On the sympathetic control of ventricular automaticity: The effects of a reflex increase of sympathetic discharge

Abstract

The reflex sympathetic control of idioventricular pacemakers in complete atrioventricular (A-V) block was studied in anesthetized dogs. The A-V block was obtained either by ligating the His bundle or by stimulating the vagus. The procedures employed to enhance reflexly the sympathetic discharge were as follows: occlusion of the carotid arteries, administration of nitroglycerine, inhalation of amyl nitrite and stimulation of the central end of the sciatic nerve. These procedures accelerated reflexly the idioventricular pacemakers to a different degree, but the acceleration was rarely as large as that obtained with high frequency sympathetic stimulation. Elimination of one stellate ganglion almost halved the reflex acceleration of ventricular pacemakers, thereby indicating that the acceleration was mainly brought about by increased neural discharge. The reflex enhancement of ventricular pacemakers was not affected by simultaneous vagal stimulation, thus suggesting that the vagal discharge has little influence on ventricular automaticity. By comparing the results obtained with direct sympathetic stimulation and those obtained with a reflex increase of sympathetic activity, it was found that the unilateral sympathetic discharge during the procedures ranged from 1 to 4 impulses/sec.