The autonomic nervous system is composed of the sympathetic and parasympathetic divisions. This system innervates and regulates visceral functions including parenchymal cells and vascular smooth muscle cells.
Preganglionic sympathetic neurons exit the central nervous system via the spinal cord between the first thoracic and second lumbar vertebrae, whereas preganglionic parasympathetic neurons exit the central nervous system via cranial nerves III, VII, IX, X and the second through fourth sacral nerves. In the thorax and abdomen, the vagus nerve dominates the parasympathetic nervous system.
Various physical maneuvers can elicit autonomic responses. Many of these maneuvers can be performed at the bedside or in an office setting with minimal risk. These maneuvers can be both diagnostic (eg, in confirming carotid sinus hypersensitivity) and therapeutic (eg, terminating paroxysmal supraventricular tachycardia). Understanding the indications, techniques, and complications of various vagal maneuvers is necessary to safe and effective clinical application.
Vagal maneuvers to evaluate and treat cardiac arrhythmias and conduction abnormalities are reviewed here. The general evaluation of parasympathetic nervous system function, of carotid sinus hypersensitivity, and of supraventricular tachycardia are presented separately. (See "Evaluation of parasympathetic nervous system function" and "Reflex syncope" and "Clinical manifestations, diagnosis, and evaluation of narrow QRS complex tachycardias".)
CARDIAC RESPONSES TO VAGAL STIMULATION
In the heart, parasympathetic (vagal) stimulation causes local release of acetylcholine, with the following effects: