Supraventricular tachyarrhythmia discrimination

1. A device comprising:

a sensing circuit configured to receive at least a first cardiac electrical signal via a sensing electrode vector;

a memory configured to store a morphology template and a first match threshold; and

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

determine a morphology match score between each of a plurality of cardiac signal segments of the first cardiac electrical signal and the morphology template;

determine that first criteria for detecting a ventricular tachyarrhythmia are met by the first cardiac electrical signal by determining that at least a threshold number of the plurality of cardiac signal segments have a morphology match score that is less than the first match threshold;

determine if supraventricular tachyarrhythmia discrimination criteria are met in response to determining that the first criteria for detecting a ventricular tachyarrhythmia are met;

when the supraventricular tachyarrhythmia discrimination criteria are met:

determine a plurality of features from the plurality of cardiac signal segments of the first cardiac electrical signal; and

determine if the plurality of features satisfy supraventricular tachyarrhythmia detection criteria;

when the supraventricular tachyarrhythmia detection criteria are satisfied, withhold detecting of the ventricular tachyarrhythmia; and

when the supraventricular tachyarrhythmia discrimination criteria are met and the supraventricular tachyarrhythmia detection criteria are not satisfied, detect the ventricular tachyarrhythmia in response to at least the first criteria being met; and

a therapy delivery circuit configured to generate an electrical stimulation therapy in response to the control circuit detecting the ventricular tachyarrhythmia.

2. The device of claim 1 , wherein the control circuit is configured to determine if the supraventricular tachyarrhythmia detection criteria are met by:

determining if variability in a first portion of the plurality of features meet monomorphic waveform criteria;

determining if a second portion of the plurality of features meet supraventricular beat criteria; and

determining that the supraventricular tachyarrhythmia detection criteria are met in response to the monomorphic waveform criteria being met and the supraventricular beat criteria being met.

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

withhold determining the plurality of features in response to the supraventricular tachyarrhythmia discrimination criteria not being met; and

detect the ventricular tachyarrhythmia in response to at least the first criteria for detecting the ventricular tachyarrhythmia being met and the supraventricular tachyarrhythmia discrimination criteria not being met.

4. The device of claim 1 , wherein the control circuit is further configured to determine that the supraventricular tachyarrhythmia discrimination criteria are met by determining that at least a second threshold number of the plurality of cardiac signal segments have a morphology match score greater than a second match threshold, the second match threshold less than the first match threshold.

5. The device of claim 1 , wherein the control circuit is further configured to determine that the first criteria for detecting the ventricular tachyarrhythmia are met by:

determining a morphology match score between each one of a preceding plurality of cardiac signal segments of the first cardiac signal and the morphology template;

setting a threshold count value in response to less than the threshold number of the preceding plurality of cardiac signal segments having a morphology match score less than the first match threshold;

adjusting a tachyarrhythmia count value in response to the threshold number of the plurality of cardiac signal segments having morphology match scores less than the first match threshold; and

determining that the first criteria are met when the tachyarrhythmia count value reaches the threshold count value.

6. The device of claim 1 , wherein:

the sensing circuit is further configured to sense R-waves; and

the control circuit is further configured to:

determine sensed event intervals between consecutive R-waves sensed by the sensing circuit;

compare the sensed event intervals to a tachyarrhythmia detection interval;

increase a count of tachyarrhythmia detection intervals in response to each one of the determined sensed event intervals that is less than the tachyarrhythmia detection interval; and

in response to a value of the count of tachyarrhythmia detection intervals being equal to or greater than a fast heart rate threshold, determine whether the first criteria for detecting the ventricular tachyarrhythmia are met.

7. The device of claim 1 , wherein the control circuit is configured to determine whether the supraventricular tachyarrhythmia detection criteria are satisfied by:

comparing a first portion of the features determined from each of the plurality of cardiac signal segments to respective features of the morphology template; and

determining that the supraventricular detection criteria are satisfied in response to at least a threshold number of the plurality of cardiac signal segments having the first portion of the features matching the respective features of the morphology template.

8. The device of claim 7 , wherein the control circuit is further configured to:

determine the first portion of the features for each one of the plurality of cardiac signal segments by determining at least a polarity pattern, a peak time interval; and a normalized width.

9. The device of claim 1 , wherein the control circuit is further configured to determine if the supraventricular tachycardia detection criteria are satisfied by:

determining a variability of each feature of a second portion of the features determined from each of the plurality of cardiac signal segments;

comparing the variability of each of the features of the second portion of the features to a respective variability threshold; and

determining that the supraventricular detection criteria are satisfied in response to at least the variability of each feature of the second portion of the features being less than the respective variability threshold.

10. The device of claim 9 , wherein the control circuit is further configured to determine the variability of each feature of the second portion of the features by:

determining the second portion of the features for each one of the plurality of cardiac signal segments by determining at least an amplitude and a timing of a maximum peak of the cardiac signal segment; and

determining an amplitude variability and a timing variability of the maximum peaks of the plurality of cardiac signal segments.

