Method and apparatus for third heart sound detection

• US 7,431,699 B2
• Filed: 12/24/2003
• Issued: 10/07/2008
• Est. Priority Date: 12/24/2003
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Carlson, Gerrard M., Siejko, Krzysztof Z.
• Primary Examiner(s): SCHAETZLE, KENNEDY
• Application Number:
  US10/746,853
• Publication Number:
  US 20050148896A1
• Time in Patent Office: 1,749 Days
• Field of Search: 600/508, 600/513, 600/528
• US Class Current: 600/528
• CPC Class Codes: A61B 7/04 Electric stethoscopes microphones, acoustic transducers therefor H04R

Abstract

A cardiac rhythm management system includes a heart sound detector providing for detection of the third heart sounds (S3). An implantable sensor such as an accelerometer or a microphone senses an acoustic signal indicative heart sounds including the second heart sounds (S2) and S3. The heart sound detector detects occurrences of S2 and starts S3 detection windows each after a predetermined delay after a detected occurrence of S2. The occurrences of S3 are then detected from the acoustic signal within the S3 detection windows.

Claims

1. A heart sound detection system, comprising:

a cardiac signal input to receive a cardiac signal indicative of ventricular events;

an acoustic signal input to receive an acoustic signal indicative of at least second heart sounds (S2) and third heart sounds (S3); and

a heart sound detector coupled to the cardiac signal input and the acoustic signal input, the heart sound detector including;

an S2 window generator to generate an S2 window after a first predetermined delay starting with each of the ventricular events;

an S2 detector to detect S2 using an S2 threshold during the S2 windows;

an S3 window generator, coupled to the S2 detector, to generate an S3 window after a second predetermined delay starting with each of the detected S2;

an S3 detector to detect S3 using an S3 threshold during the S3 windows;

a measurement module to detect an acoustic energy using the acoustic signal; and

an S3 threshold generator adapted to determine the S3 threshold based on the acoustic energy.

2. The system of claim 1, further comprising an envelope detector coupled between the acoustic signal input and the heart sound detector, the envelope detector including a rectifier and a low-pass filter coupled to the rectifier.

3. The system of claim 2, further comprising an averaging circuit to improve a signal-to-noise ratio of the acoustic signal by ensemble averaging.

4. The system of claim 3, wherein the averaging circuit is adapted to align segments of the acoustic signal using the ventricular events.

5. The system of claim 3, wherein the averaging circuit is adapted to align segments of the acoustic signal using occurrences of the S2 detection.

6. The system of claim 1, further comprising an S1 detector to detect first heart sounds (S1).

7. The system of claim 6, further comprising a measurement module, coupled to the heart sound detector, to produce parameters related to one or more of S1, S2, and S3.

8. The system of claim 7, wherein the measurement module comprises an amplitude detector to detect one or more of an S1 amplitude, an S2 amplitude, and an S3 amplitude.

9. The system of claim 8, wherein the S2 detector comprises an S2 comparator to compare the acoustic signal to a predetermined S2 threshold.

10. The system of claim 9, wherein the S3 detector comprises an S3 comparator to compare the acoustic signal to the S3 threshold.

11. The system of claim 8, wherein the S2 detector further comprises an S2 threshold generator adapted to determine the S2 threshold based on the detected S1 and S2 amplitudes.

12. The system of claim 8, wherein the S3 threshold generator is adapted to dynamically adjust the S3 threshold.

13. The system of claim 8, wherein the measurement module is adapted to detect one or more of an energy associated with S1, an energy associated with S2, an energy associated with S3, a total acoustic energy during a cardiac cycle, and a total acoustic energy during systole of the cardiac cycle.

14. The system of claim 13, wherein the S3 detector further comprises an S3 threshold generator coupled to the S3 comparator, the S3 threshold generator adapted to dynamically adjust the S3 threshold based on at least one of:

the total acoustic energy during cardiac cycle;

a mean and a standard deviation of the total acoustic energy during cardiac cycle;

the total acoustic energy during systole of the cardiac cycle;

a mean and a standard deviation of the total acoustic energy during systole of the cardiac cycle; and

a temporal average of one or more of the S1 amplitude, the S2 amplitude, the total acoustic energy in one cardiac cycle.

