DAPT composed of aspirin and P2Y12 receptor inhibitors are PCI standard treatments. Different P2Y12 receptor inhibitors (clopidogrel, pragrel, tigrilol) have different levels of potency, enabling physicians to consider individualized and precise treatment options. in reality, switching between inhibitors driven P2Y12 clinical and socio-economic factors has become increasingly common. From clopidogrel to pragrel or tigrelo (known as "upgrade ") or from pratogrel or tigrelo to clopidogrel (known as" downgrade ") has become a major area of research. Actually individualized precision switching DAPT strategies can be selected according to the clinical context (chronic coronary syndrome versus acute coronary syndrome), the stage of the disease (early versus long term), and the risk of ischemic and bleeding complications in patients. Although recent guidelines do not recommend the routine use of gene and platelet function testing in patients with PCI therapy, the application of gene and platelet function testing in individualized precision therapy has been paid more attention.
1. CYP2C19 Gene Polymorphism and Population Distribution
CYP2C19 is a highly polymorphic gene. more than 30 allelic variants have been recorded and named by the * allele the human cytochrome P 450(CYP 450) allele nomenclature database. There is increasing evidence that CYP2C19 enzyme belongs to the second subfamily of CYP450 enzymes and is a key enzyme in metabolic process, and its related genes are polymorphic expression. The *1 allele is associated with normal enzyme activity and is considered the default allele, polymorphisms associated with altered enzyme activity do not exist. the CYP2C19*2 and *3 alleles are caused by an abnormal splicing site and a precocious termination codon, respectively, which both cause loss of enzymes and are considered alleles for LOF. The *2 allele is 30-35% in Asians,*3 allele occurs 5%-10% in Asians, and CYP2C19LOF mutation rate is 60% in Asian population. In this study ,113 patients with LOF group, or 54.3%, were similar to previous studies.
2. CYP2C19 Gene Detection Method and Clinical Application
The current gene detection methods of individualized medicine mainly include: PCR direct sequencing method, PCR pyrophosphate sequencing method, quantitative fluorescence PCR method, PCR gene chip method, PCR electrophoresis analysis method, high resolution melting analysis method, allele polymorphism, in situ hybridization, etc. Among them, real-time fluorescence PCR is the most popular because of its high sensitivity, accurate classification and convenient operation. The current clinical practice generally uses proven effective rapid detection methods such as Spartan RX CYP2C19 system, Verigene CYP2C19 system for rapid genotyping. it is a FDA approved microarray-based genotyping method. the system is a fully automated genome extraction, preparation and analysis system with an analysis time of about 2 to 4 hours. There is also a portable system with low entry cost STQ3, which contains a one-step method CYP2C19 genotyping detection kit (Coyote Bioscience). compared with other kits, direct use of whole blood without nucleic acid extraction reduces test time and cost. rapid response test reports can be issued within about 75 minutes but for human diagnosis have not been approved. The population studied in this study were all Chinese people, all of them were tested with uniform kit and equipment to ensure the accuracy of the results.
3. Methods and clinical application of platelet detection
Platelets are involved in every pathological link of the ACS and affect the prognosis, so PFT is an independent risk factor to predict the adverse prognosis and bleeding risk of PCI patients, which has been confirmed by many clinical studies and become a consensus. PFT can be used to assess the biological effects of antiplatelet drugs. the main indicator is platelet aggregation rate, which can be repeatedly detected. The current platelet detection methods include :1. optical transmission turbidimetry ,2. multi-electrode coagulation ,3. VerifyNow ,4. thromboelastogram ,5. VASP ,6. Plateletworks analysis ,7. platelet function analyzer (PFA),8. lamina analyzer (Impact-R),9. p-selectin ,10. GP IIb/IIIa receptor detection, and dozens of others. The above methods of platelet function detection are numerous and different methods have their own advantages and disadvantages, which should be adapted to local conditions according to field conditions, clinical evidence and standardized detection. On the basis of the current application situation in China, it is suggested that the LTA method should be the main method, auxiliary TEG and other detection methods. A classical LTA method was used to detect platelet aggregation rate in this study, which was operated by experienced technicians to ensure accuracy.
4. Relationship between Platelet Reactivity and CYP2C19 Gene Polymorphism
It is well known that there are individual differences in platelet reactivity associated with genetic, cellular, clinical factors such as age, weight, renal function status, etc. There are 20-30% ACS patients with clinical HPR, and about 4%-30% of patients with clopidogrel resistance were found by platelet detection[20, 21]. Where genetic factors have a great influence. in EXCELSIOR trials, Hochholzer et al found that the main independent predictors of insufficient antiplatelet response to clopidogrel were CYP2C19*2 carriers. Mega et al found that plasma active metabolites containing at least one CYP2C19LOF allele carrier decreased by 32.4% compared with noncarriers in 162 healthy subjects after taking clopidogrel, and the maximum platelet aggregation rate for clopidogrel response decreased by 9%. Whereas in a study of 1016 chinese ACS patients undergoing drug-coated stent implantation, CYP2C19LOF alleles were associated with HPR, and the risk of adverse cardiovascular events a 1-year follow-up period and were more prominent in high-risk populations (e.g., ACS, complex PCI). Similar to the above results, this study suggests that the slow metabolic genotype has a significant effect on platelet aggregation rate and is an independent risk factor for clopidogrel low reactivity.
