Acute atrial fibrillation and flutter (AAFF) is characterized by rapid heart rates with onset less than seven days. It's the most common type of palpitation treated in the Emergency Department (ED). Some Canadian ED's will discharge 95% of AAFF patients whereas others admit up to 40%. With hospital and ED crowding, discharge is the most optimal, effective and safe strategy. Our aim is to improve the care and reduce the length of stay (LOS) of ED AAFF patients, while decreasing unnecessary hospitalizations. First, the investigators must understand the local barriers. In the previous study, the investigators conducted interviews of emergency physicians, cardiologists and AAFF patients. In Project 1b, the investigators created the CAEP ED AAFF Guidelines Checklist to assist physicians to manage AAFF more efficiently and safely. The Guidelines are comprised of two algorithms and four sets of checklists for ED assessment and management. They have been endorsed by CAEP and are published in CJEM.

The investigators are now planning Project 2 in which the investigators will conduct a cluster [group] randomized trial at 11 Canadian EDs and enroll 1,300 patients over thirteen months. The investigators are not randomizing individual patients or doctors; instead the investigators are randomizing the start date of individual hospitals. Our goal is to introduce the new Guidelines into these hospitals to improve the care of AAFF patients. The investigators hope to improve AAFF management, leading to a significant decrease in hospital admissions and ED LOS. Central to our plans will be engagement of our two patient partners. Our behaviorally optimized intervention will be developed using state-of-the-art implementation science approaches informed by the results of Project 1a. The investigators will also undertake within-project and end-of-project knowledge translation and implementation (KTI) strategies to facilitate scale up and roll out of our program to ED departments in small, medium, and large hospitals across Canada (future Project 3). Ultimately the investigators expect to improve ED practices and decrease AAFF admissions and LOS, without increasing visits.

All eligible patients seen in the participating EDs during the study period will be included in the trial regardless of how they are managed.

Inclusion Criteria:

• stable patients presenting with an episode of acute atrial fibrillation or flutter (AAFF) of at least 3 hours duration, where symptoms require ED management by rhythm or rate control.
• patients with a history of prior episodes of AAFF, or those with previous presentations during the study periods.

Exclusion Criteria: We will exclude patients who have any of the reasons listed below.

• have permanent (chronic) AF
• are deemed unstable and require immediate cardioversion: i) systolic blood pressure <90 mmHg; ii) rapid ventricular pre-excitation (Wolff-Parkinson-White syndrome); iii) acute coronary syndrome - ongoing severe chest pain and marked ST depression (>2mm) on ECG despite therapy; or iv) pulmonary edema - severe dyspnea requiring immediate IV diuretic, nitrates, or BIPAP;
• the primary presentation was for another condition rather than arrhythmia
• convert spontaneously to sinus rhythm prior to receiving physician-initiated therapy; or
• die while in the ED from non-AAFF related causes.