The architecture of the left lateral atrial wall: a particular anatomic region with implications for ablation of atrial fibrillation

TLDR

The left lateral ridge (LLR) spans the left atrial wall transmurally, containing myofibres from Bachmann’s bundle and septopulmonary/ septoatrial bundles, and lies adjacent to the epicardial vein or ligament of Marshall. The study aimed to elucidate the structural composition of the LLR to inform atrial fibrillation ablation strategies. The authors dissected 40 heart specimens and performed histological sectioning of the LLR and adjacent tissue. The LLR is a fold with superiorly narrower width and thicker myocardium, and its variable dimensions and close proximity (<3 mm) to Marshall structures and autonomic nerves may influence AF propagation.

Abstract

We examined the left lateral ridge (LLR) between the orifices of the left pulmonary veins and the left atrial appendage for a better understanding of its structural composition relevant to ablations for atrial fibrillation (AF). The LLR and its surrounding areas were studied in 40 heart specimens by dissection and histological sections. The LLR is a fold of the atrial wall with a mean width that was narrower superiorly than inferiorly (P < 0.001). Its myocardial thickness at the antero-superior level was thicker than at the postero-inferior level (2.8 ± 1.1 vs. 1.7 ± 0.8 mm, P < 0.001). Transmurally from subepicardium to subendocardium, the LLR comprises myofibres from the leftward extension of Bachmann's bundle together with the inferior branches of the septopulmonary bundle and the septoatrial bundle. The vein or ligament of Marshall is located on the epicardial aspect of the LLR. 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. The variability in width and thickness of the LLR, its proximity to Marshall structures and autonomic nerves, and myofibre arrangement may be significant in the fibrillatory process and spread of AF activity.