Association of Left Ventricular Remodeling and Nonuniform Electrical Recovery Expressed by Nondipolar QRST Integral Map Patterns in Survivors of a First Anterior Myocardial Infarction

Abstract

Background Progressive left ventricular dilatation after myocardial infarction is associated with a high mortality rate, the majority of which is arrhythmogenic in origin. The underlying mechanism of this relation remains unknown. It has been suggested, however, that left ventricular dilatation is accompanied by changes in repolarization characteristics that may facilitate the occurrence of life-threatening ventricular arrhythmias. Methods and Results We examined 62-lead body surface QRST integral maps during sinus rhythm in 78 patients at 349±141 days after thrombolysis for a first anterior myocardial infarction. Visual map analysis was directed at discriminating dipolar (uniform repolarization) from nondipolar (nonuniform repolarization) patterns. In addition, the nondipolar content of each map was assessed quantitatively with the use of eigenvector analysis. Nondipolar map patterns were present in almost one third of the patients (32%). Left ventricular end-systolic and end-diastolic volumes were assessed echocardiographically before discharge and after 3 and 12 months with the use of the modified biplane Simpson rule. The increase in left ventricular end-systolic volume 1 year after myocardial infarction was more pronounced in patients with nondipolar QRST integral map patterns (14.47±14.10 versus 4.22±8.44 mL/m 2 , P =.017). In patients with an increase in end-systolic volume of more than 16 mL/m 2 (upper quartile), the prevalence of nondipolar maps was 89% compared with 29% in patients with dilatation of less than 16 mL/m 2 . In addition, the nondipolar content of maps in patients in the upper quartile was significantly increased compared with the lower quartiles (49±14% versus 37±12%, P =.013). Logistic regression analysis revealed that an end-systolic volume of more than 42 mL/m 2 after 1 year contributed independently to the appearance of nondipolar maps. Patients with high-grade ventricular arrhythmias showed a higher nondipolar content (49±17% versus 39±10%, P =.013). QT c dispersion did not discriminate between patients with and those without high-grade ventricular arrhythmias. Also, the association between left ventricular remodeling and nondipolar map patterns was confirmed prospectively in an additional group of 15 patients. Conclusions Nondipolar map patterns are present in 32% of patients after thrombolysis for a first anterior myocardial infarction and are associated with increased left ventricular dilatation. These data support the hypothesis that left ventricular dilatation after myocardial infarction leads to changes in repolarization characteristics that may facilitate the occurrence of life-threatening ventricular arrhythmias.