Background: QT dispersion has been proposed as a simple, noninvasive measure for identifying patients at risk of postinfarction arrhythmia. It is assumed to reflect nonuniform ventricular repolarization, which, in turn, may result from regional differences in repolarization time as well as from localized activation delay. The aim of this study was to examine the relation between QT dispersion and intraventricular conduction abnormalities in patients with acute anterior wall myocardial infarction. Methods and Results: Standard 12-lead electrocardiographic and 12-lead signal-averaged electrocardiographic recordings were performed in 25 patients with a first Q- wave anterior wall myocardial infarction. Measures calculated by using the 6 precordial [V1 through V6) leads for QT dispersion were (1) difference between maximum and minimum QT and QTc intervals and (2) standard deviation of QT and QTc intervals. Measures calculated from the signal-averaged electrocardiogram were (1) maximum filtered QRS duration; (2) mean; and (3) standard deviation of filtered QRS duration. No relation was found between any measure of filtered QRS duration and that of QT dispersion by using linear correlation analysis. Similarly, no significant association was demonstrated between the filtered QRS duration and corresponding QT interval measurements (total 131 leads). Conclusions: The lack of correlation between signal-averaged electrocardiogram indexes of slow intraventricular conduction and electrocardiogram variables of QT dispersion suggests an independent predictive value for the 2 methods in identifying patients at risk of postinfarction arrhythmia. This suggestion is further supported by the finding that altered activation sequence is an unlikely mechanism of QT dispersion in patients with acute myocardial infarction, as indicated by the lack of association between the filtered QRS duration and corresponding QT interval measurements.