System and method for sensing and detection in an extra-cardiovascular implantable cardioverter defibrtillator

1. A medical device comprising:

a sensing circuit comprising:

a first sensing channel configured to receive a first cardiac electrical signal via a first sensing electrode vector coupled to the medical device and to sense a first plurality of R-waves in response to crossings of a first R-wave sensing threshold by the first cardiac electrical signal, and

a second sensing channel configured to receive a second cardiac electrical signal via a second sensing electrode vector coupled to the medical device and to sense a second plurality of R-waves in response to crossings of a second R-wave sensing threshold by the second cardiac electrical signal, wherein the second sensing electrode vector is different than the first sensing electrode vector; and

a control circuit coupled to the sensing circuit and configured to:

determine a first plurality of intervals between successive ones of the first plurality of R-waves sensed by the first sensing channel;

adjust at least one of a first VT interval counter or a first VF interval counter based on a comparison of each of the first plurality of intervals to respective VT or VF detection interval zones; and

determine that at least one of the first VT interval counter or the first VF interval counter exceeds a respective first VT threshold number of intervals to detect or first VF threshold number of intervals to detect;

determine a second plurality of intervals between successive ones of the second plurality of R-waves sensed by the second sensing channel;

adjust at least one of a second VT interval counter or a second VF interval counter based on a comparison of each of the second plurality of intervals to respective VT and VF detection interval zones; and

determine that at least one of the second VT interval counter or the second VF interval counter exceeds a respective second VT threshold number of intervals to detect or second VF threshold number of intervals to detect;

determine, in response to determining that both the at least one of the first VT interval counter or the first VF interval counter exceeds the respective first VT threshold number of intervals to detect or first VF threshold number of intervals to detect threshold and the at least one of the second VT interval counter or the second VF interval counter has reached the respective second VT threshold number of intervals to detect or second VF threshold number of intervals to detect, whether rejection criteria are satisfied; and

detect a VT episode or VF episode when the rejection criteria are not satisfied.

2. The medical device of claim 1 , further comprising a therapy delivery circuit, wherein the control circuit is configured to control the therapy delivery circuit to deliver an anti-tachyarrhythmia therapy in response to the detection of the VT episode or the VF episode.

3. The medical device of claim 1 , wherein the control circuit is further configured to determine whether the rejection criteria are satisfied by at least one of:

determining from the second cardiac electrical signal an amplitude ratio and determining whether the amplitude ratio is greater than a ratio threshold;

determining from the second cardiac electrical signal gross morphology parameters and whether a required number of the gross morphology parameters meet a criteria or threshold applied to the respective parameter;

determining from the second cardiac electrical signal a T-wave oversensing event count and determining whether the T-wave oversensing event counter has reached a threshold count; and

determining from the second cardiac electrical signal maximum peak amplitudes and determining whether the maximum peak amplitudes satisfy a noise rejection rule.

4. The medical device of claim 1 , further comprising a memory, wherein the control circuit is coupled to the sensing circuit and the memory and the control circuit is configured to:

store a segment of the second cardiac electrical signal in the memory in response to each one of the first plurality of R-waves sensed by the first sensing channel;

in response to at least one of the first VT interval counter or the first VF interval counter reaching an R-wave confirmation threshold, determine whether the rejection criteria are satisfied based at least on analysis of at least a portion of the stored segments of the second cardiac electrical signal.

5. The medical device of claim 4 , wherein the control circuit is further configured to pass at least the portion of the stored segments of the second cardiac electrical signal through a notch filter prior to analyzing at least the portion of the time stored segments of the second cardiac electrical signal.

6. The medical device of claim 4 , wherein the control circuit is further configured to control the memory to overwrite a segment of the stored segments of the second cardiac electrical signal without analyzing the time overwritten segment when neither the first VT interval counter or the first VF interval counter reaches the R-wave confirmation threshold.

7. The medical device of claim 4 , wherein the control circuit is configured to analyze at least the portion of the stored segments of the second cardiac electrical signal in response to at least one of:

the first VT interval counter reaching a count of at least two, or

the first VF interval counter reaching a count of at least three.

8. The medical device of claim 1 , wherein the control circuit is further configured to withhold detection of the VT episode or VF episode when the rejection criteria are satisfied.

9. The medical device of claim 1 , wherein the control circuit is further configured to determine whether the rejection criteria are satisfied by determining whether at least one of:

a noise rejection criteria is satisfied by the second cardiac electrical signal;

a T-wave oversensing rejection criteria is satisfied by the second cardiac electrical signal;

a gross morphology rejection criteria is satisfied by the second cardiac electrical signal;

a beat morphology rejection criteria is satisfied by the second cardiac electrical signal; and

an R-wave rejection criteria is satisfied by the second cardiac electrical signal.

