Heart injury caused by ischemia, may result in certain temporal changes in specific electrocardiographic (ECG) leads. Such changes can normally be detected and sometimes localized by conventional analysis of the ST-segment. However, with small and gradual occlusions, ischemia-related changes may not be measurable in the electrocardiogram. Similarly, during the early stages of acute angina, conventional ECG analysis does not rapidly capture and localize ischemic injury. Further, a fast and reliable detection of reperfusion (restored perfusion) using ECG may become a marker of reestablished blood flow after balloon angioplasty in the cardiac cath lab, or after thrombolytic therapy of patients with myocardial infarction.

There is evidence in recent literature, that ischemic events cause changes not only to the ST segment of the ECG, but also to the QRS complex. The aim of this particular project is to study intra-QRS manifestations of coronary ischemia. We have developed a new method of detecting ischemic changes in the ECG, based on wavelet analysis. Time-frequency distributions of the QRS-T complex were obtained using complex-valued wavelets of Morlet applied as a set of band-pass filters. Analysis of signals collected in controlled animal experiments revealed increased QRS spectral components in the range 20-30 Hz during short-lasting occlusion of coronary arteries. This phenomenon was reversible, disappearing with reperfusion.

In another pilot study, electrocardiographic recordings of patients with left and right coronary stenosis taken before and after percutaneous transluminal coronary angioplasty (PTCA) were analyzed using the continuous wavelet transform. Time-frequency distributions were obtained for different leads in order to examine the dynamics of the QRS-spectrum and establish features specific of ischemia in the time-frequency domain. We found relevant changes in the mid-frequency range, reflecting the ECG's response to angioplasty. The changes tended to appear in ECG leads projecting anatomically the ischemic zones. These results were confirmed in another study on ECGs taken during PTCA.

Time-frequency distributions of the ECG during the QRS may thus be another electrocardiographic indicator of ischemia, alternative to ST-level in standard ECG or body surface mapping.

by Boris Gramatikov, PhD
 

Related publications

1. Nitish V. Thakor, Boris Gramatikov and David Sherman. Wavelet (Time-Scale) Analysis in Biomedical Signal Processing. In The Biomedical Engineering Handbook, Ed. Joseph Bronzino, 2nd Edition., Volume I, Section VI (Biomedical Signal Analysis), Chapter 56, pp. 56.1 - 56.27. CRC Press LLC, IEEE Press, December 1999.

2. Gramatikov, B., Brinker, J., Yi-chun, S., Thakor, N. Wavelet analysis and time-frequency distributions of the Body Surface ECG before and after angioplasty.   Computer Methods and Programs in Biomedicine.  Vol. 62, No.2, June 2000, pp.87-98.

3. Shenai M., Gramatikov, B.I., Thakor, N.V. Computer models of depolarization alterations Induced by myocardial ischemia. The effect of superimposed ischemic inhomogeneities on propagation in space and time-frequency domains.  Journal of Biological Systems, Vol. 7, No.4, 1999,  pp. 553-574.

4. Gramatikov, B., Yi-chun, S., Rix, H., Caminal, P., Thakor, N.  Multiresolution wavelet analysis of the body surface ECG before and after angioplasty. Annals of Biomedical Engineering, Vol. 23, 1995, pp. 553-561.

5. Gramatikov, B. Iyer, V.  Ischemia-Related Depolarization Changes Detected in Body-Surface Ambulatory ECG Recordings.   Chicago 2000 World Congress on Medical Physics and Biomedical Engineering, July 23-28, 2000. Short paper. In Congress 2000 Proceedings on CD-ROM.

6. Shenai, M., Gramatikov, B., Thakor, N.V. Computer modeling of depolarization changes induced by myocardial ischemia. Computers in Cardiology 1998, Vol. 25, Cleveland, Ohio, Sept.13-16, 1998. pp. 321-324.

7. Gramatikov, B.I., Provaznik, I., Thakor, N.V. Depolarization Changes During Ischemia Detected Through Time-Frequency Analysis of the Intracardiac Electrogram. Computers in Cardiology 1998, Vol. 25, Cleveland, Ohio, Sept.13-16, 1998, pp. 289-292.

8. Gramatikov, B., Detschew, V., Grieszbach, G. Dynamische Spektralanalyse des EKG zur fruehzeitigen Erkennung von Myokardischaemie (Dynamic spectral analysis of the ECG for early detection of myocardial ischaemia). 39th International Colloquium of the Technical University Ilmenau, Sept.27-30, 1994, Ilmenau, Germany. In Proceedings, B-2.2.2., Vol.2, pp. 384-388.

9. Thakor, N., Yi-chun, S., Gramatikov, B., Rix, H., Caminal, P. Multiresolution wavelet analysis of ECG: Detection of ischemia and reperfusion in angioplasty. World Congress on Medical Physics and Biomedical Engineering, Rio de Janeiro, Brazil, August 1994, In Proceedings: RT15-2.4, p.392

10. Gramatikov, B, Thakor, N. Wavelet analysis of coronary artery occlusion related changes in ECG. 15th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, October 28-31, 1993, San Diego, California, USA. In Proceedings, p.731.

11. Thakor, N., Gramatikov, B., Mita, M. Multiresolution Wavelet Analysis of ECG during ischemia and reperfusion. Computers in Cardiology, London, 5-8 Sept. 1993. In Proceedings (IEEE Comp.Soc.Press), pp.895-898.