Implantable devices, and methods for use therewith, for performing cardiac and autonomic assessments using phase rectified signal averaging

• US 7,512,439 B1
• Filed: 10/12/2005
• Issued: 03/31/2009
• Est. Priority Date: 10/12/2005
• Status: Active Grant

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Inventors: Farazi, Taraneh Ghaffari
• Primary Examiner(s): Layno; Carl H.
• Assistant Examiner(s): MORALES, JON ERIC C
• Application Number:
  US11/249,653
• Time in Patent Office: 1,266 Days
• Field of Search: None
• US Class Current: 600/509
• CPC Class Codes: A61B 5/349 Detecting specific parameters of the electrocardiograph cycle
• CPC Class Codes: A61B 5/366 Detecting abnormal QRS complex, e.g. widening
• CPC Class Codes: A61B 5/4035 Evaluating the autonomic nervous system
• CPC Class Codes: A61B 5/7264 Classification of physiological signals or data, e.g. using neural networks, statistical classifiers, expert systems or fuzzy systems neural networks per se G06N3/00; expert systems per se G06N5/00
• CPC Class Codes: A61B 5/7275 Determining trends in physiological measurement data; Predicting development of a medical condition based on physiological measurements, e.g. determining a risk factor
• CPC Class Codes: A61B 5/7282 Event detection, e.g. detecting unique waveforms indicative of a medical condition A61B5/4094, A61B5/4818, A61B5/349, A61B5/0823 take precedence
• CPC Class Codes: A61N 1/36114 Cardiac control, e.g. by vagal stimulation stimulating the heart A61N1/362
• CPC Class Codes: A61N 1/3702 Physiological parameters A61N1/365 takes precedence; evoked response A61N1/371
• CPC Class Codes: G16H 20/10 relating to drugs or medications, e.g. for ensuring correct administration to patients
• CPC Class Codes: G16H 20/40 relating to mechanical, radiation or invasive therapies, e.g. surgery, laser therapy, dialysis or acupuncture
• CPC Class Codes: G16H 50/20 for computer-aided diagnosis, e.g. based on medical expert systems
• CPC Class Codes: G16H 50/30 for calculating health indices; for individual health risk assessment

Abstract

Provided herein are implantable devices, and methods for use therewith, that perform at least one of a cardiac assessment and an autonomic assessment. An implantable device is used to sense a cardiac electrogram (EGM) signal, and cardiac intervals are measured within a portion of the sensed EGM signal. Anchor points are identified based on the measured cardiac intervals, and for each identified anchor point, a segment of at least three consecutive said cardiac intervals that is generally centered about the anchor point is defined. The segments defined for the anchor points are averaged to produce an average segment. At least one of a cardiac assessment and an autonomic assessment is performed based on the average segment. This can include assessing a patient'"'"'s autonomic tone based on the average segment, assessing a patients risk of SCD based on the average segment and/or detecting a myocardial ischemic event based on the average segment. This abstract is not intended to describe all of the various embodiments of the present invention.

Claims

1. For use with an implantable device, a method of performing at least one of a cardiac assessment and an autonomic assessment, comprising:

(a) sensing a cardiac electrogram (EGM) signal using implanted electrodes;

(b) measuring cardiac intervals within a portion of the sensed EGM signal;

(c) identifying anchor points based on the measured cardiac intervals;

(d) defining, for each identified anchor point, a segment of at least three consecutive said cardiac intervals that is generally centered about the anchor point;

(e) averaging the segments defined for the anchor points to produce an average segment; and

(f) performing at least one of a cardiac assessment and an autonomic assessment, based on the average segment.

2. The method of claim 1, wherein:

step (c) comprises identifying each said cardiac interval that is longer than the immediately preceding cardiac interval as a positive anchor point;

step (d) comprises defining, for each identified positive anchor point, a segment of at least three consecutive said cardiac intervals that is generally centered about the positive anchor point;

step (e) comprises averaging the segments defined for the positive anchor points to produce an average deceleration segment; and

step (f) comprises performing at least one of a cardiac assessment and an autonomic assessment, based on the average deceleration segment.

3. The method of claim 1, wherein:

step (c) comprises identifying each said cardiac interval that is shorter than the immediately preceding cardiac interval as a negative anchor point;

step (d) comprises defining, for each identified negative anchor point, a segment of at least three consecutive said cardiac intervals that is generally centered about the negative anchor point;

step (e) comprises averaging the segments defined for the negative anchor points to produce an average acceleration segment; and

step (f) comprises performing at least one of a cardiac assessment and an autonomic assessment, based on the average acceleration segment.

4. The method of claim 1, wherein step (f) comprises assessing a patient'"'"'s autonomic tone based on the average segment.

