Introduction: Focal activation is believed to be an atrial fibrillation (AF) driver; however, little is known about whether all focal activations are necessary for AF persistence. The purpose of this study was to assess the electrical nature of focal activation and identify high-priority focal activations using a novel mapping system (CARTOFINDER). Methods: Thirty-five patients with persistent AF who underwent catheter ablation were assessed. Cycle length (CL) and CL standard deviation (CLSD) on unipolar recordings and voltage amplitude and electrogram morphologies on bipolar recordings were evaluated at all points of interest. The most frequent CL at each mapping site was defined as the dominant CL. We identified dominant focal activations (DFAs) that had a shorter dominant CL on the integrated CARTOFINDER map. The effect of elimination of DFAs on AF maintenance was assessed by the composite endpoint (termination to sinus rhythm, organization of the rhythm to atrial tachycardia, and AF CL slowing). Results: In all, 450 focal activations were identified among 10,868 points, and 50.4% of focal activations were DFAs. Focal activations showed relatively long CL and regularity with short CLSD. Most focal activations showed an isoelectric baseline and were located outside of the fractionated electrogram area. Both DFAs and non-DFAs were typically observed in normal voltage range. Elimination of DFAs was achieved in 19 (54.3%) patients, with a remarkable impact on AF maintenance (68.4% vs. 25.0%, p = 0.018). Conclusions: DFAs may play an important role in AF maintenance and could be an attractive therapeutic target for AF.

Introduction: The risk of developing left atrial (LA) thrombi after initial catheter ablation for atrial fibrillation (AF) and requirements for imaging evaluation for thrombi screening at repeat ablation is unclear. This study aimed to assess the occurrence of thrombus development and frequency of any imaging study evaluating thrombus formation during repeat ablation for AF. Methods: Of 2,066 patients undergoing initial catheter ablation for AF with uninterrupted oral anticoagulation, 615 patients underwent repeat ablation after 258.0 (105.0-882.0) days. We investigated which factors were associated with safety outcomes and requirements for thrombi screening. Results: All patients underwent at least one imaging examination to screen for thrombi in the first session, but the examination rate decreased to 476 patients (77%) before the repeat procedure. The frequency of imaging evaluations was 5.0%, 11%, 21%, 84%, and 91% for transesophageal echocardiography and 18%, 33%, 49%, 98%, and 99% for any imaging modality at repeat ablation performed ≤60 days, ≤90 days, ≤180 days, >180 days, and >1 year after the initial procedure, respectively. Three patients (0.5%) developed LA thrombi at repeat ablation due to identifiable causes, and no patients had thromboembolic events when no imaging evaluation was performed. Multivariate analysis revealed that repeat ablation >180 days, non-paroxysmal atrial arrhythmias, and lower left ventricular ejection fraction were predictors of the risk of thrombus development. Conclusions: The risk development of thrombus at repeat ablation for AF was low. There needs to be a risk stratification for the requirement of imaging screening for thrombi at repeat ablation for AF.