Method and apparatus for monitoring cardiac patients for T-wave alternans

• US 20030060724A1
• Filed: 07/13/2001
• Published: 03/27/2003
• Est. Priority Date: 07/13/2001
• Status: Active Grant

• Current Assignee: Welch Allyn Incorporated
• Original Assignee: Cardiac Science Operating Company (Cardica Incorporated)
• Inventors: Thiagarajan, Srikanth, Lin, Dongping
• Granted Patent: US 6,983,183 B2
• Time in Patent Office: Days
• US Class Current: 600/515
• CPC Class Codes: A61B 5/35 by template matching
• CPC Class Codes: A61B 5/363 Detecting tachycardia or bradycardia

Abstract

A system to detect the presence or absence of T wave alternans is described based on statistical tests and periodicity transform. T wave and ST segment boundaries are detected in multi-lead ECG signals acquired from the regular clinical leads. Once the fiducial point and the above boundaries are delineated, computation of regular parameters like T wave amplitude, area under the T waves or segments of T wave, ST segment slope and/or the curvature of T wave are performed. Each parameter forms a rolling array of values with each successive beat. The array of values, or the time series, is used to make the decision about the T wave alternans. Two different methods are employed based on periodicity transforms and statistical tests. A set of numerical values (e.g. norm of the projection on to p-2 space, sums of adjacent terms after the trend removal, t-value, and number of deviations from alternans pattern) are all computed and compared to threshold values. Threshold values are computed from past information and experience with clinical databases and simulations. Final system comprises a software module, which can be part of the existing ECG monitoring programs as well as external defibrillator modules, apart from being stand-alone algorithms.

Claims

1. An apparatus for detecting TWA in potential cardiac patients comprising:

a sensor adapted to sense an ECG from a patient;

a T wave detector adapted to detect a plurality of T waves in said ECG;

an analyzer adapted to perform at least one of the statistical tests and a periodicity transform on characteristics of said T waves to make a decision on whether TWA are present or not.

2. The apparatus of claim 1 wherein said analyzer is adapted to perform at least one of the following statistical tests:

difference in means, adjacent values, Raleigh and number of zero crossings.

3. The apparatus of claim 1 wherein said analyzer performs both said statistical test and said periodicity transform, said analyzer including a combining element adapted to combine the results of said tests to generate said decision.

4. The apparatus of claim 1 wherein said T wave detector is adapted to detect at least one of the following T wave characteristics:

peak value, area under the T wave, curvature, ST segment slope, and area of smaller T wave segments.

5. The apparatus of claim 4 wherein said analyzer is adapted to determine said characteristic for a plurality of consecutive T waves to form a series, said analyzer being adapted to operate on said series.

6. The apparatus of claim 5 further comprising a template generator adapted to generate a template for said T waves based on the characteristics of a plurality of T waves.

7. The apparatus of claim 6 further comprising a comparator adapted to compare a current T wave to said template, and to reject said current T waves from processing if it differs substantially from said template.

8. An apparatus for detecting TWA in potential cardiac patients comprising:

a sensor adapted to sense an ECG from a patient;

a T wave detector adapted to detect a plurality of T waves in said ECG;

an analyzer adapted to perform a periodicity transform on characteristics of said T waves to make a decision on whether TWA are present or not.

9. The apparatus of claim 8 wherein said T wave detector is adapted to detect at least one of the following T wave characteristics:

peak value, area under the T wave, curvature, ST segment slope, and area of smaller T wave segments.

10. The apparatus of claim 9 wherein said analyzer is adapted to determine said characteristic for a plurality of consecutive T waves to form a series, said analyzer being adapted to operate on said series.

11. The apparatus of claim 10 wherein said analyzer is adapted to project said series into 1-p space to detrend said series.

12. The apparatus of claim 11 wherein said analyzer is adapted to project said series into a 1-p space and a 2-p space, to determine a result for each projection and to combine the results of said projections to make said decision.

13. The apparatus of claim 8 further comprising a template generator adapted to generate a template for said T waves based on the characteristics of a plurality of T waves.

14. The apparatus of claim 13 further comprising a comparator adapted to compare a current T wave to said template, and to reject said current T waves from processing if it differs substantially from said template.

15. A method of detecting the presence of TWA in a cardiac patient comprising the steps of:

detecting an ECG from the patient;

sensing a plurality of T waves in said ECG;

determining a characteristic of said T waves;

performing a periodic transform on said characteristics;

16. The method of claim 15 further comprising the step of making a decision about the presence of TWA based on said periodic transform.

17. The method of claim 15 further comprising performing at least one statistic test on said characteristics and generating a result based on said statistic test.

18. The method of claim 16 further comprising performing a plurality of different statistic tests on said characteristics, generating a result for each test and combining said results into a single decision.

19. The method of claim 15 further comprising generating a template based on said characteristic and using said template to discriminate between normal and ectopic beats.

20. A method of detecting the presence of TWA in a cardiac patient comprising the steps of:

detecting an ECG from the patient;

sensing a plurality of T waves in said ECG;

determining a characteristic of said T waves;

performing a statistical test on said characteristics;

making a decision about the presence of TWA based on said statistical tests.