New Antiplatelet Agents and the Role of Platelet Function Testing in Acute Coronary Syndromes

Background

Dual antiplatelet therapy is a guideline mandated for patients with acute coronary syndromes (ACS). Despite its use, thrombotic events continue to occur both early and late. Platelet function testing has been used to define the in vitro effects of new antiplatelet agents, and it has been suggested that it be used to choose therapy. The role of platelet function testing, particularly with newer antiplatelet agents, remains unclear.

Objective

We review the rationale for platelet function testing and its application in monitoring patients on antiplatelet therapy. We also review recent clinical trials of newer antiplatelet agents. On the basis of this review, we reach conclusions on the current role of antiplatelet function testing in monitoring modern antiplatelet therapy and the role of the new antiplatelet agents in the treatment of ACS.

Methods

We reviewed recent publications on platelet function testing and clinical trials of newer antiplatelet therapies compared with clopidogrel.

Results

Platelet function testing is complex, but there is now a bedside test, VerifyNow. High platelet reactivity has been associated with worse cardiovascular outcomes in patients undergoing percutaneous coronary intervention. Recent clinical trials have not found any advantage in outcomes in patients who have their therapy adjusted by monitoring their platelet function. Newer agents, prasugrel, ticagrelor, and cangrelor, produce more rapid, complete, less variable effects on platelet function than clopidogrel. Prasugrel was found to improve outcomes compared with clopidogrel in patients with ACS undergoing percutaneous intervention. Ticagrelor is beneficial in all patients with ACS and reduces cardiovascular mortality compared with clopidogrel. Cangrelor improves outcomes in patients undergoing stenting. Recent studies to assess the role of platelet function monitoring of the effects of clopidogrel and modifying treatments have not been successful.

Conclusion

Recent clinical trials have indicated that newer antiplatelet agents have advantages over clopidogrel in the treatment of ACS. Platelet function testing gives us a guide to the timing, efficacy, and variability of therapy and can correlate with poor patient outcomes; however, the use of antiplatelet function testing to tailor therapy does not seem appropriate.     

Anticoagulants for secondary prevention after acute myocardial infarction: lessons from the past decade

The impact of an acute coronary syndrome (ACS) event, such as an acute myocardial infarction (MI), is not limited to the acute management phase; patients face an elevated risk of residual atherothrombotic events that commonly requires chronic management for months or even years. Significant advances have been made in both the acute and chronic management of patients with acute MI over the past decade, resulting in improved prognoses. One of the hallmarks of modern treatment strategies is more aggressive antiplatelet treatment regimens. However, the risks of further ACS events, stroke and premature death remain elevated in these patients, and addressing this residual risk is challenging owing to interpatient variability, differences in management strategies between centres and countries, incomplete understanding of the specific pathophysiology of post‐ACS thrombosis and limitations of current therapeutic approaches. The recent approval in Europe of the direct oral anticoagulant rivaroxaban for use in this setting in combination with clopidogrel and acetylsalicylic acid offers another strategy to consider in the management of these patients, and clinical strategies in this area continue to evolve. In this review, we chart the progress made over the past decade in reducing the burden of secondary thromboembolic events after acute MI and discuss the current position of and future perspectives on the inclusion of oral anticoagulants into care pathways in this setting.     

Oral antiplatelet agents in ACS: from pharmacology to clinical differences

Antiplatelet agents play an essential role in the treatment of acute coronary syndrome (ACS). Numerous clinical trials have established the value of antiplatelet therapies for ACS. Aspirin (ASA), thienopyridines and GP IIb/IIIa antagonists comprise the major classes of antiplatelet therapies demonstrated to be of benefit in the treatment of ACS. Thienopyridines are a class of drugs that function via inhibition of the adenosine diphosphate (ADP) P2Y12 platelet receptors. Currently, clopidogrel, a second generation thienopyridine, is the main drug of choice and the combination of aspirin and clopidogrel is administered orally for the treatment of ACS. Recently, a third generation of thienopyridines has been introduced represented by prasugrel that has demonstrated promising results in ACS patients treated with percutaneous coronary intervention (PCI). A number of nonthienopyridine oral antiplatelet drugs are under development, and one of them, ticagrelor has already been tested in a major phase III clinical trial, PLATO, with the inclusion of a broad spectrum of patients with ACS. The present review aims to discuss the present knowledge about the safety and efficacy of oral antiplatelet treatment of patients with ACS.     

