Ligament of Marshall: Why it is important for atrial fibrillation ablation

The ligament of Marshall (LOM) is located on the epicardium between the left atrial appendage and the left pulmonary veins. The corresponding endocardial structure is the left lateral ridge. LOM is a source of paroxysmal AF, and may activate at fast rates during persistent AF. Because of the importance of LOM in the mechanisms of AF, the techniques of LOM ablation are important to the practicing cardiac electrophysiologist. LOM contains muscle bundles (Marshall bundles) that directly connect to atrial myocardium and coronary sinus muscle sleeves. These muscle structures can serve as a source of triggers and drivers for AF, and may form the substrates of reentry. In some patients, these muscle bundles take part in accessory pathway conduction in patients with preexcitation syndrome. LOM can be mapped by either endocardial or epicardial approach. Elimination of the LOM potential during endocardial ablation confirms the successful creation of transmural lesion that includes the LOM. In patients who cannot be mapped or ablated via endocardial approach, epicardial approach is needed to map and ablate the LOM. In addition to the Marshall bundle, the LOM also has rich autonomic innervation. The ganglionated plexi are present in and around the LOM. These ganglionated plexi can be ablated during catheter ablation procedures or during open-heart surgery. In summary, LOM is important in the mechanisms of AF and may participate in accessory pathway conduction in patients with preexcitation syndrome. Mapping and catheter ablation of LOM is both feasible and clinically useful in controlling atrial arrhythmias.