Therapy-selection methods for implantable heart monitors

• US 6,681,134 B2
• Filed: 09/18/2001
• Issued: 01/20/2004
• Est. Priority Date: 06/30/1999
• Status: Expired due to Fees

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Morris, Milton M.
• Primary Examiner(s): Jastrzab, Jeffrey R.
• Application Number:
  US09/955,491
• Publication Number:
  US 20020111654A1
• Time in Patent Office: 854 Days
• Field of Search: 607/4, 607/9, 607/14, 607/17, 607/25, 600/516, 600/518
• US Class Current: 607/9
• CPC Class Codes: A61N 1/3621 for treating or preventing abnormally high heart rate
• CPC Class Codes: A61N 1/39622 Pacing therapy

Abstract

Thousands of patients prone to irregular and sometimes life threatening heart rhythms have miniature heart-monitoring devices, such as defibrillators and cardioverters, implanted in their chests. These devices detect onset of abnormal heart rhythms and automatically apply one or more shocks to their hearts. When properly sized and timed, the shocks restore normal heart function without human intervention. A critical part of these devices is the monitoring circuitry, which includes a microprocessor and stored instructions, or algorithms, that govern how the devices interpret and react to electrical signals indicative of abnormal heart rhythms. Often, the algorithms are too simple or too complex. Algorithms that are too simple lead to unnecessary shocking of the heart, while those that are too complex consume considerable battery power. Accordingly, the inventor devised a relatively simple and accurate algorithm for determining appropriate therapy options. One version of the algorithm computes three statistics—a range statistic, a minimum interval statistic, and a dispersion index—from a set of depolarization intervals. This algorithm defines the range statistic as the difference between largest and smallest depolarization intervals, the minimum interval as the smallest of the intervals, and the dispersion index as the standard deviation of the intervals. A scalar interval dispersion assessment, based on the three statistics, is then compared to a threshold to identify a rhythm as a flutter or fibrillation. The three statistics can also define a point in a three-dimensional space, with rhythm identification based on relative position of the point and a surface in the space.

Claims

1. Apparatus for monitoring heart activity in an implantable medical device, the apparatus comprising:

means for calculating a set of two or more intervals based on measured heart activity;

means for determining a minimum interval based on the set of two or more intervals;

means for calculating a range statistic based on a difference between a first subset and second subset of the intervals;

means for calculating a dispersion index based on a subset of the intervals;

means for calculating a member based on the minimum interval, the range statistic, and the dispersion index; and

means for comparing the number to a threshold to determine a therapy option.

2. The monitoring apparatus of claim 1, wherein the first subset of the intervals includes only a first one of the intervals and the second subset of the intervals includes only a second one of the intervals.

3. The monitoring apparatus of claim 1, wherein each of the set of two or more intervals is an atrial depolarization interval.

4. The monitoring apparatus of claim 1, wherein the means for calculating a number based on the minimum interval, the range statistic, and the dispersion index computes the number based on an function having one of the following forms:

5. The monitoring apparatus of claim 4, wherein K and K₃ are each approximately 1.0, and wherein K₁ and K₂ are each approximately 0.0001.

6. Apparatus for monitoring heart activity, comprising:

a minimum-interval-determination module to determine a minimum interval from a set of two or more intervals based on sensed heart activity;

a range-determination module to determine a range parameter based on a difference between a first subset and second subset of the intervals;

a dispersion-determination module to determine a dispersion parameter quantifying dispersion of a subset of the intervals;

an assessment-determination module coupled to the minimum-interval-determination module, the range-determination module, and the dispersion-index-determination module to determine an assessment value for the set of intervals, based on the minimum interval, the range parameter, the dispersion index; and

a decision module coupled to the assessment-calculation to make a decision based on the determined assessment value.

7. The apparatus of claim 6, wherein the decision is based on a comparison of the determined assessment value and a threshold.

