An optimal mounting frame to reduce flexural stresses of bioprosthetic heart valves

Recent studies suggest that sharp bending of valve leaflets during the opening phase may be the reason for much of the mechanical failure of bovine pericardial bioprostheses. Sharp bending of the valve leaflets is promoted by the rigid, non expanding stents upon which the leaflets are mounted. We hypothesized that sharp bends and the associated flexural stresses could be significantly reduced by incorporating a stent that expands with the recipient aorta during systolic valve opening. We therefore modeled the opening and closing sequence of a trileaflet bovine pericardial valve with such an expanding supporting stent using our own finite element analysis software. Six different degrees of expansion were simulated, ranging from 2% to 25% expansion measured at the level of the stent post tips. Our results show that a 15% expansion is optimal, for the analyzed valve, because it eliminates the compressive flexural stresses at the commissures. Expansions below 15% were not sufficient to reduce flexural stresses, whereas expansions greater than 20% induced excessive tension in the valve cusps.