METHOD AND APPARATUS FOR DETECTING ARRHYTHMIAS IN A MEDICAL DEVICE

• US 20070239049A1
• Filed: 04/28/2006
• Published: 10/11/2007
• Est. Priority Date: 03/29/2006
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Zhang, Xusheng, Stadler, Robert, Ghanem, Raja
• Granted Patent: US 7,734,336 B2
• Time in Patent Office: Days
• US Class Current: 600/512
• CPC Class Codes: A61B 5/287 Holders for multiple electrodes, e.g. electrode catheters for electrophysiological study [EPS]
• CPC Class Codes: A61B 5/341 Vectorcardiography [VCG]
• CPC Class Codes: A61B 5/352 Detecting R peaks, e.g. for synchronising diagnostic apparatus; Estimating R-R interval
• CPC Class Codes: A61B 5/361 Detecting fibrillation
• CPC Class Codes: A61B 5/363 Detecting tachycardia or bradycardia
• CPC Class Codes: A61B 5/364 Detecting abnormal ECG interval, e.g. extrasystoles, ectopic heartbeats
• CPC Class Codes: A61B 5/4836 Diagnosis combined with treatment in closed-loop systems or methods A61B5/0036 takes precedence
• 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: A61B 5/7221 Determining signal validity, reliability or quality A61B5/7207 and A61B5/7217 take precedence
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61N 1/05 for implantation or insertion into the body, e.g. heart electrode A61N1/06 takes precedence
• CPC Class Codes: A61N 1/3621 for treating or preventing abnormally high heart rate
• CPC Class Codes: A61N 1/3925 Monitoring; Protecting
• CPC Class Codes: A61N 1/3956 Implantable devices for applying electric shocks to the heart, e.g. for cardioversion
• CPC Class Codes: A61N 1/3987 characterised by the timing or triggering of the shock
• CPC Class Codes: Y10S 128/901 Suppression of noise in electric signal
• CPC Class Codes: Y10S 128/902 Biological signal amplifier

Abstract

A method of detecting a cardiac event in a medical device that includes sensing cardiac signals from a plurality of electrodes forming a first sensing vector and a second sensing vector, determining inflections of the sensed cardiac signals, generating a pulse amplitude threshold in response to the determined inflections, determining whether the sensed cardiac signals are corrupted by noise in response to the determined inflections and the generated pulse amplitude threshold, and determining, in response to the sensed cardiac signals being corrupted by noise, whether the sensed cardiac signals are both corrupted by noise and shockable.

Claims

1. A method of detecting a cardiac event in a medical device, comprising:

sensing cardiac signals from a plurality of electrodes, the plurality of electrodes forming a first sensing vector and a second sensing vector;

determining inflections of the sensed cardiac signals;

generating a pulse amplitude threshold in response to the determined inflections;

determining whether the sensed cardiac signals are corrupted by noise in response to the determined inflections and the generated pulse amplitude threshold; and

determining, in response to the sensed cardiac signals being corrupted by noise, whether the sensed cardiac signals are both corrupted by noise and shockable.

2. The method of claim 1, wherein the inflections are determined during a predetermined window of the sensed cardiac signals, and wherein determining whether the sensed cardiac signals are both corrupted by noise and shockable comprises:

determining whether a mean rectified amplitude for the predetermined window of the sensed cardiac signals is greater than a predetermined threshold; and

determining the sensed cardiac signals are both corrupted by noise and shockable in response to the mean rectified amplitude for the predetermined window of the sensed cardiac signals being greater than the predetermined threshold.

3. The method of claim 2, wherein determining whether a mean rectified amplitude for the predetermined window of the sensed cardiac signals is greater than a predetermined threshold comprises:

determining whether a maximum amplitude for each of a plurality of sub-segments of the predetermined window of sensed cardiac signals is less than a portion of a maximum amplitude for the entire predetermined window of sensed cardiac signals;

setting, for each sub-segment of the plurality of sub-segments, the corresponding maximum amplitude to the maximum amplitude for the entire predetermined window of sensed cardiac signals in response to the corresponding maximum amplitude being is less than the portion of the maximum amplitude for the entire predetermined window of sensed cardiac signals;

determining mean amplitudes for each sub-segment of the plurality of sub-segments;

determining normalized mean amplitudes for each sub-segment of the plurality of sub-segments in response to the maximum amplitude and the mean amplitudes; and

setting the mean rectified amplitude for the predetermined window of the sensed cardiac signals equal to the sum of the normalized mean amplitudes divided by the number of sub-segments corresponding to the plurality of sub-segments.

