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A Refined “Hemispherical” Model of Aortic Valve and Root Geometry in Normal Human Valves

J. Scott Rankin1, M. Crockett Bone1, Peter M. Fries2, Diana Aicher2, Hans-Joachim Sch�fers2, Philip S. Crooke1.
1Vanderbilt University, Nashville, TN, USA, 2University of Saarland, Homburg-Saar, Germany.


OBJECTIVE:
Better understanding of aortic root geometry could improve diagnosis and reconstruction of pathologic aortic valves. In this study, a previous model of “Hemispherical” aortic valve leaflets nested within a cylindrical aorta was applied and refined in humans with normal aortic valves.
METHODS:
Using 1 mm axial slices, high-resolution CT angiograms from 10 normal aortic roots were used to generate high-density x, y, z coordinates of valve structures in Mathematica. Three-dimensional least squares regression analyses of leaflet and sinus coordinates were employed to compare multiple geometric models of aortic valve and root geometry. Shapes and dimensions of all root structures were evaluated.
RESULTS:
Normal valve geometry could be represented roughly as 3 hemispheres nested within a cylinder. However, the base of the valve was quite elliptical (minor-major diameter ratio = 0.65), and this geometry extended vertically up the commissures (Figure). Dimensional fits of the leaflet/sinus complexes also were better using ellipsoidal geometry, with taller leaflets than predicted by hemispheres. In contrast, leaflet/sinus horizontal circumferences were fairly circular (average minor-major diameter ratio = 0.82-0.87). The commissure between the left (LC) and non-coronary (NC) cusps was located uniformly at the posterior junction of the base minor diameter and circumference, with the center of the right coronary (RC) cusp opposite. Centrums of the LC, NC, and RC leaflet/sinus ellipsoids were migrated toward the center of the valve (average fractional migration or alpha = 0.24, 0.32, and 0.09, respectively), increasing coaptation area. The sub-commissural post areas flared outward by 5-10 degrees, and the volume of the RC leaflet/sinus complex was 12.5% and 10.7% larger than the NC and LC, respectively.
CONCLUSIONS:
A hemispherical model approximates aortic valve and root geometry in normal humans, but ellipsoidal refinements improve representation. The normal aortic valve is an elliptical structure, with the LC-NC commissure located posteriorly and the RC cusp anteriorly. This model could be useful in quantifying pathologic valve geometry and in engineering devices to facilitate aortic valve reconstruction.
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