P84: The impact of temporal synchronization on platelet activation in LVAD patients: CFD and PIV study for the HeartMate3 pulsatility mode.

Abstract

Study: LVAD patients continue to experience high rates of stroke. Stasis and high shear stresses contribute to platelet activation in the left ventricle, that can lead to thrombus formation. A pulsatility mode was incorporated into the HeartMate3 to improve in-pump washout. The pump speed modulation occurs every two seconds, independently of the cardiac cycle even in patients with preserved native contractility. This study examines intraventricular washout under different LVAD pulsatility/native cardiac cycle synchronization. Methods: A patient-specific 3D time-resolved computational fluid dynamics (CFD) simulation captures the hemodynamics in the left ventricle implanted with an LVAD. Lagrangian particle tracking models platelet motion from the mitral valve, across the left ventricle and out through the outflow cannula. The residence time and shear stress history for each platelet is tracked to determine its risk of activation. Four different temporal synchronizations between the LVAD pulsatility and the native contractility are studied: contraction, peak contraction, relaxation, and peak relaxation. The flow rate through the cannula is prescribed from flow meter data in the experimental campaign. Particle image velocimetry (PIV) experiments measured the in-plane and through plane velocity fields at two orthogonal planes in the ventricle. This PIV data is compared to the CFD to benchmark the simulations. Results: The different pulsatility mode synchronizations result in significantly different time-dependent flow rates through the cannula. The difference between these flow rates results in different hemodynamics patterns in the ventricle. The velocity fields from the CFD models agree closely with the results from the PIV experiments, and take these in a new direction with the use of Lagrangian platelet tracking. Recirculation zones develop underneath the aortic valve and around the cannula/apex pocket, resulting in areas of stasis for the platelets. By identifying platelets that experience both high shear stress history and long residence time, the thrombogenicity of the different synchronizations is evaluated.