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Design Characteristics of a Three-Dimensional Geometric Aortic Valve Annuloplasty Ring
Philip S. Crooke, PhD, L. Alan Beavan, MSE, J. Scott Rankin, MD.
Vanderbilt Univ., Nashville, TN, USA.

OBJECTIVE: A full geometric annuloplasty ring that restores three-dimensional aortic valve geometry toward normal could facilitate aortic valve repair. This study performed mathematical analyses of normal human aortic valve CT angiograms, in order to design such a ring.
METHODS: Using 1 mm axial slices, high-resolution CT angiograms from 11 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-sinus coordinates assessed geometry of aortic valve and root structures. Shapes and dimensions of all valve components were quantified, and attention was given to evaluating structural symmetry and root expansion during systole.
RESULTS: Normal valve geometry could be represented as 3 leaflet-sinus hemispheres nested within an elliptical aortic root. The base of the valve was quite elliptical (minor-major diameter ratio = 0.65), which extended vertically up the commissures. In contrast, leaflet-sinus circumferences were fairly circular (minor-major diameter ratios = 0.82-0.87), and the commissural post between left and non-coronary leaflets was located at the posterior minor diameter-circumference junction; the center of the right coronary leaflet was located opposite. Commissural post location on the circumference was symmetrical, with only a +/-1-2% deviation from 33.3% symmetry on average. The commissural posts flared outward by 5-10 degrees, and the 3 leaflets were of equivalent area and volume (p=0.42). From end-diastole to mid-systole, the aortic root became less elliptical (minor-major diameter ratio increased by 0.15), but area of the aortic root expanded minimally (+4.6%). A one-piece rigid Titanium annuloplasty ring, covered with a thin layer of Dacron, was designed to mimic normal diastolic geometry, with 2:3 base ellipticality and three 10-degree outwardly flaring subcommissural posts positioned symmetrically on the circumference (Figure).
CONCLUSIONS: A hemispherical model of normal aortic valve geometry was used to design a three-dimensional aortic annuloplasty ring. The design incorporated 2:3 diastolic base ellipticality, commissural symmetry, and 10-degree outwardly flaring subcommissural posts. This device may prove useful for restoring annular geometry toward normal during aortic valve repair.


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