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A cardiac stimulation device and method detect myocardial ischemia and provide a response for alleviating the ischemia. Myocardial ischemia is detected by identifying changes in the ST-segment of the intracardiac electrogram (EGM) sensed using large sensing electrode surfaces created by electrically

A cardiac stimulation device and method detect myocardial ischemia and provide a response for alleviating the ischemia. Myocardial ischemia is detected by identifying changes in the ST-segment of the intracardiac electrogram (EGM) sensed using large sensing electrode surfaces created by electrically coupling one or more cardiac electrodes or by using larger surface area shocking coils. Myocardial ischemia monitoring is performed when stimulation parameters are adjusted for increasing cardiac output, causing an increased metabolic demand to be placed on the myocardium itself. When myocardial ischemia is detected, stimulation parameters are re-adjusted to reduce the demand placed on the myocardium and thereby alleviate the ischemia.

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1. In a cardiac stimulation device, a method of monitoring myocardial ischemia comprising:determining a sensor indicated heart rate; pacing at the sensor indicated heart rate; sensing an intracardiac electrogram signal; detecting myocardial ischemia based on a change in the electrogram signal; and i

1. In a cardiac stimulation device, a method of monitoring myocardial ischemia comprising:determining a sensor indicated heart rate; pacing at the sensor indicated heart rate; sensing an intracardiac electrogram signal; detecting myocardial ischemia based on a change in the electrogram signal; and in response to detecting myocardial ischemia, ignoring the sensor indicated rate and selectively adjusting one or more pacing parameters; wherein selectively adjusting one or more pacing parameters comprises varying an inter-ventricular timing interval. 2. In a cardiac stimulation device, a method of monitoring myocardial ischemia comprising:determining a sensor indicated heart rate; pacing at the sensor indicated heart rate; sensing an intracardiac electrogram signal; detecting myocardial ischemia based on a chance in the electrogram signal; and in response to detecting myocardial ischemia, ignoring the sensor indicated rate and selectively adjusting one or more pacing parameters; wherein selectively adjusting one or more pacing parameters comprises varying an inter-atrial timing interval. 3. In a cardiac stimulation device, a method of monitoring myocardial ischemia comprising:determining a sensor indicated heart rate; pacing at the sensor indicated heart rate; sensing an intracardiac electrogram signal; detecting myocardial ischemia based on a chance in the electrogram signal; in response to detecting myocardial ischemia, ignoring the sensor indicated rate and selectively adjusting one or more pacing parameters; and switching from a single-chamber ventricular stimulation mode to a biventricular stimulation mode; wherein detecting myocardial ischemia comprises detecting a deviation of an ST-segment of the cardiac electrogram signal; and wherein detecting the deviation of the ST-segment comprises detecting any of: an elevation of the ST-segment relative to a PQ-segment; an elevation of the ST-segment relative to a TP-segment; a depression of the ST-segment relative to a PQ-segment; a depression of the ST-segment relative to a TP-segment; and an inversion of a T-wave. 4. In a cardiac stimulation device, a method of monitoring myocardial ischemia comprising:determining a sensor indicated heart rate; pacing at the sensor indicated heart rate; sensing an intracardiac electrogram signal; detecting myocardial ischemia based on a change in the electrogram signal; and in response to detecting myocardial ischemia, ignoring the sensor indicated rate and selectively adjusting one or more pacing parameters; wherein sensing the cardiac electrogram signal comprises electrically coupling at least two sensing electrodes to form a single sensing electrode with an expanded surface. 5. The method according to claim 4, wherein selectively adjusting one or more pacing parameters comprises varying a pacing rate.6. The method according to claim 4, wherein sensing the intracardiac electrogram signal comprises sensing a differential signal between a coronary sinus lead electrode and a right ventricular lead electrode.7. The method according to claim 4, wherein sensing the intracardiac electrogram signal comprises sensing a differential signal between an active electrode and a case electrode.8. The method according to claim 4, wherein detecting myocardial ischemia comprises detecting a deviation of an ST-segment of the cardiac electrogram signal.9. The method according to claim 8, wherein detecting the deviation of the ST-segment comprises detecting any of:an elevation of the ST-segment relative to a PQ-segment; an elevation of the ST-segment relative to a TP-segment; a depression of the ST-segment relative to a PQ-segment; a depression of the ST-segment relative to a TP-segment; and an inversion of a T-wave. 10. The method according to claim 4, further comprising waiting for a predetermined time delay before responding to the detection of myocardial ischemia.11. The method according to claim 4, further comprising monitoring for myocardial ischemia when the pacing parameters are automatically adjusted, in response to a physiologic signal.12. The method according to claim 4, further comprising monitoring for myocardial ischemia on a continuous basis.13. The method according to claim 4, further comprising monitoring for myocardial ischemia on a periodic basis in a patient known to be susceptible to myocardial ischemia.14. The method according to claim 4, further comprising monitoring for myocardial ischemia following a user-programmed change