Medical literature, vena cava filters and evidence of efficacy. A descriptive review.

Up to 15% of all patients with venous thromboembolism (VTE) receive an inferior vena cava filter, and prophylactic placements are increasing. To determine whether current use of filters is based on robust evidence, a global review of the recent (2001-2012) literature on filters was undertaken. The MEDLINE database was searched for articles related to filters appearing during the period 2001-2012, updating a prior search of literature from 1975-2001. All retrieved articles were analysed, classified into predetermined categories and compared to the prior analysis; randomised and large (>100 patients with a filter) comparative non-randomised clinical studies were read in full. The 651 articles, vs 568 in the period 1975-2000, consisted mainly of retrospective series (37.8%), case reports (31.7%), reviews (14.7%, vs 6.7%, p<0.001), animal and/or in vitro studies (7.5%, vs 12.9%, p=0.002), and prospective series or trials (4.9%, vs 7.4%, p=0.07). Of 4 new randomised trials (RCT), none were designed to test the efficacy of the device; to date, only one RCT has attempted to ascertain efficacy, occurring during the period 1975-2000. Eleven large non-randomised studies compared clinical outcomes of patients with and without filters, in VTE patients (n=5) or prophylactic indications (n=6); two studies found statistically significant relationships between filter use and lower mortality rates, though none could demonstrate a causal relationship. Hence, the plethoric literature on filters parallels growing experience with these devices, but still fails to provide reliable evidence that filter use improves relevant clinical outcomes. No indication for filter placement is based on appropriate scientific evidence.