Vena Caval Filters for the Prevention of Pulmonary Embolism
Young T, Aukes J, Hughes R, Tang H. Vena caval filters for the prevention of pulmonary embolism. Cochrane Database of Systematic Reviews 2007, Issue 3. Art. No.: CD006212. DOI: 10.1002/14651858.CD006212.pub2.
ABSTRACT: BACKGROUND: Pulmonary emboli can have potentially fatal consequences. Inferior vena caval filters are metal alloy devices that mechanically trap fragmented thromboemboli from the deep leg veins en route to the pulmonary circulation. Filters in current clinical use are designed to be introduced (and in the case of retrievable filters, removed) percutaneously. Although their deployment seems of theoretical benefit, their clinical efficacy and adverse event profile is unclear. OBJECTIVES: To examine evidence for the effectiveness of vena caval filters in preventing pulmonary embolism (PE). Secondary outcomes were mortality, distal (to filter) thrombosis, and filter-related complications. SEARCH STRATEGY: Searches were conducted in the Cochrane Peripheral Vascular Diseases Group Specialised Register (last searched May 2007), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 2, 2007), MEDLINE (1966 to May 2007), and EMBASE (1966 to May 2007). Filter manufacturers and clinicians interested in filters were contacted for information. SELECTION CRITERIA: Controlled clinical trials (CCTs) and randomised controlled trials (RCTs) that examined the efficacy of filters in preventing PE were selected. DATA COLLECTION AND ANALYSIS: Three authors extracted information independently. Incidence figures were extracted from survival tables. Dichotomous outcomes were analysed as hazard ratio estimates. MAIN RESULTS: One RCT met the inclusion criteria. The PREPIC trial was an open RCT of 400 participants with documented proximal deep vein thrombosis (DVT) or pulmonary embolism and who received concurrent anticoagulation. PREPIC demonstrated the efficacy of permanent caval filters in preventing PE at eight years (HR 0.37, 95% CI 0.17 to 0.79, in favour of the filter). No reduction in mortality was seen, but this reflected an older study population (mean age 73 years); the majority of deaths were due to cancer or cardiovascular causes. There was an increased incidence of DVT in the filter group (HR 1.52, 95% CI 1.02 to 2.27). No details were recorded of adverse events of filters. No CCTs suitable for inclusion were found. AUTHORS' CONCLUSIONS: Limited generalisability prevents any conclusions to be drawn from PREPIC. PREPIC employed permanent filters and lacked statistical power to detect a reduction in PE over shorter and more clinically significant time periods. However, PREPIC demonstrated that permanent caval filters are associated with an increased risk of long term lower limb DVT. There is a marked paucity of evidence regarding caval filter outcomes when used within their currently approved indications. There is also a lack of retrievable filter trials. Further trials are needed to assess vena caval filter safety and effectiveness.
Review: Vena Caval Filters for the Prevention of Pulmonary Embolism
Review by Shadi Kalantarian, MD
The possibility of preventing PE by placing a barrier in the migration path of the clot was first introduced by Trousseau in the 19th century. Femoral vein ligation and IVC ligation were early surgical interventions that were based on this hypothesis. However, major concerns about the considerable reduction in venous return, and the risk of embolization through the well developed collaterals, led to efforts for introduction and gradual improvement of Inferior Vena Cava Filters (IVCFs) for patients with DVT.
Since the1950s, IVCFs have been increasingly used for prevention of pulmonary embolism. However, the growth rate of pertinent evidence has not been commensurate with the growing use of such devices. The seventh ACCP guidelines on antithrombotic and thrombolytic therapy recommend IVCFs for patients suffering from a proximal DVT “with a contraindication for, or a complication of anticoagulation treatment, as well as in those with recurrent thromboembolism despite adequate anticoagulation”.
This systematic review performed by Young et al. aimed at assessing the effectiveness of vena caval filters for prevention of PE. Mortality, fatal PE, filter related complications, recurrent DVT, and post-thrombotic syndrome were the secondary outcomes.
