Hi and thank you for choosing HCM to post your question.I read carefully your question and understand your concern. Pulmonary embolism usually arise from thrombi that originate in the deep venous system of the lower extremities,pelvic area,renal,and upper extremities veins. In the setting of unknown cause of pulmonary embolism ,I would recomend to perform a hypercoagulation work up. Long term anticoagulation with warfarin is critical to the prevention of recurrence because even in patients who are fully anticoagulated pulmonary embolism can recur.A prothrombin time ratio expressed as INR is monitored to assess the adequacy of warfarin therapy.The therapeutic range is an INR of 2-3.Initially,INR measurements are performed on a daily basis .Once you are stabilized on a specific dose of warfarin,the INR determinations may be performed every 1-2 weeks or at longer intervals.After 3-6 months of treatment you need to have an assessment of the risk -benefit ratio of extended therapy. Hope my opinion can be helpful. Wish you good health. Kind regards Dr.Dushi