Background: Mechanisms and changes of electrophysiological (EP) characteristics in successful radiofrequency (RF) modification of right midseptal and posteroseptal areas for controlling rapid ventricular response to atrial fibrillation (Af) are not clear.
Methods and results: We studied 50 patients with medically refractory paroxysmal Af. Group 1 consisted of 40 patients without dual atrioventricular (AV) node physiology with modification sites located in the mid/posteroseptal area. Of the 40 patients, 36 had successful modification (follow-up of 14 +/- 8 months), and 3 had AV block. Late follow-up electrophysiological study (98 +/- 10 days) showed pattern 1 (67%) with prolongation of AV node effective refractory period (ERP, > or =40 milliseconds) and Wenckebach block cycle length (WBCL, > or =40 milliseconds); pattern 2 (22%) with prolongation of AH interval (> or =20 milliseconds), ERP, and WBCL; and pattern 3 (11%) without any change in AV node conduction parameter. Change in ventricular 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 patients with dual AV node pathway; elimination of slow pathway property was performed. Late follow-up electrophysiological study (92+/-7 days) showed that change in ventricular rate negatively correlated with change in AV node ERP (r=-.926, 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).
Conclusions: RF modification of right mid/posteroseptal area is feasible in 92% of patients with paroxysmal Af. Mechanisms of successful modification might be elimination of posterior input and/or partial injury of the compact node. Furthermore, simple elimination of slow pathway might be inadequate for control of ventricular rate in patients with little difference in conduction properties between fast and slow pathways.