15. The system of claim 1, wherein the S3 threshold generator is adapted to dynamically adjust the S3 threshold based on an estimated background sound level (μ

B) measured during a predetermined period between an occurrence of S1 and an adjacent occurrence of S2.

16. The system of claim 15, wherein the S3 threshold generator comprises an S3 threshold calculator to calculate the S3 threshold as μ

B*K, where K is an adjustable multiplier.

17. The system of claim 16, further comprising a heart rate detector, couple to the cardiac signal input, to detect a heart rate, and wherein the S3 threshold generator comprises a scaling module to scale the predetermined period between the occurrence of S1 and the adjacent occurrence of S2 for the heart rate.

18. A heart sound detection method, comprising:

receiving a cardiac signal indicative of ventricular events;

receiving an acoustic signal indicative of at least second heart sounds (S2) and third heart sounds (S3);

detecting S2 by comparing the acoustic signal to an S2 threshold;

generating an S3 window after a first predetermined delay starting with each of the detected S2;

detecting S3 during the S3 windows by comparing the acoustic signal to a dynamically adjustable S3 threshold;

detecting an acoustic energy using the acoustic signal; and

determining the S3 threshold based on the acoustic energy.

19. The method of claim 18, wherein detecting S2 comprises:

detecting ventricular events from the cardiac signal;

generating an S2 window after a second predetermined delay upon each detection of the ventricular events; and

detecting S2 during the S2 windows by comparing the acoustic signal to the S2 threshold.

20. The method of claim 19, further comprising improving a signal-to-noise ratio of the acoustic signal by ensemble averaging.

21. The method of claim 20, wherein the ensemble averaging comprises aligning segments of the acoustic signal using the ventricular events.

22. The method of claim 20, wherein the ensemble averaging comprises aligning segments of the acoustic signal using occurrences of the S2 detection.

23. The method of claim 18, further comprising detecting S1 by comparing the acoustic signal to an S1 threshold.

24. The method of claim 23, further comprising detecting one or more of an S1 amplitude, an S2 amplitude, and an S3 amplitude.

25. The method of claim 24, further comprising determining the S3 threshold based on one or more of the S1 amplitude and the S2 amplitude.

26. The method of claim 25, further comprising determining the S3 threshold based on the S2 amplitude.

27. The method of claim 24, further comprising determining one or more of an energy associated with S1, an energy associated with S2, an energy associated with S3, a total acoustic energy during a cardiac cycle, and a total acoustic energy during systole of the cardiac cycle.

28. The method of claim 27, further comprising determining the S3 threshold based on the total acoustic energy during the cardiac cycle.

29. The method of claim 28, further comprising determining the S3 threshold based on at least a mean and a standard deviation of the total acoustic energy in the cardiac cycle.

30. The method of claim 27, further comprising determining the S3 threshold based on the total acoustic energy during the systole of the cardiac cycle.

31. The method of claim 30, further comprising determining the S3 threshold based on at least a mean and a standard deviation of the total acoustic energy during the systole of the cardiac cycle.

32. The method of claim 27, further comprising determining the S3 threshold based on an temporal average of one or more of the S1 amplitude, the S2 amplitude, and the total acoustic energy in one cardiac cycle.

33. The method of claim 18, further comprising:

estimating a background sound level (μ

B) measured during a predetermined period between an occurrence of S1 and an adjacent occurrence of S2; and

calculating the S3 threshold by multiplying μ

B by K, where K is an adjustable multiplier.

34. The method of claim 33, further comprising:

detecting a heart rate from the cardiac signal; and

scaling the predetermined period between the occurrence of S1 and the adjacent occurrence of S2 for the detected heart rate.

