Anticoagulation for Atrial Fibrillation

Anticoagulation in atrial fibrillation prevents stroke and systemic embolism and is based on stroke risk, not on rhythm control. A direct oral anticoagulant is the first choice in non-valvular atrial fibrillation; warfarin is used in moderate to severe mitral stenosis and mechanical valves.

Stroke risk. CHA2DS2-VASc score: heart failure 1, hypertension 1, age 75 or over 2, diabetes 1, stroke or thrombo-embolism 2, vascular disease 1, age 65 to 74 years 1, female sex 1. Anticoagulate if the score is 2 or more in men and 3 or more in women; consider at 1 in men and 2 in women.

Bleeding risk. HAS-BLED scoring identifies modifiable risks (uncontrolled hypertension, alcohol, drugs); a high score is not a reason to withhold anticoagulation but a reason to correct risks.

• Apixaban 5 mg twice daily. Reduce to 2.5 mg twice daily when two of these are present: age 80 years or over, weight 60 kg or less, serum creatinine 133 micromol/L or more.
• Rivaroxaban 20 mg once daily with the evening meal. Reduce to 15 mg once daily if creatinine clearance is 15 to 50 mL/min.
• Edoxaban 60 mg once daily. Reduce to 30 mg once daily if creatinine clearance is 15 to 50 mL/min, weight is 60 kg or less, or a strong P-glycoprotein inhibitor is used.
• Dabigatran 150 mg twice daily. Use 110 mg twice daily if age is 80 years or over, verapamil is used, or bleeding risk is high.
• Warfarin: target INR 2.0 to 3.0 (2.5). Used for rheumatic mitral stenosis, mechanical valves, direct oral anticoagulant contraindications and cost reasons.
• Aspirin is not advised for stroke prevention in atrial fibrillation.

Cardioversion. Anticoagulate for at least 3 weeks before elective cardioversion (therapeutic INR or direct oral anticoagulant) or use transoesophageal imaging, and continue for at least 4 weeks after.

Acute stroke. Time the start of anticoagulation to the infarct size: usually 1 to 2 days for a minor stroke, about 3 days for moderate and 6 to 8 days for major.

Kidney impairment. Avoid dabigatran under 30 mL/min. Rivaroxaban and edoxaban avoid under 15 mL/min. Apixaban is used with caution at 15 to 29 mL/min.

Liver impairment. Avoid in Child-Pugh C; use with caution in B.

Older adults. Do not under-dose without criteria, because that reduces stroke protection without lowering bleeding.

Antiplatelet therapy. After a stent for coronary disease, use an anticoagulant with a single antiplatelet drug (clopidogrel) for 6 to 12 months, as directed by cardiology.

Special groups. In East Africa, atrial fibrillation with rheumatic mitral stenosis is common in young adults, and warfarin is used, not direct oral anticoagulants. INR monitoring access shapes the choice.

Monitoring. Check creatinine, haemoglobin and liver tests at baseline and yearly (every 3 to 6 months if kidney function is borderline or age is 75 or over). For warfarin, keep INR in range over 70% of the time.

Referral and escalation. Seek cardiology advice for valve disease, recent stroke, planned ablation, and any major bleeding.

Stopping. Anticoagulation is long term. Stop only for a bleeding event that cannot be corrected, or a new reason that outweighs the benefit.