Apparatus and method for treating ventricular tachyarrhythmias

• US 5,978,707 A
• Filed: 10/08/1997
• Issued: 11/02/1999
• Est. Priority Date: 04/30/1997
• Status: Expired due to Term

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Gilkerson, James O., Linder, William J., Krig, David B., Zimmer, William L., Dreher, Robert D., Wald, Jan D.
• Primary Examiner(s): Kamm, William E.
• Assistant Examiner(s): EVANISKO, GEORGE ROBERT
• Application Number:
  US08/947,256
• Time in Patent Office: 755 Days
• Field of Search: 607/4, 607/5, 607/9, 607/14, 600/518
• US Class Current: 607/14
• CPC Class Codes: A61N 1/3622 comprising two or more electrodes co-operating with different heart regions
• CPC Class Codes: A61N 1/395 for treating atrial fibrillation
• CPC Class Codes: A61N 1/39622 Pacing therapy

Abstract

A system and method for selectively treating a ventricular tachycardia based on sensed atrial and ventricular intervals from the patient'"'"'s heart. A detection window of the ten most recent atrial and ventricular intervals are analyzed for the occurrence of either tachycardia or fibrillation. When a majority of the sensed intervals are satisfied, the apparatus starts a duration time interval. Ventricular intervals and atrial intervals are compare, ventricular interval greater than the atrial interval by a bias factor the system delivers tachycardia therapy to the heart. Alternatively, the method withholds tachycardia therapy to the heart when the atrial rate is classified as atrial fibrillation and the ventricular response is unstable.

Claims

1. A method, comprising:

sensing atrial events and ventricular events;

calculating an average atrial rate from the sensed atrial events;

determining an average ventricular rate from sensed ventricular events;

determining ventricular interval rates from pairs of consecutively sensed ventricular events in a detection window, wherein the detection window is a predetermined series of ventricular events;

comparing each of the ventricular interval rates in the detection window to a lower rate threshold value for each of two or more rate zones, wherein each of the two or more rate zones include a ventricular tachycardia therapy deliverable when the detection window is satisfied;

classifying a ventricular interval rate of the ventricular interval rates as a fast ventricular interval for a rate zone of the two or more rate zones when the ventricular interval rate is equal to or greater than the lower rate threshold value of the rate zone;

declaring the detection window satisfied when a first predetermined percentage of the ventricular interval rates in the detection window are classified as fast ventricular intervals for the rate zone;

starting a duration time interval once the detection window is declared satisfied; and

applying the ventricular tachycardia therapy for the rate zone when the average ventricular rate is greater than the average atrial rate by at least a bias factor during the duration time interval.

2. The method of claim 1, including determining the occurrence of atrial fibrillation from the sensed atrial events;

determining a ventricular rate from sensed ventricular events;

determining whether the ventricular rate is stable during a sustained duration time period, wherein the sustained duration time period is started when the average ventricular rate is less than or equal to the average atrial rate by at least the bias factor for the duration time interval;

determining whether the ventricular rate is unstable during the sustained duration time period;

when the ventricular rate is unstable for the sustained rate duration time period and atrial fibrillation is occurring, applying the ventricular tachycardia therapy for the rate zone after the sustained rate duration time period ends;

when the ventricular rate is stable and atrial fibrillation is occurring, applying ventricular tachycardia therapy;

when the ventricular rate is unstable for the sustained rate duration time period and atrial fibrillation is not occurring, applying the ventricular tachycardia therapy for the rate zone;

when the ventricular rate is unstable and atrial fibrillation is occurring, determining whether the atrial fibrillation terminates and the ventricular rate becomes stable during the sustained rate duration time period; and

when the unstable ventricular rate becomes stable and the atrial fibrillation terminates during the sustained rate duration time period, applying the ventricular tachycardia therapy for the rate zone.

