Medical device and method for detecting arrhythmia

1 . A medical device comprising:

a sensing circuit configured to sense at least one cardiac electrical signal including a first cardiac electrical signal;

a memory configured to store an amplitude threshold and a tachyarrhythmia detection interval;

a control circuit in communication with the sensing circuit, the control circuit configured to:

buffer in the memory a cardiac electrical signal segment of the first cardiac electrical signal sensed by the sensing circuit, the cardiac signal segment extending over a time interval that is greater than the tachyarrhythmia detection interval;

determine an amplitude metric from a plurality of peak amplitudes of the cardiac signal segment sensed over the time interval;

determine if the amplitude metric meets the amplitude threshold; and

perform a first analysis of the cardiac electrical signal segment for detecting asystole in response to the amplitude metric not meeting the amplitude threshold and detect the asystole based on the first analysis of the cardiac signal segment; and

perform a second analysis of the cardiac electrical signal segment for detecting a ventricular tachyarrhythmia in response to the amplitude metric meeting the amplitude threshold and detect the ventricular tachyarrhythmia based on the second analysis of the cardiac signal segment; and

a therapy delivery circuit in communication with the control circuit, the therapy delivery circuit configured to deliver:

a first electrical stimulation therapy in response to the control circuit detecting the asystole based on at least the first analysis; or

a second electrical stimulation therapy different than the first electrical stimulation therapy in response to the control circuit detecting the ventricular tachyarrhythmia based on at least the second analysis.

2 . The medical device of claim 1 , wherein the control circuit is further configured to determine the amplitude metric by:

identifying signal pulses from the cardiac signal segment;

determining the plurality of peak amplitudes by determining a peak amplitude of each of the identified signal pulses; and

determining the amplitude metric by computing a representative value of the determined plurality of peak amplitudes.

3 . The medical device of claim 2 , wherein the control circuit is further configured to identify the signal pulses from the cardiac signal segment by:

identifying a plurality of subsegments of the cardiac signal segment;

determining a local maximum from each of the plurality of subsegments;

determining a signal pulse amplitude threshold based on the local maximums; and

identifying the signal pulses from the cardiac signal segment by identifying pulses having an amplitude greater than the signal pulse amplitude threshold.

4 . The medical device of claim 2 , wherein the control circuit is further configured to identify the signal pulses by identifying pulses that are at least a minimum time interval apart.

5 . The medical device of claim 1 , wherein the control circuit is further configured to perform the second analysis of the cardiac signal segment for detecting the ventricular tachyarrhythmia by:

identifying signal pulse peaks from the cardiac signal segment;

determining peak intervals between the identified signal pulse peaks;

determining a peak interval metric based on the determined peak intervals; and

determining if the peak interval metric meets a ventricular tachyarrhythmia threshold interval.

6 . The medical device of claim 1 , wherein the control circuit is further configured to perform the second analysis of the cardiac signal segment for detecting the ventricular tachyarrhythmia by:

determining a noise metric from the cardiac signal segment;

determining that the noise metric does not meet noisy segment criteria; and

detecting the ventricular tachyarrhythmia based on the second analysis of the cardiac signal segment at least in response to the noise metric not meeting the noisy segment criteria.

7 . The medical device of claim 1 , wherein:

the sensing circuit is configured to sense ventricular event signals; and

the control circuit is further configured to:

determine sensed event data from the at least one cardiac electrical signal in response to each of a plurality of ventricular event signals sensed by the sensing circuit;

determine that suspected undersensing criteria are met based on the sensed event data; and

determine the amplitude metric from the cardiac signal segment in response to the suspected undersensing criteria being met.

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

determine the sensed event data by determining a ventricular sensed event interval from the ventricular event signals sensed by the sensing circuit;

determine that the ventricular sensed event interval meets an undersensing threshold interval; and

determine that the suspected undersensing criteria are met in response to the ventricular sensed event interval meeting the undersensing threshold interval.

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

determine the sensed event data by determining a peak amplitude from the ventricular event signals sensed by the sensing circuit;

determine that the peak amplitude is less than an undersensing amplitude threshold; and

determine that the suspected undersensing criteria are met in response to the peak amplitude being less than the undersensing threshold amplitude.

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

determine the sensed event data by determining a morphology matching score between each of the plurality of ventricular event signals sensed by the sensing circuit and an R-wave template;

determine that a threshold number of the morphology matching scores are less than a match threshold; and

determine that the suspected undersensing criteria are met in response to the threshold number of the morphology matching scores being less than the match threshold.

