His-Purkinje system capture detection

1. A medical device, comprising:

a sensing circuit configured to sense a first cardiac electrical signal;

a therapy delivery circuit configured to generate pacing pulses; and

a control circuit configured to:

determine, from the first cardiac electrical signal, at least a maximum peak amplitude of a positive slope of the first cardiac electrical signal and a maximum peak time interval from a first pacing pulse to the maximum peak amplitude of the positive slope;

determine a ratio of the maximum peak time interval and the maximum peak amplitude;

determine a capture type of the first pacing pulse as being one of non-selective His-Purkinje system capture or ventricular myocardial capture only without capture of the His-Purkinje system based on at least the ratio of the maximum peak amplitude and the maximum peak time interval; and

control the therapy delivery circuit to generate at least one pacing pulse based on the determined capture type.

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

compare the ratio to a threshold ratio;

determine the capture type as non-selective His-Purkinje system capture in response to the ratio being less than the threshold ratio; and

determine the capture type as ventricular myocardial capture only without capture of the His-Purkinje system in response to the ratio being greater than the threshold ratio.

3. The device of claim 2 , wherein:

the therapy delivery circuit is configured to deliver a test pacing pulse at a test pulse energy;

wherein the control circuit is configured to establish the threshold ratio by: determining a reference maximum peak amplitude of a positive slope of the first cardiac electrical signal and a reference maximum peak time interval from the test pacing pulse to the reference maximum peak amplitude;

determining a reference ratio of the reference maximum peak time interval to the reference maximum peak amplitude; and

establishing the threshold ratio based on the reference ratio.

4. The device of claim 1 , wherein the control circuit is configured to determine the maximum peak amplitude by determining a maximum positive peak amplitude that corresponds to a maximum positive slope of a negative portion the first cardiac electrical signal.

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

determine at least one evoked response signal feature from the first cardiac electrical signal;

compare the at least one evoked response signal feature to a selective His-Purkinje system capture threshold requirement;

determine that the at least one evoked response signal feature does not meet the selective His-Purkinje system capture threshold requirement; and

determine the ratio of the maximum peak time interval and the maximum peak amplitude in response to the at least one evoked response signal feature not meeting the selective His-Purkinj e system capture threshold requirement.

6. The device of claim 5 , wherein the control circuit is configured to determine the at least one evoked response signal feature by determining a feature of a negative portion of the evoked response signal in the first cardiac electrical signal.

7. The device of claim 5 , wherein the control circuit is further configured to:

determine the at least one evoked response signal feature from the first cardiac electrical signal by:

detecting a maximum positive peak of the first cardiac electrical signal; and

determine the at least one evoked response signal feature by determining a post-peak slope of the first cardiac electrical signal following the maximum positive peak;

compare the post-peak slope to a slope threshold; and

determine that the at least one evoked response signal feature does not meet the selective His-Purkinje system capture threshold requirement in response to the post-peak slope being less than the slope threshold.

8. The device of claim 1 ,

wherein the control circuit is further configured to adjust a pacing pulse output setting of the therapy delivery circuit based on the determined capture type.

9. The device of claim 1 ,

wherein the control circuit is further configured to control the therapy delivery circuit to generate pacing pulses according to a capture threshold test in response to determining the capture type as being ventricular myocardial capture only without capture of the His-Purkinje system.

10. The device of claim 1 , wherein:

the sensing circuit is further configured to sense a second cardiac electrical signal different than the first cardiac electrical signal; and

the control circuit is further configured to:

generate a differential signal from the first cardiac electrical signal;

after a second pacing pulse, determine a plurality of evoked response signal features from at least two of the first cardiac electrical signal, the differential signal, and the second cardiac electrical signal;

compare a plurality of different combinations of the plurality of evoked response signal features to respective threshold requirements, wherein comparing each one of the plurality of different combinations to the respective threshold requirements comprises comparing at least two of the plurality of evoked response signal features to respective threshold requirements; and

detect selective His-Purkinje system capture by the second pacing pulse in response to at least one of the plurality of combinations of at least two of the plurality of evoked response signal features meeting the respective threshold requirements.

