG metric, detect the stage of cerebral ischemia, and determine whether the detected concerning heart rate is HS or HU.

[0178] When a concerning heart rate is detected and slows down (from a fast rate) or increases (from a slow rate) to a rate that is not a concerning heart rate, EEG analysis can be aborted. For example, the ICD 14 can send a signal to the EEG sensor 40 to indicate that a concerning heart rate is no longer detected at any time during the process of the flowchart 300. For example, spontaneous termination of non-sustained VT may occur, in which case EEG signal analysis may no longer be needed. Thus, although the boxes 312 and 324 for detecting termination are shown as occurring after generating an output at box 312 or 322 to provide a response to HS heart rhythm detection or HU heart rhythm detection, respectively, it should be understood that the termination of a concerning heart rate can be determined by the ICD control circuit 80 (and / or the EEG sensor 40) at any time during the process of the flowchart 300. When the termination of a concerning heart rate is detected, the EEG analysis for determining cerebral ischemia can be aborted. However, in other examples, the EEG analysis for determining cerebral ischemia can continue after the termination of a concerning heart rate to verify hemodynamic recovery, for example, as described in connection with Figure 11 below. In some cases, the termination of a concerning heart rate may be falsely detected, for example, due to insufficient or excessive sensing of cardiac electrical event signals.

[0179] When a HU heart rhythm is detected in response to a concerning heart rate and cerebral ischemia detection at box 320, the processing circuit of the medical device system can generate an output at box 322 to provide a response to the detected HU heart rhythm. The output can be stored in the memory of the medical device system, for example, received and stored by the memory 82 from the control circuit 80, and used by the medical device system to perform one or more responses at box 322. The output can include a command or signal for sending an alert or notification of the HU heart rhythm. The output can be used to send an alert to the patient, clinician, caregiver, or first responder by the medical device system (e.g., via the EEG sensor communication circuit 208 or via the ICD communication circuit 88). The external device 50 or another device can receive the alert and be configured to make a phone call to the EMS. Sending an alert indicating the detection of a HU heart rhythm can be the primary response performed by the medical device system, which includes a sensing and monitoring device without therapy delivery capabilities (or only with cardiac pacing therapy capabilities but without CV / DF shock therapy capabilities), for example, when the EEG sensor 40 and the cardiac monitor 44 are co-implanted in a patient with or without a pacemaker 150.

[0180] Additionally or alternatively, the output generated by the medical device system processing circuitry at block 322 can include a therapy selection signal or a therapy control signal for providing a response at block 322, the response including delivering a therapy via a medical device of the medical device system. The generated output can include a therapy control signal that is a CV / DF shock therapy signal. The ICD 14 can deliver a CV / DF shock when determining a HU rhythm, particularly when VT or VF detection criteria are met. In some examples, ATP can be delivered prior to delivering a CV / DF shock during a first attempt to terminate a HU rhythm. ATP can be delivered if cerebral ischemia has not reached a moderate or severe stage, for example, associated with cell injury or death, or ATP can be delivered during the charging of a high-voltage capacitor to attempt to treat the HU rhythm as quickly as possible before the capacitor charging for CV / DF shock delivery is complete. Generally, one or more CV / DF shocks can be delivered as early as possible after detecting a HU rhythm to avoid or minimize the duration of loss of consciousness and / or avoid or minimize ischemic brain injury and cell death.

[0181] When the rate of concern is a slow rate determined to be HU, the response at block 322 can include generating a therapy pacing control signal based on the therapy control signal to control the delivery of cardiac pacing at a rate faster than the sensed heart rate to promote or restore hemodynamic stability. The pacing rate can be faster than a programmed lower rate such that the heart is paced at a rate faster than the intrinsic heart rate detected as a HU rhythm. The output generated by the control circuitry 80 at block 322 to provide a response to the detected HU rhythm can include a pacing control signal that can be communicated to the therapy delivery circuitry 84 to control cardiac pacing. The output generated by the control circuitry 80 at block 322 to provide a response to the detected HU rhythm can include a pacing control signal that is sent to another device, such as a pacemaker 150, to deliver cardiac pacing. In an example of a medical device system that includes a neurostimulation therapy capability, a therapy control signal can be output at block 322 to cause stimulation of the vagus nerve, spinal cord, or other nervous system tissue to be delivered to alter autonomic tone, such as increasing sympathetic nervous system activity.

[0182] When the HU heart rate is a slow or variable heart rate faster than the currently programmed pacing lower rate, the output generated at block 322 can include an adjustment to the programmed lower pacing rate. The programmed lower pacing rate can be increased or adjusted to the pacing rate required to overdrive pace the intrinsic heart rate detected as the HU heart rate. The programmed lower pacing rate can be increased to 5 bpm to 20 bpm greater than the detected rate of concern or approximately 10 bpm faster than the intrinsic rate of concern. In this way, the current episode of the HU heart rate can be treated by delivering cardiac pacing according to the adjusted lower pacing rate. Future episodes of the HU heart rate as a slow or variable heart rate can be avoided because pacing at the adjusted lower pacing rate can avoid the HU heart rate.

[0183] The increased lower pacing rate can be a temporary lower pacing rate that can be effective for a fixed period of time, which can be programmable. The increased temporary lower pacing rate can remain effective for 0.2 hours, 0.5 hours, 1 hour, 4 hours, 8 hours, 12 hours, or 24, 48 hours, or 72 hours, by way of example and not limitation. When the time period expires, the lower pacing rate can return to the programmed permanent lower pacing rate. In some examples, the EEG signal is continued to be monitored during and / or after pacing at the temporary lower pacing rate to verify that the cerebral ischemia condition has been reversed, and if not reversed, the ICD 14 or the EEG sensor 40 can send an EMS call or other emergency notification or alert signal. If the cerebral ischemia condition is still detected during the time period, the temporary lower pacing rate can be increased, for example, 5 bpm to 10 bpm until a specified maximum lower pacing rate, to attempt to alleviate the cerebral ischemia condition. If the cerebral ischemia criteria are met after the time period expires, pacing at the temporary lower pacing rate can be resumed for another time period, and the time period can optionally be increased.

[0184] In other examples, the permanent lower pacing rate can be increased in response to detecting a HU heart rate of a slow or variable heart rate. The output generated at block 322 can include a notification sent to the external device 50 to notify the clinician that the permanent (or temporary) lower pacing rate has been increased and to what rate. The clinician can reprogram the permanent lower pacing rate as needed. For example, the clinician can choose to reprogram the permanent lower pacing rate to an automatically adjusted temporary lower pacing rate.

[0185] The ICD control circuit 80 can generate an output at block 320 by storing an adjusted temporary or permanent lower pacing rate in the memory 82. When there is another co-implanted device (e.g., the pacemaker 150) providing bradycardia pacing, the control circuit 80 can control the communication circuit 88 to send a command to temporarily or permanently adjust the lower pacing rate. The pacemaker 150 can receive commands from the ICD 14 directly or via the external device 50 and adjust the permanent or temporary lower pacing rate accordingly.

[0186] At block 324, the EEG sensor 40 and / or the ICD 14 can be configured to determine whether the HU rhythm has been terminated by the delivered therapy. In some examples, if the rapid rhythm is not terminated after ATP or CV / DF shock, the control circuit 80 can control the ICD therapy delivery circuit 84 to deliver another therapy without having to re-evaluate the EEG signal to detect cerebral ischemia. In other examples, when the ICD 14 delivers one or more therapies to determine whether the detected cerebral ischemia condition has improved or is no longer detected, the EEG signal can continue to be analyzed by the EEG sensor processing circuit 200. If an improvement in cerebral ischemia is detected, such that the cerebral ischemia criteria for detecting the HU rhythm are no longer met at block 306, the EEG sensor communication circuit 208 can send a signal to the ICD 14 to indicate that cerebral ischemia is no longer detected. The medical device system can detect the HS rhythm at block 308 and can stop or delay any scheduled therapy at block 310. For example, if the first CV / DF shock has been delivered and the rapid rate has not been terminated but the EEG metric no longer meets the cerebral ischemia criteria, the next scheduled CV / DF shock can be stopped at block 310. If the VT detection criteria are still met, ATP can be delivered. In this way, the EEG sensor 40 and the ICD (and / or pacemaker), such as the ICD 14 or ICD114 (and / or the pacemaker 150), can control ATP and CV / DF therapies based on whether the detected concerning heart rate is identified as an HS or HU rhythm based on the EEG metric.

[0187] When the concerning heart rate is a slow heart rate, the control circuit 80 can determine at block 324 whether to increase the intrinsic heart rate (e.g., by stopping cardiac pacing by the therapy delivery circuit 84 and determining that the intrinsic RRI is shorter than the slow heart rate interval threshold). If the intrinsic heart rate increases, the process can return to block 302. However, when the concerning heart rate is a slow heart rate, the medical device system can be configured to determine at block 324 whether the EEG metric no longer meets the cerebral ischemia criteria to detect the termination of the HU rhythm after cardiac pacing has started.

