SYSTEM AND METHOD FOR SENSING AND DETECTION IN AN EXTRA-CARDIOVASCULAR IMPLANTABLE CARDIOVERTER DEFIBRILLATOR

1 . A medical device comprising:

a sensing circuit configured to:

sense a first cardiac signal;

sense a second cardiac signal;

sense R-waves from the first cardiac signal;

a control circuit configured to:

detect a first threshold number of tachyarrhythmia intervals from the sensed R-waves;

determine a feature of the second cardiac signal corresponding to each one of at least a portion of the R-waves sensed from the first cardiac signal;

confirm at least a second threshold number of the R-waves sensed from the first cardiac signal based on the determined features of the second cardiac signal;

detect a tachyarrhythmia episode in response to at least detecting the first threshold number of tachyarrhythmia intervals and confirming at least the second threshold number of the R-waves; and

a therapy delivery circuit configured deliver a tachyarrhythmia therapy in response to detecting the tachyarrhythmia episode.

2 . The medical device of claim 1 wherein the control circuit is further configured to:

determine the feature of the second cardiac signal by determining a peak amplitude of the second cardiac signal;

compare the peak amplitude to a threshold amplitude; and

confirm an R-wave of the sensed R-waves in response to the peak amplitude being greater than the threshold amplitude.

3 . The medical device of claim 1 wherein the control circuit is further configured to:

determine a differential signal from the second cardiac signal; and

determine the features from the differential signal.

4 . The medical device of claim 1 further comprising:

a memory configured to store cardiac signal segments; and wherein

the control circuit is further configured to:

in response to an R-wave sensed by the sensing circuit from the first cardiac signal, buffer a cardiac signal segment in the memory; and

determine the feature of the second cardiac signal by determining the feature from the buffered cardiac signal segment.

5 . The medical device of claim 4 wherein the control circuit is further configured to:

detect at least a second number of tachyarrhythmia intervals from the from the sensed R-waves, the second number being less than the first number; and

buffer the cardiac signal segment in response to detecting at least the second threshold number of tachyarrhythmia intervals.

6 . The medical device of claim 4 wherein the control circuit is further configured to:

determine the feature of the second cardiac signal by determining the feature from a subsegment of the buffered cardiac signal segment, the subsegment being in timed relation to a respective R-wave sensed from the first cardiac signal by the sensing circuit.

7 . The medical device of claim 1 wherein the control circuit is further configured to:

determine a count of R-waves sensed from the first cardiac signal that are not confirmed based on the features determined from the second cardiac signal;

determine that the count of R-waves that are not confirmed meets a rejection threshold;

determine an updated count of R-waves that are not confirmed;

determine that the updated count does not meet the rejection threshold; and

withhold the tachyarrhythmia detection at least until the updated count of R-waves that are not confirmed does not meet the rejection threshold.

8 . The medical device of claim 7 wherein the control circuit is further configured to determine that at least the second threshold number of the R-waves are confirmed by determining that the updated count does not meet the rejection threshold.

9 . The medical device of claim 1 wherein the control circuit is further configured to:

determine the feature of the second cardiac signal by determining a peak amplitude;

determine a threshold based on a time of the peak amplitude;

confirm at least the second threshold number of the R-waves sensed from the first cardiac signal based on the second threshold number of the determined features meeting the threshold.

10 . The medical device of claim 1 wherein the control circuit is further configured to:

determine a plurality of features of the second cardiac signal comprising at least one of:

a peak slew rate,

an event area,

an event signal width, and

a peak amplitude; and

compare each of the plurality of features to a respective threshold for confirming at least the second threshold number of the R-waves.

11 . A method comprising:

sensing a first cardiac signal;

sensing a second cardiac signal;

sensing R-waves from the first cardiac signal;

detecting a first threshold number of tachyarrhythmia intervals from the sensed R-waves;

determining a feature of the second cardiac signal corresponding to each one of at least a portion of the R-waves sensed from the first cardiac signal;

confirming at least a second threshold number of the R-waves sensed from the first cardiac signal based on the determined features of the second cardiac signal;

detecting a tachyarrhythmia episode in response to at least detecting the first threshold number of tachyarrhythmia intervals and confirming at least the second threshold number of the R-waves; and

delivering a tachyarrhythmia therapy in response to detecting the tachyarrhythmia episode.

12 . The method of claim 11 further comprising:

determining the feature of the second cardiac signal by determining a peak amplitude of the second cardiac signal;

comparing the peak amplitude to a threshold amplitude; and

confirming an R-wave of the sensed R-waves in response to the peak amplitude being greater than the threshold amplitude.

13 . The method of claim 11 further comprising:

determining a differential signal from the second cardiac signal; and

determining the features from the differential signal.

14 . The method of claim 11 further comprising:

in response to an R-wave sensed by the sensing circuit from the first cardiac signal, buffering a cardiac signal segment in a memory; and

determining the feature of the second cardiac signal by determining the feature from the buffered cardiac signal segment.

15 . The method of claim 14 further comprising:

detecting at least a second number of tachyarrhythmia intervals from the sensed R-waves, the second number being less than the first number; and

buffering the cardiac signal segment in response to detecting at least the second number of tachyarrhythmia intervals.

16 . The method of claim 15 further comprising:

determining the feature of the second cardiac signal by determining the feature from a subsegment of the buffered cardiac signal segment, the subsegment being in timed relation to a respective R-wave sensed from the first cardiac signal.

17 . The method of claim 11 further comprising:

determining a count of R-waves sensed from the first cardiac signal that are not confirmed based on the features determined from the second cardiac signal;

determining that the count of R-waves that are not confirmed meets a rejection threshold;

determining an updated count of R-waves that are not confirmed;

determining that the updated count does not meet the rejection threshold; and

withholding the tachyarrhythmia detection at least until the updated count of R-waves that are not confirmed does not meet the rejection threshold.

18 . The method of claim 17 further comprising determining that at least the second threshold number of the R-waves are confirmed by determining that the updated count does not meet the rejection threshold.

19 . The method of claim 11 further comprising:

determining a plurality of features of the second cardiac signal corresponding to each one of at least a portion of the R-waves sensed from the first cardiac signal, the plurality of features comprising at least one of:

a peak slew rate,

an event area,

an event signal width, and

a peak amplitude; and

comparing each of the plurality of features to a respective threshold for confirming at least the second threshold number of the R-waves.

20 . A non-transitory computer readable medium comprising instructions that, when executed by a control circuit of a medical device, cause the medical device to:

sense a first cardiac signal;

sense a second cardiac signal;

sense R-waves from the first cardiac signal;

detect a first threshold number of tachyarrhythmia intervals from the sensed R-waves;

determine a feature of the second cardiac signal corresponding to each one of at least a portion of the R-waves sensed from the first cardiac signal;

confirm at least a second threshold number of the R-waves sensed from the first cardiac signal based on the determined features of the second cardiac signal;

detect a tachyarrhythmia episode in response to at least detecting the first threshold number of tachyarrhythmia intervals and confirming at least the second threshold number of the R-waves; and

deliver a tachyarrhythmia therapy in response to detecting the tachyarrhythmia episode.