RESUMO
BACKGROUND: This study evaluates the role of RR interval distribution pattern as an outcome predictor of radiofrequency (RF) modification of atrioventricular (AV) node in chronic atrial fibrillation (AF) and attempts to elucidate the likely mechanism of rate control. METHODS AND RESULTS: Sixty-five patients with chronic AF underwent AV node modification. The RR interval distribution pattern was derived from 24-hour ECG recordings obtained before and after the procedure. The preablation pattern 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 fluoroscopy 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 pattern (P<0.001 for both). The location of successful ablation was posteroseptal and lower midseptal in 26 patients (81%) with B pattern versus 2 (13%) with U pattern (P<0.001). Mean and maximal ventricular rates and heart rate at peak exercise were reduced after the procedure in both groups (P<0.001 for all). Long-term success rate, AV block incidence, and pacemaker implantation rate were 89%, 0%, and 8%, respectively, in patients with B pattern versus 52% (P<0.001), 21% (P=0.006), and 48% (P<0.001) in patients with U pattern. 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 distribution 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.