[0188] Regardless of the intrinsic heart rate after cardiac pacing has been initiated in response to a slow heart rate that is HU, the medical device system can verify that cerebral ischemia is no longer detected, particularly if cardiac pacing is stopped. Cardiac pacing can continue and the EEG metric can be re-determined at block 324 to detect termination of the HU rhythm. In other examples, cardiac pacing can be terminated and the EEG metric can be re-determined at block 324 to detect termination of the HU rhythm. If cerebral ischemia is still detected such that the HU rhythm has not terminated (the "no" branch of block 324), then if the EEG metric again meets the cerebral ischemia criteria (as determined at blocks 304 and 306), cardiac pacing can be restarted. Cardiac pacing initiated at block 322 in response to detection of a slow heart rate that is HU can be delivered for a fixed time interval, such as 30 seconds to one hour of cardiac pacing, or a fixed number of cardiac pacing pulses, such as 10 to 100 pacing pulses. After the specified cardiac pacing time interval has expired (or the specified number of pacing pulses have been delivered), the EEG metric can be re-determined at block 324 to verify that the HU rhythm has been terminated (regardless of whether a slow heart rate is still detected).

[0189] Figure 7 FIG. 400 is a diagram of various examples of EEG signals 402, 404, 406, 408, and 410 that can be sensed by EEG sensor 40 during different stages (1 to 5) of cerebral ischemia. Cerebral perfusion can be measured as the blood volume per unit time per unit mass of brain tissue (e.g., milliliters (mL)), and can generally average about 50 mL / 100 grams / minute. However, it should be appreciated that under normal physiological conditions, when blood flow to the brain is unimpaired, different parts of the brain (e.g., white matter versus gray matter) can have perfusion rates that are higher or lower than this general average. Cerebral blood flow (CBF) can be measured as the blood volume per unit time. CBF can generally be 700 mL / minute to 800 mL / minute or about 750 mL / minute, and can be about 10% to 20% or about 15% of the cardiac output.

[0190] The EEG power spectrum representing brain electrical activity can include multiple frequency bands known as the beta, alpha, delta, and theta frequency bands. Beta waves can be defined as neural oscillations of the EEG power spectrum at 12 Hz or higher (e.g., in the range of 12 Hz to 38 Hz, in the range of 14 Hz to 30 Hz, or in the range of 15 Hz to 40 Hz). Alpha waves are neural oscillations in a range that can be defined by a lower limit of about 6 Hz to 8 Hz to an upper limit of about 12 Hz to about 15 Hz. Theta waves are neural oscillations that can be in a range defined by a lower limit of about 3 Hz to 5 Hz to an upper limit of about 6 Hz to about 8 Hz. Delta waves are neural oscillations in a frequency range less than 5 Hz, less than 4 Hz, less than 3 Hz, or less than 2.5 Hz. The delta band can be defined as having a lower limit of 0.5 Hz to 1 Hz. As cerebral ischemia progresses and cerebral perfusion decreases, the EEG power spectrum can shift from a relatively higher dominant frequency band to a relatively lower dominant frequency band to completely or nearly completely suppress brain electrical activity, as shown by EEG signal 410 in stage 5 cerebral ischemia.

[0191] During normal waking consciousness, during normal cerebral perfusion, and during an initial relatively small reduction in cerebral perfusion (e.g., a reduction of less than 30%), beta waves are present in the EEG. EEG signal 402 represents a normal EEG signal during normal CBF or stage 1 ischemia during waking consciousness, when CBF can be reduced but there is no significant change in brain electrical activity compared to normal brain electrical activity. For example, when cerebral perfusion is still within 80%, 75%, or even 70% of the normal perfusion rate, the dominant frequency of EEG signal 402 can be in the beta band. Thus, EEG signal 402 illustrates the EEG signal that can be sensed by EEG sensor 40 during normal CBF or during "stage 1" of the 5 possible stages of cerebral ischemia. Cerebral blood flow (CBF) or cerebral perfusion can be reduced by less than 30%, less than 25%, or less than 20% from the normal average cerebral perfusion rate of a given patient or from the normal average cerebral perfusion rate representative of a patient population. Stage 1 can be detected by the processing circuit 200 of EEG sensor 44, for example, based on an EEG metric determined from EEG signal 402, which is within the normal range of an analog EEG metric determined from EEG signals sensed during normal, non-impaired CBF conditions in a waking patient.

[0192] Thresholds based on normal values of EEG metrics representative of a patient population can be programmed in the EEG sensor memory 202 for comparison with EEG metrics determined by the processing circuit 200 from sensed brain electrical activity. In other examples, thresholds applied to EEG metrics to detect stages of cerebral ischemia can be customized for a patient. For example, as further described below, the EEG sensor processing circuit 200 can establish a baseline or normal EEG metric for a given patient by determining the EEG metric during normal sinus rhythm (e.g., a heart rate within a normal resting range, such as less than 100 bpm and greater than at least 40 bpm or within a range of approximately 60 bpm to 90 bpm). The EEG sensor 40 can confirm the normal resting range by determining the heart rate based on ECG data extracted from signals sensed by the EEG sensor electrodes 42 and / or based on communication signals sent by another device (e.g., external device 50, cardiac monitor 44, ICD 14, ICD 114, or pacemaker 150). In some examples, the normal resting range for a given patient can be programmed by the user using the external device 50 or can be "learned" by the medical device system based on tracking the heart rate history of the given patient.

[0193] EEG signals 404, 406, 408, and 410 represent stages of cerebral ischemia that increase (deteriorate) as cerebral perfusion decreases (e.g., due to HU arrhythmia). The higher frequency content present in EEG signal 402 (e.g., in the beta band) decreases in EEG signal 404. As an example, the dominant frequency in EEG signal 404 can be in the alpha band, such as in the range of about 7 Hz to 15 Hz or about 8 Hz to 14 Hz. Stage 2 EEG signal 402 can correspond to a cerebral perfusion reduction of 30% to 50% from normal cerebral perfusion. For example, the stage 2 EEG signal can be sensed by the EEG sensor 40 in the range of approximately 25 mL / 100g / minute to 35 mL / 100g / minute during cerebral perfusion.

[0194] EEG signal 406 represents an EEG signal that can be sensed by the EEG sensor 40 during a further reduction in cerebral perfusion (e.g., a 50% to 70% reduction in CBF, or in the range of about 18 mL / 100g / minute to 25 mL / 100g / minute). A further loss of higher frequency content can occur as cerebral ischemia increases, as shown in Figure 7 stage 3. The dominant frequency during stage 3 can be in the theta band, such as between 4 Hz and 7 Hz. In addition to the reduction of higher frequency band content in the EEG signal during ischemia, from Figure 7 it can be observed that the amplitude of the brain electrical activity oscillations can increase. Thus, the EEG sensor processing circuit 200 can be configured to determine frequency metrics and / or amplitude metrics from the sensed EEG signals to determine the stage of cerebral ischemia.

[0195] As cerebral perfusion is further reduced, the EEG signal 408, shown as representative of stage 4 cerebral ischemia, can be sensed by the EEG sensor 40. During stage 4 cerebral ischemia, the dominant frequency of the EEG signal 408 can be in the delta band, e.g., between 0.5 Hz and 4 Hz. Stage 4 cerebral ischemia with a dominant delta band frequency can be associated with the onset of ischemic brain injury. The amplitude of the oscillations of the EEG signal 408 is further increased compared to the lower stages 1 to 3. In stage 5 cerebral ischemia, suppression of neural oscillations occurs. During stage 5 cerebral ischemia, cell death and cerebral infarction may occur. In some examples, the thresholds for detecting the HU rhythm and the HS rhythm can correspond to the detection of stage 2 or 3 cerebral ischemia. Detection at stage 2 or higher or detection at stage 3 or higher can be evidence of the HU rhythm, e.g., when a concerning heart rate is detected. Detection of the stage 1 EEG metric can indicate the HS rhythm.

[0196] In general examples, when one or more amplitude metrics and / or one or more frequency metrics determined from electroencephalographic activity indicate stage 1 cerebral ischemia, the HS rhythm can be detected by the medical device system. If the rhythm is a rapid heart rate that can be associated with VT or VF, the CV / DF shock can be stopped or delayed when the medical device system is capable of delivering a high voltage shock. If one or more amplitude metrics and / or one or more frequency metrics determined from electroencephalographic activity indicate moderate cerebral ischemia, e.g., stage 2, 3, or 4, the medical device system can detect a concerning heart rate as the HU rhythm. Detection of moderate cerebral ischemia can be based on the relatively increased amplitude and / or relatively decreased frequency of neural oscillations in the sensed electroencephalographic activity. When the rhythm is a rapid heart rate that can be associated with VT or VF, a CV / DF shock can be delivered to terminate the HU rhythm. When the sensed electroencephalographic activity is determined to be severe ischemia (e.g., stage 5), a CV / DF shock can be delivered or may not be delivered in various examples.

