Methods for quantifying the morphology and amplitude of cardiac action potential alternans

• US 20050222513A1
• Filed: 03/30/2004
• Published: 10/06/2005
• Est. Priority Date: 03/30/2004
• Status: Active Grant

• Current Assignee: Mortara Instrument, Inc. (Baxter International Inc.)
• Original Assignee: Cardiac Science Operating Company (Cardica Incorporated)
• Inventors: Sagiroglu, Mustafa Hikmet, Hadley, David Milton
• Granted Patent: US 7,174,204 B2
• Time in Patent Office: Days
• US Class Current: 600/515
• CPC Class Codes: A61B 5/349 Detecting specific parameters of the electrocardiograph cycle
• CPC Class Codes: A61B 5/355 Detecting T-waves
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives

Abstract

Methods and apparatus for determining T-wave alternan signatures (i.e., morphology and polarity) derived from a physiologic signal representative of a subject'"'"'s heart activity; assessing changes in the myocardium Action Potential (“AP”) through analysis of the alternan signature derived from a physiologic signal representative of a subject'"'"'s heart activity; and/or assessing spatial disassociation of alternan characteristics that are likely associated with the initiation of re-entrant arrhythmias.

Claims

1. A method of processing data for conditioning T-wave segments of a waveform used in estimating T-wave alternans, comprising:

ascertaining T-wave segments from a physiologic signal having substantially repetitive waveforms of a heart beat;

determining a correction factor based on a set of the repetitive waveforms and a reference waveform; and

applying the correction factor to the T-wave segments to compensate for noise in the signal.

2. The method of claim 1 wherein ascertaining T-wave segments comprises (a) determining an average/median beat estimate having a QRS complex and a T-wave segment and (b) cross-correlating the QRS complexes of the repetitive waveforms with the QRS complex of the average/median beat estimate to align the beats.

3. The method of claim 1 wherein ascertaining T-wave segments comprises determining a heart rate according to an R-R interval and a P-Q interval, and computing a T-wave duration period for the T-wave segment in the beat based on the R-R interval and the P-Q interval.

4. The method of claim 3 wherein ascertaining the T-wave segments further comprises defining an onset time corresponding with the end of a Q-wave segment and an endpoint at the T-wave duration period after the onset time.

5. The method of claim 1 further comprising determining the reference waveform by computing an average/median beat waveform from a set of the repetitive waveforms.

6. The method of claim 5 wherein determining the correction factor comprises determining an amplitude gain factor and/or a DC shift factor by comparing the average/median beat waveform with individual waveforms in the set of repetitive waveforms.

7. The method of claim 5 wherein determining the correction factor comprises determining an amplitude gain factor and/or a DC shift factor by comparing a P-S segment of the average/median beat waveform with corresponding P-S segments of individual waveforms in the set of repetitive waveforms.

8. The method of claim 1 wherein applying the correction factor comprises (a) determining an amplitude gain factor and/or a DC shift factor, (b) computing a polynomial function F_G for the amplitude gain factor and F_C for the DC shift factor, and (c) normalizing the T-wave segments according to the following equation.

9. A method for improving signal to noise ratio in data obtained from a physiologic signal representative of a subject'"'"'s heart activity having plurality of substantially repeating physiologic waveforms, the method comprising:

(a) isolating a plurality of repeating physiologic waveforms from the signal to define a plurality of isolated waveforms;

(b) computing a representative waveform from the isolated waveforms;

(c) comparing the representative waveform with individual isolated waveforms to determine a correction factor having an amplitude gain correction factor G(m) and/or a DC shift correction factor C(m); and

(d) establishing a correction curve fit to the correction factor from the isolated individual waveforms.

10. The method of claim 9, further comprising normalizing the isolated individual waveforms by applying the correction curve to the isolated individual waveforms.

11. The method of claim 9 further comprising deriving a respiration rate from a sequence of amplitude gain correction factors G(m) after determining the correction factor in procedure (c).

12. The method of claim 9, further comprising deriving a respiration rate by computing from a sequence of amplitude gain factors G(m) the time between peaks of the sequence, the average time between a plurality of peaks in the sequence, and/or the peak in the power of a Fourier transform computed from the sequence.

