The Marshall Complex in the Human Heart: Embryology, Microanatomy, Autonomic Features and Clinical Implications for Atrial Fibrillation-A State-of-the-Art Narrative Review.

The vein and ligament of Marshall (VOM and LOM) are embryological remnants that have gained increasing recognition due to their anatomical complexity, arrhythmogenic potential, and relevance during catheter ablation and structural heart interventions. This review summarizes current evidence on their embryology, morphology, anatomical variability, imaging characteristics, and clinical implications. A structured literature search across PubMed, Embase, and Scopus identified anatomical, histological, electrophysiological, and interventional studies. The VOM is present in most hearts, but its topographic variants and ostial positions show substantial interindividual diversity. The LOM displays a segmental architecture with distinct muscular and fibrotic components that interface with the atrial myocardium and the coronary sinus, providing a substrate for atrial fibrillation. Advances in cardiac imaging have improved delineation of the VOM-LOM region, enhancing pre-procedural assessment and guidance for ethanol infusion and ablation strategies. Recognition of the variability and functional significance of these structures is essential for optimizing procedural outcomes and avoiding complications. Taken together, the VOM and LOM represent key atrial venous remnants whose detailed characterization contributes to a deeper understanding of atrial arrhythmogenesis and contemporary interventional electrophysiology.