10. The medical device of claim 1 , further comprising a lead coupled to the medical device and including a plurality of electrodes, wherein the first sensing electrode vector has a first inter-electrode spacing and the second sensing electrode vector has a second inter-electrode spacing, the second inter-electrode spacing being greater than the first inter-electrode spacing.

11. The medical device of claim 1 , wherein the medical device includes a housing enclosing the sensing circuit, the medical device further comprising a lead coupled to the medical device and including a plurality of electrodes wherein the first sensing electrode vector is a short bipole between electrodes of the lead and the second sensing electrode vector is a relatively long bipole between an electrode along a distal portion of the lead and the housing of the medical device.

12. A method comprising:

obtaining a first cardiac electrical signal sensed via a first sensing electrode vector;

sense a first plurality of R-waves in response to crossings of a first R-wave sensing threshold by the first cardiac electrical signal;

obtaining a second cardiac electrical signal sensed via a second sensing electrode vector coupled to the medical device;

sensing a second plurality of R-waves in response to crossings of a second R-wave sensing threshold by the second cardiac electrical signal, wherein the second sensing electrode vector is different than the first sensing electrode vector;

determining a first plurality of intervals between successive ones of the first plurality of R-waves sensed by the first sensing channel;

adjusting at least one of a first VT interval counter or a first VF interval counter based on a comparison of each of the first plurality of intervals to respective VT or VF detection interval zones;

determining that at least one of the first VT interval counter or the first VF interval counter exceeds a respective first VT threshold number of intervals to detect or first VF threshold number of intervals to detect;

determining a second plurality of intervals between successive ones of the second plurality of R-waves sensed by the second sensing channel;

adjusting at least one of a second VT interval counter or a second VF interval counter based on a comparison of each of the second plurality of intervals to respective VT and VF detection interval zones; and

determining that at least one of the second VT interval counter or the second VF interval counter exceeds a respective second VT threshold number of intervals to detect or second VF threshold number of intervals to detect;

determining, in response to determining that both the at least one of the first VT interval counter or the first VF interval counter exceeds the respective first VT threshold number of intervals to detect or first VF threshold number of intervals to detect and the at least one of the second VT interval counter or the second VF interval counter has reached the respective second VT threshold number of intervals to detect or second VF number of intervals to detect, whether rejection criteria are satisfied; and

detecting a VT episode or VF episode when the rejection criteria are not satisfied.

13. The method of claim 12 , further comprising delivering an anti-tachyarrhythmia therapy in response to the detection of the VT episode or the VF episode.

14. The method of claim 12 , wherein determining whether the rejection criteria are satisfied comprises at least one of:

determining from the second cardiac electrical signal an amplitude ratio and determining whether the amplitude ratio is greater than a ratio threshold;

determining from the second cardiac electrical signal gross morphology parameters and whether a required number of the gross morphology parameters meet a criteria or threshold applied to the respective parameter;

determining from the second cardiac electrical signal a T-wave oversensing event count and determining whether the T-wave oversensing event count has reached a threshold; and

determining from the second cardiac electrical signal maximum peak amplitudes and determining whether the maximum peak amplitudes satisfy a noise rejection rule.

15. The method of claim 12 , further comprising:

storing a segment of the second cardiac electrical signal in a memory in response to each one of the first plurality of R-waves sensed by the first sensing channel; and

in response to at least one of the first VT interval counter or the first VF interval counter reaching an R-wave confirmation threshold, analyzing at least a portion of the stored segments of the second cardiac electrical signal;

wherein determining whether the rejection criteria are satisfied comprises determining whether the rejection criteria are satisfied based at least on the analysis of at least a portion of the stored segments of the second cardiac electrical signal.

16. The method of claim 15 , further comprising passing at least the portion of the stored segments of the second cardiac electrical signal through a notch filter prior to analyzing at least the portion of the stored segments of the second cardiac electrical signal.

17. The method of claim 15 , further comprising overwriting a segment of the stored segments of the second cardiac electrical signal in the memory without analyzing the overwritten segment when neither the first VT interval counter or the first VF interval counter reaches the R-wave confirmation threshold.

18. The method of claim 15 , further comprising analyzing at least the portion of the stored segments of the second cardiac electrical signal in response to at least one of:

the first VT interval counter reaching a count of at least two, or

the first VF interval counter reaching a count of at least three.

19. The method of claim 12 , further comprising withholding detection of the VT episode or VF episode when the rejection criteria are satisfied.

20. The method of claim 12 , wherein the first sensing electrode vector has a first inter-electrode spacing and the second sensing electrode vector has a second inter-electrode spacing, the second inter-electrode spacing being greater than the first inter-electrode spacing.