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Techniques for detecting ischemia and classifying a type of ischemia are described. Electrograms of cardiac activity may be generated using implanted or external electrodes, e.g., electrodes carried on vascular leads within the heart and a housing electrode. In some examples, ischemia is detected an

Techniques for detecting ischemia and classifying a type of ischemia are described. Electrograms of cardiac activity may be generated using implanted or external electrodes, e.g., electrodes carried on vascular leads within the heart and a housing electrode. In some examples, ischemia is detected and classified as benign or malignant based on whether a change an electrogram metric is detected, or first detected, in an endocardial electrogram or a non-endocardial electrogram. The relative timing of the change in the electrogram metric and a change in heart rate or patient activity may also be considered. In some examples, the system may create a stress test for detecting ischemia by instructing the patient to exercise or increasing the cardiac pacing rate.

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1. A system comprising: a first electrode and a second electrode both implanted within a heart of a patient;a third electrode outside of the heart;a processor configured to generate an endocardial electrogram of the heart with an endocardial electrode vector between the first electrode and the secon

1. A system comprising: a first electrode and a second electrode both implanted within a heart of a patient;a third electrode outside of the heart;a processor configured to generate an endocardial electrogram of the heart with an endocardial electrode vector between the first electrode and the second electrode during a time period and generate a non-endocardial electrogram of the heart with an epicardial electrode vector comprising the third electrode during the time period; andan ischemia detection module configured to detect a change in at least one electrogram metric of at least one of the non-endocardial electrogram or the endocardial electrogram, and classify an ischemia of the heart during the time period as one of a plurality of ischemia types based on the detection. 2. The system of claim 1, wherein the ischemia detection module is configured to detect a change in an ST segment of at least one of the non-endocardial electrogram or the endocardial electrogram, and classify the ischemia based on the detection of the change of the ST segment. 3. The system of claim 1, wherein the ischemia detection module is configured to classify the ischemia as one of a plurality of severities based on the detection. 4. The system of claim 1, wherein the ischemia detection module classifies the ischemia as a subendocardial ischemia when the electrogram metric change is detected only in the endocardial electrogram during the time period. 5. The system of claim 4, wherein the ischemia detection module: detects an increase in at least one of a heart rate or an activity level of the patient during or before the detected electrogram metric change; andclassifies the ischemia type as a stress induced subendocardial ischemia based on the detection of the increase in the at least one of the heart rate or the activity level. 6. The system of claim 1, wherein the ischemia detection module: detects an increase in at least one of a heart rate or an activity level of the patient after the detected electrogram metric change; andclassifies the ischemia as malignant based on the detection of the increase in heart rate after the detected electrogram metric change. 7. The system of claim 1, wherein the ischemia detection module detects ST segment elevation in the non-endocardial electrogram, and classifies the ischemia as a transmural ischemia based on the detection of the T segment elevation in the non-endocardial electrogram. 8. The system of claim 1, further comprising a user interface of an external computing device, wherein: the ischemia detection module, based on the ischemia type, automatically transmits at least one of a notification to a healthcare professional of the ischemia type and an instruction to the patient to seek medical treatment; andthe user interface presents the at least one of the notification to the healthcare professional of the ischemia type and the instruction to the patient to seek medical treatment. 9. The system of claim 1, wherein the processor at least one of generates an instruction to be presented to the patient to induce an increase in heart rate via exercise or increases a pacing rate to artificially induce the increase in heart rate. 10. The system of claim 1, further comprising: a first lead comprising the first electrode and the second electrode, wherein the first electrode is a tip electrode located at a distal end of the first lead and configured to contact cardiac tissue and the second electrode is a ring electrode located proximal to the tip electrode; andan implantable medical device housing comprising the third electrode. 11. The system of claim 10, further comprising a fourth electrode outside of the heart, wherein one of the third electrode and the fourth electrode is coupled to an implantable medical device housing, the fourth electrode is an external surface electrode, or the third electrode and the fourth electrode are carried on a lead implanted within a coronary sinus of the heart. 12. The system of claim 1, further comprising an implantable medical device coupled to the electrodes that comprises the processor and the ischemia detection module. 13. A system comprising: means for generating a endocardial electrogram of a heart with an endocardial electrode vector within a patient during a time period and generating a non-endocardial electrogram of the heart with an epicardial electrode vector during the time period;means for detecting a change in at least one electrogram metric of at least one of the non-endocardial electrogram or the endocardial electrogram; andmeans for classifying an ischemia of the heart during the time period as one of a plurality of ischemia types based on the detection. 14. The system of claim 13, wherein the means for detecting a change in at least one electrogram metric comprises means for detecting a change in an ST segment of the electrogram, andwherein the means for classifying the ischemia:classifies the ischemia as a subendocardial ischemia when the ST segment change is detected only in the endocardial electrogram; andclassifies the ischemia as a transmural ischemia when an ST segment elevation is detected in the non-endocardial electrogram. 15. The system of claim 1, wherein the ischemia detection module is configured to monitor both of the endocardial electrogram and the non-endocardial electrogram for a change to at least one electrogram metric of at least one of the non-endocardial electrogram or the endocardial electrogram. 16. A method comprising: generating, by a processor, a endocardial electrogram of a heart during a period of time with an endocardial electrode vector between a first electrode implanted within the heart and a second electrode implanted within the heart;generating, by the processor, a non-endocardial electrogram of the heart during the period of time with an epicardial electrode vector comprising a third electrode outside of the heart;detecting, by an ischemia detection module, a change in at least one electrogram metric of at least one of the non-endocardial electrogram or the endocardial electrogram; andclassifying, by the ischemia detection module, an ischemia of the heart during the time period as one of a plurality of ischemia types based on the detection. 17. The method of claim 16, wherein detecting a change in an electrogram metric comprises detecting a change in an ST segment of the electrogram. 18. The method of claim 16, wherein classifying the ischemia of the heart during the time period comprises classifying the ischemia as one of a plurality of severities based on the detection. 19. The method of claim 16, wherein classifying the ischemia further comprises classifying the ischemia as a subendocardial ischemia when the electrogram metric change is detected only in the endocardial electrogram during the time period. 20. The method of claim 19, further comprising: detecting an increase in at least one of a heart rate or an activity level of the patient during or before the detected electrogram metric change; andclassifying the ischemia type as a stress induced subendocardial ischemia based on the detection of the increase in the at least one of the heart rate or the activity level. 21. The method of claim 16, further comprising: detecting an increase in at least one of a heart rate or an activity level of the patient after the detected electrogram metric change; andclassifying the ischemia as malignant based on the detection of the increase in heart rate after the detected electrogram metric change. 22. The method of claim 16, wherein detecting a change in at least one electrogram metric comprises detecting ST segment elevation in the non-endocardial electrogram, and wherein classifying the ischemia comprises classifying the ischemia as a transmural ischemia based on the detection of the ST segment elevation in the non-endocardial electrogram. 23. The method of claim 16, further comprising, based on the ischemia type, at least one of automatically notifying a healthcare professional of the ischemia type and automatically instructing the patient to seek medical treatment via an external computing device. 24. The method of claim 16, further comprising one of presenting an instruction to the patient to induce an increase in heart rate via exercise or increasing a pacing rate to artificially induce the increase in heart rate.