Objective:

To investigate the association between remnant cholesterol inflammatory index (RCII) and the occurrence of in-hospital new-onset atrial fibrillation (NOAF) in patients with ST-segment elevation myocardial infarction (STEMI).

Approach:

• Study Design: Single-center retrospective observational study enrolling patients with first-time acute STEMI undergoing emergency percutaneous coronary intervention (PCI) from January 2022 to December 2025.
• RCII Definition: RCII was defined as the product of remnant cholesterol (RC) and high-sensitivity C-reactive protein (hs-CRP).
• Statistical Analysis: Multivariable logistic regression and restricted cubic spline analysis were used to assess the relationship between RCII and NOAF.

Key Findings:

• Out of 945 STEMI patients, 79 (8.36%) developed NOAF.
• Patients with NOAF had significantly higher levels of RCII, RC, and hs-CRP compared to those without NOAF.
• Multivariable logistic regression showed hs-CRP (OR = 2.96), RCII (OR = 4.71), and RC (OR = 2.78) were independently associated with NOAF.
• RCII demonstrated a significant nonlinear dose–response relationship with NOAF risk.
• RCII identified NOAF with an area under the curve of 0.756, outperforming RC and hs-CRP alone.
• interpretation
• limitations
• conclusion

Interpretation:

Higher RCII is independently associated with an increased risk of in-hospital NOAF and shows moderate discriminatory ability.

Limitations:

• Single-center study may limit generalizability.
• Retrospective design may introduce selection bias.

Conclusion:

RCII may serve as a simple, cost-effective, and efficient early risk stratification tool for identifying patients at high risk of NOAF.