BEAT-MORPHOLOGY MATCHING SCHEME FOR CARDIAC SENSING AND EVENT DETECTION

• US 20140276155A1
• Filed: 03/14/2013
• Published: 09/18/2014
• Est. Priority Date: 03/14/2013
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Zhang, Xusheng
• Granted Patent: US 8,983,586 B2
• Time in Patent Office: Days
• US Class Current: 600/515
• CPC Class Codes: A61B 5/35 by template matching
• CPC Class Codes: A61B 5/352 Detecting R peaks, e.g. for synchronising diagnostic apparatus; Estimating R-R interval
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61N 1/3622 comprising two or more electrodes co-operating with different heart regions
• CPC Class Codes: A61N 1/3624 occurring in the atrium, i.e. atrial tachycardia
• CPC Class Codes: A61N 1/3627 for treating a mechanical deficiency of the heart, e.g. congestive heart failure or cardiomyopathy
• CPC Class Codes: A61N 1/36507 controlled by gradient or slope of the heart potential
• CPC Class Codes: A61N 1/37 Monitoring; Protecting
• CPC Class Codes: A61N 1/3702 Physiological parameters A61N1/365 takes precedence; evoked response A61N1/371

Abstract

A medical device and associated method for classifying an unknown cardiac signal that includes sensing a cardiac signal over a plurality of cardiac cycles, 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, determining a template alignment point and an unknown cardiac signal alignment point in response to the fourth order difference signal;

• • 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, determining a morphology analysis window in response to the R-wave width, and determining a first morphology match metric across the morphology analysis window.

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;

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;

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;

determining a morphology analysis window in response to the R-wave width; and

determining a first morphology match metric across the morphology analysis window.

2. The method of claim 1, wherein the morphology analysis window comprises a first number of sample points of the unknown cardiac signal, and the alignment window comprises a second number of sample points of the unknown cardiac signal, the second number greater than the first number.

3. 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; and

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

4. The method of claim 3, 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 in response to 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.

5. The method of claim 3, wherein generating the template comprises:

enabling a processor to compute a fourth order difference signal from 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.

6. The method of claim 3, wherein aligning 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.

7. The method of claim 6, 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.

8. The method of claim 3, 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;

selecting 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.

9. The method of claim 3, 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;

selecting 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 selected one of the first morphology match metric and the morphology match metrics for the plurality of alignments.

10. The method of claim 3, wherein determining the morphology match metric comprises computing a normalized waveform area difference between the aligned template and the unknown cardiac signal.

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. determine a template alignment point and an unknown cardiac signal alignment point in response to the fourth order difference signal, 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, determine a morphology analysis window in response to the R-wave width, and determine a first morphology match metric across the morphology analysis window.

12. The medical device of claim 11, wherein the morphology analysis window comprises a first number of sample points of the unknown cardiac signal, and the alignment window comprises a second number of sample points of the unknown cardiac signal, the second number greater than the first number.

13. The medical device of claim 11, wherein the processor is configured to 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, and determine the first morphology match metric between the aligned template and the unknown cardiac signal.

14. The medical device of claim 13, 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 in response to 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.

15. The medical device of claim 13, wherein generating the template comprises:

enabling a processor to compute a fourth order difference signal from 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.

16. The medical device of claim 13, wherein aligning 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.

17. The medical device of claim 16, 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.

18. The medical device of claim 13, wherein the processor is configured 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, select 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.

19. The medical device of claim 13, wherein the processor is configured 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, select 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 selected one of the first morphology match metric and the morphology match metrics for the plurality of alignments.

20. The medical device of claim 13, wherein determining the morphology match metric comprises computing a normalized waveform area difference between the aligned template and the unknown cardiac signal.

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;

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

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;

determine a morphology analysis window in response to the R-wave width; and

determine a first morphology match metric across the morphology analysis window.