Determinants of Suboptimal INR Control in Eritrean Post–Cardiac Surgery Patients: Insights from a Low-Resource Setting

Background: Warfarin remains the mainstay of long-term anticoagulation in low-resource settings; however, maintaining optimal international normalized ratio (INR) control is challenging, particularly in countries with limited follow-up services. In Eritrea, patients requiring lifelong anticoagulation often undergo cardiac surgery abroad yet face barriers to consistent INR monitoring upon return. Objective: To identify demographic, clinical, and treatment-related factors associated with poor anticoagulation control among Eritrean patients on long-term warfarin following cardiac surgery. Methods: We conducted a retrospective observational cohort study of Eritrean adults (≥18 years) who underwent cardiac surgery at the Salam Centre for Cardiac Surgery in Sudan and returned to Eritrea for follow-up. Data were collected from patients followed between February 2020 and July 2021 (median follow-up: 60 days, IQR: 24-120 days). INR control was assessed using Time in Therapeutic Range (TTR) via the Rosendaal method. Linear mixed-effects modeling identified predictors of INR variability. Results: Ninety-three patients (37.5% male, median age 45 years) met inclusion criteria. Median TTR was 47.8% (IQR: 33.2-62.9%), with only 25% achieving optimal control (TTR ≥60%). Valvular heart disease was the leading indication (62%), with 67% having metallic valve replacement. Mixed-effects modeling identified mechanical valve replacement (exp(β)=1.26, 95% CI: 1.17-1.37), higher therapeutic target (exp(β)=1.21), COPD/asthma (exp(β)=0.71), and specific co-medications (aspirin, digoxin, enalapril) as significant determinants of INR variability. Conclusion: In this cohort, anticoagulation control was suboptimal for the majority. Mechanical valve replacement, therapeutic targets, and specific co-medications were significant determinants of INR variability. These findings, while limited by sample size and single-center design, suggest that targeted medication review and individualized therapeutic targets may improve anticoagulation outcomes in similar low-resource settings.