Mitral isthmus block in a case of persistent left superior vena cava.

Persistent left superior vena cava (LSVC), an uncommon venous anomaly, could be an arrhythmogenic source of atrial fibrillation. Multiple electrical connections were reported between the LSVC and the left atrium, which may negatively impact the achievement of conduction block during linear ablation of left mitral isthmus. We describe a case with perimitral atrial flutter (AFL) in a patient with isolated LSVC. AFL was successfully treated and complete perimitral conduction block was achieved following a lengthy epicardial radiofrequency application.