EFFECTS OF DIFFERENT ATRIAL-PACING MODES ON ATRIAL ELECTROPHYSIOLOGY - IMPLICATING THE MECHANISM OF BIATRIAL PACING IN PREVENTION OF ATRIAL-FIBRILLATION

Background Multiple-site atrial pacing has been shown to prevent recur rence of atrial fibrillation. However, information about the mechanism s of different atrial pacing modes in prevention of atrial fibrillatio n was not clear. Methods and Results Forty-two patients without struct ural heart disease were classified into group 1 and group 2 according to absence or presence of clinical atrial fibrillation, respectively. Atrial conduction time and electrogram width of the right posterior in teratrial septum (RPS) were measured during drive-train stimulation (S 1) and early extrastimulation (S2). The locations of S1 were the high right atrium (HRA), distal coronary sinus (DCS), or both sites simulta neously. Effective refractory periods (ERPs) of the HRA and DCS were a lso determined during S1 stimulation at each site and during biatrial pacing. The ERPs were not different between single-site atrial pacing and biatrial pacing. In contrast, early S2 stimulation at the HRA caus ed greater atrial conduction delay and greater increment of electrogra m width of the RPS in patients with a history of atrial fibrillation. Biatrial pacing significantly reduced the conduction delay and electro gram width of the RPS caused by HRA extrastimulation. In addition, in 17 group 2 patients, atrial fibrillation was induced by an early HRA S 2 coupled to HRA pacing. However, with the same coupling interval of S 2 at HRA only 6 of them had the arrhythmia induced during biatrial pac ing. Furthermore, conduction delay and increase of electrogram width c aused by early S2 at the HRA were reduced by biatrial pacing only in p atients whose arrhythmia induction was successfully prevented by biatr ial pacing. Conclusions Biatrial pacing reduced both the atrial conduc tion delay and increase of electrogram width at the RPS caused by earl y S2 at HRA, and these effects could prevent induction of atrial fibri llation.