This is a retrospective cohort study to describe the effect of adding direct oral anticoagulants to the Kaiser Permanente formulary on overall rates of oral anticoagulant initiation at the time of discharge for emergency department and inpatients with high-risk non-valvular atrial fibrillation or flutter across 21 medical centers from 2010-2017. The results of this study will inform the design of an electronic clinical decision support tool to aid emergency physicians and hospitalists in the comprehensive management of patients with atrial fibrillation or flutter. The tool will include evidence-based guidance on rate reduction, cardioversion, and stroke prevention. The tool will be evaluated in a pilot study at three large Kaiser Permanente medical centers in Northern California. If the tool improves outcomes of patient care, expansion of tool access across the region for further study will be considered.