Authors' objectives: There has been an increase in the diagnosis of subsegmental pulmonary embolism since the advent of computed tomography pulmonary angiogram to investigate patients with suspected pulmonary embolism. Subsegmental pulmonary embolism is not often detectable with older nuclear medicine-based diagnostic imaging for ventilation/perfusion mismatch. The case fatality of pulmonary embolism has reduced as subsegmental pulmonary embolism diagnoses from computed tomography pulmonary angiogram have increased. There is growing equipoise about the optimal treatment for patients with subsegmental pulmonary embolism, given that full anticoagulation has significant risks of bleeding and subsegmental pulmonary embolism was not often diagnosed previously with ventilation/perfusion scanning and therefore most likely left predominantly untreated prior to the introduction of computed tomography pulmonary angiogram scanning. Determine whether withholding anticoagulation for isolated or incidental subsegmental pulmonary embolism (i.e. subsegmental pulmonary embolism with no coexisting deep-vein thrombosis) reduces the harms of recurrent thromboembolism and major bleeding compared with 3 months of full anticoagulation at 3, 6 and 12 months. Determine the rate of complications of anticoagulation therapy (predominantly bleeding) in patients with isolated subsegmental pulmonary embolism. Determine whether not treating isolated subsegmental pulmonary embolism is acceptable to clinicians and patients. Determine the reclassification rate of subsegmental pulmonary embolism diagnoses made by general reporting radiologists when reviewed by specialist respiratory radiologists and develop a set of rules to improve general radiologists’ diagnoses of subsegmental pulmonary embolism. Assess cost-effectiveness of not treating patients with isolated subsegmental pulmonary embolism with anticoagulation, taking a health service perspective.

Authors' methods: Prospective individually randomised open controlled trial with blinded end-point committee assessment for outcomes, powered for non-inferiority for recurrent venous thromboembolism and for superiority for bleeding events. An internal pilot phase is included for feasibility and acceptability of no anticoagulation. We planned to recruit 1466 patients from at least 50 acute hospital sites. Allowing for a dropout rate of 15%, this would have given us 90% power to detect a reduction in major and clinically relevant non-major bleeding from 7.3% in the anticoagulation arm to 3% in the intervention arm. We were powered to determine that a strategy of no anticoagulation was non-inferior to anticoagulation with an upper margin of a 2.3% increase in recurrent venous thromboembolism from an expected rate of 2% in those who receive full anticoagulation. We also planned to undertake a study comparing acute reporting radiologists’ diagnoses of subsegmental pulmonary embolism from all computed tomography pulmonary angiograms with specialist respiratory radiologists. This would have allowed us to determine safety in the pilot study (i.e. patients with pulmonary embolism that was in fact larger than subsegmental would have been identified) and develop guidance for subsegmental pulmonary embolism diagnosis for general radiologists. Patients with lived experience of thrombosis contributed to all aspects of the trial design and were part of the Trial Management Group.

Project Status: Completed

URL for project: https://www.journalslibrary.nihr.ac.uk/programmes/hta/NIHR135832

Year Published: 2024

URL for published report: https://www.journalslibrary.nihr.ac.uk/hta/published-articles/HRCW7937

URL for additional information: English

English language abstract: An English language summary is available

Publication Type: Full HTA

Country: England, United Kingdom

DOI: 10.3310/HRCW7937

Organisation Name: NIHR Health Technology Assessment programme

Contact Address: NIHR Journals Library, National Institute for Health and Care Research, Evaluation, Trials and Studies Coordinating Centre, Alpha House, University of Southampton Science Park, Southampton SO16 7NS, UK

Contact Name: journals.library@nihr.ac.uk

Contact Email: journals.library@nihr.ac.uk