AF is an established independent risk factor for ischemic stroke as shown by many previous studies [1]. Anticoagulants are highly effective in reducing the risk of subsequent stroke in AF patients [2]. They have been recommended by the American Heart Association to prevent ischemic stroke [3]. Some AF patients will develop ischemic stroke although they are treated with anticoagulants [4]. It is thus important to identify risk factors that are associated with an increased risk of stroke in AF patients.