Dependency of t-wave alternans predictive power for the occurrence of ventricular arrhythmias on heart rate

T-wave alternans (TWA), a promising index of cardiac electrical instability, is known to increase its amplitude (TWAA) with heart rate. Still, the effect of heart rate on the TWA predictive power for the occurrence of ventricular arrhythmias remains unclear. Thus, aim of the present study was to evaluate if fast heart rates, besides inducing higher amplitude TWA, also enhances TWA ability to discriminate patients at increased risk of major cardiac events. To this aim, our heart-rate adaptive match filter was used to measure TWA at 80 bpm and at 120 bpm in exercise ECGs of 266 ICD patients, 76 of which developed ventricular tachycardia or fibrillation during the 4-year follow-up (ICD_Cases), and 190 did not (ICD_Controls). TWA ability to discriminate ICD_Cases from ICD_Controls was evaluated using the area under the receiver operating characteristic (AUC). At 80 bpm TWAA was significantly higher in the ICD_Cases than the ICD_Controls (median: 23 μV vs. 16 μV, P=0.0018; AUC=0.672), whereas at 120 bpm TWAA was comparable in the two groups (median: 36 μV for both the ICD_ Cases and ICD_Controls; AUC=0.487). Thus, in our ICD populations, TWA predictive power for the occurrence of ventricular arrhythmias was higher at 80 bpm, when TWAA was smaller, than at 120 bpm, when TWAA was higher.