Prognostic Utility of the Combination of Platelet Count with Neutrophil-to-Lymphocyte Ratio in Aged Patients with Acute Myocardial Infarction Undergoing Percutaneous Coronary Intervention

Method This was a study recording 637 patients who were diagnosed with acute myocardial infarction. Our patients were grouped according to the combination of platelet count and neutrophil-to-lymphocyte ratio. The prognostic role of the combination of platelet count and neutrophil-to-lymphocyte ratio on mortality was assessed by the univariate and multivariate Cox regression analysis. Result Our study population was divided into three parts according to the median values of platelet count and neutrophil-to-lymphocyte ratio. It was indicated that platelet count and neutrophil-to-lymphocyte ratio were correlative mutually to a certain degree (p=0.010). The Kaplan–Meier analysis showed that the combination of high platelet count and high neutrophil-to-lymphocyte ratio had a greater risk of death in short- and long-term endpoints (log-rank p=0.046, p < 0.001, respectively). Moreover, by multivariate analysis, both high platelet count and high neutrophil-to-lymphocyte ratio groups were an independent predictor (hazard ratio: 2.132, 95% confidence interval: 1.020–4.454, p=0.044) and long-term mortality (hazard ratio: 2.791, 95% confidence interval: 1.406–5.538, p=0.003). Conclusion The combination of platelet count and neutrophil-to-lymphocyte ratio could be a useful predictor for the prediction of in-hospital and long-term mortality in aged patients with acute myocardial infarction.


Introduction
Acute myocardial infarction (AMI) is the leading cause of cardiac death, especially for the aged people [1,2]. Along with the prolongation of the life expectancy in the elderly population, cardiac death is more frequent in patients aged over 65 years old [3,4]. e severe condition with insidious onset is one of the reasons for the increasing mortality in elderly AMI patients [3,5,6]. e current dilemma for clinical workers is figuring out a simple and powerful prognostic biomarker to identify high-risk patients.
Clinical and experimental evidence found that inflammation played a crucial role in the development and progression of AMI [7][8][9]. Previous studies showed that inflammatory markers, such as platelet count (PLC) and neutrophil-to-lymphocyte ratio (NLR), were connected with poor clinical outcomes in patients with AMI [10,11]. Pathologically increased PLC in peripheral blood contributed to the initiation, progression, and complication of atherosclerosis [12][13][14]. According to a population-based cohort study, elevated PLC was associated with higher mortality and increased risk of cardiovascular events in AMI patients [15]. However, previous conflicting results showed that there was no correlation between elevated PLC and poorer cardiovascular endpoints [16][17][18].
Neutrophils and lymphocytes mirror the inflammatory status and have an effect on the destabilization of atherosclerotic plaque [19]. Accordingly, NLR has been assessed as a prognostic biomarker for cardiovascular diseases. A retrospective study by Han et al. showed that elevated NLR was a useful marker to predict long-term all-cause death in patients with AMI [20]. Nonetheless, the predictive value of NLR varies slightly in different studies, which is an imperfection for the risk stratification in AMI patients [21,22]. us, to optimize the predictive value of PLC and NLR, some studies evaluated an original inflammation-related prognostic marker, named the combination of PLC and NLR (COP-NLR) [23,24]. ese studies showed that COP-NLR was a better prognostic predictor in patients with inflammatory diseases [23,24]. However, to the best of our knowledge, the usefulness of COP-NLR has not been evaluated in AMI.
erefore, in the present study, we intended to investigate the prognostic value of COP-NLR in aged AMI patients.

Participants.
is was a retrospective study which reviewed the data of 637 patients with AMI at the Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, between January 2015 and October 2017. AMI was defined as either ST-segment elevation myocardial infarction (STEMI, typical symptoms of myocardial ischemia lasting for >30 min, with ST-segment elevation >1 mm in ≥2 contiguous standard or precordial leads and/or new onset of left bundle branch block) [25] and without ST-segment elevation myocardial infarction (NSTEMI, a rise of myocardial injury markers in combination with typical angina pectoris and without ST-segment elevation) [26]. e exclusion criteria were as follows: (a) all patients who were younger than 65 or older than 85 years; (b) patients with sepsis or trauma; (c) patients who were diagnosed with active cancer, autoimmune diseases, hematological proliferative diseases, chronic pulmonary disease, renal failure, and end-stage liver disease; and (d) patients who received steroid therapy or chemotherapy around the diagnosis index during six months.
is study has got approval by the ethics committee of Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology (TJ-C20141112), and is in accordance with the Helsinki Declaration.

