Comparison of the Hemodynamic and Thrombogenic Performance of Two Bileaflet Mechanical Heart Valves Using a CFD/FSI Model

Abstract

The hemodynamic and the thrombogenic performance of two commercially available bileaflet mechanical heart valves (MHVs)--the ATS Open Pivot Valve (ATS) and the St. Jude Regent Valve (SJM), was compared using a state of the art computational fluid dynamics-fluid structure interaction (CFD-FSI) methodology. A transient simulation of the ATS and SJM valves was conducted in a three-dimensional model geometry of a straight conduit with sudden expansion distal the valves, including the valve housing and detailed hinge geometry. An aortic flow waveform (60 beats/min, cardiac output 4 l/min) was applied at the inlet. The FSI formulation utilized a fully implicit coupling procedure using a separate solver for the fluid problem (FLUENT) and for the structural problem. Valve leaflet excursion and pressure differences were calculated, as well as shear stress on the leaflets and accumulated shear stress on particles released during both forward and backward flow phases through the open and closed valve, respectively. In contrast to the SJM, the ATS valve opened to less than maximal opening angle. Nevertheless, maximal and mean pressure gradients and velocity patterns through the valve orifices were comparable. Platelet stress accumulation during forward flow indicated that no platelets experienced a stress accumulation higher than 35 dyne x s/cm2, the threshold for platelet activation (Hellums criterion). However, during the regurgitation flow phase, 0.81% of the platelets in the SJM valve experienced a stress accumulation higher than 35 dyne x s/cm2, compared with 0.63% for the ATS valve. The numerical results indicate that the designs of the ATS and SJM valves, which differ mostly in their hinge mechanism, lead to different potential for platelet activation, especially during the regurgitation phase. This numerical methodology can be used to assess the effects of design parameters on the flow induced thrombogenic potential of blood recirculating devices.

Numerical Model of Full-Cardiac Cycle Hemodynamics in a Total Artificial Heart and the Effect of Its Size on Platelet Activation

“…6). It is interesting to mention that leakage flow patterns are found even though the sizes of the discs was not altered, unlike in previous simulations that reduced the discs sizes, and therefore increased the gaps width [15,31]. This strong leakage may also be an artifact of the non-physiologic combination of the boundary conditions and diaphragm motion.…”

“…This method for modeling the valves was later used by Medvitz et al [23] and Topper et al [24] for different types of Penn State VAD. Current literature describing flow through bileaflet mechanical heart valves (MHVs) on the other hand, do employ FSI models that also simulate the leaflets motion [15,17,13,14,21]. In bileaflet MHV the leaflets can only rotate around their hinges and their motion is defined by one degree of freedom.…”

The Syncardia™ total artificial heart: in vivo, in vitro, and computational modeling studies

“…Of all presently available, FDA approved bi-leaflet valves the Medtronic Open Pivot (formerly ATS) has previously been demonstrated to have more desirable flow characteristics and is the least platelet activating (Dumont et al, 2007; Xenos et al, 2010). Bileaflet MHVs offer better hemodynamic performance but may be more sensitive to their orientation in respect to the flow field.…”

Mechanical Platelet Activation Potential in Abdominal Aortic Aneurysms

“…Previous studies of biomechanical platelet activation have typically modeled platelets as either infinitesimal [22,23,25,[31][32][33] or finite-sized [26,[34][35][36][37][38] particles. In either case, Lagrangian particle tracking of the position and stress histories of individual platelet surrogates in the flow is used.…”