Design and rationale of a randomized trial comparing standard versus ultrasound-assisted thrombolysis for submassive pulmonary embolism

Background Catheter-directed interventions for the treatment of patients with submassive pulmonary embolism (sPE) have shown promise in rapidly improving right-sided heart strain and preventing decompensation to massive pulmonary embolism. Among various catheter interventions, ultrasound-assisted thrombolysis (USAT) has attracted interest as potentially having more efficient lytic effect that could achieve thrombolysis faster and with a reduced lytic dose. However, based on clinical evidence, it is unclear whether USAT is superior to standard catheter-directed thrombolysis (SCDT). We herein describe the study design of the Standard vs UltrasouNd-assiSted CathEter Thrombolysis for Submassive Pulmonary Embolism (SUNSET sPE) trial, an ongoing randomized clinical trial designed to address this question. Methods Adults with sPE presenting or referred to our institution are considered for enrollment in the trial. At the discretion of the treatment team, all patients undergo a catheter-directed intervention plus concomitant therapeutic anticoagulation. Participants are randomized 1:1 to a USAT catheter or an SCDT catheter. Study assessors are blinded to treatment group. The primary outcome is clearance of pulmonary thrombus burden, assessed by postprocedure computed tomography angiography. Secondary outcomes include resolution of right ventricular strain by echocardiography; improvement in pulmonary artery pressures; and 3- and 12-month improvement in echocardiographic, functional capacity, and quality of life measures. The study is powered to detect a 50% improvement in pulmonary artery thrombus clearance. Our enrollment target is 40 patients per treatment arm. Conclusions SUNSET sPE is an ongoing randomized, head-to-head, single-blinded clinical trial with the goal of assessing whether USAT results in superior thrombus clearance compared with SCDT in patients with sPE. We expect the results of our study to inform future guidelines on choice of thrombolysis modality in this population of challenging patients.