3. The method of claim 2, wherein determining whether the ventricular rate is stable or unstable during the sustained duration time period includes programming a stability interval threshold value;

calculating a ventricular interval difference from a series of ventricular intervals of the sensed ventricular events, wherein the series of ventricular intervals includes a current ventricular interval and a previous ventricular interval;

calculating an average ventricular interval difference from the series of ventricular intervals;

determining a variance value, VAR(n), wherein n is an integer which represents a ventricular interval of the series of ventricular intervals, and wherein VAR(n) is determined by an absolute value of a difference between the current ventricular interval and the previous ventricular interval for the series of ventricular intervals;

determining an initial ventricular interval variance value, VAR_SEED, wherein the VAR_SEED is an average variance value of VAR(1), VAR(2), VAR(3) and VAR(4), wherein VAR(1) through VAR(4) occur immediately before the start of the duration time interval;

calculating a new average ventricular interval variance after the start of the duration timer from VAR_SEED *Kvar+VAR(5)*(1-Kvar), wherein Kvar is equal to 0.875 and VAR(5) is the ventricular interval pair following the start of the duration time interval;

calculating a subsequent average ventricular interval variance, VAR_avg (NEW), after VAR(5) using a weighted average formula;

VAR_avg (NEW)=VAR_avg (NEW-1)*Kvar+VAR(n)*(1-Kvar), wherein Kvar=0.875 and n is the integer representing the current ventricular interval; and

comparing the subsequent average ventricular interval variance to the programmed stability interval threshold value, wherein;

when the subsequent average ventricular interval variance is equal to or greater than the programmed stability interval threshold value, the ventricular interval rate is unstable; and

when the subsequent average ventricular interval variance is less than the programmed stability interval threshold value, the ventricular interval rate is stable.

4. The method of claim 2, wherein determining the occurrence of atrial fibrillation from the sensed atrial events includes identifying an atrial fibrillation after the duration time interval ends when more than a predetermined majority number of a set of atrial intervals is shorter than an atrial fibrillation interval threshold value, and when more than a predetermined quorum number of subsequent sets of atrial intervals remain shorter than the atrial fibrillation interval threshold value.

5. The method of claim 4, wherein the set of atrial intervals consists of ten consecutive atrial intervals of the atrial events sensed prior to the expiration of the duration time interval, the predetermined majority number is six, and the predetermined quorum number is four of each of the subsequent sets of atrial intervals.

6. The method of claim 4, including:

determining whether an onset rate for the ventricular rate is sudden; and

when the onset rate for the ventricular rate is sudden and atrial fibrillation is not occurring, applying the ventricular tachycardia therapy for the rate zone.

7. The method of claim 1, including determining a ventricular rate from sensed ventricular events;

programming an onset rate value;

determining an onset rate for the ventricular rate; and

when the onset rate of the ventricular rate is below the programmed onset rate value, inhibiting applying the ventricular tachycardia therapy for the sustained rate duration time period.

8. The method of claim 7, wherein determining the onset rate includes:

programming an onset threshold value;

determining a pivot point interval, wherein the pivot point interval is a pair of adjacent ventricular intervals which has the largest decrease in value in a series of ventricular intervals occurring before the detection window is declared satisfied;

calculating a baseline average ventricular interval value from four of six ventricular intervals prior to the pivot point interval;

determining the difference between the baseline average ventricular interval value and the pivot point interval;

determining the difference between the baseline average ventricular interval value and each of a series of three ventricular intervals following the pivot point interval; and

declaring the onset rate to be sudden when the value of at least three of any combination of the difference between the baseline average ventricular interval value and the pivot point interval and the difference between the baseline average ventricular interval value and the series of three ventricular intervals following the pivot point interval is equal to or greater than the onset threshold value; and

declaring the onset rate to be gradual when the value of less than three of any combination of the difference between the baseline average ventricular interval value and the pivot point interval and the difference between the baseline average ventricular interval value and the series of three ventricular intervals following the pivot point interval is equal to or greater than the onset threshold value.

9. The method of claim 1, including declaring the detection window remains satisfied when a second predetermined percentage of the ventricular interval rates following the detection window are classified as fast ventricular intervals for the rate zone;

and

resetting the duration time interval to zero when the detection window fails to remain satisfied during the duration time interval.

10. The method of claim 9, wherein the first predetermined percentage is greater than or equal to 65 percent, and the second predetermined percentage is greater than or equal to 45 percent.

