Atrioventricular node modification in patients with chronic atrial fibrillation - Role of morphology of RR interval variation

Background-This study evaluates the role of RR interval distribution patter n as an outcome predictor of radiofrequency (RF) modification of atrioventr icular (AV) node in chronic atrial fibrillation (AF) and attempts to elucid ate the likely mechanism of rate control. Methods and Results-Sixty-five patients with chronic AF underwent AV node m odification. The RR interval distribution pattern was derived from 24-hour ECC recordings obtained before and after the procedure. The preablation pat tern was bimodal (B) in 36 patients (55%) and unimodal (U) in 29 patients ( 45%). After the modification procedure, the B pattern shifted to U (78%) or became modified B (22%). The mean number of RF pulses delivered and the fl uoroscopy time were n=8+/-5 and 24+/-11 minutes. respectively, in patients with B pattern versus n=18+/-7 and 45+/-17 minutes in patients with U patte rn (P<0.001 for both). The location of successful ablation was posterosepta l and lower midseptal in 26 patients (81%) with B pattern versus 2 (13%) wi th U pattern (P<0.001). Mean and maximal ventricular rates and heart rate a t peak exercise were reduced after the procedure in both groups (P<0.001 fo r all). Long-term success rate, AV block incidence, and pacemaker implantat ion rate were 89%, 0%, and 8%, respectively, in patients with B pattern ver sus 52% (P<0.001), 21% (P=0.006), and 48% (P<0.001) in patients with U patt ern. Conclusions-RF modification of the AV node is expected to be more effective , safe, and expeditious in patients with chronic AF and B RR interval distr ibution pattern. Posterior atrionodal input ablation may be the prevailing mechanism of rate control in these patients, whereas U-pattern patients may benefit from partial injury to the AV node.