Background: We aimed to determine the association of atrial fibrillation (AF) with 1-year outcome in STEMI patients undergoing primary PCI. Methods: Patients (n=8,830) enrolled in the Trial of Routine Aspiration Thrombectomy with PCI versus PCI Alone in Patients with STEMI (TOTAL) were followed for one year. The primary outcome was a composite of cardiovascular death, recurrent MI, cardiogenic shock or new or worsening class IV heart failure. The presence or absence of AF was determined from a single pre-PCI ECG. Results: Patients with AF (n=437, 4.9%) were older, and more often had a history of stroke, hypertension or MI. The rate of the primary outcome was higher in the AF group than in the sinus rhythm (SR) group (17.4% vs. 7.4%, p