Project Summary: The principal investigator?s long-term goal is to develop evidence-based emergency care guidelines for management of common cardiovascular conditions--including new atrial fibrillation (AF), and (2) translate these guidelines into practice using dissemination and implementation methods. The overall objective of this K08 Mentored Clinical Career Development Award proposal is to develop the principal investigator into an independent clinical investigator to improve the emergency care of AF patients. This proposal is in keeping with NHLBI?s mission, with the potential to significantly change the paradigm of an acute care emergency department (ED) evaluation by changing the trajectory of care of patients with new AF and improving both short and long-term clinical outcomes. Atrial fibrillation affects more than 2 million Americans, and is associated with significant mortality and morbidity, with an increased risk of stroke, heart failure, and death; in appropriate candidates, oral anticoagulants (OAC) can prevent up to 2/3 of strokes. And yet, there is high inter-variability in ED OAC prescribing for stroke prophylaxis. Existing guidelines pertain to chronic, rather than acute AF?and ED populations are different, with increased mortality and morbidity compared to outpatient populations. Before ED-based prescribing of OACs can be recommended for AF, it is essential to determine whether prognosis and response to treatment for ED patients with new AF are similar to published studies of outpatient patients with chronic AF. To address this objective, we propose a comparative observational study of a clinical cohort of 21 hospitals from a large, demographically diverse, integrated health care system. Aim 1 will describe the incidence, time lag, and predictors of OAC prescribing after an ED discharge diagnosis of new AF. Aim 2 will determine whether validated outpatient risk stratification scores can identify a subgroup of ED patients discharged with new AF at high-risk for adverse events (stroke and death). Aim 3 will compare the rates of adverse events (stroke and death) for patients prescribed ED OACs vs patients not prescribed OACs at their ED visit. The results of this research have the potential to positively impact the more than half-million patients annually who present to US emergency departments with AF. The research and training will allow the PI to gain skills and knowledge in the area of observational comparative effectiveness studies, advanced biostatistics, randomized trials, and dissemination and implementation science needed to develop, evaluate and implement guidelines to improve cardiovascular outcomes for emergency department AF patients.