Zoneless tachyarrhythmia detection with real-time rhythm monitoring

• US 20070135848A1
• Filed: 12/13/2005
• Published: 06/14/2007
• Est. Priority Date: 12/13/2005
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Bocek, Joseph, Kim, Jaeho, Stoklosa, Karl, Walczak, Scott
• Granted Patent: US 7,702,384 B2
• Time in Patent Office: Days
• US Class Current: 607/5
• CPC Class Codes: A61B 5/361 Detecting fibrillation
• CPC Class Codes: A61N 1/0504 Subcutaneous electrodes
• CPC Class Codes: A61N 1/3956 Implantable devices for applying electric shocks to the heart, e.g. for cardioversion

Abstract

A system including an implantable medical device (IMD). The IMD includes a ventricular contraction sensing circuit that provides a sensed ventricular contraction signal, a timer circuit that provides a ventricular time interval between ventricular contractions, and a controller circuit coupled to the timer circuit, the controller circuit determines the ventricular contraction rate using the ventricular time interval. The controller circuit further includes a tachyarrhythmia detection module that declares tachyarrhythmia, in response to detecting a sudden rate increase, without comparing a ventricular rate or time interval to a respective tachyarrhythmia detection rate or time interval threshold.

Claims

1. A system comprising:

an implantable medical device (IMD) comprising;

a ventricular contraction sensing circuit operable to provide a sensed ventricular contraction signal;

a timer circuit operable to provide a ventricular time interval between ventricular contractions; and

a controller circuit coupled to the timer circuit, the controller circuit operable to determine the ventricular contraction rate using the ventricular time interval, and wherein the controller circuit further includes a tachyarrhythmia detection module operable to declare tachyarrhythmia, in response to detecting a sudden rate increase, without comparing a ventricular rate or time interval to a respective tachyarrhythmia detection rate or time interval threshold.

2. The system of claim 1, wherein a sudden rate increase is defined as a specified number of consecutive accelerated beats, wherein an accelerated beat is defined by at least one specified accelerated beat criterion other than a comparison to a fixed rate threshold.

3. The system of claim 2, wherein the tachyarrhythmia detection module is operable to deem a current heartbeat as an accelerated beat if a difference between a last average ventricular contraction interval (V-V interval) and the current V-V interval is greater than a specified percentage of the last average V-V interval.

4. The system of claim 1, further comprising an atrial contraction sensing circuit configured to sense a cardiac signal of an atrium of the heart, and wherein the controller circuit is operable to monitor a ventricular and an atrial contraction rate and the tachyarrhythmia detection module is operable to declare tachyarrhythmia when at least one of the ventricular contraction rate exceeds the atrial contraction rate by a specified rate threshold or when detecting a sudden rate increase.

5. The system of claim 4, wherein the tachyarrhythmia detection module is operable to declare tachyarrhythmia when both the ventricular contraction rate exceeds the atrial contraction rate by a specified rate threshold and a sudden rate increase is detected.

6. The system of claim 4, wherein the controller circuit further includes a rhythm discrimination module to discriminate between ventricular tachyarrhythmia and supraventricular tachyarrhythmia, wherein the controller circuit enables the rhythm discrimination module when the controller circuit detects that a) the sudden rate increase is sustained for a specified period of time, or b) the ventricular rate which exceeds the atrial rate by a specified rate threshold is sustained for a specified period of time, or c) both the sudden rate increase and the ventricular rate are sustained for a specified period of time.

7. The system of claim 6, further including a memory circuit coupled to the controller circuit, wherein at least one first area of the memory circuit is allocated to store a digitized representation of at least one episode of ventricular tachyarrhythmia and at least one second area of the memory circuit is allocated to store a digitized representation of at least one episode of supraventricular tachyarrhythmia.

8. The system of claim 6, wherein the rhythm discrimination module discriminates between ventricular tachyarrhythmia and supraventricular tachyarrhythmia by performing at least one of:

(a) a rhythm discrimination method that includes recurrently updating an average ventricular contraction interval (V-V interval) and determining that an average ventricular contraction rate exceeds an average atrial contraction rate by more than a specified rate threshold value;

(b) comparing a morphology of a sensed cardiac signal to a template morphology;

(c) determining that a specified number of atrial rate intervals measured over a consecutive number of heartbeats are shorter than an atrial fibrillation rate threshold interval; and

(d) assessing the stability of the ventricular rhythm.

9. The system of claim 6, further including a therapy circuit coupled to the controller circuit, the therapy circuit operable to deliver anti-tachyarrhythmia therapy when the rhythm discrimination module detects ventricular tachyarrhythmia.

