A prospective ex vivo biomechanical analysis of retrievable inferior vena cava filters

Objective: In the present study, we investigated the structural integrity of inferior vena cava (IVC) filters after their retrieval. Methods: A prospective ex vivo biomechanical analysis was performed of the structural integrity of 100 IVC filters used in a randomized controlled trial to evaluate the effectiveness of prophylactic IVC filters in preventing mortality or symptomatic pulmonary embolism in major trauma patients. Results: Of the 100 included patients, 7 (7%) had required more than one attempt to remove the filter. The median duration of the filter left in situ was 54 days (interquartile range, 17-101 days). During the initial attempt to remove six filters (6%), thrombi were found entrapped and required 4 weeks of systemic anticoagulation therapy before the filters could be removed in a second attempt. A positive correlation was found between the duration of the filter left in situ and the loss in metallic elasticity of the nitinol alloy of the filter struts (Pearson correlation coefficient, 0.232; P = .008). One filter was adherent to the IVC wall and required open surgical removal 227 days after its initial placement. One of the six long struts of the filter had been fractured during the removal process, with evidence of hardening to bending stress in the remaining five struts of the fractured filter compared with the struts of the 25 intact filters. Fibrous endothelial tissue (73%) and thrombi (33%) adherent to the retrieved filters were frequently observed. The presence of adherent fibrous tissue was not significantly related statistically to the duration of the filter left in situ (P = .353) but was more common among the patients who had had a delay in receiving prophylactic anticoagulation therapy (mean difference, 2 days; 95% confidence interval, 0.6-3.3; P = .039). Conclusions: Metallic fatigue might account for IVC filter strut fractures. Fibrous endothelial tissue adherent to the filters was common, especially for those with a delay in receiving prophylactic anticoagulation therapy.