Relation of low response to clopidogrel assessed with point-of-care assay to periprocedural myonecrosis in patients undergoing elective coronary stenting for stable angina pectoris

Viscoelastic Hemostatic Assays and Platelet Function Testing in Patients with Atherosclerotic Vascular Diseases

Platelets play crucial role in acute vascular atherosclerotic diseases, including myocardial infarction and stroke. Additionally, platelet aggregation is a key target of antiplatelet agents, forming the keystone of pharmacotherapy of various atherosclerotic cardiovascular diseases. Thromboelastography and thromboelastometry, representing currently available viscoelastic hemostatic assays (VHA), are designed as whole blood, real-time analyzers of clot formation and clot resolution. These assays could, in theory, overcome some limitations of currently available platelet function testing assays. This article reviews the current experience with the use of VHA for platelet function testing and for monitoring of the response to antiplatelet therapy.

Periprocedural Myocardial Injury: Pathophysiology, Prognosis, and Prevention

The definition and clinical implications of myocardial infarction occurring in the setting of percutaneous coronary intervention have been the subject of unresolved controversy. The definitions of periprocedural myocardial infarction (PMI) are many and have evolved over recent years. Additionally, the recent advancement of different imaging modalities has provided useful information on a patients' pre-procedural risk of myocardial infarction. Nonetheless, questions on the benefit of different approaches to prevent PMI and their practical implementation remain open. This review aims to address these questions and to provide a current and contemporary perspective.

How to improve the concept of individualised antiplatelet therapy with P2Y12 receptor inhibitors – is an algorithm the answer?

Within the past decade, high on-treatment platelet reactivity (HTPR) on clopidogrel and its clinical implications have been frequently discussed. Although it has been previously assumed that HTPR is a phenomenon occurring only in patients treated with clopidogrel, recent data show that HTPR might also occur during treatment with prasugrel or ticagrelor in the acute phase of ST-elevation myocardial infarction. Moreover, it has been postulated that there is a therapeutic window for P2Y12 receptor blockers, thus indicating that HTPR is associated with thrombotic events whereas low on-treatment platelet reactivity (LTPR) is associated with bleeding events. The current paper focuses on tools to identify risk factors for HTPR (pharmacogenomic testing, clinical scoring and drug-drug interactions) and on the use of platelet function testing in order to identify patients who might not respond adequately to clopidogrel. The majority of recent clinical randomised trials have not supported the hypothesis that platelet function testing and tailored antiplatelet therapy are providing a favourable clinical outcome. These trials, mainly performed in low-to-moderate risk patients, will be reviewed and discussed. Finally, an algorithm based on current knowledge is suggested, which might be of use for design of clinical trials.

The use of intravenous tPA for the treatment of severe frostbite

OBJECTIVE

tPA and anticoagulation for treatment of severe frostbite have been reported suggesting differences in imaging techniques, route of tPA administration and management of patients after tPA infusion. This is a report of our results following a protocol of Tc-99m scanning, intravenous tPA administration, followed by either systemic anticoagulation or antiplatelet therapy.

METHODS

Patients admitted to our burn center between February 13, 2015 and February 13, 2016 for frostbite who met inclusion criteria were treated with Tc-99m scan and intravenous tPA followed by systemic anticoagulation or antiplatelet therapy. Inclusion criteria included rewarming had not started more than 24h prior to the scan and no contraindications to the use of tPA.

RESULTS

Fifteen patients met inclusion criteria and 12 were treated according to the protocol. Nine received scans with 2 showing normal perfusion. Seven displayed perfusion defects and received intravenous tPA. Five recovered fully after tPA. Two who showed improved but abnormal scans after tPA experienced bleeding complications necessitating stopping heparin/Coumadin. Those two went on to partial amputation of digits.

CONCLUSION

The use of intra-arterial or intravenous tPA along with angiography or Tc-99m scanning followed by systemic anticoagulation or antiplatelet therapy may be beneficial to patients suffering frostbite.

Higher body weight patients on clopidogrel maintenance therapy have lower active metabolite concentrations, lower levels of platelet inhibition, and higher rates of poor responders than low body weight patients

Body weight is a predictor of clopidogrel response. However, no prospective studies have compared pharmacodynamic (PD) and pharmacokinetic (PK) data based on body weight. We compared PD and PK effects of clopidogrel 75 mg in low body weight (LBW, <60 kg) and higher body weight (HBW, ≥60 kg) patients with stable coronary artery disease. LBW (n = 34, 56.4 ± 3.7 kg) and HBW (n = 38, 84.7 ± 14.9 kg) aspirin-treated patients received clopidogrel 75 mg for 10-14 days. The area under the concentration-time curve of active metabolite (Clop-AM) calculated through the last quantifiable concentration up to 4 h postdose, AUC(0-tlast), was calculated by noncompartmental methods. Light transmission aggregometry (LTA) (maximum platelet aggregation and inhibition of platelet aggregation to 20 μM adenosine diphosphate (ADP), and residual platelet aggregation to 5 μM ADP), VerifyNow(®) P2Y12 reaction units (PRU), and vasodilator-associated stimulated phosphoprotein phosphorylation platelet reactivity index (VASP-PRI) were performed. Mean AUC(0-tlast) was lower in HBW than LBW patients: 12.8 versus 17.9 ng h/mL. HBW patients had higher platelet reactivity as measured by LTA (all p ≤ 0.01), PRU (207 ± 68 vs. 152 ± 57, p < 0.001), and VASP-PRI (56 ± 18 vs. 39 ± 17, p < 0.001). More HBW patients exhibited high on-treatment platelet reactivity (HPR) using PRU (35 vs. 9%) and VASP-PRI (65 vs. 27%). Body weight correlated with PRU and VASP-PRI (both p < 0.001), and inversely with log transformed AUC(0-tlast) (p < 0.001). In conclusion, HBW patients had lower levels of Clop-AM, and higher platelet reactivity and rates of HPR than LBW subjects, contributing to their suboptimal response to clopidogrel.

