QT dispersion and early arrhythmic risk during acute myocardial infarction

It has been suggested that QT dispersion (maximal minus minimal QT interval calculated on a standard 12-lead electrocardiogram) could reflect regional variations of ventricular repolarization and could provide a substrate for reentry ventricular arrhythmias. The present study evaluates QT dispersion in patients with acute myocardial infarction, assessing its relation with early severe ventricular arrhythmias and some clinical features. Three hund red 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 symp toms onset and on the electrocardiogram taken in the control group. The ave rage values of QT and QTc dispersions (ms) were as follows: 70.5 +/- 42.5-8 7 +/-45.6 (12th hour), 66.7 +/- 37.6-76.8 +/- 43.6 (day 3), 68.8 +/- 42.7-7 6.8 +/- 42.8 (day 10), versus 43 +/- 13.2-53.9 +/-16.2 (control group). The re were statistically significant differences between QT and QTc dispersion recorded in normal subjects and in each of the three electrocardiograms ta ken in patients with infarction. A greater QT dispersion was recorded in pa tients 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 i n patients treated and untreated with thrombolysis, whereas on day 10 it wa s 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 ve ntricular tachycardia. Higher early values of QT and QTc dispersion were fo und in patients who developed severe ventricular arrhythmias (107.8 +/-62 a nd 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 myocardia l infarction. (2) The values were higher in the early hours and fell late a fter infarction with thrombolysis. (3) Greater QT dispersion is associated with severe ventricular arrhythmias.