Association Between Eosinophil-to-Monocyte Ratio and ST-Segment Resolution in Young STEMI Patients Undergoing Primary Percutaneous Coronary Intervention.

OBJECTIVE: Impaired myocardial reperfusion after primary percutaneous coronary intervention (pPCI) is associated with adverse outcomes in ST-segment elevation myocardial infarction (STEMI). This study investigated the relationship between the eosinophil-to-monocyte ratio (EMR) and ST-segment resolution in young patients with STEMI undergoing pPCI. METHOD: This retrospective, single-center study included 492 consecutive patients with STEMI younger than 45 years who underwent pPCI between January 2022 and January 2026. The primary endpoint was incomplete ST-segment resolution (<70%), while no-reflow was evaluated as a secondary endpoint. Univariable and multivariable logistic regression, restricted cubic spline, and receiver operating characteristic (ROC) analyses were performed. RESULTS: Lower EMR was associated with greater thrombus burden, impaired postprocedural Thrombolysis in Myocardial Infarction (TIMI) flow, increased glycoprotein IIb/IIIa inhibitor use, incomplete ST-segment resolution, and no-reflow (all P < 0.001). Incomplete ST-segment resolution occurred in 52 patients (10.6%), no-reflow in 25 (5.1%), and in-hospital death in 1 (0.2%). Lower EMR remained independently associated with incomplete ST-segment resolution (odds ratio [OR] 0.245, 95% confidence interval [CI] 0.127-0.475, P < 0.001). In a secondary analysis, lower EMR was associated with no-reflow (adjusted OR 0.079, 95% CI 0.021-0.238, P < 0.001). Restricted cubic spline analysis showed a nonlinear inverse association between EMR and impaired myocardial reperfusion. EMR demonstrated acceptable discriminatory performance for incomplete ST-segment resolution (area under the curve [AUC] 0.757) and no-reflow (AUC 0.827). CONCLUSION: Lower admission EMR was associated with impaired myocardial reperfusion in young patients with STEMI undergoing pPCI. EMR may represent an admission reperfusion-associated marker, but its biological and clinical significance remains uncertain and requires prospective external validation.