TOPIC: Cardiovascular Disease TYPE: Original Investigations PURPOSE: The prevalence of cardiac arrhythmias, including atrial fibrillation (AF) in COVID-19 patients, has been evolving. Although data on the prevalence of AF is well established, its effect on mortality and survival has been inconsistent. The study aims to assess the mortality risk in Covid-19 patients who had AF during hospitalization. METHODS: A retrospective cohort study of consecutive patients admitted with a PCR confirmed COVID 19. We estimated 7-day and 30-day mortality through Kaplan-Meier survival curves and covariate-adjusted logistic regression and Cox Proportional Hazards models. We also obtained patient demographics, length of stay (LOS), Intensive Care Unit (ICU) admission, and co-morbidities, including the history of asthma, Diabetes Mellitus (DM), congestive heart failure (CHF), chronic obstructive pulmonary disease (COPD), hypertension (HTN), acute kidney injury (AKI), and chronic kidney disease (CKD). RESULTS: Five hundred and fifty-four patients with COVID 19 were reviewed. A group of 82 (15%) patients were identified with AF, of which 32 (40%) patients had no prior history of AF. Compared to the non-AF group, these patients were significantly older (78 vs. 69 years old), more likely to be white (77% vs. 63%), have a longer LOS (11 vs. 7), and have an ICU admission (55% vs. 24%). They also had significantly increased 7-day (16% vs. 5%) and 30-day mortality (43% vs. 12%). Additionally, they were more likely to have a history of DM, CHF, AKI, and HTN. AF during admission was associated with an increased risk of 7-day and 30-day mortality (OR=2.28, p=0.039 and OR = 3.56, p < 0.001, respectively). This group also had a significantly lower survival probability at 7 days and 30 days (p=0.005, p < 0.0001, respectively). New-onset AF was associated with an increased risk of 30-day mortality (OR = 5.72 p < 0.001) and lower survival probability at 30 days (p=0.005) only. Cox Proportional Hazards regression analysis for AF on admission and new-onset AF were significant at 30-days (HR=1.9 [1.2-3] p=0.0037 and HR=2 [1.1-3.4] p=0.0173, respectively). CONCLUSIONS: Our study shows that COVID 19 patients with AF have significantly worse outcomes than patients without AF. In our population, since AF patients were older and had more co-comorbidities, higher LOS, and ICU admission, a cause-and-effect relationship cannot be confidently determined. However, adjusting for these co-variates still produced a statistically significant negative effect on mortality and survival. CLINICAL IMPLICATIONS: The driving force behind the high incidence of AF, whether due to systemic illness or Covid 19 infection, remains to be determined, but it should be noted that COVID 19 patients with AF, especially new-onset AF have higher mortality. DISCLOSURES: No relevant relationships by Abasin Amanzai, source=Web Response No relevant relationships by Amerpreet Brar, source=Web Response No relevant relationships by Jamil Masood, source=Web Response No relevant relationships by NIRZARI PANDYA, source=Web Response No relevant relationships by Manasi Sejpal, source=Web Response No relevant relationships by Aaron Walker, source=Web Response No relevant relationships by Syed Arsalan Zaidi, source=Web Response