Persistent tachycardia with a 2:1 exit block within an isolated pulmonary vein.

We describe a patient with drug-resistant, paroxysmal atrial fibrillation who underwent segmental pulmonary vein (PV) isolation. After complete isolation of the right superior PV, a persistent regular tachycardia was recorded within the vein. A tachycardia focus with a cycle length of 114 ms was found 2.5 cm away from the ostium of the PV. The cycle lengths of the PV tachycardia near the ostium and near the focus were 400 ms and 200 ms, respectively, which indicates the presence of a 2:1 exit block within the vein. This PV tachycardia was completely eliminated with the application of radiofrequency energy at the focus.