11 . The medical device of claim 1 , wherein the control circuit is further configured to perform the second analysis of the cardiac signal segment for detecting the ventricular tachyarrhythmia by:

determining at least one of:

a low slope content from the cardiac signal segment;

a spectral width from the cardiac signal segment; and

a mean period from the cardiac signal segment;

determining that at least one of the low slope content, the spectral width and the mean period meet ventricular tachyarrhythmia segment criteria; and

detecting the ventricular tachyarrhythmia at least in response to at least one of the low slope content, the spectral width and the mean period meeting the ventricular tachyarrhythmia segment criteria.

12 . The medical device of claim 1 , wherein the control circuit is further configured to perform the second analysis of the cardiac signal segment for detecting the ventricular tachyarrhythmia arrhythmia at least by:

determining a spectral width from the cardiac signal segment;

determining a mean period from the cardiac signal segment;

determining that the mean period meets a first threshold;

determining that a ratio of the spectral width and the mean period meets a second threshold; and

detecting the ventricular tachyarrhythmia at least in response to the mean period meeting the first threshold and the ratio of the spectral width and the mean period meeting the second threshold.

13 . The medical device of claim 1 , wherein the control circuit is further configured to detect the asystole based on the first analysis of the cardiac signal segment by:

determining a gradient signal from the cardiac signal segment;

determining that the gradient signal is within an asystole amplitude range for a detection time interval; and

detecting the asystole at least in response to the gradient signal being within the asystole amplitude range for the detection time interval.

14 . The medical device of claim 1 , wherein the therapy delivery circuit is further configured to:

deliver the first electrical stimulation therapy by delivering at least one pacing pulse; and

deliver the second electrical stimulation therapy by delivering a tachyarrhythmia therapy.

15 . A method comprising:

sensing at least one cardiac electrical signal including a first cardiac electrical signal;

storing an amplitude threshold and a tachyarrhythmia detection interval in a memory;

buffering in the memory a cardiac electrical signal segment of the first cardiac electrical signal, the cardiac signal segment extending over a time interval that is greater than the tachyarrhythmia detection interval;

determining an amplitude metric from a plurality of peak amplitudes of the cardiac signal segment sensed over the time interval;

determining if the amplitude metric meets the amplitude threshold; and

performing a first analysis of the first cardiac electrical signal segment for detecting asystole in response to the amplitude metric not meeting the amplitude threshold and detecting the asystole based on the first analysis of the cardiac signal segment; and

performing a second analysis of the first cardiac electrical signal segment for detecting a ventricular tachyarrhythmia in response to the amplitude metric meeting the amplitude threshold and detecting the ventricular tachyarrhythmia based on the second analysis of the cardiac signal segment; and

delivering:

a first electrical stimulation therapy in response to detecting the asystole based on at least the first analysis; or

a second electrical stimulation therapy different than the first electrical stimulation therapy in response to detecting the ventricular tachyarrhythmia based on at least the second analysis.

16 . The method of claim 15 , wherein determining the amplitude metric comprises:

identifying signal pulses from the cardiac signal segment;

determining the plurality of peak amplitudes by determining a peak amplitude of each of the identified signal pulses; and

determining the amplitude metric by computing a representative value of the determined plurality of peak amplitudes.

17 . The method of claim 16 , wherein identifying the signal pulses from the cardiac signal segment comprises:

identifying a plurality of subsegments of the cardiac signal segment;

determining a local maximum from each of the plurality of subsegments;

determining a signal pulse amplitude threshold based on the local maximums; and

identifying the signal pulses from the cardiac signal segment by identifying pulses having an amplitude greater than the signal pulse amplitude threshold.

18 . The method of claim 16 , wherein identifying the signal pulses further comprises identifying pulses that are at least a minimum time interval apart.

19 . The method of claim 15 , wherein performing the second analysis of the cardiac signal segment for detecting the ventricular tachyarrhythmia comprises:

identifying signal pulse peaks from the cardiac signal segment;

determining peak intervals between the identified signal pulse peaks;

determining a peak interval metric based on the determined peak intervals; and

determining if the peak interval metric meets a ventricular tachyarrhythmia threshold interval.

20 . The method of claim 15 , wherein performing the second analysis of the cardiac signal segment for detecting the ventricular tachyarrhythmia further comprises:

determining a noise metric from the cardiac signal segment;

determining that the noise metric does not meet noisy segment criteria; and

detecting the ventricular tachyarrhythmia based on the second analysis of the cardiac signal segment at least in response to the noise metric not meeting the noisy segment criteria.

