Effect of heart rate and autonomic tone on the QT interval.

Effect of Heart Rate and Autonomic Tone on the QT IntervalTo the Editor: I read with interest the paper "Influence of Heart Rate and Inhibition of Autonomic Tone on the QT Interval" by Ahnve and Vallin.I Their study confirms observations previously made in man in our laboratory.'Ahnve and Vallin also questioned in their discussion that "both heart rate and adrenergic activity affect the duration of the QT interval, but it is not clear as to what extent these effects are interrelated or whether the heart rate effects are independent of autonomic tone.We demonstrated in intact unanesthesized man and in one patient after cardiac transplantation that intravenous infusion of isoproterenol did not modify the dura- tion of the QT interval independent of its effects on heart rate.3In the patient with the cardiac transplant, the QT interval was markedly short- ened at any given heart rate; however, we did not know whether that could be a normal finding in the denervated human heart.