Identification of time-varying T-wave alternans from 20-minute ECG recordings - Issues related to TWA magnitude threshold and length of ECG time series

Aim of this study was the assessment of a T-wave alternans (TWA) identification procedure based on application of an adaptive match filter (AMF) method, recently developed by ourselves, to a 20-minute digital ECG recording (ECG20). Three-lead ECG20 tracings from 35 patients who survived an acute myocardial infarction (AMI-group) and 35 healthy subjects (H-group) were analysed. The AMI-group showed, on average, increased levels of TWA (P<0.01). Considering that noise may cause false positive TWA detection, a threshold (THR(TWA)) was defined for TWA magnitude (TWAM) as the mean TWAM +2SD over the H-group. TWAM exceeding this threshold identified a TWA-positive (TWA+) subject as one at increased risk of sudden cardiac death. Fifteen (43%) AMI-patients vs. zero H-subjects were detected as TWA+. This result meets clinical expectation. TWA manifested as a non stationary phenomenon that could even be missed in all TWA+ subjects if our AMF (as well as any other technique) was applied to a single short-term 128-beat ECG series, as usually done in previous reports. In conclusion, our AMF-based TWA identification technique, applied to 20-minute ECG recordings, yields a good compromise between reliability of time-varying TWA identification and computational efforts.