Dispersions of the QT interval in postmyocardial infarction patients presenting with ventricular tachycardia or with ventricular fibrillation

Increased QT interval dispersion is associated with ventricular arrhythmias. The aim of this study was to examine if in postmyocardial infarction patients with impaired left ventricular function, increased QT dispersion is associated with ventricular tachycardia (VT) and ventricular fibrillation (VF). Measures of QT dispersion, calculated as maximum-minimum (D) and standard deviation (SD) of QT(end), QT(apex), JT(end), JT(apex), and T-end intervals in the 12-lead electrocardiogram; were compared in patients who late after myocardial infarction experienced sustained VT (VT group) only, VF (VF group) only, or had no ventricular arrhythmias (controls). The 25 patients in each group were individually matched for age, gender, number of diseased coronary vessels, location of the previous myocardial infarction, and left ventricular ejection fraction. Dispersion measures of QT(end), QT(apex), and JT(apex) intervals separated VI group from controls, but none of the measures separated the VF group from controls. QT(end)D was 49 +/- 18 ms in controls, 57 +/- 18 ms in the VF group (controls vs VF group, p = NS), and 65 +/- 29 ms in the VT group (controls vs VT group, p <0.05). VT group had increased QT(apex)SD, JT(apex)SD, and JT(apex)D compared with the VF group. The cycle length of induced sustained monomorphic VT, present in 19 VT and 19 VF patients, correlated with several dispersion indexes in the VT group, but not with those in the VF group. Thus, in postmyocardial infarction patients with a severely damaged left ventricle, increased QT dispersion is associated with susceptibility to sustained VT, but not to VF. (C) 1998 by Excerpta Medica, Inc.