Ischemia detection using intra-cardiac signals
An implanted cardiac rhythm management device is disclosed that is operative to detect myocardial ischemia. This is done by evaluating electrogram features to detect an electrocardiographic change; specifically, changes in electrogram segment during the early part of an ST segment. The early part of the ST segment is chosen to avoid the T-wave.
1. A system for detecting ischemia comprising:
at least one lead configured for placement within a patient, the at least one lead comprising a sensor operative to sense ventricular activity and to generate a corresponding signal; and
an implantable medical device configured for connection to the at least one lead, the implantable medical device comprising circuitry operative to receive signals from the sensor corresponding to ventricular activity, to open a window a predetermined time after sensing the ventricular activity, wherein the window is shorter than a ST segment, the circuitry being further operative to determine an amplitude value within the window, and to process the amplitude value to detect ischemia;
wherein the circuitry is operative to open a window by opening the window at a first time if the ventricular activity is intrinsic, and at a second time if the ventricular activity is paced.
2. The system of claim 1 wherein the first time is between 50 and 100 milliseconds after the onset of a Q wave.
3. The system of claim 1 wherein the first time is between 100 and 150 milliseconds after the onset of a Q wave.
4. The system of claim 1 wherein the circuitry is operative to compare the amplitude value to a threshold to detect ischemia.
5. The system of claim 4 wherein the threshold is a historical baseline value.
6. The system of claim 5 wherein the threshold is a long-term average value.
7. The system of claim 1 wherein the circuitry is operative to determine the amplitude value by measuring the amplitude value relative to an isoelectric baseline.
8. The system of claim 7 wherein the isoelectric baseline is measured during an interval between a T-wave and subsequent P-wave.
9. The system of claim 1 wherein the circuitry is operative to determine the amplitude value by taking a plurality of measurements and determining an average value.
10. The system of claim 9 wherein the plurality of measurements are taken over multiple cycles.
11. The system of claim 1 and wherein the circuitry is further operative to compute an ischemia burden value based on the processing and detecting of ischemia.
12. The system of claim 1 wherein the second time is greater than the first time.