[0197] For example, when a HU rhythm is detected based on moderate cerebral ischemia criteria and a rapid heart rate, a limited number of CV / DF shocks, such as one to eight shocks, may be delivered. However, when stage 5 cerebral ischemia is detected, the patient may experience extensive irreversible brain damage or clinical death. Delivery of CV / DF shocks may be futile. Thus, when stage 5 cerebral ischemia (e.g., suppression or disappearance of neural oscillations) is detected based on analysis of sensed brain electrical activity by the medical device system, in some examples, the medical device system does not deliver CV / DF shocks. In particular, if one or more CV / DF shocks have been delivered in response to detection of a HU rhythm prior to detection of stage 5 cerebral ischemia (e.g., when stage 2, 3, or 4 is detected), any additional CV / DF shocks that are scheduled or programmed to occur in the therapy menu may be aborted. If stage 5 cerebral ischemia is reached, in some examples, cardiac electrical stimulation therapy for terminating the HU rhythm may be aborted.

[0198] Figure 8 is a flow chart 450 of a method for detecting cerebral ischemia to classify a heart rhythm as HU or HS according to some examples. For ease of illustration, the processes of flow chart 450 are described as being performed by EEG sensor 40. However, it should be understood that in some examples, the EEG signal may be extracted from cardiac electrical signals sensed by cardiac monitor 44 or another IMD, or sent from EEG sensor 40 to another co-implanted IMD or an external device (e.g., external device 50) for analysis to detect cerebral ischemia.

[0199] At block 452, EEG sensor 40 may initiate an EEG analysis to determine EEG metrics for differentiating HU and HS heart rhythms. In some examples, EEG sensor 40 begins the process of flow chart 450 in response to a communication signal received from a co-implanted IMD that has detected a concerning heart rate. As described above, the concerning heart rate may be a heart rate, a rapid heart rate that meets a rapid heart rate criterion, a slow heart rate that meets a slow heart rate criterion, or a variable heart rate that meets a variable heart rate criterion. In some examples, when monomorphic VT is detected or when a tachyarrhythmia is detected without a high degree of confidence (as described below in connection with Figure 10As further described, the communication signal can be sent by a co-implanted IMD. In other examples, the EEG sensor 40 can filter or extract cardiac electrical activity from the electrical signals sensed using the electrodes 42 and determine the heart rate from the cardiac electrical activity. If a rapid heart rate is detected, such as greater than 120 bpm, greater than 140 bpm, greater than 160 bpm, greater than 180 bpm, or greater than 200 bpm, the EEG sensor 40 can initiate EEG analysis to detect cerebral ischemia without a command or request received from another medical device. If a slow heart rate is detected, such as less than 60 bpm, less than 55 bpm, less than 50 bpm, or less than 40 bpm, the EEG sensor 40 can initiate EEG analysis. In other examples, the EEG sensor 40 can be configured to continuously or intermittently monitor the EEG signal, for example, at regular time intervals, such as once every 30 seconds, once per minute, or on some other scheduled basis. In such cases, the processing circuit 200 can store EEG signal episodes in the memory 202 in a rolling fashion such that the processing circuit 200 can determine EEG metrics at regular time intervals to detect changes in the EEG metrics indicative of cerebral ischemia.

[0200] At block 454, the EEG signal episode can be stored in the memory 202 for the processing circuit 200 to determine the EEG metric. In some examples, the EEG signal episode cached in the memory 202 can begin when a communication signal requesting EEG analysis is received from another device or when a concerning heart rate is detected by the processing circuit 200. In other examples, the EEG signal episode can begin at a time delay after a concerning heart rate is detected, an arrhythmia tachycardia detection is performed, or a communication signal requesting EEG analysis is received. The EEG signal changes associated with cerebral ischemia can be delayed in time from the HU rhythm onset. Thus, the EEG signal episode can be cached in the memory 202 starting 5 seconds, 10 seconds, 15 seconds, 20 seconds, or 30 seconds after a triggering event (e.g., rapid heart rate detection or VT detection) that initiates the EEG signal analysis. Additionally or alternatively, as described above, the EEG signal episode can be stored in the memory 202 based on a rolling basis such that the electroencephalogram activity can be monitored independent of the heart rate or received requests. In this manner, if cerebral ischemia is detected, a notification can be sent by the EEG sensor 40 for use by co-implanted devices to determine if a therapy response is needed based on the notification and the analysis of the cardiac electrical activity.

[0201] EEG signal episodes can be extended for a specified duration, e.g., between 0.25 seconds and sixty seconds or between about 1 second and 5 seconds in various examples. In some examples, instead of caching one relatively long EEG signal episode, multiple EEG signal episodes can be cached during a desired monitoring period, each episode corresponding to a specified duration. For example, the duration of each of the multiple EEG signal episodes can be from 0.25 seconds to 6 seconds and cached at intervals of 0 seconds to 30 seconds to achieve a total monitoring period of, e.g., several seconds, minutes, or up to an hour. By way of illustration, after starting the EEG analysis process of flowchart 450, the processing circuit 200 can cache in the memory 202 EEG signal episodes each having a duration of 0.5 seconds to 3 seconds every 5 seconds to 60 seconds until the medical device system no longer detects a concerning heart rate or until termination criteria are met after detecting VT or VF or other arrhythmias.

[0202] At block 456, the processing circuit 200 determines one or more EEG metrics from each of the one or more EEG signal episodes cached in the memory 202. In some examples, the processing circuit 200 determines one or more EEG amplitude metrics. Example amplitude metrics can include the absolute maximum peak amplitude of the entire EEG signal episode, the average or median of all signal peaks during the EEG signal episode, the average amplitude across all sample points of the rectified EEG signal episode, or the average amplitude of all sample points of the rectified amplitude having a magnitude greater than a threshold amplitude during the EEG signal episode. One or more EEG amplitude metrics can be determined to detect a decrease in the amplitude of neural oscillations in the EEG signal, which can occur when CBF decreases due to a decreased cardiac output during HU rhythm. For example, see Figure 7 the relative increase in the amplitude of neural oscillations in stage 3 compared to stage 2, or stage 4 compared to stage 3.

[0203] Additionally or alternatively, the processing circuit 200 can determine one or more EEG frequency metrics at block 456. The frequency metrics can be determined in the frequency domain or the time domain. For example, a Fourier transform or other time domain to frequency domain transformation method can be performed by the processing circuit 200 to determine the frequency content of the EEG signal episode. In some examples, the dominant frequency, center frequency, mean frequency, median frequency, or other representative frequency can be determined as the frequency metric of the EEG signal episode. Additionally or alternatively, the power of each of the beta band, alpha band, theta band, and delta band of the EEG signal frequency can be determined from the EEG signal episode after performing a Fourier transform. A quantitative or qualitative relationship between the frequency bands can be determined for classifying the EEG signal episode into one of stages 1 to 5, as Figure 7 generally shown in.

[0204] For example, an offset of the dominant frequency band from the dominant frequency band of a previous EEG signal episode determined previously, or an offset of the dominant frequency from the beta band to the alpha band or from the alpha band to the theta band can be detected as a change in the cerebral ischemia phase as an example. For example, at block 458, the processing circuit 200 can determine whether the EEG metric meets the cerebral ischemia criteria by comparing the dominant frequency determined from the EEG signal episode with each of a plurality of frequency ranges that define the frequency bands associated with each phase of cerebral ischemia as described in conjunction with Figure 7 and determining whether the EEG metric meets the cerebral ischemia criteria. For example, when the dominant frequency is lower than the beta band, the cerebral ischemia criteria can be met.

[0205] In other examples, a time-domain frequency metric can be determined, which can reduce the processing burden and time required and the current consumption of the EEG sensor power supply 210 compared to the calculations performed in the frequency domain for determining the EEG frequency metric. For example, the frequency metric can be determined as the number of oscillations during an EEG signal episode. As an example, the number of oscillations can be determined by counting the number of zero crossings (or other thresholds), counting the number of peaks, or counting the signal inflection points. The number of oscillations determined during an EEG signal episode of a specified duration can be compared with different thresholds, each threshold corresponding to the lower limit of the frequency band of each phase of cerebral ischemia described above. The processing circuit 200 can determine the cerebral ischemia phase at block 458 based on the number of oscillations in the EEG signal episode of the specified duration. For example, when the number of oscillations counted in the EEG signal episode of the specified duration is less than a threshold number, the processing circuit 200 can determine that the cerebral ischemia criteria are met.

[0206] Another example of a frequency metric that can be determined by the processing circuit 200 in the time domain involves determining a derivative or difference signal from the EEG signal episode. The EEG frequency metric can be determined as the maximum peak of the derivative signal, the average value, median, or other representative value of the peak amplitude of the derivative signal, or the average value or other quantitative relationship of the amplitude difference between the derivative signal and the original EEG signal.

