The Microvolt T-Wave Alternans Test

Sudden cardiac death (SCD) still remains a major cause of mortality among patients with ischaemic and nonischaemic cardiomyopathy, and implantable cardioverter-defibrillator (ICD) therapy has been shown to improve survival in these patients. However, the use of a prophylactic ICD therapy in clinical practice needs accurate identification of patients likely to benefit from it, considering the high incidence of device-related complications, the psychological consequences of ICD implantation and social costs. Current risk stratification for SCD is mainly based on assessment of ejection fraction and it is strongly influenced by the largest clinical trials on primary prevention: the MADIT II and SCD-HeFT studies. In recent years, the microvolt T-wave alternans test (MTWA) is emerging as a powerful non-invasive tool for risk stratification of SCD. MWTA is a beat-to-beat alternation in the amplitude of the T wave on the order of microvolts, which can be assessed during an exercise test, pharmacological stress or atrial pacing. MTWA has been associated with unidirectional block, re-entry and initiation of ventricular fibrillation in animal studies. There is strong evidence that intracellular calcium cycling plays a key role in the mechanism of MTWA. Several large clinical trials have shown that MTWA is comparable or superior to other noninvasive markers and to electrophysiological study in risk stratification of SCD. The very high negative predictive value of MTWA may provide a better selection of patients who would be likely or not likely to benefit from ICD implantation. Broad evidence-based data suggest that non-invasive MTWA may improve the accuracy of primary prevention of SCD in patients with ischaemic and non-ischaemic cardiomyopathy. Further studies are needed to evaluate the role of MTWA testing as an integral part of risk stratification, in combination with additional risk markers.