Background: Systemic immune-inflammatory index (platelet count × neutrophil–lymphocyte ratio) is a new marker that predicts adverse clinical outcomes in coronary artery diseases. Our aim was to investigate the relationship between the systemic immune-inflammatory index and residual SYNTAX score in patients with ST-segment elevation myocardial infarction undergoing primary percutaneous coronary intervention.

Methods: In this retrospective study, 518 consecutive patients who underwent primary percutaneous coronary intervention (PCI) with the diagnosis of ST-segment elevation myocardial infarction were analyzed. The severity of coronary artery diseases was determined by residual SYNTAX score. In the receiver operating characteristic curve analysis, systemic immune-inflammatory index with an optimal threshold value of 1025.1 could detect the presence of a high residual SYNTAX score; the patients were divided into 2 groups as low (326) and high (192) according to the threshold value. In addition, binary multiple logistic regression analysis methods were used to evaluate independent predictors of high residual SYNTAX score.

Results: In binary multiple logistic regression analysis, systemic immune-inflammatory index [odds ratio = 6.910; 95% CI = 4.203-11.360; P <.001] was an independent predictor of high residual SYNTAX score. In addition, there was a positive correlation between the systemic immune-inflammatory index and residual SYNTAX score (r = 0.350, P <.001). In the receiver operating characteristic curve analysis, the systemic immune-inflammatory index with an optimal threshold value of 1025.1 could detect the presence of a high residual SYNTAX score with 73.8% sensitivity and 72.3% specificity.

Conclusion: Systemic immune-inflammatory index, an inexpensive and easily measurable laboratory variable, was an independent predictor of the increased residual SYNTAX score in patients with ST-segment elevation myocardial infarction.