11. The device of claim 1 , wherein:

the sensing circuit is further configured to sense R-waves; and

the control circuit is further configured to:

determine event intervals between consecutive R-waves sensed by the sensing circuit;

compare the event intervals to a tachyarrhythmia detection interval;

increase a count of tachyarrhythmia detection intervals in response to each one of the determined event intervals that is less than the tachyarrhythmia detection interval;

determine that second criteria for detecting the ventricular tachyarrhythmia are met in response to a value of the count of tachyarrhythmia detection intervals being equal to or greater than a detection threshold value; and

detect the ventricular tachyarrhythmia when both the first criteria and the second criteria are met and at least one of: the supraventricular tachyarrhythmia discrimination criteria are not met or the supraventricular tachyarrhythmia detection criteria are not satisfied.

12. The device of claim 1 , wherein:

the sensing circuit is further configured to:

sense a second cardiac signal; and

sense R-waves from the second cardiac signal;

the control circuit is further configured to:

determine sensed event intervals between consecutive pairs of the R-waves sensed by the sensing circuit;

compare the sensed event intervals to a tachyarrhythmia detection interval;

determine that a threshold number of the sensed event intervals are less than the tachyarrhythmia detection interval; and

buffer the plurality of cardiac signal segments from the first cardiac signal in response to the threshold number of the sensed event intervals being less than the tachyarrhythmia detection interval, each one of the plurality of cardiac signal segments corresponding to an R-wave sensed by the sensing circuit.

13. The device of claim 1 , wherein the control circuit is further configured to adjust the first criteria in response to the supraventricular detection criteria being satisfied.

14. The device of claim 1 , further comprising a housing enclosing the therapy delivery circuit, the sensing circuit and the control circuit and having a connector block for receiving an extra-cardiovascular lead carrying at least one electrode of the sensing electrode vector.

15. A method comprising:

receiving by a sensing circuit at least a first cardiac electrical signal via a sensing electrode vector;

storing a morphology template and a first match threshold;

determining a morphology match score between each a plurality of cardiac signal segments of the first cardiac electrical signal and the morphology template;

determining that first criteria for detecting a ventricular tachyarrhythmia are met by the first cardiac electrical signal by determining that at least a threshold number of the plurality of cardiac signal segments have a morphology match score that is less than a first match threshold;

determining if supraventricular tachyarrhythmia discrimination criteria are met in response to determining that the first criteria for detecting a ventricular tachyarrhythmia are met;

when the supraventricular tachyarrhythmia discrimination criteria are met:

determining a plurality of features from the plurality of cardiac signal segments of the first cardiac electrical signal; and

determining if the plurality of features satisfy supraventricular tachyarrhythmia detection criteria;

when the supraventricular tachyarrhythmia detection criteria are satisfied, withholding detecting of the ventricular tachyarrhythmia; and

when the supraventricular tachyarrhythmia discrimination criteria are met and the supraventricular tachyarrhythmia detection criteria are not satisfied, detecting the ventricular tachyarrhythmia in response to at least the first criteria being met; and

generating an electrical stimulation therapy in response to detecting the ventricular tachyarrhythmia.

16. The method of claim 15 , wherein determining if the supraventricular tachyarrhythmia detection criteria are met comprises:

determining if variability in a first portion of the plurality of features meet monomorphic waveform criteria;

determining if a second portion of the plurality of features meet supraventricular beat criteria; and

determining that the supraventricular tachyarrhythmia detection criteria are met in response to the monomorphic waveform criteria being met and the supraventricular beat criteria being met.

17. The method of claim 15 , further comprising:

withholding determining the plurality of features in response to the supraventricular tachyarrhythmia discrimination criteria not being met; and

detecting the ventricular tachyarrhythmia in response to at least the first criteria for detecting the ventricular tachyarrhythmia being met and the supraventricular tachyarrhythmia discrimination criteria not being met.

18. The method of claim 15 , further comprising determining that the supraventricular tachyarrhythmia discrimination criteria are met by determining that at least a second threshold number of the plurality of cardiac signal segments have a morphology match score greater than a second match threshold, the second match threshold less than the first match threshold.

19. The method of claim 15 , further comprising determining that the first criteria for detecting the ventricular tachyarrhythmia are met by:

determining a morphology match score between each one of a preceding plurality of cardiac signal segments of the first cardiac signal and the morphology template;

setting a threshold count value in response to less than the threshold number of the preceding plurality of cardiac signal segments having a morphology match score less than the first match threshold;

adjusting a tachyarrhythmia count value in response to the threshold number of the plurality of cardiac signal segments having morphology match scores less than the first match threshold; and

determining that the first criteria are met when the tachyarrhythmia count value reaches the threshold count value.

20. The method of claim 15 , further comprising:

sensing R-waves by the sensing circuit;

determining sensed event intervals between consecutive R-waves sensed by the sensing circuit;

comparing the sensed event intervals to a tachyarrhythmia detection interval;

increasing a count of tachyarrhythmia detection intervals in response to each one of the determined sensed event intervals that is less than the tachyarrhythmia detection interval; and

in response to a value of the count of tachyarrhythmia detection intervals being equal to or greater than a fast heart rate threshold, determining whether the first criteria for detecting the ventricular tachyarrhythmia are met.