Study Procedures and Laboratory Analysis.
Venous blood samples were collected from all patients at the time of admission. Collection patients' demographic data were documented during hospitalization, including vital signs at admission, risk factors, medical history, and drug use. Laboratory results included creatinine, aminopherase, N-terminal prohormone of brain natriuretic peptide (NT-ProBNP), cardiac troponin I (CTnI), total cholesterol (TC), triglycerides, high-density lipoprotein cholesterol (HDL), and low-density lipoprotein cholesterol (LDL). e NLR was calculated as the ratio of the neutrophils to lymphocytes. Besides, echocardiographic parameters included left ventricular ejection fraction (LVEF).
Angiographic data including thrombolysis in myocardial infarction trial blood flow grade (TIMI) and Gensini score during the in-hospital period were obtained from the electronic medical records database. All included patients underwent coronary angiography. And the results of coronary angiography were determined by two professional cardiovascular doctors. Based on the results of coronary angiography and clinical findings, doctors selected using different treatment strategies according to the guideline [27]. In the perioperative period, anticoagulants, heparin/low molecular heparin, and tirofiban were used. For the patients with coronary stent placement, they were treated with aspirin and clopidogrel (or ticagrelor) as adjuvant antiplatelet therapy.

Study Endpoint and Follow-Up.
e endpoints of our study were all-cause mortality that happened in-hospital and during the follow-up period. All-cause death was defined as mortality from any cause. e data during the hospitalization were obtained from the hospital administration system. And the information during follow-up was regularly collected from hospital records or the telephone interviews with patients or their relatives.

Statistical Analysis.
In baseline characteristics analysis, continuous variables were presented as mean ± standard deviation and tested for normal distribution by the Kolmogorov-Smirnov test. e sample size of 224 patients was calculated to give a power of 90%, a type I error of 0.05, and a 10% drop-out rate. Comparative analyses between groups for continuous variables were performed by Student's t-test or Mann-Whitney U test. Categorical variables were summarized as percentages and compared with the χ 2 test. Correlation between PLC and NLR was tested using the Spearman correlation coefficient. e mortality according to the median values of PLC and NLR were analyzed by the Kaplan-Meier method, and results were compared using the log-rank test. Univariate and multivariate analyses were performed to determine the significance of prognostic variables using the Cox proportional hazards model. Any variables examined in the univariate analysis for which the p value was <0.10 were contained in the multivariate model. A value of p < 0.05 was supposed to be statistically significant.

Baseline Characteristics.
A total of 637 patients with AMI were enrolled in this study. A detailed description of demographic and laboratory characteristics is presented in Table 1. Median values of PLC and NLR were 198.00 and 4.88, respectively. ere was a weak but negative correlation between PLC and NLR (Spearman r � −0.102, p � 0.010; Figure 1). e patients were divided into 3 groups: low PLC (PLC < 198.00) and low NLR (NLR < 4.88) (n � 145) versus either low PLC or low NLR (n � 351) versus high PLC (PLC ≥ 198.00) and high NLR (NLR ≥ 4.88) (n � 141), as noted in Table 1. Both groups were predominantly male. e mean age of patients was 72.40 ± 5.28, 71.95 ± 5.20, and 72.31 ± 4.83 years, respectively, with an age range from 65 to 85 years. e high PLC and high NLR group had shorter reperfusion time (p < 0.001), longer hospitalization day, (p � 0.024), and worse heart function (p < 0.001).
As shown in Table 2, in terms of the angiographic and procedural characteristics, no significant differences were discovered in the Gp IIbIIIa inhibitor use, stent use, TIMI grade, and Gensini score between the three groups, except for the culprit vessel quantity and the use of thrombus aspiration.

Clinical Outcomes.
During hospitalization and the average follow-up period was 771.71 ± 16.39 days, the all-cause mortality was significantly higher in patients with both high PLC and high NLR group (p � 0.013 for in-hospital mortality, p < 0.001 for long-term mortality; Figure 2). e Kaplan-Meier curves based on the median values of NLR and PLC are shown in Figure 3. When PLC and NLR were compared between patients with and without death during short-and long-term follow-up, NLR was significantly higher in patients with death (both log-rank: p < 0.001; Figures 3(a) and 3(b)). However, there was no significant difference in PLC (log-rank: p � 0.478 and p � 0.482, resp.; Figures 3(c) and 3(d)). e Kaplan-Meier survival analysis according to the combination of PLC and NLR is shown in Figure 4. e mortality increased significantly in the high PLC and high NLR group during hospitalization (log-rank: p � 0.046; Figure 4(a)) and long-term follow-up (log-rank: p < 0.001, Figure 4(b)).

