A trial to determine if withholding anticoagulation is not worse than standard anticoagulation therapy in the treatment of blood clots in the lungs

INTERVENTION: The design is a prospective randomised open blinded end point (PROBE) trial, with individual level randomisation. The researchers have used an open design because of the importance of understanding how the knowledge of a diagnosis of SSPE yet being sent home without anticoagulation affects health seeking behaviour. This would be the situation in real clinical practice, were the results of the trial to support no anticoagulation. If the researchers had opted for a placebo‐controlled trial they would not be able to predict the impact of the management strategy in routine practice. An internal pilot (first 12 months of recruitment) will inform progression criteria to the main trial and a nested study of diagnostic accuracy will ensure safety for participants. Process evaluation: The researchers will focus on acceptability and the potential consequences of a no treatment approach, through conducting interviews with a range of patients (n=30) and healthcare professionals (HCP; n=30). The topic guide will be developed drawing on existing literature on reporting of, attitudes to, and outcomes from incidental diagnoses. The researchers will explore attitudes and practical issues surrounding tolerance of risk by patients and HCPs. If having a PE and knowingly not being treated changes how one responds to transient symptoms (e.g. leg or chest pain) then a potential outcome may be excess scans and emergency presentations in the untreated group. Distress at receiving a diagnosis of VTE, particularly as an incidental finding and the harm of repeated diagnostic imaging in this context will therefore be important to assess. Interviews will be audio recorded and transcribed verbatim, prior to qualitative analysis using the framework method. If patient/ CONDITION: Isolated or incidental subsegmental pulmonary embolism ; Circulatory System ; Pulmonary embolism PRIMARY OUTCOME: Recurrent venous thromboembolism (VTE), death‐related VTE, or clinically relevant bleeding, assessed using case report forms at the 12 and 24 week follow up timepoints INCLUSION CRITERIA: 1. Age =18 years 2. SSPE diagnosed by the radiologist at the trial site by CTPA or CT thorax with IV contrast 3. No evidence of proximal deep vein thrombosis on doppler ultrasonography or CT/MR venography 4. Heart rate (<110 bpm) 5. Systolic blood pressure (=100 mmHg) 6. Oxygen saturation (=90%) 7. Written signed informed consent to the trial SECONDARY OUTCOME: ; 1. Reduction in recurrent VTE and bleedings event assessed using case report forms at the 12, 24 and 52‐week timepoints; 2. Reclassification rate of SSPE diagnoses made by acute reporting radiologists when reviewed by thoracic radiologists, recorded on a case report form at registration/randomisation; 3. Healthcare resource use: hospitalisations, bed days, unscheduled primary and secondary care visits for recurrent VTE, clinically relevant bleeding or potentially related symptoms, measured using case report forms at the 12, 24 and 52‐week timepoints; 4. Healthcare costs assessed using case report forms at the 12, 24 and 52‐week timepoints; 5. Health‐related quality of life measured using the EQ‐5D‐5L questionnaire at baseline, 12 and 24 weeks; 6. Cost‐utility (cost per QALY) measured using a case report form at 24 weeks and cost‐effectiveness (cost per VTE avoided) measured at 52 weeks; 5. Acceptability to patients and clinicians and health‐seeking behaviours and health utilisation of a no anticoagulation treatment strategy for isolated SSPE, assessed through audio‐recorded interviews which can occur at any point throughout the trial;