Antiplatelet options for secondary prevention in acute coronary syndromes

Current guidelines recommend dual antiplatelet therapy, a combination of aspirin and a P2Y(12) inhibitor, for 6?12 months after percutaneous coronary intervention with drug-eluting stent implantation in all patients and for 1 year in all patients after an acute coronary syndrome (ACS), irrespective of revascularization strategy. Clopidogrel has a pharmacokinetic and pharmacodynamic profile that results in a delayed and/or subtherapeutic antiplatelet effect, and wide variability in antiplatelet response. New P2Y(12) inhibitors, such as prasugrel and ticagrelor, have favorable pharmacodynamics and clinical efficacy over clopidogrel and offer an alternative antiplatelet treatment strategy in specific patients. Prasugrel has more potent, rapid, and consistent effects on inhibiting ADP-induced platelet aggregation than clopidogrel. Ticagrelor also appears to have more rapid and consistent antiplatelet effects than clopidogrel. The higher levels of antiplatelet inhibition provided by prasugrel and ticagrelor compared with standard-dose clopidogrel result in improved ischemic outcomes in patients with ACS. Despite an increase in bleeding risk, prasugrel and ticagrelor appear to have a better net clinical benefit, especially in higher-risk patients with ACS.     

Genotype- and phenotype-directed antiplatelet therapy selection in patients with acute coronary syndromes

Although dual antiplatelet therapy (DAPT) has been a standard treatment in patients with acute coronary syndrome (ACS) for over a decade, only recently have therapeutic options beyond aspirin and clopidogrel become available. Additional treatment options are particularly useful because of the documented history of variability in antiplatelet response. This article reviews the current treatment options for DAPT in ACS, and reviews both genotype- and phenotype-guided methods for determining optimal antiplatelet therapy for patients with ACS. Additionally, recommendations from current guidelines as well as expert commentary are provided for the use of available testing methods to determine optimal DAPT for ACS patients.     

Antiplatelet therapy for secondary prevention of acute coronary syndrome, transient ischemic attack, and noncardioembolic stroke in an era of cost containment

Physicians are aware of the profound impact of oral antiplatelet therapy for secondary prevention of acute coronary syndrome (ACS), transient ischemic attack, and noncardioembolic stroke. Numerous clinical studies have compared the benefits of aspirin (ASA) alone with those of combination therapy with extended-release dipyridamole or with those of clopidogrel, with or without ASA, for secondary stroke prevention; and of ASA monotherapy compared with ASA plus clopidogrel combination therapy for secondary prevention in various ACS populations. More recently, ASA plus prasugrel has been compared with ASA plus clopidogrel in a high-risk ACS population. However, given the different treatment modalities and methods used in the various trials, it is difficult to make generalizations as to which therapy is most effective with the lowest risk of bleeding. Further complicating physician's decision making are cost considerations, particularly with the newer oral antiplatelet agents, which are considerably more expensive than ASA. This review provides a brief overview of the clinical data on each of the currently marketed oral antiplatelet agents and the available data on cost-effectiveness for the secondary prevention of ACS, transient ischemic attack, and noncardioembolic stroke.     

Antiplatelet options for secondary prevention in acute coronary syndromes

Current guidelines recommend dual antiplatelet therapy, a combination of aspirin and a P2Y₁₂ inhibitor, for 6–12 months after percutaneous coronary intervention with drug-eluting stent implantation in all patients and for 1 year in all patients after an acute coronary syndrome (ACS), irrespective of revascularization strategy. Clopidogrel has a pharmacokinetic and pharmacodynamic profile that results in a delayed and/or subtherapeutic antiplatelet effect, and wide variability in antiplatelet response. New P2Y₁₂ inhibitors, such as prasugrel and ticagrelor, have favorable pharmacodynamics and clinical efficacy over clopidogrel and offer an alternative antiplatelet treatment strategy in specific patients. Prasugrel has more potent, rapid, and consistent effects on inhibiting ADP-induced platelet aggregation than clopidogrel. Ticagrelor also appears to have more rapid and consistent antiplatelet effects than clopidogrel. The higher levels of antiplatelet inhibition provided by prasugrel and ticagrelor compared with standard-dose clopidogrel result in improved ischemic outcomes in patients with ACS. Despite an increase in bleeding risk, prasugrel and ticagrelor appear to have a better net clinical benefit, especially in higher-risk patients with ACS.     

