Hemodynamic Analysis of VenaTech Convertible Vena Cava Filter Using Computational Fluid Dynamics

Abstract

The VenaTech convertible filter (VTCF) has been widely used as an inferior vena cava (IVC) filter to prevent fatal pulmonary embolism in patients. However, its hemodynamics that greatly affect the filter efficacy and IVC patency are still unclear. This paper uses computational fluid dynamics with the Carreau model to simulate the non-Newtonian blood flows around the VTCF respectively deployed in the normal, reverse and three converted states in an IVC model. The results show that the prothrombotic stagnation zones are observed downstream from the normal, reverse and small open VTCFs, with the streamwise length is nearly eight times the IVC diameter. The no-slip boundary conditions of the thin-wire VTCF arms lead to the "viscous block" effect. The viscous block accelerates the blood flow by 5-15% inside the IVC and enhances the filter wall shear stress up to nearly 20 times that of the IVC only, which contributes to clot capture and thrombus lysis. The relative flow resistance is defined to evaluate the filter-induced resistance on the IVC blood flow that can be regarded as an index of IVC patency with the filter deployment. The flow resistance of the normal VTCF deployment increases dramatically by more than 60% compared with that of the IVC only and is a little higher (6%) than that of the reverse case. As the VTCF converts to a fully open configuration, the flow resistance gradually decreases to that of no filter. This work shows that even very thin VTCF arms can result in the viscous block effect and may cause significant hemodynamic impacts on clot capture, potential thrombosis and flow impedance inside the IVC. The present study also shows that CFD is a valuable and feasible in silico tool for analyzing the IVC filter hemodynamics to complement in vivo clinical and in vitro experimental studies.

Evaluation of hemodynamic effects of different inferior vena cava filter heads using computational fluid dynamics

“…Due to the continuity of blood flow, the low-speed zones around filter wires creates an acceleration effect inside the cone and between any two wires, as shown in Figures 8B,C . Wang et al (2020) called this acceleration mechanism the “viscous block”.…”

“…The results indicated that there is the obvious stagnant and recirculating flow downstream of the filter head, which possibly traps emboli for potential thrombogenesis. The simulation data of VenaTech convertible filter (B. Braun, Melsungen, Germany) by Wang et al (2020) also showed the stagnation and recirculation zone downstream the filter head. At present, there are remarkable differences in the structure pattern of filter head between different IVCFs used in clinic.…”

“…For simplicity, three-dimensional model of the IVC is constructed as a rigid cylindrical tube with a diameter ( D ) of 20 mm as many previous studies have done. Flow extensions are added at the inlet and outlet sections, respectively, the lengths of which are both nearly 20 times D to ensure fully developed laminar flow and avoid the unreasonable boundary effects of simulation ( Wang et al, 2020 ).…”

“…For 2), the maximum velocity magnitude ( U max ) on the centric line and the area-weighted average WSS ( WSS avg ) at the filter surface are used as the target parameters to calculate the convergence orders ψ and GCI for mesh 3 to 6, respectively. In Table 2 WSS avg is formulated as follows ( Wang et al, 2020 ): where φ is the surface area of the Denali filter. As the total number of grids increases, the GCIs show a decreasing trend from mesh 3 to 6.…”

“…Viscous drag, pressure drag and flow resistance for four filters with different heads (unit: dyne).Frontiers in Bioengineering and Biotechnology frontiersin.org as shown in Figures8B,C Wang et al (2020). called this acceleration mechanism the "viscous block".…”