Method and apparatus for prediction of cardiac electrical instability by simultaneous assessment of T-wave alternans and QT interval dispersion

• US 5,560,370 A
• Filed: 05/26/1995
• Issued: 10/01/1996
• Est. Priority Date: 02/20/1991
• Status: Expired due to Term

• Current Assignee: Georgetown University
• Original Assignee: Georgetown University
• Inventors: Nearing, Bruce D., Verrier, Richard L.
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US08/450,143
• Time in Patent Office: 494 Days
• Field of Search: 128/702-705
• US Class Current: 600/518
• CPC Class Codes: A61B 5/02405 Determining heart rate variability
• CPC Class Codes: A61B 5/349 Detecting specific parameters of the electrocardiograph cycle
• CPC Class Codes: A61B 5/35 by template matching
• CPC Class Codes: A61B 5/355 Detecting T-waves
• CPC Class Codes: A61B 5/36 Detecting PQ interval, PR interval or QT interval
• CPC Class Codes: A61B 5/361 Detecting fibrillation
• CPC Class Codes: A61B 5/4035 Evaluating the autonomic nervous system
• CPC Class Codes: Y10S 128/925 Neural network

Abstract

A method and apparatus for predicting cardiac electrical instability simultaneously assesses T-Wave Alternans and QT Interval Dispersion. T-wave alternation is an excellent predictor of cardiac electrical instability but can be influenced by mechano-electrical coupling. Thus, a measure of alternation has a high degree of sensitivity but a low degree of specificity. The low specificity of alternation is addressed by simultaneously analyzing QT interval dispersion. Dispersion is not a measure of excitable stimulus and is not sensitive to mechano-electrical coupling. The resulting combination of alternans and dispersion yields an accurate predictor of cardiac electrical instability caused by intrinsic factors.

Claims

1. A method of assessing cardiac electrical instability comprising the steps of:

sensing a plurality of ECG signals from a plurality of sites adjacent a heart;

detecting T-waves in at least one of said plurality of ECG signals;

detecting a QT interval in each of said plurality of EGG signals;

analyzing an amplitude of beat-to-beat alternation in said T-waves of successive R-R intervals of said at least one ECG signal to obtain an alternans measure;

analyzing a magnitude of dispersion of repolarization in said QT interval across said plurality of ECG signals to obtain a dispersion measure; and

simultaneously analyzing said alternans measure and said dispersion measure to assess cardiac electrical instability.

2. The method of claim 1, wherein said step of sensing a plurality of ECG signals comprises:

placing an ECG reference lead on the surface of a subject'"'"'s body;

placing, for each ECG signal to be sensed, a precordial ECG lead on the surface of the subject'"'"'s body proximate to the subject'"'"'s heart to sense one of said plurality of ECG signals;

amplifying each ECG signal;

low-pass filtering each ECG signal; and

sampling each ECG signal.

3. The method of claim 1, wherein said step of analyzing an amplitude of beat-to-beat alternation comprises:

predicting the location in said at least one ECG signal of a T-wave in each R-R interval;

partitioning each T-wave in said at least one ECG signal into a plurality of time divisions;

summing the samples in each of said time divisions of said at least one ECG signal;

forming a time series for each of said time divisions, each time series including corresponding sums from corresponding time divisions from successive ones of said T-waves; and

performing dynamic estimation on each said time series to estimate the amplitude of beat-to-beat alternation for each said time division.

4. The method of claim 1, wherein said step of analyzing dispersion of repolarization comprises:

analyzing a magnitude of dispersion of repolarization in said QT interval, wherein said QT interval includes at least a portion of said ECG signals between the beginning of a Q-wave and the end of the T-wave.

5. The method of claim 4, wherein said step of analyzing dispersion of repolarization comprises:

analyzing a magnitude of dispersion of repolarization in said QT interval across said plurality of ECG signals, wherein each of said QT intervals includes a portion of said respective ECG signal between the beginning of the Q-wave and the end of the T-wave.

6. The method of claim 1, wherein said step of analyzing dispersion of repolarization comprises:

for each of said plurality of ECG signals,

locating the peak amplitude in each R-R interval to find the apex of each R-wave,

determining the temporal location of the beginning of each Q-wave based on the apex of each R-wave,

determining the temporal location of the end of each T-wave, and

calculating each QT interval as a time difference from the beginning of the Q-wave to the end of the T-wave; and

estimating a measure of dispersion of repolarization of said QT intervals across said plurality of ECG signals.

