Duration of anti coagulation in patients who had thrombosis – Are we sure about it?

The recommended duration of anticoagulation in the VTE patients is dependent on the persisting risk of re-thrombosis and bleeding.  It was noted that in 10 years follow up after cessation of the anticoagulation nearly 50% of the patients develop a recurrent VTE episode. This indicates that there is hidden risk of thrombosis in these patients. It may be due to underlying known or unknown, old or new risk factors. In these patients may have persistent old factors (of varying intensity) or newly added risk factors. So, in the beginning it was felt that the anticoagulation should be continued even after discharge from the hospital, but they were not sure about the duration. Now, the prophylaxis guidelines recommend us to extend the thrombo-prophylaxis after hip replacement surgery for at least 35 days.  Similarly, in the treatment segment also, there was discussion about continuation anti coagulation beyond 6 months after the indexed event. Placebo controlled trials were done and they showed 82% relative risk reduction of VTE (Einstein II).  In the recent past (Einstein Choice study) in another study, the anticoagulation was extended for another 1 year to its to study effect on prevention of rec VTE! It was again found that there is benefit of anticoagulation (Relative risk reduction of recurrent VTE up to 60%) without increasing the significant bleeding risk. The relative risk reduction can be as high as 60% with rivaroxaban. That leaves us with a question that is - how far is far enough with anticoagulation therapy?  Someone can consider giving anticoagulation for 10 years with annual reviews of the risk factors for re-thrombosis and bleeding.  This means, we need to use the existing drugs optimally or find out drugs which are effective and safe across all subsets of patients with thrombotic (VTE) complications, for a period of one decade after the indexed event of VTE.