Paroxysmal Vagally Mediated AV Block with Recurrent Syncope

Summary: Paroxysmal complete atrioventricular (AV) block without associated electrocardiographic (ECG) ab- normality is not a well recognized entity. A mother and her daughter had recurrent syncopal episodes, but a nor- mal ECG. The episodes were preceded by nausea and vomiting. ECG during these episodes revealed complete heart block. In the mother, one episode was promptly reversed by atropine. Electrophysiological evaluation of the sinus and AV nodal function and atrial and ventricu- lar effective refractory periods before and after autonom- ic blockade was normal. Provocative manoeuvres failed to induce AV block. Paroxysmal block was vagally mediated in one of the patients, as indicated by prompt response to atropine. In the second case, the vagal depen- dence could not be proved but appears to be the most likely explanation. It thus appears that paroxysmal, vagally mediated complete AV block should be seriously consi- dered in patients with unexplained syncope. Key words: