Effect of Aspirin Versus Low-Molecular-Weight Heparin for Thromboprophylaxis in High-Risk and Fracture Location Subpopulations: A Secondary Analysis of the PREVENT CLOT Trial

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OBJECTIVES: To compare the effectiveness and safety of aspirin versus low-molecular-weight heparin (LMWH) for thromboprophylaxis in 11 high-risk or fracture location subpopulations. METHODS: Design: A post-hoc secondary analysis of the published PREVENT CLOT trial. SETTING: 21 trauma centers. PATIENT SELECTION CRITERIA: Adult patients with an operatively treated extremity fracture or any pelvic or acetabular fracture were enrolled from April 2017 through August 2021. Patients with only hand or foot fractures, presenting >48 hours after injury, or with a history of VTE within 6 months of injury were excluded. The 11 subpopulations included i) a head injury, ii) an abdominal injury, iii) a spinal injury, iv) a thoracic injury, v) multiply injured patients, vi) obesity, vii) previous VTE ≥ 6 months, viii) isolated upper extremity fracture, ix) isolated lower extremity fracture, x) isolated pelvic or acetabular fracture, and xi) geriatric femur fracture. OUTCOME MEASURES AND COMPARISONS: The primary outcome was 90-day all-cause mortality. Secondary outcomes included non-fatal pulmonary embolism, proximal deep vein thrombosis (DVT), distal DVT, and bleeding events. Outcomes were assessed using Kaplan-Meier estimators and Cox proportional hazards models comparing 81 mg of aspirin versus 30 mg of LMWH twice daily. The threshold for statistical significance was a Bonferroni-corrected alpha of 0.001 to account for multiple comparisons. RESULTS: The largest subpopulations were isolated lower extremity fractures (n=6,289), obesity (n=4,234), and polytrauma with Injury Severity Score (ISS) >16 (n=1,596). No comparison of aspirin vs LMWH within the 11 subpopulations for the 5 outcomes reached the corrected threshold for statistical significance of P < 0.001. However, 5 comparisons of aspirin vs LMWH were less than the conventional P-value of 0.05. Specifically, the aspirin group demonstrated lower mortality in patients with a head injury (difference, -3.2%; 95% CI -6.1% to -0.3%; P = 0.03) or a spine injury (difference, -6.0%; 95% CI -11.7% to -0.3%; P = 0.04) than the LMWH group. The LMWH group demonstrated a lower rate of distal DVTs for patients with a head injury (difference, 4.4%; 95% CI, 0.8% to 8.1%; P = 0.03), thoracic injury (difference, 1.5%; 95% CI, 0.0% to 2.9%; P=0.034) or with ISS >16 (difference, 1.7%; 95% CI, 0.2% to 3.3; P = 0.03) than the aspirin group. CONCLUSIONS: Within 11 high-risk or fracture location-specific subpopulations, there were no statistically significant differences between aspirin or LMWH in the 90-day rates of all-cause mortality, non-fatal PE, proximal DVT, distal DVT, or bleeding complications at a threshold corrected for multiple comparisons (P < 0.001). LEVEL OF EVIDENCE: Therapeutic Level I.

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