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Prevention of stroke in atrial fibrillation: an update
1University of Texas Health Science Center, San Antonio 78284.
Insights
Anticoagulation significantly reduces stroke risk in atrial fibrillation (AF) patients by 70%. Identifying high-risk patients with hypertension or heart failure ensures optimal use of warfarin for stroke prevention.
Area of Science:
- Cardiology
- Neurology
- Pharmacology
Background:
- Atrial fibrillation (AF) significantly elevates ischemic stroke risk.
- Antithrombotic prophylaxis is crucial for AF patients.
- Previous studies highlighted the need for risk stratification.
Purpose of the Study:
- To evaluate the efficacy of anticoagulation and aspirin in preventing stroke in AF patients.
- To identify predictors of stroke risk in AF.
- To guide antithrombotic therapy selection based on individual risk.
Main Methods:
- Aggregate analysis of five randomized clinical trials.
- Multivariate analysis of placebo-treated AF patients.
- Assessment of clinical and echocardiographic predictors of thromboembolism.
Main Results:
- Anticoagulation reduced arterial thromboembolism by a mean of 70%.
- Aspirin (ASA) showed less efficacy than anticoagulation and was better for nonembolic strokes.
- Hypertension, heart failure, prior TIA/stroke, enlarged left atrium, and impaired LV function predicted higher stroke risk.
Conclusions:
- Anticoagulation is highly effective in reducing stroke risk for AF patients.
- Warfarin (INR 2-3) is recommended for AF patients with identified risk factors.
- Risk stratification aids in tailoring antithrombotic therapy for secondary stroke prevention in AF.
Abstract:
Atrial fibrillation (AF) is associated with a substantially increased risk of ischemic stroke. Recently, five randomized clinical trials independently assessed the value of antithrombotic prophylaxis in AF patients. The rate of ischemic stroke in patients receiving a placebo averaged 5% per year. On aggregate, anticoagulation (INR 1.5 to 4.0) was shown to substantially (mean = 70%) reduce the risk of arterial thromboembolism. The effect of acetylsalicylic acid (ASA) studied in two trials was not uniform, but the efficacy of ASA was less than anticoagulation. ASA appeared to prevent nonembolic strokes better than embolic strokes in AF patients. The characterization of subgroups of AF patients who have relatively high or low absolute stroke rates determines which patients gain greater or lesser benefit from anticoagulant therapy. A multivariate analysis of a large cohort of placebo-treated patients yielded three independent clinical predictors of an increased risk of arterial thromboembolism: a history of hypertension, recent (within three months) congestive heart failure and prior transient ischemic attack (TIA) or stroke, and two echocardiographic predictors--left atrial size of greater than 4.6 cm and impaired left ventricular function. At present, anticoagulation with warfarin (INR 2 - 3) is recommended in AF patients with one or more of these risk factors. The European Atrial Fibrillation Trial studied only AF patients with prior stroke and TIA and confirmed the superiority of warfarin over ASA for secondary prevention.