Modeling blood flow in a tilted inferior vena cava filter: does tilt adversely affect hemodynamics?

PURPOSE: Filter tilt is often seen with conical filters and adversely affects retrievability and clot trapping efficiency. In addition, tilt may also alter flow dynamics. This study uses computational fluid dynamics to evaluate flow past an unoccluded and partially occluded Celect inferior vena cava filter (Cook, Bloomington, Indiana). In particular, the hemodynamic response to thrombus volume and filter tilt is examined, and the results are compared with flow conditions known to be thrombogenic.
MATERIALS AND METHODS: Computer models of an upright and tilted Celect filter are constructed using high-resolution digital photographs and methods of computer-aided design. The three-dimensional models are placed inside a model cava, and steady-state flow past unoccluded and partially occluded filters is computed.
RESULTS: The volume of stagnant and recirculating flow increases with thrombus volume. In addition, as filter tilt increases, the cava wall in the direction of filter tilt is subjected to low-velocity flow and gives rise to regions of low wall shear stress.
CONCLUSIONS: Flow conditions caused by the tilted Celect filter may elevate the risk of intra/perifilter thrombosis and facilitate vascular remodeling. This latter condition may increase the potential for incorporation of the hook of the filter into the vena cava wall, thereby complicating filter retrieval. These findings also suggest that further long-term clinical follow-up with conical filters should be pursued with a specific evaluation of tilt as a factor of intrafilter thrombus and thrombosis.