Effects of postmyocardial infarction scar size, cardiac function, and severity of coronary artery disease on QT interval dispersion as a risk factor for complex ventricular arrhythmia.

The aim of the study was to determine the relation between QT dispersion and ventricular arrhythmia after myocardial infarction, as well as the effects of postinfarction scar size, cardiac function, and severity of coronary artery disease on QT dispersion. Three hundred three patients, 3 months after myocardial infarction, and a group of 21 healthy subjects were evaluated. QT dispersion was the difference between maximal and minimal QT interval in 12-ECG leads. Postinfarction scar size was determined by Selvester's QRS scoring system. Cardiac function was evaluated by echocardiography and exercise stress test, and the severity of coronary artery disease by the number and degree of coronary artery stenoses. QT dispersion increased significantly in relation to the severity of arrhythmia (< 50 premature ventricular complexes vs ventricular tachycardia; 61.6 [+/- 12.3] vs 84.8 [+/- 16.4] ms, P < 0.001). QT dispersion > 80 ms was associated with ventricular tachycardia with the sensitivity of 68% and specificity of 88%. QT dispersion also increased significantly, dependent on the postinfarction scar size (0% vs > or = 33% of left ventricular myocardium; 61.8 [+/- 16.4] vs 74.7 [+/- 16] ms, P < 0.001), as well as in the case of significantly impaired cardiac function. Although QT dispersion increased with the number of diseased vessels and the degree of stenoses, the differences were not significant (P > 0.05). In conclusion, QT dispersion is a risk marker of complex ventricular arrhythmia in the chronic stage of myocardial infarction. Multiple regression analysis indicates that only the postinfarction scar size has an independent effect on QT dispersion (R2 = 0.39, P < 0.05).