Method and apparatus for determining T-wave marker points during QT dispersion analysis

• US 5,792,065 A
• Filed: 03/18/1997
• Issued: 08/11/1998
• Est. Priority Date: 03/18/1997
• Status: Expired due to Term

• Current Assignee: Marquette Medical Systems, Inc.
• Original Assignee: Marquette Medical Systems, Inc.
• Inventors: Xue, Qiuzhen, Reddy, Shankara
• Primary Examiner(s): Kamm, William E.
• Assistant Examiner(s): Layno, Carl H.
• Application Number:
  US08/819,075
• Time in Patent Office: 511 Days
• Field of Search: 600/516, 600/518
• US Class Current: 600/516
• CPC Class Codes: A61B 5/35 by template matching

Abstract

A method and apparatus for analyzing QT dispersions in ECG lead signals, comprising acquiring a plurality of ECG lead signals, filtering said signals to remove noise without distorting the T-wave morphology, determining critical T-wave marker points, and calculating QT dispersion and their heart rate corrected values from the determined markers. The apparatus comprises a processor programmed to perform these functions.

Claims

1. A method of analyzing QT dispersions in ECG lead signals, comprising the steps of:

acquiring a plurality of ECG lead signals,

filtering said signals to reduce noise without distorting the T-wave morphology,

determining critical T-wave marker points,

calculating QT dispersion and their heart rate corrected values from the determined T-wave maker points.

2. The method set form in claim 1 and including the step of classifying the T-waves into different groups.

3. The method set forth in claim 1 wherein said filtering step comprises storing each of said ECG lead signals in a column-wise matrix and reconstructing each ECG signal by decomposing the matrix by the dimension reduction technique.

4. The method set forth in claim 1 wherein the step of determining critical T-wave maker points comprises the steps of determining T-wave peak and T-wave end.

5. The method set forth in claim 1 wherein said filtering step comprises storing each of said ECG lead signals in a column-wise matrix A and reconstructing each ECG signal by decomposing the matrix A by the dimension reduction technique into three matrices:

A₁ =U₁ S₁ V₁^T

where;

U and V are each orthogonal matrices;

S is a diagonal matrix;

S₁,S₂, . . . S_k !diag whose elements have monotonically decreasing values, i.e., S₁ >

S₂ >

. . . >

S_k ; and

k<

n, original dimension.

6. The method set forth in claim 5 and including the step of generating a detection function from the absolute difference between successive samples of at least some of the reconstructed ECG signals and determining the T-peak from the valley points of the detection functions.

7. The method set forth in claim 6 and including the step of determining the valley point of the detection function by regional centering.

8. The method set forth in claim 7 wherein the step of determining critical T-wave marker points includes the steps of determining T-end from the intersection of the maximum slope of the reconstituted ECG signals after T-peak and a threshold value plus a non-linear correction function based on T-wave amplitude.

9. The method set forth in claim 8 and including the steps of disregarding those ECG signals which are noisy, have flat T-waves or T-waves with undefined patterns.

10. The method set forth in claim 9 and including the step of classifying the T-waves into different groups.

11. The method set forth in claim 6 wherein the step of determining critical T-wave marker points includes the steps of generating templates of at least some of the ECG lead signals and matching measured ECG signals to said templates.

12. The method set forth in claim 11 and including the steps of disregarding those ECG signals which are noisy, have flat T-waves or T-waves with undefined patterns.

13. The method set forth in claim 12 and including the step of classifying the T-waves into different groups.

14. The method set forth in claim 1 and including the steps of determining the absolute difference between successive samples of at least some of the reconstructed ECG signals, generating a detection function from said absolute difference, and determining the T-peak from the valley points of the detection functions.

15. The method set forth in claim 14 wherein the steps of determining the valley point of the detection function comprises regional centering.

16. The method set forth in claim 14 wherein the step of determining critical T-wave marker points includes the steps of determining T-end from the intersection of the least-square fitted line around the maximum slope of the reconstituted ECG signals after T-peak and the threshold plus a non-linear correction function based on T-amplitude.

17. The method set forth in claim 16 and including the steps of disregarding those ECG signals which are noisy, have flat T-waves or T-waves with undefined patterns.

18. The method set forth in claim 14 wherein the step of determining critical T-wave marker points includes the steps of generating templates of at least some of the ECG lead signals and matching measured ECG signals to said templates.