[0207] At block 458, the processing circuit 200 can compare the EEG metric determined at block 456 with the criteria for detecting cerebral ischemia. In some examples, the phase of cerebral ischemia is determined based on frequency and / or amplitude metrics, and when the phase is greater than the threshold phase for detecting cerebral ischemia, the EEG sensor communication circuit 208 can send a cerebral ischemia notification at block 462. When the phase of cerebral ischemia is less than the threshold phase for detecting cerebral ischemia, the communication circuit 208 can send a non-ischemia notification at block 460. In some examples, the identified cerebral ischemia phase can be sent at one of blocks 460 and 462. The cerebral ischemia criteria can be met at block 458 when at least one amplitude metric and / or at least one frequency metric corresponds to phase 2 or phase 3 or a higher phase.

[0208] One or more EEG metrics determined at block 456 can be compared at block 458 with corresponding thresholds or ranges for detecting cerebral ischemia that serve as evidence of HU rhythm. For example, if the EEG amplitude metric is greater than the applied threshold and / or the frequency metric is less than the applied threshold, at block 456, the processing circuit 200 can determine that the cerebral ischemia criteria are met. The thresholds or ranges applied to a given EEG metric can be stored in the memory 202 and can be established based on empirical data from a patient population or based on a baseline measure of the EEG metrics determined from the patient during normal sinus rhythm, which can be updated over time. The EEG sensor communication circuit 206 sends a notification at block 460 or 462 based on whether the EEG metrics meet the cerebral ischemia criteria, and optionally sends other EEG metric data or cerebral ischemia stage classification.

[0209] In some examples, the onset rate of ischemic changes in the EEG metrics can be determined to distinguish HU rhythm from other conditions that can cause frequency and amplitude changes in neural oscillations. For example, when one or more EEG metrics meet the cerebral ischemia criteria, the time from when the EEG metrics did not meet the cerebral ischemia criteria to when the EEG metrics meet the cerebral ischemia criteria can be determined when analyzing multiple consecutive EEG signal episodes. The time of onset of ischemic changes in the EEG metrics can be distinguishable from other possible causes of EEG changes not associated with HU rhythm. For example, if one or more EEG metrics have met the cerebral ischemia criteria before the start of a detected concerning heart rate or within a threshold time interval, the EEG metrics can indicate another condition, such as deep sleep, drug effects, or other conditions that can mimic the frequency and amplitude characteristics of the cerebral ischemia stage. In some examples, if the onset of cerebral ischemia-like EEG metrics appears too early relative to the start of a detected concerning heart rate caused by a change in heart rhythm, the cerebral ischemia determination may be unknown. In such a case, the EEG sensor 40 can send a notification of indeterminate or unknown cerebral ischemia at block 460. In some examples, when cerebral ischemia cannot be determined because the EEG metrics encounter cerebral ischemia changes at the start of a rapid heart rate, for example if the patient is asleep when a concerning heart rate is detected, a co-implanted device can determine that a detected VT or VF is default HU, especially when a rapid heart rate is detected or a life-threatening tachyarrhythmia is detected. For example, when an EEG signal that already has a dominant delta band frequency is detected, the co-implanted device can determine that a detected VT or VF is default HU and accordingly select ATP and / or CV / DF therapy delivery.

[0210] Additionally or alternatively, the medical device system may determine sleep based on time of day and / or other sensor inputs. As described above, one or more implantable devices (e.g., EEG sensor 40, cardiac monitor 44, ICD 14, ICD 114, pacemaker 150) may include one or more sensors for sensing another physiological signal (e.g., patient body activity, temperature, and / or respiration). The processing circuitry of the medical device system may determine that the patient is likely asleep when the cerebral ischemia criteria are met and the time of day is night, the patient body activity is at rest, the body temperature is not elevated, the respiration rate is low or at a resting level, or any combination thereof. In such a case, to avoid false cerebral ischemia detection, the medical device system may select a therapy response based on cardiac electrical activity without regard to electroencephalogram activity. At block 460, the EEG sensor 40 may send a notification of indeterminate cerebral ischemia.

[0211] In addition, it should be recognized that in some examples, there may be additional sensors in the medical device system for monitoring other metrics of HU. For example, an implanted medical device may include an oxygen sensor, a blood pressure sensor, a blood volume (e.g., impedance) sensor, or other sensors of physiological signals responsive to changes in hemodynamic stability. Thus, when the EEG metric meets the cerebral ischemia criteria but an indeterminate cerebral ischemia detection is made based on the rate of onset of cerebral ischemia and / or the likelihood of detecting sleep, other sensor signals may be analyzed to confirm or reject the cerebral ischemia detection. For example, an oxygen sensor, a blood pressure sensor, a blood volume sensor (e.g., impedance), or other sensors may be included in the medical device system. When the EEG metric meets the cerebral ischemia criteria and a conclusive change (e.g., decreased blood or tissue oxygen saturation or decreased blood pressure) is detected from the secondary sensor signals, cerebral ischemia may be detected at block 458. When no conclusive change is detected from the secondary sensor signals, an indeterminate cerebral ischemia detection or no cerebral ischemia detection may be made by the medical device system (e.g., by control circuit 80) using information from sensor 89 and the transmitted signal from the EEG sensor 40.

[0212] Figure 9 is a flowchart 500 of a method according to some examples, which method may be performed by a medical device system such as that described above in connection with Figures 1 to 3performed by any of the systems shown or described, for detecting tachyarrhythmias and selecting a therapy response. At block 502, the EEG sensor 40 may be configured to determine EEG metrics for detecting cerebral ischemia during normal sinus rhythm. The normal sinus rhythm may require a heart rate that is less than the tachyarrhythmia detection rate or less than a specified rate (e.g., less than 100 bpm), and there is no ongoing tachyarrhythmia detection (e.g., VT and VF interval counters are zero). According to any of the examples described herein, the EEG metrics may be determined during normal sinus rhythm and during the daytime hours when the patient is expected to be awake. The EEG metrics may be used as a baseline metric for establishing a threshold or other criteria for detecting EEG changes indicative of cerebral ischemia. The EEG metrics determined at block 502 and / or the threshold or other criteria established by the EEG sensor processing circuitry 200 based on the determined EEG metrics may be stored in the EEG sensor memory 202. When the processing circuitry 200 uses the EEG metrics determined at block 502 to update the baseline metric, the EEG metrics may first be compared to a previous metric to avoid using new EEG metrics determined during electroencephalographic activity that does not correspond to normal brain activity or cerebral ischemia such as stage 1 cerebral ischemia as shown in Figure 7 during electroencephalographic activity.

[0213] At block 504, the processing circuitry of the medical device system detects a rapid heart rate. When a rapid heart rate is not detected (the "no" branch of block 504), the EEG sensor 40 may periodically or scheduledly re-determine the EEG metrics at block 502 when normal sinus rhythm is detected, to update the baseline value of the EEG metrics and / or to update the criteria or threshold for detecting cerebral ischemia. One or more co-implanted devices may be configured to detect a rapid heart rate at block 504. When two or more IMDs of the medical device system are configured to detect a rapid heart rate, these two or more IMDs may simultaneously detect a rapid heart rate at block 504 to enable coordinated detection of HU or HS rhythms. For illustration, the process of flowchart 500 is described as being performed by the ICD 14 ( Figure 1The co-implanted EEG sensor 40 shown in performs. The ICD control circuit 80 can detect a rapid heart rate at block 504 and, in some examples, can send a request to the EEG sensor 40 to begin determining EEG metrics such that a change in the EEG metrics and the time course of any change can be determined. In other examples, the EEG sensor 40 can extract an ECG signal from the signals sensed via the electrodes 42 and detect a rapid heart rate at block 504, which can occur concurrently with the rapid heart rate detection performed by the ICD 14. When a rapid heart rate is detected (e.g., greater than 140 bpm, 160 bpm, 180 bpm, or 200 bpm), the EEG sensor 40 can begin caching EEG signal episodes such that if the ICD 14 requires the hemodynamic state of the heart rhythm for therapy delivery selection, the EEG metrics can be determined and made available.

[0214] At block 506, the ICD control circuit 80 can detect monomorphic VT. For example, when the RRI determined from the sensed ECG signal reaches the NID for VT detection, the ICD control circuit 80 can analyze the regularity of the RRI. The RRI tends to be more regular and can occur at a slower rate (longer RRI) during monomorphic VT than during polymorphic VT or VF. SVT can sometimes be distinguished from monomorphic VT based on the irregularity of the RRI because atrial depolarization can conduct irregularly to the ventricles during SVT. Example techniques for detecting monomorphic VT based on RRI analysis are generally disclosed in U.S. Patent No. 9,808,637 (Sharma et al.), which is incorporated herein by reference in its entirety.

