The effect of the duration of anticoagulation and other risk factors on the recurrence of venous thromboembolisms. Duration of Anticoagulation Study Group.

BACKGROUND: In order to find the optimal balance of anticoagulation, avoiding recurrent events as well as major hemorrhage, it is important to know the impact of different risk factors over time. METHODS: Based on a randomized, multicenter trial on different durations of anticoagulation after a first episode of venous thromboembolism, the probability of recurrence over 6 years of follow-up was analyzed. The contribution of the site of the thrombus, the nature of the triggering risk factor and the presence of cardiolipin antibodies to the risk of recurrence was also calculated. RESULTS: There is a cumulative risk of recurrence of 4 to 5% per year, which continues through year 6 after the index event, independent of the initial duration of anticoagulation. Deep vein thrombosis proximal to the knee joint or symptomatic pulmonary embolism confers a risk of recurrence that is higher than of distal thrombosis but equal to the risk when the triggering factor is permanent or unknown. The combination of proximal deep vein thrombosis or symptomatic pulmonary embolism and permanent/unknown triggering factor increases the risk, and the presence of cardiolipin antibodies generates an additional risk in all subgroups. CONCLUSION: It is necessary to tailor the duration of anticoagulation individually, according to the presence of different risk factors.