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Clot Site May Affect DVT Treatment Outcome

Kate Traynor

Canadian researchers say the location of the clot may be a critical factor in predicting whether standard anticoagulant therapy will succeed in patients diagnosed with deep vein thrombosis (DVT) in a lower limb.

About 5.2 percent of patients whose initial clot was in a vein near the knee or along the femur had a recurrent symptomatic thrombosis within three months of starting anticoagulation therapy. The rate of recurrence was more than twice as high, 11.8 percent, among patients whose initial clot extended into the pelvic region. Although this difference in recurrence did not reach the threshold of statistical significance, the researchers said their findings suggest that patients with iliofemoral vein thrombosis may need a regimen more aggressive than standard anticoagulant therapy.

The study involved 633 men and 516 women who had been diagnosed with symptomatic lower-limb DVT. They were participating in two randomized clinical studies of anticoagulation therapy and were, on average, 60 years old. The patients had had a previous venous thromboembolism; had a trauma or surgery in the past four weeks; been immobile in the past four weeks; or had cancer.

All study participants underwent at least four days of anticoagulant therapy with intravenous unfractionated heparin, subcutaneous enoxaparin, or subcutaneous reviparin. These treatments were accompanied by at least three months' therapy with a coumarin derivative, with dosages adjusted to attain a target International Normalized Ratio of 2.0–3.0.

On entry into the study, 453 patients had been diagnosed with popliteal vein thrombosis. In 654 patients, the thrombosis involved the femoral vein only; and in 51, the clot was located in the iliofemoral vein. Venography or duplex ultrasound were used to diagnose each patient’s initial thrombosis. These tests were also used to diagnose a recurrent thrombosis in the leg; ventilation-perfusion lung scan or pulmonary angiography was used to detect pulmonary embolism.

In all, 5.5 percent of the study participants had a recurrent thrombosis within three months of starting anticoagulation therapy. Seventy percent of the recurrent clots were in a leg vein, and 27 percent were in a pulmonary artery. In 3 percent of the recurrences, the patients had DVT and a pulmonary embolism.

An editorial accompanying the report, which appeared in the May American Journal of Medicine, concurred on the likely clinical relevance of the study. The editorialist, National Institutes of Health clinician McDonald K. Horne III, M.D., urged that additional research be done to discover effective ways to treat iliac-vein thrombosis. But Horne noted that until clinical studies are done, standard therapy is the only advisable treatment option, even though such regimens are "obviously inadequate" for some patients.