Dual Antiplatelet Therapy: Guidance for Nurse Practitioners

Long-term dual antiplatelet therapy (DAPT) with aspirin and a P2Y12 inhibitor (clopidogrel, prasugrel, or ticagrelor) is recommended after acute coronary syndrome (ACS) to reduce the risk of secondary ischemic events. DAPT is recommended for at least 12 months after ACS, with prolonged DAPT suggested in patients with low bleeding risk. Nurse practitioners have an important role in managing patients after ACS, acting as patient advocates and collaborating with the cardiology provider to ensure adherence to DAPT. This review describes current recommendations for DAPT in patients with ACS and the nurse practitioners role in maximizing benefits of antiplatelet therapy.     

三联抗血小板药物对非ST段抬高性急性冠脉综合征患者血清炎症因子及内皮功能的影响

目的探讨短期三联抗血小板药物对非ST段抬高性急性冠脉综合征(ACS)患者血清炎症因子和血管内皮功能的影响,为三联抗血小板药物治疗非ST段抬高性ACS提供进一步的临床依据。方法急性非ST段抬高性ACS患者82例,随机分为三联抗血小板药物治疗组(治疗组)和二联抗血小板治疗组(对照组);观察组患者给予阿司匹林、氯吡格雷、替罗非班三联抗血小板药物;对照组患者给予阿司匹林,氯吡格雷二联抗血小板药物。观察治疗48 h后患者血清炎症因子(hs-CRP、IL-6)及反映血管内皮功能的指标(ET-1、NO、PGI2)的水平变化情况。结果三联抗血小板药物较二联抗血小板药物更有效地降低非ST段抬高性ACS患者血清炎症因子及改善血管内皮功能,主要的不良反应为皮下瘀斑、牙龈出血。结论对于非ST段抬高性ACS患者,三联抗血小板药物在短期的抗炎、改善血管功能方面要优于二联抗血小板治疗,值得临床推广应用。     

Glycoprotein IIIA gene (PlA) polymorphism and aspirin resistance: is there any correlation?

BACKGROUND: Platelet glycoprotein (GP) IIb/IIIa receptors play an inevitable role in platelet aggregation. The GP IIIa gene is polymorphic (PlA1/PlA2) and the presence of a PlA2 allele might be associated with an increased risk for acute coronary syndrome (ACS). OBJECTIVE: To examine the prevalence of the PlA2 allele in patients with ACS and in subjects with or without aspirin resistance. METHODS: The prevalence of the PlA2 allele was assessed in 158 patients with ACS and PlA2 compared with its prevalence in 199 healthy volunteers. The antiplatelet efficacy of aspirin was examined in all patients with ACS, as well as in 69 individuals who had suffered ischemic stroke and in 58 high-risk subjects without any known ischemic vascular events. RESULTS: PlA2 prevalence was significantly higher in patients with ACS (59/158) than in the control group (51/199; p < 0.05). Carriers of the PlA2 allele had a significantly higher risk of developing ACS, even after an adjustment to the risk factors (OR 5.74; 95% CI 1.75 to 18.8; p = 0.004). The occurrence of the PlA2 allele was significantly higher among patients with aspirin resistance than in subjects who demonstrated an appropriate response to the drug (allele frequencies, 0.21 vs 0.14; p < 0.05). All patients homozygous for the PlA2 allele had an inadequate platelet response to aspirin. CONCLUSIONS: Our results support the hypothesis that carriers of the PlA2 allele might have an increased risk for ACS. PlA2 homozygosity was associated with an inadequate response to aspirin therapy. Our data further suggest that patients with PlA2 allele homozygosity might benefit from antiplatelet therapy based on adenosine diphosphate antagonists throughout secondary treatment for prevention of ACS.     

Acute coronary syndromes: identifying the appropriate patient for prasugrel

Acute coronary syndrome (ACS) remains the leading cause of morbidity and mortality. More than half of patients presenting with ACS will experience a recurrent ischemic event; thus, preventing recurrent events is essential to reduce morbidity and mortality associated with ACS. While dual antiplatelet therapy with aspirin and clopidogrel has been the foundation of management for patients presenting with ACS, clopidogrel is limited by delayed antiplatelet effect and a variable patient response. Prasugrel is more potent, has a more rapid and consistent antiplatelet effect, and has been associated with improved outcomes compared with clopidogrel in select patients with ACS. Although prasugrel reduces the risk of recurrent cardiovascular events, it also increases the risk of major bleeding. Careful patient selection will improve the likelihood that patients treated with prasugrel will experience the benefit of this antiplatelet agent with the lowest possible risk of an adverse event. This article reviews the data supporting the use of prasugrel in ACS with an emphasis on characteristics that will help identify the most appropriate patient for this therapy.     