11. A method, comprising:

sensing a first cardiac electrical signal;

determining at least a maximum peak amplitude of a positive slope of the first cardiac electrical signal and a maximum peak time interval from a first pacing pulse to the maximum peak amplitude;

determining a ratio of the maximum peak time interval and the maximum peak amplitude;

determining a capture type of the first pacing pulse as being one of non-selective His-Purkinje system capture or ventricular myocardial capture only without capture of the His-Purkinje system based on at least the ratio of the maximum peak amplitude and the maximum peak time interval; and

generating at least one pacing pulse based on the determined capture type.

12. The method of claim 11 , further comprising:

comparing the ratio to a threshold ratio;

determining the capture type as non-selective His-Purkinje system capture in response to the ratio being less than the threshold ratio; and

determining the capture type as ventricular myocardial capture only without capture of the His-Purkinje system in response to the ratio being greater than the threshold ratio.

13. The method of claim 12 , further comprising:

generating a test pacing pulse at a test pulse energy;

establishing the threshold ratio by:

determining a reference maximum peak amplitude of a positive slope of the first cardiac electrical signal and a reference maximum peak time interval from the test pacing pulse to the reference maximum peak amplitude;

determining a reference ratio of the reference maximum peak time interval to the reference maximum peak amplitude; and

establishing the threshold ratio based on the reference ratio.

14. The method of claim 11 , wherein determining the maximum peak amplitude comprises determining a maximum peak amplitude that corresponds to a maximum positive slope of a negative portion the first cardiac electrical signal.

15. The method of claim 11 , further comprising:

determining at least one evoked response signal feature from the first cardiac electrical signal;

comparing the at least one evoked response signal feature to a selective His-Purkinje system capture threshold requirement;

determining that the at least one evoked response signal feature does not meet the selective His-Purkinje system capture threshold requirement; and

determining the ratio of the maximum peak time interval and the maximum peak amplitude in response to the at least one evoked response signal feature not meeting the selective His-Purkinje system capture threshold requirement.

16. The method of claim 15 , wherein determining the at least one evoked response signal feature comprises determining a feature of a negative portion of the evoked response signal in the first cardiac electrical signal.

17. The method of claim 15 , further comprising:

determining the at least one evoked response signal feature from the first cardiac electrical signal by:

detecting a maximum positive peak of the first cardiac electrical signal; and

determining the at least one evoked response signal feature by determining a post-peak slope of the first cardiac electrical signal following the maximum positive peak;

comparing the post-peak slope to a slope threshold; and

determining that the at least one evoked response signal feature does not meet the selective His-Purkinje system capture threshold requirement in response to the post-peak slope being less than the slope threshold.

18. The method of claim 11 , further comprising adjusting a pacing pulse output setting based on the determined capture type.

19. The method of claim 11 , further comprising performing a capture threshold test in response to determining the capture type as being ventricular myocardial capture only without capture of the His-Purkinje system.

20. The method of claim 11 , further comprising:

sensing a second cardiac electrical signal different than the first cardiac electrical signal;

generating a differential signal from the first cardiac electrical signal;

after a second pacing pulse determining a plurality of evoked response signal features from at least two of the first cardiac electrical signal, the differential signal, and the second electrical signal;

comparing a plurality of different combinations of the plurality of evoked response signal features to respective threshold requirements, wherein comparing each one of the plurality of different combinations to the respective threshold requirements comprises comparing at least two of the plurality of evoked response signal features to respective threshold requirements; and

detecting selective His-Purkinje system capture by the second pacing pulse in response to at least one of the plurality of combinations of at least two of the plurality of evoked response signal features meeting the respective threshold requirements.

21. A non-transitory, computer-readable storage medium comprising a set of instructions which, when executed by a controller of a medical device cause the medical device to:

generate a pacing pulse;

sense a cardiac electrical signal;

determine from the cardiac electrical signal at least a maximum peak amplitude of a positive slope of the cardiac electrical signal and a maximum peak time interval from the pacing pulse to the maximum peak amplitude of the positive slope;

determine a ratio of the maximum peak time interval and the maximum peak amplitude;

determine a capture type of the pacing pulse as being one of non-selective His-Purkinje system capture or ventricular myocardial capture only without capture of the His-Purkinje system based on at least the ratio of the maximum peak amplitude and the maximum peak time interval; and

generate at least one pacing pulse based on the determined capture type.