Acute and chronic effects of sotalol and propranolol on ventricular repolarization using constant-rate pacing

Sotalol and propranolol were administered both intravenously and orally in conventional equipotent beta-blocking doses to 8 patients with permanent programmable ventricular pacemakers to study their effects on ventricular repolarization. Sotalol prolonged the QT interval by 6.5% (430 to 455 ms) after intravenous administration (p less than 0.01) and by up to 11.5% (430 to 483 ms) after 4 weeks of oral treatment (p less than 0.001). This was entirely due to prolongation of the JT interval, since there was no effect on QRS duration. The magnitude of QT and JT prolongation related to the serum level but the correlation was not statistically significant. QT prolongation was exaggerated after chronic treatment despite lower serum levels of sotalol (2.0 micrograms/ml) compared with levels after acute administration (3.5 micrograms/ml). After propranolol was given, there was no consistent change in QT or JT intervals, and although there was a tendency to slight prolongation of QT interval, by 2.5% after chronic oral administration, this was not statistically significant. This suggests that the prolongation of ventricular repolarization by sotalol is not caused by beta-blockade, but by its class III activity, and that chronic treatment increases the effect. There was no significant effect on chronic ventricular pacing threshold after intravenous or oral administration of either drug.