Relation between QT and QS2 intervals during exercise and recovery. Response in patient with coronary artery disease and age-matched control subjects.

We investigated the relationship between QT interval and QS2 (electromechanical systole) during exercise and recovery in patients with coronary artery disease (CAD) and exercise-induced myocardial ischemia (n = 12), and in age-matched controls (n = 20). Upright bicycle exercise was performed (50 watts/min + 20 watts/min every 2 min), recording electrocardiographic lead 2 (100 mm/sec) for QT and QS2 measurement at rest, at each step of uninterrupted exercise and every 60 sec during a 3-min recovery period. Resting data showed a QT less than QS2 finding in both groups; during exercise, QT and QS2 decreased. The values of QT and QS2, collected at each step of exercise and plotted against heart rate (HR) separately for both groups, showed a significant correlation coefficient. Comparing the regression lines of HR-QT and HR-QS2 separately for both groups, we found that both intervals decreased in parallel and the mean QT remained shorter than QS2 in both groups during exercise. The QT/QS2 ratio remained unchanged significantly during exercise and recovery in CAD. In control subjects, the ratio remained unchanged during exercise and the first min of recovery, while a significant change was detected in late (2,3 min) recovery from an adrenergic-induced effect. The mean exercise-induced response of QT-QS2 relationship includes a QT less than QS2 pattern in both groups. In CAD patients, an abnormal pattern was found in two patients during recovery by a relative prolongation of QT, suggesting the possibility of a risk factor for dangerous arrhythmias or sudden death.