Arrhythmia memory for tachyarrhythmia discrimination

• US 20060111643A1
• Filed: 11/23/2004
• Published: 05/25/2006
• Est. Priority Date: 11/23/2004
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Lin, Yayun, Thompson, Julie, Cazares, Shelley
• Granted Patent: US 7,277,747 B2
• Time in Patent Office: Days
• US Class Current: 600/518
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: A61B 5/35 by template matching
• CPC Class Codes: A61B 5/363 Detecting tachycardia or bradycardia
• CPC Class Codes: A61B 5/726 using Wavelet transforms
• CPC Class Codes: A61N 1/3622 comprising two or more electrodes co-operating with different heart regions

Abstract

This document discusses, among other things, a method of identifying a non-fatal tachyarrhythmia episode by determining a degree of similarity between the episode and a template generated from a previous tachyarrhythmia episode.

Claims

1. A machine-assisted method comprising:

sensing an intrinsic electrical heart signal using an implantable medical device;

identifying a tachyarrhythmia portion of the intrinsic electrical heart signal and storing at least part of the tachyarrhythmia portion of the intrinsic electrical heart signal;

receiving user input declaring the tachyarrhythmia portion of the intrinsic electrical heart signal to be indicative of SVT;

generating a SVT template from the tachyarrhythmia portion of the heart signal;

determining at least one degree of similarity between a second portion of the heart signal from a later tachyarrhythmia episode and the SVT template; and

declaring the second portion of the heart signal to represent an SVT episode if the at least one degree of similarity exceeds at least one threshold value.

2. The method of claim 1, further comprising presenting the tachyarrhythmia portion of the intrinsic electrical heart signal to a user and receiving input indicating a segment of the tachyarrhythmia portion of the intrinsic electrical heart signal to be used to generated the SVT template.

3. The method of claim 2, further comprising presenting a plurality of portions of the intrinsic electrical heart signal corresponding to a plurality of tachyarrhythmia episodes to a user and receiving input indicating which of the plurality of portions of the intrinsic electrical signal are to be used to generate one or more SVT templates.

4. The method of claim 1, further comprising suppressing a ventricular tachyarrhythmia therapy during the declared SVT episode.

5. The method of claim 1, further comprising selecting the SVT template from a group of two or more candidate SVT templates.

6. The method of claim 1, further comprising:

monitoring a heart rate; and

if the heart rate exceeds a rate threshold, declaring a tachyarrhythmia.

7. The method of claim 6, further comprising:

comparing the second portion of the electrical signal with a normal sinus rhythm (NSR) template; and

if the second portion of the electrical signal sufficiently correlates to the NSR template, declaring the second portion of the electrical signal to be a SVT episode and suppressing a ventricular tachyarrhythmia therapy during the declared SVT episode.

8. A machine-assisted method comprising:

sensing an intrinsic electrical heart signal using an implantable medical device;

identifying a tachyarrhythmia portion of the heart signal that is indicative of a tachyarrhythmia episode;

receiving user input declaring the tachyarrhythmia portion of the heart signal to be indicative of the tachyarrhythmia episode that does not require ventricular antitachyarrhythmia therapy;

generating from the tachyarrhythmia portion of the heart signal at least one template representative of the tachyarrhythmia episode that does not require therapy;

detecting a heart rate using the heart signal; and

if the heart rate exceeds a rate threshold value at a later time, then declaring a later tachyarrhythmia, and if a later tachyarrhythmia is declared, then;

determining at least one degree of similarity between a second portion of the heart signal from the later tachyarrhythmia and at least one template representative of a tachyarrhythmia episode that does not require therapy; and

if the at least one degree of similarity exceeds at least one threshold value, suppressing a ventricular tachyarrhythmia therapy, otherwise delivering a ventricular antitachyarrhythmia therapy.

9. A machine-assisted method comprising:

sensing an intrinsic electrical heart signal;

monitoring information about a patient;

using the information about the patient to select at least one supraventricular tachyarrhythmia (SVT) template from a group of two or more candidate SVT templates;

determining at least one degree of similarity between a portion of the heart signal from a tachyarrhythmia episode and the at least one SVT template; and

declaring the portion of the heart signal from the tachyarrhythmia episode to represent a SVT episode if the at least one degree of similarity exceeds at least one threshold value.

