Method and apparatus for verifying bradycardia/asystole episodes via detection of under-sensed events

1. An insertable cardiac monitor comprising:

a housing configured for subcutaneous implantation within a patient, the housing having a length, a width, and a depth,

wherein the length is greater than the width and the width is greater than the depth,

wherein the length is within a range from 40 millimeters (mm) to 60 mm,

wherein the width is within a range from 3 mm to 10 mm, and

wherein the depth is within a range from 2 mm to 5 mm;

a distal electrode;

a proximal electrode; and

circuitry comprising a processer within the housing, the circuitry configured to:

sense a cardiac signal of the patient via the distal electrode and the proximal electrode;

compare an amplitude of the cardiac signal to a primary threshold;

detect an R-wave based on the comparison of the amplitude of the cardiac signal to the primary threshold;

detect an asystole based on a comparison of the amplitude of the cardiac signal subsequent to the detected R-wave to the primary threshold; and

in response to detecting the asystole:

determine a secondary threshold based on the detected R-wave;

determine whether a value that is based on the cardiac signal sensed during a pause interval that is subsequent to the detected R-wave satisfies the secondary threshold, wherein at least one under-sensed R-wave during the pause interval is present when the value satisfies the secondary threshold; and

determine whether the detection of the asystole is false based on the determination of whether the value satisfies the secondary threshold.

2. The insertable cardiac monitor of claim 1 , wherein the circuitry is configured to:

determine an amplitude of the R-wave; and

determine the secondary threshold based on the amplitude of the R-wave.

3. The insertable cardiac monitor of claim 1 , wherein the length is within a range from 40 mm to 45 mm.

4. The insertable cardiac monitor of claim 1 , wherein a spacing between the distal electrode and the proximal electrode is within a range from 35 mm to 55 mm.

5. The insertable cardiac monitor of claim 4 , wherein the spacing between the distal electrode and the proximal electrode is within a range from 35 mm to 40 mm.

6. The insertable cardiac monitor of claim 4 , wherein the distal electrode is substantially flat, and the proximal electrode comprises a three-dimensional, curved configuration.

7. The insertable cardiac monitor of claim 1 , wherein a volume of the insertable cardiac monitor is less than 1.5 cubic centimeters.

8. The insertable cardiac monitor of claim 7 , wherein a spacing between the distal electrode and the proximal electrode is within a range from 35 mm to 55 mm.

9. The insertable cardiac monitor of claim 1 , wherein the distal electrode is substantially flat, and the proximal electrode comprises a three-dimensional, curved configuration.

10. The insertable cardiac monitor of claim 1 , wherein the housing defines an elongated rectangular prism comprising a rounded distal end and a rounded proximal end.

11. The insertable cardiac monitor of claim 1 , wherein, to determine whether the value that is based on the cardiac signal sensed during the pause interval satisfies the secondary threshold, the circuitry is configured to determine whether an amplitude of the cardiac signal during the pause interval exceeds the secondary threshold.

12. The insertable cardiac monitor of claim 1 , wherein the circuitry is configured to:

buffer the cardiac signal sensed during the pause interval; and

determine whether the value satisfies the secondary threshold subsequent to the pause interval.

13. The insertable cardiac monitor of claim 1 , wherein the circuitry is configured to determine whether the value satisfies the secondary threshold during the pause interval.

14. A system comprising:

an external programmer; and

an insertable cardiac monitor comprising:

a housing configured for subcutaneous implantation within a patient, the housing having a length, a width, and a depth,

wherein the length is greater than the width and the width is greater than the depth,

wherein the length is within a range from 40 millimeters (mm) to 60 mm,

wherein the width is within a range from 3 mm to 10 mm, and

wherein the depth is within a range from 2 mm to 5 mm;

a distal electrode;

a proximal electrode; and

circuitry comprising a processer, the circuitry configured to:

sense a cardiac signal of the patient via the distal electrode and the proximal electrode;

compare an amplitude of the cardiac signal to a primary threshold;