Personalized antiplatelet therapy with P2Y12 receptor inhibitors: benefits and pitfalls

Antiplatelet therapy with P2Y₁₂ receptor inhibitors has become the cornerstone of medical treatment in patients with acute coronary syndrome, after percutaneous coronary intervention and in secondary prevention of atherothrombotic events. Clopidogrel used to be the most broadly prescribed P2Y₁₂ receptor inhibitor with undisputable benefits especially in combination with aspirin, but a considerable number of clopidogrel-treated patients experience adverse thrombotic events in whom insufficient P2Y₁₂-inhibition and a consequential high on-treatment platelet reactivity is a common finding. This clinically relevant limitation of clopidogrel has driven the increased use of new antiplatelet agents. Prasugrel (a third generation thienopyridine) and ticagrelor (a cyclopentyl-triazolo-pyrimidine) feature more potent and predictable P2Y₁₂-inhibition compared to clopidogrel, which translates into improved ischemic outcomes. However, excessive platelet inhibition and consequential low on-treatment platelet reactivity comes at the price of increased risk of major bleeding. The majority of randomized clinical trials failed to demonstrate improved clinical outcomes with platelet function testing and tailored antiplatelet therapy, but results of all recent trials of potent antiplatelets and prolonged antiplatelet durations point towards a need for individualized antiplatelet approach in order to decrease thrombotic events without increasing bleeding. This review focuses on potential strategies for personalizing antiplatelet treatment.

Monitoring aspirin and clopidogrel response: testing controversies and recommendations

Antiplatelet therapy is the cornerstone of the treatment for patients with coronary artery disease (CAD). Dual therapy with clopidogrel and aspirin is currently the standard treatment after percutaneous coronary interventions. However, despite the use of clopidogrel, a considerable number of patients continue to suffer major adverse cardiac events. There is a growing degree of evidence supporting high on-treatment platelet reactivity (HPR) as a predictive factor for recurrent ischemic complications. Numerous studies have shown an interindividual variability of responsiveness to clopidogrel and aspirin, which is one of the reasons for HPR. There is yet to be established an assay for antiplatelet drug response as the gold standard. This paper provides a background to the current controversies surrounding the issue of testing for the effectiveness of antiplatelet therapy and reviews the various genetic and phenotype-based laboratory tests to measure aspirin and clopidogrel response and their correlation with clinical outcomes. On the basis of the current evidence and trying to be cost-effective, testing should be considered on a case-by-case basis, especially in patients who present with an acute coronary syndrome or stent thrombosis. In the case of stable CAD, we think that testing might be helpful in particular risk groups of patients to avoid ischemic or bleeding complications.

Influence of platelet reactivity and inflammation on peri-procedural myonecrosis in East Asian patients undergoing elective percutaneous coronary intervention

BACKGROUND AND OBJECTIVES

The contribution of multiple risk factors to peri-procedural myocardial infarction (PMI) in East Asians remains controversial. To assess the influence of clinical or laboratory covariates on PMI in these patients.

METHODS

Stable patients (n=341) undergoing elective percutaneous coronary intervention (PCI) were enrolled. Platelet reactivity was measured by conventional aggregometry and VerifyNow. Inflammation markers and lipid profile were determined by standard methods. PMI was defined according to Universal definition (troponin I or CK-MB ≥ 3 times the 99th percentile of the upper reference limit).

RESULTS

PMI (defined by troponin I and CK-MB) occurred in 47 (13.8%) and 30 (8.8%) patients, respectively. There was no significant difference in ADP-induced platelet reactivity between patients with vs. without PMI. Patients with PMI (troponin I) had higher levels of 6 μg/mL collagen-induced platelet aggregation (PA) and VerifyNow 'BASE' compared with those without PMI. The combination of '6 μg/mL collagen-induced PA>40%'+'BASE>318' (odds ratio, 14.08; 95% confidence intervals, 1.68 to 111.11; p=0.015) or 'WBC>6550/mm(3)'+'C-reactive protein>2.3mg/L' (odds ratio, 7.75; 95% confidence intervals, 2.49 to 24.39; p<0.001) was associated with an increased risk of PMI (troponin I). The greatest likelihood ratio was observed when cholesterol, inflammation marker and platelet function were combined together.

CONCLUSION

This is the first study to demonstrate that heightened platelet responsiveness to collagen and thrombin may be a risk factor for myonecrosis in patients undergoing elective PCI. The utility of the combining measures of platelet function, inflammation and cholesterol to enhance risk stratification and thus facilitate personalized therapy deserves further study.

