Aspirin is the Appropriate Treatment
For a patient with atrial fibrillation and no other risk factors, aspirin 325 mg daily is the recommended antithrombotic therapy. 1
Risk Stratification Framework
The decision hinges on identifying this patient as low-risk for stroke based on the absence of additional risk factors. According to ACC/AHA/ESC guidelines, patients are stratified by specific clinical features: 1
Low-Risk Criteria (Aspirin Indicated)
- Age <60 years with no heart disease (lone AF): Aspirin 325 mg daily or no therapy (Class I recommendation) 1
- Age <60 years with heart disease but no risk factors: Aspirin 325 mg daily (Class I recommendation) 1
- Age ≥60 years with no risk factors: Aspirin 325 mg daily (Class I recommendation) 1
High-Risk Factors That Would Change Management
Risk factors that would necessitate warfarin anticoagulation include: 1
- Prior stroke, TIA, or systemic embolism (high-risk factor) 1
- Age ≥75 years (moderate-risk factor) 1
- Heart failure or LV ejection fraction ≤35% (moderate-risk factor) 1
- Hypertension (moderate-risk factor) 1
- Diabetes mellitus (moderate-risk factor) 1
Why Not Warfarin?
Warfarin is reserved for patients with ≥1 high-risk factor OR >1 moderate-risk factor. 1 The question explicitly states "no other risk factors," which excludes this patient from warfarin indication. The annual stroke risk in truly low-risk AF patients is approximately 1.0% (95% CI 0.3-3.0%), which does not justify the bleeding risks of anticoagulation. 2
Warfarin reduces stroke risk by 68% but carries a 1.3% annual major bleeding rate compared to 1.0% with aspirin. 2 For low-risk patients, treating more than 100 patients for 1 year with warfarin would be required to prevent one stroke—an unfavorable risk-benefit ratio. 1
Why Not Clopidogrel or Aspirin/Clopidogrel Combination?
Neither clopidogrel alone nor the aspirin/clopidogrel combination are recommended in any AF guideline for stroke prevention. 1 The combination of aspirin and clopidogrel has been studied only in the context of concurrent coronary intervention in AF patients already on anticoagulation, where it increases bleeding risk without established benefit. 1
Evidence Quality and Consistency
The recommendation for aspirin in low-risk AF is remarkably consistent across multiple guideline iterations (2001,2008,2011,2013) with Level of Evidence A. 1 Pooled analysis of five randomized trials showed aspirin reduces stroke risk by 36% (95% CI 4-57%) in AF patients, though less effectively than warfarin's 68% reduction. 2
Contemporary Context
While the 2025 Praxis Medical Insights notes that DOACs are now preferred over warfarin when anticoagulation is indicated, 3 this does not change the fundamental risk stratification approach. Patients without risk factors remain in the aspirin-appropriate category regardless of whether DOACs or warfarin would be chosen if anticoagulation were indicated. 3
Critical Pitfall to Avoid
Do not confuse "no other risk factors" with "age alone." If the patient is ≥75 years old, this itself constitutes a moderate-risk factor requiring anticoagulation (warfarin or DOAC), not aspirin. 1 The question's phrasing "no other risk factor" implies the patient lacks all established risk factors including advanced age.