Abstract
BACKGROUND: Perimitral atrial flutter is a complex atrial tachycardia involving endocardial and epicardial structures. The standard ablation strategy includes endocardial radiofrequency and vein of Marshall ethanol infusion, but restoring sinus rhythm can be challenging even in experienced centres. CASE SUMMARY: We report the cases of three male patients (60-, 75-, and 58-year-old) with persistent and symptomatic atypical atrial flutter. They shared a previous history of numerous atrial fibrillation catheter ablations. Endocardial left atrial activation mapping found a perimitral macro-reentry, refractory to radiofrequency on the mitral isthmus line and in the coronary sinus. Vein of Marshall ethanol infusion was feasible in one patient, but failed to achieve complete mitral isthmus line block. The vein of Marshall was absent in the other two patients. A subxiphoid approach was performed under general anaesthesia, and mapping confirmed an epicardial critical isthmus located between the musculature of the coronary sinus (anteriorly) and the left inferior pulmonary vein (posteriorly). Epicardial radiofrequency applications resulted in conversion to sinus rhythm and complete conduction block along the mitral isthmus line. No complication was observed, and patients remained in sinus rhythm after at least 2 years of guideline-directed follow-up and without the need for antiarrhythmic drugs. DISCUSSION: Epicardial bridging may account for a significant proportion of catheter ablation failure in perimitral atrial flutters. In such cases, a subxiphoid percutaneous epicardial approach appears to be a safe and effective strategy to target the epicardial gap, restore sinus rhythm, and obtain complete mitral isthmus line block.