The Marshall Complex in Atrial Fibrillation: Anatomy, Mechanisms, and Ablation Strategies

Researchers commonly regard the ligament of Marshall (LoM), an embryologic remnant of the left superior vena cava (LSVC), as a vestigial structure. However, despite its vestigial origin, the LoM retains functionally significant myocardial fibers, autonomic nerves, and venous elements. These muscular and neural components give LoM the capacity to trigger, sustain, or modulate atrial arrhythmias, particularly atrial fibrillation (AF). Recent studies have demonstrated that the LoM can serve as both an arrhythmogenic focus and a substrate for reentry, and its epicardial connections may undermine conventional ablation lines. Hence, researchers have developed new therapies to target this region. This review summarizes the anatomy, embryology, and electrophysiological properties of the LoM. It evaluates the clinical impact of Marshall complex targeted therapies, including vein of Marshall ethanol infusion (VoM-EI), in contemporary AF management.