10. The method of claim 9, wherein each candidate SVT template is associated with a heart rate at which the prior tachyarrhythmia episode used to generate the SVT template was observed, the method comprising monitoring a patient'"'"'s heart rate from the intrinsic electrical heart signal from a tachyarrhythmia episode and selecting the candidate SVT template having the associated heart rate that is closest to the monitored heart rate.

11. The method of claim 10, in which using the heart rate to select at least one SVT template further includes selecting the candidate SVT template having the associated heart rate that is second closest to the heart rate of the tachyarrhythmia episode.

12. The method of claim 9, wherein determining at least one degree of similarity includes determining degrees of similarity between the portion of the heart signal from the tachyarrhythmia episode and multiple SVT templates.

13. The method of claim 9, further comprising:

identifying portions of the heart signal that are indicative of SVT; and

storing the portions of the heart signal that are indicative of SVT as candidate SVT templates.

14. The method of claim 13, wherein the storing includes storing SVT templates in a medium, and further comprising discarding an oldest one of the SVT templates.

15. The method of claim 13, wherein the storing includes storing SVT templates in a medium, and further comprising discarding a SVT template associated with a discontinued drug therapy regimen.

16. The method of claim 13, wherein the storing includes storing SVT templates in a medium, and further comprising receiving an input from a user designating a SVT template to be discarded, and discarding the designated SVT template.

17. The method of claim 13, further comprising tracking the degree of similarity of the heart signal from a tachyarrhythmia episode to the candidate SVT templates, and discarding a candidate SVT template exhibiting the least frequent similarity with the heart signal.

18. The method of claim 13, wherein the storing includes storing SVT templates in a medium, and further comprising discarding an SVT template with a heart rate similar to heart rates at which other SVT templates were identified.

19. The method of claim 13, wherein the storing includes storing SVT templates in a medium, and further comprising discarding an SVT template that is most similar to other SVT templates.

20. The method of claim 9, wherein determining at least one degree of similarity between a portion of the heart signal and the at least one SVT template includes:

determining at least one degree of similarity between a portion of the heart signal from a tachyarrhythmia episode and a first SVT template;

if the degree of similarity between the portion of the heart signal and the first template does not exceed a threshold, determining at least one degree of similarity between the portion of the heart signal from the tachyarrhythmia episode and a second template.

21. The method of claim 12, wherein determining at least one degree of similarity includes computing a feature correlation coefficient for each of a plurality of portions of the intrinsic electrical heart signal detected during a tachyarrhythmia episode and withholding treatment if at least a predetermined fraction of the feature correlation coefficients exceed a predetermined threshold.

22. The method of claim 21, wherein the method comprises computing a feature correlation coefficient for each of a plurality of sequential heart beats.

23. The method of claim 22, wherein the predetermined fraction and the predetermined threshold are programmably selectable.

24. The method of claim 23, wherein the threshold is selected using statistics from patients having similar characteristics.

25. The method of claim 24, wherein the threshold is selected based upon the patient'"'"'s age, disease history, and medication.

26. The method of claim 9, wherein monitoring information about the patient includes monitoring the patient'"'"'s neural activity, sleep state, hemodynamic status, transthoracic impedance and cardiac impedance.

27. The method of claim 9, further comprising:

comparing the portion of the electrical signal from a tachyarrhythmia episode with a normal sinus rhythm (NSR) template; and

if the portion of the electrical signal sufficiently correlates to the NSR template, declaring the portion of the electrical signal to be an SVT episode.

29. The apparatus of claim 21, wherein the processor is further configured to store in the memory as a candidate SVT template a portion of the intrinsic heart signal representative of a SVT episode.

30. The apparatus of claim 29, wherein the processor is further configured to discard the oldest candidate template from the memory system to make room for a new SVT template.

31. The apparatus of claim 29, wherein the processor is further configured to discard from the processing system the SVT template that has been least frequently selected.

