Relationships Between Neutrophil-to-Lymphocyte Ratio and Index of Microcirculatory Resistance in ST-segment Elevation Myocardial Infarction Patients Undergone Primary Percutaneous Coronary Intervention

A total of 123 consecutive STEMI patients who underwent successful primary PCI and coronary physiologic study immediately after PCI were retrospectively enrolled in the study. All patients underwent index PCI between May 2009 and October 2014 at INHA university hospital. The definition of STEMI was determined by the current guidelines.

Complete blood counts, including total and differential WBC counts, were obtained at the time of admission. Total counts of WBC, neutrophils, and lymphocytes were assessed using an automated blood cell counter (XE-2100, Sysmex Inc., Japan). NLR was calculated as the ratio of the neutrophil counts to the lymphocyte counts. All patients were divided into 3 groups according to the NLR tertiles.

The IMR was assessed shortly after primary PCI by using thermodilution-derived method. After successful interventional reperfusion, intracoronary nitroglycerin (100~200μg) was administered and coronary pressure guidewire (Radi Pressure Wire 5, Radi Medical Systems, Uppsala, Sweden) was calibrated outside the patient. The guidewire was equalized at the distal tip of guiding catheter, and then advanced towards the distal third of infarct related artery (IRA). Three times of saline injection (3~5 ml) were administered to IRA and baseline mean transit time was assessed. Microcirculatory hyperemia was induced by using an adenosine infusion (140 μg/kg.min) administered via peripheral venous line. During maximal hyperemia, hyperemic mean transit time (Tmn) was measured using same method as prior separate saline injections. Mean aortic (Pa) and distal coronary pressures (Pd) was measured during hyperemia. The IMR was calculated the formula as follows: IMR = Pd x hyperemic Tmn. Fractional flow reserve (FFR) was calculated by ratio of Pd to Pa during maximal hyperemic status. Coronary flow reserve (CFR) was derived from dividing the resting Tmn by hyperemic Tmn.

Continuous variables were presented as mean ± standard deviation (SD) and categorical variables as the number of patients (percentages). The one way analysis of variance (ANOVA) was used for comparing continuous variables. Additionally, post-hoc analysis was performed for evaluating to be significant by ANOVA. The Pearson's chi-square test or Fisher's exact test was used for analyzing categorical variables. Linear regression analysis was performed for investigating the association between NLR and variables using clinical, laboratory, echocardiographic, and angiographic data. A p value <0.05 was regarded statistically significant. All statistical analyses were carried out with SPSS version 19.0 (SPSS inc., Chicago, Illinois, USA).