[0215] Additionally or alternatively, the ICD control circuit 80 can distinguish monomorphic VT from polymorphic VT or VF (and in some cases, SVT) at block 506 based on ECG (or EGM) morphology analysis. The ICD control circuit 80 can compare the waveform morphologies of the sensed signals with each other or with an R-wave template stored in the memory 82, and / or analyze other sensed waveform characteristics to distinguish monomorphic VT from polymorphic VT or VF. Example techniques for distinguishing monomorphic and polymorphic tachyarrhythmias can include determining the frequency content of the sensed QRS waveform, determining one or more slopes of the QRS waveform, and determining a morphological match score between the sensed QRS waveforms and / or between the sensed QRS waveforms and the R-wave template stored in the memory 82. Example techniques for distinguishing polymorphic and monomorphic tachyarrhythmias are generally disclosed in U.S. Patent No. 7,076,289 (Sarkar et al.) and U.S. Patent No. 7,130,677 (Brown et al.), the entire contents of both of which are incorporated herein by reference. The techniques disclosed herein for determining whether a detected tachyarrhythmia is HU or HS are not limited to any particular tachyarrhythmia detection and discrimination technique. A variety of techniques for detecting and distinguishing monomorphic VT, polymorphic VT or VF, and SVT can be employed in combination with the techniques disclosed herein.

[0216] When the ICD control circuit 80 detects monomorphic VT at block 506, the control circuit 80 can control the therapy delivery circuit 84 to deliver ATP at block 520. After the first delivery sequence of ATP pulses, the ICD control circuit 80 determines at block 522 whether termination of the VT is detected. For example, termination can be detected based on a threshold number of RRIs being greater than the tachycardia detection threshold. When termination of the monomorphic VT is detected after ATP delivery, the process can return to block 502. The ICD control circuit 80 can continue to monitor the RRIs to detect a rapid heart rate at block 504. The EEG sensor 40 can update the EEG metric during normal sinus rhythm at block 502, as described above.

[0217] When termination of the VT is not detected at block 522 after the first ATP sequence, the EEG metric can be analyzed at block 524 to determine whether the detected VT is HU or HS. The ICD 14 can send a communication signal to the EEG sensor 40 requesting a determination of whether cerebral ischemia based on the EEG metric is detected as evidence of HU VT. The EEG sensor 40 can cache one or more EEG signal episodes and according to the above, for example, in combination with Figure 7 and Figure 8Any of the described examples determines an EEG metric. The EEG sensor 40 may analyze the EEG metric at block 524 by comparing the EEG metric to a cerebral ischemia criterion. In some examples, the EEG sensor 40 may have cached one or more EEG signal episodes and determine an EEG metric from each cached episode for comparison to the cerebral ischemia criterion at block 524 upon receipt of a request from the ICD 14, such as when the EEG sensor 40 is configured to continuously or intermittently monitor EEG signals or is configured to detect a rapid heart rate to trigger EEG signal analysis. In other examples, when a rapid heart rate is detected at block 504, when monomorphic VT is detected at block 506, or when termination is not detected at block 522 following a first ATP therapy, the EEG sensor 40 begins EEG signal episode caching and EEG metric determination in response to receiving a request from the ICD 14 sent by the ICD communication circuit 88. As indicated above, in some cases, the EEG sensor 40 may begin caching EEG signal episodes after a specified time delay to account for a lag between the onset of cerebral ischemia and the onset or timing of the detection of a rapid heart rate or VT.

[0218] The EEG sensor 40 may determine whether the EEG metric meets the cerebral ischemia criterion, which may include determining the stage of cerebral ischemia based on the determined EEG metric as described in the various examples given above. If the cerebral ischemia criterion is not met (which may include determining stage 1 of cerebral ischemia as described in the examples given above (or in some examples, stage 2)), the EEG sensor 40 may send a notification of no cerebral ischemia (or a notification of HS rhythm) to the ICD 14. In response to receiving the notification of no cerebral ischemia, the ICD 14 may detect HS VT at block 526 ("no" branch). If VT is still detected, the ICD 14 may return to block 520 to deliver another ATP therapy. When it is determined at block 526 that the detected VT is HS, if termination was not detected at block 522 following the previous ATP sequence and the VT detected at block 526 continues to be determined as HS, multiple ATP sequences may be delivered at block 520. When termination was not detected following the previous ATP therapy and the detected VT does not accelerate and / or is not HU, the clinician may program a menu of ATP therapies to be delivered continuously. In some examples, when the detected VT is not terminated by the delivered ATP therapy, the control circuit 80 may adjust the interval between ATP pulses, such as by providing a sequence of ATP pulses at a shorter ATP interval than in the previous ATP sequence.

[0219] Accordingly, when the VT detected at block 526 ("No" branch) is recognized as HS, the ICD control circuit 80 may determine at block 528 whether there are any additional ATP therapies remaining in the programmed menu or series of ATP therapies. The ICD control circuit 80 may verify that the detected ventricular rate has not accelerated, for example, by determining that the most recent RRI determined after ATP delivery is not shorter than the rapid VT or VF threshold interval. If all ATP therapies have been delivered in the programmed series of ATP therapies or the maximum number of ATP therapy attempts has been reached, or if the ventricular rate has accelerated since the initial monomorphic VT detection, the ICD control circuit 80 may proceed to block 512 to deliver one or more CV / DF shocks to terminate the tachyarrhythmia. As described above in connection with Figure 7 As indicated, if the amplitude and / or frequency metrics determined from the sensed brain electrical activity after detecting a HU rhythm associated with a rapid heart rate meet the severe brain ischemia criteria (e.g., corresponding to stage 5, where suppression of neural oscillations occurs), then in some examples, the CV / DF shock (and any other therapies) may be canceled or aborted, particularly if one or more shocks have been attempted and / or stage 5 brain ischemia has been detected for a threshold period of time (e.g., several minutes).

[0220] Referring again to block 506, if monomorphic VT is not detected at block 506, the ICD control circuit 80 may determine at block 510 whether polymorphic VT or VF is detected. In some cases, the rapid heart rate may be SVT, such as normal sinus tachycardia or a conducted atrial tachyarrhythmia, such as rapidly conducted AF. In some examples, rapid VT or VF may be detected at block 510 based on the sensed ventricular rate (e.g., based on the RRI being shorter than the rapid VT or VF interval threshold). In some examples, an SVT limit may be applied such that an RRI shorter than the SVT limit (and the rapid VT or VF detection interval) may result in the detection of polymorphic VT or VF at block 510. Interval- and morphology-based methods for differentiating polymorphic VT or VF from monomorphic VT are generally disclosed in U.S. Patent No. 9,808,637 (Sharma et al.), U.S. Patent No. 7,076,289 (Sarkar et al.), and U.S. Patent No. 7,130,677 (Brown et al.), which are incorporated herein by reference. Additionally, as an example, SVT may optionally be differentiated from VT or VF based on rate, irregularity of the RRI, and / or a morphology match score between the sensed QRS waveform and the R-wave template. Example techniques for differentiating SVT and VT / VF are generally disclosed in U.S. Patent No. 9,675,261 (Cao et al.), which is incorporated herein by reference in its entirety. Other example techniques for rejecting VT / VF detection based on SVT evidence are generally disclosed in U.S. Patent No. 10,555,684 (Zhang et al.), which is incorporated herein by reference.

[0221] If polymorphic VT or VF is not detected at block 510 ("No" branch), the ICD control circuit 80 may return to block 504 and continue to monitor the RRI. When polymorphic VT or VF is detected at block 510, the ICD control circuit 80 may control the therapy delivery circuit to deliver therapy at block 512 without requiring determination of whether the rhythm is HS or HU based on the EEG signal. The therapy delivery circuit 84 may generate and deliver one or more CV / DF shocks until termination is detected at block 514. In some cases, ATP may be delivered prior to the CV / DF shock, e.g., when the programmed therapy sequence delivered in response to VT / VF detection includes one or more ATP therapy sequences prior to the CV / DF shock therapy. In some cases, during preparation for CV / DF shock delivery, ATP may be delivered during high voltage capacitor charging. When termination is detected at block 514 after therapy delivery, the process may return to block 502. It should be understood that in some cases, non-sustained tachyarrhythmias may occur. The ICD control circuit 80 may be configured to detect spontaneous termination of the detected VT or VF prior to therapy delivery (e.g., during high voltage capacitor charging), and cancel the pending therapy and return to block 502.

[0222] In the example of flow chart 500, when monomorphic VT is detected and the monomorphic VT does not terminate after an initial ATP therapy attempt, the medical device system determines HU or HS VT. However, it should be understood that in other examples, the determination of HU or HS tachyarrhythmia may be made at any time during the process of flow chart 500 to guide therapy delivery selection and timing. For example, the EEG sensor 40 may be configured to cache EEG signal episodes in a rolling manner to monitor evidence of cerebral ischemia based on EEG metrics, which may be independent of the timing or type of the detected heart rhythm. The EEG sensor 40 may send a signal indicating whether cerebral ischemia is detected. As long as cerebral ischemia is not detected, the therapy delivery circuit 84 may be controlled to select a therapy response that may include delivering one type of therapy (e.g., ATP) while stopping or delaying the delivery of another type of therapy (e.g., stopping CV / DF shocks). The ICD 14 (or ICD 114 or pacemaker 150) may continue to deliver ATP until the tachyarrhythmia terminates or HU VT is detected based on the detection of cerebral ischemia.

