Electrophysiologic effects of isoproterenol on cardiac conduction system in man.

The effects of isoproternol (ISOP) on the functional properties of the A-V conduction system were studied in 16 patients using His-bundle recordings and the atrial extrastimulus technique. In all patients, ISOP at an infusion rate of 1 mcg. per minute resulted in sinus acceleration and enhancement of A-V nodal conduction, but had no effect on His-Purkinje conduction time. ISOP significantly decreased both functional and effective refractory periods of the A-V node. The relative refractory period of the His-Purkinje system decreased by a small amount in five patients in whom the parameter could be compared before and after the drug.