Modeling High Residence Time Platelets in LVAD patients. Intraventricular Flow and Lagrangian Statistics in a Patient-Specific Model of a Deformable Ventricle.

A numerical model of LVAD-supported intraventricular flow is used to study the trajectory of platelets in the left ventricle(LV) of an advanced Heart Failure patient implanted with an LVAD. The anatomy and motion of the LV walls are measured from 4D Computed Tomography (CT). Ventricular motion is enforced to the computational model by assigned mesh deformation. Inflow and outflow through valves and LVAD cannula are applied as boundary conditions, balanced with the ventricular volume change. After transients have been eliminated (discarding 3 cycles), flow tracers were injected during multiple mitral fillings and tracked for more than 15 cardiac cycles. Lagrangian statistics reveal the dynamics of platelets in the failing LV with remaining contractability, assisted by an LVAD. The study identifies a small but crucial portion of extremely high residence time platelets in the left ventricle, despite continuous flow from LVAD (5 L/min), and the characteristics of the trajectories of these anomalous “pockets” of platelets that do not mix with the incoming mitral flow and do not evacuate the ventricle. These trajectories could shed light on the persistence of thrombogenic conditions in LVAD patients despite recent improvements in LVAD performance and reduction of in-pump thrombosis.