Assessing post-treatment platelet reactivity: a focus on patient selection and setting

Dual antiplatelet therapy is critical to inhibit platelet reactivity in order to prevent ischemic recurrences in stented patients. However, studies have observed a variable blockade of the P2Y12 adenosine diphosphate receptor between patients following clopidogrel intake. This interindividual variability in the biological response is not uncommon with clopidogrel (about 50%) and even prasugrel (20%). High on-treatment platelet reactivity (HTPR) is correlated with thrombotic events following percutaneous coronary intervention. Several studies suggested that tailoring of antiplatelet therapy based on platelet reactivity (PR) monitoring could safely reduce the rate of major adverse cardiovascular events in HTPR patients. In addition, low on-treatment PR was recently associated with bleeding events both in patients treated with prasugrel and clopidogrel. Of importance, bleedings are associated with a poor prognosis in stented patients. Overall, the potential of PR monitoring to individualize antiplatelet therapy might benefit stented patients by reducing both ischemic and bleeding risks. However, such strategies remain to be evaluated in adequately designed large-scale randomized clinical trials.

CYP-mediated pharmacologic interference with optimal platelet inhibition

Variability of response to clopidogrel and prasugrel is a multifactorial process, with clinical consequences, and drug-drug interactions have been proposed as potential factors. Biological modulation of clopidogrel response has been demonstrated for atorvastatin and omeprazole. However, investigations assessing clinical relevance of these findings have been heterogeneous, and real clinical impact is still debatable. For new P2Y12 blockers, such as prasugrel, with less variability of platelet inhibition, these interactions are not significant; accordingly, no dose adjustment is required. The present review aims to summarize available scientific evidence about CYP-mediated pharmacologic interference with optimal platelet inhibition in patients treated with thienopyridine.

Novel antiplatelet agents: ALX-0081, a Nanobody directed towards von Willebrand factor

This manuscript reviews the studies performed with ALX-0081 (INN: caplacizumab), a Nanobody targeting von Willebrand factor, in the context of current antithrombotic therapy in coronary artery disease. ALX-0081 specifically inhibits platelet adhesion to the vessel wall, and may control platelet aggregation and subsequent clot formation without increasing bleeding risk. A substantial number of antithrombotics are aimed at this cascade; however, their generally indiscriminative mode of action can result in a narrow therapeutic window, defined by the risk for bleeding complications, and thrombotic events. Nonclinically, ALX-0081 compared favorably to several antithrombotics. In Phase I studies in healthy subjects and stable angina patients undergoing percutaneous coronary intervention (PCI), ALX-0081 was well tolerated, and effectively inhibited pharmacodynamic markers. Following these results, a phase II study was initiated in high-risk acute coronary syndrome patients undergoing PCI. Based on its mechanism of action, ALX-0081 is also being developed for acquired thrombotic thrombocytopenic purpura.

Effect of tailored antiplatelet therapy on periprocedural myonecrosis in patients with diabetes mellitus (from the DM-Verify Now Trial)

We investigated whether additional platelet inhibition with a glycoprotein IIb/IIIa inhibitor would be beneficial in reducing the risk of periprocedural myocardial infarction (PMI) in diabetic patients with high residual platelet reactivity (HPR). Patients with diabetes mellitus were administered aspirin and clopidogrel at a 300-mg loading dose 1 day before the procedure, and the VerifyNow P2Y(12) assay was performed just before percutaneous coronary intervention. Patients with HPR, defined as a P2Y(12) reaction unit of ≥270 were randomly assigned to group A or control group C1. Patients without HPR were assigned to control group C2. Conventional anticoagulation with heparin was given to groups C1 and C2, and group A received additional abciximab treatment. Clinically relevant PMI was defined as any elevation in the biomarkers creatine kinase-MB isoenzyme and cardiac troponin I >3 times the upper normal limit measured 8, 16, or 24 hours after percutaneous coronary intervention. Of the patients, 47 and 51 were assigned to group A and C1; the clinical and procedural characteristics in the 2 groups were balanced. Of the 47 patients in group A and 51 patients in group C1, 9 (19%) and 9 (18%), respectively, experienced a PMI event according to the creatine kinase-MB cutoff (p = 1.00), and 27 in group A (57%) and 29 in group C1 (57%) experienced a PMI event according to the troponin I cutoff (p = 1.00). Five minor bleeding events, including small and localized hematomas, were observed immediately after the procedure (4 in group A and 1 in group C1). Only 1 major bleeding event, retroperitoneal hemorrhage, was observed in group A. The patients in group C2 had a PMI event rate (50% of 32 patients, p = 1.00) similar to that of group C1. In conclusion, additional platelet inhibition using a tailored approach and a point-of-care assay did not improve the periprocedural outcome in diabetic patients with HPR.

von Willebrand factor inhibition improves endothelial function in patients with stable angina

ALX-0081 is a novel nano-antibody inhibiting von Willebrand factor (vWF). We evaluated whether direct inhibition of vWF by ALX-0081 improves endothelial function. Stable patients (pts, n = 55) with single vessel disease undergoing percutaneous coronary intervention (PCI) were randomized to ALX-0081 (n = 38) or placebo (n = 17). vWF inhibition was assessed by vWF antigen level (vWF:Ag) and activity by ristocetin test (vWF:RiCo). Endothelial function was assessed before (BL), 6 h and 24 h after PCI by: (a) endothelial peripheral arterial tonometry (Endoscore); (b) endothelial microparticles (EMPs) by flow cytometry. vWF:Ag and vWF:RiCo decreased within 1 h from ALX-0081. In the placebo group, no significant Endoscore changes occurred from BL to 24 h. In ALX-0081 group, Endoscore increased from BL to 24 h (p = 0.014). A decrease in EMPs was observed after ALX-0081 (p < 0.01), while no changes occurred in placebo pts. An inhibition of vWF with ALX-0081 significantly improves peripheral endothelial function.