5. The method of claim 4, wherein step (f) includes:

determining a metric of a central wavelet of the average segment; and

comparing the determined metric to one or more threshold to thereby assess a patient'"'"'s autonomic tone.

6. The method of claim 4, wherein step (f) includes:

determining a time constant of the average segment; and

comparing the determined time constant to one or more threshold to thereby assess a patient'"'"'s autonomic tone.

7. The method of claim 4, wherein step (f) includes:

determining a slope of the average segment; and

comparing the determined slope to one or more threshold to thereby assess a patient'"'"'s autonomic tone.

8. The method of claim 4, further comprising:

comparing the assessed autonomic tone for the patient with a previously assessed autonomic tone for the patient to monitor changes in autonomic tone.

9. The method of claim 4, further comprising:

comparing the assessed autonomic tone for the patient with a threshold corresponding to an imminent risk of an arrhythmia, to determine whether the patient is at risk of an imminent arrhythmia; and

triggering delivery of cardiac therapy in response to a determination that the patient is at risk of an imminent arrhythmia.

10. The method of claim 4, wherein:

step (c) comprises identifying each said cardiac interval that is longer than the immediately preceding cardiac interval as a positive anchor point;

step (d) comprises defining, for each identified positive anchor point, a segment of at least three consecutive said cardiac intervals that is generally centered about the positive anchor point;

step (e) comprises averaging the segments defined for the positive anchor points to produce an average deceleration segment; and

step (f) includes at least one of the following, based on the average deceleration segment,

recognizing a decrease in a metric of a central wavelet of the average deceleration segment as being indicative of a decrease in parasympathetic tone;

recognizing a decrease in a metric of a central wavelet of the average deceleration segment as being indicative of an increase in sympathetic tone;

recognizing an increase in a metric of a central wavelet of the average deceleration segment as being indicative of an increase in parasympathetic tone; and

recognizing an increase in a metric of a central wavelet of the average deceleration segment as being indicative of a decrease in sympathetic tone.

11. The method of claim 4, wherein:

step (c) comprises identifying each said cardiac interval that is shorter than the immediately preceding cardiac interval as a negative anchor point;

step (d) comprises defining, for each identified negative anchor point, a segment of at least three consecutive said cardiac intervals that is generally centered about the negative anchor point;

step (e) comprises averaging the segments defined for the negative anchor points to produce an average acceleration segment; and

step (f) includes at least one of the following, based on the average acceleration segment,

recognizing an increase in a metric of a central wavelet of the average acceleration segment as being indicative of a decrease in parasympathetic tone;

recognizing an increase in a metric of a central wavelet of the average acceleration segment as being indicative of an increase in sympathetic tone;

recognizing a decrease in a metric of a central wavelet of the average acceleration segment as being indicative of an increase in parasympathetic tone; and

recognizing a decrease in a metric of a central wavelet of the average acceleration segment as being indicative of a decrease in sympathetic tone.

12. The method of claim 4, wherein step (f) includes at least one of the following:

recognizing a decrease in a time constant of the average segment as being indicative of a decrease in parasympathetic tone;

recognizing a decrease in a time constant of the average segment as being indicative of an increase in sympathetic tone;

recognizing an increase in a time constant of the average segment as being indicative of an increase in parasympathetic tone; and

recognizing an increase in a time constant of the average segment as being indicative of a decrease in sympathetic tone.

13. The method of claim 4, wherein step (f) includes at least one of the following:

recognizing a decrease in a slope of the average segment as being indicative of an increase in parasympathetic tone;

recognizing a decrease in a slope of the average segment as being indicative of a decrease in sympathetic tone;

recognizing an increase in a slope of the average segment as being indicative of a decrease in parasympathetic tone; and

recognizing an increase in a slope of the average segment as being indicative of an increase in sympathetic tone.

14. The method of claim 4, comprising repeating steps (a) through (f) over time to monitor changes in the patient'"'"'s autonomic tone.

15. The method of claim 1, wherein step (f) comprises assessing a patient'"'"'s risk of sudden cardiac death (SCD) based on the average segment.

16. The method of claim 15, further comprising:

comparing the assessed risk of SCD for the patient with a previously assessed risk of SCD for the patient to determine whether there has been an increase or a decrease in the patient'"'"'s risk of SCD.

17. The method of claim 15, further comprising:

comparing the assessed risk of SCD for the patient with a threshold corresponding to an imminent risk of an arrhythmia, to determine whether the patient is at risk of an imminent arrhythmia; and

triggering delivery of cardiac therapy in response to a determination that the patient is at risk of an imminent arrhythmia.

