Spontaneous paroxysmal atrioventricular block in patients with positive tilt tests and negative electrophysiological studies

A subgroup of patients with neurocardiogenic syncope and negative electroph ysiologic studies and adenosine tests (in 5 of 6 cases), who developed symp tomatic paroxysmal atrioventricular block in the natural, ambulatory state, had positive tilt tests without advanced block. Lack of concordance betwee n electrocardiographic changes may have reflected differential effects of t he autonomic nervous system in the sinus and atrioventricular nodes, occurr ing in diverse circumstances and less likely because of the protocol used f or tilt testing.