When should anticoagulation (anticoagulant therapy) be started in patients with atrial fibrillation (AFib)?

When to Start Anticoagulation in Atrial Fibrillation

Anticoagulation should be initiated as soon as atrial fibrillation is diagnosed in patients with a CHA₂DS₂-VASc score ≥2 for men or ≥3 for women, with direct oral anticoagulants (DOACs) preferred over warfarin for non-valvular AF. 1, 2

Risk Stratification and Decision to Anticoagulate

• All patients with AF require stroke risk assessment using the CHA₂DS₂-VASc score before deciding on anticoagulation. 1
• Anticoagulation is strongly recommended for patients with CHA₂DS₂-VASc score ≥2 in men or ≥3 in women, regardless of whether AF is paroxysmal, persistent, or permanent. 1, 2
• Young patients with lone atrial fibrillation (no structural heart disease, hypertension, or other risk factors) have low embolic risk and do not require anticoagulation. 3
• The pattern of AF (paroxysmal vs. chronic) should not influence the decision to anticoagulate, as stroke risk is similar in both. 3

Choice of Anticoagulant Agent

Preferred Agents for Non-Valvular AF

• Direct oral anticoagulants (apixaban, dabigatran, rivaroxaban, or edoxaban) are preferred over warfarin for non-valvular AF due to superior safety profiles and reduced intracranial hemorrhage risk. 1

Standard dosing regimens: 1

• Apixaban: 5 mg twice daily (reduce to 2.5 mg twice daily if ≥2 of: age ≥80 years, weight ≤60 kg, serum creatinine ≥1.5 mg/dL)
• Dabigatran: 150 mg twice daily (110 mg twice daily available in some regions for patients ≥80 years or at high bleeding risk)
• Rivaroxaban: 20 mg once daily (reduce to 15 mg once daily if CrCl 30-50 mL/min)
• Edoxaban: 60 mg once daily (reduce to 30 mg once daily if weight ≤60 kg, CrCl 30-50 mL/min, or concurrent P-glycoprotein inhibitors)

When Warfarin is Used

• If warfarin is selected, target INR should be 2.0-3.0, with INR monitoring at least weekly during initiation and monthly when stable. 1, 2
• Time in therapeutic range (TTR) should ideally be ≥70%; if TTR <65%, implement measures to improve control or switch to a DOAC. 1
• Initial warfarin dosing should be 2-5 mg daily, with adjustments based on INR response; loading doses are not recommended. 2

Special Timing Considerations

Cardioversion Scenarios

For AF >48 hours or unknown duration: 1

• Anticoagulation must be established for at least 3 weeks before cardioversion (electrical or pharmacological)
• Alternative approach: perform transesophageal echocardiography (TEE) to exclude left atrial thrombus, then proceed with cardioversion after at least one DOAC dose ≥4 hours before the procedure (≥2 hours after apixaban loading dose)
• After cardioversion, continue anticoagulation for at least 4 weeks regardless of CHA₂DS₂-VASc score
• Long-term anticoagulation decisions beyond 4 weeks should be based on stroke risk scores, not on successful cardioversion

For AF <48 hours duration: 1

• Start anticoagulation at presentation with therapeutic-dose heparin or LMWH and proceed to cardioversion
• In high-risk patients (CHA₂DS₂-VASc ≥4) or when AF duration is uncertain, use TEE-guided approach or 3-week anticoagulation strategy

For hemodynamically unstable patients requiring urgent cardioversion: 1

• Start therapeutic-dose parenteral anticoagulation immediately if possible, but do not delay emergency cardioversion
• After successful cardioversion, continue therapeutic anticoagulation for at least 4 weeks

Post-Acute Ischemic Stroke

• In patients with AF who have suffered an acute ischemic stroke, anticoagulation should be started within 2 weeks but avoid initiating within the first 48 hours. 4
• Heparinoids or warfarin should not be started within 48 hours of stroke onset due to increased risk of symptomatic intracranial hemorrhage without net benefit. 4
• Observational data suggest starting DOACs between days 4-7 post-stroke may be reasonable, with improved outcomes and no early intracranial hemorrhage. 4

Stable Coronary Artery Disease

• For AF patients with stable CAD, anticoagulation alone (without additional antiplatelet agents) is sufficient for most patients. 1
• There is no strong evidence to prefer one DOAC over another based solely on the presence of stable CAD. 1

Common Pitfalls and How to Avoid Them

• Do not substitute aspirin for anticoagulation in AF patients at elevated thromboembolic risk; aspirin offers substantially less benefit than oral anticoagulation. 1, 3
• Do not underdose DOACs without meeting specific manufacturer criteria, as this increases stroke risk without improving safety. 1
• Do not withhold anticoagulation based solely on bleeding risk scores; the stroke prevention benefit typically outweighs bleeding risk in appropriate candidates. 1
• Do not discontinue anticoagulation after successful cardioversion if the patient's CHA₂DS₂-VASc score indicates ongoing stroke risk. 1
• Ensure medication adherence is emphasized with DOACs, as their short half-lives mean missed doses quickly lose anticoagulant effect. 1, 5

Monitoring and Follow-Up

• For warfarin: INR monitoring weekly during initiation, then monthly when stable with TTR ≥70%. 1, 2
• For DOACs: no routine coagulation monitoring required, but assess renal function periodically (annually or more frequently if CrCl <60 mL/min) to ensure appropriate dosing. 1
• Reassess stroke and bleeding risk periodically, particularly when clinical status changes. 1