Atrial fibrillation raises the risk of ischemic stroke by a factor of four to five, primarily as a result of cardioembolism of a fibrin-rich thrombus. (See figure below.) The annual rates of stroke among participants with atrial fibrillation in this study receiving clopidogrel plus aspirin was 2.4% and was 3.3% in patients receiving aspirin alone. These rates were both notably higher than those reported in previous studies among patients at high risk for stroke who received high-quality vitamin K–antagonist therapy (approximately 1.1 to 1.3%).
Oral Vitamin K Antagonists
Oral vitamin K antagonists are currently the most effective form of stroke-prevention therapy in patients with atrial fibrillation. However, vitamin K–antagonist therapy approximately doubles the risk of intracranial hemorrhage, is challenging to deliver in a high-quality fashion (i.e., maintaining an international normalized ratio of 2.0 to 3.0), and can diminish the quality of life because of frequent testing, dietary restrictions, and the possibility of drug–drug interactions.
New England Journal of Medicine - Vol. 360, No. 20, May 14, 2009