A multicentre observational study of the prevalence, management, and outcomes of subsegmental pulmonary embolism

Background
The incidence of subsegmental pulmonary embolism (SSPE) has increased with improvements in imaging technology. There is clinical equipoise for SSPE treatment, with conflicting evidence of improved mortality or reduced venous thromboembolism recurrence with anticoagulation. SSPE studies have significant heterogeneity and often lack adequately matched disease comparator groups.

Objectives
To determine the prevalence, management, and outcomes of SSPE and compare them to patients with main, lobar, segmental, and no pulmonary embolism (PE).

Patients/Methods
All adult patients undergoing CT pulmonary angiography (CTPA) between 2013 and 2019, at 3 UK hospitals were included in the study. CTPA reports were text mined for language relating to PE, and then further manually screened for the presence and anatomical location of PE. Patient groups were propensity matched by age, sex, and year of CTPA prior to analysis. 3-month outcomes of major bleeding, VTE recurrence, and death were recorded.

Results
79 (3.8%) SSPEs were identified from 2,055 diagnoses of PE, and 14,300 CTPA reports. 44 (56%) of SSPEs were single artery emboli, 25 (32%) were multiple unilateral emboli, and 10 (13%) were multiple bilateral emboli. Mortality, VTE recurrence and major bleeding were similar at 3 months across all groups. 87.3% of SSPE imaging reports had an additional radiological diagnosis, with pleural effusion (30%), consolidation (19%), and cardiomegaly (19%) being the most common.

Conclusion
The prevalence of SSPE was 3.8% of all PEs and there were a substantial number of additional radiological findings in the SSPE group that may have accounted for their symptoms.