Slow junctional rhythm during catheter ablation of right posteroseptal accessory pathway causing transient atrioventricular block.

A male patient with palpitations and syncope during an episode of atrial fibrillation was evaluated. After DC cardioversion, the ECG showed a pattern of pre-excitation compatible with right posteroseptal bypass tract. The patient was submitted to RF. During energy application a slow junctional rhythm without AV block was noted. Twenty-four hours after the procedure AV block was observed. The AV conduction was resumed spontaneously 48 hours later with unremarkable outcome up to 1 year. We postulated that the edema caused by RF application damaged the compact AV node, causing transient AV block. The AV node lesion has been manifested by a fast junctional rhythm, but in this case we observed that even a slow junctional rhythm could do it.