T-wave alternans immediately after an acute myocardial infarction

Abstract

The article by Yu et al published ahead of print in the Journal on September 13, 2011, assessed the value of T-wave alternans (TWA) in predicting sudden cardiac death (SCD) in 227 consecutive patients 1 to 15 days after an acute myocardial infarction (AMI) using the modified moving average in 24-hour ambulatory electrocardiograms. The authors showed that TWA 47 μV or more predicted SCD or malignant ventricular arrhythmia, and its predictive value improved further when the frequency of TWA to 5 episodes or more, with this threshold, increased. What is unique about the study is that it focuses on the immediate period after an AMI in contrast to the bulk of relevant studies that have evaluated patients with chronic myocardial infarction leading to ischemic cardiomyopathy and the introduction of the frequency of 5 or more episodes of TWA above the threshold of 47 μV or more chosen a priori as a predictive variable of SCD, which was evaluated in a multivariate analysis. I would like to engage the authors on the following issues, hoping that I will receive a response. (1) The authors “selected 2 precordial leads V2 and V5 because TWA is a regionally specific phenomenon, and unipolar leads are capable of detecting TWA in ischemic and scar area of cardiac muscle,” to use their words verbatim, yet they did not use an inferior lead or consider the different culprit coronary artery in AMI, or AMI location, as variables; is it not possible that an inferior and/or posterior AMI would not yield a TWA of 47 μV or more by the V2 and V5 precordial leads? (2) The authors used “one maximum TWA value, for each 15 seconds of the ECG recording, calculated as the maximum difference between successive T waves of the respective moving averages for each 15-second beat stream” in “the section between the end points of QRS wave (J point) and T wave” and “the resulting maximum value was recorded.” Cardiologists routinely interpreting Holter recordings of ambulatory electrocardiograms witness a massive change of the amplitude of the T waves and the J-T intervals, with variation in the different leads used, and occurring without an explanation over the course of 24 hours. Is it not possible that the TWA magnitude is affected by the T-wave amplitude? Is it not possible that 1 threshold value (as herein, ≥47 μV) does not fit all patients, irrespective of the sometimes massive differences in the amplitude of the T waves in their electrocardiograms? The