METHOD AND APPARATUS FOR DETECTING AND DISCRIMINATING TACHYCARDIA

• US 20110270110A1
• Filed: 04/28/2010
• Published: 11/03/2011
• Est. Priority Date: 04/28/2010
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Stadler, Robert W., Zhang, Xusheng
• Granted Patent: US 8,983,585 B2
• Time in Patent Office: Days
• US Class Current: 600/518
• CPC Class Codes: A61B 5/363 Detecting tachycardia or bradycardia
• CPC Class Codes: A61B 5/686 Permanently implanted devices, e.g. pacemakers, other stimulators, biochips A61B5/6861 takes precedence
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61N 1/3622 comprising two or more electrodes co-operating with different heart regions
• CPC Class Codes: A61N 1/39622 Pacing therapy

Abstract

A medical device and associated method for monitoring a patient'"'"'s heart rhythm sensing a cardiac signal determine whether a cardiac signal is noise corrupted by obtaining cardiac signal pulses and generating a pulse amplitude threshold in response to the plurality of signal pulses. The number of signal sample points exceeding the pulse amplitude threshold in each of the of signal pulses is computed. The cardiac signal is determined to be noise corrupted or non-corrupted in response to the computed number of signal sample points.

Claims

1. A method, comprising:

sensing a cardiac signal;

obtaining a plurality of signal pulses;

generating a pulse amplitude threshold in response to the plurality of signal pulses;

computing a number of signal sample points exceeding the pulse amplitude threshold in each of the plurality of signal pulses; and

determining whether the cardiac signal is noise corrupted in response to the computed number of signal sample points.

2. The method of claim 1, wherein obtaining the plurality of signal pulses comprises:

locating a plurality of zero-crossings of the cardiac signal;

identifying a signal point adjacent to each one of the plurality of zero-crossings; and

setting the identified signal points to a value of zero to demarcate the signal pulses.

3. The method of claim 2, further comprising rectifying the signal to obtain the plurality of signal pulses demarcated by the signal points set to a value of zero.

4. The method of claim 1, further comprising:

sensing a cardiac event; and

setting a time window extending a predetermined time interval earlier than the sensed cardiac event and ending upon the sensed cardiac event, wherein the plurality of signal pulses are located within the time window.

5. The method of claim 4, further comprising classifying a detected tachycardia episode as a non-treatable rhythm for the cardiac sensed event in response to determining that the cardiac signal is noise corrupted.

6. The method of claim 4, further comprising:

sensing a plurality of cardiac events and setting a plurality of time windows in response to the plurality of cardiac events;

determining whether the cardiac signal is noise corrupted in at least a predetermined portion of the plurality of time windows in response to the computed number of signal sample points for each of the plurality of time windows; and

classifying a detected tachycardia episode as a non-treatable rhythm in response to at least the predetermined portion of the time intervals being noise-corrupted.

7. The method of claim 6, wherein each of the plurality of time windows is overlapping with at least one other of the plurality of time windows.

8. The method of claim 6, further comprising:

sensing a next cardiac event and setting a next time window in response to the next cardiac event;

determining whether the cardiac signal is noise corrupted in the next time window;

determining whether the cardiac signal is noise corrupted in at least a predetermined portion of the plurality of time windows and the next time window in response to the computed number of signal sample points for each of the plurality of time windows and the next time window; and

reclassifying the detected tachycardia episode as a treatable rhythm in response to the cardiac signal being noise corrupted in less than the predetermined portion.

9. The method of claim 1, wherein generating a pulse amplitude threshold comprises:

determining a maximum amplitude of the plurality of signal pulses; and

setting the pulse amplitude threshold equal to a predetermined portion of the maximum amplitude.

10. The method of claim 1, wherein generating the pulse amplitude threshold comprises:

sensing a plurality of cardiac event intervals from the cardiac signal;

estimating a heart rate from the plurality of cardiac event intervals; and

generating the pulse amplitude threshold based on the heart rate.

11. The method of claim 1, wherein determining whether the cardiac signal is noise corrupted comprises:

generating a noise threshold; and

comparing the computed number of signal sample points to the noise threshold.

12. The method of claim 11, further comprising:

sensing a plurality of cardiac event intervals from the cardiac signal;

estimating a heart rate from the plurality of cardiac event intervals; and

generating the noise threshold based on the heart rate.

