Methods:

This was a cluster randomized trial of four New York tertiary academic hospitals (two hospitals were in the intervention group [n = 11, 309] and two hospitals were in the control group [n = 8, 514]) that were selected based on historical admissions for medical illness diagnoses. Patients were enrolled consecutively upon admission to study hospitals from December 21, 2020, to January 21, 2022. Eligible inpatients were medically ill over the age of 60 years with a primary diagnosis of at least one of five medical illness categories and additional risk factors per the IMPROVE-DD VTE (International Medical Prevention Registry on Venous Thromboembolism plus D-Dimer) score. All patients were assumed to have had relative immobility for at least one day during hospitalization. Patients were excluded if they were on therapeutic anticoagulation prehospitalization or within 24 hours of admission and had a history of atrial fibrillation. All patients in the trial had an IMPROVE-DD VTE score of 2. The primary outcome was rate of appropriate thromboprophylaxis. Secondary outcomes included venous, arterial, and total thromboembolism; major bleeding; and all-cause mortality through 30 days post-discharge. Patients in the intervention group were also prescribed extended prophylaxis post-discharge.