[0223] In addition, although the process of flowchart 500 has been described in connection with a medical device system that includes a co-implanted ICD 14 and EEG sensor 40, it should be understood that in other examples, a cardiac monitor 40 can be co-implanted with the ICD 14 and EEG sensor 40, and the processing circuitry of the cardiac monitor 40 can perform processing and analysis for detecting and differentiating heart rhythms and communicating with the EEG sensor 40 and / or ICD 14 for collaboratively detecting HU or HS tachyarrhythmias and selecting and controlling therapy delivery responses. In still other examples, a pacemaker 150 can be included in the medical device system and can be configured to deliver ATP therapy when ATP is delivered to treat HS monomorphic VT or prior to CV / DF shock for treating HU VT / VF. Additionally, if an ICD is not co-implanted for delivering CV / DF shock, an implanted pacemaker (such as pacemaker 150) can be configured to deliver ATP upon detection of HU VT. In other examples, the process of flowchart 600 can be performed by a medical device system that includes an ICD (e.g., ICD 114 as shown Figure 2 as) that is connected to a transvenous lead and collaborates with the EEG sensor 40.

[0224] Figure 10 FIG. 600 is a flowchart of a method according to another example that can be performed by a medical device system (such as any of the systems shown or described above in connection with Figures 1 to 3 FIGS.) for detecting tachyarrhythmias and selecting therapy responses. Some tachyarrhythmia detection algorithms can include "gray" zones or overlapping criteria that can be met during different heart rhythms. For example, some criteria applied to sensed cardiac electrical signals can be met during SVT and monomorphic VT or during monomorphic VT and polymorphic VT / VF. For example, the RRIs that occur during SVT may overlap with the RRIs that occur during monomorphic VT. The RRIs that occur during monomorphic VT may overlap with the RRIs that may occur during polymorphic VT. In another example, the morphological match score determined between a sensed QRS waveform and an R-wave template may be very high (e.g., greater than 70%) to confirm SVT, or very low (e.g., less than 30%) to confirm VF with a high degree of confidence. However, sometimes, the morphological match score may fall somewhere in the middle of a so-called "gray" zone, where the morphological match score may not be able to differentiate SVT, VT, and VF with a high degree of confidence. Example tachyarrhythmia detection techniques that include a gray zone for the morphological match score are generally disclosed in U.S. Patent No. 8,437,842 (Zhang et al.), which is incorporated herein by reference in its entirety. Tachyarrhythmia detection can be performed with relatively low or high confidence, depending on whether various parameters determined from the cardiac electrical signals for comparison with tachyarrhythmia detection criteria fall within a confidence detection zone or a gray zone.

[0225] Additionally or alternatively, some tachyarrhythmia detection algorithms may include oversensing analysis to minimize the likelihood of detecting tachyarrhythmia due to oversensed electrical noise or other signals as false R-waves. For example, a rapid heart rate may be falsely detected due to oversensing of non-cardiac noise such as skeletal muscle myopotentials or electromagnetic interference, oversensing of P-waves across chambers as false R-waves, or oversensing of T-waves. When possible oversensing of noise or other signals is identified based on cardiac electrical signal analysis, the confidence in detecting VT or VF based on meeting other tachyarrhythmia detection criteria (such as NID) may be reduced.

[0226] Some tachyarrhythmia detection algorithms may rely on AI models or probabilistic models that can output a rhythm classification with an associated confidence level (e.g., as a percentage or total probability). In a tachyarrhythmia detection model, a relatively low confidence level or probability may be output when the rhythm classification is SVT, VT, or VF. Example methods of detecting tachyarrhythmia using a probability-based model are generally disclosed in U.S. Patent No. 8,301,233 (Zhang et al.) and U.S. Publication 2020 / 0038671 (Schulhauser et al.), both of which are incorporated herein by reference in their entirety. Some examples of AI techniques that can be used to classify arrhythmia episodes in a medical device system are generally disclosed in U.S. Publication 2020 / 0357519 (Chakravarthy et al.), which is incorporated herein by reference in its entirety.

[0227] Thus, depending on the particular tachyarrhythmia detection technique implemented in the IMD co-implanted with the EEG sensor 40, SVT, VT, or VF can be detected with different levels of confidence or probability. When a rapid heart rate is detected but the tachyarrhythmia detection confidence or probability level is relatively low, a medical device system operating in accordance with the techniques disclosed herein can analyze EEG metrics to detect evidence of cerebral ischemia. The threshold confidence level can be programmable or predefined, depending on the particular tachyarrhythmia detection technique employed. For example, tachyarrhythmia detection may be determined to be highly credible when the probability or confidence level is at least 60%, at least 70%, at least 80%, or at least 90%.

[0228] In flow chart 600, at block 602, EEG sensor 40 may establish or update a baseline EEG metric for a given patient during normal sinus rhythm, as generally described above. EEG metric thresholds or other criteria for detecting or identifying different stages of cerebral ischemia may be established based on the baseline EEG metric determined from the patient. In other examples, the EEG metric thresholds or other criteria applied to detect or identify different stages of cerebral ischemia may be programmed by a user or previously established based on empirical data and stored in memory 202 of EEG sensor 40.

[0229] For illustrative purposes, the description is made in connection with ICD 14 and EEG sensor 40 Figure 10 , where the ICD and EEG sensor are co-implanted and communicate with each other to collaboratively detect tachyarrhythmias and identify the tachyarrhythmias as HU or HS. However, it should be understood that other combinations of medical devices as described in any of the examples given above may be configured to perform all or part of the method of flow chart 600.

[0230] At block 604, ICD 14 may detect a rapid heart rate. When a rapid heart rate is detected, a tachyarrhythmia detection algorithm may be started or in progress, which may include counting VT and VF intervals, morphological analysis of cardiac electrical signal segments, or determining other parameters of cardiac electrical activity to detect tachyarrhythmias from one or more cardiac electrical signals sensed by ICD 14. However, it should be understood that detecting a rapid heart rate at block 604 may be optional in some examples. For example, cardiac electrical signal segments may be analyzed to classify according to rhythm type without relying on interval- or rate-based criteria that require detecting a rapid heart rate based on RRI.

[0231] At block 606, ICD control circuit 80 may detect SVT with high confidence. For example, when the ventricular rate (as determined from the RRI) is slower than the rapid VT or VF threshold rate (or SVT limit) but faster than the VT threshold rate and one or more QRS waveform morphology match scores are greater than a credible SVT match threshold, SVT may be detected with high confidence. In other probability models, when the confidence level of the rhythm classification model is greater than a high confidence threshold (e.g., greater than 70% or greater than 80%), a credible SVT detection at block 606 may be performed. When SVT is detected with high confidence, ICD control circuit 80 may determine at block 608 that no therapy is to be delivered. During SVT, cardiac output may be sufficient to maintain CBF at a normal or near-normal level, such that no change in the EEG is expected. Thus, when SVT is detected with high confidence, the medical device system may not perform EEG signal analysis.

[0232] However, in other examples, it is contemplated that when SVT is detected at block 606, the process may proceed to block 624 to determine EEG metrics to identify the heart rhythm as HU or HS. In some cases, SVT may conduct irregularly to the ventricles or occur at a very rapid rate, resulting in a HU rhythm.

[0233] When SVT is not detected or is not detected with high confidence (the "No" branch of block 606), the ICD control circuit 80 may detect monomorphic VT with high confidence at block 610. If monomorphic VT is detected with high confidence, the control circuit 80 may control the therapy delivery circuit 84 to deliver ATP at block 620. When termination is detected after ATP delivery (block 622), the process of flowchart 600 may return to block 602. If termination is not detected after ATP, or if insufficient sensing of the R wave is suspected, at block 624, the EEG sensor 40 may determine EEG metrics for comparison with cerebral ischemia criteria. Insufficient sensing may be suspected when the peak amplitude of the sensed R wave approaches the programmed sensitivity such that some R waves may be undersensed. As described above, the EEG sensor 40 may receive a communication signal from the ICD 14 requesting EEG analysis to detect cerebral ischemia as evidence of HU tachyarrhythmia. In other examples, the EEG sensor 40 may be configured to detect a rapid heart rate and begin monitoring the EEG signal to detect cerebral ischemia based on EEG metrics according to any of the examples described herein. The EEG sensor 40 may send a determination of cerebral ischemia (or no ischemia) for receipt by the ICD 14.