5. genotype associated with MACE occurrence and guide PCI benefit from postoperative P2Y12 inhibitor escalation
Mega et al performed a Meta analysis of CYP2C19 genotypes and clinical outcomes in 9685 patients (91.3% PCI postoperative patients and 54.5% ACS patients), with 26.3% carrying at least one LOF allele and 2.2% carrying two LOF alleles. the results found a significant increase in the risk of cardiovascular death, myocardial infarction, or cardiovascular disease complex endpoints in patients carrying LOF alleles compared to Non-LOF allele carriers. The results of this study were similar to those of the above studies, and found that there were significant differences between the three groups (P<0.05) between the incidence of recurrent and overall MACE of unstable angina pectoris. the inter-group comparison suggested that the LOF allele unupgraded group had the highest and significant difference compared with the Non-LOF allele (P<0.05) in the incidence of recurrent and overall MACE of unstable angina pectoris, indicating that the functional deletion gene was associated with MACE occurrence.
Many studies have shown[2, 17, 25] that the use of genotyping to guide the upgrade from clopidogrel to pragrelot after PCI CYP2C19 nonfunctional allele carriers reduces the risk of atherosclerosis. While in patients with stable coronary heart disease undergoing PCI, although CYP2C19 loss of function was observed to be associated with increased risk of ischemia, there is still no evidence that genotype-guided P2Y12 inhibitor can benefit. So far, no randomized genotyping trial has been conducted to guide ACS patient P2Y12 inhibitor escalation. TAILOR-PCI study included 5302 patients with PCI due to ACS or stable coronary heart disease who were randomly assigned to gene-directed and routine treatment groups. The routine treatment group was treated with aspirin combined with clopidogrel, and the gene detection group CYP2C19 the gene detection first, and the patients allele were treated with aspirin combined with clopidogrel. patients with LOF alleles were upgraded to tigrilol with clopidogrel, and the incidence of MACE was finally observed after 1 year. as a result, gene testing guided antiplatelet drug selection failed to reduce the incidence of MACE and there was no significant difference in the risk of bleeding events. This study found no significant difference in the incidence MACE Non-LOF allele versus LOF allele upgrade group (P>0.05), and no significant benefit after upgrading treatment was found. but this may be related to the LOF allele upgrade group screened in this study were all platelet hyperresponsiveness populations.
6. Platelet testing guidance PCI benefit from P2Y12 inhibitor upgrade after surgery
although platelet function testing can help identify high-risk patients with clopidogrel HPR, treatment escalation should be strongly considered. nevertheless, ACS postoperative use of PFT to guide clopidogrel escalation in patients still has no evidence of benefit. while there is no evidence that the use of PFT guidance therapy in these patients can benefit, if the patient's risk of bleeding is not high and the risk of embolism is high, the use of PFT may also be considered to decide whether to escalate.
RECLOSE 2-ACS study is the first large-scale prospective study to guide clinical individualized selection of antiplatelet drug therapy based on platelet function test results. ACS patients enrolled in 1789 routine PCI procedures at the Italian Careggi Hospital were treated with clopidogrel loading (600mg), followed by maintenance (75mg/d) combined with aspirin for at least 6 months. The LTA method was used to define the platelet aggregation rate≥70% as high residual platelet reactivity (HRPR) and to intervene to increase the dosage of clopidogrel from 150 mg to 300 mg or to convert to thichloropyridine (500-1000mg/d). the incidence of MACE events was followed up within 2 years. The results showed that the incidence MACE events increased significantly in the HRPR group compared with the non- HRPR group, and the intervention did not significantly improve the incidence of MACE events. Subsequent large-scale prospective clinical trial studies of individualized antiplatelet therapy based on the guidance of platelet function testing also focused on negative results, such as GRAVITAS studies, TRIGGER-PCI studies, ARCTIC studies, etc. This study was based on the combination of gene and platelet detection to screen HPR patients for clopidogrel upgrade therapy. the results showed that there was no significant difference in the incidence of clopidogrel upgrade compared with MACE LOF allele upgrade group (P>0.05), similar to the above study. But there are also some studies that suggest that individualized antiplatelet drug therapy based on platelet function testing can improve the prognosis of patients, such as MADONNA studies, IDEAL-PCI studies. The reasons for the difference in the above results may be related to the following points: arterial thrombosis is a complex dynamic process that occurs at the damaged site of the intravascular plaque, while platelet function testing is performed in vitro and can only respond to one of the links, which does not truly reflect the state of the whole thrombus and the true condition of the lesion site. At present, there are many and immature methods for platelet function detection, different test methods draw different conclusions and lack uniform standards. Different thresholds and different disease populations were determined HPR the same platelet function test method.