Fifty-nine patients ( @ years ) with acute main or lower lobe pulmonary embolism and echocardiographic RV to left ventricular dimension ( RV/LV ) ratio @ were randomized to receive unfractionated heparin and an USAT regimen of @ to @ mg recombinant tissue plasminogen activator over @ hours ( n = @ ; USAT group ) or unfractionated heparin alone ( n = @ ; heparin group ) .