detect an R-wave based on the comparison of the amplitude of the cardiac signal to the primary threshold;

detect an asystole based on a comparison of the amplitude of the cardiac signal subsequent to the detected R-wave to the primary threshold; and

in response to detecting the asystole:

determine a secondary threshold based on the detected R-wave;

determine whether a value that is based on the cardiac signal sensed during a pause interval that is subsequent to the detected R-wave satisfies the secondary threshold, wherein at least one under-sensed R-wave during the pause interval is present when the value satisfies the secondary threshold; and

determine whether the detection of the asystole is false based on the determination of whether the value satisfies the secondary threshold.

15. The insertable cardiac monitor of claim 14 , wherein the circuitry is configured to:

determine an amplitude of the R-wave; and

determine the secondary threshold based on the amplitude of the R-wave.

16. The insertable cardiac monitor of claim 14 , wherein the length is within a range from 40 mm to 45 mm.

17. The insertable cardiac monitor of claim 14 , wherein a spacing between the distal electrode and the proximal electrode is within a range from 35 mm to 55 mm.

18. The insertable cardiac monitor of claim 17 , wherein the spacing between the distal electrode and the proximal electrode is within a range from 35 mm to 40 mm.

19. The insertable cardiac monitor of claim 14 , wherein the distal electrode is substantially flat, and the proximal electrode comprises a three-dimensional, curved configuration.

20. The insertable cardiac monitor of claim 14 , wherein a volume of the insertable cardiac monitor is less than 1.5 cubic centimeters.

21. The insertable cardiac monitor of claim 20 , wherein a spacing between the distal electrode and the proximal electrode is within a range from 35 mm to 55 mm.

22. The insertable cardiac monitor of claim 20 , wherein the distal electrode is substantially flat, and the proximal electrode comprises a three-dimensional, curved configuration.

23. The insertable cardiac monitor of claim 14 , wherein the housing defines an elongated rectangular prism comprising a rounded distal end and a rounded proximal end.

24. The insertable cardiac monitor of claim 14 , wherein, to determine whether the value that is based on the cardiac signal sensed during the pause interval satisfies the secondary threshold, the circuitry is configured to determine whether an amplitude of the cardiac signal during the pause interval exceeds the secondary threshold.

25. The insertable cardiac monitor of claim 14 , wherein the circuitry is configured to:

buffer the cardiac signal sensed during the pause interval; and

determine whether the value satisfies the secondary threshold subsequent to the pause interval.

26. The insertable cardiac monitor of claim 14 , wherein the circuitry is configured to determine whether the value satisfies the secondary threshold during the pause interval.

27. The system of claim 14 , wherein the circuitry is configured to transmit data to the external programmer via Bluetooth® communication based on the determination of whether the detection of the asystole is false.

28. An insertable cardiac monitor comprising:

a housing configured for subcutaneous implantation within a patient, the housing having a length, a width, and a depth,

wherein the length is greater than the width and the width is greater than the depth,

wherein the length is within a range from 40 millimeters (mm) to 60 mm,

wherein the width is within a range from 3 mm to 10 mm, and

wherein the depth is within a range from 2 mm to 5 mm;

a distal electrode;

a proximal electrode; and

circuitry comprising a processer within the housing, the circuitry configured to:

sense a cardiac signal of the patient via the distal electrode and the proximal electrode;

compare an amplitude of the cardiac signal to a primary threshold;

detect an R-wave based on the comparison of the amplitude of the cardiac signal to the primary threshold;

detect an asystole based on a comparison of the amplitude of the cardiac signal subsequent to the detected R-wave to the primary threshold;

means for determining a secondary threshold based on the detected R-wave in response to detecting the asystole;

means for determining whether a value that is based on the cardiac signal sensed during a pause interval that is subsequent to the detected R-wave satisfies the secondary threshold, wherein at least one under-sensed R-wave during the pause interval is present when the value satisfies the secondary threshold; and

means for determining whether the detection of the asystole is false based on the determination of whether the value satisfies the secondary threshold.