Combined hemodynamic and EGM-based arrhythmia detection

1. A method for detecting an arrhythmia, comprising;

sensing cardiac electrical signals;

detecting from the sensed electrical signals an episode of cardiac electrical event intervals meeting cardiac arrhythmia detection criteria;

detecting one of the cardiac electrical event intervals of the detected episode as a long interval not meeting an arrhythmia interval criteria;

sensing a hemodynamic signal;

determining a first cardiac mechanical event measurement from the hemodynamic signal immediately following the long interval; and

withholding a cardiac arrhythmia detection of the episode in response to the first cardiac mechanical event measurement.

2. The method of claim 1 further comprising:

computing a first baseline mechanical event measurement from the hemodynamic signal; and

withholding the cardiac arrhythmia detection in response to the measured cardiac mechanical event being at least approximately equal to the first baseline.

3. The method of claim 2 wherein the first baseline is computed over at least a twenty-four hour period.

4. The method of claim 2 further comprising:

detecting an interval of increased metabolic demand prior to the episode;

computing a second baseline mechanical event measurement from the hemodynamic signal sampled during the interval of increased metabolic demand;

identifying from the hemodynamic signal a plurality of mechanical event intervals during the episode;

computing a second mechanical event measurement from the plurality of mechanical event intervals;

comparing the second mechanical event measurement to the second baseline measurement; and

withholding an arrhythmia detection of the episode in response to the second mechanical event measurement exceeding the second baseline measurement.

5. The method of claim 4 wherein detecting an interval of increased metabolic demand comprises detecting a heart rate of at least approximately 90 beats per minute.

6. The method of claim 2 further comprising:

computing a measurement of a plurality of cardiac mechanical events occurring during the episode; and

withholding the cardiac arrhythmia detection in response to the measurement of the plurality of cardiac mechanical events being at least approximately equal to the first baseline.

7. The method of claim 1 further comprising:

identifying from the hemodynamic signal a plurality of mechanical event intervals during the episode;

computing a mechanical event interval measurement from the plurality of mechanical event intervals;

computing from the electrical signal an electrical event interval measurement during the episode;

comparing the mechanical event interval measurement to the electrical event interval measurement; and

withholding the cardiac arrhythmia detection of the episode in response to the comparing.

8. The method of claim 7 wherein the cardiac arrhythmia detection is withheld if the mechanical event interval measurement is greater than approximately 1.8 times the electrical event interval measurement.

9. The method of claim 7 further comprising:

computing a first baseline mechanical event measurement from the hemodynamic signal;

computing a measurement of a plurality of cardiac mechanical events occurring during the episode,

detecting hemodynamic collapse in response to the measurement of the plurality of cardiac mechanical events being less than a percentage of the first baseline; and

confirming a cardiac arrhythmia detection of the episode in response to detecting hemodynamic collapse.

10. The method of claim 9 further comprising overriding a programmed menu of arrhythmia therapies in response to the detected hemodynamic collapse.

11. An implantable medical device for detecting an arrhythmia, comprising;

a sensing module sensing cardiac electrical signals and a hemodynamic signal; and

a control module coupled with the sensing module and detecting from the sensed electrical signals an episode of cardiac electrical event intervals meeting cardiac arrhythmia detection criteria, detecting one of the cardiac electrical event intervals of the detected episode as a long interval not meeting an arrhythmia interval criteria, determining a first cardiac mechanical event measurement from the hemodynamic signal immediately following the long interval, and withholding a cardiac arrhythmia detection of the episode in response to the first cardiac mechanical event measurement.

12. The device of claim 11 wherein the control module computes a first baseline mechanical event measurement from the hemodynamic signal, and withholds the cardiac arrhythmia detection in response to the first cardiac mechanical event measurement being at least approximately equal to the first baseline.

13. The device of claim 12 wherein the first baseline is computed over at least a twenty-four hour period.

14. The device of claim 12 wherein the control module:

detects an interval of increased metabolic demand prior to the episode,

computes a second baseline mechanical event measurement from the hemodynamic signal sampled during the interval of increased metabolic demand;

identifies from the hemodynamic signal a plurality of mechanical event intervals during the episode;

computes a second mechanical event measurement from the plurality of mechanical event intervals;

compares the second mechanical event measurement to the second baseline measurement; and

withholds an arrhythmia detection of the episode in response to the second mechanical event measurement exceeding the second baseline measurement.

15. The device of claim 14 wherein detecting an interval of increased metabolic demand comprises detecting a heart rate of at least approximately 90 beats per minute.

16. The device of claim 12 wherein the control module:

computes a measurement of a plurality of cardiac mechanical events occurring during the episode; and

withholds the cardiac arrhythmia detection in response to the measurement of the plurality of cardiac mechanical events being at least approximately equal to the first baseline.

17. The device of claim 12 wherein the control module:

identifies from the hemodynamic signal a plurality of mechanical event intervals during the episode;

computes a mechanical event interval measurement from the plurality of mechanical event intervals;

computes from the electrical signal an electrical event interval measurement during the episode;

compares the mechanical event interval measurement to the electrical event interval measurement; and

withholds the cardiac arrhythmia detection of the episode in response to the comparison.

18. The device of claim 17 wherein the cardiac arrhythmia detection is withheld if the mechanical event interval measurement is greater than approximately 1.8 times the electrical event interval measurement.

19. The device of claim 17 wherein the control module:

computes a first baseline mechanical event measurement from the hemodynamic signal;

computes a measurement of a plurality of cardiac mechanical events occurring during the episode,

detects hemodynamic collapse in response to the measurement of the plurality of cardiac mechanical events being less than a percentage of the first baseline; and

confirms a cardiac arrhythmia detection of the episode in response to detecting hemodynamic collapse.

20. The device of claim 19 further comprising:

a therapy delivery module; and

a therapy delivery control coupled to the therapy delivery module for delivering a menu of tiered therapies in response to the confirmed cardiac arrhythmia detection;

wherein the control module overrides the programmed menu of arrhythmia therapies in response to the detected hemodynamic collapse to cause the therapy delivery module to delivery a shock therapy.