BACKGROUND:Cerebral microthromboembolism after atrial fibrillation (AF) ablation has been reported in 4-20% with perioperative warfarin. Dabigatran is a new anticoagulant in patients with nonvalvular AF. We investigated the incidence of asymptomatic cerebral microthromboembolism after AF ablation with perioperative warfarin or dabigatran using diffusion-weighted and T2-weighted magnetic resonance imaging (MRI). METHODS AND RESULTS:Our study included 210 consecutive patients with AF (111 paroxysmal and 99 persistent) who underwent complex fractionated atrial electrogram-guided ablation (combined with pulmonary vein isolation, n = 110). Catheter irrigation was performed in all cases. Uninterrupted warfarin therapy was used in 180 patients (warfarin group) and interrupted only on the morning of the procedure with dabigatran in 30 (dabigatran group). All patients underwent cerebral MRI the day after ablation. New microthromboemboli were detected in 10.0% of the warfarin group and 26.7% of the dabigatran group (P < 0.05). The incidence of hemopericardium treated with pericardiocentesis was lower in the warfarin group than in the dabigatran group (2.5% vs 11.1%, P < 0.05). In multivariate analysis, the use of cardioversion was a predictor of new microthromboembolism development after AF ablation. CONCLUSIONS:The incidence of asymptomatic cerebral microthromboembolism and hemopericardium after AF ablation was significantly lower with perioperative warfarin therapy than with dabigatran therapy. Dabigatran may not be an effective alternative to warfarin for AF ablation, especially in patients who undergo cardioversion.