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

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.