Identification of repolarization-alternans time occurrence improves discrimination of abnormal cases

Repolarization alternans (RA) is characterized by its amplitude and instant of occurrence along the JT segment, but only the amplitude is generally used to discriminate abnormal cases. The role of RA timing was focused in the present study. ECGs from 201 coronary-artery-disease (CAD) patients and 167 control-healthy (CH) subjects were analyzed by our heart-rate adaptive match filter (AMF) method to parameterize RA in terms of amplitude (RAA; mu V) and time distance (RAD; ms) from the T-wave apex, and to identify an RA normality region out of which abnormal cases (RA+) are expected to fall. Compared to our CH subjects, the CAD patients showed significant higher mean RAA (19 +/- 9 mu V vs. 17 +/- 15 mu V) and RAD variability (-33 +/- 37 ms vs. -27 +/- 23 ms). Especially, RA+ cases occurring abnormally early (RAD<-82 ms) or late (RAD>28 ms) were, overall, 29, more than twice of those (11) characterized by an abnormally high RAA (RAA>35 mu V).