Bretylium tosylate--induced stabilization of electrical systole duration in patients with acute myocardial infarction.

The electrical systole duration (QTc), heart rate, and the QTc/QTt ratio were studied during the hospital course of an uncomplicated AMI in 13 patients treated with bretylium tosylate (10 mg/mg/24 hr over 5 days since confirmation of AMI) and in 19 controls. The QTc/QTt ratio showed prolongation of electrical systole duration in control subjects with a maximal value at the second day after AMI. QTc increased in these patients from day 1 to day 2 after AMI (402 +/- 4 msec vs. 430 +/- 3 msec, p less than 0.05) and decreased in the following days (p less than 0.05). During hospitalization cardiac rate was constant in both groups. In contrast, patients treated with bretylium tosylate showed a stable duration of QTc and the QTc/QTt ratio did not indicate prolongation of electrical systole duration. After drug discontinuation a slight increase in QTc duration was noticed (391 +/- 6 msec vs. 413 +/- 5 msec, p less than 0.05). These observations may contribute to the understanding of the antiarrhythmic action of bretylium and would indicate its usefullness in AMI patients with prolonged QTc and high risk of life-threatening arrhythmias.