Motivation: Anti-coagulation for acute DVT and PE does not make complete sense to me. I understand that anti-coagulation stops clot extension, but what about the big DVT stranded in the vein? Nothing really prevents it from chipping off in the next few days to the pulmonary vasculature. Seems to me that a temporary IVC filter while beginning anti-coagulation may prevent PE while buying time for the DVT to be naturally absorbed. Two days ago, while contemplating this apparently novel strategy, I was surprised to see that this idea had not only been thought about but also been tested through a randomized trial.
Paper: Decousus, H. et. al. "A Clinical Trial of Vena Caval Filters in the Prevention of Pulmonary Embolism in Patients with Proximal Deep-Vein Thrombosis." NEJM (1998); 338: 409-416.
Methods: Multicenter, open label randomized trial in France. Two-by-two factorial design randomizing patients with proximal DVT to permanent IVC filter vs no filter and to low molecular weight heparin (LMWH) vs unfractionated heparin. Patients on LMWH and UFH were transitioned to coumadin treatment starting on day 4. Inclusion criteria were adults with proximal DVT with or without concomitant PE. Important exclusion criteria were contraindication to anti-coagulation and hereditary thrombophilia. Primary outcome was occurrence of pulmonary embolism within first 12 days after randomization. All patients were evaluated first by V/Q scan and then by pulmonary angiography if necessary. Patients were followed for two years.
Results:
Cohort: In total, 400 patients were recruited and randomized to IVC filter (200 to filter, 200 to no filter) and anti-coagulation (195 to LMWH and 205 to UFH). Mean age was 72 years and 47.5% were male. 49% of patients presented with PE in addition to DVT. About 35% had prior thromboembolism and 14% had known cancer. About 11% had surgery in the past 60 days.
Primary Outcome: Within the first 12 days, there were 2 PE in group with filter compared to 9 in the group with no filter (OR: 0.22, CI: 0.05-0.90), p=0.03. There were 5 deaths in each group. Within the first 12 days, there were no differences in PE incidence, major bleeding, or death between the LMWH or unfractionated heparin.
2 Year Follow-Up: At two years post-randomization, patients with IVC filter had significantly more DVT compared to no filter (20.8% vs. 11.6%, OR: 1.87, CI: 1.10-1.45), p = 0.02. There were no differences in symptomatic PE or mortality. For patients treated initially with UFH or LMWH, there were no differences in outcomes after two years.
Discussion: This trial shows that while IVC filter may prevent PE in the short term, presence of a filter increases risk of DVT in the long term. The paper also shows that on average, there is no difference between LMWH and UFH for acute treatment of DVT. The trial still leaves open the possibility though that an IVC filter inserted for the short tem may decrease the incidence of PE. While there was no difference in mortality between the two groups, a larger cohort may have shown mortality benefit in addition to the short-term decrease in PE. This question, however, is probably going to be hard to address since this trial is one of the very few randomized trials evaluating IVC filter. Perhaps, the makes of the IVC filter may be interested in supporting such a trial!
Discussion: This trial shows that while IVC filter may prevent PE in the short term, presence of a filter increases risk of DVT in the long term. The paper also shows that on average, there is no difference between LMWH and UFH for acute treatment of DVT. The trial still leaves open the possibility though that an IVC filter inserted for the short tem may decrease the incidence of PE. While there was no difference in mortality between the two groups, a larger cohort may have shown mortality benefit in addition to the short-term decrease in PE. This question, however, is probably going to be hard to address since this trial is one of the very few randomized trials evaluating IVC filter. Perhaps, the makes of the IVC filter may be interested in supporting such a trial!
