Relationship between the membranous septum and the virtual basal ring of the aortic root in candidates for transcatheter implantation of the aortic valve

Knowledge of the anatomy of the membranous septum, as a surrogate to the location of the atrioventricular conduction axis, is a prerequisite for those undertaking transcatheter implantation of the aortic valve (TAVI). Equally important is its relationship of the virtual basal ring. This feature, however, has yet to be adequately described in the living heart. We analyzed computed tomographic angiographic datasets from 107 candidates (84.1 ± 5.2 years, 68% women) for TAVI. Using multiplanar reconstructions, we measured the height and width of the membranous septum, and the distances of its superior and inferior margins from the virtual basal ring plane. We also assessed the extent of wedging of the aortic root between the mitral valve and the ventricular septum. Mean heights and widths of the membranous septum were 6.6 ± 2.0, and 10.2 ± 3.1 mm, respectively, with its size significantly associated with that of the aortic root (P < 0.05). Its superior and inferior margins were 4.5 ± 2.3 and 2.1 ± 2.1 mm, respectively, from the plane of the basal ring. The inferior distance, the surrogate for the adjacency of the atrioventricular conduction axis, was ≤ 5mm in 91% of the patients. Deeper wedging of the aortic root was independently correlated with a shorter inferior distance (β = 0.0569, P = 0.0258). The membranous septum is appreciably closer to the virtual basal ring than previously appreciated. These findings impact on estimations of the risk of damage to the atrioventricular conduction axis during TAVI. Clin. Anat. 31:525–534, 2018. © 2018 Wiley Periodicals, Inc.