Relation between heart rate and QT interval in exercise-induced myocardial ischemia.

The relation between heart rate and QT interval during dynamic upright exercise on a bicycle ergometer was investigated in control subjects (n = 18) and in patients with coronary artery disease (CAD), stable angina on effort, and angiographically documented significant coronary stenoses (n = 23). Both groups had a significant negative linear relation between heart rate and QT, with a higher correlation coefficient in control subjects (r = -0.78) than in patients with CAD (r = -0.64). This response may be a result of the nonhomogeneous response to ischemia in patients with CAD, particularly with regard to the different impact of exercise-induced ischemia. When the 2 regression lines were compared, a flatter slope was found in the CAD group (p less than 0.001) as a consequence of a faster decrease in the QT-increasing rate in control subjects. It is suggested that in control subjects exercise-induced increase in adrenergic tone causes a rapid and relevant decrease in QT-interval duration. In the CAD group, exercise-induced ischemia relatively prolonged the QT interval; this may have been the result of an impairment of myocardium in response to catecholamines release during exercise or the consequence of a direct effect of exercise-induced ischemia prolonging the duration of myocardial tension.