148 - Defining the Left Atrial Appendage Neck: Subdivision, Morphometrical Description and Clinical Significance

Poster Board Number: 148
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Abstract Body : Introduction: the left atrial appendage is a clinically important structure located in the left atrium. There are several studies describing the distal part of the left atrial appendage. However, there is a lack of studies on its proximal part, which is clinically referred to as the neck of the left atrial appendage. The aim of this study is to anatomically define the neck of the left atrial appendage, analyze its morphometry, and investigate clinically important relationships.
Materials and Methods: The left atrial appendage, left ventricle, left atrium, pulmonary veins, and left coronary artery with its branches were segmented from 200 contrast-enhanced computed tomography scans and visualized using three-dimensional semiautomated algorithms. The neck of the left atrial appendage was defined as the area bounded proximally by the orifice of the left atrium and distally by the origin of the lobular portion of the left atrial appendage. The presence of the left atrial appendage neck was assessed and further divided into walls: venous, aortic, mitral, and free wall based on relationships to clinically important cardiac structures. Each wall and orifice was accurately measured. The lobular type of the left atrial appendage was assessed. P < 0.05 was considered statistically significant.
Results: The neck of the left atrial appendage was present in 98% of cases. The anteroposterior diameter of the proximal neck opening was 18.0±4.3 mm, and the distal anteroposterior diameter was 17.1±4.1 mm (statistically different, p=0.024). The transverse diameter of the proximal neck opening was 26.3±5.4 mm, the distal transverse diameter was 17.7±3.9 mm (statistically different, p < 0.001). Wall height was: 24.1±5.7 mm for venous, 16.6±4.2 mm for aortic, 6.4±3.2 mm for mitral, and 15.4±4.8 mm for free wall (all significantly different, p < 0.001, except for aortic/free wall comparison). The walls were proximally wide: 16.4±4.0 and for the venous, 14.0±5.5 for the aortic, 17.8±5.1 for the mitral, and 13.5±5.9 for the free wall (all significantly different p < 0.001, except for the aortic/free wall comparison and the mitral/venous comparison). There were no statistically significant differences in left atrial appendage morphology and left atrial appendage neck morphometric characteristics.
CONCLUSION: The left atrial appendage is present in most human hearts. The mitral wall is significantly lower than other walls. The neck of the left atrial appendage is adjacent to clinically important structures, such as the left coronary artery, the left superior pulmonary vein, and the mitral annulus. Three-dimensional reconstruction is a useful tool for analyzing the morphometry of the left atrial appendage.
Significance: The study provides the first complete definition and precise analysis of the neck of the left atrial appendage. Its classification creates the field for a better understanding of this region and provides a nomenclature that facilitates communication between researchers and clinical specialists. There are no differences between the types of the left atrial appendage. This means that the neck of the left atrial appendage should be analyzed separately from the morphologic type of its body. Accurate preoperative analysis of the neck of the left atrial appendage can reduce anatomically related postoperative complications. The neck of the left atrial appendage should be further studied in autopsied hearts and in a larger population to find rare variants of its anatomy.