ABSTRACT
The autonomic nervous system exerts major functional control on the heart through the interaction of adrenergic and cholinergic reflex mechanisms. Sympathetic and parasympathetic influences and interactions are prominent in the control of sinoatrial (SA) and atrioventricular (AV) nodal function. This chapter reviews peripheral autonomic control of heart rate and AV nodal conduction. The rapid membrane hyperpolarization primarily is responsible for the majority of the chronotropic and dromotropic effects at the SA and AV nodes. Changes in heart rate and AV nodal conduction result not simply from an increase or decrease in either sympathetic or vagal tone, but from opposing variations in the tone of both branches of the autonomic nervous system. Catecholamines or sympathetic stimulation decrease AV nodal conduction time. The changes in AV nodal conduction in response to various parasympathetic stimulation frequencies were practically linear. When the AV nodal conduction effects of vagal stimulation were compared during stellate stimulation versus during norepinephrine infusions, a significant sympathetic-parasympathetic interaction was apparent.
