Early and late new-onset of atrial fibrillation in acute coronary syndromes: Their differences in mortality and cardiac event.

Background: In a stressful situation like acute coronary syndrome (ACS), the occurrence of the first episode of atrial fibrillation is more frequent. The impact of the timing occurrence of AF new-onset (nAF) in the setting of ACS is still debatable. Methods: Multicenter retrospective study based on the Acute Coronary Syndrome Portuguese National Registry, including 29 851 patients admitted for ACS between 1/10/2010 and 4/09/2019. The group with early nAF - nAF in the first 48 h of hospitalization; and late nAF - patients with nAF after the first 48 h of in-hospital admission. Results: New-onset AF was identified in 1067 patients, nonetheless, just 38.1% had late nAF. The group with late nAF presented more cardiovascular comorbidities and worse left ventricular ejection fraction. Late nAF patients received more anti-arrhythmic therapy, and early nAF had a higher beta-block prescription. Early nAF had higher rates of in-hospital complications, on the other hand, late nAF group exhibited more mortality and readmission at one year follow-up. Multiple logistic regression revealed that symptoms onset to the first medical contact time, admission hemoglobin <12 g/dl, right bundle branch block at admission, and diuretic therapy during the hospitalization for ACS were predictors of late nAF in ACS. Conclusions: The ACS population could be divided by the timing of nAF occurrence into the two groups with different characteristics, therapeutic approaches, and outcomes. Late nAF patients had a worse prognosis at 1 year follow-up, however, the early nAF group had more major adverse cardiac events during the hospitalization for ACS.