In patients with acute, isolated, distal DVT of the leg who are managed with serial imaging, we (i) recommend no anticoagulation if the thrombus does not extend (Grade 1B), (ii) suggest anticoagulation if the thrombus extends but remains con ned to the distal veins (Grade 2C), and (iii) recommend anticoagulation if the thrombus extends into the proximal veins (Grade 1B). CDT for Acute DVT of the Leg Summary of the Evidence At the time of AT9, there was one small randomized comparing the effect of CDT vs anticoagulant alone on development of PTS, and another larger randomized trial (Catheter-Directed Venous Thrombolysis in Acute Iliofemoral Vein Thrombosis [CAVENT] Study) assessing short-term (eg, venous patency and bleeding) but not long-term (eg, PTS) The CAVENT Study has since reported that CDT reduced PTS, did not alter quality of life, and appears to be cost-effective (Table 14, e-Table 15).89-92 A retrospective analysis found that CDT (3649 patients) was associated with an increase in transfusion (twofold), intracranial bleeding (threefold), PE (1.5-fold), and vena caval lter insertion (twofold); long-term outcomes and PTS were not reported.93 A single-center prospective registry found that US-assisted CDT in acute iliofemoral (87 patients) achieved high rates of venous patency, was rarely associated with bleeding, and that only 6% of patients had PTS at 1 year.94 This new evidence has not led to a change in our recommendation for the use of CDT in patients with 334 Evidence-Based Medicine [ 1 4 9 # 2 C H E S T F E B R U A R Y 2 0 1 6 ] DVT. Although the quality of the evidence has improved, the overall quality is still low because of very serious imprecision. 