STOPping Anticoagulation for Isolated or Incidental Subsegmental Pulmonary Embolism

Pulmonary embolisms (PE) occur when blood clots cause a blockage of the blood supply to the lungs. A small PE located in the subsegmental pulmonary vasculature is identified as a subsegmental PE (SSPE). Anticoagulants are used to treat SSPE and work by preventing new clots from forming whilst the body's own mechanisms break down the clots, however they can also increase the risk of major and potentially life threatening bleeding. More recent observational data of routine care for SSPE showed very high complication rates of anticoagulation but in patients where treatment was withheld, this proved to be a safe strategy in terms of recurrent venous thromboembolism (VTE).

Computed tomography pulmonary angiography (CTPA) scans are now able to detect SSPE, however there are concerns that there is an over-diagnosis due to the incorrect interpretation of small artefacts. 1466 patients from approximately 50 sites will be recruited, these sites will consist of hospitals across the United Kingdom (UK). Patients 18 and over with isolated SSPE, confirmed by either CTPA or CT thorax with IV contrast, will be eligible for the trial. Patients will be randomised to either receive standard anticoagulation for at least 3 months (control) or no anticoagulation for at least 3 months (intervention). The participant will receive telephone follow up calls at 4, 12 and 24 weeks following the end of their treatment, and additional data will also be taken from their medical records at these time points. The participant isn't required to be contacted for the 52 week follow up as the data will be extracted from the National Health Service (NHS) Digital collection of Hospital Episode Statistics (HES). In total participation in the study will last 12 months. In addition the cost-effectiveness of no treatment versus treatment with full anticoagulation will be looked at and also improving on radiological diagnosis of SSPE.


Eligibility Criteria:
Inclusion Criteria:

* Age ≥18 years
* SSPE diagnosed by the radiologist at the trial site by CTPA or CT thorax with IV contrast
* No evidence of proximal deep vein thrombosis on doppler ultrasonography or CT / Magnetic Resonance venography
* Heart rate (\<110bpm)
* Systolic blood pressure (≥100 mmHg)
* Oxygen saturation (≥90%)
* Written signed informed consent to the trial

Exclusion Criteria:

* Indication for hospital admission
* \>7 days empirical anticoagulation treatment immediately prior to randomisation
* \<28 days since first symptoms of proven or clinically suspected Coronavirus disease (COVID-19)
* Known stage 5 chronic kidney disease
* Patients with active cancer defined as cancer diagnosed within the past 6 months, cancer for which anticancer treatment was being given at the time of enrolment or during 6 months before randomisation, or recurrent locally advanced or metastatic cancer
* Patients with previous unprovoked PE, thrombophilia or requiring long term anticoagulation for another reason
* Patients with a Deep Vein Thrombosis / thrombus of an unusual site (e.g. upper limbs, associated with a line) that requires anticoagulation
* Patients with active bleeding
* Any condition which, in the opinion of the investigator, makes the participant unsuitable for trial entry due to prognosis/terminal illness with a projected survival of less than 3 months
* Pregnancy confirmed by positive pregnancy test or post-partum period or actively trying to conceive
* Inability to comply with the trial schedule and follow-up
* Participation in a Clinical Trial of Investigative Medicinal Product (CTIMP) study