The A That Did Not Fib:Two Roads Both Traveled By.

A 64-year-old woman presented with palpitations. Her 24-hour Holter monitor revealed runs of presumed atrial fibrillation (AF). The patient was referred for EP study and AF ablation. At EPS, an anterograde A-H jump was noted. Spontaneous bursts of tachycardia were seen, consisting of sinus atrial beats with dual ventricular responses, each preceded by a His deflection. There was no atrial fibrillation during the study. Radiofrequency ablation of the slow AV node pathway was performed. There were no inducible tachycardias and no A-H jump following the ablation. The patient had no recurrence post-procedure. This case presents a rare example of simultaneous dual anterograde AV-nodal conduction. The conditions leading to this phenomenon include dual AVN pathways, markedly slowed conduction in the slow pathway, and lack of retrograde conduction up either pathway such that reentry was impossible. An irregular, narrow-complex tachycardia resulted, initially interpreted as AF. Slow-pathway ablation was curative.