Primary Outcome:
To determine if withholding anticoagulation is non-inferior to standard anticoagulation therapy in the treatment of isolated or incidental subsegmental pulmonary embolism for preventing recurrent venous thromboembolism (VTE), or death related VTE, or superior for clinically relevant bleeding over 3 months, compared with at least 3 months of full anticoagulation.
Secondary Outcomes:
These objectives are measured 4, 12, 24 and 52 weeks post randomisation. There are multiple secondary objectives for the study, including economic and behavioural objectives.
- Recurrent VTE or clinically relevant bleeding at 6 months and 12 months (as assessed through HES records).
- Net clinical benefit - composite of clinically relevant bleeding and recurrent VTE at 3 and 6 months.
- New diagnosis of pulmonary hypertension or right ventricular dysfunction within 12 months of SSPE, defined from HES clinical coding and supported where possible by additional radiological data and echocardiograms undertaken in tertiary pulmonary hypertension centres.
- All-cause mortality at 3, 6 and 12 months.
- VTE related mortality at 3, 6 and 12 months.
- Cardiovascular mortality at 3, 6 and 12 months defined as cardiac deaths (e.g. cardiogenic shock, fatal arrhythmia, cardiac rupture) and vascular deaths (e.g. VTE-related, fatal stroke, ruptured aortic aneurysm, aortic dissection).
- Reclassification rate from thoracic radiologist review.
Economic Objectives:
- Healthcare resource use: hospitalisations, bed days, unscheduled primary and secondary care visits for recurrent VTE, clinically relevant bleeding or potentially related symptoms.
- Healthcare costs.
- Health-related quality of life (EQ-5D-5L at baseline, 3 and 6 months).
- Cost-utility at 6 months (cost per QALY) and cost-effectiveness at 12 months (cost per VTE avoided).
Mechanistic (behavioural) Objectives:
- Themes from qualitative interviews which inform optimal recruitment strategies including information presentation and attitudes to risk.