Background. Thrombus regression in heparin-treated, acute deep venous thrombosis of the lower extremity is poorly documented in the literature; different rates of thrombus resolution and recanalization are reported. Methods and Results. In a prospective follow-up study, duplex scanning was used to evaluate the thrombus regression in patients with documented acute femoropopliteal thrombosis. Eighty vein segments in 20 legs of 18 patients were subjected to repeat duplex scans at 1, 3, 6, 12, and 26 weeks after diagnosis; 49 segments showed thrombus at diagnosis. The popliteal vein showed the highest thrombus load at diagnosis, followed in descending order by the superficial femoral, profunda femoris, and common femoral vein segments (p<0.001). Thrombus regression was significant (p<0.001) in all segments and proceeded at an exponential rate that was equal in the different vein segments of the upper leg. Both thrombus resolution and recanalization appeared to be a function of the initial thrombus load and could not be related to individual vein segments. Recanalization was seen in 23 of 31 initially occluded segments and occurred within the first 6 weeks after diagnosis in 20 of 23 segments. Extension of thrombus despite anticoagulant therapy was observed in 15 vein segments and was not related to the initial thrombosis score (p=0.1) or individual vein segments (p=0.23). Thrombus extension in seven patients with prethrombotic conditions was not different (p=0.9) from the other patients. Conclusions. Duplex scanning is an important noninvasive tool to quantify thrombus regression in acute deep venous thrombosis in detail without unnecessary discomfort to the patient.
