Optimal duration of secondary prevention of VTE

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Treatment of venous thrombosis is aimed to prevent thrombus extension and embolization and to reduce the risk of recurrence. Recurrent venous thrombosis may occur within the first few days or weeks, but also after several months or years. This risk is, at lease in part, determined by the presence or absence of major risk factors at the time of the index event. Randomized controlled trials have shown that all patients with proximal deep vein thrombosis or pulmonary embolism benefit from a minimum of three months of anticoagulant therapy. After this period, it has been suggested that patients with an expected annual recurrence rate of less than 5% can safely discontinue treatment. These patients are those with major transient risk factors such as surgery, immobilization, trauma, pregnancy or hormonal therapy. For all other patients, including those with previous VTE, cancer or unprovoked events, this treatment duration may not be sufficiently protective and indefinite treatment duration should be considered. Because case-fatality rate for major bleeding in patients taking warfarin for more than three months is higher than case-fatality rate of recurrent venous thromboembolism, an individual patient approach to identify lower risk patients who can safely discontinue treatment at three months is warranted. Clinical prediction rules or management strategies based on D-dimer levels or residual vein thrombosis have been proposed and need further refinement and validation. Meanwhile, alternative treatment strategies with the direct oral anticoagulants or with aspirin have been proposed. The results of extended treatment studies with the direct oral anticoagulants suggest that these compounds are highly effective as compared to placebo and may reduce the risk of bleeding as compared to warfarin, while aspirin results in a less striking risk reduction when indirectly compared to any oral anticoagulant drug, but with a lower incidence of major bleeding events.