2000 Volume 31 Issue 2 Pages 145-157
QT dispersion (QTd) is affected by inhomogenous ventricular repolarization, and increased QTd is associated with a higher risk of ventricular tachycardia. Recent studies have shown an increase in QTd in patients with myocardial infarction (MI). However, the importance of changes in QTd with exercise has not been carefully investigated in MI patients. The aims of this study were to identify factors associated with changes in QTd induced by exercise in MI patients and to elucidate their clinical significance. QTd immediately after exercise was studied in 41 control patients and 128 MI patients, 1 month after the onset of MI, using treadmill exercise electrocardiography. The MI patients were divided into two groups based on the results: those with a QTd >50 msec immediately after exercise (the long QTd group), and those with a QTd ≦50 msec immediately after exercise (the short QTd group). The clinical findings for the two groups were then compared. Maximum ST-segment depression in the noninfarct-related leads (p<0.01), the defect score and incidence of redistribution at the infarct site on exercise thallium-201 scintigraphy (p<0.05), the prevalence of multivessel disease (p<0.01), and the incidence of detectable late potentials (p<0.05) were significantly higher, and the left ventricular ejection fraction (p<0.01) and heart rate immediately after exercise (p<0.01) were significantly lower in the long QTd group than in the short QTd group. The cumulative survival rate was significantly higher (p<0.001) in the short QTd group than in the long QTd group. In conclusion, increased QTd with exercise in MI patients is associated with transient myocardial ischemia, a large infarct size, and depressed left ventricular function. Measurements of QTd with exercise may be useful for determining the long-term prognosis of MI patients.