[0234] If the ICD 14 does not receive an indication of cerebral ischemia from the EEG sensor 40, the control circuit 80 may determine at block 626 that the detected VT is not HU. At block 628, the control circuit 80 may control the therapy delivery circuit 84 to deliver another ATP therapy. As described above, another ATP therapy may be delivered in a series of programmed ATP therapies or a menu of programmed ATP therapies until all ATP therapies have been delivered or until termination is detected at block 622. Although not explicitly shown in Figure 10 it should be understood that an accelerated rhythm may be detected by the control circuit 80 after ATP therapy, in which case the control circuit 80 may control the therapy delivery circuit 84 to deliver a CV / DF shock, as described above in connection with Figure 9 generally described. Referring again to block 624, when the ICD 14 receives a notification of cerebral ischemia from the EEG sensor 40, the control circuit 80 detects a HU tachyarrhythmia at block 626 and proceeds to block 614 to deliver a CV / DF shock (in some cases, ATP may precede the CV / DF shock, such as during high voltage charging).

[0235] Referring again to block 610, when a monomorphic VT is not detected or the monomorphic VT is not detected with high confidence, the control circuit 80 may detect polymorphic VT or VF at block 612. If polymorphic VT or VF is detected with high confidence, the control circuit 80 may control the therapy delivery circuit 84 to deliver CV / DF shock therapy at block 614 (if an ATP sequence is programmed in the therapy menu and / or when ATP therapy can be delivered during high voltage capacitor charging, the ATP therapy may precede the CV / DF shock). One or more therapies may be delivered at block 614 to terminate the polymorphic VT or VF detected with high confidence without having to determine and analyze EEG metrics. When termination is detected at block 616, the process may return to block 602.

[0236] If polymorphic VT or VF is not detected with high confidence at block 612, the medical device system may determine EEG metrics at block 624 for comparison with cerebral ischemia criteria. In some examples, when SVT, VT, or VF is detected with low confidence, the EEG signal may be analyzed to determine whether the heart rhythm is HU or HS. If the EEG metrics meet the cerebral ischemia criteria, the heart rhythm may be detected as HU at block 626. The ICD control circuit 80 may proceed to block 614 to deliver CV / DF therapy. If the EEG metrics do not meet the cerebral ischemia criteria, the therapy delivery circuit 84 may deliver ATP at block 628. In other examples, if the cerebral ischemia criteria are not met, which indicates an HS heart rhythm, the control circuit 80 may stop all therapies. A persistent rapid rate may be an HS SVT that does not require any therapy. The therapy decision made when the cerebral ischemia criteria are not met may depend on the heart rhythm detected with low confidence. For example, if SVT is detected with low confidence and the cerebral ischemia criteria are not met, all ATP and CF / DF shock therapies may be stopped. If monomorphic VT is detected with low confidence and the cerebral ischemia criteria are not met, ATP may be delivered and CV / DF shock may be stopped or delayed. After delivery (or stopping of ATP), the process may return to block 622 and continue to monitor the cardiac electrical signal to detect termination of the rapid heart rate or tachyarrhythmia. As long as termination is not detected at block 622, EEG metrics may be determined from the onset of the EEG signal (block 624) to detect whether the heart rhythm has changed to HU (block 626).

[0237] In addition, after detection of termination of the tachyarrhythmia, the EEG metrics may continue to be detected and monitored for a specified time interval to verify restoration of hemodynamic stability. In some cases, VT / VF may be sensed inadequately, for example due to low amplitude R waves or fibrillation waves, etc. Thus, termination may be detected erroneously. By continuing EEG signal analysis after detection of termination, the medical device system may verify that an HS heart rhythm has been restored.

[0238] Figure 11 is a flow diagram of method 700 for detecting HU and HS heart rhythms according to another example. Figure 11 The blocks 302 to 322 in Figure 6 may roughly correspond to the blocks of the same number shown and described above. In some examples, when the EEG metric meets the cerebral ischemia criteria at block 306, the processing circuitry of the medical device system may be configured to determine at block 702 whether a concerning heart rate is still being detected. If not, the concerning heart rate may have spontaneously terminated. However, in some cases, a false termination of the concerning heart rate may be detected. For example, when P waves, T waves, noise, or other artifacts are overly sensed as false R waves, a slow heart rate may be erroneously determined to have terminated due to over-sensing. In other cases, when true R waves are under-sensed, such as during VT or VF, a fast heart rate may be erroneously determined to have terminated due to under-sensing. When the EEG metric meets the cerebral ischemia criteria but a concerning heart rate is no longer detected at block 702, the medical device system processing circuitry may continue to monitor the EEG metric to verify cerebral ischemia recovery (indicating recovery of HS rhythm).

[0239] In some examples, the ICD control circuitry 80 may be configured to adjust control parameters for detecting a concerning heart rate to avoid over-sensing when a slow heart rate is no longer detected, or to avoid under-sensing when a fast heart rate is no longer detected. For example, the control circuitry 80 may adjust parameters for controlling the R wave sensing threshold (such as ventricular sensitivity, one or more decay rates or times, one or more fall time intervals or step-downs, or any other parameters for controlling automatic adjustment of the R wave sensing threshold). Additionally or alternatively, other R wave sensing control parameters, such as the ventricular blanking period or refractory period, may be adjusted. Additionally or alternatively, when the EEG metric meets the cerebral ischemia criteria, particularly if no cerebral ischemia recovery is detected after a concerning heart rate is no longer detected, the control circuitry 80 may adjust VT / VF detection parameters to be more sensitive to detecting VT / VF.

[0240] The adjustment at block 704 can be temporary. The cardiac event signal sensing and / or arrhythmia detection control parameters adjusted at block 704 can revert to the previously programmed settings after a specified time period or if the termination of a concerning heart rate is still detected at block 312 after the adjustment is made. If the termination of a concerning heart rate is not detected, the monitoring of the EEG metric can continue by returning to block 304 (the "no" branch of block 312) until the termination of a concerning heart rate is detected, which can include one or more adjustments to the sensing and / or detection control parameters at block 704. In some examples, the adjustment of the control parameters used to detect a concerning heart rate from cardiac electrical activity at block 704 can include determining whether insufficient or excessive sensing of cardiac electrical event signals (e.g., R waves) is suspected. When insufficient or excessive sensing of cardiac electrical event signals is suspected, for example, based on the sensed event intervals (e.g., RRI) and / or peak amplitudes, the ICD control circuit 80 can detect the termination of a concerning rhythm at block 312.

[0241] In some cases, after a concerning heart rate is no longer detected, the EEG metric can continue to meet the cerebral ischemia criteria. Cerebral ischemia may be falsely detected or may be caused by other conditions besides the HU rhythm. In such cases, the delivery of therapy for treating the HU rhythm can be appropriately stopped. For example, after a concerning heart rate is no longer detected, even if the cerebral ischemia criteria are still met after adjusting the detection of cardiac electrical activity or considering insufficient or excessive sensing, this may be caused by a stroke or other patient conditions that cannot be remedied by delivering electrical stimulation therapy. However, in such cases, it should be understood that the processing circuitry of the medical device system can generate an output for sending an alert to call EMS, alert a clinician or other caregiver, and / or alert the patient. Medical attention may be required, and / or the cerebral ischemia detection and / or concerning heart rate detection control parameters may need to be reprogrammed.

[0242] In some examples, when the EEG metric meets the cerebral ischemia criteria at block 306 and a concerning heart rate is still detected at block 702, the processing circuitry of the medical device system can determine at block 706 whether the sleep criteria are met. The control circuit 80 can detect sleep, for example, based on at least one of the time of day and / or the available sensor signals received by the processing circuitry according to any of the examples given above. For example, if the time of day is night, the patient's posture is non-upright, the patient's body activity is at rest, the onset of cerebral ischemia is too early or too late relative to the detection time of the concerning heart rate, the respiratory rate is less than a threshold rest rate, or any combination thereof, the ICD control circuit 80 can determine at block 706 that the sleep criteria are met.

[0243] In other examples, the ICD control circuit 80 may generate a wake-up signal at block 706 (e.g., by buzzing an accelerometer in the ICD 14 or generating an audible sound from a microphone) to cause the patient to wake up while the patient is sleeping. A change in the EEG metric after the wake-up signal may indicate that an EEG metric that meets the cerebral ischemia criteria may be a false ischemia detection due to the patient being asleep. In this case, if the EEG metric changes after the wake-up signal (e.g., the cerebral ischemia criteria are no longer met or the cerebral ischemia stage decreases towards stage 1 or 2), the ICD control circuit 80 may determine that the sleep criteria are met (the "yes" branch of block 706). If the sleep criteria are not met, e.g., if the EEG metric does not change after the wake-up signal, the control circuit 80 may detect a HU rhythm based on the electroencephalogram activity sensed after the wake-up signal at block 320. The processing circuit may generate an output at block 322 for providing a response to the HU rhythm at block 322, as generally described above.

[0244] If the sleep criteria are met at block 706, the medical device system processing circuit may optionally determine at block 708 whether another sensor signal is available to confirm the HU rhythm. For example, when an oxygen sensor, blood pressure sensor, or other physiological sensor signal in response to hemodynamic changes is received by the medical device processing circuit, the sensor signal may be analyzed to detect a change that may indicate the HU rhythm. If there is a likelihood that another sensor signal is available to confirm the HU rhythm (e.g., a decrease in oxygen saturation, a decrease in blood pressure, etc.), the control circuit 80 may proceed to block 320 to detect the HU rhythm.

