Warfarin Quality, Adherence, Range, Determinants, and Events in Egyptian Rheumatic Heart Disease and Atrial Fibrillation

Rheumatic heart disease (RHD) remains the most prevalent acquired cardiac condition in low- and middle-income countries (LMICs), disproportionately affecting young adults in sub-Saharan Africa, South Asia, and the Middle East.1-3 In Egypt, RHD continues to be a leading cause of cardiac morbidity, particularly among women of reproductive age and rural populations with limited access to primary prophylaxis.4,5 Atrial fibrillation (AF) is among the most frequent and clinically dangerous complications of RHD. Unlike non-valvular AF, RHD-AF carries a substantially higher thromboembolic risk - estimated at five to twenty times that of the general population.6 Mitral stenosis is the dominant lesion predisposing to AF and left atrial thrombus formation. For these patients, anticoagulation with vitamin K antagonists (VKAs) remains the standard of care.7 The INVICTUS trial (2022), the largest randomized controlled trial in RHD-AF, definitively established that warfarin is superior to rivaroxaban in patients with RHD-associated AF. The warfarin arm demonstrated significantly lower rates of the composite primary endpoint (stroke, systemic embolism, myocardial infarction, or death from vascular or unknown cause) compared to rivaroxaban (8.2% vs. 12.2% per 100 patient-years; HR 0.65, 95% CI 0.58-0.73; p<0.001). Direct oral anticoagulants (DOACs) are therefore not recommended in RHD-AF, cementing the central role of warfarin in this population for the foreseeable future.5 Warfarin efficacy is critically dependent on the quality of anticoagulation control, best captured by time in therapeutic range (TTR) - the proportion of time that a patient's INR remains within the target range (typically 2.0-3.0 for RHD-AF). TTR calculated by the Rosendaal linear interpolation method is the accepted standard.9

Inclusion criteria

• Inclusion Criteria

• Age ≥18 years
• Confirmed diagnosis of rheumatic heart disease (echocardiographic evidence of rheumatic valve morphology, prior history of rheumatic fever, or cardiology consultant diagnosis recorded in medical records)
• Electrocardiographically or holter-confirmed atrial fibrillation (paroxysmal, persistent, or permanent)
• On warfarin therapy for at least 6 consecutive months prior to enrollment with the intent to continue
• At least 3 recorded INR values in the preceding 12 months in the center's logbook (minimum data requirement for Rosendaal TTR calculation)
• Willingness to attend scheduled follow-up visits for 12 months and to provide written informed consent

Exclusion criteria

1. Anticipated cardiac surgery, valvuloplasty, or cardioversion within the next 6 months 2. Pregnancy or planned pregnancy during the study period 3. Active malignancy or other life-limiting condition with expected survival <12 months 4. Current or recent (≤12 months) use of a direct oral anticoagulant or heparin as primary anticoagulation 5. Severe hepatic impairment (Child-Pugh C) or known bleeding diathesis 6. Residence in a geographic area making 12-month follow-up participation unreasonably burdensome (as judged by the site investigator) 7. Fewer than 3 documented INR values in the preceding 12 months (insufficient data for Rosendaal TTR calculation) 6. Presence of a mechanical prosthetic heart valve (MPHV) in any position (aortic or mitral), regardless of thrombogenicity category. Patients with bioprosthetic (tissue) valves are not excluded, provided the prescribed INR target is 2.0-3.0 and all other inclusion criteria are met.

Patients with mechanical prosthetic heart valves (MPHVs) are excluded from this study. With all enrolled patients having native RHD-AF, a uniform INR therapeutic target of 2.0-3.0 applies to every participant, eliminating patient-specific target adjustments and rendering valve type non-informative as an analytical predictor. The overwhelming majority of warfarin-treated RHD-AF patients at Assiut University Heart Hospital have rheumatic mitral stenosis as the dominant lesion, making this a clinically homogeneous and internally valid study population. Patients with bioprosthetic (tissue) valves on warfarin for AF are not excluded, provided their prescribed INR target is 2.0-3.0 and all other inclusion criteria are satisfied.

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