Tackling the thrombotic burden in patients with acute coronary syndrome and diabetes mellitus

Patients with diabetes mellitus (DM) and coronary artery disease, particularly those presenting with acute coronary syndromes (ACS), have a higher risk of developing ischemic complications than their nondiabetic counterparts. Although ACS patients with DM benefit more than normoglycemic ACS patients from early coronary angiography and revascularization, they remain at a higher risk of complications following percutaneous coronary intervention and bypass surgery. The DM-associated prothrombotic state has been implicated in the pathogenesis of these complications and growing data supports the notion that potent platelet inhibition is of paramount importance in order to optimize outcomes of DM patients presenting with ACS. This article focuses on the evidence supporting the concept that augmented platelet reactivity and impaired responsiveness to oral antiplatelet agents are influential drivers of the increased propensity of DM patients with ACS to develop thrombotic complications. In particular, strategies to enhance platelet P2Y(12) receptor inhibition, a key factor to improve outcomes in this patient population, are reviewed.     

Tackling the thrombotic burden in patients with acute coronary syndrome and diabetes mellitus

Patients with diabetes mellitus (DM) and coronary artery disease, particularly those presenting with acute coronary syndromes (ACS), have a higher risk of developing ischemic complications than their nondiabetic counterparts. Although ACS patients with DM benefit more than normoglycemic ACS patients from early coronary angiography and revascularization, they remain at a higher risk of complications following percutaneous coronary intervention and bypass surgery. The DM-associated prothrombotic state has been implicated in the pathogenesis of these complications and growing data supports the notion that potent platelet inhibition is of paramount importance in order to optimize outcomes of DM patients presenting with ACS. This article focuses on the evidence supporting the concept that augmented platelet reactivity and impaired responsiveness to oral antiplatelet agents are influential drivers of the increased propensity of DM patients with ACS to develop thrombotic complications. In particular, strategies to enhance platelet P2Y₁₂ receptor inhibition, a key factor to improve outcomes in this patient population, are reviewed.     

Implication of the new low-density lipoprotein goals in dyslipidemia management of patients with acute coronary syndrome

OBJECTIVE: To assess the ability of patients with an acute coronary syndrome (ACS) to meet the recommended low-density lipoprotein cholesterol (LDL-C) goal of 100 mg/dL and optional aggressive lowering to 70 mg/dL. PATIENTS AND METHODS: Patients diagnosed as having ACS who had lipid levels measured within 24 hours of admission from January 1, 1998, through December 31, 2002, were assessed for the ability to meet the 2 target LDL-C levels. Patients were considered to have ACS if they were diagnosed as having myocardial infarction, had significant disease on angiography, or had a history of coronary artery disease. Patients were classified into 1 of 4 groups on the basis of the degree of LDL-C lowering required to meet the 2 different goals: less than 33%, 33% to 39%, 40% to 49%, and 50% or more. Patients with myocardial infarction who had lipid sampling performed more than 24 hours after admission were excluded. RESULTS: The mean plus-or-minus SD LDL-C level was 111 plus-or-minus 43 mg/dL in the 1322 patients who met criteria for ACS and had LDL-C levels assessed. On the basis of a target LDL-C value of less than 100 mg/dL, 43% of patients were at goal and did not require treatment, and only 2.5% had an LDL-C level that required a 50% or greater reduction to meet goal. In contrast, using the newer LDL-C target of 70 mg/dL, 85% patients required treatment, and 23% of patients required a 50% or greater decrease in LDL-C level and therefore were likely to require more than 1 lipid-lowering agent. CONCLUSION: Decreasing the LDL-C target to less than 70 mg/dL substantially increases the number of patients with ACS who would require treatment. A significant proportion of patients will require a reduction in LDL-C level of 50% or more, which is not easily achievable with current lipid-lowering monotherapy.     

Clopidogrel,prasugrel, ticagrelor or vorapaxar in patients with renal impairment: do we have a winner?

