T-wave alternans (TWA), consisting in an
alternation of the electrocardiographic (ECG) repolarization segment (T-wave),
is a promising index of the risk of sudden cardiac death. By definition, it is
characterized by a frequency component, termed fTWA, that matches
half heart rate. The heart-rate adaptive match filter (AMF) based method is a
technique for automatic TWA identification from the digital ECG. Aim of the
present study was to provide a complete technical description of the filter
able to explain its methodological principles. The AMF is usually realized as a
6th order Butterworth filter with a narrow (0.12 Hz) passing band
centered in fTWA. It is applied in a bidirectional fashion, so that
final filtering order is 12. While extracting the TWA component, the AMF
simultaneously filters out every ECG component including noise and artefacts,
and thus results are very robust. Goodness of the technique was tested using 8
synthetic ECG tracings corrupted by typical noisy factors, such as white random
noise, baseline wanderings, heart-rate variability, and others. Six ECG
tracings were affected by 100 μV TWA, whereas two were not. Results indicate
that the AMF-based method is able to prevent false-positive and false-negative
detections and, thus, represents a useful tool for a reliable TWA
identification.