ELECTROPHYSIOLOGICAL MECHANISMS IN SUCCESSFUL RADIOFREQUENCY CATHETERMODIFICATION OF ATRIOVENTRICULAR JUNCTION FOR PATIENTS WITH MEDICALLYREFRACTORY PAROXYSMAL ATRIAL-FIBRILLATION

Background Mechanisms and changes of electrophysiological (EP) charact eristics in successful radiofrequency (RF) modification of right midse ptal and posteroseptal areas for controlling rapid ventricular respons e to atrial fibrillation (Af) are not clear. Methods and Results We st udied 50 patients with medically refractory paroxysmal Af. Group 1 con sisted of 40 patients without dual atrioventricular (AV;) node physiol ogy with modification sites located in the mid/posteroseptal area. Of the 40 patients, 36 had successful modification (follow-up of 14+/-8 m onths), and 3 had AV block. Late follow-up electrophysiological study (98+/-10 days) showed pattern 1 (67%) with prolongation of AV node eff ective refractory period (ERP, greater than or equal to 40 millisecond s) and Wenckebach block cycle length (WBCL, greater than or equal to 4 0 milliseconds); pattern 2 (22%) with prolongation of AH interval (gre ater than or equal to 20 milliseconds), ERP, and WBCL; and pattern 3 ( 11%) without any change in AV node conduction parameter. Change in ven tricular rate negatively correlated with change of WBCL in patterns 1 (r=-.691, P=.019) and 2 (r=-.90, P=.01). Group 2 consisted of 10 patie nts with dual AV node pathway; elimination of slow pathway property wa s performed. Late follow-up electrophysiological study (92+/-7 days) s howed that change in ventricular rate negatively correlated with chang e in AV node ERP (r=-.976, P=.0001) and WBCL (r=-.969, P=.0001). Four patients without significant modification effect had success after RF energy was delivered to higher levels (follow-up. 15+/-7 months). Conc lusions RF modification of right mid/posteroseptal area is feasible in 92% of patients with paroxysmal Af. Mechanisms of successful modifica tion might be elimination of posterior input and/or partial injury of the compact node. Furthermore, simple elimination of slow pathway migh t be inadequate for control of ventricular rate in patients with littl e difference in conduction properties between fast and slow pathways.