A 'hemispherical' model of aortic valvar geometry

An improved understanding of aortic valvar anatomy could assist in further developing surgical repair of the valve. The study aim was to evaluate the three-dimensional (3-D) geometry of the aortic valve in normal human hearts.

In eight human cadaver hearts, the aorta and valve were opened longitudinally through the zone of apposition between the right and left coronary leaflets, and photographed. A leaflet of the valve was photographed individually. Valvar circumference (C) was measured as the distance across the aorta at the base of the leaflets. The radius of the valvar orifice (r) was calculated as C/2pi, and the distance between commissures (the peripheral attachments of the zones of apposition between the leaflets at the sinotubular junction) (D') as C/3. The height (h) of the commissural zone of apposition between the leaflets, and also the length (L) of the free-edge, were measured. A model was developed in which three hemispheres, representing the leaflets supported within the sinuses, intersected a cylinder, representing the aorta, all of equivalent radii. The model was tested using dimensional data and paired t-tests.

In the model, the hemispheres met at the center of the valvar orifice, and each subtended 120 degrees of aortic circumference. The mean (+/- SD) D' (24.7 +/- 2.4 mm) was similar to L (24.5 +/- 2.1 mm), and h (11.9 +/- 1.0 mm) was similar to r (12.0 +/- 1.6 mm) (all p > 0.68), consistent with the model. A series of equations was developed to describe the 3-D geometry of the hemispheres and cylinder in hemispherical and cylindrical coordinates. The areas of coaptation between the leaflets could be calculated, and the intersections between the hemispheres and the cylinder mathematically defined the attachments of the leaflets. Conceivably, the measurement of L could be used to calculate other geometric parameters necessary for valvar competence.

The normal human aortic valve may be represented as three hemispheres intersecting a cylinder, all with equivalent radii. This simple approach may better define normal anatomic variability, pathologic abnormalities, and strategies for surgical repair.