T-wave alternans rate of change with exercise for cardiac risk assessment

T-wave alternans (TWA ) amplitude is an index of risk for arrhythmic events. It increases with heart rate (HR) so that its evaluation is often performed under exercise. This study aims to investigate if TWA rate of change with HR can be also used for risk assessment. Our HR adaptive match filter for automatic TWA identification was applied to exercise ECG recordings of 266 ICD patients, 76 of which developed ventricular arrhythmias during the 4-year follow-up (ICD_Cases), and 190 did not (ICD_Controls). TWA amplitude was measured at 80 bpm (TWA80) and at 115 bpm (TWA115). Instead, TWA rate of change was evaluated as the ratio (TWAratio) and difference (TWAdiff) between TWA115 and TWA80. TWA predictive power was quantified as the area under the receiver operating curve (AUC) when discriminating the two ICD groups. Compared to ICD_Controls, ICD_Cases showed significantly higher TWA80 (22 μV vs. 16 μV) but not TWA115 (24 μV vs. 30 μV vs). The latter group also showed significantly lower TWAratio (1.05 vs. 1.63) and TWAdiff (1 μV vs. 11 μV). TWAratio showed the highest AUC (0.6914) followed by TWAdiff (0.6816), TWA80 (0.6414) and TWA115 (0.4547). Thus, TWA rate of change with HR provided better risk assessment for the occurrence of ventricular arrhythmias than TWA amplitude at both fast (115 bpm) and slow (80 bpm) HRs.