13. The method of claim 9 further comprising repeating procedures (a) through (d) for each of a plurality of signals representative of a subject'"'"'s heart activity.

14. The method of claim 9 further comprising acquiring the physiological signal while performing a stress test on the subject.

15. The method of claim 9 further comprising acquiring the physiological signal by obtaining ECG data of the subject'"'"'s heart.

16. The method of claim 9 wherein identifying the T-wave segments comprises (a) determining an average/median beat estimate having a QRS complex and a T-wave segment and (b) cross-correlating the QRS complexes of the repetitive waveforms with the QRS complex of the average/median beat estimate to align the beats.

17. The method of claim 9 wherein identifying T-wave segments comprises temporally identifying an onset and a conclusion of individual T-wave segments.

18. The method of claim 9 wherein identifying T-wave segments comprises temporally identifying an onset and a pre-determined T-wave duration to set a time-defined conclusion of at least some of the T-wave segments.

19. The method of claim 9 further comprising aligning a plurality of the T-wave segments before computing the estimated alternan signatures.

20. The method of claim 19 wherein aligning the T-wave segments comprises using a consistently identifiable portion common to several of the repeating waveforms to temporally align the T-wave segments before computing the estimated alternan signatures in procedure (b).

21. The method of claim 9 further comprising determining a beat estimate from the repeating physiological waveforms and using the beat estimate to establish a best estimate for the onset of the T-wave segments.

22. The method of claim 21 wherein the best estimate for the onset of the T-wave segments comprises a time-window definition for identifying the T-wave segments.

23. A system for collecting and conditioning data regarding T-wave segments for use in estimating T-wave alternans, the system comprising:

a data source configured to obtain and/or retain digitized data of a physiologic signal having substantially repetitive waveforms of a heart beat; and

a computer operatively coupled to the data source, the computer having a computer operable medium containing instructions for (a) ascertaining T-wave segments from the physiologic signal, (b) determining a correction factor related to noise in the signal based on a set of the repetitive waveforms and a reference waveform, and (c) applying the correction factor to the T-wave segments to compensate for noise in the signal.

24. The system of claim 23 wherein the data source further comprises a stress test device and electrodes for recording the physiologic signal.

25. The system of claim 23 wherein the instructions contained in the computer operable medium for ascertaining T-wave segments comprise (a) determining an average/median beat estimate having a QRS complex and a T-wave segment and (b) cross-correlating the QRS complexes of the repetitive waveforms with the QRS complex of the average/median beat estimate to align the beats.

26. The system of claim 23 wherein the instructions contained in the computer operable medium for ascertaining T-wave segments comprise determining a heart rate according to an R-R interval and a P-Q interval, and computing a T-wave duration period for the T-wave segment in the beat based on the R-R interval and the P-Q interval.

27. The system of claim 23 wherein the instructions contained in the computer operable medium for ascertaining T-wave segments comprise defining an onset time corresponding with the end of a Q-wave segment and an endpoint at a predetermined T-wave duration period after the onset time.

28. The system of claim 23 wherein the instructions contained in the computer operable medium for determining a correction factor related to noise further comprise determining the reference waveform by computing an average/median beat waveform from a set of the repetitive waveforms.

29. The system of claim 23 wherein the instructions contained in the computer operable medium for determining a correction factor related to noise comprise determining an amplitude gain factor and/or a DC shift factor by comparing the average/median beat waveform with individual waveforms in the set of repetitive waveforms.

30. The system of claim 23 wherein the instructions contained in the computer operable medium for determining a correction factor related to noise comprise determining an amplitude gain factor and/or a DC shift factor by comparing a P-S segment of the average/median beat waveform with corresponding P-S segments of individual waveforms in the set of repetitive waveforms.

31. The system of claim 23 wherein the instructions contained in the computer operable medium for applying the correction factor comprise (a) determining an amplitude gain factor and/or a DC shift factor, (b) computing a polynomial function F_G for the amplitude gain factor and F_C for the DC shift factor, and (c) normalizing the T-wave segments according to the following equation.