Anterior Mitral Line Ablation-Induced Complete Heart Block: A Cautionary Case Study

BACKGROUND Atrial flutter is associated with significant morbidity and mortality. Standard treatment involves rate and rhythm control medications, with ablation procedures reserved for more persistent cases. While ablation is generally successful, it carries risks, such as complete heart block, as in this case. CASE REPORT A 73-year-old woman presented for ablation of recurrent atypical atrial flutter. Electro-anatomic mapping demonstrated counterclockwise mitral annular flutter. An anterior ablation line was initially created from the right superior pulmonary vein to the mitral valve annulus. As the line was extended to the anterior mitral valve annulus at the 9 o'clock position, complete heart block occurred, and ablation was immediately terminated. Complete recovery of atrioventricular (AV) conduction occurred within 1 min. The catheter tip was within 1.8 cm from the His bundle, as denoted by the yellow tag on the CARTO map. A second mitral line was created anteriorly at the 11 o'clock position on the mitral valve annulus and extended to the left atrial roof line, with the termination and creation of a bi-directional mitral isthmus block. She remained in sinus rhythm after ablation, with PR prolongation and no AV block. The following day, she developed severe bradycardia due to complete heart block, with a slow ventricular escape rhythm, requiring implantation of a permanent pacemaker. CONCLUSIONS This case underscores the importance of precise catheter positioning during anterior mitral line ablation to prevent complications, such as AV block. Anterior mitral line ablation should be performed in a more anterior location away from the septum to minimize the risk of AV block.