Platelet Function Monitoring And Effects Of Genetic Variants On Clopidogrel Response In Patients With Acute Coronary Syndrome

Part I Platelet function monitoring by Thrombelastograph in patients with acute coronary syndrome receiving drug-eluting stentsObjective:Platelet activation and aggregation play pivotal roles in the pathophysiological development of coronary artery atherosclerosis and thrombus formation. We sought to evaluate the clinical usefulness of Thrombelastograph(TEG) in patients with acute coronary syndrome(ACS) receiving drug-eluting stents(DES).Method:We consecutively enrolled447Chinese patients with ACS receiving DES and dual anti-platelet treatment. At24-36h after clopidogrel and aspirin loading, blood for TEG analysis was sampled. Thrombin-induced clot strength (MAthrombin) reflects the paitent’s maximal potential platelet reactivity. MAFibrin reflects the contribution of fibrin alone to clot strength. MAADP or MAAA represents the contribution of platelets not inhibited by aspirin or clopidogrel. Platelet aggregation in response to ADP or AA is calculated with computerized software on the basis of theformula:%Aggregation=[(MAADP or AA-MAFibrin)/(MAThrombim—MAFibrin)]×100. Clopidogrel low-responsiveness was defined as＞70%ADP-induced aggregation as measured by TEG. Aspirin low-responsiveness was defined as more than50%platelet aggregation after stimulation by AA. Presence of multi-vessel disease (MVD, defined as coronary artery stenosis≥50%in at least2major epicardial coronary arteries) was used as a surrogate marker of atherosclerosis severity and extension. Ischemic event was the composite of cardiovascular death, nonfatal myocardial infarction, or stroke.Result:Maximal platelet reactivity (MAthrombin) was higher in patients with STEMI than in those with non-ST elevation ACS (NSTACS)(64.6±5.6mm vs.63.3±5.2mm, p=0.016). Higher prevalence of STEMI was observed in subjects with MAthrombin>70mm (52.0%vs.32.3%in subjects with MAthrombin≤70mm, p=0.006). Moreover, patients with MVD showed a higher MAThrombin compared with single vessel disease (SVD) patients (65.1±5.4mm vs.62.5±4.9mm, p<0.001). The frequency of MVD increased with the strength of MAThrombin (<65mm:37.0%;65-70mm:57.3%;>70mm:76.0%; p<0.001). Heterogeneous anti-platelet effects of clopidogrel were observed in the overall patient population as depicted by the normal bell-shaped distribution of platelet aggregation. Of the447patients,18.3%(82) were categorized as clopidogrel low-responsiveness. However, only43(9.6%) patients were categorized as aspirin low-responsiveness. A total of233patients with NSTACS undergoing elective PCI were included in the evaluation of PMI. PMI was documented in33of233patients (14.2%). ADP-induced platelet aggregation was significantly higher in patients with PMI than in those without PMI as measured by TEG (60.0±24.4%vs.43.0±24.0%, p<0.001). After adjustment for confounding factors, the risk for developing PMI increased by the presence of clopidogrel low-responsiveness (ORadj=5.050,95%CI:1.684-15.149, p=0.004) and diabetes mellitus (ORadj=2.471,95%CI:1.110-5.501, p=0.027). Ischemic events occurred within1month in13(2.9%) patients; on-clopidogrel platelet aggregation was significantly higher in patients with events than in those without events (64.3+22.8%vs.45.3±24.7%, p=0.010). Multivariable logistic regression analyses showed a significant correlation of clopidogrel low-responsiveness (ORadj=4.664,95%CI:1.430-15.079, p=0.011), as well as diabetes mellitus with one-month clinical outcome (ORadj=3.826,95%CI:1.171-12.505, p=0.026). Ischemic events occurred within half year in28(6.3%) patients; patients with events also showed a higher ADP-induced platelet aggregation compared with those without events (65.3+21.7%vs.44.5+24.4%, p<0.001). In multivariable Cox regression analysis, clopidogrel low-responsiveness (HR=3.740,95%CI:1.750-7.933, p=0.001) was a significant contributor linked to the occurrence of ischemic events within half year.Conclusion:MAThrombin as measured by TEG, reflecting the maximal potential platelet reactivity, was associated with the clinical type of ACS and the severity of coronary atherosclerosis. Furthermore, clopidogrel low-responsiveness might partly account for higher risk of PMI and poor clinical outcome.Part II Effects of genetic variants on platelet reactivity and clinical outcomes: a cohort study of Chinese ACS patients receiving drug-eluting stents and dual-antiplatelet treatmentObjective:The primary source of clopidogrel variability might lie in its pharmacogenetics. The frequency of genetic alleles varies considerably according to ethnicity. Whether the pharmacogenetic variants are associated with clopidogrel response in Chinese patients has yet to be defined.Methods:We consecutively enrolled447Chinese patients with acute coronary syndromes (ACS) receiving drug-eluting stents and clopidogrel treatment. We then assessed the relation of fourteen SNPs within seven genes modulating clopidogrel absorption(ABCB1), metabolic activation(CYP2B6、CYP2D6、CYP3A4、CYP2C9 and CYP2C19), and biologic activity(P2RY12) to the response of clopidogrel as measured by ex-vivo platelet reactivity and ischemic events during1month and half year of follow-up. High platelet reactivity (HPR) was defined as≥70%ADP-induced aggregation as measured by TEG. Ischemic event was the composite of cardiovascular death, nonfatal myocardial infarction, or stroke.Results:Only CYP2C19*2and*3, out of the investigated polymorphism, were associated with ADP-induced platelet aggregation and HPR. Among the study population, the frequency of CYP2C19*2allele was53.7%, and the prevalence of CYP2C19*3allele was10.5%. After adjustment for confounding factors, carriage of CYP2C19*2allele (ORadj=2.339,95%CI:1.369-3.966, p=0.002) and carriage of CYP2C19*3allele (ORadj=3.028,95%CI:1.453-6.310, p=0.003) were independent predictors for HPR. On-clopidogrel platelet aggregation and the rate of HPR did not differ between the CYP2C19*2versus*3allele carriage. Half year and1month clinical outcomes were not associated with the carriage of CYP2C19*2or*3alone. Regardless of the carriage of CYP2C19*2or*3loss-of-function allele (LOF), ADP-induced platelet aggregation increased depending on the number of the LOF allele (0LOF carriers:38.6±22.7%vs.1LOF carriers:48.2%±25.2%, p<0.001;1LOF carriers:48.2%±25.2%vs.2LOF carriers:57.6%±22.9%, p=0.008). Moreover, ischemic events within half year occurred more frequently in2LOF carriers than in1LOF carriers (13.6%vs.5.9%, p=0.040) and than in0LOF carriers (13.6%vs.4.0%, p=0.016). However, the occurrence of ischemic events within half year did not differ between0LOF carriers and1LOF carriers. In multivariable Cox regression analysis,2CYP2C19LOF carriage (HR=3.369,95%CI:1.244-9.128,0.017) was a significant contributor linked to the occurrence of ischemic events within half year.Conclusions:The carriage of CYP2C19*2or*3increased the propensity for on-clopidogrel HPR, but was not associated with short-term clinical outcome. Furthermore, LOF alleles in CYP2C19, regardless of the carriage of CYP2C19*2or*3, have a gene-dose effect on post-clopidogrel platelet reactivity. However, only2LOF carriage was associated with increased risk for ischemic events at half year follow-up.