The noninvasive assessment of microvolt T-wave alternans (TWA) has been established as a useful tool to identify individuals at elevated risk for sudden cardiac death (SCD) from ventricular tachyarrhythmias. Microvolt TWA refers to the presence of subtle beat-to-beat fluctuations in the electrocardiogram’s (ECG) T-wave amplitude and morphology. Although the precise link with arrhythmogenesis is as yet unclear, microvolt TWA probably reflects increased heterogeneity in ventricular repolarization that is a substrate for promoting electrical wavebreak and development of ventricular tachycardia (VT) and ventricular fibrillation (VF).
The results of numerous clinical studies showed that TWA predicts arrhythmic events and all-cause mortality in high-risk patients with ischemic cardiomyopathy and reduced left ventricular (LV) function.Because of its high negative predictive value, TWA could potentially be used to identify those patients who would not benefit from the implantation of an implantable cardioverter-defibrillator (ICD).The prognostic value of microvolt TWA has also been shown for other populations such as post myocardial infarction (MI) patients with preserved cardiac function.
Microvolt TWA testing requires controlled increase of heart rate that is usually achieved by means of physical exercise. In patients who cannot exercise, an atrial pacing protocol upon invasive electrophysiologic study has been shown to yield similar TWA results. For situations when atrial pacing is impossible because of complete atrioventricular (AV) block or atrial fibrillation, recent studies have investigated right ventricular (RV) pacing as an alternative. Their findings were, however, equivocal and only patients with an LV ejection fraction ≤ 40% were studied. Importantly, none of the studies provided follow-up data and information on the prognostic value of the employed pacing protocols.