Discussion
e inflammatory process has a central role in the development of atherosclerosis, instability of atherosclerotic plaques, and formation of thrombus [28][29][30].
e role of inflammatory markers on the prognosis of AMI has been suggested in previous studies [31,32]. A large study of postmenopausal women showed that high PLC was associated with increased cardiovascular mortality [33]. Previous studies revealed that an elevated level of NLR was related to increased cardiovascular risk in patients with AMI [34,35]. However, in the current study, PLC had no predictive significance in univariate or multivariate analysis. Some case-control studies and observational studies have also shown that there was no association between high PLC and risk of death [18,36]. In the present study, NLR had a strong association with death in a patient with AMI. Yet, our results showed that NLR was not an independent predictor of short-and long-term mortality. us, further clinical studies are needed to explore a better biomarker to predict the death prognosis in AMI patients.
Recent studies found that the interaction of platelet and leukocyte is involved in the complex pathologic process of atherosclerosis [37]. Platelet-leukocyte interactions also activated cytokine expression, caused adhesion of endothelial cell, and promoted arterial thrombosis [38]. Based on this interaction of platelet with leukocyte, we made further research for the prognostic value of the combination of PLC and NLR in aged patients with AMI. e COP-NLR consisted of two biomarkers (PLC and NLR) related to cellular inflammation. It may reflect the balance of inflammation in the body more comprehensively, has stronger predictive potential for clinical outcomes, and contributes more to the risk stratification. COP-NLR has been identified as a novel predictive factor in patients with inflammatory diseases in previous studies [23,24]. Our study showed that an increased level of COP-NLR was associated with a higher risk of in-hospital and long-term mortality in aged patients with AMI. Compared with individual PLC or NLR, the COP-NLR was a stronger predictor of mortality in aged AMI patients.
Although the pathologic mechanism between thrombocytosis and death prognosis has not been fully understood, several potential mechanisms have been described. Increased release of inflammatory mediators might lead to higher PLC [39]. e elevated platelet concentration represented greater possibilities to attach to the vessel wall, leading to platelet-dependent thrombus formation. In addition, on vulnerable coronary plaques, forming platelet-rich thrombi resulted in worse outcomes [40,41]. e high NLR might probably be due to an increased neutrophil count and a decreased lymphocyte count. After the onset of AMI, increased cytokines, such as TNF-α and IL-6 Emergency Medicine International caused relative neutrophilia [42]. Increased neutrophil counts predicted larger infarct size and adverse long-term cardiac prognosis [43]. Conversely, it was suggested that lymphocytopenia had a connection with AMI [44]. Similarly, Shiyovich and colleagues' study showed that there was a significant negative linear association between lymphocytes and death in the long-term follow-up period [45]. Lower lymphocyte counts might be owing to an abruptly increased level of corticosteroids and increased inflammation-related lymphocytes apoptosis [46,47]. e NLR integrated for two cellular subtypes with opposite actions when it comes to vascular inflammation. According to Ayca's study, preprocedural NLR >4.9 was significantly related to stent thrombosis and higher mortality in patients with AMI [22]. However, the predictive value of NLR varied slightly in different studies [21,22]. is was probably because of the differences in study design, population selection, statistical methods, outcome measurement.
It was indicated that LVEF and Killip class were important parameters for predicting adverse outcomes [48,49]. Our study showed a similar result for predicting in-hospital and long-term prognosis of AMI. Along with COP-NLR, we also identified LVEF and Killip class as independent predictors of clinical outcomes in patients with AMI. us, this observation may support that the prognosis for patients with AMI is likely to be multifactorial. e identification of the potential predictor may provide a certain clinical assist for the risk stratification of AMI patients.
In the present study, our results showed that the COP-NLR was an independent predictor of all-cause mortality in AMI.
is is the first report to investigate the value of combined PLC and NLR to predict the in-hospital and longterm mortality in aged AMI patients. Both PLC and NLR could be easily and widely available, calculated from WBC subtype counts, which were routinely performed at  In-hospital mortality Long-term mortality    We have to acknowledge that there are some limitations in this study. Firstly, the retrospective design of the study sets a limit to the convincement of our study. Due to the nature of our study, the results must be explained with caution, given the possibility of confounders. Secondly, our endpoints are so simple that we have not investigated the relationship between COP-NLR with other major adverse cardiovascular events, including reinfarction, target vessel revascularization, arrhythmia, cerebrovascular accident, and congestive heart failure. irdly, we could not compare COP-NLR with other conventional inflammatory markers, for instance, C-reactive protein, fibrinogen, or myeloperoxidase. Because they were not routinely obtained in our study population.

Conclusion
In conclusion, a higher level of COP-NLR was independently associated with poor prognosis in aged patients with AMI. e COP-NLR was a potential predictor for short-and long-term mortality in aged AMI patients.

Data Availability
e data used to support the findings of this study are available from the corresponding author upon request.

Conflicts of Interest
e authors declare that they have no conflicts of interest regarding this submission.