"BLURRED TEMPLATE" APPROACH FOR ARRHYTHMIA DETECTION

• US 20100185109A1
• Filed: 01/22/2009
• Published: 07/22/2010
• Est. Priority Date: 01/22/2009
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Gillberg, Jeffrey M., Zhang, Xin, Brown, Mark L., Zhang, Xusheng
• Granted Patent: US 8,428,697 B2
• Time in Patent Office: Days
• US Class Current: 600/515
• CPC Class Codes: A61B 5/35 by template matching
• CPC Class Codes: A61B 5/361 Detecting fibrillation
• CPC Class Codes: A61B 5/363 Detecting tachycardia or bradycardia
• CPC Class Codes: A61B 5/7264 Classification of physiological signals or data, e.g. using neural networks, statistical classifiers, expert systems or fuzzy systems neural networks per se G06N3/00; expert systems per se G06N5/00
• CPC Class Codes: A61N 1/3956 Implantable devices for applying electric shocks to the heart, e.g. for cardioversion
• CPC Class Codes: G16H 50/20 for computer-aided diagnosis, e.g. based on medical expert systems

Abstract

An implantable medical device and associated method sense cardiac signals for deriving a template representing a known EGM waveform morphology and for classifying an unknown waveform morphology. A boundary of the template, offset from the template, is computed and compared to an unknown waveform morphology for classifying the unknown waveform morphology.

Claims

1. A method for use in an implantable medical device, comprising:

sensing a cardiac signal;

deriving a template representing a known waveform morphology from the cardiac signal;

shifting the template in time;

computing a boundary of the template, the boundary offset from the template and computed using a sample point of the template shifted in time;

acquiring an unknown waveform morphology from the cardiac signal;

comparing the unknown waveform morphology to the boundary; and

classifying the unknown waveform morphology in response to the comparison.

2. The method of claim 1 wherein computing the boundary further comprises shifting the template in amplitude and selecting points from the time-shifted template and the amplitude-shifted template for defining the boundary.

3. The method of claim 2 wherein computing the boundary comprises computing an upper boundary and a lower boundary, the upper boundary and the lower boundary each offset from the template.

4. The method of claim 3 wherein computing each of the upper boundary and the lower boundary comprises:

computing a plurality of adjusted templates, each adjusted template computed by shifting the template in one of time and amplitude;

selecting an amplitude of one of the adjusted templates at each of a plurality of time points; and

defining the upper and lower boundaries using the selected amplitudes.

5. The method of claim 4 wherein comparing the unknown waveform to the boundary comprises:

aligning in time a selected point of the unknown waveform with a corresponding selected point of the template; and

computing an estimated area of the unknown waveform falling outside an area defined by the upper boundary and the lower boundary.

6. The method of claim 5 wherein computing the estimated area comprises identifying a sample point of the unknown waveform falling outside the area defined by the upper and lower boundaries;

and

computing a distance of the identified sample point from a nearest one of the upper boundary and the lower boundary.

7. The method of claim 6 wherein computing the distance comprises determining a smallest amplitude difference between the identified sample point and a plurality of sample points along the nearest one of the upper and lower boundaries.

8. The method of claim 6 wherein computing the estimated area comprises multiplying the distance by a weighting factor and summing the distance with other distances computed using other identified sample points of the unknown waveform falling outside the upper and lower boundaries.

9. The method of claim 8 further comprising:

computing an outer boundary offset from the upper boundary and the lower boundary; and

determining the weighting factor in response to the location of the identified sample point relative to the outer boundary.

10. The method of claim 9 wherein computing the outer boundary comprises shifting one of the upper boundary and the lower boundary in one of time and amplitude.

11. The method of claim 6 further comprising:

determining an adjusted unknown waveform by shifting the unknown waveform in time relative to the template;

computing an adjusted estimated area of the adjusted unknown waveform falling outside the area defined by the upper and lower boundaries; and

classifying the unknown waveform using the lowest one of the estimated area and the adjusted estimated area.

12. An implantable medical device, comprising;

electrodes for sensing a cardiac signal;

memory for storing a template representing a known waveform morphology of the cardiac signal;

a processor receiving the cardiac signal and coupled to the memory, the processor shifting the template in time, computing a boundary of the template, the boundary offset from the template and computed using a sample point of the template shifted in time, the processor acquiring an unknown waveform morphology from the cardiac signal, comparing the unknown waveform morphology to the boundary; and

classifying the unknown waveform morphology in response to the comparison.

13. The device of claim 12 wherein the processor shifting the template in amplitude and selecting points from the time-shifted template and the amplitude-shifted template for computing the boundary.

14. The device of claim 13 wherein computing the boundary comprises computing an upper boundary and a lower boundary, the upper boundary and the lower boundary each offset from the template.

15. The device of claim 14 wherein computing each of the upper boundary and the lower boundary comprises:

computing a plurality of adjusted templates, each adjusted template computed by shifting the template in one of time and amplitude;

selecting an amplitude of one of the adjusted templates at each of a plurality of time points; and

defining the upper and lower boundaries using the selected amplitudes.

16. The device of claim 15 wherein comparing the unknown waveform to the boundary comprises:

aligning in time a selected point of the unknown waveform with a corresponding selected point of the template; and

computing an estimated area of the unknown waveform falling outside an area defined by the upper boundary and the lower boundary.

17. The device of claim 16 wherein computing the estimated area comprises identifying a sample point of the unknown waveform falling outside the area defined by the upper and lower boundaries;

and

computing a distance of the identified sample point from a nearest one of the upper boundary and the lower boundary.

18. The device of claim 17 wherein computing the distance comprises determining a smallest amplitude difference between the identified sample point and a plurality of sample points along the nearest one of the upper and lower boundaries.

19. The device of claim 18 wherein computing the estimated area comprises multiplying the distance by a weighting factor and summing the distance with other distances computed using other identified sample points of the unknown waveform falling outside the upper and lower boundaries.

20. The device of claim 19 wherein computing the estimated area further comprises:

computing an outer boundary offset from the upper boundary and the lower boundary; and

determining the weighting factor in response to the location of the identified sample point relative to the outer boundary.

21. The device of claim 20 wherein computing the outer boundary comprises shifting one of the upper boundary and the lower boundary in one of time and amplitude.

22. The device of claim 16 wherein comparing unknown waveform to the boundary further comprises:

determining an adjusted unknown waveform by shifting the unknown waveform in time relative to the template;

computing an adjusted estimated area of the adjusted unknown waveform falling outside the area defined by the upper and lower boundares; and

classifying the unknown waveform using the lowest one of the estimated area and the adjusted estimated area.

23. A computer readable medium storing a set of instructions which when implemented in a medical device system cause the system to:

sense a cardiac signal;

derive a template representing a known waveform morphology from the cardiac signal;

shift the template in time;

compute a boundary of the template, the boundary offset from the template and computed using a sample point of the template shifted in time;

acquire an unknown waveform morphology from the cardiac signal;

compare the unknown waveform morphology to the boundary; and

classify the unknown waveform morphology in response to the comparison.