Selective hypervagotonia isolated to the atrioventricular node.

Thirteen patients with recurrent unexplained syncope or presyncope underwent electrophysiological evaluation. A prolonged effective refractory period and functional refractory period of the atrioventricular node as well as slow paced rate to atrioventricular block were the only abnormalities found. Ventricular tachycardia could not be induced. All electrophysiological abnormalities reverted to normal following atropine administration. These patients have selective hypervagotonia isolated to the atrioventricular node. Three of thirteen patients required permanent pacing, and one required propantheline to control recurrent symptoms. Selective hypervagotonia may be a distinct clinical entity that can cause symptoms and require therapy.