The power of exercise-induced T-wave alternans to predict ventricular arrhythmias in patients with implanted cardiac defibrillator

Exercise-induced T-wave alternans (TWA) predictive power for the occurrence of ventricular arrhythmias was evaluated in 67 patients with an implanted cardiac defibrillator (ICD). During the 4-year follow-up, electrocardiographic (ECG) tracings were recorded while performing a bicycle ergometer test with increasing workload ranging from zero (NoWL) to the patient’s maximal capacity (MaxWL). After the follow-up, patients were classified as either ICD_Cases (n=29), if developed ventricular tachycardia/fibrillation, or ICD_Controls (n=38). TWA was quantified using our heart-rate adaptive match filter. Compared to NoWL, MaxWL was characterized by faster heart rates and higher TWA in both ICD_Cases (12-18 µV vs. 20-39 µV; P<0.05) and ICD_Controls (9-15 µV vs. 20-32 µV; P<0.05 ). Still, TWA was able to discriminate the two ICD groups during NoWL (sensitivity=59-83%, specificity=53-84%) but not MaxWL (sensitivity =55-69%, specificity=39-74%). Thus, this retrospective observational case-control study suggests that TWA predictive power for the occurrence of ventricular arrhythmias could increase at low heart rates.