METHOD AND APPARATUS FOR DETECTING ARRHYTHMIAS IN A SUBCUTANEOUS MEDICAL DEVICE

Abstract

A method and apparatus for detecting a cardiac event in a medical device that includes sensing cardiac signals from a plurality of electrodes, determining a relationship between a plurality of characteristics associated with a morphology of the cardiac signals sensed during a predetermined sensing window, generating a threshold in response to the determined relationship, comparing a first characteristic of the plurality of characteristics with the threshold, and determining whether the sensed cardiac signals are associated with the cardiac event in response to the comparing of the first characteristic.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects and features of the present invention will be appreciated as the same becomes better understood by reference to the following detailed description of the embodiments of the invention when considered in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic diagram of an exemplary subcutaneous device in which the present invention may be usefully practiced;

FIG. 3 is an exemplary schematic diagram of electronic circuitry within a hermetically sealed housing of a subcutaneous device of the present invention;

FIG. 4 is a schematic diagram of signal processing aspects of a subcutaneous device according to an exemplary embodiment of the present invention;

FIG. 5 is a state diagram of detection of arrhythmias in a subcutaneous device according to an embodiment of the present invention;

FIG. 6 is a flow chart of a method for detecting arrhythmias in a subcutaneous device according to an embodiment of the present invention;

FIGS. 7A-71 are flow charts of a method for detecting arrhythmias in a subcutaneous device according to an embodiment of the present invention;

FIG. 8 is a graphical representation of sensing of cardiac activity according to an embodiment of the present invention;

FIG. 9A is a graphical representation of a determination of whether a signal is corrupted by muscle noise according to an embodiment of the present invention;

FIG. 9B is a flowchart of a method of determining whether a signal is corrupted by muscle noise according to an embodiment of the present invention;

FIG. 9C is a flowchart of a method of determining whether a signal is corrupted by muscle noise according to an embodiment of the present invention;

FIG. 10 is a graphical representation of a VF shock zone according to an embodiment of the present invention;

FIGS. 11A and 11B are graphical representations of the determination of whether an event is within a shock zone according to an embodiment of the present invention;

FIG. 12 is a graphical representation of a shock zone according to an embodiment of the present invention; and

FIG. 13 is a graphical representation of the determination of whether an event is within a shock zone according to an embodiment of the present invention.

Claims

1. A method of detecting a cardiac event in a medical device, comprising: sensing cardiac signals from a plurality of electrodes;determining a relationship between a plurality of characteristics associated with a morphology of the cardiac signals sensed during a predetermined sensing window;generating a threshold in response to the determined relationship;comparing a first characteristic of the plurality of characteristics with the threshold; anddetermining whether the sensed cardiac signals are associated with the cardiac event in response to the comparing of the first characteristic.

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 in a medical device, comprising: sensing cardiac signals from a plurality of electrodes, the plurality of electrodes forming a first sensing vector and a second sensing vector different from the first sensing vector;determining a relationship between a plurality of characteristics associated with cardiac signals sensed along the first sensing vector and along the second sensing vector during a predetermined sensing window;generating a threshold in response to the determined relationship;comparing a characteristic of the plurality of characteristics with the threshold;determining whether the cardiac signals sensed along the first sensing vector are associated with the cardiac event in response to the comparing of the characteristic with the threshold for the first sensing vector; anddetermining whether the cardiac signals sensed along the second sensing vector are associated with the cardiac event in response to the comparing of the characteristic with the threshold for the second sensing vector.

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, comprising: means for sensing cardiac signals from a plurality of electrodes;means for determining a relationship between a plurality of characteristics associated with a morphology of the cardiac signals sensed during a predetermined sensing window;means for generating a threshold in response to the determined relationship;means for comparing a first characteristic of the plurality of characteristics with the threshold; andmeans for determining whether the sensed cardiac signals are associated with the cardiac event in response to the comparing of the first characteristic.

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.