4. The method of claim 1, wherein the inflections are determined during a predetermined window of the sensed cardiac signals, the method further comprising:

determining the number of sub-segments of the window having a predetermined number of inflections greater than a minimum pulse count threshold; and

determining whether the number of sub-segments having the predetermined number of sub-segments is greater than or equal to a pulse count threshold.

5. The method of claim 4, further comprising determining the first sensing vector and the second sensing vector is corrupted by noise in response to the corresponding predetermined window of sensed cardiac signals having the predetermined number of sub-segments being greater than or equal to the pulse count threshold.

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

determining a mean of the inflections during a predetermined window of the sensed cardiac signals; and

setting the pulse amplitude threshold equal to a predetermined portion of the determined mean of the inflections.

7. The method of claim 6, wherein generating a pulse amplitude threshold further comprises:

determining a maximum inflection of inflections determined during sub-segments of the predetermined window of the sensed cardiac signals;

determining local maximums of the inflections determined during the sub-segments of the predetermined window of the sensed cardiac signals; and

replacing the local maximums with the determined maximum inflection in response to the local maximums being less than a portion of the determined maximum inflection for the corresponding sub-segment.

8. The method of claim 1, wherein determining inflections comprises:

applying the sensed cardiac signals to a first order derivative to generate a derivative signal; and

determining zero crossings of the derivative signal.

9. The method of claim 8, wherein determining inflections further comprises:

determining data pairs corresponding to a first data point prior to the zero crossings and a second data point subsequent to the zero crossings; and

determining the smallest absolute values of the first data point and the second data point as the determined inflections to generate.

10. The method of claim 9, wherein the inflections are determined during a predetermined window of the sensed cardiac signals, and wherein determining inflections further comprises:

determining a first maximum of the data pairs determined during the predetermined window of the sensed cardiac signals;

determining second maximums of data pairs determined during sub-segments of the predetermined window of the sensed cardiac signals; and

setting the second maximums equal to the first maximum in response to the second maximum being less than a predetermined portion of the first maximum.

11. The method of claim 10, wherein generating a pulse amplitude threshold comprises:

determining a mean of the second maximums during the predetermined window of the sensed cardiac signals; and

setting the pulse amplitude threshold equal to a predetermined portion of the determined mean of the second maximums.

12. The method of claim 1, wherein the plurality of electrodes are positioned non-intravenously.

13. A method of detecting a cardiac event in a medical device, comprising:

sensing cardiac signals from a plurality of electrodes, the plurality of electrodes forming a first sensing vector and a second sensing vector;

determining inflections of the sensed cardiac signals;

generating a pulse amplitude threshold in response to the determined inflections;

determining the sensed cardiac signals are not corrupted by noise in response to the pulse amplitude threshold being less than a pulse threshold; and

determining, in response to the sensed cardiac signals being corrupted by noise, whether the sensed cardiac signals are both corrupted by noise and shockable.

14. The method of claim 13, wherein the inflections are determined during a predetermined window of the sensed cardiac signals, and wherein determining whether the sensed cardiac signals are both corrupted by noise and shockable comprises:

determining whether a mean rectified amplitude for the predetermined window of the sensed cardiac signals is greater than a predetermined threshold; and

determining the sensed cardiac signals are both corrupted by noise and shockable in response to the mean rectified amplitude for the predetermined window of the sensed cardiac signals being greater than the predetermined threshold.

15. The method of claim 14, wherein determining whether a mean rectified amplitude for the predetermined window of the sensed cardiac signals is greater than a predetermined threshold comprises:

determining whether a maximum amplitude for each of a plurality of sub-segments of the predetermined window of sensed cardiac signals is less than a portion of a maximum amplitude for the entire predetermined window of sensed cardiac signals;

setting, for each sub-segment of the plurality of sub-segments, the corresponding maximum amplitude to the maximum amplitude for the entire predetermined window of sensed cardiac signals in response to the corresponding maximum amplitude being is less than the portion of the maximum amplitude for the entire predetermined window of sensed cardiac signals;

determining mean amplitudes for each sub-segment of the plurality of sub-segments;

determining normalized mean amplitudes for each sub-segment of the plurality of sub-segments in response to the maximum amplitude and the mean amplitudes; and

setting the mean rectified amplitude for the predetermined window of the sensed cardiac signals equal to the sum of the normalized mean amplitudes divided by the number of sub-segments corresponding to the plurality of sub-segments

