Unmasking of fast and slow atrioventricular nodal pathways by successful radiofrequency ablation of two accessory atrioventricular connections.

Electrophysiologic findings suggesting the coexistence of dual atrioventricular (AV) nodal pathways and accessory AV connections have been previously described. Anterograde conduction through the accessory pathway (AP) may preclude the diagnosis of AV nodal dual pathway physiology during atrial stimulation. This study reports on a patient with manifest Wolff-Parkinson-White syndrome with clinically documented paroxysmal atrial fibrillation, in whom dual AV nodal pathways were unmasked after successful radiofrequency ablation of two accessory AV connections. In spite of detailed investigation, fast and slow AV nodal pathways were not detected in the first electrophysiologic study 8 years before ablation, nor were they detected during preablation study because of exclusive anomalous anterograde conduction. The anterograde AP effective refractory period was shorter than that of the fast and slow AV nodal pathways, and was limited by atrial refractoriness at 190 ms. The present findings strongly suggest the necessity for a careful postablation eletrophysiologic study before and after isoproterenol administration with specific evaluation of AV nodal conduction. This is the first documented report on the finding of AV nodal dual pathway physiology and reentry after successful radiofrequency ablation of two APs. This finding may be of great therapeutic significance in light of the feasibility of slow pathway ablation also during a single session, had AV nodal reentry been induced in a sustained manner after ablation of the AP to prevent late recurrence of tachycardia.