SAN DIEGO – The “holy grail” of thrombosis prevention is the ability to determine the risk of recurrence with or without continuation of anticoagulant treatment, according to Philip S. Wells, MD.
“Very little data exists for the comparison of active treatment to placebo in the acute and long-term phases of treatment,” he said at the biennial summit of the Thrombosis & Hemostasis Societies of North America. “With low molecular weight heparin, vitamin K antagonists, and direct-acting oral anticoagulants, the relative risk reduction is about 90% in the acute phase and 80%-85% in the extended phase. After discontinuing anticoagulants, the absolute risk of recurrence varies depending on VTE category.”
Dr. Wells, chair and chief of the department of medicine at The Ottawa Hospital and the University of Ottawa, said that after 3 months of anticoagulation the chance of recurrence in postsurgical VTE patients is less than 1% per year. After 3 months of anticoagulant use in nonsurgical patients with provoked risk factors, it is around 4%. This includes medical patients, trauma victims, pregnant women, and patients wearing a plaster cast.
In patients who survive an unprovoked VTE, after 3-6 months of anticoagulant therapy their overall recurrence risk is 10% in the first year and 30% after 5 years. The risk of recurrence is 50% higher if a patient experiences a second unprovoked VTE, and the risk of fatality is 50% higher if the initial event was a pulmonary embolism (PE), he said.
According to the ongoing prospective Austrian Study on Recurrent Venous Thromboembolism, the risk of recurrent VTE is 20% in men and 6% in women (N Engl J Med. 2004 Jun 17;350[25]:2558-63). A multicenter prospective study in Canada yielded similar results. It found that the risk of recurrent VTE is 19% in men versus 9% in women (CMAJ 2008;179[5]:417-26).
That Canadian prospective study, led by Marc Rodger, MD, described the development of the HERDOO2 clinical decision rule for determining a patient’s risk for a recurrent VTE. This includes hyperpigmentation, edema, or redness in either leg (signs of postthrombotic syndrome), D-dimer level of 250 mcg/L or greater while on warfarin, body mass index of 30 kg/m2 or greater, and age of 65 years or older.
If patients have zero or one risk factor, the annual risk of VTE after 6 months of treatment is 1.6%, while two or more risk factors bumps the annual risk of VTE to 14.1%, according to the researchers.