DVT Burden and the Risk of Post-thrombotic Syndrome

Inclusion Criteria: 1. Age ≥ 18 years 2. Patients with symptomatic acute deep venous thrombosis of the lower limbs confirmed by ultrasound on the criteria of venous incompressibility and direct image of the thrombus (patients with stable pulmonary embolism associated with a symptomatic deep venous thrombosis can be included) 3. Affiliates or beneficiaries of a social security scheme. Exclusion Criteria: 1. Pregnant women, women in labour or breastfeeding mothers. 2. Pulmonary embolism haemodynamically unstable defined by systolic blood pressure \< 90 mmHg or a drop in systolic blood pressure of at least 40 mmHg during at least 15 min, shock or cardiac arrest. 3. Asymptomatic venous thrombosis. 4. Symptomatic venous thrombosis of both lower limbs (patients with bilateral deep venous thrombosis but symptomatic on one side only can be included). 5. History of ipsilateral or contralateral venous thrombosis of the lower limb. 6. Fracture or orthopedic surgery of the lower limbs in the last 3 months. 7. Dependance caused by age or secondary to a chronic affection, going from the inability to stand up or walk alone without help to bed or armchair rest over. 8. Prophylactic or therapeutic anticoagulant treatment \> 5 days. 9. Expected duration of anticoagulant treatment \< 3 months (all patients must have a minimum treatment of 3 months). 10. Patient estimated at high risk of bleeding according to investigator clinical judgment (renal, platelet, digestive, hepatic, neurological... origin) . 11. Indication for interruption of the inferior vena cava or venous recanalisation (endovascular, thrombolysis or surgery). 12. Refusal or inability to give written informed consent to participate in the study. 13. Life expectancy \< 6 months. 14. Patients under legal protection (guardianship, curatorship, etc.) or safeguard of justice. 15. Patients taking part in a research project for venous thromboembolism that can interfere with the conduct of DVT-BURDEN research.