A randomized trial of low-dose thrombolysis, ultrasound-assisted thrombolysis, or heparin for intermediate-high risk pulmonary embolism-the STRATIFY trial: design and statistical analysis plan.

Background: Intermediate-high risk pulmonary embolism (PE) carries a significant risk of hemodynamic deterioration or death. Treatment should balance efficacy in reducing clot burden with the risk of complications, particularly bleeding. Previous studies on high-dose, short-term thrombolysis with alteplase (rtPA) showed a reduced risk of hemodynamic deterioration but no change in mortality and increased bleeding complications. Catheter-based techniques, including ultrasound-assisted thrombolysis (USAT), and low-dose thrombolysis may offer reasonable efficacy with lower risk. However, studies comparing these methods have been few. This trial aims to address this gap by randomizing patients to three treatment modalities.

Methods: Multicenter, randomized trial with 1:1:1 allocation of 210 patients with acute intermediate-high risk PE, excluding those with absolute contraindications to thrombolysis. Patients are eligible for inclusion if they are > 18 years of age, have had symptoms < 14 days, and are able to give informed consent. Patients are allocated 1:1:1 into three treatment strategies: (1) unfractionated heparin (UFH)/low molecular weight heparin (LMWH), (2) UFH/LMWH + 20 mg rtPA/6 h intravenously (IV), or (3) UFH + 20 mg rtPA/6 h via USAT. Co-primary outcomes include reduction in clot burden as assessed by refined Miller score from pre-treatment to follow-up (48-96 h) computed tomography pulmonary angiogram (CTPA) comparing low-dose rtPA (± USAT) groups to UFH/LMWH group (p < 0.01, N = 210) and reduction in refined Miller score on follow-up CT angiography comparing low-dose rtPA by USAT to intravenous rtPA, p < 0.04, N = 140). Secondary outcomes comprise bleeding complications, duration of index admission, FiO₂, blood pressure, respiratory and heart rate at the time of follow-up CT angiography, mortality in the three groups, incidence of tricuspid regurgitation pressure gradient < 40 mmHg at 3 months follow-up echocardiography, 6-min walk test at 3 months comparing the three groups, and health-related quality of life at 3 months follow-up comparing the three groups.

Discussion: We hypothesize that in patients with intermediate-high risk PE (1) administration of 20 mg rtPA leads to a greater reduction in clot burden compared to heparins and (2) administration of 20 mg rtPA via USAT results in a greater reduction in clot burden compared to 20 mg rtPA intravenous.

Trial registration: ClinicalTrials.gov NCT04088292. Registered in September 2019 (retrospectively registered).