Pressure and flow fields in the hinge region of bileaflet mechanical heartvalves

Background and aim of the study: Recent clinical thrombotic experiences wit h the Medtronic Parallel(TM) (MP) bileaflet heart valve have highlighted th e need for new methods to assess preclinical valve hinge flow. The aim of t he current study was to investigate hinge pivot flow fields in bileaflet me chanical heart valves using flow visualization in scaled x5 magnification t ransparent polymer models and computational fluid dynamic (CFD) analysis us ing CFD 2000 STORM code. Methods: Polymeric x5 flow models of the On-X(R), St. Jude Medical (STM) an d MP bileaflet heart valves were constructed using laser stereolithography to replicate the interior geometry while maintaining realistic manufacturin g tolerances. Each hinge flow experiment was carried out by installing the transparent x5 model in a pulsatile flow loop, which was designed according to Womersley number similitude requirements. Motions of suspended micropar ticles in the valve hinge area, recorded by laser imaging techniques, were used to visualize hinge flow. Experimentally measured parameters were used as input for CFD analysis. CFD simulations were made by solving the Navier- Stokes equation using a finite volume method with the pressure-based algori thm for continuity, and a pressure-implicit with splitting of operators (PI SO) algorithm for pressure-velocity coupling. Moving grid methodology was e mployed to simulate periodic motion of the valve leaflets. CFD hinge flow r esults were visualized on four parallel planes at different depths in the h inge socket. The hinge flow patterns of the three types of bileaflet heart valve design are discussed. Results: Prominent vortex formation and stagnant flow areas were noticed in the pivot region of the MP valve. Vortices persisted throughout both the f orward- and reverse-flow phases. These flow structures were not observed in the hinge areas of the SJM and On-X valves. Conclusions: Vortex formation observed in the MP valve may contribute to th e high thrombogenic potential of this valve. The absence of such vortices a nd areas of stagnant flow in the On-X and SJM valves indicate that hinge fl ow conditions in these valves do not favor mechanically induced thrombogene sis or thromboembolic events.