Electrophysiologic effects of epinephrine in humans.

The electrophysiologic effects of circulating epinephrine in humans were examined in four study groups of 10 subjects each. In 10 subjects without structural heart disease (Group 1) and in 10 patients with coronary disease or dilated cardiomyopathy (Group 2) epinephrine infusion at 25 and 50 ng/kg body weight per min for 14 min resulted in an elevation of the plasma epinephrine concentration in the physiologic range. In both groups it produced a dose-dependent decrease in the effective refractory period of the atrium, atrioventricular (AV) node and ventricle and improvement in AV node conduction. Epinephrine facilitated the induction of sustained ventricular tachycardia in 3 of the 20 subjects. In Group 3, a beta-adrenergic blocking dose of propranolol was added to the infusion of 50 ng/kg per min of epinephrine. Propranolol not only reversed the effects of epinephrine, but also lengthened these variables compared with baseline values. In Group 4, propranolol was administered first, followed by 50 ng/kg per min of epinephrine. Propranolol alone slowed AV node conduction and mildly prolonged the refractory periods. In the presence of beta-blockade, epinephrine had no effect on AV node properties but resulted in a lengthening of the atrial and ventricular effective refractory periods. In conclusion, epinephrine in physiologic doses shortens the effective refractory period of the atrium, AV node and ventricle, improves AV node conduction and may facilitate the induction of sustained ventricular tachycardia. The overall electrophysiologic effects of epinephrine result from stimulation of beta-receptors. Stimulation of alpha-receptors by epinephrine has no effect on the AV node but prolongs the effective refractory period of the atrium and ventricle, partially offsetting the shortening of refractory periods mediated by beta-receptor stimulation.