21 . The method of claim 15 , further comprising:

sensing ventricular event signals;

determining sensed event data from the at least one cardiac electrical signal in response to each of a plurality of sensed ventricular event signals;

determining that suspected undersensing criteria are met based on the sensed event data; and

determining the amplitude metric from the cardiac signal segment in response to the suspected undersensing criteria being met.

22 . The method of claim 21 , further comprising:

determining the sensed event data by determining a ventricular sensed event interval from the sensed ventricular event signals;

determining that the ventricular sensed event interval meets an undersensing threshold interval; and

determining that the suspected undersensing criteria are met in response to the ventricular sensed event interval meeting the undersensing threshold interval.

23 . The method of claim 21 , further comprising:

determining the sensed event data by determining a peak amplitude from the sensed ventricular event signals;

determining that the peak amplitude is less than an undersensing amplitude threshold; and

determining that the suspected undersensing criteria are met in response to the peak amplitude being less than the undersensing threshold amplitude.

24 . The method of claim 21 , further comprising:

determining the sensed event data by determining a morphology matching score between each of the plurality of sensed ventricular event signals and an R-wave template;

determining that a threshold number of the morphology matching scores are less than a match threshold; and

determining that the suspected undersensing criteria are met in response to the threshold number of the morphology matching scores being less than the match threshold.

25 . The method of claim 15 , wherein performing the second analysis of the cardiac signal segment for detecting the ventricular tachyarrhythmia further comprises:

determining at least one of:

a low slope content from the cardiac signal segment;

a spectral width from the cardiac signal segment;

a mean period from the cardiac signal segment;

determining that at least one of the low slope content, the spectral width and the mean period meet ventricular tachyarrhythmia segment criteria; and

detecting the ventricular tachyarrhythmia at least in response to the least one of the low slope content, the spectral width and the mean period meeting the ventricular tachyarrhythmia segment criteria.

26 . The method of claim 15 , wherein performing the second analysis of the cardiac signal segment for detecting the ventricular tachyarrhythmia arrhythmia further comprises:

determining a spectral width from the cardiac signal segment;

determining a mean period from the cardiac signal segment;

determining that the mean period meets a first threshold;

determining that a ratio of the spectral width and the mean period meet a second threshold; and

detecting the ventricular tachyarrhythmia at least in response to the mean period meeting the first threshold and the ratio of the spectral width and the mean period meeting the second threshold.

27 . The method of claim 15 , further comprising detecting the asystole based on the first analysis of the cardiac signal segment by:

determining a gradient signal from the cardiac signal segment;

determining that the gradient signal is within an asystole amplitude range for a detection time interval; and

detecting the asystole at least in response to the gradient signal being within the asystole amplitude range for the detection time interval.

28 . The method of claim 15 , further comprising:

delivering the first electrical stimulation therapy by delivering at least one pacing pulse; and

delivering the second electrical stimulation therapy by delivering a tachyarrhythmia therapy.

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

sense at least one cardiac electrical signal including a first cardiac electrical signal;

buffer a cardiac electrical signal segment of the first cardiac electrical signal, the cardiac signal segment extending over a time interval that is greater than a tachyarrhythmia detection interval;

determine an amplitude metric from a plurality of peak amplitudes of the cardiac signal segment sensed over the time interval;

determine if the amplitude metric meets an amplitude threshold; and

perform a first analysis of the cardiac electrical signal segment for detecting asystole in response to the amplitude metric not meeting the amplitude threshold and detect asystole based on the first analysis of the cardiac signal segment; and

perform a second analysis of the cardiac electrical signal segment for detecting a ventricular tachyarrhythmia in response to the amplitude metric meeting the amplitude threshold and detecting the ventricular tachyarrhythmia based on the second analysis of the cardiac signal segment; and

deliver:

a first electrical stimulation therapy in response to detecting the asystole based on at least the first analysis; or

a second electrical stimulation therapy different than the first electrical stimulation therapy in response to detecting the ventricular tachyarrhythmia based on at least the second analysis.

30 . The medical device of claim 13 wherein the control circuit is further configured to determine that the gradient signal is within the asystole amplitude range for a detection time interval by determining that a first threshold number of sample points of the gradient signal are within the asystole amplitude range during each of a second threshold number of consecutive time windows of the cardiac signal segment, wherein each of the consecutive time windows comprise a specified number of sample points of the gradient signal.