The Standard vs ultrasound-assisted catheter thrombolysis for submassive pulmonary embolism(SUNSET sPE) trial, is an ongoing randomised, head-to-head, single-blinded clinical trial comparing ultrasound-assisted thrombolysis to standard catheter-directed thrombolysis. While comparative data is not yet available, Efthymios Avgerinos (University of Pittsburgh Medical Center, Pittsburgh, USA) presented the interim results of the overall outcomes today at the Society for Vascular Surgery (SVS) Vascular Annual Meeting (VAM; 12–15 June, National Harbor, USA) in a late-breaking scientific session.

Introducing the presentation, Avgerinos explained that pulmonary embolism is classified in three categories, based on mortality risk: from non-massive with low risk, and submassive with intermediate risk, up to massive pulmonary embolism with high risk. Calculating the appropriate care for PE therefore similarly creates a scale of intervention, from anticoagulation alone to systemic thrombolysis—“as severity increases, we need to escalate our treatment”, said Avgerinos.

Catheter-directed interventions for the treatment of patients with submassive pulmonary embolism (sPE) have shown promise in rapidly improving right heart strain and preventing decompensation to massive pulmonary embolism, Avgerinos and colleagues state in their abstract. However, Avgerinos noted at VAM, “it is unclear whether ultrasound-assisted thrombolysis is superior to standard catheter-directed thrombolysis. […] There is a lot of literature right now supporting EKOS (BTG), and it is the only FDA approved device right now [for ultrasound-assisted thrombolysis] that we have for pulmonary embolism, but the reality is that there is no clear evidence of clinical superiority to justify the increased cost compared to the standard catheter.”

The SUNSET sPE trial, he explained, is therefore enrolling adult patients presenting to the University of Pittsburgh Medical Center with sPE, based on a multidisciplinary pulmonary embolism response team algorithm. Participants are randomised 1:1 to treatment with EKOS or standard catheter thrombolysis. The study began in 2017 and anticipates completion in spring of 2020, according to Avgerinos.

The primary endpoint is thrombus reduction assessed by post-procedure CT angiogram, and the study is powered for 80 patients to detect a 50% improvement in pulmonary artery thrombus clearance. Secondary outcomes include 48-hour RV/LV ratio improvement by CT pulmonary arteriogram, and three- and 12-month functional capacity and quality-of-life measures.

“We have 45 patients now,” Avgerinos reported, with in the 23 EKOS arm and 22 in the standard catheter arm (mean age 55.0 ± 15.0, 62.2% male, 66.7% with concurrent DVT), all with acute sPE.

On average, patients were lysed for 13 hours (±6 hours). The investigators outline their results in the abstract: all but two patients showed RV/LV ratio improvement. The mean RV/LV ratio was reduced from 1.59±0.29 at baseline to 1.11±0.23 within 48 hours. One (2.2%) major (haemorrhagic stroke) and two (4.4%) minor bleeding episodes were observed during the post-interventional period. At 30 and 90 days, there were no deaths and no recurrent venous thromboembolism.

Avgerinos underlined these findings at VAM, highlighting that “there was no decompensation and no associated mortality”. Looking at functional capacity, a six-minute walking test at three months showed a 22% exercise intolerance or dyspnea at rest, while 56% developed “very light or light” dyspnea after a six-minute walk. “Regarding the quality of life,” Avgerinos said, “it was not as good as you would expect from the general population, but still the scores do not qualify for a poor quality of life.

Comparative data from SUNSET sPE is set to be announced at the completion of the study enrolment—“hopefully by the end of the year”, said Avgerinos, “but we can conclude that catheter thrombolytic techniques can achieve significant quick thrombus and RV/LV reduction, and that catheter thrombolysis is safe and effective”.