Vena caval filters for the prevention of pulmonary embolism.

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.