13. The method of claim 11, wherein generating the noise threshold comprises:

identifying a single one of the plurality of pulses having a greatest number of sample points exceeding the pulse amplitude threshold; and

computing a multiple of the greatest number of sample points.

14. The method of claim 4, wherein the cardiac signal is sensed using a first electrode pair and the cardiac event is sensed using a second electrode pair different than the first electrode pair.

15. A medical device, comprising:

a pair of electrodes sensing a cardiac signal;

a noise detector to obtain a plurality of signal pulses and to generate a pulse amplitude threshold in response to the plurality of signal pulses; and

a processor configured to compute a number of signal sample points exceeding the pulse amplitude threshold in each of the plurality of signal pulses and to determine whether the cardiac signal is noise corrupted in response to the computed number of signal sample points.

16. The device of claim 15, wherein obtaining the plurality of signal pulses by the noise detector comprises:

locating a plurality of zero-crossings of the cardiac signal;

identifying a signal point adjacent to each one of the plurality of zero-crossings; and

setting the identified signal points to a value of zero to demarcate the signal pulses.

17. The device of claim 16, wherein the noise detector rectifies the signal to obtain the plurality of signal pulses demarcated by the signal points set to a value of zero.

18. The device of claim 16 wherein the noise detector sets a time window extending a predetermined time interval earlier than a sensed cardiac event and ending upon the sensed cardiac event, wherein the plurality of signal pulses are located within the time window.

19. The device of claim 18, wherein the processor is further configured to classify a detected tachycardia episode as a non-treatable rhythm for the sensed cardiac event in response to determining that the cardiac signal is noise corrupted.

20. The device of claim 18, wherein the noise detector senses sets a plurality of time windows in response to a plurality of cardiac events, and the processor is further configured to determine whether the cardiac signal is noise corrupted in at least a predetermined portion of the plurality of time windows in response to the computed number of signal sample points for each of the plurality of time windows, and classify a detected tachycardia episode as a non-treatable rhythm in response to at least the predetermined portion of the time intervals being noise-corrupted.

21. The device of claim 20, wherein each of the plurality of time windows is overlapping with at least one other of the plurality of time windows.

22. The device of claim 20, wherein the noise detector sets a next time window in response to a next cardiac event, and the processor is further configured to determine whether the cardiac signal is noise corrupted in the next time window, determine whether the cardiac signal is noise corrupted in at least a predetermined portion of the plurality of time windows and the next time window in response to the computed number of signal sample points for each of the plurality of time windows and the next time window, and reclassify the detected tachycardia episode as a treatable rhythm in response to the cardiac signal being noise corrupted in less than the predetermined portion.

23. The device of claim 15, wherein generating a pulse amplitude threshold comprises:

determining a maximum amplitude of the plurality of signal pulses; and

setting the pulse amplitude threshold equal to a predetermined portion of the maximum amplitude.

24. The device of claim 15, wherein generating the pulse amplitude threshold comprises:

sensing a plurality of cardiac event intervals from the cardiac signal;

estimating a heart rate from the plurality of cardiac event intervals; and

generating the pulse amplitude threshold based on the heart rate.

25. The device of claim 15, wherein determining whether the cardiac signal is noise corrupted comprises:

generating a noise threshold; and

comparing the computed number of signal sample points to the noise threshold.

26. The device of claim 25, wherein generating the noise threshold comprises:

sensing a plurality of cardiac event intervals from the cardiac signal; and

estimating a heart rate from the plurality of cardiac event intervals; and

generating the noise threshold based on the heart rate.

27. The device of claim 25, wherein generating the noise threshold comprises:

identifying a single one of the plurality of pulses having a greatest number of sample points exceeding the pulse amplitude threshold; and

computing a multiple of the greatest number of sample points.

28. The device of claim 18, further comprising a first electrode pair and a second electrode pair different than the first electrode pair, wherein the cardiac signal is sensed using the first electrode pair and the cardiac event is sensed using the second electrode pair.

29. A computer-readable medium storing a set of instructions, which when implemented in a processor of a medical device causes the device to:

sense a cardiac signal;

obtain a plurality of signal pulses;

generate a pulse amplitude threshold in response to the plurality of signal pulses;

compute a number of signal sample points exceeding the pulse amplitude threshold in each of the plurality of signal pulses; and

determine whether the cardiac signal is noise corrupted in response to the computed number of signal sample points.