Current developments in microvolt T-wave alternans.
Microvolt T-wave alternans (MTWA), the beat-to-beat fluctuation in T wave amplitude and morphology, is closely linked to vulnerability to ventricular arrhythmias in various experimental and clinical conditions. Clinically, MTWA is most commonly measured using the spectral method, although non-spectral methods for its assessment from ambulatory electrocardiographical recordings also have been developed. Recent studies suggest that the quantitative assessment of TWA may also be clinically relevant. The standardisation of the criteria for abnormal MTWA test still needs to be completed. The expansion of indications for implantable cardioverter-defibrillator (ICD) therapy following the positive results of the MADIT-II and SCD-HeFT trials might have unacceptable economic and medical consequences, and therefore new tests are needed to better discriminate patients who will and will not benefit from ICD implantation. A recent meta-analysis of MTWA studies revealed an overall positive predictive value for arrhythmic events of 19.3%, negative predictive value of 97.2%, and 3.77% univariate relative risk of arrhythmic events. The negative predictive value of MTWA in MADIT-II type patients has been reported to be 97.5%. The predictive value of the test varied significantly in different patient population. Current data support the use of MTWA testing for evaluation of patients with low ejection fraction who are considered for ICD implantation. The independence of the prognostic value of MTWA from other clinical and electrophysiological variables needs further confirmation.