Session P79.2

Analysis of the T Wave Alternans Phenomenon with ECG Amplitude Modulation and Baseline Wander

O Meste*, D Janusek, R Maniewski

Université de Nice
Sophia Antipolis, France

It is well known that the event called T wave alternans (TWA) is a marker of cardiac instability and high risk of sudden death. Recently, index of presence of such event are used to decide whether a device has to be implanted. This phenomenon is observable with high rate of internal pacing, during coronary angioplasty intervention or when patients perform graded and maximal exercise test. The latter experiment does not need surgery and is a good candidate for TWA investigation. Unfortunately, because of the body motion observable during the exercise and an increasing tidal volume due to the effort, it exists a large modulation of the ECG signal added to a baseline wander larger than during resting conditions. Note that the ECG amplitude modulation and the baseline are also present in classical TWA records. It exists very few studies linking the TWA analysis performance to these sources of artifacts.
In the work presented here we propose a new approach of the TWA modeling. For this aim, the ECG amplitude modulation and the baseline wander in the ST-T segment are approximated by a scaling factor applied to the T wave added to a constant. It is clear than even with this simple modeling, any TWA detector and estimator will perform badly as the random values of these two parameters increase. Thanks to this simplification, the proposed global model of each ST-T segment is constituted by the scaled T wave, an offset and the shape of the alternans. Note that since these components are not known, the problem of the estimation is ill posed. In addition to the modeling we also introduce a method to address the problem of the estimation of the T wave, the offset and the alternans shape and their respective coefficients.
Finally, results from the application of the proposed method to realistic simulated records exhibit better performances compared to classical approaches. Even with real data, we show that the TWA phenomenon can be considered without suffering from the artifacts under the scope of this work.

(Abstract Control Number: 17)