METHOD AND APPARATUS FOR DETECTING ARRHYTHMIAS IN A MEDICAL DEVICE

• US 20070239045A1
• 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 7,734,333 B2
• Time in Patent Office: Days
• US Class Current: 600/509
• 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 a cardiac signal from a plurality of electrodes, determining amplitudes of the sensed cardiac signal during a predetermined sensing window, determining a noise to signal ratio corresponding to the determined amplitudes, and determining the sensed cardiac signal during the predetermined sensing window is corrupted by noise in response to the determined noise to signal ratio being greater than a noise to signal ratio threshold.

Claims

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

sensing a cardiac signal from a plurality of electrodes;

determining amplitudes of the sensed cardiac signal during a predetermined sensing window;

determining a noise to signal ratio corresponding to the determined amplitudes; and

determining the sensed cardiac signal during the predetermined sensing window is corrupted by noise in response to the determined noise to signal ratio being greater than a noise to signal ratio threshold.

2. The method of claim 1, wherein determining a noise to signal ratio comprises determining a ratio of a highpass mean rectified amplitude corresponding to the sensed cardiac signal during the predetermined sensing window to a lowpass mean rectified amplitude corresponding to the sensed cardiac signal during the predetermined sensing window.

3. The method of claim 2, further comprising:

determining an average of absolute values of lowpass sample amplitudes corresponding to the determined amplitudes as the lowpass mean rectified amplitude;

determining an average of absolute values of the determined amplitudes to generate a raw mean rectified amplitude; and

determining a difference between the raw mean rectified amplitude and the lowpass mean rectified amplitude as the highpass mean rectified amplitude.

4. The method of claim 1, further comprising:

determining a metric of signal energy content associated with the sensed cardiac signal during the predetermined sensing window; and

determining the sensed cardiac signal during the predetermined sensing window is corrupted by noise in response to the metric of signal energy content being greater than a first signal energy content threshold corresponding to a value greater than a signal energy content associated with the detected cardiac event.

5. The method of claim 1, further comprising:

determining a metric of signal energy content associated with the sensed cardiac signal during the predetermined sensing window; and

determining the sensed cardiac signal during the predetermined sensing window is corrupted by noise in response to the metric of signal energy content being one of greater than a first signal energy content threshold and less than a second signal energy content threshold, the first signal energy content threshold corresponding to a value greater than a signal energy content associated with the detected cardiac event and the second signal energy content threshold corresponding to asystole episodes.

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

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

determining amplitudes of the sensed cardiac signal during a predetermined sensing window for each of the first sensing vector and the second sensing vector;

determining a noise to signal ratio corresponding to the determined amplitudes; and

determining the sensed cardiac signal during the predetermined sensing window is corrupted by noise in response to the determined noise to signal ratio being greater than a noise to signal ratio threshold.

7. The method of claim 6, wherein determining a noise to signal ratio comprises determining a ratio of a highpass mean rectified amplitude corresponding to the sensed cardiac signal during the predetermined sensing window to a lowpass mean rectified amplitude corresponding to the sensed cardiac signal during the predetermined sensing window.

8. The method of claim 7, further comprising:

determining an average of absolute values of lowpass sample amplitudes corresponding to the determined amplitudes as the lowpass mean rectified amplitude;

determining an average of absolute values of the determined amplitudes to generate a raw mean rectified amplitude; and

determining a difference between the raw mean rectified amplitude and the lowpass mean rectified amplitude as the highpass mean rectified amplitude.

9. The method of claim 6, wherein the noise to signal ratio threshold is 0.0703.

10. The method of claim 6, wherein the plurality of electrodes are positioned non-intravenously.

11. The method of claim 6, further comprising:

determining a metric of signal energy content associated with the sensed cardiac signal during the predetermined sensing window for each of the first sensing vector and the second sensing vector; and

determining the sensed cardiac signal during the predetermined sensing window is corrupted by noise in response to the metric of signal energy content being greater than a first signal energy content threshold corresponding to a value greater than a signal energy content associated with the detected cardiac event.

12. The method of claim 11, the first signal energy content threshold is approximately 0.013 mV.

13. The method of claim 6, further comprising:

determining a metric of signal energy content associated with the sensed cardiac signal during the predetermined sensing window for each of the first sensing vector and the second sensing vector; and

determining the sensed cardiac signal during the predetermined sensing window is corrupted by noise in response to the metric of signal energy content being one of greater than a first signal energy content threshold and less than a second signal energy content threshold, the first signal energy content threshold corresponding to a value greater than a signal energy content associated with the detected cardiac event and the second signal energy content threshold corresponding to asystole episodes.

14. The method of claim 13, wherein the first signal energy content threshold is approximately 0.013 mV and the second signal energy content threshold is approximately 1.5 mV.

15. The method of claim 13, wherein the metric of signal energy content corresponds to a mean rectified amplitude associated with the determined amplitudes during the predetermined sensing window.

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

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

determining amplitudes of the sensed cardiac signal during a predetermined sensing window for each of the first sensing vector and the second sensing vector;

determining a noise to signal ratio corresponding to the determined amplitudes as a ratio of a highpass mean rectified amplitude corresponding to the sensed cardiac signal during the predetermined sensing window to a lowpass mean rectified amplitude corresponding to the sensed cardiac signal during the predetermined sensing window;

determining the sensed cardiac signal during the predetermined sensing window is corrupted by noise in response to the determined noise to signal ratio being greater than the noise to signal ratio threshold;

determining a metric of signal energy content associated with the sensed cardiac signal during the predetermined sensing window for each of the first sensing vector and the second sensing vector; and

determining the sensed cardiac signal during the predetermined sensing window is corrupted by noise in response to the metric of signal energy content being one of greater than a first signal energy content threshold and less than a second signal energy content threshold, the first signal energy content threshold corresponding to a value greater than a signal energy content associated with the detected cardiac event and the second signal energy content threshold corresponding to asystole episodes.

17. The method of claim 16, further comprising:

determining an average of absolute values of lowpass sample amplitudes corresponding to the determined amplitudes as the lowpass mean rectified amplitude;

determining an average of absolute values of the determined amplitudes to generate a raw mean rectified amplitude; and

determining a difference between the raw mean rectified amplitude and the lowpass mean rectified amplitude as the highpass mean rectified amplitude.

18. The method of claim 17, wherein the metric of signal energy content corresponds to a mean rectified amplitude associated with the determined amplitudes during the predetermined sensing window.

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

sensing a cardiac signal from a plurality of electrodes;

determining amplitudes of the sensed cardiac signal during a predetermined sensing window;

determining a noise to signal ratio corresponding to the determined amplitudes; and

determining the sensed cardiac signal during the predetermined sensing window is corrupted by noise in response to the determined noise to signal ratio being greater than a noise to signal ratio threshold.

20. The computer readable medium of claim 19, wherein determining a noise to signal ratio comprises determining a ratio of a highpass mean rectified amplitude corresponding to the sensed cardiac signal during the predetermined sensing window to a lowpass mean rectified amplitude corresponding to the sensed cardiac signal during the predetermined sensing window, the method further comprising:

determining an average of absolute values of lowpass sample amplitudes corresponding to the determined amplitudes as the lowpass mean rectified amplitude;

determining an average of absolute values of the determined amplitudes to generate a raw mean rectified amplitude; and

determining a difference between the raw mean rectified amplitude and the lowpass mean rectified amplitude as the highpass mean rectified amplitude.