Stroke Prevention in Atrial Fibrillation II Study - SPAF II


Warfarin vs. aspirin for ischemic stroke in atrial fibrillation.


Warfarin is superior to aspirin by decreasing the risk of primary events by an absolute rate of 2% or more per year in patients <75 years and by 4% or more per year in patients older than 75 years of age.

Study Design

Study Design:

Patients Screened: Not given
Patients Enrolled: 1,100
Mean Follow Up: 2.3 years

Patient Populations:

Adults >60 years of age with ECG documentation of atrial fibrillation in the preceding 12 months without prosthetic heart valves, echocardiographic evidence of mitral stenosis, other requirements for or contraindication to aspirin or warfarin therapy.


<60 years of age
Lone atrial fibrillation

Primary Endpoints:

Ischemic stroke or systemic embolism

Secondary Endpoints:

Death, myocardial infarction (MI), transient ischemic attack, or unstable angina requiring hospital admission

Drug/Procedures Used:

Warfarin adjusted to prolong prothrombin time to create an international normalized ratio between 2.0 and 4.5, or aspirin, 325 mg/day.

Principal Findings:

In the younger patients (<75 years of age), warfarin decreased the absolute rate of primary events by 0.7% per year (95% CI-0.4 to 1.7). The primary event rate per year was 1.3% with warfarin and 1.9% with aspirin (relative risk [RR] 0.67, p = 0.24). The absolute rate of primary events in low-risk younger patients (without hypertension, recent heart failure, or previous thromboembolism) on aspirin was 0.5% per year (95% CI 0.1 to 1.9).

Among older patients (>75 years of age), warfarin decreased the absolute rate of primary events by 1.2% per year (95% CI-1.7 to 4.1). The primary event rate per year was 3.6% with warfarin and 4.8% with aspirin (RR 0.73, p = 0.39). In this older group, the rate of all stroke with residual deficit (ischemic or hemorrhagic) was 4.3% per year with aspirin and 4.6% per year with warfarin (RR 1.1).


Warfarin may be more effective than aspirin for prevention of ischemic stroke in patients with atrial fibrillation, but the absolute reduction in stroke rate by warfarin is small. Younger patients (<75 years of age) without risk factors had a low rate of stroke when treated with aspirin. In older patients (>75 years of age), the rate of stroke (ischemic and hemorrhagic) was substantial, irrespective of which agent was given. Patient age and the inherent risk of thromboembolism should be considered in the choice of antithrombotic prophylaxis for patients with atrial fibrillation.


1. Lancet 1994; 343:687-691. Final results
2. Prog Cardiovasc Dis 1996; 38(4): 337-342. Review

Clinical Topics: Anticoagulation Management, Arrhythmias and Clinical EP, Heart Failure and Cardiomyopathies, Prevention, Valvular Heart Disease, Anticoagulation Management and Atrial Fibrillation, Atrial Fibrillation/Supraventricular Arrhythmias, Acute Heart Failure, Hypertension

Keywords: Stroke, Platelet Aggregation Inhibitors, Warfarin, Risk Factors, Electrocardiography, International Normalized Ratio, Thromboembolism, Prothrombin Time, Heart Failure, Mitral Valve Stenosis, Atrial Fibrillation, Hypertension

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