BACKGROUND:Recent clinical trials' findings have revealed the therapeutic noninferiority of direct oral anticoagulant (DOAC) to standard therapy with vitamin K antagonist (VKA) in patients with pulmonary thromboembolism (PTE). However, few studies have quantitatively analyzed thrombus reduction in the pulmonary artery. METHODS:This observational study included 38 symptomatic PTE patients with stable hemodynamics. All patients received an intravenous heparin bolus followed by continual heparin injections immediately after the PTE diagnosis. The heparin was discontinued after edoxaban therapy began in the DOAC group (n = 22) or after the therapeutic range for the prothrombin time-international normalized ratio was achieved in the VKA group (n = 16). The thrombus volumes in the pulmonary arteries were quantitatively analyzed using contrast-enhanced computed tomography scans, and they were compared at baseline and at 2 weeks after admission. RESULTS:The pulmonary thrombus volumes declined in the VKA and DOAC groups from 7.9 to 4.2 cm3 (P = 0.048) and from 7.1 to 3.7 cm3 (P < 0.01), respectively, and the thrombus reduction rates did not differ significantly between the groups (-34% vs. -64%, respectively; P = 0.38). The fibrinogenolysis parameter changes during the14 days after admission were similar in both groups. Compared with the VKAgroup, the average hospital stay was 9days shorter in the DOAC group. There were no in-hospital deaths, and 1 case experienced major bleeding in the VKA group. CONCLUSIONS:In relation to pulmonary artery thrombus volume reduction, DOAC monotherapy for PTE may be comparable with standard therapy involving VKAs.