The Efficiency-Hemocompatibility Paradox: A Comparative Lagrangian and Eulerian Analysis of Micro-axial p-LVAD...

Percutaneous Left Ventricular Assist Devices (p-LVADs) require a delicate balance between hydraulic efficiency and hemocompatibility. While Eulerian turbulence models offer computational speed, their reliability in predicting mechanical blood damage in complex micro-axial geometries compared to established Lagrangian frameworks remains poorly understood.

We employed computational fluid dynamics to evaluate four p-LVAD configurations across 20 operating conditions. Models 1-3 utilized a discharge-type architecture, while Model 4 utilized a suction-type configuration with an expanding hub. Hemocompatibility was assessed using two Eulerian turbulence-based indices (HI₁, HI₂) and two Lagrangian metrics: Median Stress Accumulation (Median SA) and Mean Supra-threshold Exposure Time (t_ATA).

A critical design paradox was identified in the suction-type pump: while the expanding hub improved hydraulic efficiency by preventing flow separation, it created a high-velocity bottleneck that significantly elevated bulk shear. Consequently, higher hydraulic efficiency in suction designs was associated with increased Lagrangian blood damage. Eulerian indices functioned primarily as "RPM trackers," showing a near-perfect correlation with the Womersley number (R > 0.94) but failing to capture geometry-induced stress peaks. In contrast, Lagrangian metrics provided a sensitive, multivariate assessment of mechanical loading.

Eulerian models are insufficient for evaluating micro-axial pumps where bulk shear is the dominant damage mechanism. Lagrangian particle tracking (median SA and t_ATA) remains the necessary high-fidelity standard for p-LVAD optimization. These findings highlight the fluid dynamic advantages of discharge-type pump architectures, offering a compelling engineering strategy to mitigate high-shear stress exposure compared to suction devices.