BEAT-MORPHOLOGY MATCHING SCHEME FOR CARDIAC SENSING AND EVENT DETECTION

• US 20140276158A1
• 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 8,825,145 B1
• Time in Patent Office: Days
• US Class Current: 600/516
• CPC Class Codes: A61B 5/35 by template matching
• CPC Class Codes: A61B 5/363 Detecting tachycardia or bradycardia
• CPC Class Codes: A61B 5/366 Detecting abnormal QRS complex, e.g. widening
• CPC Class Codes: A61N 1/3622 comprising two or more electrodes co-operating with different heart regions
• CPC Class Codes: A61N 1/36507 controlled by gradient or slope of the heart potential

Abstract

A medical device and associated method for classifying an unknown cardiac signal operate to sense a cardiac signal over known cardiac cycles and generate a template of the known cardiac cycles. An unknown cardiac signal is sensed over an unknown cardiac cycle. A template alignment point and an unknown cardiac signal alignment point are identified by using a fourth order difference signal. The template and the unknown cardiac signal are aligned across an alignment window by aligning the template alignment point and the unknown cardiac signal alignment point. A morphology match metric measuring a similarity between the aligned template and the unknown cardiac signal is computed.

Claims

6-1. The method of claim 1, 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. A medical device for classifying cardiac beats for use in detecting cardiac rhythms, comprising:

a plurality of electrodes for sensing an electrocardiogram (ECG) signal;

a sensing module coupled to the electrodes for sensing a cardiac signal over a plurality of cardiac cycles and an unknown cardiac signal over an unknown cardiac cycle; and

a processor coupled to the sensing module and configured to;

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

determine a template alignment point and an unknown cardiac signal alignment point, wherein determining the template alignment point and the unknown cardiac signal alignment point comprises determining a 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; and

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

10. The device of claim 9, 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.

11. The device of claim 9, 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 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.

12. The device of claim 9, 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.

13. The device of claim 12, wherein determining the unknown cardiac signal alignment point comprises:

determining an unknown fourth order difference signal from 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.

14. The device of claim 9, wherein the processor is further configured to:

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

determine an R-wave width in response to a 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 the first morphology match metric across the morphology analysis window.

15. The device of claim 14, 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.

16. The device of claim 9, wherein the processor is further 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;

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 determined one of the first and second morphology match metrics.

17. The device of claim 9, wherein the processor is further 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;

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.

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

19. The device of claim 9, wherein determining the morphology match metric comprises determining a fourth order difference signal corresponding to the template and a fourth order difference signal of the unknown cardiac signal;

and

determining the morphology match metric between the template fourth order difference signal and the fourth order difference signal of the unknown cardiac signal.

20. 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;

generate 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 template alignment point and an unknown cardiac signal alignment point, wherein determining the template alignment point and the unknown cardiac signal alignment point comprises determining a 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; and

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