Computational Investigation of Outflow Graft Variation Impact on Hemocompatibility Profile in LVADs

Abstract

<h3>Purpose</h3> Hemocompatibility related adverse events (HRAE) such as pump thrombosis, stroke, and gastrointestinal (GI) bleeding occur commonly in patients with left ventricular assist devices (LVADs). It is unclear whether the outflow graft orientation can impact flow conditions leading to HRAE. This study, used a simulation-based approach to investigate the influence that the cannula orientation has in modulating flow conditions leading to HRAEs. <h3>Methods</h3> A 3D model of a proximal aorta and outflow graft was reconstructed from a computer tomography (CT) scan of an LVAD patient and virtually modified to account for multiple cannula orientations (n=10) by varying polar (n=5) and off-set (n=2) angles. Time-dependent computer flow simulations were then performed and flow metrics as time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), endothelial cell activation potential (ECAP), flow shear (S), particle residence time (PRT), and platelet activation potential (PLAP) estimated. <h3>Results</h3> Flow shear was highest and lowest at the proximal aorta closer to the anastomosis and aortic sinus, respectively, in all configurations. Among all angles, time and space-averaged flow shear values were lowest at polar angles of 65° and 75° for 0° and 12° off-set angles, respectively. Flow metrics associated to thrombosis such as low TAWSS and high PRT, OSI, and ECAP were high at the aorta proximal to the sinus. <h3>Conclusion</h3> Acuter polar angles are commonly associated to flow conditions leading to fewer HRAEs. Using a time-depend flow simulation, this study suggests that an "ideal acute" rather than an acuter polar angle might lead to such flow conditions.