Anatomical and morphometric variation of the orifice of the left atrial appendage

Background. Knowledge of the anatomical variations of the shape and size of the left atrial appendage orifice, along with the relationship of its size with the number of left atrial appendage lobes, the size of its neck, the left atrioventricular orifice, the left atrioventricular fibrous ring and the distance to it, as well as with the overall dimensions of the heart is important in personalized surgical planning for the installation of occluder device and left atrial appendage clipping to prevent thromboembolic complications. Aim. To identify anatomical variations in the shape and size of the left atrial appendage orifice and analyze the dependence of these parameters on the number of left atrial appendage lobes, cardiac dimensions, mitral orifice area and the distance from the orifice to the left atrioventricular fibrous ring. Material and methods. We studied 37 heart specimens fixed in 10% formalin in adults who died of non-cardiac causes. Morphometry was performed by an ShTsTs-1-200 digital calliper, drawing needle calliper and 4UM goniometer. We used nonparametric analysis of variance, Spearman correlation coefficient (Rs), univariate regression analysis, cross-tabulation analysis. The results are presented as the mean and standard deviation. The significance of differences was assessed by using the MannWhitney U-test. Results. The left atrial appendage was single-lobed in 16.2% of cases, two-lobed in 62.2%, and three-lobed in 18.9%. The length of the orifice was 12.74.03 mm, and the width was 9.53.62 mm. The elliptical shaped orifices were 3.1 times more common than round ones (28/37 and 9/37, p=0.0027). In 17 of 28, oval orifices were located predominantly horizontally, in nine predominantly vertical, in one case obliquely. Vertically oriented orifices were significantly longer and slightly wider compared with others. The number of the left atrial appendage lobes was not a reliable predictor for the orifice shape (p=0.055). The size of the appendage orifice, variants of its shape and the distance to the left atrioventricular opening were unrelated to each other. The length and width of the orifice were correlated with each other (Rs 0.68) and correlated with the diameters of the left atrioventricular fibrous ring size. The orifice length correlated with the length of the ventricular complex (Rs 0.47) and heart width (Rs 0.53). The orifice width correlated only with the heart width (Rs 0.4) but not with other dimensions. As the length and width of the ventricular complex increased, the orifice length increased exponentially. The distance from the left atrial appendage orifice to the left atrioventricular opening did not depend on either the orifice shape or its orientation. Conclusion. In a normal human adult heart, the shape of the left atrial appendage orifice was oval, less often round, and the size of the orifice depends on the length and the width of the ventricles.