in stimulation parameters.15. The method of claim 4, wherein electrically coupling at least two sensing electrodes comprises temporarily shorting at least two sensing electrodes during a sensing window, within a ST segment.16. The method of claim 15, wherein coupling at least two sensing electrodes comprises extending the ST segment for the full length of the ST segment.17. The method according to claim 15, wherein electrically coupling at least two sensing electrodes comprises temporarily coupling at least two sensing electrodes by means of a switch.18. The method according to claim 4, wherein electrically coupling at least two sensing electrodes comprises coupling at least two sensing electrodes on a coronary sinus lead.19. The method according to claim 4, wherein electrically coupling at least two sensing electrodes comprises coupling at least two sensing electrodes on a right ventricular lead.20. In a cardiac stimulation device, a method of monitoring myocardial ischemia comprising:electrically coupling at least two sensing electrodes to form a single sensing electrode with an expanded surface; sensing an intracardiac electrogram signal using the single sensing electrode; and detecting myocardial ischemia based on a change in the electrogram signal. 21. The method according to claim 20, wherein electrically coupling at least two sensing electrodes comprises temporarily shorting at least two sensing electrodes during a sensing window, within a ST segment.22. The method of claim 21, wherein coupling at least two sensing electrodes comprises extending the ST segment for the full length of the ST segment.23. The method according to claim 21, wherein electrically coupling at least two sensing electrodes comprises coupling at least two sensing electrodes on a coronary sinus lead.24. The method according to claim 21, wherein electrically coupling at least two sensing electrodes comprises coupling at least two sensing electrodes on a right ventricular lead.25. The method according to claim 20, wherein electrically coupling at least two sensing electrodes comprises temporarily coupling at least two sensing electrodes by means of a switch.26. A cardiac stimulation device that monitors myocardial ischemia, comprising:an electrode having at least two sensing electrodes, the at least two sensing electrodes electrically coupled to form a single sensing electrode with an expanded surface; a sensing circuit coupled to the electrode to sense an intracardiac electrogram signal; a control circuit that determines a sensor indicated heart rate; a pulse generator that generates stimulation pulses at the sensor indicated heart rate; an ischemia detector, connected to the ischemia sensing circuit, that detects myocardial ischemia based on a change in the electrogram signal; and wherein the control circuit is responsive to detection of myocardial ischemia to ignore the sensor indicated rate and to selectively adjust one or more pacing parameters. 27. The device according to claim 26, wherein the pacing parameters comprise a pacing rate.28. The device according to claim 26, wherein the pacing parameters comprise an inter-ventricular timing interval.29. The device according to claim 26, wherein the pacing parameters comprise an inter-atrial timing interval.30. The device according to claim 26, wherein the change in the cardiac electrogram signal comprises a differential signal between a coronary sinus lead electrode and a right ventricular lead electrode.31. The device according to claim 26, wherein the change in the cardiac electrogram signal comprises a differential signal between an active electrode and a case electrode.32. The device according to claim 26, wherein the myocardial ischemia is confirmed when a deviation of an ST-segment of the cardiac electrogram signal is detected.33. The device according to claim 32, wherein the deviation of the ST-segment comprises any of:an elevation of the ST-segment relative to a PQ-segment; an elevation of the ST-segment relative to a TP-segment; a depression of the ST-segment relative to a PQ-segment; a depression of the ST-segment relative to a TP-segment; and an inversion of a T-wave. 34. The device according to claim 26, further comprising a switch to electrically couple the at least two sensing electrodes to form a single sensing electrode with an expanded surface.35. The device of claim 34, wherein the switch temporarily shorts the at least two sensing electrodes during a sensing window, within a ST segment.36. The device of claim 35, wherein the ST segment extends for substantially the length of the ST segment.37. The device according to claim 34, wherein the at least two sensing electrodes are located on a coronary sinus lead.38. The device according to claim 34, wherein the at least two sensing electrodes are located on a right ventricular lead.39. A cardiac stimulation device that monitors myocardial ischemia, comprising:circuitry that is operative to electrically couple at least two sensing electrodes to form a single sensing electrode with an expanded surface; an ischemia sensing circuit that senses a cardiac electrogram signal, using the coupled electrodes; and an ischemia detector, connected to the ischemia sensing circuit, that detects myocardial ischemia based on a change in the electrogram signal. 40. The device according to claim 39, wherein a switch shorts the at least two sensing electrodes during a sensing window, within a ST segment.41. The device of claim 40, wherein the ST segment extends for substantially the length of the ST segment.42. The device according to claim 39, wherein the at least two sensing electrodes are located on any one or more of a coronary sinus lead and a right ventricular lead.43. A cardiac stimulation device that monitors myocardial ischemia, comprising:means for determining a sensor indicated heart rate; means for pacing at the sensor indicated heart rate; means for coupling at least two sensing electrodes to form a single sensing electrode with an expanded surface; means for sensing an intracardiac electrogram signal; means for detecting myocardial ischemia based on a change in the electrogram signal; and wherein in response to detected myocardial ischemia the pacing means comprises means for ignoring the sensor indicated rate and for adjusting one or more pacing parameters. 