Racing hearts in the ED: When atrial tachyarrhythmias Herald hidden culprits

Atrial Fibrillation (AF) is the most common sustained arrhythmia in the general population. Patients with atrial fibrillations commonly go to Emergency Departments (ED) with complications or aggravation of symptoms. They eventually receive rate or rhythm control intervention for rapid ventricular response and other interventions to prevent further worsening. -We present a case of atrial fibrillation with rapid ventricular rate later found to have an undiagnosed gastrointestinal stromal tumor (GIST) along the lesser curvature, resulting in abrupt exsanguination. Initial symptoms were non-specific until manifesting acutely as new-onset atrial fibrillation with rapid ventricular response. Despite recovering sinus rhythm, unremitting evidence of concealed hemorrhagic shock directed attention toward occult bleeding. Emergent operative treatment controlled bleeding and prevented fatality. An emergency physician should know this because atrial fibrillation does not always require acute rate/rhythm control. Newly diagnosed atrial fibrillation with rapid ventricular response in critically ill patients could be compensatory. Investigating underlying atrial fibrillation triggers can unveil precipitating factors. Occult shock demands urgent evaluation, as medications might precipitate overt shock and rapid deterioration. Even in cardiac patients, new-onset atrial fibrillation could be secondary.