A Numerical Investigation of Blood Damage in the Hinge Area of Aortic Bileaflet Mechanical Heart Valves During the Leakage Phase

Abstract

Previous experimental and numerical blood studies have shown that high shear stress levels, long exposure times to these shear stresses, and flow recirculation promote thromboembolism. Artificial heart valves, in particular bileaflet mechanical heart valves (BMHVs), are prone to developing thromboembolic complications. These complications often form at the hinge regions of BMHVs and the associated geometry has been shown to affect the local flow dynamics and the associated thrombus formation. However, to date no study has focused on simulating the motion of realistically modeled blood elements within the hinge region to numerically estimate the hinge-related blood damage. Consequently, this study aims at (a) simulating the motion of realistically modeled platelets during the leakage (mid-diastole) phase in different BMHV hinge designs placed in the aortic position and (b) quantitatively comparing the blood damage associated with different designs. Three designs are investigated to assess the effects of hinge geometry and dimensions: a 23 mm St. Jude Medical Regent™ valve hinge with two different gap distances between the leaflet ear and hinge recess; and a 23 mm CarboMedics (CM) aortic valve hinge. The recently developed lattice-Boltzmann method with external boundary force method is used to simulate the hinge flow and capture the dynamics and surface shear stresses of individual platelets. A blood damage index (BDI) value is then estimated based on a linear shear stress-exposure time BDI model. The velocity boundary conditions are obtained from previous 3D large-scale simulations of the hinge flow fields. The trajectories of the blood elements in the hinge region are found to be qualitatively similar for all three hinges, but the shear stresses experienced by individual platelets are higher for the CM hinge design, leading to a higher BDI. The results of this study are also shown to be in good agreement with previous studies, thus validating the numerical method for future research in BMHV flows. This study provides a general numerical tool to optimize the hinge design based on both hemodynamic and thromboembolic performance.

Highly resolved pulsatile flows through prosthetic heart valves using the entropic lattice-Boltzmann method

“…The authors have demonstrated in previous studies that LBM in combination with the EBF method is able to accurately quantify platelet damage in BMHV flows on a smaller scale in the hinges when compared with blood damage experiments (Wu et al 2011;Yun et al 2012). The LBM-EBF method can now be included to accurately quantify platelet damage in pulsatile flows throughout the entire BMHV geometry in future studies across varying physiologic conditions.…”

“…This would increase the chances of thromboembolic complications incurred in diastolic flows, beyond those complications already known to occur in the hinge regions. Using the platelet damage quantification method with LBM-external boundary force (EBF) (Wu et al 2011;Yun et al 2012), these high-risk regions can be further analysed in future simulations.…”

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.…”

Towards computational prediction of flow-induced damage of blood cells using a time-accumulated model

“…De Wachter and Verdonck, 2002;Yun et al, 2012). However, still there is a lack of reliable mathematical model to correlate differential shear stress and the exposure time to damage experienced by blood cells.…”