Temporal trend and geographic variation in anticoagulation of patients hospitalized with acute pulmonary embolism: the RIETE registry 2013-2024

Background: A recent U.S. study of initial anticoagulation in adults with acute pulmonary embolism (PE) requiring hospitalization found intravenous unfractionated heparin (UFH) use exceeded 50%. Guidelines, however, recommend low molecular weight heparin (LMWH) over UFH for most patients requiring parenteral anticoagulation. Use patterns in other geographic regions are unclear. Methods: We analyzed data from RIETE, a prospective multinational registry of consecutive patients with venous thromboembolism. We included adults hospitalized for acute PE from 2013 through 2024 in 273 hospitals across 31 countries. We assessed temporal trend and regional variation in initial anticoagulation. Using multivariable regression, we identified variables independently associated with UFH. Results: Among 36,210 adults, 83.2% received subcutaneous LMWH, 7.1% UFH, and 6.8% direct oral anticoagulants. LMWH use decreased slightly from 2013 to 2024 (85.8% to 79.2%; unadjusted), while UFH increased (8.9% to 10.4%). Wide geographic variation was observed in overall use of LMWH (37%--95%) and UFH (2%--39%). When adjusted for demographic and clinical covariates, increased weight, recent surgery, recent major bleeding, severe anemia, thrombocytopenia, severe renal dysfunction, abnormal vital signs, and early reperfusion therapy were positively associated, whereas age >80 years, active cancer, chronic lung disease, prior ischemic stroke, and year were negatively associated with UFH. Compared with Spanish hospitals, hospitals in other European countries, the United States, and Asia were independently associated with UFH use. Conclusions: Results highlight opportunities for some geographic regions to align anticoagulation practices more closely with evidence-based guidelines recommending LMWH as the preferred parenteral agent in most patients with PE requiring hospitalization.