Periprocedural variations of platelet reactivity during elective percutaneous coronary intervention

BACKGROUND

Percutaneous coronary intervention (PCI) modulates platelet reactivity (PR).

OBJECTIVES

To assess: (i) the impact of coronary interventions on periprocedural variations (Δ) of PR; (ii) whether ΔPR correlates with periprocedural myocardial infarction (PMI); and (iii) the mechanisms of these variations in vitro.

METHODS AND RESULTS

We enrolled 65 patients on aspirin (80-100 mg day(-1)) and clopidogrel (600 mg, 12 h before PCI): 15 with coronary angiography (CA group), 40 with PCI (PCI group), and 10 with rotational atherectomy plus PCI (RA group). PR was assessed by ADP, high-sensitivity ADP and thrombin receptor activator peptide 6 tests prior to, immediately after and 24 h after the procedure. E-selectin and ICAM-1 were assessed prior to and immediately after the procedure. In vitro, PR was measured during pulsatile blood flow at baseline, after balloon inflation and after stent implantation in six porcine carotid arteries and five plastic tubes. PR declined in the CA group, but significantly increased in the PCI and RA groups immediately postprocedure, and decreased to baseline at 24 h. ΔPR increased across the three groups (P < 0.0001). In the PCI group, ΔPR was directly related to total inflation time (r = 0.435, P = 0.005) and total stent length (r = 0.586, P < 0.001). The change in E-selectin significantly and inversely correlated with ΔPR (P < 0.001). No correlation was found with sICAM-1. PR increased significantly more in patients with PMI than in patients without PMI (P = 0.013). In vitro, platelet activation was observed in the presence of carotid arteries but not in the presence of plastic tubes.

CONCLUSIONS

Despite dual antiplatelet therapy, PCI affected platelet function proportionally to procedural complexity and the extent of vascular damage.

The influence of omeprazole on platelet inhibition of clopidogrel in various CYP2C19 mutant alleles

Currently, concerns of clopidogrel and proton pump inhibitors (especially omeprazole) interaction are raised, because they are both metabolized by CYP2C19. What is more, omeprazole can also inhibit the activity of CYP2C19. The study was to compare the influence of omeprazole on platelet inhibition of clopidogrel in various CYP2C19 mutant alleles. One hundred forty-two consecutive patients undergoing elective coronary stenting received aspirin and clopidogrel, and were randomized to omeprazole or the placebo. Enrolled patients were analyzed for adenosine diphosphate-induced platelet aggregation (ADP-Ag), and CYP2C19*2 and CYP2C19*3 were identified by polymerase chain reaction-restriction fragment length polymorphism. Of the patients included, 47 (33.1%) belonged to homozygous extensive metabolizers (homEMs) (CYP2C19*1/*1), 70 (49.3%) belonged to heterozygous extensive metabolizers (hetEMs) (*1/*2 or *1/*3), and 25 (17.6%) belonged to poor metabolizers (PMs) (*2/*3 or *2/*2). ADP-Ag had a significant difference among the three genotypic groups (p<0.01). Moreover, the present study revealed that the degree of the interaction between clopidogrel and omeprazole was not homogeneous within the various genotypes of CYP2C19. The difference of ADP-Ag between the patients with and without omeprazole was significantly largest in homEMs (45.7%±14.2% vs. 35.5%±16.0%, p<0.05). However, any significant difference of ADP-Ag between the patients with and without omeprazole was not observed in other two genotypic groups (hetEMs and PMs, p>0.05). In conclusion, concomitant therapy with omeprazole appears to reduce the antiplatelet effect of clopidogrel most significantly in homEMs of CYP2C19.

Latest evidence in personalized antiplatelet therapy in patients with acute coronary syndromes undergoing percutaneous coronary intervention

In patients with acute coronary syndromes undergoing percutaneous coronary intervention, the combination of aspirin and clopidogrel, a P2Y12 adenosine diphosphate (ADP) receptor antagonist, is the gold standard of antiplatelet therapy. Two more potent P2Y12 ADP receptor antagonists are now available. Pharmacodynamic studies have revealed a large interindividual variability in the biological response to clopidogrel that is primarily related to variable active metabolite generation, depending on clinical factors, drug-drug interactions, and genetic polymorphisms. Several assays to measure platelet function are available and have revealed a high prevalence of high on-treatment platelet reactivity (HTPR). Patients exhibiting HTPR after a clopidogrel loading dose have a higher risk of thrombotic recurrence after percutaneous coronary intervention. A recent consensus has defined HTPR for the main platelet assays available (using receiver operating characteristic curve analysis) to define the optimal cutoff value for each assay in order to predict thrombotic recurrences. In this article, we present several lines of evidence that suggest a therapeutic window of platelet reactivity inhibition with P2Y12 ADP receptor antagonists. Such a paradigm shift is supported by the results of the Platelet Inhibition and Patient Outcomes (PLATO) trial and the Trial to Assess Improvement in Therapeutic Outcomes by Optimizing Platelet Inhibition with Prasugrel-Thrombolysis in Myocardial Infarction (TRITON-TIMI) 38, which showed the superiority of ticagrelor and prasugrel on thrombotic events compared with clopidogrel; however, these 2 medications had an increased bleeding rate. With the results of these trials, in addition to the evidence of a therapeutic window with P2Y12 ADP receptor antagonists, we summarize the potential of platelet reactivity monitoring and pharmacogenomics to tailor therapy.

