Combined Prognostic Value of Systemic Immune-Inflammation Index (SII) and LDL-C in AMI Patients After Primary Percutaneous Coronary Intervention ( PPCI )

Background: To evaluate the prognostic significance of the systemic immune-inflammation index (SII) in combination with low-density lipoprotein cholesterol (LDL-C) for out-of-hospital outcomes in patients with acute myocardial infarction (AMI) undergoing primary percutaneous coronary intervention (PPCI). Methods: A retrospective study was conducted on 487 patients with AMI who underwent PPCI at Xuzhou Medical University Affiliated Hospital between January 2019 and December 2021. SII and LDL-C levels were dynamically monitored, with particular emphasis on values measured one month after discharge. Least absolute shrinkage and selection operator (LASSO) regression and multivariate logistic regression were used to identify independent prognostic factors. Receiver operating characteristic (ROC) curve analysis determined the optimal cut-off value for SII at 676.6 × 10⁹/L. Based on whether patients met the one-month post-discharge targets for SII (≤676.6 × 10⁹/L) and LDL-C (<1.4 mmol/L or a ≥50% reduction from baseline), they were stratified into four groups: (1)both SII and LDL-C achieved, (2) only SII achieved, (3) only LDL-C achieved, and (4)neither SII nor LDL-C achieved. Adverse events were defined as a composite of all-cause death, recurrent myocardial infarction, repeat revascularization, and ventricular arrhythmia. Prognosis was evaluated using Cox regression models and Kaplan–Meier survival analysis. Results: Patients who achieved both SII and LDL-C targets exhibited the most favorable long-term outcomes, whereas those who met neither target had the poorest prognosis (P < 0.001). Importantly, patients with SII control alone outperformed those with LDL-C control alone in terms of survival. At one month post-discharge, the SII level demonstrated good predictive accuracy for adverse events, with an area under the curve (AUC) of 0.76. Conclusion: Dual achievement of SII and LDL-C targets improves outcomes in AMI patients post-PPCI, highlighting the need for combined lipid and inflammation control in secondary prevention.