Biomedical Engineering Reference
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time (ms)
Fig. 3.4
Six consecutive segmented T waves, concatenated to aid visualization. The alternans
phenomenon is visible in the horizontal slab delimited by the two
horizontal bold lines
hidden in the observed ECG. This is illustrated by the two particular problems
addressed throughout the chapter, which are presented next.
3.1.2
Two ECG Signal Processing Problems
3.1.2.1
T-Wave Alternans Detection
As introduced in the previous section, the T wave corresponds to the ventricular
repolarization stage of the cardiac cycle. The study of this cardiac wave is often
included in the global analysis for risk stratification of cardiac patients. The reason
is that deviations from a normal T-wave template is often linked to future arrhythmia
such as ventricular fibrillation, a serious heart condition leading to sudden cardiac
death. In the T-wave alternans (TWA) phenomenon, the amplitude of consecutive T
waves can vary as little as a few
V. As an example, six successive T waves observed
in a particular ECG lead (data from the STAFF III database [
15
]) are concatenated
in Fig.
3.4
, where the alternans effect is visible between the two horizontal lines:
the alternans amplitude is of the order of 10
μ
V here. Since these subtle variations
are not always apparent to the specialist, specific ECG signal processing techniques
are required for a reliable automatic detection and quantitative estimation of the
alternans phenomenon.
μ
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