10. The system of claim 1, wherein the controller circuit is further operable to deem an episode of tachyarrhythmia as an episode of slow tachyarrhythmia when the ventricular rate is less than a specified tachyarrhythmia detection rate.

11. The system of claim 10, wherein the specified tachyarrhythmia detection rate is 140 beats per minute (bpm).

12. The system of claim 10, wherein the specified tachyarrhythmia detection rate is less than a maximum pacing rate.

13. The system of claim 10, further including a memory circuit coupled to the controller circuit, the memory circuit to store a digitized representation of at least one episode of slow tachyarrhythmia.

14. The system of claim 13, wherein the memory circuit is operable to store a plurality of slow tachyarrhythmia episode representations and wherein the controller circuit overwrites the oldest stored slow tachyarrhythmia episode representation with the most recent episode representation when the storage available for slow tachyarrhythmia episode representations is full.

15. The system of claim 10, further including an external device and wherein the IMD further includes a communication circuit coupled to the controller circuit, wherein the controller circuit is operable to communicate information related to a detected slow tachyarrhythmia to the external device.

16. The system of claim 10, further including an external device coupled to a network, wherein the IMD further includes a communication circuit coupled to the controller circuit, and wherein the controller circuit is operable to communicate an indication of a detected slow tachyarrhythmia to the external device.

17. The system of claim 16, wherein the system includes means for providing an alarm indicating slow tachyarrhythmia.

18. A system comprising:

an implantable medical device (IMD) comprising;

a ventricular contraction sensing circuit operable to provide a sensed ventricular contraction signal;

an atrial contraction sensing circuit operable to provide a sensed atrial contraction signal;

a timer circuit operable to provide a time interval between heart contractions; and

a controller circuit coupled to the timer circuit, the controller circuit operable to monitor a ventricular and an atrial contraction rate, and wherein the controller circuit further includes a tachyarrhythmia detection module operable to;

declare tachyarrhythmia in response to at least one of the ventricular contraction rate exceeding the atrial contraction rate by a specified rate difference, or detecting a sudden ventricular rate change; and

to deem an episode of tachyarrhythmia as an episode of slow tachyarrhythmia when the ventricular rate is less than a specified tachyarrhythmia detection rate.

19. The system of claim 18, wherein a sudden rate increase is defined as a specified number of consecutive accelerated beats, and wherein the tachyarrhythmia detection module is operable to deem a current heartbeat as an accelerated beat if a difference between a last average ventricular contraction interval (V-V interval) and the current V-V interval is greater than a specified percentage of the last average V-V interval.

20. The system of claim 18, wherein the specified tachyarrhythmia detection rate is 140 beats per minute (bpm).

21. The system of claim 18, further including a memory circuit coupled to the controller circuit, the memory circuit to store a digitized representation of at least one episode of slow tachyarrhythmia.

22. A method of using an implantable medical device (IMD) comprising:

monitoring ventricular contraction intervals (V-V intervals) of a subject;

detecting a sudden rate increase in the V-V intervals, the sudden rate increase including a specified number of consecutive accelerated beats, wherein an accelerated beat is a V-V interval having a shorter duration than one or more previous V-V intervals;

determining that the sudden rate increase is sustained for a specified period of time; and

deeming the sudden rate increase indicative of tachyarrhythmia.

23. The method of claim 22, further including:

monitoring an atrial contraction rate of the subject;

detecting whether the ventricular contraction rate exceeds the subject'"'"'s atrial contraction rate by more than specified rate threshold; and

declaring tachyarrhythmia if the sudden rate increase is sustained for a specified period of time or the ventricular contraction rate which exceeds the atrial contraction rate by more than specified rate threshold is sustained for a specified period of time, or both the sudden rate increase and the ventricular rate are sustained for a specified period of time.

24. The method of claim 22, further including discriminating between ventricular tachyarrhythmia heart rhythms and supraventricular tachyarrhythmia heart rhythms upon detecting that the sudden rate increase is sustained for a specified period of time, wherein discriminating between ventricular tachyarrhythmia and supraventricular tachyarrhythmia includes at least one of:

(a) determining that an average ventricular contraction rate exceeds an average atrial contraction rate by more than a specified rate threshold value;

(b) comparing a morphology of a sensed cardiac signal to a template morphology;

(c) determining that an atrial rate exceeds an atrial fibrillation rate threshold; and

(d) assessing the stability of the ventricular rhythm.

