Vein of Marshall in AF Ablation IntroductionThe ligament of Marshall may hinder the creation of mitral isthmus (MI) block or pulmonary vein (PV) isolation (PVI) in radiofrequency (RF) catheter ablation of atrial fibrillation (AF). We aimed to assess the benefit of RF ablation targeting the vein of Marshall (VOM) in failed cases of MI block or PVI. Methods and ResultsWe reviewed the medical records of patients who underwent RF ablation targeting the VOM after failed MI ablation or left PVI using the conventional method, which included circumferential point-by-point ablation around the PV antrum and carina for PVI, and endocardial MI and epicardial distal coronary sinus (CS) ablation for MI block. The VOM was identified by using selective VOM venography with an external irrigation RF ablation catheter. RF ablation targeting the VOM was performed with RF application at the ostium of the VOM inside the CS or at the endocardial region facing the VOM course. During the set period, CS venography was performed in 42 patients after failure of left PVI (n = 5) or MI block (n = 37). Under CS venography, the VOM was visualized in 22 of 42 patients (MI = 19 and PVI = 3). During selective venography of the VOM, no procedure-related complication was observed. RF application targeting the VOM successfully achieved MI block in 13 patients (68.4%) and PVI in 2 patients (66.7%). ConclusionSelective VOM venography using an irrigated ablation catheter is feasible and safe. RF ablation targeting the VOM may provide additional benefit in failed cases of MI block or PVI.