Discrepancy In Measuring On-Clopidogrel Platelet Responsiveness By Light Transmission Aggregometry And Vasodilator-Stimulated Phosphoprotein Phosphorylation Following ST-Elevation Myocardial Infarction

Objective:The most common cause of death nowadays is acute myocardial infarction (MI), which is caused by coronary artery thrombosis. Platelets play a central role in cardiovascular thrombosis. They adhere to the subendothelial matrix after endothelial damage due to a ruptured atherosclerotic plaque, then aggregate with each other to form a prothrombotic surface that promotes clot formation and subsequently vascular occlusion. As a result, therapies targeting key pathways of platelet activation-including thromboxane A2synthesis, adenosine diphosphate (ADP)-mediated signaling and GPIIb/IIIa signaling-have established a role in the treatment of cardiovascular arterial disease. The most common of these antiplatelet agents include aspirin, clopidogrel and integrin GPIIb/IIIa receptor antagonists. Mounting evidence shows that the mortality and cardiovascular events of acute MI patients could be significantly reduced by antiplatelet therapy. There was still parts of patients had a high cardiovascular events though dual antiplatelet therapy were used,which was previously called variability of response. There was multiple factors that could cause variability of response, include baseline clinical and demographic factors, drug-drug interactions, such as use proton pump inhibitors (PPI), and cytochrome P450genetic polymorphisms and so on. Now several methods were used to assess platelet function, such as ADP induced platelet aggregation (PAG) measured by light transmission aggregometry (LTA), vasodilator-stimulated phosphoprotein (VASP) phosphorylation assay by flow cytometric analysis whose assessing index was platelet reactivity index (PRI) and thromboelastography. Among these methods, LTA and VASP phosphorylation were most widely used in research. In the present study, we simultaneously used LTA and VASP phosphorylation methods to assess the reactivity of platelets to clopidogrel in acute MI patients, to explore the possible factors that are associated the discrepancy by these two methods which may be useful for the detection of low responders to antiplatelet therapy.Methods:A total of90consecutive ST segment elevated myocardial infarction (STEMI) patients admitted for emergency primary percutaneous coronary intervention (PCI) in the Heart Center of Pingjin Hospital, Logistics University of the Chinese People’s Armed Police Forces, were recruited in this study. The diagnose was consistent with the current STEMI guideline of ACC/AHA in2013. All the recruited patients were administered with aspirin300mg and clopidogrel300mg immediately after admission. Median cubital vein blood were collected6days after PCI to determine CYP2C19*2/*3genetic polymorphisms, PAG, and PRI. Both LTA and VASP phosphorylation methods were used to explore the influencing factors of diversity results of reactivity of platelets to clopidogrel in AMI patients, to evaluate consistency and diversity of the two detecting methods on platelets function and to analyze its possible affecting factors.Results:There were70male patients enrolled, mean age58.83±10.47;20female patients enrolled, mean age64.80±9.39.1) All patients were divided into2groups by PAG median level (65.5%) which was assessed by LTA analysis:PAG-normal responder, group PAG<65.5%, consisted of39male and10female; PRI-low responder (PAG-LR) group, PRI>65.5%, consisted of30male,11female. There no significant differences in age, gender, smoking, body mass index (BMI), CYP2C19*2/*3genetic polymorphisms, medications, disease history, blood cell parameters and laboratory parameters were found between the two groups (P>0.05).Correlation analysis demonstrated that no significant correlation were found between PAG and age, BMI, blood cell parameters and laboratory parameters (jP>0.05).2) All patients were divided into2groups by PRI median level (41.85%) which was assessed by VASP phosphorylation assay by flow cytometric analysis:PRI-normal responder group (PRI-NR), PRI<41.85%, consisted of34male and11female; PRI-low responder group (PRI-LR), PRI>41.85%, consisted of36male,9female. There no statistical differences in age, gender, smoking, body mass index (BMI), and CYP2C19*2/*3genetic polymorphisms medications, disease history, blood cell parameters and laboratory parameters were found between the two groups (P>0.05).Correlation analysis demonstrated that no significant correlation were found between PRI and age, BMI, blood cell parameters and laboratory parameters (P>0.05). 3) Correlation analysis demonstrated that a positive correlation between PAG and PRI was found in the present study (r=0.4278, P<0.0001); Bland-Altman analysis demonstrated that the PRI and PAG method have a Bias=-19.07, SD=21.64.4) Both the PAG and PRI evaluated as low platelet reactivity or both normal platelet reactivity were difined as consistency group, The PRI evaluated as low platelet reactivity while PAG evaluated as normal platelet reactivity or The PRI evaluated as low platelet reactivity while PAG evaluated as normal platelet reactivity were defined as inconsistency group, to explore the possible factors that lead to diversity of the results detected by the two methods. Univariate logistic regression analysis showed that BMI, WBC counts, MON counts, smoking, hypertension, stroke and apply ARB drugs may affect the consistency of the results detected by the two methods. Multi-variable logistic regression analysis demonstrated that smoking is an independent factors affect the consistency of the results detected by the two methods (OR:3.333,95%CI:1.120-9.917, P=0.030), even after adjusted by traditional cardiovascular risk factors, such as age, gender, hypertension, diabetes (OR:4.399,95%CI:1.105-17.522, P=0.036).Conclusions:The present study is to explore the possible causes of inconsistency results of evaluating platelet reactivity using LTA and VASP phosphorylation methods in patients with STEMI. The results showed that smoking is an independent factors associated with the discrepancy of the results detected by the two methods. These results may be useful for the detection of low responders to antiplatelet therapy, Future clinical study with large sample size is warranted to validate this result.