8. A method of selecting one of at least first and second cardiac therapy options, the method comprising:

calculating a set of two or more intervals based on data indicative of heart activity;

selecting a subset of intervals from the set of intervals, with the subset including at least two intervals;

determining a minimum interval based on the subset of intervals;

determining a range parameter based on a difference between a first interval in the subset and a second interval in the subset;

determining a dispersion parameter based on the subset of intervals;

determining an assessment parameter based on the minimum interval, the range parameter, and the dispersion parameter; and

selecting the first or second therapy option based on the assessment parameter.

9. The method of claim 8, wherein the range parameter is based on the minimum interval and the maximum interval in the subset.

10. The method of claim 8, wherein each of the set of two or more intervals is an atrial depolarization interval.

11. The method of claim 8, wherein the assessment parameter is inversely proportional to the duration of the minimum interval and directly proportional to the range parameter and to the dispersion parameter.

12. The method of claim 8, wherein determining the assessment parameter includes calculating

13. The method of claim 8, wherein the assessment parameter is based on a sum of at least first, second, and third components, with the first component directly proportional to the range parameter, the second component directly proportional to the dispersion parameter, and the third component inversely proportional to the duration of the minimum interval.

14. The method of claim 8, wherein calculating the assessment parameter includes calculating

15. The method of claim 14, wherein K₃ is approximately 1.0, and wherein K₁ and K₂ are each approximately 0.0001.

16. A method of selecting a therapy option in a medical device, comprising:

defining a surface in a space having at least three dimensions;

calculating a set of two or more intervals based on data representative of at least a portion of an electrogram;

calculating a minimum interval based on the set of intervals;

calculating a range parameter based on a first subset and a second subset of the intervals;

calculating a dispersion parameter based on a subset of the intervals;

defining a point in the space based on the minimum interval, the range parameter, and the dispersion parameter; and

selecting one of at least two therapy options based on position of the point relative to the surface.

17. A method of selecting a therapy option in a medical device, comprising:

defining a surface in a space having at least three dimensions;

calculating a set of two or more intervals based on data representative of at least a portion of an electrogram

calculating a minimum interval based on the set of intervals;

calculating a range parameter based on a first subset and a second subset of the intervals;

calculating a dispersion parameter based on a subset of the intervals;

defining a point in the space based on the minimum interval, the range parameter, and the dispersion parameter; and

selecting one of at least two therapy options based on positions of the point relative to the surface, wherein the assessment parameter is inversely proportional to the duration of the minimum interval and directly proportional to the range parameter and to the dispersion parameter.

18. A method of selecting a therapy option in a medical device, comprising:

defining a surface in a space having at least three dimensions;

calculating a set of two or more intervals based on data representative of at least a portion of an electrogram;

calculating a minimum interval based on the set of intervals;

calculating a range parameter based on a first subset and a second subset of the intervals;

calculating a dispersion parameter based on a subset of the intervals;

defining a point in the space based on the minimum interval, the range parameter, and the dispersion parameter; and

selecting one of at least two therapy options based on position of the point relative to the surface,

wherein the assessment parameter is based on a sum of at least first, second, and third components, with the first component directly proportional to the range parameter, the second component directly proportional to the dispersion parameter, and the third component inversely proportional to the duration of the minimum interval.

19. A method of selecting a therapy option in a medical device, comprising:

defining a surface in a space having at least three dimensions;

calculating a set of two or more intervals based on data representative of at least a portion of an electrogram;

calculating a minimum interval based on the set of intervals;

calculating a range parameter based on a first subset and a second subset of the intervals;

calculating a dispersion parameter based on a subset of the intervals;

defining a point in the space based on the minimum interval, the range parameter, and the dispersion parameter; and

selecting one of at least two therapy options based on position of the point relative to the surface;

wherein the assessment parameter is based on a sum of at least first, second, and third components, with the first component directly proportional to the range parameter, the second component directly proportional to the dispersion parameter, and the third component inversely proportional to the duration of the minimum interval; and

wherein calculating the assessment parameter includes calculating