16. The method of claim 13, wherein the inflections are determined during a predetermined window of the sensed cardiac signals, and further comprising:

determining a sub-segment of a plurality of sub-segments of the window of sensed cardiac signals having a maximum number of inflections; and

determining the sensed cardiac signals are corrupted by noise in response to the maximum number of inflections being greater than a noise pulse number threshold.

17. The method of claim 13, wherein the inflections are determined during a predetermined window of the sensed cardiac signals, and further comprising:

determining the number of inflections in each of a plurality of sub-segments of the window of sensed cardiac signals;

determining a sub-segment of the plurality of sub-segments having a maximum number of inflections and a number of the plurality of sub-segments having a predetermined number of inflections greater than a predetermined minimum threshold; and

determining the sensed cardiac signals are corrupted by noise in response to one of the maximum number of inflections being greater than a noise pulse number threshold and the number of the plurality of sub-segments having a predetermined number of inflections greater than a predetermined minimum threshold being greater than or equal to a sub-segment pulse count threshold.

18. The method of claim 16, further comprising:

determining the number of inflections in each of a plurality of sub-segments of the window of sensed cardiac signals;

determining a sub-segment of the plurality of sub-segments having a maximum number of inflections and a number of the plurality of sub-segments having a predetermined number of inflections greater than a predetermined minimum threshold; and

determining the sensed cardiac signals are corrupted by noise in response to one of the maximum number of inflections being greater than a noise pulse number threshold and the number of the plurality of sub-segments having a predetermined number of inflections greater than a predetermined minimum threshold being greater than or equal to a sub-segment pulse count threshold.

19. The method of claim 16, wherein generating a pulse amplitude threshold comprises:

determining a mean of the inflections during a predetermined window of the sensed cardiac signals; and

setting the pulse amplitude threshold equal to a predetermined portion of the determined mean of the inflections.

20. The method of claim 19, wherein generating a pulse amplitude threshold further comprises:

determining a maximum inflection of inflections determined during sub-segments of the predetermined window of the sensed cardiac signals;

determining local maximums of the inflections determined during the sub-segments of the predetermined window of the sensed cardiac signals; and

replacing the local maximums with the determined maximum inflection in response to the local maximums being less than a portion of the determined maximum inflection for the corresponding sub-segment.

21. The method of claim 16, wherein determining inflections comprises:

applying the sensed cardiac signals to a first order derivative to generate a derivative signal; and

determining zero crossings of the derivative signal.

22. The method of claim 21, wherein determining inflections further comprises:

determining data pairs corresponding to a first data point prior to the zero crossings and a second data point subsequent to the zero crossings; and

determining the smallest absolute values of the first data point and the second data point as the determined inflections to generate.

23. The method of claim 22, wherein the inflections are determined during a predetermined window of the sensed cardiac signals, and wherein determining inflections further comprises:

determining a first maximum of the data pairs determined during the predetermined window of the sensed cardiac signals;

determining second maximums of data pairs determined during sub-segments of the predetermined window of the sensed cardiac signals; and

setting the second maximums equal to the first maximum in response to the second maximum being less than a predetermined portion of the first maximum.

24. The method of claim 23, wherein generating a pulse amplitude threshold comprises:

determining a mean of the second maximums during the predetermined window of the sensed cardiac signals; and

setting the pulse amplitude threshold equal to a predetermined portion of the determined mean of the second maximums.

25. A computer readable medium having computer executable instructions for performing a method comprising:

sensing cardiac signals from a plurality of electrodes, the plurality of electrodes forming a first sensing vector and a second sensing vector;

determining inflections of the sensed cardiac signals;

generating a pulse amplitude threshold in response to the determined inflections;

determining whether the sensed cardiac signals are corrupted by noise in response to the determined inflections and the generated pulse amplitude threshold; and

determining, in response to the sensed cardiac signals being corrupted by noise, whether the sensed cardiac signals are both corrupted by noise and shockable.