In emergent situations, systemic thrombolytic therapy can be given while CDT is being arranged, and active thrombus fragmentation and aspiration (see below) can be combined with CDT. A single randomized trial of 59 patients found that, compared with anticoagulation alone, US-assisted CDT improved right ventricular function at 24 h.154 Observational studies also suggest that CDT is effective at removing thrombus, lowering pulmonary arterial pressure, and improving right ventricular function without being associated with a high risk of Most of these studies are small (fewer than 30 patients) and retrospective, although a recent prospective registry of 101 patients and a prospective cohort study of 150 patients also support the ef cacy of Whereas there was no major bleeding in the registry, there were 15 episodes in the cohort study 342 Evidence-Based Medicine [ 1 4 9 # 2 C H E S T F E B R U A R Y 2 0 1 6 ] (10%; no intracranial or fatal bleeds). An older randomized trial of 34 patients with massive PE found that infusion of recombinant tissue plasminogen activator into a pulmonary artery as opposed to a peripheral vein did not accelerate thrombolysis, but caused more frequent bleeding at the catheter insertion No randomized trials or observational studies have compared contemporary CDT with systemic thrombolytic therapy. For patients who require thrombolytic therapy and do not have a high risk of bleeding, the AT10 panel favored systemic thrombolytic therapy over CDT because, compared with anticoagulation alone, there is a higher quality of evidence in support of systemic thrombolytic therapy than for CDT. 