REJECTION OF NOISES CAUSED BY POSTURAL CHANGES DURING ACUTE MYOCARDIAL INFARCTION DETECTION

• US 20070179392A1
• Filed: 01/30/2006
• Published: 08/02/2007
• Est. Priority Date: 01/30/2006
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Zhang, Yi
• Granted Patent: US 7,567,836 B2
• Time in Patent Office: Days
• US Class Current: 600/512
• CPC Class Codes: A61B 5/341 Vectorcardiography [VCG]
• CPC Class Codes: A61B 5/349 Detecting specific parameters of the electrocardiograph cycle
• CPC Class Codes: A61B 5/7207 of noise induced by motion artifacts
• CPC Class Codes: A61B 5/7285 for synchronising or triggering a physiological measurement or image acquisition with a physiological event or waveform, e.g. an ECG signal A61B6/5205, A61B6/541, A61B8/5207, A61B8/543 take precedence

Abstract

A system comprising a processor that includes a cardiac signal vector module and an ischemia detection module. The cardiac signal vector module is configured to measure a first dominant vector corresponding to a direction and magnitude of maximum signal power of a first segment of at least one cardiac cycle of a subject and at least a second dominant vector corresponding to a direction and magnitude of maximum signal power of a second segment of the cardiac cycle from an electrical cardiac signal. The ischemia detection module is configured to measure a change in the first dominant vector, to form a difference by subtracting a measured change in the second dominant vector from a measured change in the first dominant vector, and to declare whether an ischemic event occurred using the difference.

Claims

1. A system comprising:

a processor including;

a cardiac signal vector module configured to measure, from an electrical cardiac signal, a first dominant vector corresponding to a direction and magnitude of maximum signal power of a first segment of at least one cardiac cycle of a subject and at least a second dominant vector corresponding to a direction and magnitude of maximum signal power of a second segment of the cardiac cycle; and

an ischemia detection module configured to measure a change in the first dominant vector, to form a difference by subtracting a measured change in the second dominant vector from the measured change in the first dominant vector, and to declare whether an ischemic event occurred using the difference.

2. The system of claim 1, wherein the first segment includes a ST-T segment and the second segment includes a P-QRS segment of the cardiac cycle, and reducing noise due to posture of the subject by the subtracting the measured change in the second dominant vector from the measured change in the first dominant vector.

3. The system of claim 1, wherein the cardiac signal vector module is further configured to establish first and second baseline vectors for the first and second dominant vectors, and wherein the ischemia detection module is further configured to measure a change in a dominant vector relative to a baseline vector.

4. The system of claim 3, wherein the ischemia detection module is further configured to:

subtract the first baseline vector from a later-measured first dominant vector to obtain a first change representative of a change due to posture during the first segment;

subtract the second baseline vector from a later-measured second dominant vector to obtain a second change representative of a change due to posture and ischemia during the second segment; and

subtract the first change from the second change to obtain a third change representative of a change due to ischemia.

5. The system of claim 3, wherein the ischemia detection module is configured to measure a change in a dominant vector by measuring at least one of a change in angle, a change in magnitude, a variance of the angle or the magnitude, a power spectral density, a rate of change of the angle, a rate of change of the magnitude, and a rate of change of the variance of the angle or the magnitude.

6. The system of claim 1, wherein the ischemia detection module declares that an ischemic event occurred when the difference exceeds a specified threshold value.

7. The system of claim 6, wherein the ischemia detection module declares that an ischemic event occurred if the difference exceeds a specified threshold value in X of Y consecutive cardiac cycles, wherein X and Y are integers and X is less than or equal to Y.

8. The system of claim 1, wherein the processor is included in an implantable medical device (IMD) and wherein the IMD further includes:

a plurality of implantable electrodes adapted for spatial distribution within the subject; and

at least one cardiac signal sensing circuit in communication with the electrodes, the cardiac signal sensing circuit operable to produce the electrical cardiac signal representative of cardiac activity of the subject, and wherein the processor is coupled to the cardiac signal sensing circuit.

9. The system of claim 3, wherein the processor is operable to calculate trend data of measured subsequent changes from at least one baseline vector, and wherein the system includes a memory circuit coupled to the processor to store the trend data.

10. The system of claim 9, further including an ischemia indicator stored in the memory circuit, wherein the processor is operable to establish a value of the ischemia indicator using the trend data.

11. The system of claim 8, wherein the plurality of implantable electrodes includes at least a first electrode and a second electrode adapted for placement to sense a cardiac signal approximating a surface electrocardiogram (ECG).

12. The system of claim 1, further including:

an implantable medical device (IMD) comprising;

a plurality of implantable electrodes adapted for spatial distribution within the subject;

at least one cardiac signal sensing circuit in communication with the electrodes, the cardiac signal sensing circuit operable to produce the electrical cardiac signal representative of cardiac activity of the subject;

a controller circuit coupled to the cardiac signal sensing circuit; and

a communication circuit coupled to the controller circuit; and

an external device, wherein the IMD is operable to communicate information to the external device and wherein the processor is included in the external device.