[0245] If another sensor signal is not available or does not indicate the HU rhythm (e.g., the blood pressure has not decreased or the oxygen saturation is normal), the processing circuit (e.g., the ICD control circuit 80) may select a therapy based on the sensed cardiac electrical activity at block 710, ignoring the sensed electroencephalogram activity. An EEG metric that meets the cerebral ischemia criteria may be a false positive, e.g., when the patient is asleep or due to other physiological conditions. Thus, when the sleep criteria are met at block 706, the control circuit 80 may select a therapy response based on the cardiac electrical activity rather than the electroencephalogram activity at block 710. The cardiac electrical activity may be a slow heart rate that requires cardiac pacing or a fast heart rate that requires ATP and / or CV / DF therapy. The process may proceed to block 324 to determine whether the concerning heart rate has been terminated, and if the concerning heart rate is still detected, the EEG metric may continue to be monitored, as described above in conjunction with Figure 6 the general description.

[0246] 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 entirely omitted (e.g., not all of the described actions or events are necessary for practicing the method). Additionally, in some examples, the actions or events may be performed simultaneously, e.g., via multithreading, interrupt processing, or multiple processors, rather than sequentially. Further, for clarity purposes, although some 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, e.g., a medical device.

[0247] In one or more examples, the described functionality may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functionality may be stored on a computer-readable medium as one or more instructions or code and executed by a hardware-based processing unit. The computer-readable medium may include a computer-readable storage medium, which corresponds to a tangible medium such as a data storage medium (e.g., RAM, ROM, EEPROM, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that is accessible by a computer).

[0248] The instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPLAs), or other equivalent integrated or discrete logic circuitry. Thus, as used herein, the term "processor" may refer to any of the foregoing structures or any other structure suitable for implementing the techniques described herein. Additionally, the techniques may be fully implemented in one or more circuits or logic elements.

[0249] Accordingly, a medical device system has been presented in the foregoing description with reference to specific examples. It should be understood that the various aspects disclosed herein may be combined in combinations different from the specific combinations presented in the figures. It should be understood that various modifications may be made to the reference embodiments without departing from the scope of the present disclosure and the following claims.

Claims

1. A medical device system, the medical device system comprising: a sensing circuit configured to sense electroencephalographic activity and cardiac electrical activity; a processing circuit configured to: detect a concerning heart rate from the sensed cardiac electrical activity; determine, based on the sensed electroencephalographic activity, that the concerning heart rate is a hemodynamically unstable cardiac rhythm; and generate an output for providing a response to the determination that the concerning heart rate is a hemodynamically unstable cardiac rhythm; and a memory configured to store the output generated by the processing circuit.

2. The medical device system according to claim 1, the medical device system further comprising a therapy delivery circuit configured to deliver an electrical stimulation therapy, wherein: the control circuit is further configured to generate the output by generating a therapy control signal; and the therapy delivery circuit is configured to deliver an electrical stimulation therapy according to the therapy control signal.

3. The medical device system according to any one of claims 1 to 2, wherein the processing circuit is further configured to: determine at least one amplitude metric from the electroencephalographic activity or one or more of at least one frequency metric from the electroencephalographic activity; compare the amplitude metric or one or more of the frequency metrics with an ischemic brain criterion; in response to the amplitude metric or the frequency metric satisfying the ischemic brain criterion, determine that the concerning heart rate is a hemodynamically unstable cardiac rhythm.

4. The medical device system according to claim 3, wherein the processing circuit is further configured to: determine the at least one frequency metric from the electroencephalographic activity by determining at least one of: a dominant frequency of the electroencephalographic activity; a number of oscillations of the electroencephalographic activity during a time interval ； and an amplitude of a signal derivative of the electroencephalographic activity; determine that the frequency metric satisfies the ischemic brain criterion; and in response to the frequency metric satisfying the ischemic brain criterion, determine that the concerning heart rate is a hemodynamically unstable cardiac rhythm.

5. The medical device system according to any one of claims 1 to 4, wherein the processing circuit is further configured to: determine at least one metric of the electroencephalographic activity; determine an ischemic brain stage from a plurality of ischemic brain stages based on the at least one metric; and based on the ischemic brain stage, determine that the concerning heart rate is a hemodynamically unstable cardiac rhythm.

6. The medical device system according to any one of claims 1 to 5, wherein the processing circuit is further configured to: determine a metric from the electroencephalographic activity for each of a plurality of time intervals; determine that a change in the metric determined for each of the plurality of time intervals satisfies the ischemic brain criterion; based on the change in the metric satisfying the ischemic brain criterion, determine that the concerning heart rate is a hemodynamically unstable cardiac rhythm.

7. The medical device system according to claim 6, wherein the processing circuit is further configured to determine that the change in the metric meets the cerebral ischemia criterion by at least determining that the change in the metric occurs within a threshold time interval from the onset of the concerning heart rate.

8. The medical device system according to any one of claims 1 to 7, wherein the processing circuit is further configured to detect the concerning heart rate by detecting a heart rate faster than a threshold rate, and the system further includes a therapy delivery circuit configured to deliver cardioversion / defibrillation shocks. Wherein: The processing circuit is further configured to determine that the sensed brain electrical activity meets a severe cerebral ischemia criterion; and In response to determining that the sensed brain electrical activity meets the severe cerebral ischemia criterion, control the therapy delivery circuit to abort cardioversion / defibrillation shocks.

9. The medical device system according to any one of claims 1 to 8, the medical device system further includes a therapy delivery circuit configured to generate cardiac electrical stimulation therapy. Wherein the processing circuit is further configured to: Detect a monomorphic ventricular tachyarrhythmia associated with the concerning heart rate based on the sensed cardiac electrical activity; In response to detecting the monomorphic ventricular tachyarrhythmia, control the therapy delivery circuit to deliver a first antitachycardia pacing therapy; Determine that the monomorphic ventricular tachyarrhythmia is not terminated by the first antitachycardia pacing therapy; In response to determining that the monomorphic ventricular tachyarrhythmia is not terminated, determine at least one metric from the sensed brain electrical activity; Based on the at least one metric, determine that the monomorphic ventricular tachyarrhythmia is a hemodynamically unstable rhythm, and based on the sensed brain electrical activity, determine that the concerning heart rate is a hemodynamically unstable rhythm; And Generate the output for providing the response by generating a cardioversion / defibrillation shock therapy signal.

10. The medical device system according to any one of claims 2 to 9, wherein the processing circuit is further configured to: Detect polymorphic ventricular tachycardia or ventricular fibrillation associated with the concerning heart rate; and In response to detecting the polymorphic ventricular tachycardia or ventricular fibrillation, control the therapy delivery circuit to deliver cardioversion / defibrillation shock therapy without determining that the polymorphic ventricular tachycardia or ventricular fibrillation is hemodynamically unstable based on the sensed brain activity.

11. The medical device system according to any one of claims 1 to 10, wherein the processing circuit is further configured to: Detect the concerning heart rate by detecting either a heart rate slower than a threshold rate or a heart rate meeting a variable heart rate criterion; and Generate the output by generating either a cardiac pacing delivery signal or increasing a lower pacing rate or both.

12. The medical device system according to any one of claims 1 to 11, the medical device system further includes a communication circuit. Wherein the processing circuit is further configured to generate the output for providing the response by generating an alarm signal; and The communication circuit is configured to transmit the alarm signal.

13. The medical device system according to any one of claims 1 to 12, wherein the medical device system further comprises at least one sensor configured to sense a sensor signal received by the processing circuit; wherein the processing circuit is further configured to: detect sleep based on at least one of the time of day or the sensor signal; determine whether the concerning heart rate is hemodynamically unstable or indeterminable based on the sensed electroencephalographic activity in response to detecting sleep.

14. The medical device system according to any one of claims 1 to 13, wherein the medical device system further comprises at least one sensor configured to sense a sensor signal received by the processing circuit; the processing circuit is configured to: detect sleep based on at least one of the time of day or the sensor signal; generate a wake-up signal; detect cerebral ischemia based on the electroencephalographic activity sensed after the wake-up signal; and determine that the concerning heart rate is a hemodynamically unstable heart rhythm based on detecting the cerebral ischemia based on the electroencephalographic activity sensed after the wake-up signal.

15. The medical device system according to any one of claims 1 to 14, wherein the processing circuit is further configured to: detect the termination of the concerning heart rate; after detecting the termination of the concerning heart rate, determine that the sensed electroencephalographic activity still meets the cerebral ischemia criteria; and in response to determining that the sensed electroencephalographic activity still meets the cerebral ischemia criteria, adjust the control parameters for detecting the concerning heart rate from the sensed cardiac electrical activity.

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