A Clinical Trial of Vena Caval Filters in the Prevention of PE in patients with proximal DVT
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Posted By: A Delaney
Posted Date: 4/6/03
Title: A Clinical Trial of Vena Caval Filters in the Prevention of PE in patients with proximal DVT
Authors: Hervé Decousus, M.D., Alain Leizorovicz, M.D., Florence Parent, M.D., Yves Page, M.D., Bernard Tardy, M.D., Philippe Girard, M.D., Silvy Laporte, B.S., René Faivre, M.D., Bernard Charbonnier, M.D., Fabrice-Guy Barral, M.D., Yann Huet, M.D., Gérald Simonneau, M.D., for The Prévention du Risque d'Embolie Pulmonaire par Interruption Cave Study Group
Reference: N Engl J Med 1998;338:409-15
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Abstract: Background The efficacy and safety of vena caval filters in the prevention of pulmonary embolism in patients with proximal deep-vein thrombosis are still a matter of debate.
Methods Using a two-by-two factorial design, we randomly assigned 400 patients with proximal deep-vein thrombosis who were at risk for pulmonary embolism to receive a vena caval filter (200 patients) or no filter (200 patients), and to receive low-molecular-weight heparin (enoxaparin, 195 patients) or unfractionated heparin (205 patients). The rates of recurrent venous thromboembolism, death, and major bleeding were analyzed at day 12 and at two years.
Results At day 12, two patients assigned to receive filters (1.1 percent), as compared with nine patients assigned to receive no filters (4.8 percent), had had symptomatic or asymptomatic pulmonary embolism (odds ratio, 0.22; 95 percent confidence interval, 0.05 to 0.90). At two years, 37 patients assigned to the filter group (20.8 percent), as compared with 21 patients assigned to the no-filter group (11.6 percent), had had recurrent deep-vein thrombosis (odds ratio, 1.87; 95 percent confidence interval, 1.10 to 3.20). There were no significant differences in mortality or the other outcomes. At day 12, three patients assigned to low-molecular-weight heparin (1.6 percent), as compared with eight patients assigned to unfractionated heparin (4.2 percent), had had symptomatic or asymptomatic pulmonary embolism (odds ratio, 0.38; 95 percent confidence interval, 0.10 to 1.38).
Conclusions In high-risk patients with proximal deep-vein thrombosis, the initial beneficial effect of vena caval filters for the prevention of pulmonary embolism was counterbalanced by an excess of recurrent deep-vein thrombosis, without any difference in mortality. Our data also confirmed that low-molecular-weight heparin was as effective and safe as unfractionated heparin for the prevention of pulmonary embolism.
Are the Results Valid?
1. Was the assignment of patients to treatments randomized? ( Was allocation concealment maintained?)
Yes, consecutive patients were randomised via a computerised central telephone system, stratified accordong to centre
2. Were all patients who entered the trial properly accounted for and attributed at its conclusion?
2a. Was followup complete?
There were 28 patients who were not followed up at 8-12 days with regards to the primary end-point. Which groups these patients were randomised to is not mentioned
2b. Were patients analyzed in the groups to which they were randomized?
Yes, the analyses were done on an intention to treat basis.
3. Were patients, health workers, and study personnel blind to treatment?
The patients and health care workers were not blinded to the treatment. Outcomes were assessed by adjudicators who were blinded to treatment allocation.
4. Were the groups similar at the start of the trial?
The two groups were similar with regards to the reported baseline characteristics.
5. Aside from the experimental intervention, were the groups treated equally?
Patient randomised to unfractionated (UF) heparin had extra blood tests ordered to control the level of anticoagulation. Apart from this the 4 groups were treated equally.
What are the Results?
1. How large was the treatment effect?
With regards to the primary outcome of the occurance of pulmonary embolism (PE) by day 12, there were significantly fewer patients with PE in the IVC filter group 2 (1.1%) v's 9 (4.8%).
With regards to the comparison of low molecular weight heparin (LMWH) and UF heparin, there was a trend towards fewer patients with PE by day 12, 3(1.6%) v's 8(4.2%) in the LMWH group which was not statistically significant.
2. How precise was the estimate of the treatment effect?
The odds ratio for the reduction in PE with the use of IVC filters was 0.22 with 95% confidence intervals from 0.05-0.90.
The odds ratin for the reduction in PE with the use of LMWH compared to UF heparin was 0.38 with 95% confidence intervals from 0.10-1.38.
Will the Results Help Me In Caring For My Patients?
1. Can the results be applied to my patient care?
Patients who have a DVT and are at risk of PE is a common problem in many clinical situations. The question of whether to place an IVC filter often arises in this setting.
2. Were all clinically important outcomes considered?
There were many secondary end-points examined in this trial. In the short term there was no significant difference in the incidence of major bleeding or death in any of the groups. IVC filters were associted with a trend towards fewer pulmonary emboli 6(3.4%) v's 12(6.3%) (p=0.16), but an increase in the number of recurrent DVT's 37(20.8%) v's 21(11.6%) (p=0.02). There were no differences between LMWH and the UF heparin in the 2 year follow-up.
3. Are the likely treatment benefits worth the potential harms and costs?
The use of LMWH as an option for the treatment of venous thromboembollic disease is now well accepted. The place of IVC filters in the management of patients with venous thromboembolic disease remains uncertain. This study would suggest that IVC filters may prevent early pulmonary embolism in patients with DVT and high risk of PE. Over a longer period of time, if the IVC filter is left in-situ then the increase in the incidence of DVT becomes significant. A strategy that involves either the use of removable IVC filters or the continuation of anticoagulation for as long as the IVC filter is in-situ may be needed tested to define the optimal use of this therapy.

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