44. The device according to claim 43, wherein the pacing parameters comprise any one or more of:a pacing rate; an inter-ventricular timing interval; and an inter-atrial timing interval. 45. The device according to claim 43, wherein the change in the cardiac electrogram signal comprises a differential signal between a coronary sinus lead electrode and a right ventricular lead electrode.46. The device according to claim 43, wherein the change in the cardiac electrogram signal comprises a differential signal between an active electrode and a case electrode.47. The device according to claim 43, wherein the myocardial ischemia is confirmed when a deviation of an ST-segment of the cardiac electrogram signal is detected.48. The device according to claim 47, wherein the deviation of the ST-segment comprises any of:an elevation of the ST-segment relative to a PQ-segment; an elevation of the ST-segment relative to a TP-segment; a depression of the ST-segment relative to a PQ-segment; a depression of the ST-segment relative to a TP-segment; and an inversion of a T-wave. 49. The device according to claim 43, further comprising a switch that electrically couples the at least two sensing electrodes to form the single sensing electrode with the expanded surface.50. The device of claim 49, wherein the switch temporarily shorts the at least two sensing electrodes during a sensing window, within a ST segment.51. The device of claim 50, wherein the ST segment extends for substantially the length of the ST segment.52. The device according to claim 49, wherein the at least two sensing electrodes are located on any one or more of: a coronary sinus lead and a right ventricular lead.53. A cardiac stimulation device that monitors myocardial ischemia, comprising:means for electrically coupling at least two sensing electrodes to form a single sensing electrode with an expanded surface; means for sensing a cardiac electrogram signal, using the coupled electrodes; and means for detecting myocardial ischemia based on a change in the electrogram signal. 54. The device according to claim 53, further comprising a switch means to short the at least two sensing electrodes during a sensing window, within a ST segment.55. The device of claim 54, wherein the ST segment extends for substantially the length of the ST segment.56. The device according to claim 55, wherein the at least two sensing electrodes are located on any one or more of a coronary sinus lead and a right ventricular lead.57. In a cardiac stimulation device, a method of monitoring myocardial ischemia comprising:implementing a pacing scheme; sensing an intracardiac electrogram signal; detecting myocardial ischemia based on a change in the electrogram signal; and in response to detecting myocardial ischemia, varying an inter-chamber timing interval in the pacing scheme. 58. The method according to claim 57, wherein varying the inter-chamber timing interval comprises varying an inter-ventricular timing interval.59. The method according to claim 57, wherein varying the inter-chamber timing interval comprises varying an inter-atrial timing interval.60. The method according to claim 57, wherein sensing the intracardiac electrogram signal comprises sensing a differential signal between a coronary sinus lead electrode and a right ventricular lead electrode.61. The method according to claim 57, wherein sensing the intracardiac electrogram signal comprises sensing a differential signal between an active electrode and a case electrode.62. The method according to claim 57, wherein detecting myocardial ischemia comprises detecting a deviation of an ST-segment of the cardiac electrogram signal by detecting any of:an elevation of the ST-segment relative to a PQ-segment; an elevation of the ST-segment relative to a TP-segment; a depression of the ST-segment relative to a PQ-segment; a depression of the ST-segment relative to a TP-segment; and an inversion of a T-wave. 63. The method according to claim 62, further comprising switching from a single-chamber ventricular stimulation to biventricular stimulation.64. The method according to claim 57, further comprising waiting for a predetermined time delay before responding to the detection of myocardial ischemia.65. The method according to claim 57, further comprising monitoring for myocardial ischemia on a continuous basis.66. The method according to claim 57, further comprising monitoring for myocardial ischemia on a periodic basis.67. The method according to claim 57, further comprising monitoring for myocardial ischemia following a user-programmed change in stimulation parameters.68. The method according to claim 57, wherein sensing the intracardiac electrogram signal comprises electrically coupling at least two sensing electrodes to form a single sensing electrode.69. The method of claim 68, wherein electrically coupling the at least two sensing electrodes comprises temporarily shorting at least two sensing electrodes.70. The method according to claim 69, wherein electrically coupling the at least two sensing electrodes comprises temporarily coupling at least two sensing electrodes by means of a switch.71. The method according to claim 68, wherein electrically coupling the at least two sensing electrodes comprises coupling at least two sensing electrodes on a coronary sinus lead.72. The method according to claim 68, wherein electrically coupling the at least two sensing electrodes comprises coupling at least two sensing electrodes on a right ventricular lead.