BEAT-MORPHOLOGY MATCHING SCHEME FOR CARDIAC SENSING AND EVENT DETECTION

• US 20140276159A1
• Filed: 03/14/2013
• Published: 09/18/2014
• Est. Priority Date: 03/14/2013
• Status: Abandoned Application

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Zhang, Xusheng
• Application Number:
  US13/826,248
• Publication Number:
  US 20140276159A1
• Time in Patent Office: Days
• US Class Current: 600/517
• CPC Class Codes: A61B 5/35 by template matching
• CPC Class Codes: A61B 5/364 Detecting abnormal ECG interval, e.g. extrasystoles, ectopic heartbeats
• CPC Class Codes: A61B 5/686 Permanently implanted devices, e.g. pacemakers, other stimulators, biochips A61B5/6861 takes precedence
• CPC Class Codes: A61N 1/3621 for treating or preventing abnormally high heart rate
• CPC Class Codes: A61N 1/3622 comprising two or more electrodes co-operating with different heart regions

Abstract

A medical device and associated method for classifying an unknown cardiac signal sensing a cardiac signal over a plurality of cardiac cycles using a plurality of electrodes coupled to a sensing module, determining a template of a known cardiac signal in response to the cardiac signal sensed over the plurality of cardiac cycles, sensing an unknown cardiac signal over an unknown cardiac cycle, determining a fourth order difference signal corresponding to the template and a fourth order difference signal of the unknown cardiac signal, determining a first morphology match metric between the template fourth order difference signal and the fourth order difference signal of the unknown cardiac signal, and classifying the unknown cardiac signal in responsed to the determined first morphology match score.

Claims

1. A method for classifying cardiac beats for use in detecting cardiac rhythms, comprising:

sensing a cardiac signal over a plurality of cardiac cycles using a plurality of electrodes coupled to a sensing module;

determining a template of a known cardiac signal in response to the cardiac signal sensed over the plurality of cardiac cycles;

sensing an unknown cardiac signal over an unknown cardiac cycle;

determining a fourth order difference signal corresponding to the template and a fourth order difference signal of the unknown cardiac signal;

determining a first morphology match metric between the template fourth order difference signal and the fourth order difference signal of the unknown cardiac signal; and

classifying the unknown cardiac signal in responsed to the determined first morphology match score.

2. The method of claim 1, further comprising:

determining a template alignment point and an unknown cardiac signal alignment point in response to the fourth order difference signal;

aligning the template and the unknown cardiac signal across an alignment window by aligning the template alignment point and the unknown cardiac signal alignment point;

determining the first morphology match metric measuring a similarity between the aligned template and the unknown cardiac signal.

3. The method of claim 2, wherein determining the template comprises:

determining a fourth order difference signal in response to the cardiac signal over each of the plurality of cardiac cycles;

determining an alignment point from the fourth order difference signal of each of the plurality of cardiac cycles;

aligning the plurality of cardiac cycle signals by aligning the alignment points in each of the plurality of cardiac cycles; and

averaging the aligned plurality of cardiac cycle signals.

4. The method of claim 2, wherein determining the template comprises:

determining a fourth order difference signal in response to the cardiac signal over each of the plurality of cardiac cycles;

determining an alignment point from the fourth order difference signal of each of the plurality of cardiac cycles;

aligning the plurality of fourth order difference signals of each of the cardiac cycle signals by aligning the alignment points; and

averaging the aligned plurality of fourth order difference signals.

5. The method of claim 2, wherein determining the template alignment point comprises determining a peak amplitude and a polarity of a dominant pulse of a fourth order difference signal corresponding to the template.

6. The method of claim 5, wherein determining the unknown cardiac signal alignment point comprises:

determining an unknown fourth order difference signal of the unknown cardiac cycle signal; and

determining a peak amplitude of a dominant pulse of the unknown fourth order difference signal that matches the polarity of the template alignment point.

7. The method of claim 2, further comprising:

after aligning the template alignment point and the unknown cardiac signal alignment point, shifting the template by shifting the template alignment point relative to the unknown cardiac signal alignment point by at least one sample point;

determining a second morphology match metric as a measure of a similarity between the shifted template and the unknown cardiac signal;

determine a greatest one of the first morphology match metric and the second morphology match metric; and

classifying the unknown cardiac signal in response to the selected one of the first and second morphology match metrics.

8. The method of claim 2, further comprising:

after aligning the template alignment point and the unknown cardiac signal alignment point, shifting the template a plurality of times by shifting the template alignment point relative to the unknown signal alignment point by at least one sample point to obtain a plurality of alignments between the template and the unknown cardiac signal;

determining a morphology match score for each one of the plurality of alignments;

determining a greatest one of the first morphology match metric and the morphology match metrics for the plurality of alignments; and

classifying the unknown cardiac signal in response to the determined one of the first morphology match metric and the morphology match metrics for the plurality of alignments.

