Non-invasive, dynamic tracking of cardiac vulnerability by simultaneous analysis of heart rate variability and T-wave alternans

• US 5,842,997 A
• Filed: 04/30/1997
• Issued: 12/01/1998
• Est. Priority Date: 02/20/1991
• Status: Expired due to Term

• Current Assignee: Georgetown University
• Original Assignee: Georgetown University
• Inventors: Verrier, Richard L., Nearing, Bruce D.
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US08/841,548
• Time in Patent Office: 580 Days
• Field of Search: 600/515, 600/518
• 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 5/352 Detecting R peaks, e.g. for synchronising diagnostic apparatus; Estimating R-R interval
• 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 5/363 Detecting tachycardia or bradycardia
• CPC Class Codes: A61B 5/4035 Evaluating the autonomic nervous system
• CPC Class Codes: A61B 5/4884 inducing physiological or psychological stress, e.g. applications for stress testing
• CPC Class Codes: A61B 5/7275 Determining trends in physiological measurement data; Predicting development of a medical condition based on physiological measurements, e.g. determining a risk factor
• CPC Class Codes: G16H 50/30 for calculating health indices; for individual health risk assessment

Abstract

A method and an apparatus for the non-invasive, dynamic tracking and diagnosing of cardiac vulnerability to ventricular fibrillation are disclosed. T-wave alternans and heart rate variability are simultaneously evaluated. T-wave alternation is an absolute predictor of cardiac electrical stability. Heart rate variability is a measure of autonomic influence, a major factor in triggering cardiac arrhythmias. By simultaneously analyzing both phenomena, the extent and cause of cardiac vulnerability can be assessed.

Claims

1. A method for assessing cardiac vulnerability comprising the steps of:

receiving an ECG signal;

analyzing T-waves in said ECG signal to estimate an amplitude of beat-to-beat alternation, said amplitude of beat-to-beat alternation representing cardiac electrical stability;

analyzing R--R intervals in said ECG signal to estimate a magnitude of heart rate variability, said magnitude of heart rate variability indicating neural influence on the heart; and

analyzing said amplitude of beat-to-beat alternation and said magnitude of heart rate variability to assess said cardiac electrical stability.

2. The method of claim 1, wherein said step of receiving an ECG signal comprises the following steps:

placing a precordial ECG lead on the surface of a subject'"'"'s body proximate to the subject'"'"'s heart to sense said ECG signal;

amplifying said ECG signal;

low-pass filtering said ECG signal; and

sampling said ECG signal.

3. The method of claim 2, wherein said step of analyzing T-waves comprises the following steps:

predicting the location in said ECG signal of the T-wave in each R--R interval;

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

summing the samples in each of said time divisions of said 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 3, wherein said step of performing dynamic estimation includes performing complex demodulation on each said time series.

5. The method of claim 2, wherein said step of analyzing R--R intervals comprises the following steps:

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

computing the time between successive R-waves to determine a magnitude of each said R--R interval;

forming a time series with said magnitudes of said R--R intervals;

performing dynamic estimation on said time series to estimate a magnitude of a high frequency component of heart rate variability and to estimate a magnitude of a low frequency component of heart rate variability; and

forming a ratio of said magnitudes of said low frequency and said high frequency components of heart rate variability, said ratio indicating sympathetic neural activity.

6. The method of claim 5, wherein said step of performing dynamic estimation includes performing complex demodulation on said time series.

7. An apparatus for assessing cardiac vulnerability by simultaneously analyzing T-wave alternation and heart rate variability in an ECG, said apparatus comprising:

means for analyzing T-waves in said ECG to determine an amplitude of beat-to-beat alternation;

means for computing the magnitude of each R--R interval to determine a heart rate;

means for analyzing said heart rate to determine a magnitude of variability therein, said magnitude of variability indicating neural influence on said heart; and

means for presenting said amplitude of beat-to-beat alternation and said magnitude of variability to a user.