Monitoring the effectiveness of antiplatelet therapy: opportunities and limitations

Previous clinical studies have shown heterogeneity in individual patient responses to antiplatelet therapy and high residual platelet reactivity is associated with increased risk of adverse clinical events. Monitoring response to antiplatelet therapy and tailoring treatment accordingly is currently not recommended in routine clinical practice largely due to the lack of a standardized definition of antiplatelet therapy hyporesponse and the need for a widely accepted point-of-care platelet function test that can be reliably utilized in frontline clinical practice. Recent data have shown that titrating the dose of clopidogrel in patients undergoing percutaneous coronary intervention significantly reduces the incidence of major adverse cardiovascular events and large-scale clinical trials are currently underway to investigate whether individually tailored treatment based on results of platelet function testing leads to improved clinical outcome. Furthermore, genetic testing has demonstrated a link between CYP2C19 genetic polymorphisms, altered clopidogrel metabolite concentrations and adverse clinical events. Clinical studies are currently underway to investigate the potential clinical benefit associated with genotype-guided tailoring of antiplatelet therapy. With the advent of newer, more potent antiplatelet agents and their associated increased bleeding risks, it will become imperative in the future to select the most appropriate, safe and effective drug.

Prasugrel overcomes high on-clopidogrel platelet reactivity in chronic coronary artery disease patients more effectively than high dose (150 mg) clopidogrel

BACKGROUND

High on-treatment platelet reactivity (HTPR) is present in a substantial percentage of patients on chronic clopidogrel treatment and may have prognostic implications. Strategies to optimize platelet inhibition in such patients are not clear.

METHODS

We performed a prospective, single-center, single-blinded, investigator-initiated randomized, crossover study of platelet inhibition by prasugrel 10 mg/day versus high-dose 150 mg/day clopidogrel, with a 14 day treatment period, in 31 patients with HTPR (out of 99 screened, 31.3%) while on chronic (≥ 12 months) treatment with clopidogrel. All patients had stable coronary artery disease and 87.1% of them had a prior percutaneous coronary intervention. Platelet reactivity (PR) was assessed by the VerifyNow assay measured in platelet reactivity units (PRU).

RESULTS

The primary end point of PR at the end of the two treatment periods was lower in patients receiving prasugrel compared with high dose clopidogrel ( least squares estimate 148.1, 95% CI 127.1-169.2 and 219.8, 95% CI 198.6-240.9 respectively, P < .001). The secondary end point of HTPR rate was lower for prasugrel compared with clopidogrel, 11.5% vs 46.3%, P = .003.

CONCLUSIONS

Prasugrel appears more effective than double clopidogrel in inhibiting PR in patients with HTPR following chronic clopidogrel treatment.

Antiplatelet drug therapy: role of pharmacodynamic and genetic testing

Antiplatelet therapy represents the cornerstone of treatment for the short- and long-term prevention of atherothrombotic disease processes, in particular in high-risk settings such as in patients with acute coronary syndrome and those undergoing percutaneous coronary intervention. Currently, dual antiplatelet therapy with aspirin and clopidogrel represents the most commonly used treatment regimen in these settings. However, a considerable number of patients continue to experience adverse outcomes, including both bleeding and recurrent ischemic events. Numerous investigations have demonstrated that this phenomenon may be, in part, attributed to the broad variability in individual response profiles to this standard antiplatelet treatment regimen, as identified by various assays of platelet function testing. In addition, recent studies have demonstrated that genetic polymorphisms may also have an important role in determining levels of platelet inhibition and may be considered as a tool to identify patients at risk of adverse events. This article provides an overview on antiplatelet drug response variability, an update on definitions, including the role of pharmacodynamic testing, underlying mechanisms – with emphasis on recent understandings on pharmacogenetics and drug–drug interactions – and current and future perspectives on individualized antiplatelet therapy.

Residual platelet reactivity: predicting short- and long-term clinical outcome in patients undergoing percutaneous coronary revascularization

Adequate platelet inhibition is mandatory in patients undergoing percutaneous coronary intervention in order to prevent recurrent thrombotic events. Dual antiplatelet therapy with aspirin and thienopyridine (e.g., clopidogrel) is the treatment of choice in this setting, providing clear clinical benefit in most of the patients. However, a wide interindividual variability exists in the response to antiplatelet drugs and several factors may contribute to determine fluctuation in platelet reactivity, even within the individual patient. Several methodologies and devices have been developed to monitor individual response to antiplatelet treatment, assessing different pathways of platelet activation and aggregation. Studies performed with the use of these methodologies have clearly demonstrated that patients with high post-treatment residual platelet reactivity present a higher risk of ischemic events both at short (during or soon after percutaneous coronary intervention) and long term. In these patients, more aggressive antithrombotic strategies, based on the results of platelet function tests, may be beneficial in order to reduce ischemic complications after percutaneous coronary intervention.

Dual low response to acetylsalicylic acid and clopidogrel is associated with myonecrosis and stent thrombosis after coronary stent implantation

BACKGROUND

Impaired response to antiplatelet therapy with acetylsalicylic acid (ASA) and clopidogrel (CLO) has been associated with an increased risk of stent thrombosis and ischemic events after coronary stent implantation. We sought to investigate whether patients with a low response (LR) to ASA or CLO are at increased risk for periprocedural and short-term ischemic events after coronary stent implantation.