9. The method of claim 2, wherein determining the morphology match metric comprises determining a normalized waveform area difference between the aligned template and the unknown cardiac signal.

10. The method of claim 1, further comprising:

determining an R-wave onset and an R-wave offset in response to the fourth order difference signal of the unknown cardiac cycle signal;

determining an R-wave width as the difference between the R-wave onset and the R-wave offset; and

determining a morphology analysis window in response to the R-wave width, wherein the first morphology match metric is determined across the morphology analysis window.

11. A medical device for classifying cardiac beats for use in detecting cardiac rhythms, comprising:

a plurality of electrodes for sensing sensing a cardiac signal over a plurality of cardiac cycles; and

a processor configured to determine a template of a known cardiac signal in response to the cardiac signal sensed over the plurality of cardiac cycles;

sense an unknown cardiac signal over an unknown cardiac cycle;

determine a fourth order difference signal corresponding to the template and a fourth order difference signal of the unknown cardiac signal;

determine a first morphology match metric between the template fourth order difference signal and the fourth order difference signal of the unknown cardiac signal; and

classify the unknown cardiac signal in responsed to the determined first morphology match score.

12. The medical device of claim 11, wherein the processor is configure to determine a template alignment point and an unknown cardiac signal alignment point in response to the fourth order difference signal, align the template and the unknown cardiac signal across an alignment window by aligning the template alignment point and the unknown cardiac signal alignment point, determine the first morphology match metric between the aligned template and the unknown cardiac signal.

13. The medical device of claim 12, wherein determining the template comprises:

determining a fourth order difference signal in response to the cardiac signal over each of the plurality of cardiac cycles;

determining an alignment point from the fourth order difference signal of each of the plurality of cardiac cycles;

aligning the plurality of cardiac cycle signals by aligning the alignment points in each of the plurality of cardiac cycles; and

averaging the aligned plurality of cardiac cycle signals.

14. The medical device of claim 12, wherein determining the template comprises:

determining a fourth order difference signal in response to the cardiac signal over each of the plurality of cardiac cycles;

determining an alignment point from the fourth order difference signal of each of the plurality of cardiac cycles;

aligning the plurality of fourth order difference signals of each of the cardiac cycle signals by aligning the alignment points; and

averaging the aligned plurality of fourth order difference signals.

15. The medical device of claim 12, wherein determining the template alignment point comprises determining a peak amplitude and a polarity of a dominant pulse of a fourth order difference signal corresponding to the template.

16. The medical device of claim 15, wherein determining the unknown cardiac signal alignment point comprises:

determining an unknown fourth order difference signal of the unknown cardiac cycle signal; and

determining a peak amplitude of a dominant pulse of the unknown fourth order difference signal that matches the polarity of the template alignment point.

17. The medical device of claim 12, wherein the processor is configure to, after aligning the template alignment point and the unknown cardiac signal alignment point, shift the template by shifting the template alignment point relative to the unknown cardiac signal alignment point by at least one sample point, determine a second morphology match metric as a measure of a similarity between the shifted template and the unknown cardiac signal, determine a greatest one of the first morphology match metric and the second morphology match metric, and classify the unknown cardiac signal in response to the selected one of the first and second morphology match metrics.

18. The medical device of claim 12, wherein the processor is configure to, after aligning the template alignment point and the unknown cardiac signal alignment point, shift the template a plurality of times by shifting the template alignment point relative to the unknown signal alignment point by at least one sample point to obtain a plurality of alignments between the template and the unknown cardiac signal, determine a morphology match score for each one of the plurality of alignments, determine a greatest one of the first morphology match metric and the morphology match metrics for the plurality of alignments, and classify the unknown cardiac signal in response to the determined one of the first morphology match metric and the morphology match metrics for the plurality of alignments.

19. The medical device of claim 12, wherein determining the morphology match metric comprises determining a normalized waveform area difference between the aligned template and the unknown cardiac signal.

20. The medical device of claim 11, wherein the processor is configure to determine an R-wave onset and an R-wave offset in response to the fourth order difference signal of the unknown cardiac cycle signal, determine an R-wave width as the difference between the R-wave onset and the R-wave offset, and determine a morphology analysis window in response to the R-wave width, wherein the first morphology match metric is determined across the morphology analysis window.

21. A non-transitory, computer-readable medium storing a set of instructions, which when executed by a processor of a medical device causes the device to:

sense a cardiac signal over a plurality of cardiac cycles using a plurality of electrodes coupled to a sensing module;

determine a template of a known cardiac signal in response to the cardiac signal sensed over the plurality of cardiac cycles;

sense an unknown cardiac signal over an unknown cardiac cycle;

determine a fourth order difference signal corresponding to the template and a fourth order difference signal of the unknown cardiac signal;

determine a first morphology match metric between the template fourth order difference signal and the fourth order difference signal of the unknown cardiac signal; and

classify the unknown cardiac signal in responsed to the determined first morphology match score.