The clinical significance of pulmonary embolism (PE) limited to the subsegmental pulmonary arteries, so called isolated subsegmental pulmonary embolism (SSPE), remains controversial. Whether isolated SSPE represents "true" PE, a clinically more benign form of PE, a physiologic lung clearing process, or a false positive result (artifact) is currently unclear and hence, whether patients with isolated SSPE benefit from anticoagulant treatment is uncertain. Despite growing evidence from observational studies that withholding anticoagulation may be a safe option in selected patients with isolated SSPE (i.e., those without concomitant deep vein thrombosis, cancer, etc.), most patients with isolated SSPE receive anticoagulant treatment, which is associated with an increased risk of bleeding. The overall objective of the randomized controlled SAFE-SSPE trial is to evaluate the efficacy and safety of clinical surveillance without anticoagulation compared to anticoagulation treatment in low-risk patients with isolated SSPE.

Inclusion Criteria:

1. Informed Consent as documented by signature
2. Age ≥18 years
3. Objective diagnosis of symptomatic or asymptomatic isolated SSPE

Exclusion Criteria:

1. Presence of leg deep vein thrombosis (DVT) or upper extremity DVT (subclavian vein or above)
2. Active cancer, defined as cancer treated with surgery, chemotherapy, radiotherapy, or palliative care during the last 6 months
3. ≥1 prior episode of unprovoked VTE (absence of a transient or permanent risk factor)
4. Clinical instability (systolic blood pressure <100 mm Hg or arterial Oxygen saturation <92% at ambient air) at the time of presentation
5. Active bleeding or at high risk of bleeding
6. Severe renal failure (creatinine clearance <30ml/min)
7. Severe liver insufficiency (Child-Pugh B or C)
8. Concomitant use of strong CYP3A4 inhibitors or strong CYP3A4 inducers
9. Known hypersensitivity to rivaroxaban
10. Need for therapeutic anticoagulation for another reason
11. Therapeutic anticoagulation for >72 hours for any reason at the time of screening
12. Hospitalized for >72 hours prior to the diagnosis of isolated SSP (hospital-acquired VTE)
13. Known pregnancy or breast feeding (pregnancy test to be performed for women of childbearing potential)
14. Lack of safe contraception in women of childbearing potential
15. Refusal or inability to provide informed consent
16. Prior enrolment in this trial

After publication of the study results, a de-identified patient-level data set relating to the primary publication along with the latest version of the study protocol, the informed consent form, the statistical analysis plan, the code used for the analyses, and the Data Management and Quality Plan describing all data management aspects of the study will be made publicly available for replication of the study results and secondary data analyses in the Bern Open Repository and Information System (BORIS) Research Data, an online non-commercial data repository that meets Swiss National Science Foundation requirements for FAIR Data Principles (www.force11.org/group/fairgroup/fairprinciples)

After publication of the study results

Data will be publicly available for replication of the study results and secondary data analyses in the Bern Open Repository and Information System (BORIS) Research Data