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 the mechanical function of a new retrieval unit. Methods: Stainless steel, titanium, and two prototype Greenfield filters ( n = 82) were placed in 15 sheep at multiple sites and retrieved acutely and 7, 14, and 21 days after placement. The animals were killed, and appropriate tissues were submitted for histopathologic evaluation. Results: Eighty-two percent of all filters were retrieved. Two animals died during the procedure of cardiac tamponade. Retrieval was easiest immediately after placement, but it was least successful from the right atrium and associated with the highest incidence of damage. By 21 days, the intima around the filter hooks had thickened with myointimal hyperplasia and variable amounts of endothelial regeneration. Guide wire–hook modification was used to improve filter capture. Conclusions: All models of the Greenfield filter can be retrieved 14 to 21 days after placement, although there is high risk to retrieval from the right atrium and ventricle. The long-term safety of the Greenfield filter in man makes it difficult to justify removal in any but exceptional cases. (J V ASC S URG 1994;20:744-50.)