T-wave Alternans Dependency on T-wave Amplitude in Exercise Electrocardiographic Recordings

T-wave alternans (TWA), an electrophysiologic phenomenon which manifests as an everyother-beat alternation of the electrocardiographic (ECG) T-wave amplitude or shape, is generally associated to malignant ventricular arrhythmias and sudden cardiac death. TWA is usually identified with no adjustment for T-wave amplitude. However, a possible dependency of TWA on T-wave amplitude has been recently hypothesized. Evaluation of such dependency in exercise ECG tracings was the aim of the present work. Exercise ECG recordings from 58 patients with an implanted cardiac defibrillator were analyzed. TWA was identified using our heart-rate adaptive match filter based method, whereas T-wave amplitude was quantified as the absolute value of the ECG amplitude along the repolarization segment. Inter-patients and intra-patient (inter-leads) TWA dependency on T-wave amplitude was evaluated by computing the correlation coefficient (ρ) between the two quantities. Results indicate a weak (0.28≤ρ≤0.51, P<0.05) inter-patients association between TWA and T-wave amplitude, which were instead linked by a strong (r=0.86, P<0.05) intra-patient (inter-leads) association.