METHODS

A total of 219 patients pretreated with ASA and CLO underwent percutaneous coronary intervention (PCI) with stent implantation. Whole blood impedance platelet aggregometry was performed with the Multiplate analyzer (Dynabyte, Munich, Germany) to test the response to ASA (ASPI test) and CLO (ADP test) within 12 to 18 hours after PCI. Patients were classified as ASA-LR, CLO-LR, dual LR, and controls. Study end points included myocardial infarction, stent thrombosis, and death assessed during the periprocedural period and at 30 days.

RESULTS

Acetylsalicylic acid-LR was present in 34 (16%), CLO-LR in 33 (15%), and dual LR in 19 (9%) patients. Percutaneous coronary intervention-related myocardial infarction was encountered in 19 (9%) patients, with the highest incidence in dual-LR group (26.3%, P = .039). Composite ischemic events at 30 days were significantly more frequent in the dual-LR group than in other groups (36.8% vs 8.8% ASA-LR vs 6.1% CLO-LR vs 6.8% controls, P < .001). In multivariable analysis, dual LR (odds ratio 7.35, 95% CI 2.21-24.42, P < .001) and multivessel PCI (odds ratio 4.56, 95% CI 1.33-15.62, P = .016) were independently associated with ischemic events at 30 days.

CONCLUSION

Dual LR to ASA and CLO is associated with an increased risk for short-term ischemic events after coronary stent implantation.

Individualised assessment of response to clopidogrel in patients presenting with acute coronary syndromes: a role for short thrombelastography?

INTRODUCTION

There is considerable interindividual variation in response to the antiplatelet agent clopidogrel. Hyporesponse predicts negative outcomes in patients presenting with a variety of ischemic cardiac conditions and following intracoronary stent placement. Many tests of clopidogrel activity are time consuming and complex. Short thromboelastography (s-TEG) allows rapid measurement of platelet clopidogrel response.

AIMS

We initiated this study to investigate the utility of s-TEG in assessing the response to clopidogrel in patients presenting with acute coronary syndromes (ACS) and to compare these results with established clopidogrel monitoring techniques.

METHODS

Patients admitted with unstable angina (UA) or Non ST elevation myocardial infarction (NSTEMI) undergoing coronary angiography were recruited. After routine loading with clopidogrel, all patients were tested with s-TEG and Accumetrics Verify-Now rapid platelet function analyzer (VN-RPFA). We used the modified TEG technique of measuring area under the curve at 15 min (AUC15), which allows a rapid estimation of antiplatelet response. Vasodilator-stimulated phosphoprotein phosphorylation (VASP) was also tested in a subgroup of patients. Clinical follow-up was obtained at 1 year. s-TEG results were correlated with VN-RPFA and VASP findings.

RESULTS

A total of 49 patients (33 male, mean age 63) were recruited and tested with s-TEG and VN-RPFA and a total of 39 patients were also assessed with VASP. s-TEG readings correlated well with VN-RPFA (r(2)= 0.54, P < 0.0001) and VASP (r(2)= 0.26, P= 0.001).

CONCLUSION

s-TEG provides timely results which compare to current tests of clopidogrel activity. This technique can also be used to measure a variety of other clotting parameters and as such could develop into a valuable near patient test for the interventional cardiologist.

Relation of endothelial function to residual platelet reactivity after clopidogrel in patients with stable angina pectoris undergoing percutaneous coronary intervention

Platelet reactivity is greater in patients with stable angina and with more extensive peripheral vascular atherosclerosis. We sought to evaluate whether impaired peripheral microcirculatory endothelial function might correlate with platelet reactivity after clopidogrel and therefore predispose to an unfavorable outcome after percutaneous coronary intervention (PCI). In 52 consecutive patients with stable angina undergoing elective PCI, endothelial function was assessed by (1) endothelial peripheral arterial tonometry (measuring the "Endoscore"); (2) the von Willebrandt factor antigen level and ristocetin co-factor activity. Basal platelet reactivity was assessed by soluble P-selectin. Patients then received a 600-mg clopidogrel loading dose > or = 12 hours before PCI. A blood sample was withdrawn 12 hours later, but before PCI, to assess platelet reactivity using the P2Y12 reaction unit and percentage of P2Y12 inhibition with the point-of-care VerifyNow P2Y12 assay. Troponin T was assessed 24 hours after PCI. The Endoscore inversely correlated with von Willebrandt factor antigen activity (r = -0.52, p = 0.0001) and soluble P-selectin concentration (r = -0.36, p = 0.021), suggesting greater platelet reactivity with increased impaired endothelial function. After clopidogrel, the Endoscore correlated directly with the percentage of P2Y12 inhibition (r = 0.36, p = 0.009) and inversely with the P2Y12 reaction unit (r = -0.41, p = 0.002), suggesting greater residual platelet reactivity with more impaired endothelial function. The average Endoscore was significantly lower in patients with troponin T elevation (troponin positive group 0.267 + or - 0.091) than in patients without troponin T elevation (troponin negative group 0.508 + or - 0.041, p = 0.015 vs troponin positive). In conclusion, an impaired endothelial response before clopidogrel was associated with greater platelet reactivity after clopidogrel. This link might explain the unfavorable PCI outcomes in patients with more severe endothelial impairment.

Clopidogrel response: head-to-head comparison of different platelet assays to identify clopidogrel non responder patients after coronary stenting

OBJECTIVES

We investigated the agreement between different platelet tests to identify clopidogrel non response.

