QT dispersion(QTd) has been shown to be ventricular electrical instability, especially predictor of ventricular arrythmia and indicator of antiarrythmic effect. It was reported that there was a relationship between acute myocardial infarction and increased QTd in that QTd is dependent of the degree of reperfusion as well as the site and size of infarction. In this study, we intended to verify a significant association between myocardial ischemia and QTd by comparing the changes in QTd with or without chest pain in patients with unstable angina who had proven myocardial ischemic changes.

We studied 20 patients (12 men and 8 women : mean age, 58±3.4 years) with unstable angina who had proven myocardial ischemic changes and perfusion defect by 24 hour Holter monitoring, Treadmill test, or coronary angiography. Each case was measured QTd during chest patin and resting state 24 hours after chest pain.

All standard 12-lead ECGs were recorded at a speed of 25 mm/sec and examined retrospectively by one observer. QTd corrected for heart rate (QTcd) was calculated by Bazett's formula. The difference of QTd was assessed by comparing by paired t-test.

The mean values of QTd were 117.9±49.9 msec and 69.7±30.2 msec with existence and the absence of chest pain. There was significant increment of QTd when the paients with unstable angina had chest pain(p<0.01).

QTcd also significantly increased with the mean value of 119.7±57.1 and 74.9±36.6 msec (p=0.015).

The results of this study clarified the change of QTd with myocardial ischemia. We expect QTd using a single, noninvasive method to indicate that the chest pain is induced by myocardial ischemic changes. For the furture, it may be possible to study as to the significance of QTd as a predictor of cardiovascular accidents in patients with unstable angina by measuring the serial QTd.