13. The system of claim 12, wherein the external device includes an IMD programmer.

14. The system of claim 1, wherein the processor is configured to activate an alarm indicative of a deemed ischemic event.

15. The system of claim 1, further including:

an implantable medical device (IMD) comprising;

a plurality of implantable electrodes adapted for spatial distribution within the subject;

at least one cardiac signal sensing circuit in communication with the electrodes, the cardiac signal sensing circuit operable to produce the electrical cardiac signal representative of cardiac activity of the subject;

a controller circuit coupled to the cardiac signal sensing circuit; and

a communication circuit coupled to the controller circuit;

an external device, wherein the IMD is operable to communicate information to the external device; and

a server in communication with a network, wherein the server includes the processor, and wherein the external device is operable to communicate with the server via the network.

16. The system of claim 15, wherein the server initiates at least one dominant vector measurement.

17. The system of claim 1, wherein the ischemia detection module is configured to deem whether an ischemic event occurred from whether the difference exceeds a specified threshold value in combination with a measured output provided from one or more sensors.

18. The method of claim 17, wherein the ischemia detection module is configured to deem whether an ischemic event occurred by blending the output provided by the sensor and the difference according to at least one rule.

19. A method comprising:

sensing at least one cardiac signal representative of cardiac activity of a subject using an implantable medical device (IMD);

calculating, from the cardiac signal, a first dominant vector corresponding to a direction and magnitude of maximum signal power of a first segment of a cardiac cycle and a second dominant vector corresponding to a direction and magnitude of maximum signal power of a second segment of a cardiac cycle;

measuring a change in the first dominant vector;

measuring a change in the second dominant vector; and

subtracting the change in the second dominant vector from the measured change in the first dominant vector to form a difference.

20. The method of claim 19, further including deeming an ischemic event to have occurred at least in part from whether the difference exceeds a specified threshold value.

21. The method of claim 20, further including activating an alarm indicative of the deemed ischemic event.

22. The method of claim 20, wherein deeming an ischemic event to have occurred further includes deeming an ischemic event if the difference exceeds the specified threshold value in X of Y consecutive cardiac cycles, wherein X and Y are integers and X is less than or equal to Y.

23. The method of claim 19, comprising establishing a baseline vector for at least one of the first and second dominant vectors and measuring a change from the baseline vector.

24. The method of claim 23, wherein establishing a baseline vector includes calculating a central tendency for at least one of the first and second dominant vectors.

25. The method of claim 23, comprising reducing noise related to posture by subtracting the change in the second dominant vector from the change in the first dominant vector to form a difference.

26. The method of claim 23, wherein measuring the change from the baseline vector includes:

subtracting a first baseline vector from a later-measured first dominant vector to obtain a first change representative of a change due to posture during the first segment;

subtracting a second baseline vector from a later-measured second dominant vector to obtain a second change representative of a change due to posture and ischemia during the second segment; and

subtracting the first change from the second change to obtain a third change representative of a change due to ischemia.

27. The method of claim 19, wherein the first segment includes a ST-T segment and the second segment includes a P-QRS segment.

28. The method of claim 19, comprising measuring a trend in at least one of the first and second dominant vectors.

29. The method of claim 19, comprising measuring at least one of a change in angle, a change in magnitude, a variance of the angle or the magnitude, a power spectral density, a rate of change of the angle, a rate of change of the magnitude, and a rate of change of the variance of the angle or the magnitude.

30. The method of claim 19, further including deeming an ischemic event to have occurred from whether the difference exceeds a specified threshold value in combination with a measured output from one or more sensors.

31. The method of claim 30, wherein deeming an ischemic event to have occurred includes blending the output of at least one sensor and the difference according to at least one rule.

32. A system comprising

an implantable medical device (IMD) comprising:

a plurality of implantable electrodes adapted for spatial distribution within a subject; and

at least one cardiac signal sensing circuit in communication with the electrodes, the cardiac signal sensing circuit operable to produce an electrical cardiac signal representative of cardiac activity of the subject; and

means for calculating, from the electrical cardiac signal, a first dominant vector corresponding to a direction and magnitude of maximum signal power of a first segment of at least one cardiac cycle of the subject and at least a second dominant vector corresponding to a direction and magnitude of maximum signal power of a second segment of the cardiac cycle, and forming a difference by subtracting a measured change in the second dominant vector from a measured change in the first dominant vector, and using the difference to reduce noise in the measured change in the first dominant vector.

33. The system of claim 32, further including means to create trend data of changes in at least one dominant vector.

34. The system of claim 32, further including means for communicating the trend data to a network server system.

35. The method of claim 32, wherein the first segment includes a ST-T segment and the second segment includes a P-QRS segment.