AF becomes increasingly persistent and resistant to therapy over time, perhaps due to the development of atrial brosis, as well as other pathophysiological processes (e-Fig 2). AF and atrial utter frequently co-exist, and share similar risk factors for arrhythmia development and stroke risk.39 Lone AF 1142 Evidence-Based Medicine [ 1 5 4 # 5 C H E S T N O V E M B E R 2 0 1 8 ] is a low risk patient group that is a diagnosis of exclusion, after ensuring no comorbidity risk factors are Lone atrial utter (without any recognizable underlying disease), like lone AF, is also rare: only 2% of atrial utter patients.41 The role of anticoagulation in atrial utter has not been assessed in clinical trials, but since individuals with atrial utter often have concomitant AF or are at increased risk of developing AF, the risk of stroke and thromboembolism is assumed to be the same, and the same risk strati cation approaches are recommended. Risk Factors for Ischemic Stroke: Clinical Risk Factors for Ischemic Stroke in AF: Although AF is an independent risk factor for stroke, not all patients with AF have equal stroke risk. To correctly assess the risk of stroke in order to inform anticoagulation, risk prediction or strati cation tools have been developed, based on the risk factors most strongly and consistently associated with stroke. A systematic review of stroke risk factors found that prior stroke or transient ischemic attack (TIA) (15 of 16 studies positive; RR, 2.86), hypertension (11 of 20 studies positive; RR, 2.27), aging (9 of 13 studies positive; RR, 1.46 per decade increase), structural heart disease (9 of 13 studies positive; RR, 2.0), and diabetes (9 of 14 studies positive; RR, 1.62) were independent predictors of stroke. 