Two levels of block within a pulmonary vein

We present a 37-year-old woman with drug refractory atrial fibrillation referred for a pulmonary vein (PV) isolation procedure who manifested a tachycardia with 2:1 intra-PV block within a dissociated PV. During ablation in the right superior PV, the surface rhythm became normal sinus, with persistent atrial fibrillation within the PV. Shortly thereafter, an atrial tachycardia with a cycle length of 190 ms and 2:1 distal to proximal exit block was observed within the isolated PV. Conduction block within a PV electrically isolated from the left atrium is a newly observed phenomenon that may have implications to the electrophysiologic properties of the PV muscular sleeves.