25. The method of claim 22, wherein determining that sudden rate increase is sustained for a specified period of time includes determining that the accelerated beats are sustained over A of B ventricular time intervals, where A and B are integers, and A≦

B.

26. The method of claim 22, further including deeming an end of tachyarrhythmia if the intervals are sustained over less than C of D V-V intervals, where C and D are integers, and C<

D.

27. The method of claim 22, wherein detecting a sudden rate increase in the V-V intervals includes:

recurrently updating an average V-V interval;

deeming that a current V-V interval indicates an accelerated beat if a difference between a last average V-V interval and the current V-V interval exceeds a specified percentage of the last average V-V interval; and

excluding the current V-V interval from an updated average V-V interval calculation if the current V-V interval indicates an accelerated beat after the specified number of consecutive accelerated beats.

28. The method of claim 27, wherein recurrently updating an average V-V interval includes recurrently calculating an average V-V interval, wherein a previous calculated average interval is given a greater weight than a current rate interval.

29. The method of claim 22, including deeming an episode of tachyarrhythmia as slow tachyarrhythmia when the ventricular rate is less than a specified tachyarrhythmia detection rate.

30. The method of claim 29, including communicating an indication of slow tachyarrhythmia to an external device.

31. The method of claim 29, including storing at least one episode of slow tachyarrhythmia in the IMD.

32. The method of claim 31, including:

storing a plurality of episodes of slow tachyarrhythmia in the IMD; and

overwriting an oldest stored episode with a most recent episode when the storage available for slow tachyarrhythmia episodes is full.

33. The method of claim 31, including storing at least one episode of slow tachyarrhythmia detected as ventricular in origin in a first area of memory allocated to store a digitized representation of at least one episode of slow ventricular tachyarrhythmia, and storing at least one episode of supraventricular tachyarrhythmia detected as supraventricular in origin in a second area of memory allocated to store a digitized representation of at least one episode of supraventricular tachyarrhythmia.

34. The method of claim 22, further including delivering anti-tachyarrhythmia therapy when the sudden rate increase is deemed indicative of tachyarrhythmia.

35. A method of using an implantable medical device (IMD) comprising:

monitoring a ventricular contraction rate of a subject;

monitoring an atrial contraction rate of the subject; and

if the ventricular contraction rate exceeds the atrial contraction rate, declaring tachyarrhythmia.

36. The method of claim 35, wherein detecting that the ventricular contraction rate exceeds the atrial contraction rate includes:

calculating an average ventricular rate and an average atrial rate; and

deeming that the ventricular contraction rate exceeds the atrial contraction rate when the average ventricular rate is faster than the average atrial rate by more than a specified rate threshold value.

37. The method of claim 36, wherein calculating an average ventricular rate includes recurrently updating an average ventricular rate interval by summing a weighted previous average ventricular rate interval with a weighted current ventricular rate interval.

38. The method of claim 36, wherein calculating an average atrial rate includes recurrently updating an average atrial rate interval by summing a weighted previous average atrial rate interval with a weighted current atrial rate interval.

39. The method of claim 35, including discriminating between ventricular tachyarrhythmia heart rhythms and supraventricular tachyarrhythmia heart rhythms upon detecting that a ventricular contraction rate of a subject exceeds the subject'"'"'s atrial contraction rate, wherein discriminating between ventricular tachyarrhythmia and supraventricular tachyarrhythmia includes at least one of:

(a) determining that an average ventricular contraction rate exceeds an average atrial contraction rate by more than a specified rate threshold value;

(b) comparing a morphology of a sensed cardiac signal to a template morphology;

(c) determining that an atrial rate exceeds an atrial fibrillation rate threshold; and

(d) assessing the stability of the ventricular rhythm.

40. The method of claim 39, comprising discriminating between ventricular tachyarrhythmia and supraventricular tachyarrhythmia when a ventricular contraction rate of a subject exceeds the subject'"'"'s atrial contraction rate for a specified period of time.

41. The method of claim 35, comprising:

declaring slow tachyarrhythmia when the ventricular rate is less than a specified tachyarrhythmia detection rate; and

communicating an indication of slow tachyarrhythmia from the IMD.

42. The method of claim 35, comprising:

declaring slow tachyarrhythmia when the ventricular rate is less than a specified tachyarrhythmia detection rate; and

storing at least one episode of slow tachyarrhythmia in the IMD.

43. The method of claim 42, comprising:

storing a plurality of episodes of slow tachyarrhythmia in the IMD; and

overwriting an oldest stored episode with a most recent episode when the storage available for episodes is full.