Impedance sensing

1. A medical device system comprising:

an electrode;

impedance measurement circuitry coupled to the electrode, the impedance measurement circuitry configured to generate an impedance signal indicating impedance proximate to the electrode; and

processing circuitry configured to identify a plurality of first components within the impedance signal, each of the first components caused by a respective one of a plurality of cardiac depolarizations, wherein the impedance signal further comprises a plurality of second components, each of the second components caused by a respective one of a plurality of cardiac contractions,

wherein, to identify each first component of the plurality of first components, the processing circuitry is configured to:

detect a change in at least one of an amplitude or a slope in the impedance signal that exceeds a respective threshold; and

identify the first component based on detecting the change in at least one of the amplitude or the slope of the impedance signal that exceeds the respective threshold.

2. The medical device system of claim 1 , wherein the processing circuitry is configured to:

process the impedance signal using one or more of a filter, a transform function, or a derivative; and

analyze the processed impedance signal to identify the plurality of first components.

3. The medical device system of claim 1 further comprising:

therapeutic signal generation circuitry configured to generate and deliver a therapeutic signal;

wherein the processing circuitry is further configured to:

detect a cardiac arrhythmia based on the plurality of identified first components within the impedance signal; and

control the therapeutic signal generation circuitry to generate the therapeutic signal in response to detection of the cardiac arrhythmia.

4. The medical device system of claim 3 , wherein, to detect the cardiac arrhythmia, the processing circuitry is configured to:

determine one or more of a rate of the identified plurality of first components, a regularity of the identified plurality of first components, or a morphology of the identified plurality of first components; and

detect the cardiac arrhythmia based on at least one of the rate, the regularity, or the morphology of the identified plurality of first components.

5. The medical device system of claim 3 , further comprising sensing circuitry configured to sense an electrogram signal, wherein the processing circuitry is configured to:

identify a plurality of cardiac depolarizations within the electrogram signal;

detect a cardiac arrhythmia based on the plurality of identified cardiac depolarizations; and

confirm the detected cardiac arrhythmia based on the plurality of first components within the impedance signal.

6. The medical device system of claim 5 , wherein the processing circuitry is further configured to:

determine a rate based on the plurality of identified cardiac depolarizations;

determine the rate is greater than a threshold tachyarrhythmia rate; and

initiate the impedance measurement circuitry to begin obtaining the impedance signal in response to the rate being greater than the threshold tachyarrhythmia rate.

7. The medical device system of claim 5 , wherein the processing circuitry is configured to:

determine a first rate of the first components within the impedance signal;

determine a second rate of the cardiac depolarizations within the electrogram signal;

compare the first rate and the second rate;

confirm the detected cardiac arrhythmia based on the comparison of the first rate and the second rate; and

control the therapeutic signal generation circuitry to deliver the therapeutic signal in response to the confirmation.

8. The medical device system of claim 5 , wherein the processing circuitry is configured to:

determine a first rate based on the plurality of identified cardiac depolarizations;

determine the rate is greater than a threshold tachyarrhythmia rate;

initiate the impedance measurement circuitry to begin obtaining the impedance signal in response to the rate being greater than the threshold tachyarrhythmia rate;

determine a second rate of the first components within the impedance signal;

compare the first rate and the second rate;

confirm the detected cardiac arrhythmia based on the comparison of the first rate and the second rate; and

control the therapeutic signal generation circuitry to deliver the therapeutic signal in response to the confirmation.

9. The medical device system of claim 5 , wherein the processing circuitry is configured to confirm the detected cardiac arrhythmia based on one or more of a rate, a regularity or a morphology of the plurality of first components within the impedance signal.

10. A method comprising:

generating an impedance signal indicating impedance proximate an electrode; and

identifying a plurality of first components within the impedance signal, each of the first components caused by a respective one of a plurality of cardiac depolarizations, wherein the impedance signal further comprises a plurality of second components, each of the second components caused by a respective one of a plurality of cardiac contractions,

wherein the identifying of each first component of the plurality of first components further comprises:

detecting a change in at least one of an amplitude or a slope in the impedance signal that exceeds a respective threshold; and

identifying the first component based on detecting the change in at least one of the amplitude or the slope of the impedance signal that exceeds the respective threshold.

11. The method of claim 10 , wherein identifying the plurality of first components comprises:

processing the impedance signal using one or more of a filter, a transform function, or a derivative; and

analyzing the processed impedance signal to identify the plurality of first components.

12. The method of claim 10 , further comprising:

detecting a cardiac arrhythmia based on the plurality of identified first components within the impedance signal; and

controlling a therapeutic signal generation circuitry to generate a therapeutic signal in response to detecting cardiac arrhythmia.

13. The method of claim 12 , wherein detecting the cardiac arrhythmia comprises:

determining one or more of a rate of the identified plurality of first components, a regularity of the identified plurality of first components, or a morphology of the identified plurality of first components; and

detecting the cardiac arrhythmia based on at least one of the rate, the regularity, or the morphology of the identified plurality of first components.

14. The method of claim 12 , further comprising:

identifying a plurality of cardiac depolarizations within an electrogram signal; and

detecting a cardiac arrhythmia based on the plurality of identified cardiac depolarizations;

wherein detecting the cardiac arrhythmia based on the plurality of identified first components within the impedance signal comprises confirming the detected cardiac arrhythmia based on the plurality of first components within the impedance signal.

15. The method of claim 14 , further comprising:

determining a rate based on the plurality of identified cardiac depolarizations;

determining the rate is greater than a threshold tachyarrhythmia rate; and

initiating the impedance measurement circuitry to begin obtaining the impedance signal in response to the rate being greater than the threshold tachyarrhythmia rate.

16. The method of claim 14 , further comprising:

determining a first rate of the first components within the impedance signal;

determining a second rate of the cardiac depolarizations within the electrogram signal;

comparing the first rate and the second rate; and

confirming the detected cardiac arrhythmia based on the comparison of the first rate and the second rate; and

controlling the therapeutic signal generation circuitry to generate the therapeutic signal in response to the confirmation.

17. The method of claim 14 , wherein confirming the detected cardiac arrhythmia based on the plurality of first components within the impedance signal comprises confirming the detected cardiac arrhythmia based on one or more of a rate, a regularity or a morphology of the plurality of first components within the impedance signal.

18. A computer-readable medium comprising processor-executable instructions that, when executed by processing circuitry, cause a medical device system to:

generate an impedance signal indicating impedance proximate to an electrode; and

identify a plurality of first components within the impedance signal, each of the first components caused by a respective one of a plurality of cardiac depolarizations, wherein the impedance signal further comprises a plurality of second components, each of the second components caused by a respective one of a plurality of cardiac contractions,

wherein, to identify each first component of the plurality of first components, the processor-executable instructions further cause the medical device system to:

detect a change in at least one of an amplitude or a slope in the impedance signal that exceeds a respective threshold; and

identify the first component based on detecting the change in at least one of the amplitude or the slope of the impedance signal that exceeds the respective threshold.