Several observational non-controlled series have demonstrated the efficacy of catheter-directed techniques in improving clinical and hemodynamic parameters and reducing clot burden while demonstrating a favorable safety profile. The ULTIMA trial was the first randomized controlled trial to include CDIs for sPE comparing standardized fixed-dose of USAT (10mg rtPA per lung over 15 hours) and AC to AC alone. In the USAT group, but not in the heparin group, the mean RV/LV ratio was significantly reduced at 24 hours, but became comparable between the two groups at 90 days. The RV systolic function was significantly improved in the USAT group vs. the heparin group at both 24 hours and 90 days. In both study groups minor bleeding complications were rare and there were no major bleeding complications. The SEATTLE II trial, a single-arm study evaluating the effectiveness of USAT, showed also an RV/LV ratio improvement at 48 hours.