11. An implantable cardioverter-defibrillator comprising:

an atrial catheter having at least one atrial sensing and pacing electrode;

a ventricular catheter having at least one ventricular sensing and pacing electrode, and at least one ventricular defibrillation coil electrode; and

electronic control circuitry connected to the atrial catheter and the ventricular catheter, wherein the electronic control circuitry includes a microcontroller, read only memory, sensing hardware, and therapy delivery hardware;

wherein the sensing hardware is adapted to sense atrial events and ventricular events;

wherein the read only memory is adapted to store a lower rate threshold value for each of two or more rate zones, a ventricular tachycardia therapy for each of the two or more rate zones, a first predetermined percentage, and a bias factor; and

wherein the microcontroller is adapted to calculate an average atrial rate from the sensed atrial events, and is adapted to determine an average ventricular rate from sensed ventricular events, and to determine ventricular interval rates from pairs of consecutively sensed ventricular events in a detection window, wherein the detection window is a predetermined series of ventricular events, and wherein the microcontroller is further adapted to compare each of the ventricular interval rates in the detection window to the lower rate threshold value for each of two or more rate zones, and to classify a ventricular interval rate of the ventricular interval rates as a fast ventricular interval for a rate zone of the two or more rate zones when the ventricular interval rate is equal to or greater than the lower rate threshold value of the rate zone;

the microcontroller further adapted to declare the detection window satisfied when the first predetermined percentage of the ventricular interval rates in the detection window are classified as fast ventricular intervals for the rate zone, and to start a duration time interval once the detection window is declared satisfied, and wherein the microcontroller is adapted to control the therapy delivery hardware to apply the ventricular tachycardia therapy of the rate zone when the average ventricular rate is greater than the average atrial rate by at least the bias factor during the duration time interval.

12. The implantable cardioverter-defibrillator of claim 11, wherein the microcontroller is adapted to determine the occurrence of atrial fibrillation from the sensed atrial events, and a ventricular rate from sensed ventricular events, and wherein the microcontroller further adapted to determine whether the ventricular rate is unstable during a sustained duration time period, wherein the microcontroller is adapted to start the sustained duration time period when the average ventricular rate is less than or equal to the average atrial rate by at least the bias factor for the duration time interval, and where the microcontroller is adapted to control the therapy delivery hardware to apply the ventricular tachycardia therapy of the rate zone when the ventricular rate is unstable for the sustained rate duration time period and atrial fibrillation is occurring.

13. The implantable cardioverter-defibrillator of claim 12, wherein the microcontroller is adapted to determine whether the ventricular rate is stable during a sustained duration time period, and where the microcontroller is adapted to control the therapy delivery hardware to apply the ventricular tachycardia therapy of the rate zone when the ventricular rate is stable and atrial fibrillation is occurring.

14. The implantable cardioverter-defibrillator of claim 12, wherein the microcontroller is adapted to control the therapy delivery hardware to apply the ventricular tachycardia therapy of the rate zone when the ventricular rate is unstable for the sustained rate duration time period and atrial fibrillation is not occurring.

15. The implantable cardioverter-defibrillator of claim 11, wherein the microcontroller is adapted to determine whether atrial fibrillation terminates and the ventricular rate becomes stable during the sustained rate duration time period, and wherein the microcontroller is adapted to control the therapy delivery hardware to apply the ventricular tachycardia therapy of the rate zone when the unstable ventricular rate becomes stable and the atrial fibrillation terminates during the sustained rate duration time period.

16. The implantable cardioverter-defibrillator of claim 11, wherein the read only memory is adapted to store an onset rate value, and the microcontroller is adapted to determine a ventricular rate from sensed ventricular events and an onset rate from the ventricular rate, and wherein the microprocessor is adapted to control the therapy delivery hardware to inhibit the ventricular tachycardia therapy for the sustained rate duration time period when the onset rate of the ventricular rate is below the onset rate value.

17. The implantable cardioverter-defibrillator of claim 11, wherein the read only memory is adapted to store a second predetermined percentage of the ventricular intervals, and the microcontroller is adapted to declare the detection window remains satisfied when the second predetermined percentage of the ventricular interval rates following the detection window are fast ventricular intervals for the rate zone, and wherein the microprocessor is adapted to reset the duration time interval to zero when the detection window fails to remain satisfied during the duration time interval.

18. The implantable cardioverter-defibrillator of claim 17, wherein the first predetermined percentage is greater than or equal to 65 percent, and the second predetermined percentage is greater than or equal to 45 percent.