Abstract-Patients who have a first episode of venous thromboembolism (VTE) have an elevated risk of a recurrent episode, and this necessitates secondary prophylaxis. Anticoagulant therapy is a double-edged sword, however, as it reduces the risk of recurrent VTE but increases the risk of hemorrhage. This balance must be taken into account when assessing the risk-benefit ratio of long-term anticoagulation. , is a common and preventable disease. The incidence of VTE in industrialized countries is around 1 to 2 cases per 1000 person-years. 1-3 DVT mostly arises in the lower extremities but may also occur in the arms, cerebral sinuses, and viscera. DVT restricted to the calf veins is associated with smaller clots and fewer long-term sequelae. By contrast, proximal DVT involving the popliteal, femoral, or iliac veins frequently leads to pulmonary embolism and often produces the post-thrombotic syndrome. Each year around 300 000 people in the United States die from acute PE, many cases only being diagnosed at autopsy. 4 A recent epidemiological study confirmed that VTE is a major public health burden, with an estimated 370 012 related deaths in 2004 in a group of 6 European countries. 5 Patients with a first episode of VTE are at an increased risk of new episodes. The risk of recurrence varies with time after the incident event, being highest during the first 6 to 12 months and never falling to zero. 1 The cumulative rate of recurrence is about 25% at 5 years and 30% at 10 years. 6,7 VTE should thus be considered a chronic rather than an acute illness. Recurrent DVT is associated with a substantially higher likelihood of the postthrombotic syndrome, 8 -10 and recurrent PE is fatal in about 4% to 9% of cases. 11,12 Recurrent VTE also predisposes patients to chronic pulmonary hypertension. 13 Thus, anticoagulant treatment should aim not only to prevent thrombus extension but also to prevent both early and late recurrences.Inadequate anticoagulant therapy leaves the patient with VTE at an elevated risk of early recurrence. Two randomized controlled trials have shown the need for secondary prophylaxis after a first VTE. Patients with proximal DVT who receive low-dose subcutaneous unfractionated heparin (5000 U bid) have a 47% risk of recurrent VTE within 3 months, 14 and 20% of patients with symptomatic calf vein thrombosis who receive a 5-day course of heparin without relaying oral anticoagulation have a recurrence within 3 months. 15 By contrast, the recurrence rate in patients with VTE is less than 1% during the period of treatment if they receive adequate anticoagulation. 16 -19 Secondary prophylaxis (ie, long-term anticoagulant treatment) has some drawbacks, however, such as the need for frequent laboratory monitoring and vitamin K antagonist (VKA) dose adjustment and an increased risk of major hemorrhage. The annual risk of anticoagulant-related major bleeding is around 1% to 3% and hemorrhagic risk increases in older patients, the very group at higher risk for VTE. 20 In addition, even chronic treatment loses its...

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