Tachycardia and bradycardia coexisting in the same pulmonary vein.

During segmental isolation of the pulmonary veins (PVs) in a patient with paroxysmal atrial fibrillation, there was a PV bradycardia that was dissociated from the left atrium in a segment of the right superior PV, whereas the remaining segments showed passive activation of a PV fascicle during sinus rhythm. Rapid atrial pacing induced a PV tachycardia in the nonisolated fascicles, and the dissociated PV bradycardia persisted in a segment of the same PV. These observations indicate that PV fascicles are insulated from each other and that a dissociated PV rhythm does not necessarily indicate complete isolation of a PV.