Vena caval filters for the prevention of pulmonary embolism
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 methods
We searched the Cochrane Peripheral Vascular Diseases Group Specialised Register (last searched November 2007), the Cochrane Central Register of Controlled Trials (CENTRAL) in The Cochrane Library 2007, Issue 4, MEDLINE (1966 to November 2007), and EMBASE (1966 to November 2007). Filter manufacturers 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 independentlyextracted information. Incidence figures were extracted from survival tables. Dichotomous outcomes were analysed as hazard ratio estimates.
Main results
One RCT was included. The PREPIC (Prévention du Risque d'Embolie Pulmonaire par Interruption Cave) trial was an open RCT of 400 participants with documented proximal deep vein thrombosis (DVT) or PE and who received concurrent anticoagulation. Permanent caval filters prevented 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.
Authors' conclusions
No recommendations can be drawn from the one included study in which permanent filters were used. The study lacked statistical power to detect a reduction in PE over shorter and more clinically significant time periods. However, the PREPIC trial demonstrated that permanent caval filters were associated with an increased risk of long term lower limb DVT.
There is a marked paucity of caval filter outcomes evidence 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.
PICOs
Plain language summary
Vena caval filters for the prevention of pulmonary embolism
Blood clots in the lungs are called pulmonary emboli. They originate in the legs, fragment and travel to the lungs via the inferior vena cava. Vena caval filters are metal alloy devices inserted within the inferior vena cava to trap blood clots and thus prevent pulmonary emboli. Further emboli are usually prevented by blood thinning medications (anticoagulants).
In some instances (approximately 4% of cases), anticoagulation alone is insufficient to prevent more emboli or it is too dangerous for anticoagulation to be given because the person has a high risk of bleeding. Blood clots are known to ocur as a result of certain types of surgery or injuries, and are more likely to fragment if they extend into the thigh or pelvis.
Vena caval filters have been in use since the 1970s and were designed to be left permanently within the inferior vena cava. The latest generation of filters is temporary or 'retrievable'. They can be removed at the manufacturer's recommendation between 2 to 12 weeks, if their use is no longer required. However, despite being called retrievable, a number of retrievable filters cannot be removed because of complications. The long‐term safety profile of these devices left inside the body remains to be seen. We looked for articles comparing permanent and temporary (or retrievable) filters and comparisons between the different filter designs.
The review found only one randomised controlled trial with 400 participants. No controlled clinical trials were found of satisfactory quality.
No recommendations can be made regarding filter efficacy in preventing pulmonary embolism. In the one included trial, caval filters were associated with an increased risk of blood clots following their insertion. This study did not demonstrate any difference in the death rates between the two groups; the participants were older (average age 73 years) with co‐existing medical conditions and the majority of people died from cancer‐related causes or heart problems. No details were recorded of adverse events of filters, but the numbers in this single trial were not of sufficient size to detect them.
There is a marked paucity of information on the effectiveness of caval filters in other clinical scenarios, especially in the two situations where they are used most frequently and thought to be the most advantageous namely when patients cannot be anticoagulated or when pulmonary embolism occurs despite anticoagulation. Vena caval filter use is increasing and more trials are needed to confirm their benefit and accurately assess their safety.