Peripheral Vascular Diseases Group Specialized Register, MEDLINE, CENTRAL, and EMBASE were searched for RCTs and CCTs examining efficacy of filters for PE prevention.
Of the originally evaluated eleven papers, only one RCT was found, with a 2-year primary report and an updated 8-year follow up report. Eight studies were excluded because of poor methodological quality, and one was a cost-effectiveness analysis.
The PREPIC trial (a centralized RCT with two-by-two factorial design, on 400 patients with the mean age of 73 years, assessing the efficacy of IVCF as an adjunct to UFH or LMWH for PE prevention in patients with proximal DVT) was the only study included. Four types of filters were used in this trial but no clear data is available about subgroup analysis based on filter type. In summary, at an eight year follow-up, IVCF reduced the total number of symptomatic PE events (hazard ratio 0.37, 95% CI 0.17 to 0.79 in favor of a filter) whilst increasing the rate of documented recurrent DVT events (hazard ratio 1.52, 95% CI 1.02 to 2.27). No significant difference was observed at any time point in overall symptomatic venous thromboembolic events, all-cause mortality, or occurrence of post-thrombotic syndrome. It is important to recognize that this study examined the potential extension of IVCF to anticoagulation candidates, not its more common current indications for patients with contraindications to or failure of anticoagulant therapy.
Due to the lack of robust well designed studies, this systematic review, similar to the previous review by Girard et al., failed to find generalizable conclusions about the outcomes or indications of IVC filter placement. The current generalizability of PREPIC is limited by its lack of statistical power to assess for differences in symptomatic PE rates at the earlier (2-year) time point, the unavailability of validated measures of post-thrombotic syndrome at the time the study was conducted, and interval improvements in anticoagulant therapy which have since occurred. Anticoagulation remains the cornerstone of treatment of VTE and should be initiated and maintained as indicated by the guidelines as soon as there is no contraindication for it. Retrievable filters are theoretically superior to permanent filters but they need to be meticulously examined.
This systematic review emphasizes the enormous knowledge gap for indications and outcomes of IVC filter placement, highlighting priorities for further research.
References:
- Young T, Aukes J, Hughes R, Tang H. Vena caval filters for the prevention of pulmonary embolism. Cochrane Database of Systematic Reviews 2007, Issue 3. Art. No.: CD006212. DOI: 10.1002/14651858.CD006212.pub2.
- Hann CL, Streiff MB. The role of vena caval filters in the management of venous thromboembolism. Blood Rev. 2005;19(4):179-202.
- Büller HR, Agnelli G, Hull RD, Hyers TM, Prins MH, Raskob GE. Antithrombotic therapy for venous thromboembolic disease: the Seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy. Chest. 2004;126(3 Suppl):401S-428S.
- The PREPIC Study Group. Eight-year follow-up of patients with permanent vena cava filters in the prevention of pulmonary embolism: the PREPIC (Pre´vention du Risque d’Embolie Pulmonaire par Interruption Cave) randomized study. Circulation. 2005;112:416–422.
- Decousus H, Leizorovicz A, Parent F, Page Y, Tardy B, Girard P. et al. A clinical trial of vena caval filters in the prevention of pulmonary embolism in patients with proximal deep-vein thrombosis. Prévention du Risque d'Embolie Pulmonaire par Interruption Cave Study Group. N Engl J Med. 1998 12;338(7):409-15.
- Girard P, Stern JB, Parent F. Medical literature and vena cava filters: so far so weak. Chest. 2002 Sep;122(3):963-7.
About Shadi Kalantarian, MD: Shadi Kalantarian is student of medicine and a research fellow at Modarres Cardiovascular Research Center, Shaheed Beheshti University of Medical Sciences. Her research subjects of interest are atherosclerosis, thromboembolic disease, and arrhythmology. Currently she is heading a systematic review on surgical AF ablation with the Cochrane Collaboration.