Background: Intermediate-high risk acute pulmonary embolism (PE) remains associated with substantial mortality despite standard anticoagulation therapy. Previous efforts to decrease mortality in these patients via administration of systemic thrombolysis have failed due to an increased rate of major bleeding complications. Catheter-directed thrombolysis (CDT) has already shown some promising results in terms of efficacy and safety, including the results of our randomized pilot study. However, large randomized trials with clinical endpoints comparing catheter-directed local thrombolysis versus standard anticoagulation therapy are still lacking, thus the treatment of intermediate-high risk acute PE patients has not changed for decades. Hypothesis: Catheter-directed local thrombolysis is superior to standard anticoagulation therapy in the treatment of intermediate-high risk acute pulmonary embolism, with no additional safety concerns. Statistical considerations: Estimated incidence of the primary endpoint of 1.5% in the CDT group and 6.0% in the standard anticoagulation group, 80% power for each arm with a 2-sided alpha of 0.05. Five hundred fifty-eight should provide the requisite number of events. Statistical Analysis - Intention to Treat. Methods and

Results: A Multicentre, Randomized Trial of Catheter-directed thrombolysis in intermediate-high risk acute pulmonary embolism (PRAGUE-26) is a noncommercial, multicentre, randomized, controlled parallel-group comparison trial. The trial plans to include 558 patients with intermediate-high risk acute PE. Patients will be randomized in a 1:1 ratio to CDT or to standard anticoagulation therapy. The primary outcome of the study is a clinical composite of all-cause mortality, PE recurrence or cardiorespiratory decompensation, within 7 days of randomization. Secondary objectives cover all bleeding complications, functional and patient-reported outcomes over a follow-up period of 24 months and cost-effectiveness analysis.