18. The method of claim 15, wherein:

step (c) comprises identifying each said cardiac interval that is longer than the immediately preceding cardiac interval as a positive anchor point;

step (d) comprises defining, for each identified positive anchor point, a segment of at least three consecutive said cardiac intervals that is generally centered about the positive anchor point;

step (e) comprises averaging the segments defined for the positive anchor points to produce an average deceleration segment; and

step (f) includes at least one of the following, based on the average deceleration segment,

recognizing a decrease in a metric of a central wavelet of the average deceleration segment as being indicative of an increase in risk of SCD; and

recognizing an increase in a metric of a central wavelet of the average deceleration segment as being indicative of a decrease in risk of SCD.

19. The method of claim 15, wherein:

step (c) comprises identifying each said cardiac interval that is shorter than the immediately preceding cardiac interval as a negative anchor point;

step (d) comprises defining, for each identified negative anchor point, a segment of at least three consecutive said cardiac intervals that is generally centered about the negative anchor point;

step (e) comprises averaging the segments defined for the negative anchor points to produce an average acceleration segment; and

step (f) includes at least one of the following, based on the average deceleration segment;

recognizing a decrease in a metric of a central wavelet of the average acceleration segment as being indicative of a decrease in risk of SCD; and

recognizing an increase in a metric of a central wavelet of the average acceleration segment as being indicative of an increase in risk of SCD.

20. The method of claim 15, wherein step (f) includes at least one of the following:

recognizing a reduction in a time constant of the average segment as being indicative of an increase in risk of SCD; and

recognizing an increase in a time constant of the average segment as being indicative of a reduction in risk of SCD.

21. The method of claim 15, wherein step (f) includes at least one of the following:

recognizing a decrease in a slope of the average segment as being indicative of a decrease in risk of SCD; and

recognizing an increase in a slope of the average segment as being indicative of an increase in risk of SCD.

22. The method of claim 15, comprising repeating steps (a) through (f) over time to monitor changes in the patient'"'"'s risk of SCD.

23. The method of claim 1, wherein step (f) comprises detecting a myocardial ischemic event based on the average segment.

24. The method of claim 23, wherein:

step (c) comprises identifying each said cardiac interval that is longer than the immediately preceding cardiac interval as a positive anchor point;

step (d) comprises defining, for each identified positive anchor point, a segment of at least three consecutive said cardiac intervals that is generally centered about the positive anchor point;

step (e) comprises averaging the segments defined for the positive anchor points to produce an average deceleration segment; and

step (f) includes recognizing a temporary decrease in a metric of a central wavelet of the average deceleration segment as being indicative of a myocardial ischemic event.

25. The method of claim 23, wherein:

step (c) comprises identifying each said cardiac interval that is shorter than the immediately preceding cardiac interval as a negative anchor point;

step (d) comprises defining, for each identified negative anchor point, a segment of at least three consecutive said cardiac intervals that is generally centered about the negative anchor point;

step (e) comprises averaging the segments defined for the negative anchor points to produce an average acceleration segment; and

step (f) includes recognizing a temporary increase in a metric of a central wavelet of the average acceleration segment as being indicative of a myocardial ischemic event.

26. The method of claim 23, wherein step (f) includes recognizing a temporary decrease in a time constant of the average segment as being indicative of a myocardial ischemic event.

27. The method of claim 23, wherein step (f) includes recognizing a temporary increase in a slope of the average segment as being indicative of a myocardial ischemic event.

28. The method of claim 23, comprising repeating steps (a) through (f) over time and assessing an ischemic burden based on identified myocardial ischemic events.

29. An implantable device for assessing autonomic tone, comprising:

implantable electrodes for sensing a cardiac electrogram (EGM) signal;

means for measuring cardiac intervals within a portion of the sensed EGM signal;

means for identifying anchor points based on the measured cardiac intervals;

means for defining, for each identified anchor point, a segment of at least three consecutive said cardiac intervals that is generally centered about the anchor point;

means for averaging the segments defined for the anchor points to produce an average segment; and

means for assessing autonomic tone based on the average segment.

30. An implantable device for assessing a risk of sudden cardiac death (SCD), comprising:

implantable electrodes for sensing a cardiac electrogram (EGM) signal;

means for measuring cardiac intervals within a portion of the sensed EGM signal;

means for identifying anchor points based on the measured cardiac intervals;

means for defining, for each identified anchor point, a segment of at least three consecutive said cardiac intervals that is generally centered about the anchor point;

means for averaging the segments defined for the anchor points to produce an average segment; and

means for assessing risk of SCD based on the average segment.

31. An implantable device for detecting myocardial ischemic events, comprising:

implantable electrodes for sensing a cardiac electrogram (EGM) signal;

means for measuring cardiac intervals within a portion of the sensed EGM signal;

means for identifying anchor points based on the measured cardiac intervals;

means for defining, for each identified anchor point, a segment of at least three consecutive said cardiac intervals that is generally centered about the anchor point;

means for averaging the segments defined for the anchor points to produce an average segment; and

means for detecting a myocardial ischemic event based on the average segment.