Lateral ridge of left atrium

The lateral ridge of the left atrium (Left lateral ridge; Left atrial ridge; warfarin ridge; Coumadin ridge) is an infolding of the atrial wall located between the orifice of the left atrial appendage and the ostia of the left-sided pulmonary veins.

This structure contains epicardial adipose tissue and small vessels, most notably the vein or ligament of Marshall on its epicardial aspect.

The ridge is a variable anatomical structure present in approximately 59.5% of humans. When present, it has a mean length of 22.4 ± 5.1 mm and is wider at its inferior sector (9.1 ± 5.0 mm) compared to its superior sector (7.9 ± 3.2 mm). The myocardial composition includes fibers from the leftward extension of Bachmann's bundle along with inferior branches of the septopulmonary and septoatrial bundles.

The ridge can appear as a single muscular protuberance or may end with a bulbous configuration known as the "Q-tip sign." This bulbous appearance was historically misdiagnosed as thrombus on early transesophageal echocardiography, which explains the alternative names "Coumadin ridge" or "Warfarin ridge."

The left lateral ridge is important in electrophysiology as a potential source of arrhythmias and can present an obstacle during ablation procedures. The Marshall structures and autonomic nervous system are in close proximity (<3 mm) to the endocardial surface at the superior level of the ridge in 70% of specimens. Knowledge of this anatomy is essential for left atrial appendage closure procedures to properly define the appendage orifice boundaries and avoid complications.