Anatomy of the Left Atrium:

TLDR

The renewed interest in radiofrequency ablation for atrial fibrillation has prompted a detailed review of the left atrium’s gross anatomy, including its septum, appendage, pulmonary vein insertions, and the limited true septal component relevant to transseptal procedures. The study aims to clarify the left atrium’s muscular architecture to enhance linear and focal ablation strategies for atrial fibrillation. The authors performed a gross anatomical review of normal hearts, examining the septum, appendage, and pulmonary vein insertions of the left atrium. The left atrium’s musculature consists of overlapping fiber bundles forming characteristic patterns, with muscular sleeves extending into pulmonary veins—longest in the left upper veins—alongside Bachmann’s bundle and posterior wall extensions into the coronary sinus, revealing greater complexity than previously thought.

Abstract

The feasibility of treating atrial fibrillation with radiofrequency ablation has revived interest in the structure of the left atrium, a chamber that has been neglected in many textbooks of anatomy.We reviewed the gross structure of the left atrium by examining the septum, the appendage, and insertions of the pulmonary veins in normal hearts. The limited extent of the true septal component is relevant to procedures using the transseptal approach. On gross examination, the musculature of the atrial wall is composed of overlapping bundles of aligned fibers that, in the majority of hearts, are arranged in characteristic patterns with only minor individual variations. Muscular sleeves extend into the walls of the pulmonary veins to varying distances. The longest sleeves are in the left upper veins. Bachmann's bundle anteriorly, and other smaller bundles superiorly and posteriorly, bridge the septal raphe to blend with musculature of the right atrium. Tongues of left atrial musculature from the posterior wall also extend into the wall of the coronary sinus.The left atrium is more complex than usually conceived. Understanding its structure, and the arrangement of its musculature, will help in improving strategies for linear lesions when attempting to compartmentalize the chamber, or when placing focal lesions for ablating ectopic sources.