Ischemia detection using a heart sound sensor

• US 20060282000A1
• Filed: 06/08/2005
• Published: 12/14/2006
• Est. Priority Date: 06/08/2005
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Zhang, Yi, Siejko, Krzysztof Z., Fogoros, Richard, Dalal, Yousufali, Haro, Carlos, Brockway, Marina
• Granted Patent: US 7,922,669 B2
• Time in Patent Office: Days
• US Class Current: 600/528
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: A61B 5/024 Detecting, measuring or recording pulse rate or heart rate A61B5/0205, A61B5/021 take precedence
• CPC Class Codes: A61B 5/349 Detecting specific parameters of the electrocardiograph cycle
• CPC Class Codes: A61B 5/352 Detecting R peaks, e.g. for synchronising diagnostic apparatus; Estimating R-R interval
• CPC Class Codes: A61B 7/04 Electric stethoscopes microphones, acoustic transducers therefor H04R
• CPC Class Codes: A61N 1/3627 for treating a mechanical deficiency of the heart, e.g. congestive heart failure or cardiomyopathy
• CPC Class Codes: A61N 1/36578 controlled by mechanical motion of the heart wall, e.g. measured by an accelerometer or microphone
• CPC Class Codes: A61N 1/395 for treating atrial fibrillation

Abstract

A system comprising an implantable medical device (IMD) includes an implantable heart sound sensor to produce an electrical signal representative of at least one heart sound. The heart sound is associated with mechanical activity of a patient'"'"'s heart. Additionally, the IMD includes a heart sound sensor interface circuit coupled to the heart sound sensor to produce a heart sound signal, and a signal analyzer circuit coupled to the heart sound sensor interface circuit. The signal analyzer circuit measures a baseline heart sound signal, and deems that an ischemic event has occurred using, among other things, a measured subsequent change in the heart sound signal from the established baseline heart sound signal.

Claims

1. A system comprising:

an implantable medical device (IMD) comprising;

an implantable heart sound sensor operable to produce an electrical signal representative of at least one heart sound, the heart sound associated with mechanical activity of a patient'"'"'s heart;

a heart sound sensor interface circuit coupled to the heart sound sensor to produce a heart sound signal; and

a signal analyzer circuit coupled to the heart sound sensor interface circuit, wherein the signal analyzer circuit is operable to measure a baseline heart sound signal, and to deem that an ischemic event occurred using a measured subsequent change in the heart sound signal from the established baseline heart sound signal.

2. The system of claim 1, wherein the signal analyzer circuit is operable to deem that an ischemic event occurred using a measured subsequent change in a characteristic of the heart sound signal from an established baseline value of the characteristic, wherein the characteristic of the heart sound is selected from the group consisting of:

an amplitude of at least one heart sound of the heart sound signal;

a power spectrum of the heart sound signal;

an amplitude of a first heart sound of the heart sound signal normalized with respect to an amplitude of a second heart sound;

an amplitude of a first heart sound normalized with respect to a measured power of the heart sound signal measured during systole;

a frequency of occurrence of a heart sound in the heart sound signal; and

a duration of an occurrence of a heart sound in the heart sound signal.

3. The system of claim 1, further including a memory circuit coupled to the signal analyzer circuit, the memory circuit to store a segment of a sampled heart sound signal, the segment including the heart sound signal sampled before the change in the heart sound signal, and to store the heart sound signal sampled after the change in the heart sound signal.

4. The system of claim 1, wherein the IMD includes a posture sensor and the IMD is operable to measure a heart sound signal in association with a posture of a patient.

5. The system of claim 1, wherein the IMD includes an activity sensor and the IMD is operable to measure a heart sound signal in association with patient activity.

6. The system of claim 1, the signal analyzer circuit is operable to activate an alarm indicative of a deemed ischemic event.

7. The system of claim 1, wherein the signal analyzer circuit is operable to distinguish between an ischemic event that occurred and a congestive heart failure condition that has worsened by using a time constant of the measured subsequent change from the baseline signal.

8. The system of claim 7, the signal analyzer circuit is operable to activate an alarm indicative of a worsening condition of congestive heart failure.

9. The system of claim 1, wherein the signal analyzer circuit is operable to calculate trend data of measured subsequent changes from the baseline signal, and wherein the IMD includes a memory circuit to store the trend data.

10. The system of claim 9, wherein the signal analyzer circuit is operable to generate a congestive heart failure status indication using the trend data.

11. The system of claim 9, wherein the IMD includes a communication circuit coupled to the signal analyzer circuit and the IMD is operable to communicate information about the measured subsequent change in the heart sound signal to an external device.

12. The system of claim 11, wherein the external device initiates at least one heart sound measurement.

13. The system of claim 9, including an external device in communication with a computer network and the IMD.

14. The system of claim 1, including at least one implantable cardiac signal sensing circuit coupled to the signal analyzer circuit, the implantable cardiac signal sensing circuit operable to produce an electrical cardiac signal representative of cardiac activity of the patient, and wherein the signal analyzer circuit is further operable to measure a heart sound signal in association with the electrical cardiac activity signal.

