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

Samuel Tekle Mengistu,1 Desawit Hagos Siyum,2 Habtemichael M Teklemariam,3 Henok Gebremedhin,4 Bissirat Negusse Habteab,5 Elias Tafesse Yeshitila,6 Merhawi Mussa Kidane,7 Salman Ahmed Negash,7 Nahom Tesfaldet Berhe,8 Lidya Goitom Weldu,8 Yemane Seyoum4 1Department of Primary Care and Public Health, University of Cambridge, Cambridge, UK; 2Department of Internal Medicine, Halibet National Referral Hospital, Asmara, Eritrea; 3Sutter Health, Sutter Pacific Medical Foundation, San Francisco, CA, USA; 4Department of Cardiology, Orotta National Referral Hospital, Asmara, Eritrea; 5Department of Internal Medicine, Akordat Hospital, Akordat, Eritrea; 6Department of Public Health and Primary Care, University of Cambridge, Cambridge, UK; 7Department of Internal Medicine, Keren Zonal Referral Hospital, Keren, Eritrea; 8Department of Internal Medicine, Barentu Referral Hospital, Barentu, EritreaCorrespondence: Samuel Tekle Mengistu, Department of Primary Care and Public Health, University of Cambridge, Cambridge, UK, Email [email protected]; [email protected]: 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.Keywords: warfarin, time in therapeutic range, INR variability, mechanical heart valve, stability-adjusted TTR, Sub-Saharan Africa, low-resource setting, anticoagulation quality