Characteristics of QT Interval and QT Dispersion in Exercise Electrocardiogram: Healthy Persons versus Stable Angina Patients

ABSTRACT

BACKGROUND AND OBJECTIVES: The QT interval (QTi) and QT dispersion (QTd), which represent the myocardial electrical heterogeneity of repolarization, were studied to recognize the differences between normal controls (n=32) and stable angina patients (n=78). SUBJECTS AND METHODS: During the treadmill exercise test, standard 12 lead Electrocardiogram (ECG) was obtained at every stage, with the QTi and QTd measured. The corrected QT interval (cQTi) and QT dispersion (cQTd) were calculated using Bazett's formula, with the Delta QT interval (DeltaQTi) measured on leads V5 and aVF. RESULTS: During exercise, the QTi had a reverse relationship with the heart rate in both groups, but was decreased by a lesser extent in the patient group. The QTd also had a tendency to decrease according to increasing heart rate in both groups and was significantly greater in the patient group. The corrected QTi increased during exercise in both groups, and reached maximum during the pre-peak stage, but was minimized during a 1 minute recovery stage in the patient group. The corrected QTd reached a maximum during the peak exercise stage in both groups, but the values between the two groups were significantly different. Both the QTi and cQTi had tendencies to increase according to the number of vessels with stenosis. The DeltaQTi tended to reflect a regional ischemia in a single vessel disease. CONCLUSION: The QTi, QTd, cQTi and cQTd were increased in the stable angina patients compared with the normal controls, and augmented during the exercise test.