Abstract Body (Do not enter title and authors here): INTRODUCTION
The ACTION-ICU Score is a tool to assess the risk of complications associated with non-ST-segment elevation myocardial infarction (NSTEMI) requiring intensive care unit (ICU) admission. Limited studies have investigated the effectiveness of risk scores in predicting the need for ICU care in patients with NSTEMI. We evaluated the performance of the ACTION-ICU Score in Mexican patients with NSTEMI.

METHODS
A retrospective cohort study of patients over 18 years old who were admitted to a coronary care unit in Mexico City, Mexico, between January 1, 2017, and December 31, 2023, with a diagnosis of NSTEMI according to the fourth universal definition of myocardial infarction; patients with cardiac arrest or shock on admission were excluded from the study. The ACTION-ICU score was applied to all patients based on the collected data. The cut-off score for ICU admission is 5, with a 9.3% risk of complications. During hospitalization, the composite primary outcome included cardiac arrest, shock, heart block requiring a pacemaker, respiratory failure, stroke, or death. The score's performance was estimated with a conditional multivariable logistic regression analysis, and the area under the curve (AUC) was calculated.

RESULTS
Among 345 patients with NSTEMI, 41 (14.2%) developed the primary outcome. The most common complications were shock (12.5%) and respiratory failure (8.1%). Regarding the score, heart failure was the variable with a significant risk of developing the primary outcome [OR: 4.78; 95% CI 2.17-10.5, p-value <0.01]. A score of 0 to 5 points was present in 187 patients (54.2%), ten of whom (5.3%) developed the primary outcome. The score had an AUC of 0.77 [CI 0.64-0.97, p-value 0.01], better than the original study.

CONCLUSION
The ACTION-ICU score identifies Mexican patients with NSTEMI who need ICU care, providing a valuable tool for predicting complications and implementing best practices in medical units with limited resources.