Association Between Admission Calculated Serum Osmolality and New-Onset Atrial Fibrillation in Patients with Non-ST-Segment Elevation Myocardial Infarction Undergoing Percutaneous Coronary Intervention

Background: New-onset atrial fibrillation (AF) is a common complication of non-ST-segment elevation myocardial infarction (NSTEMI) and is associated with adverse outcomes. We evaluated whether admission calculated serum osmolality is associated with new-onset AF in NSTEMI. Methods: This retrospective study included 656 eligible NSTEMI patients undergoing percutaneous coronary intervention (PCI) between March 2021 and April 2022. Only patients in sinus rhythm at admission whose blood sample preceded any AF episode were analyzed. Osmolality was calculated as 2 × sodium + glucose/18 + blood urea nitrogen/2.8. Prespecified logistic models were assessed for discrimination, bootstrap internal validation, calibration, and incremental value. Results: New-onset AF developed in 136 patients (20.7%). Osmolality was higher in patients with AF (297.4 ± 8.9 vs. 291.6 ± 15.7 mOsm/kg, p < 0.001). In the complete-case model (n = 570; 130 events), osmolality was associated with AF (adjusted OR 1.565 per 10 mOsm/kg, 95% CI 1.102–2.223; p = 0.012). Adding osmolality increased the AUC from 0.927 to 0.933 (DeLong p = 0.081; likelihood-ratio p = 0.012; optimism-corrected AUC 0.924). The association was attenuated without renal-function adjustment (p = 0.060). Conclusions: Admission calculated serum osmolality was associated with new-onset AF in NSTEMI patients undergoing PCI, but its incremental predictive value was modest. External validation is required.