STAGING OF FIXATION AND RETRIEVABILITY OF GREENFIELD FILTERS

Purpose: The purpose of this study was to determine the retrievability of the Greenfield filter, to characterize fixation, and to evaluate t he mechanical function of a new retrieval unit. Methods: Stainless ste el, titanium, and two prototype Greenfield filters (n = 82) were place d in 15 sheep at multiple sites and retrieved acutely and 7, 14, and 2 1 days after placement. The animals were killed, and appropriate tissu es were submitted for histopathologic evaluation. Results: Eighty-two percent of all filters were retrieved. Two animals died during the pro cedure of cardiac tamponade. Retrieval was easiest immediately after p lacement, but it was least successful from the right atrium and associ ated with the highest incidence of damage. By 21 days, the intima arou nd the filter hooks had thickened with myointimal hyperplasia and vari able amounts of endothelial regeneration. Guide wire-hook modification was used to improve filter capture. Conclusions: All models of the Gr eenfield filter can be retrieved 14 to 21 days after placement, althou gh there is high risk to retrieval from the right atrium and ventricle . The long-term safety of the Greenfield filter in man makes it diffic ult to justify removal in any but exceptional cases.