Evoked response sensing for ischemia detection

• US 20030060854A1
• Filed: 09/25/2001
• Published: 03/27/2003
• Est. Priority Date: 09/25/2001
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Zhu, Qingsheng
• Granted Patent: US 7,340,303 B2
• Time in Patent Office: Days
• US Class Current: 607/25
• CPC Class Codes: A61N 1/36507 controlled by gradient or slope of the heart potential
• CPC Class Codes: A61N 1/3712 Auto-capture, i.e. automatic adjustment of the stimulation threshold

Abstract

A cardiac pacemaker in which an electrogram is recorded from an evoked response sensing channel in order to detect changes indicative of cardiac ischemia. If such changes are detected, the maximum allowable pacing rate can be decreased for those pacing modes that allow the pacing rate to change with metabolic demand.

Claims

1. A cardiac pacemaker, comprising:

one or more sensing channels for sensing intrinsic cardiac activity and for sensing an evoked response to a pace;

a pacing channel for pacing a cardiac chamber;

a controller for delivering paces to the cardiac chamber in accordance with a programmed pacing mode such that a pace is delivered after expiration of an escape interval without sensing intrinsic activity in the chamber, and wherein the rate at which paces are delivered is limited to be below a specified maximum pacing rate; and

,

wherein the controller is programmed to record an electrogram from the sensed evoked response and analyze the recorded electrogram in order to detect a change indicative of cardiac ischemia.

2. The pacemaker of claim 1 wherein the controller is further programmed to log a detected change in the electrogram indicative of cardiac ischemia as a clinically significant event.

3. The pacemaker of claim 1 further comprising an exertion level sensor and wherein the controller is further programmed to:

sense an exertion level and map the sensed exertion level to a particular sensor-indicated rate with a rate-response curve, wherein the sensor-indicated rate is limited to a specified maximum sensor-indicated rate;

adjust the escape interval in order to enforce the sensor-indicated rate; and

,

decrease the specified maximum sensor-indicated rate if a change in the electrogram indicative of cardiac ischemia is detected.

4. The pacemaker of claim 3 wherein the controller is further programmed to adjust the response factor of the rate-response curve so that a particular exertion level particular is mapped to a lower sensor-indicated rate if a change in the electrogram indicative of cardiac ischemia is detected.

5. The pacemaker of claim 1 wherein the paced heart chamber is a ventricle and the programmed pacing mode is an atrial tracking mode such that a ventricular pace is delivered after expiration of an atrio-ventricular interval without a ventricular sense, the atrio-ventricular interval being started by an atrial sense, and further wherein the controller is programmed to decrease a maximum tracking rate that limits the rate at which ventricular paces can be delivered in response to atrial senses if a change in the electrogram indicative of cardiac ischemia is detected.

6. The pacemaker of claim 1 wherein the controller is programmed to detect a change in the recorded electrogram indicative of cardiac ischemia by looking for an increased current of injury in the recorded electrogram.

7. The pacemaker of claim 6 wherein the controller is programmed to look for an increased current of injury by cross-correlating the recorded electrogram with a reference electrogram.

8. The pacemaker of claim 6 wherein the controller is programmed to look for an increased current of injury by locating starting and end points of an ST segment using first and second derivatives of the recorded electrogram.

9. The pacemaker of claim 6 wherein the controller is programmed to look for an increased current of injury by comparing the slope of an ST segment in the recorded electrogram with an ST segment slope of a reference electrogram.

10. The pacemaker of claim 6 wherein the controller is programmed to look for an increased current of injury by comparing the amplitude of an ST segment with an ST segment amplitude of a reference electrogram.

12. The method of claim 1 further comprising:

sensing an exertion level and mapping the sensed exertion level to a particular sensor-indicated rate with a rate-response curve;

adjusting the escape interval in order to enforce the sensor-indicated rate; and

,

wherein the specified maximum pacing rate is a maximum sensor-indicated rate.

13. The method of claim 12 further comprising adjusting the rate-response curve so that a particular exertion level particular is mapped to a lower sensor-indicated rate if a change in the electrogram indicative of cardiac ischemia is detected.

11. A method for operating a cardiac pacemaker, comprising:

sensing intrinsic cardiac activity in one or more cardiac chambers;

delivering paces to a cardiac chamber in accordance with a programmed pacing mode such that a pace is delivered after expiration of an escape interval without sensing intrinsic activity in that chamber, and wherein the rate at which paces are delivered is limited to be below a specified maximum pacing rate;

sensing an evoked response to a pace and recording an electrogram therefrom;

analyzing the recorded electrogram in order to detect a change indicative of cardiac ischemia; and

,

decreasing the specified maximum pacing rate if a change in the electrogram indicative of cardiac ischemia is detected.

14. The method of claim 11 wherein the paced heart chamber is a ventricle and the programmed pacing mode is an atrial tracking mode such that a ventricular pace is delivered after expiration of an atrio-ventricular interval without a ventricular sense, the atrio-ventricular interval being started by an atrial sense, and further wherein the specified maximum pacing rate is a maximum tracking rate that limits the rate at which ventricular paces can be delivered in response to atrial senses.

15. The method of claim 11 wherein a change in the recorded electrogram indicative of cardiac ischemia are detected by looking for an increased current of injury in the recorded electrogram.

16. The method of claim 15 wherein an increased current of injury is looked for by cross-correlating the recorded electrogram with a reference electrogram.

17. The method of claim 15 wherein an increased current of injury is looked for by locating starting and end points of an ST segment using first and second derivatives of the recorded electrogram.

18. The method of claim 15 wherein an increased current of injury is looked for by comparing an integration of an ST segment with a reference value.

19. The method of claim 15 an increased current of injury is looked for by comparing the slope of an ST segment in the recorded electrogram with a reference value.

20. The method of claim 15 wherein an increased current of injury is looked for by computing the amplitude of an ST segment and comparing the amplitude with a reference value.