Retrievable IVC square stent filter: Experimental study

Purpose: In vitro and in vivo evaluation of a new retrievable, home-made, i nferior vena cava (IVC) Square stent filter (SSF) with two trapping levels. Methods: In vitro, the SSF was compared in a flow model with the stainless steel Greenfield filter (SGF) for emboli-trapping efficiency by serially pa ssing 300 emboli of 3 and 6 mm in diameter and 15-30 mm in length in each t ype of filter. Nine swine were used for the in vivo testing of the SSF for deployment and retrievability, emboli-trapping efficiency, stability, and s elf-centering ability and two were used (total of II swine) for testing rep ositioning and retrievability of the SSF at 2 weeks and for gross and histo logic IVC changes at 2 months. Results: In vitro, the SSF and SGF had similar efficiency in trapping large emboli but the SSF had significantly better efficiency than the SGF for tr apping all sizes of emboli (91.7% vs 81%), medium size emboli (93% vs 80%), and small emboli (86% vs 69%). Efficiency decreased in both filters from t he first to the fifth embolus in each series but was still significantly be tter for the SSF. With the SSF, 89% of emboli were caught at the primary an d 11% at the secondary filtration level. In the nine animals used for acute studies, the SSF was easily placed in all 27 attempts, assumed a central p osition 26 times, and was easily retrieved in 21 of 22 attempts. One tilted filter needed additional manipulation for retrieval. During emboli injecti on in five swine, the SSF had 97.2% emboli-napping efficiency and demonstra ted good stability. In the two animals used for longer-term evaluation, the filters were easily retrieved 2 weeks after implantation. Histologic evalu ation at 2 months showed neointimal proliferation around the SSF wires in c ontact with the IVC wall, which was otherwise normal. Conclusion: The SSF is a promising filter. It is easy to place and retrieve , is stable after placement, and has high efficiency for trapping emboli. P romising results justify further experimental and eventual clinical studies with a commercially manufactured SSF.