QT dispersion and early arrhythmic risk during acute myocardial infarction

QT dispersion (maximal minus minimal QT interval calculated on a standard 12-lead electrocardiogram) has been suggested to reflect regional variations of ventricular repolarization and to provide a substrate for reentry ventricular arrhythmias. In this study we evaluate QT dispersion in patients with acute myocardial infarction and assess its relation with early severe ventricular arrhythmias.

We studied 101 patients with acute myocardial infarction and a control group of 97 healthy subjects. We determined QT and QTc dispersion on the electrocardiograms performed 12 hours and 3 and 10 days after the onset of symptoms in myocardial infarction patients and on the control group. The average values of QT and QTc dispersion (measured hereafter in milliseconds, ms) were as follows: 70.5 +/- 42.5-87 +/- 46.6 (after 12 hours), 66.5 +/- 37.8-76.9 +/- 43.5 (on day 3), 68.9 +/- 42-76.3 +/- 43.8 (on day 10) and 44 +/- 13.4-54.2 +/- 16.3 (in control group). We observed statistically significant differences in QT and QTc dispersion between the electrocardiogram of normal subjects and each of the three electrocardiograms performed on patients with infarction (p < 0.0005, p < 0.005). We recorded a greater QT dispersion in patients with anterior infarction with respect to those with inferior/lateral infarction (79 +/- 38.6 vs 65.2 +/- 43.16, p < 0.05) and in patients with ejection fraction < 45% (93.1 +/- 28.4 vs 68.3 +/- 34.1 p < 0.005). During the first three days, QT dispersion did not differ in patients treated with thrombolytic agents with respect to those who were untreated, while on day 10 untreated patients showed higher values (74.9 +/- 45.3 vs 60.5 +/- 37.7, p < 0.05). Creatine kinase peak level, sex and age of the patients did not influence QT dispersion. Thirteen patients (12.8%) developed severe ventricular arrhythmias within 72 hours after infarction: 8 patients (7.9%) had ventricular fibrillation and 5 patients (4.9%) had sustained ventricular tachycardia. We found higher early QT and QTc dispersion values in patients who developed severe ventricular arrhythmias (108.8 +/- 63.2 and 125.8 +/- 68.5) with respect to patients who did not (63.3 +/- 32.9 and 80.8 +/- 38.9, p < 0.0005, p < 0.0005).

Our data suggest that QT dispersion: 1) increases during acute myocardial infarction; 2) peaks in the early hours after symptom onset; 3) drops late after infarction in patients treated with thrombolytic agents; 4) is associated with early severe ventricular arrhythmias.