7. The method of claim 1, wherein said step of analyzing dispersion of repolarization comprises:

for each of said plurality of ECG signals,

locating the peak amplitude in each R-R interval to find the apex of each R-wave,

determining the temporal location of each Q-wave based on the apex of each R-wave,

determining the temporal location of each T-wave, and

calculating each QT interval as a time difference from the Q-wave to the T-wave; and

estimating a measure of dispersion of repolarization of said QT intervals across said plurality of ECG signals.

8. The method of claim 7, wherein said step of estimating a measure of dispersion comprises:

calculating a maximum difference between said QT intervals taken across said plurality of ECG signals to estimate said measure of dispersion.

9. The method of claim 7, wherein said step of estimating a measure of dispersion comprises:

calculating a standard deviation for said QT intervals taken across said plurality of ECG signals to estimate said measure of dispersion.

10. The method of claim 7, wherein said step of estimating a measure of dispersion comprises:

calculating a variance for said QT intervals taken across said plurality of ECG signals to estimate said measure of dispersion.

11. The method of claim 7, wherein said step of estimating a measure of dispersion comprises:

calculating each R-R interval as a time difference between successive R-waves;

using each R-R interval to correct a corresponding QT interval to produce a corrected QT interval for each QT interval; and

calculating a maximum difference between said corrected QT intervals taken across said plurality of ECG signals to estimate said measure of dispersion.

12. The method of claim 7, wherein said step of estimating a measure of dispersion comprises:

averaging said QT intervals to produce an average QT interval;

dividing each QT interval by said average QT interval to produce a QT ratio for each QT interval;

averaging said QT ratios to produce an average QT ratio; and

calculating a standard deviation of said QT ratio to estimate said measure of dispersion.

13. The method of claim 7, wherein said step of estimating a measure of dispersion comprises:

calculating each R-R interval as a time difference between successive R-waves;

using each R-R interval to correct a corresponding QT interval to produce a corrected QT interval for each QT interval;

averaging said corrected QT intervals to produce an average corrected QT interval;

dividing each corrected QT interval by said average corrected QT interval to produce corrected QT ratios;

averaging said corrected QT ratios to produce an average corrected QT ratio; and

calculating a standard deviation of said corrected QT ratio to estimate said measure of dispersion.

14. The method of claim 7, wherein said step of estimating a measure of dispersion comprises:

calculating, for each R-R interval across said plurality of ECG signals, an average ECG signal;

calculating, for each R-R interval of said plurality of ECG signals, an RMS deviation using said average ECG signal; and

taking an amplitude of a maximum one of said RMS deviations as said measure of dispersion.

15. An apparatus for predicting cardiac electrical stability, comprising:

means for receiving an ECG of a patient'"'"'s heart;

first means for detecting and analyzing beat-to-beat alternation in a T-wave of said ECG to assess excitable stimulus and heterogeneity of repolarization;

second means for detecting and analyzing dispersion of repolarization in said ECG to assess heterogeneity of repolarization; and

third means for simultaneously analyzing assessment of excitable stimulus and heterogeneity of repolarization from said first means and heterogeneity of repolarization from said second means to assess cardiac electrical stability.

16. The apparatus of claim 15, further comprising:

means for sensing, coupled to said receiving means, a plurality of ECG signals from a plurality of sites adjacent a heart, each of said plurality of ECG signals having a plurality of R-R intervals; and

means for digitizing said plurality of ECG signals.

17. The apparatus of claim 16, wherein said first means comprises:

means for predicting the location in a selected ECG signal of a T-wave in each R-R interval;

means for partitioning each T-wave in said selected ECG signal into a plurality of time divisions;

means for summing the samples in each of said time divisions of said selected ECG signal;

means for forming a time series for each of said time divisions, each time series including corresponding sums from corresponding time divisions from successive ones of said T-waves; and

means for dynamically estimating on each said time series to estimate the amplitude of beat-to-beat alternation for each said time division.

18. The apparatus of claim 18, wherein said second means comprises:

means for locating the peak amplitude in each R-R interval to find the apex of each R-wave in each of said plurality of ECG signals;

means for determining the temporal location of the beginning of each Q-wave based on the apex of each R-wave;

means for determining the temporal location of the end of each T-wave;

means for calculating each QT interval as a time difference from the beginning of the Q-wave to the end of the T-wave; and

means for estimating a measure of dispersion of repolarization of said QT intervals across said plurality of ECG signals.