QT Dispersion and Early Arrhythmic Risk During Acute Myocardial Infarction

Abstract

It has been suggested that QT dispersion (maximal minus minimal QT interval calcu lated on a standard 12-lead electrocardiogram) could reflect regional variations of ventricular repolarization and could provide a substrate for reentry ventricular arrhyth mias. The present study evaluates QT dispersion in patients with acute myocardial infarc tion, assessing its relation with early severe ventricular arrhythmias and some clinical features. Three hundred three patients with acute myocardial infarction and a control group of 297 healthy subjects were studied. QT and QTc dispersion were determined on the electrocardiogram taken after 12 hours and on days 3 and 10 after symptoms onset and on the electrocardiogram taken in the control group. The average values of QT and QTc dispersions (ms) were as follows: 70.5 ±42.5-87 ±45.6 (12th hour), 66.7 ±37.6-76.8 ±43.6 (day 3), 68.8 ±42.7-76.8 ±42.8 (day 10), versus 43 ±13.2- 53.9 ±16.2 (control group). There were statistically significant differences between QT and QTc dispersion recorded in normal subjects and in each of the three electrocardio grams taken in patients with infarction. A greater QT dispersion was recorded in patients with anterior infarction (78.9 ±38.5 vs 64.9 ±42.8 in inferior/lateral infarction). In the first 3 days QT dispersion was not different in patients treated and untreated with throm bolysis, whereas on day 10 it was greater in untreated patients (74.9 ±45.3 vs 60.5 ±37.2). Creatine kinase peak level did not influence QT dispersion. In the first 72 hours of infarction, 37 patients developed ventricular fibrillation or sustained ventricular tachy cardia. Higher early values of QT and QTc dispersion were found in patients who developed severe ventricular arrhythmias (107.8 ±62 and 124.8 ±67.5 ms) than in patients without serious arrhythmias (62.9 ±32.2 and 80.1 ±37.9 ms). These data suggest that: (1) QT dispersion increased during acute myocardial infarc tion. (2) The values were higher in the early hours and fell late after infarction with throm bolysis. (3) Greater QT dispersion is associated with severe ventricular arrhythmias.