BACKGROUND

Biological definition of clopidogrel non response remains controversial. Different platelet tests have been linked with recurrent ischemic events and proposed for daily practice.

METHODS

We prospectively investigated the agreement of platelet tests to isolate clopidogrel non response in patients receiving high 150 mg clopidogrel maintenance dose after coronary stenting. Clopidogrel response was assessed with ADP-induced aggregation (ADP-Ag) (non response if >70%), Platelet reactivity index VASP (PRI VASP) (non response if >50%) and Verify Now Point-of-care assay (VN) (non response if PRU > 240 AU).

RESULTS

Seventy consecutive patients were included. The rates of non-responders were respectively: 13% (n = 9) with the ADP-Ag, 39% (n = 27) with the PRI VASP and 33% (n = 23) with the VN. We observed significant correlation between different platelet tests assessing clopidogrel response: r = 0.55 (p < 0.0001) for ADP-Ag and PRI VASP, r = 0.64 (p < 0.0001) for ADP-Ag and VN and r = 0.59 (p < 0.0001) for PRI VASP and VN. However, using the most common thresholds, the agreement between the difference tests was poor: 0.35 for ADP-Ag and PRI VASP, 0.36 for ADP-Ag and VN and 0.46 for PRI VASP and VN.

CONCLUSION

This study showed that assessment of platelet function inhibition by clopidogrel is highly test-specific. Indeed, our results demonstrated a poor agreement between different platelet assays and suggested that identification of clopidogrel non responders is test-dependent.

Prevalence of unresponsiveness to aspirin and/or clopidogrel in patients with stable coronary heart disease

This study sought to assess whether inadequate platelet responses to aspirin and clopidogrel are distinct phenomena caused by different mechanisms or different facets of the same phenomenon (i.e., general platelet hyperactivity). A total of 85 patients with stable coronary artery disease who were taking aspirin and clopidogrel daily for > or =3 months were enrolled in the present study. Platelet aggregation was measured by light transmission aggregometry (LTA) stimulated with 1.6 mM of arachidonic acid and 5, 10 and 20 microM of adenosine diphosphate, and by the VerifyNow Aspirin and VerifyNow P2Y12 point-of-care assays. An inadequate platelet response was defined as aggregation greater than or equal to the mean + 2 SDs. The prevalence of an inadequate platelet response varied greatly among the assays. For aspirin, the prevalence was 2.4% using arachidonic acid-induced LTA and 5.9% using the VerifyNow Aspirin assay. For clopidogrel, the prevalence varied from 1.2% to 3.9% using adenosine diphosphate-induced LTA and was 2.4% using the VerifyNow P2Y12 assay. The point-of-care assays did not select the same patients as LTA. No subject was unresponsive to both aspirin and clopidogrel, regardless of the assay used, suggesting that separate mechanisms govern platelet unresponsiveness to aspirin and clopidogrel. In conclusion, an inadequate platelet response to either aspirin or clopidogrel is rare, and the definition is dependent on the platelet function assay used. Because no subject was found to be unresponsive to both agents, the unresponsiveness is suspected to occur through distinct mechanisms of platelet activation.

Predictive values of post-treatment adenosine diphosphate-induced aggregation and vasodilator-stimulated phosphoprotein index for stent thrombosis after acute coronary syndrome in clopidogrel-treated patients

A low response to clopidogrel has been associated with an increased risk of stent thrombosis. However, the definition of a nonresponse to clopidogrel remains controversial, and different tests have been used to assess the clopidogrel response. The present study was designed to assess the predictive value of adenosine diphosphate (ADP)-induced platelet aggregation (ADP-Ag) and the Platelet Reactivity Index of vasodilator-stimulated phosphoprotein for the occurrence of stent thrombosis in patients admitted for non-ST-elevation acute coronary syndrome undergoing percutaneous coronary intervention. A total of 598 consecutive patients with non-ST-elevation acute coronary syndrome undergoing coronary stenting were prospectively included. They received 600 mg of clopidogrel >or=12 hours before percutaneous coronary intervention. Acute or subacute definite or probable stent thrombosis occurred in 11 patients (1.8%). These patients had significantly greater ADP-Ag compared to patients free of stent thrombosis (68 +/- 14% vs 56 +/- 19%, p = 0.002) but only a trend toward a greater Platelet Reactivity Index of vasodilator-stimulated phosphoprotein (62 +/- 14% vs 53 +/- 23%, p = 0.19). The construction of receiver operating characteristic curves to examine the most predictive value of ADP-Ag for stent thrombosis gave a threshold of ADP-Ag of >67% to identify low responders. These patients were at a greater risk of stent thrombosis than the clopidogrel responders (4.3% vs 0.8%, odds ratio 5.8, 95% confidence interval 1.9 to 24.6, p = 0.003). In conclusion, in patients with non-ST-elevation acute coronary syndrome undergoing percutaneous coronary intervention, ADP-Ag is a good parameter to identify clopidogrel nonresponders who are at increased risk of stent thrombosis, with a cutoff value of ADP-Ag of >67%.

