Cardiac arrhythmias of sympathetic origin in the dog.

The effects of ventrolateral and ventromedial cardiac nerve (left sympathetics) stimulation on cardiac force, on rate, and on arrhythmogenic responses were characterized and quantitated. The stimulation of left sympathetic nerves produced augmentation in cardiac contraction in 45% of the experiments, an augmentation of both a cardiac rate and force in 47%, and in cardioacceleration alone in 8%. Two characteristic patterns of arrhythmogenic responses were elicited from stimulations of 100 sympathetic nerves. The two types of neurally induced arrhythmias were atrioventricular junctional or ventricular in origin. The onset and duration of the arrhythmias were quantitated. Both types of neurally induced arrhythmias were prevented either by blocking the beta receptors with propranolol or by preventing the neural release of norepinephrine with bretylium tosylate. The neurally induced arrhythmias were probably the result of enhanced automaticity in the atrioventricular junction area and in the ventricles produced by stimulating the sympathetic nerve fibers. This report thus implicates the ventromedial cardiac nerve in the genesis of cardiac arrhythmias.