Isoproterenol antagonizes drug-induced prolongation of action potential duration in humans

The effects of an isoproterenol infusion on the duration of the human right ventricular endocardial monophasic action potential at 90% repolarization were recorded in the absence and in the presence of an antiarrhythmic drug regimen containing class III effects in two similar groups of patients. The drugs used were amiodarone (N = 3, 300 +/- 50 mg), sotalol plus quinidine (N = 11, 156 +/- 13 mg sotalol, 1688 +/- 594 mg quinidine), and sotalol alone (N = 3, 300 +/- 20 mg). All patients had underlying coronary disease but no evidence of inducible ischemia. In the absence of antiarrhythmic drug, isoproterenol did not significantly change the relationship of action potential duration at 90% repolarization to cycle length; there was a linear decrease in action potential duration by 19.8% between a paced cycle length of 600 and 300 ms. Isoproterenol did not significantly shorten the action potential duration at any cycle length. However, isoproterenol decreased the ventricular effective refractory period at 400 ms drive from 240 +/- 5.0 to 225 +/- 6.0 ms (p < 0.05) accompanied by no change in the ratio of refractory period to steady-state action potential duration. In the presence of class III drug effects, the action potential duration was increased by an average of 9.2% at all paced cycle lengths longer than 300 ms (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)