Recent developments in clopidogrel pharmacology and their relation to clinical outcomes

Oral antiplatelet therapy with clopidogrel and aspirin is an important and widely prescribed strategy to prevent ischemic events in patients with cardiovascular diseases. However, the occurrence of thrombotic events including stent thrombosis is still high (> 10%). Current practice guidelines are mainly based on large-scale trials focusing on clinical endpoints and 'one size fits all' strategies of treating all patients with the same clopidogrel doses. Pharmacodynamic studies have demonstrated that the latter strategy is associated with wide response variability where a substantial percentage of patients show nonresponsivenes. Translational research studies have established the relation between clopidogrel nonresponsivenes or high on-treatment platelet reactivity to adverse clinical events, thereby establishing clopidogrel nonresponsivenes as an important emerging clinical entity. Clopidogrel response variability is primarily a pharmacokinetic phenomenon associated with insufficient active metabolite generation that is secondary to i) limited intestinal absorption affected by an ABCB1 gene polymorphism; ii) functional variability in P450 isoenzyme activity; and iii) a genetic polymorphism of CYP450 isoenzymes. Personalized antiplatelet treatment with higher clopidogrel doses in selected patients or with newer more potent P2Y(12) receptor blockers based on individual platelet function measurement can overcome some of the limitations of current clopidogrel treatment.

Contemporary issues on clopidogrel therapy

In this paper, data from available studies regarding some contemporary issues on clopidogrel therapy are analyzed. In particular, the following clinical questions have been considered and addressed: (a) Is early clopidogrel treatment needed in patients with acute coronary syndromes treated medically or undergoing percutaneous coronary intervention (PCI)? (b) What is the optimal clopidogrel loading dose in patients undergoing PCI? (c) Is pre-treatment with clopidogrel before PCI needed, or can clopidogrel loading be given in the catheter laboratory before intervention, but after coronary anatomy is known? (d) What is the optimal clopidogrel strategy in patients on chronic clopidogrel therapy undergoing PCI? (e) Does the degree of clopidogrel response influence clinical outcome in patients undergoing PCI?

Predictors of heightened platelet reactivity despite dual-antiplatelet therapy in patients undergoing percutaneous coronary intervention

Small studies have indicated that drug-drug interactions and such clinical characteristics as diabetes mellitus may increase residual platelet reactivity in patients on clopidogrel therapy. The independent contribution of these variables to high residual platelet reactivity (HRPR) is not well studied. Residual platelet reactivity was assessed using the VerifyNow P2Y12 assay (Accumetrics Inc., San Diego, California) in 377 patients with stable coronary artery disease on maintenance clopidogrel therapy. HRPR was defined using a threshold previously shown to predict adverse clinical outcomes. Residual platelet reactivity was significantly higher in women (220 +/- 82 vs 200 +/- 77 P2Y12 reaction units [PRU]; p = 0.041), non-Caucasians (229 +/- 79 vs 202 +/- 78 PRU; p = 0.047), patients with diabetes mellitus (220 +/- 73 vs 196 +/- 80 PRU; p = 0.005), and those treated with nitrates (233 +/- 70 vs 200 +/- 80 PRU; p = 0.018) or proton-pump inhibitors (218 +/- 79 vs 198 +/- 78 PRU; p = 0.02), whereas residual platelet reactivity was significantly lower in active smokers (168 +/- 82 vs 208 +/- 77 PRU; p = 0.006). Independent predictors of HRPR were female gender (odds ratio [OR] 1.91, 95% confidence interval [CI] 1.14 to 3.19, p = 0.014), non-Caucasian ethnicity (OR 3.05, 95% CI 1.49 to 6.28, p = 0.002), use of proton-pump inhibitors (OR 1.64, 95% CI 1.03 to 2.59, p = 0.035), and active smoking (OR 0.37, 95% CI 0.14 to 0.94, p = 0.037). HRPR was associated with increased 6-month mortality rates (3.0% vs 0%; p = 0.016). In conclusion, our findings support the hypothesis that clopidogrel nonresponsiveness is primarily the result of genetic mechanisms and factors that may influence activity of the cytochrome P-450 system.

Evaluation of the platelet count drop method for assessment of platelet function in comparison with "gold standard" light transmission aggregometry

INTRODUCTION

Hyporesponsiveness to antiplatelet agents has been linked to an increased risk of major adverse cardiovascular events. However, light transmission aggregometry (LTA), the gold standard methodology for assessing platelet function, requires expertise and is labour-intensive, which render its use in clinical settings impractical. We assessed whether platelet count drop (PCD), a technique widely available in any haematology laboratory, could replace LTA in testing for inhibition of platelet aggregation induced by antiplatelet agents.

MATERIALS AND METHODS

One hundred and sixty-one coronary artery disease patients taking aspirin alone and 91 patients taking a combination of aspirin and clopidogrel were enrolled. Platelet aggregation was measured by LTA and PCD stimulated with 1.6 mM of arachidonic acid (AA) for aspirin and 5 and 20 microM of adenosine diphosphate (ADP) for clopidogrel.

RESULTS

Correlation between AA-induced LTA and PCD was nonexistent (r=-0.043, p=0.587), while correlation between ADP-induced LTA and PCD was low (r=0.374, p<0.0001 for ADP 5 microM and r=0.402, p<0001 for ADP 20 microM ). PCD, whether stimulated with AA or ADP, overestimated platelet aggregation as assessed by LTA, by 13-18%. The wide 95% limits of agreement suggest that the assays can disagree significantly in individual patients.

CONCLUSIONS

Although the PCD method is widely available in non-specialized laboratories, our results demonstrate that there is poor correlation with the current gold standard, i.e. LTA. Thus, PCD should not be used in replacement of LTA to assess antiplatelet responsiveness.