Intracardiac electrophysiologic techniques in recurrent syncope of unknown case.

Twenty-five patients with recurrent episodes of syncope, unexplained despite thorough medical and neurologic evaluation, underwent intracardiac electrophysiologic study with programmed stimulation. Electrophysiologic study yielded a presumptive diagnosis in 17 patients: nine with rapid ventricular tachycardia by programmed stimulation, three with intra-His conduction delays, one with symptomatic atrial flutter, one with sick sinus syndrome, and three with persistent hypervagotonia manifested as atropine-reversible prolongation of atrioventricular nodal refractoriness. Therapy based on these findings provided complete symptomatic relief in 14 and improvement in one of these 17 patients during a mean follow-up of 18 +/- 10 months. Therapy based on electrophysiologic testing was ineffective in two of the 17 patients. Syncope persisted in four of the eight patients in whom electrophysiologic study did not define a probable arrhythmic mechanism. These observations indicate that full electrophysiologic evaluation with programmed stimulation is useful in the diagnosis and therapy of recurrent unexplained syncope.