The geriatric nutritional risk index as a prognostic risk factor for critically ill patients with atrial fibrillation: a retrospective study based on MIMIC-IV and local hospital cohort external validation.

Background: Malnutrition is known to worsen outcomes in many diseases. This study explored its effect on prognosis in critically ill patients with atrial fibrillation (AF). Methods: A total of 4,564 patients were studied. Their nutritional status was assessed using the Geriatric Nutritional Risk Index (GNRI), and they were divided into four groups based on GNRI quartiles, with a median of 100.23 and interquartile range of 90.31-111.27. The primary outcome was 28-day mortality. Kaplan-Meier analysis evaluated survival differences among the GNRI groups, and a multivariate Cox model assessed GNRI's independent effect on mortality risk. A restricted cubic spline (RCS) analysis explored potential non-linear associations between GNRI and 28-day mortality. Results: There is a negative correlation between GNRI and 28-day mortality, a finding supported by a log-rank test result with Conclusion: Among critically ill patients, elevated GNRI scores are associated with improved outcomes in patients with new-onset AF, but this association is not present in patients with preexisting AF. In the subgroup of septic patients with new-onset AF, GNRI may not reliably predict clinical prognosis, emphasizing the need for further validation prior to clinical use. The GNRI provides a straightforward, unbiased assessment of both nutritional status and systemic inflammation burden.