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 lCD patients, 76 of which developed ventricular tachycardia or fibrillation during the 4-year follow-up (lCD_Cases), and 190 did not (lCD_Controls). TWA ability to discriminate lCD_Cases from lCD_Controls was evaluated using the area under the receiver operating characteristic (AUC). At 80 bpm TW AA was significantly higher in the lCD_Cases than the lCD_Controls (median: 23 mu V vs. 16 mu V, P= 0.0018; AUC= 0.672), whereas at 120 bpm TWAA was comparable in the two groups (median: 36 mu V for both the lCD_Cases and lCD_Controls; AUC= 0.487). Thus, in our lCD populations, TWA predictive power for the occurrence of ventricular arrhythmias was higher at 80 bpm, when TW AA was smaller, than at 120 bpm, when TW AA was higher.