Cardiac signal recording using dynamically generated detection thresholds

1. A method, comprising:

sensing cardiac signals and comparing the signals to an initial detection threshold;

automatically generating an additional detection threshold in response to a predetermined number of the cardiac signals meeting or exceeding: the initial detection threshold or a previously generated detection threshold;

concurrently counting each occurrence of a cardiac signal meeting or exceeding each of the detection thresholds; and

recording cardiac signal data only for a cardiac signal of the sensed cardiac signals that meets or exceeds the highest of the detection thresholds.

2. The method of claim 1 , wherein automatically generating the additional detection threshold comprises:

automatically generating a plurality of additional detection thresholds;

recording cardiac signal data only for a cardiac signal of the sensed cardiac signals that meets or exceeds the highest of the detection thresholds; and

counting each occurrence of a cardiac signal that meets or exceeds the initial detection threshold and each of the plurality of additional detection thresholds.

3. The method of claim 1 , comprising removing the highest of the additional detection thresholds in response to an absence of a cardiac signal of the sensed cardiac signals that meets or exceeds the highest additional detection threshold over a fixed or adaptive time period.

4. The method of claim 3 , comprising repeating removing the highest additional detection threshold until only the initial detection threshold is operative for recording cardiac signals.

5. The method of claim 1 , wherein the additional detection threshold is offset from the initial detection threshold or the previously generated detection threshold by a fixed value.

6. The method of claim 1 , wherein the additional detection threshold is offset from the initial detection threshold or the previously generated detection threshold by a value that can vary over time.

7. The method of claim 1 , wherein the predetermined number of cardiac signals needed to meet or exceed the initial detection threshold or a previously generated detection threshold is a fixed or varying integer.

8. The method of claim 1 , wherein the additional detection thresholds are indicators of a cardiac status of the patient.

9. The method of claim 8 , comprising trending the additional detection thresholds over time.

10. A method, comprising:

(a) setting an initial detection threshold Th 1 and an occurrence threshold X, where X is a positive integer;

(b) sensing cardiac signals from a patient;

(c) recording cardiac signals up to X times in response to sensing cardiac signals that meet or exceed the initial detection threshold Th 1 ;

(d) automatically generating an additional detection threshold Th 2 in response to sensing X cardiac signals that meet or exceed the initial detection threshold Th 1 ;

(e) in response to sensing up to Y cardiac signals that meet or exceed the additional detection threshold Th 2 :

(i) recording cardiac signals that meet or exceed the additional detection threshold Th 2 up to Y times; and

(ii) automatically generating another additional detection threshold Th 3 ; and

(f) for each of the respective detection thresholds Th 1 , Th 2 , and Th 3 , counting each occurrence of a cardiac signal that meets or exceeds each respective detection threshold, Th 1 , Th 2 , and Th 3 .

11. The method of claim 10 , wherein processes (d) and (e) are repeated in response to sensing a predetermined number of cardiac signals that meet or exceed a previously generated detection threshold.

12. The method of claim 10 , comprising removing the highest of the additional detection thresholds in response to an absence of a cardiac signal that meets or exceeds the highest additional detection threshold over a fixed or adaptive time period.

13. The method of claim 10 , wherein the additional detection threshold is offset from the initial detection threshold or the previously generated detection threshold by a fixed value or a value that can vary over time.

14. The method of claim 10 , comprising trending the additional detection thresholds over time to assess changes in a cardiac status of the patient.

15. The method of claim 10 , wherein setting the initial detection threshold or generating an additional detection threshold comprises:

determining a typical range for the cardiac signals specific to the patient; and

setting the initial detection threshold or the additional detection threshold to a value that is beyond the typical range.

16. A medical device, comprising:

a housing configured for implantation within a body of a patient;

detection circuitry disposed in the housing and coupled to an electrode arrangement, the detection circuitry configured to sense cardiac signals from the patient; and

a processor coupled to the detection circuitry, the processor configured to compare the cardiac signals to an initial detection threshold, automatically generate an additional detection threshold in response to a predetermined number of the cardiac signals meeting or exceeding: the initial detection threshold or a previously generated detection threshold, concurrently count each occurrence of a cardiac signal meeting or exceeding each of the respective detection thresholds, and record cardiac signal data only for a cardiac signal of the sensed cardiac signals that meets or exceeds the highest of the detection thresholds.

17. The device of claim 16 , wherein the processor is configured to automatically generate a plurality of additional detection thresholds, record cardiac signal data only for a cardiac signal of the sensed cardiac signals that meets or exceeds the highest of the detection thresholds, and count each occurrence of a cardiac signal of the sensed cardiac signals that meets or exceeds the initial detection threshold and each of the plurality of additional detection thresholds.

18. The device of claim 16 , wherein the processor is configured to remove the highest of the additional detection thresholds in response to an absence of a cardiac signal of the sensed cardiac signals that meets or exceeds the highest additional detection threshold.

19. The device of claim 16 , wherein the additional detection thresholds are indicators of a cardiac status of the patient, and the processor is configured to trend the additional detection thresholds over time.

20. The device of claim 16 , wherein the processor is configured to determine a typical range for the cardiac signals, and set the initial detection threshold or the additional detection threshold to a value that is beyond the typical range.