Hemodynamic Effects of Clot Entrapment in the TrapEase Inferior Vena Cava Filter

Abstract

The TrapEase vena cava filter has a symmetric design. Emboli can be trapped in the outlet conical section (superior cone) or between the filter and vessel wall at the inlet end (inferior cone). The purpose of this in vitro study is to investigate the hemodynamic effects of clot entrapment by the TrapEase filter and to examine the possibility of flow-induced filter thrombosis. Velocity and wall shear stress maps were determined for steady flow with use of the photochromic flow visualization technique. Experiments were done for a filter without clot and for three other cases: an asymmetric clot in the inferior zone, a symmetric clot in the superior zone, and a filter with both zones partially occluded. Each simulated clot was 1500 mm(3) and the vessel diameter was 2 cm. The unoccluded filter did not significantly affect the flow field. However, for a partially occluded filter, flow stagnation/recirculation and turbulence developed downstream from the clot. The greatest effect was noted when the clot was against the vessel wall in the inferior trapping region. The tendency for clots to be trapped between the filter and the vessel wall in the inferior (inlet) region may play an important role in the performance of the TrapEase filter. A clot in this configuration will generate a large region of flow stagnation/recirculation that is considered to be prothrombotic. In addition, a significant amount of the filter wire will be embedded in this region, which may also promote thrombosis.