35. A system, comprising:

an implantable lead to sense a cardiac signal indicative of ventricular events;

an implantable acoustic sensor to sense an acoustic signal indicative of at least second heart sounds (S2) and third heart sounds (S3); and

an implantable medical device including;

a cardiac signal input to receive the cardiac signal;

an acoustic signal input to receive the acoustic signal; and

a heart sound detector coupled to the cardiac signal input and the acoustic signal input, the heart sound detector including;

an S2 window generator to generate an S2 window after a first predetermined delay starting with each of the ventricular events;

an S2 detector to detect S2 using an S2 threshold during the S2 windows;

an S3 window generator, coupled to the S2 detector, to generate an S3 window after a second predetermined delay starting with each of the detected S2;

an S3 detector to detect S3 using an S3 threshold during the S3 windows;

a measurement module to detect an acoustic energy using the acoustic signal; and

an S3 threshold generator adapted to dynamically adjust the S3 threshold based on the acoustic energy.

36. The system of claim 35, wherein the implantable acoustic sensor comprises an accelerometer.

37. The system of claim 35, wherein the implantable acoustic sensor comprises a microphone.

38. The system of claim 35, wherein the implantable medical device further comprises an envelope detector coupled between the acoustic signal input and the heart sound detector, the envelope detector including a rectifier and a low-pass filter coupled to the rectifier.

39. The system of claim 38, wherein the implantable medical device further comprises an averaging circuit to improve a signal-to-noise ratio of the acoustic signal by ensemble averaging.

40. The system of claim 39, wherein the averaging circuit is adapted to align segments of the acoustic signal using the ventricular events.

41. The system of claim 39, wherein the averaging circuit is adapted to align segments of the acoustic signal using occurrences of the S2 detection.

42. The system of claim 35, wherein the implantable medical device further comprises an S1 detector to detect first heart sounds (S1).

43. The system of claim 42, wherein the implantable medical device further comprises a measurement module, coupled to the heart sound detector, to produce parameters related to one or more of S1, S2, and S3.

44. The system of claim 43, wherein the measurement module comprises an amplitude detector to detect one or more of an S1 amplitude, an S2 amplitude, and an S3 amplitude.

45. The system of claim 44, wherein the S2 detector comprises an S2 comparator to compare the acoustic signal to a predetermined S2 threshold.

46. The system of claim 44, wherein the S2 detector further comprises an S2 threshold generator coupled to the S2 comparator, the S2 threshold generator adapted to determine the S2 threshold based on the detected S1 and S2 amplitudes.

47. The system of claim 44, wherein the S3 detector comprises an S3 comparator to compare the acoustic signal to a predetermined S3 threshold.

48. The system of claim 47, wherein the S3 threshold generator is adapted to dynamically adjust the S3 threshold based on at least one of the detected S1 and S2 amplitudes and a percentage of the detected S2 amplitude.

49. The system of claim 47, wherein the measurement module to detect one or more of an energy associated with S1, an energy associated with S2, an energy associated with S3, a total acoustic energy during an cardiac cycle, and a total acoustic energy during systole of the cardiac cycle.

50. The system of claim 49, wherein the S3 threshold generator adapted to dynamically adjust the S3 threshold based on at least one of:

the total acoustic energy during cardiac cycle;

a mean and a standard deviation of the total acoustic energy during cardiac cycle;

the total acoustic energy during systole of the cardiac cycle;

a mean and a standard deviation of the total acoustic energy during systole of the cardiac cycle; and

a temporal average of one or more of the S1 amplitude, the S2 amplitude, the total acoustic energy in one cardiac cycle.

51. The system of claim 47, wherein the S3 detector further comprises an S3 threshold generator coupled to the S3 comparator, the S3 threshold generator adapted to dynamically adjust the S3 threshold based on an estimated background sound level (μ

B) measured during a predetermined period between an occurrence of S1 and an adjacent occurrence of S2.

52. The system of claim 51, wherein the S3 threshold generator comprises an S3 threshold calculator to calculate the S3 threshold as μ

B*K, where K is an adjustable multiplier.

53. The system of claim 52, wherein the implantable medical device further comprises a heart rate detector, couple to the cardiac signal input, to detect a heart rate, and wherein the S3 threshold generator comprises a scaling module to scale the predetermined period between the occurrence of S1 and the adjacent occurrence of S2 for the heart rate.