Effect of fixed-rate vs. rate-RESPONSIve pacing on exercise capacity in patients with permanent, refractory atrial fibrillation and left ventricular dysfunction treated with atrioventricular junction aBLation and bivEntricular pacing (RESPONSIBLE): a prospective, multicentre, randomized, single-blind study.

<bold>Aims: </bold>Atrioventricular junction (AVJ) ablation followed by biventricular pacing is an established strategy for improving symptoms and morbidity in patients with permanent atrial fibrillation (AF), reduced left ventricular ejection fraction (LVEF), and uncontrolled ventricular rate. There is no clear evidence that such patients benefit from rate-responsive (RR) pacing.<bold>Methods and Results: </bold>This prospective, randomized, single-blind, multicentre study was designed as an intra-patient comparison and enrolled 60 patients (age 69.5 ± 11.8 years, males 63.3%, NYHA 3.0 ± 0.6) with refractory AF and reduced LVEF (mean 32.4 ± 8.3%) treated with AVJ ablation and biventricular pacing. Two 6-minute walking tests (6MWT) were performed 1 week apart: one during VVI 70/min biventricular pacing and the other during VVIR 70-130/min biventricular pacing; patients were randomly and blindly assigned to Group A (n = 29, first 6MWT in VVIR mode) or B (n = 31, first 6MWT in VVI mode). Rate-responsive activation determined an increase of 18.8 ± 24.4 m in the distance walked during the 6MWT (P < 0.001). The increase was similar in both groups (P = 0.571). A >5% increase in the distance walked was observed in 76.7% of patients. The increase in the distance walked was linearly correlated with the increase in heart rate recorded during the 6MWT in the VVIR mode (r = 0.54; P < 0.001).<bold>Conclusion: </bold>In permanent AF patients with uncontrolled rate and reduced LVEF who had undergone AVJ ablation and biventricular pacing, RR pacing yields a significant gain in exercise capacity, which seems to be related to the RR-induced frequency during effort. [ABSTRACT FROM AUTHOR]