Effects of individual cardiac nerve stimulation on atrioventricular conduction.

This study investigated the effects of individual canine cardiac nerve stimulation on atrioventricular conductions as measured by His bundle electrograms. A-H and H-V intervals were measured before and during stimulation of each nerve in paced hearts (200 beats/min) and before and after blocking doses of either atropine or propranolol. Increases in A-H or H-V intervals were evidence of parasympathetic innervation; decreases in intervals were evidence of sympathetic innervation. Separation by autonomic composition produced 3 categories: sympathetic, parasympathetic, and mixed input to the atrioventricular junction. The sympathetic nerves were the left and right ansae subclavia, the ventrolateral cardiac nerve, and the right stellate cardiac nerve. The parasympathetic nerve was the right thoracic vagus, and the mixed nerves were the left thoracic vagus, and the innominate, ventromedial, craniovagal, caudovagal, and right recurrent cardiac nerves. The cardiac nerves eliciting a major response were the left and right ansae subclavia, the ventrolateral, right recurrent, craniovagal, and caudovagal cardiac nerves, and the left and right thoracic vagi. In theory, the nerves of the right side, because of their innervation of both sinoatrial and atrioventricular nodes, may be expected to elicit a balanced heart rate-atrioventricular conduction response when stimulated, thus matching atrial and ventricular rates. On the other hand, stimulation of the ventrolateral cardiac nerve regularly produces dysrhythmia, due to increased automaticity at the atrioventricular junction. Production of such arrhythmias indicates the possible implication of imbalanced autonomic activity in arrhythmogenesis. Three cardiac nerves produced little or no effect on atrioventricular conduction. These were the innominate, ventromedial, and right stellate cardiac nerves. Because of its limited distribution and marked sinus rate effects, the right stellate cardiac nerve can be considered almost a purely positive chronotropic nerve. Its possible role in heart rate-atrioventricular conduction mismatching has not been delineated but, because of its nearly exclusive action at the sinoatrial node, may be of considerable importance.