Effect of Leaflet Geometry on Mechanical Performance of Stentless Pericardial Aortic Valves - A Dynamic Simulation

摘要

Recent developments in aortic valve replacement include the truly stentless pericardial bioprostheses with Single Point Attached Commissures (SPAC). The leaflet geometry available for these valves can be a simple tubular or a complex three-dimensional molded structure resembling the natural valve. We compared mechanical performance of these two valve designs via dynamic simulation. Surface models representing a tubular valve and a molded valve incorporating the aortic root of 25 mm in diameter were created. An elastic modulus of 8 MPa and a density of 1,100 kg/m3 were assigned to the pericardial leaflet tissue. Time-varying physiological pressure loadings over a full cardiac cycle were applied on the upper and lower aortic root wall, and aorto-ventricular pressure gradient applied on the valve leaflets. The maximum effective valve orifice area during systole is 400.6 and 633.5 mm2 for the tubular and the molded valves, respectively. When fully closed, the free edges in the molded valve form S-shaped lines characterized by twisting at the valve center, a phenomenon not apparent in the tubular valve. Consequently, the coap-tation height in the former is nearly four times greater than in the latter, being 4.5 and 1.2 mm, respectively. Computed com-pressive stress indicates that high magnitude in the tubular valve prevails at the commissure, along the inter-leaflet margin and the leaflet basal attachment line, while in the molded valve it occurs at the center of the free edge and on the leaflet belly. The highest stress magnitude in the tubular is 3.83 MPa versus 1.80 MPa in the molded. The molded leaflet geometry resembling the natural valve performs better than the simple tubular geometry for the SPAC valves, by producing greater effective orifice area, better coaptation properties, and lower magnitude in compressive stress, which should translate into enhanced valve efficacy and durability.