Microvolt T Wave Alternans Test (MTWA) not Predictive of Ventricular Arrhythias Following MI

November 6, 2007 By Alexandra M. Palmer [mailto:apalmer@perfuse.org]

Orlando, FL: Results from the MASTER I trial show the Microvolt T Wave Alternans Test (MTWA) is unable to predict arrhythmias in post-heart attack patients with abnormal ejection fraction (EF). The study data was presented at the American Heart Association 2007 Scientific Sessions.

The MASTER I trial was a multicenter study which analyzed 575 patients receiving standardized therapy at 50 U.S. centers. Investigators went into the study with the vision that MTWA testing would be able to single out the participants who would most benefit from ICD implantation. The inclusion criteria selected patients who 1) were not in atrial fibrillation and 2) met the MADIT-2 indications for implanting implantable cardioverter defibrillators (ICDs). The duration of follow-up was a minimum of 2 years.

Microvolt T Wave Alternans (MTWA) testing followed by ICD implantation was performed on the patients. The MTWA test is a measure of the presence of fluctuations known as “alternans” in the T wave of an ECG.

The outcome of the trial revealed MTWA testing to be negative, positive and indeterminate in 214, 293 and 68 patients, respectively. Assessment of the primary endpoint, ICD shocks, suggested no significant difference in prediction of arrhythmias between positive and negative-testing patients. Although a higher risk of all-cause death was associated with patients displaying abnormal MTWA tests, ICD shocks did not indicate a higher chance of arrhythmias in this group of people.

Further areas of study include finding the reason for the connection between high mortality and nonnegative MTWA tests as well as an answer to what makes MTWA testing a better predictor of total mortality than of ICD shocks.

The fact that ICD shocks, known to overestimate true mortality events, served as the primary endpoint, limits the accuracy of the results. This is in agreement with previous studies that have shown MTWA testing to be less predictive with ICD shocks as the endpoint. The analysis was underpowered due to a low overall event rate introduced to the study by the exclusion of patients with the highest event rates: those with atrial fibrillation. In addition, the fact that the study only enrolled U.S. patients limits the broad applicability of the results.

This study extends two prior observations: 1) the aforementioned “alternans” may signal the possibility of cardiac arrest and 2) an abnormal MTWA test translates into a greater chance of arrhythmias.

This study was supported by Medtronic Inc.

References 1. Dr. Theodore Chow. Lindner Center at Christ Hospital, Cincinnati, OH. As presented at AHA 2007.