28. An apparatus comprising:

at least one electrical sensor configured to sense an intrinsic electrical heart signal;

a memory circuit configured to store candidate supraventricular tachyarrhythmia (SVT) templates;

a processor configured to interpret the intrinsic heart signal to determine whether antitachyarrhythmia therapy should be delivered in response to a tachyarrhythmia episode by determining a heart rate from the intrinsic heart signal, selecting a SVT template having a heart rate that is closest to the heart rate of the intrinsic heart signal, determining at least one degree of similarity between a portion of the heart signal and at least one SVT template representative of a previous SVT episode; and

further configured to suppress a ventricular antitachyarrhythmia therapy if the at least one degree of similarity exceeds at least one threshold value.

32. The apparatus of claim 28, wherein the processor is further configured to compare the intrinsic electrical heart from the tachyarrhythmia episode signal to an NSR template that represents a normal sinus rhythm, and to suppress antitachyarrhythmia therapy if at least one degree of similarity between the portion of the heart signal and the NSR template exceeds at least one threshold.

33. A cardiac rhythm management system comprising:

a sensing circuit configured to sense an intrinsic electrical heart signal from a tachyarrhythmia episode;

an antitachyarrhythmia therapy circuit configured to deliver ventricular antitachyarrhythmia therapy;

a processing circuit configured to interpret the intrinsic heart signal to determine whether a ventricular antitachyarrhythmia therapy should be delivered in response to the tachyarrhythmia episode by determining a heart rate from the intrinsic heart signal, selecting a supraventricular tachyarrhythmia (SVT) template having a heart rate that is closest to the heart rate of the intrinsic heart signal, determining at least one degree of similarity between a portion of the heart signal from the tachyarrhythmia episode and at least one SVT template representative of a previous SVT episode; and

further configured to suppress a ventricular antitachyarrhythmia therapy if the at least one degree of similarity exceeds at least one threshold value.

34. The cardiac rhythm management system of claim 33, further comprising a memory circuit configured to store at least a portion of the intrinsic electrical heart signal from a tachyarrhythmia episode.

35. The cardiac rhythm management system of claim 33, wherein at least a portion of the cardiac rhythm management system is implantable, the cardiac rhythm management system further comprising a wireless communication system, wherein a recorded portion of the intrinsic electrical heart signal can be communicated to a non-implanted device through the wireless communication system.

36. The cardiac rhythm management system of claim 33, wherein the non-implanted device includes a display system that is configured to display a graphical representation of a recorded portion of the intrinsic heart signal to a user.

37. A machine-assisted method comprising:

sensing an intrinsic electrical heart signal using an implantable medical device;

identifying a tachyarrhythmia episode from the heart signal and storing a portion of the intrinsic electrical heart signal from the tachyarrhythmia episode;

receiving user input declaring the portion of the heart signal to be indicative of a tachyarrhythmia that does not require ventricular antitachyarrhythmia therapy;

generating a template from the portion of the heart signal;

determining at least one degree of similarity between a second tachyarrhythmia portion of the heart signal from a later tachyarrhythmia episode and the template; and

suppressing an antitachyarrhythmia therapy for the later tachyarrhythmia episode if the at least one degree of similarity exceeds at least one threshold value.

38. The method of claim 37, further comprising selecting a template from a group of candidate templates by comparing a current drug therapy regimen to drug therapy regimens associated with the respective templates, wherein determining the at least one degree of similarity includes comparing the second tachyarrhythmia portion of the heart signal to the selected template.

39. A machine-assisted method comprising:

generating a normal sinus rhythm (NSR) template;

generating a supraventricular tachyarrhythmia (SVT) template from an electrical signature of a known SVT episode;

comparing heart beat signatures from a tachyarrhythmia episode to the NSR template and suppressing a ventricular antitachyarrhythmia therapy if a predetermined fraction of the heart beat signatures match the NSR template;

if a predetermined fraction of the plurality of heart beat signatures do not match the NSR template, comparing the heart beat signatures from the tachyarrhythmia episode to the SVT template and suppressing the ventricular antitachyarrhythmia therapy if a predetermined fraction of the heart beat signatures match the SVT template.