Method and apparatus for detecting arrhythmias in a subcutaneous medical device

1. A method of detecting a cardiac event with a medical device comprising a processor and a plurality of electrodes, comprising the steps of:

sensing cardiac signals from the plurality of electrodes during a predetermined sensing window;

determining a relationship between a plurality of characteristics associated with a morphology of the cardiac signals;

generating a threshold in response to the relationship between the plurality of characteristics associated with the morphology of the cardiac signals;

comparing a first characteristic of the plurality of characteristics with the threshold to obtain a comparison indicative of an association of the cardiac signals with the cardiac event; and

delivering a therapeutic output based, at least in part, on the comparison indicative of an association of the cardiac signals with the cardiac event.

2. The method of claim 1 , wherein the plurality of characteristics include an amplitude of the sensed cardiac signals and a range of the sensed cardiac signals.

3. The method of claim 2 , wherein the first characteristic corresponds to the amplitude.

4. The method of claim 3 , wherein the amplitude corresponds to a normalized mean rectified amplitude and the range corresponds to a spectral width.

5. The method of claim 4 , wherein the threshold corresponds to the normalized rectified mean amplitude being equal to 0.2×spectral width +3.

6. The method of claim 1 , wherein the predetermined sensing window is between approximately 0.5 and 10 seconds.

7. The method of claim 1 , wherein the plurality of electrodes are positioned non-transvenously.

8. A method of detecting a cardiac event with a medical device comprising a processor and a plurality of electrodes forming a first sensing vector and a second sensing vector different from the first sensing vector, comprising:

sensing cardiac signals from the plurality of electrodes during a predetermined sensing window;

determining a first relationship between a first plurality of characteristics associated with cardiac signals sensed along the first sensing vector and a second relationship between a second plurality of characteristics along the second sensing vector during the predetermined sensing window;

generating a threshold in response to the first relationship between the first plurality of characteristics and the second relationship between the second plurality of characteristics;

comparing an individual one of the first plurality of characteristics with the threshold to obtain a first comparison indicative of an association of the cardiac signals sensed along the first sensing vector with the cardiac event;

comparing an individual one of the second plurality of characteristics with the threshold to obtain a second comparison indicative of an association of the cardiac signals sensed along the second sensing vector with the cardiac event; and

delivering a therapeutic output based, at least in part, on the first comparison indicative of an association of the cardiac signals sensed along the first sensing vector with the cardiac event and the second comparison indicative of an association of the cardiac signals sensed along the second sensing vector with the cardiac event.

9. The method of claim 8 , wherein the plurality of characteristics include an amplitude of the sensed cardiac signals and a range of the sensed cardiac signals.

10. The method of claim 9 , wherein the characteristic corresponds to the amplitude.

11. The method of claim 10 , wherein the amplitude corresponds to a normalized mean rectified amplitude and the range corresponds to a spectral width.

12. The method of claim 11 , wherein the threshold corresponds to the normalized rectified mean amplitude being equal to 0.2×spectral width +3.

13. The method of claim 12 , wherein the predetermined sensing window is between approximately 0.5 and 10 seconds.

14. The method of claim 8 , wherein the plurality of electrodes are positioned non-transvenously.

15. A medical device for delivering a therapeutic output to a patient having a heart generating cardiac signals, comprising:

a plurality of electrodes;

a sensor operatively coupled to the plurality of electrodes and configured to sense the cardiac signals from the plurality of electrodes during a predetermined sensing window;

a processor, operatively coupled to the sensor and configured to:

determine a relationship between a plurality of characteristics associated with a morphology of the cardiac signals;

generate a threshold in response to the relationship between a plurality of characteristics associated with a morphology of the cardiac signals; and

compare a first characteristic of the plurality of characteristics with the threshold to obtain a comparison indicative of an association of the cardiac signals with the cardiac event; and

a therapy module, operatively coupled to the processor and the plurality of electrodes, configured to deliver a therapeutic output based, at least in part, on the comparison indicative of an association of the cardiac signals with the cardiac event.

16. The device of claim 15 , wherein the plurality of characteristics include an amplitude of the sensed cardiac signals and a range of the sensed cardiac signals.

17. The device of claim 16 , wherein the first characteristic corresponds to the amplitude.

18. The device of claim 17 , wherein the amplitude corresponds to a normalized mean rectified amplitude and the range corresponds to a spectral width.

19. The device of claim 18 , wherein the threshold corresponds to the normalized rectified mean amplitude being equal to 0.2×spectral width +3.

20. The device of claim 19 , wherein the predetermined sensing window is between approximately 0.5 and 10 seconds.

21. The device of claim 15 , wherein the plurality of electrodes are positioned non-transvenously.