19. The method set forth in claim 18 and including the step of disregarding those ECG signals which are noisy, have flat T-waves or T-waves with undefined patterns.

20. Apparatus for analyzing QT dispersions in ECG lead signals, said apparatus including:

means for acquiring a plurality of ECG lead signals,

means for filtering said signals to reduce noise without distorting the T-wave morphology,

means for determining critical T-wave marker points, and

means for calculating QT dispersion and their heart rate corrected values from the determined markers.

21. The apparatus set forth in claim 20 and including means for classifying the T-waves into different groups.

22. The apparatus set forth in claim 20 wherein means for filtering comprises means for storing each of said ECG lead signals in a column-wise matrix and means for reconstructing each ECG signal by decomposing the matrix by the dimension reduction technique.

23. The apparatus set forth in claim 20 wherein said means for filtering comprises means for storing each of said ECG lead signals in a column-wise matrix A and means for reconstructing each ECG signal by decomposing the matrix A by the dimension reduction technique into three sub-matrices:

A₁ =U₁ S₁ V₁^T

where;

U and V are each orthogonal matrices;

S is a diagonal matrix;

S₁,S₂, . . . S_k !diag whose elements have monotonically decreasing values, i.e., S₁ >

S₂ >

. . . >

S_k.

24. The apparatus set forth in claim 20 wherein the means for determining critical T-wave marker points comprises means for determining T-wave peak and T-wave end.

25. The apparatus set forth in claim 20 and including means for generating a detection function from the absolute difference between successive samples of at least some of the reconstructed ECG signals and means for determining the T-peak from the valley points of the detection functions.

26. The apparatus set forth in claim 25 wherein the means for determining the T-peak includes means for the regional centering of the valley points.

27. The apparatus set forth in claim 25 wherein the means for determining critical T-wave marker points includes means for determining T-end from the intersection of the maximum slope of the reconstituted ECG signals after T-peak and the threshold plus a non-linear correction function based on T-amplitude.

28. The apparatus set forth in claim 25 and including means for disregarding those ECG signals which are noisy, have flat T-waves or T-waves with undefined patterns.

29. The apparatus set forth in claim 25 wherein the means for determining critical T-wave marker points includes means for generating templates of at least some of the ECG lead signals and matching measured ECG signals to said templates.

30. The apparatus set forth in claim 29 and including means for disregarding those ECG signals which are noisy, have flat T-waves or T-waves with undefined patterns.

31. The apparatus set forth in claim 20 and including means for generating a detection function from the absolute difference between successive samples of at least some of the reconstructed ECG signals and means for determining the T-peak from the valley points of the detection functions.

32. The apparatus set forth in claim 31 wherein the means for determining the T-peak includes means for the regional centering of the valley points.

33. The apparatus set forth in claim 32 wherein the means for determining critical T-wave marker points includes means for determining T-end from the intersection of the maximum slope of the reconstituted ECG signals after T-peak and the threshold plus a non-linear correction function based on T-amplitude.

34. The apparatus set forth in claim 33 and including means for disregarding those ECG signals which are noisy, have flat T-waves or T-waves with undefined patterns.

35. The method set forth in claim 34 and including means for classifying the T-waves into different groups.

36. The apparatus set forth in claim 32 wherein the means for determining critical T-wave marker points includes means for generating templates of at least some of the ECG lead signals and matching measured ECG signals to said templates.

37. The apparatus set forth in claim 36 and including means for disregarding those ECG signals which are noisy, have flat T-waves or T-waves with undefined patterns.

38. The apparatus set forth in claim 37 and including means for classifying the T-waves into different groups.

39. A method of analyzing QT dispersions in acquired ECG lead signals, comprising the steps of:

determining critical T-wave markers of the acquired ECG signals,

calculating QT dispersion and their heart rate corrected values from the determined T-wave markers.

40. The method set forth in claim 39 wherein the step of determining the T-wave markers comprises determining T-peak and T-end.

41. Apparatus for analyzing QT dispersions acquired in ECG lead signals, said apparatus including:

means for determining critical T-wave markers, and

means for calculating QT dispersion and their heart rate corrected values from the determined T-wave markers.

42. The method set forth in claim 41 and wherein the means for determining the T-wave markers comprises means for determining T-wave peak and T-wave end.