Atrial fibrillation and effective refractory period of the pulmonary vein ostia.

Background: The pathogenesis of atrial fibrillation (AF) is not completely understood. The role of pulmonary veins (PV) in AF initiation is documented, and the recent demonstration of persistent fibrillatory activity in an isolated PV suggests that the PV play a role in the maintenance of AF.
Objective: Since AF is facilitated by multiple reentry circuits in atrial tissue with short effective refractory periods (ERP) and prolonged conduction times, we investigated whether PV have shorter ERP compared with the left atrium (LA).
Population and Methods: The study population consisted of five male patients, between 45 and 78 years of age, with normal sized LA; three had coronary artery bypass surgery (and no previous history of atrial arrhythmias) and two had paroxysmal lone AF refractory to antiarrhythmic drugs and were referred for percutaneous ablation with radiofrequency energy. In the surgical patients, epicardial bipolar pacing wires were inserted in the PV ostia and LA roof at the end of the procedure. Post-operatively, the pacing wires were used to determine atrial thresholds and ERP in the PV ostia and LA roof. In the AF patients, atrial thresholds and ERP at these locations were obtained with the mapping/ablation catheter before and after PV isolation. ERP were determined with a basic pacing cycle length of 500 ms and a single extrastimulus with an initial coupling interval of 350 ms, gradually decreased (10 ms at a time) until atrial capture failure or AF induction.
Results: ERP in the LA roof were longer than 210 ms. The shortest ERP was always obtained in a PV ostium, with the shortest in the left PV ostia. The ERP values of the right inferior PV most resembled those of the LA roof. In patients referred for ablation, AF was induced when PV ostia with ERP shorter than 200 ms were stimulated.
Conclusion: In the present study, the ERP of PV ostia were shorter than LA ERP, possibly explaining not only the presence of ectopic foci in the PV ostia, but also sustained fibrillatory activity in isolated PV, despite conversion of the atria to sinus rhythm. This fact may also explain the higher success rate and the preference for PV isolation in AF ablation.