In vitro and in vivo experimental evaluation of a new vena caval filter.

Objective: A new stainless steel (MP35N alloy) vena cava filter without a central stasis point was evaluated in vitro and in vivo.

Methods: The clot-trapping efficiency and hemodynamic flow pattern of the filter were assessed in a flow model and were compared with those of currently available commercial filters including the Vena Tech-LGM, Simon nitinol, Greenfield, and Bird's Nest filters. The new filter was placed in the inferior vena cava (IVC) of 31 dogs; 21 of the 31 dogs were followed up with cavography for up to 3 months. At the termination of the study, the filters and IVCs were examined grossly and histologically. An in vivo clot-trapping test was carried out in five dogs.

Results: The least turbulence was noted with the new filter and the titanium Greenfield filter. The stainless steel Greenfield and Simon nitinol filters caused major flow disturbances. Migration within 5 cm of initial placement occurred in two animals (9.5%). There were no IVC thromboses, perforations, or filter embolizations. An in vivo clot-trapping study showed an 80% efficiency for small thrombi (3 x 20 mm) and 100% efficiency for large thrombi (6 x 20 mm) with the new filter. The Simon and the new filter had the best clot-trapping capabilities. The Vena Tech-LGM and Bird's Nest filters were slightly inferior and the Greenfield filter demonstrated by far the lowest trapping capacity.

Conclusions: The new vena cava filter is easily introduced percutaneously through a 12-F sheath and appears to be very promising due to its high filtering capability, low turbulence, nonmagnetic properties, good mechanical stability, and hypothrombogenicity. Clinical trials are warranted.