15. The system of claim 14, wherein the signal analyzer circuit is further operable to deem an ischemic event occurred in accordance with at least one of a measured change in the electrical cardiac signal from an established baseline electrical cardiac signal and the measured subsequent change in the heart sound signal from the established baseline heart sound signal.

16. The system of claim 14, wherein the signal analyzer circuit is further operable to deem an ischemic event occurred using both a measured change in the electrical cardiac signal from an established baseline electrical cardiac signal and the measured subsequent change in the heart sound signal from the established baseline heart sound signal.

17. The system of claim 14, wherein the signal analyzer circuit initiates at least one heart sound measurement in response to a sensed cardiac signal.

18. The system of claim 14, wherein the signal analyzer is operable to deem an ischemic event occurred using a temporal relationship of a measured change in the cardiac signal from an established baseline cardiac signal and the measured subsequent change in the heart sound signal from the established baseline heart sound signal.

19. A method comprising:

sensing a baseline heart sound signal using an implantable medical device (IMD), the heart sound associated with mechanical vibration of a heart of a patient;

sensing at least one subsequent heart sound signal for the patient using the IMD; and

deeming that an ischemic event occurred using at least a measured change in at least one heart sound signal from the baseline heart sound signal.

20. The method of claim 19, wherein deeming that an ischemic event occurred using at least a measured change includes deeming using a measured change in at least one heart sound signal characteristic from an established baseline value of the characteristic, the characteristic of the heart sound is selected from the group consisting of:

an amplitude of at least one heart sound of the heart sound signal;

a power spectrum of the heart sound signal;

an amplitude of a first heart sound of the heart sound signal normalized with respect to an amplitude of a second heart sound;

an amplitude of a first heart sound normalized with respect to a measured power of the heart sound signal measured during systole;

a frequency of occurrence of a heart sound in the heart sound signal; and

a duration of an occurrence of a heart sound in the heart sound signal.

21. The method of claim 19, wherein deeming that an ischemic event occurred is inferred at least in part by detecting a merging of S3 and S4 heart sounds in the heart sound signal.

22. The method of claim 19, wherein the baseline heart sound signal and subsequent heart sound signal are sensed in association with a posture of a patient.

23. The method of claim 19, wherein the baseline heart sound signal and subsequent heart sound signal are sensed in association with patient activity.

24. The method of claim 19, wherein the baseline heart sound signal and subsequent heart sound signal are sensed in association with an electrical cardiac signal representative of cardiac activity of the patient.

25. The method of claim 19, wherein deeming that an ischemic event occurred includes ongoing monitoring for any measured changes from the baseline heart sound signal.

26. The method of claim 19, further including activating an alarm indicative of the deemed ischemic event.

27. The method of claim 19, wherein deeming that an ischemic event occurred is inferred at least in part using a measured change in the heart sound signal from the baseline signal when a time constant of the change has a range of several seconds to several minutes, and wherein the method includes determining a heart failure condition of a patient using the measured change in the heart sound signal from the baseline heart sound signal when the time constant has a range of several hours to several days.

28. The method of claim 27, further including activating an alarm indicative of the heart failure condition.

29. The method of claim 19, wherein deeming that an ischemic event occurred is inferred at least in part using both a measured change in a cardiac signal from an established baseline cardiac signal sensed using the IMD and the measured change in the heart sound signal.

30. The method of claim 29, wherein deeming an ischemic event occurred is inferred at least in part using a temporal relationship between the measured change in the heart sound signal from the established baseline heart sound signal and the measured change in a cardiac signal from the established baseline cardiac signal.

31. The method of claim 30, wherein deeming an ischemic event occurred includes using the temporal relationship of a sensed event indicated by the sensed cardiac signal and the measured change in the heart sound signal from the established baseline heart sound signal.

32. The method of claim 19, wherein deeming that an ischemic event occurred includes discriminating a transient ischemic event from an acute myocardial infarction (AMI) event using the measured change in the heart sound signal from the established baseline heart sound signal.

33. The method of claim 32, wherein discriminating a transient ischemic event from an AMI event includes discriminating based on a duration of the measured subsequent change from the established baseline heart sound signal.

34. The method of claim 32, wherein discriminating a transient ischemic event from an AMI event includes discriminating based on an amplitude of the measured subsequent change from the established baseline heart sound signal.

35. The method of claim 32, wherein discriminating a transient ischemic event from an AMI event includes discriminating using a sensed event indicated by a sensed cardiac electrical signal and deeming the event an AMI event when the sensed cardiac event is no longer indicated by the sensed cardiac electrical signal while the measured change in the heart sound signal persists.

36. The method of claim 32, wherein discriminating a transient ischemic event from an AMI event includes discriminating using the measured change in the heart sound signal in association with at least one of a posture of a patient, patient activity, and a sensed cardiac electrical signal.