The optimal utilization of antiplatelet therapy in patients with renal impairment (RI) following acute coronary syndromes (ACS) represents an urgent, unmet and yet unsolved need with regards to the choice of agents, duration of treatment and potential dose/regimen adjustment. The lack of any large randomized trials designed and powered specifically in such high-risk patients, absence of the uniformed efficacy and safety data reporting policy to the FDA and endless overoptimistic publications based on post hoc analyses of primary trials sometimes exaggerating benefits and hiding risks, clouds reality. In addition, triaging RI patients is problematic due to ongoing kidney deterioration and the fact that such patients are prone to both vascular occlusions and bleeding. The authors summarize available FDA-confirmed evidence from the latest trials with approved antiplatelet agents, namely clopidogrel (CAPRIE, CURE, CREDO, CLARITY, CHARISMA); prasugrel (TRITON, TRILOGY); ticagrelor (PLATO, and PEGASUS); and vorapaxar (TRACER and TRA2P) in RI patient cohorts on top of aspirin as part of dual antiplatelet therapy (DAPT). We deliberately avoided any results unless they were verified by the FDA, with the exception of the recent PEGASUS, since Agency reviews are not yet available. Despite differences among the trials and DAPT choices, RI patients universally experience much higher (HR = 1.3–3.1) rates of primary endpoint events, and bleeding risks (HR = 1.7–3.6). However, only ticagrelor increases creatinine and uric acid levels above that of clopidogrel; has the worst incidence of serious adverse events, more adverse events, and inferior outcomes in patients with severe (eGFR <30 ml/min), especially in the lowest (eGFR <15 ml/min) RI subsets. Clopidogrel, prasugrel and vorapaxar appear safer. Moreover, less aggressive half dose (5 mg/daily) prasugrel and strict DAPT, are well justified in RI, but not predominantly triple strategies with vorapaxar as tested in TRA2P and especially in TRACER. In conclusion, data from clinical trials, their sub-studies and affiliated FDA reviews indicate that RI cause more vascular occlusions and bleeding in ACS patients treated with DAPT. Among the novel antiplatelet agents, prasugrel and vorapaxar, but probably not ticagrelor, offer advantage in RI patients.     

Prasugrel in acute coronary syndrome patients undergoing percutaneous coronary intervention

Currently, dual antiplatelet therapy with aspirin and clopidogrel represents the key treatment strategy for the prevention of ischemic events in patients with acute coronary syndrome (ACS) and/or undergoing percutaneous coronary intervention (PCI). However, there is a broad inter-individual response variability to such treatment strategy, and a considerable number of patients persist with inadequate platelet inhibition, which has been associated with an increased risk of ischemic events. Overall, these findings underscore the need for novel antiplatelet agents able to achieve greater platelet inhibition; this can potentially reduce ischemic event rates. Prasugrel (CS-747; LY 640315), a novel third-generation oral thienopyridine, is a specific, irreversible antagonist of the platelet adenosine diphosphate P2Y₁₂ receptor. Laboratory studies have shown prasugrel to be associated with more prompt, potent and predictable degrees of platelet inhibition compared with clopidogrel. In a large-scale clinical study, which was comprised of high-risk ACS patients undergoing PCI, prasugrel was shown to significantly reduce the short- and long-term risk of ischemic events, including stent thrombosis. However, such significant reduction in ischemic events occurred at the expense of a higher risk of bleeding. Recent clinical trial data analyses have led to a better understanding of the efficacy and safety of prasugrel. This article reviews the currently available data regarding the efficacy and safety of prasugrel in ACS patients.     

Antithrombotic therapy of acute coronary syndromes

Recent advances in the diagnosis and the treatment of acute coronary syndromes (ACS) have led to a substantial reduction of major coronary events, to an improvement in patient outcome, and to the definition of new guidelines. Current strategies for the treatment of patients with non-ST-elevation ACS recommend a combined antithrombotic therapy (including acetyl salicylic acid, clopidogrel, low-molecular weight or unfractionated heparins and, eventually glycoprotein IIb/IIIa receptor antagonists). This combined antithrombotic therapy allows to increase the benefit of an early invasive strategy including coronary angiogram with stent percutaneous coronary angioplasty. The purpose of this review is to discuss and highlight the actual recommendations for the appropriate use of antithrombotic strategies for ACS patients.     

Genetic testing in patients with acute coronary syndrome undergoing percutaneous coronary intervention: a cost‐effectiveness analysis

Summary. Background: The CYP2C19 genotype is a predictor of adverse cardiovascular events in acute coronary syndrome (ACS) patients undergoing percutaneous coronary intervention (PCI) treated with clopidogrel. Objectives: We aimed to evaluate the cost‐effectiveness of a CYP2C19*2 genotype‐guided strategy of antiplatelet therapy in ACS patients undergoing PCI, compared with two ‘no testing’ strategies (empiric clopidogrel or prasugrel). Methods: We developed a Markov model to compare three strategies. The model captured adverse cardiovascular events and antiplatelet‐related complications. Costs were expressed in 2010 US dollars and estimated using diagnosis‐related group codes and Medicare reimbursement rates. The net wholesale price for prasugrel was estimated as $5.45 per day. A generic estimate for clopidogrel of $1.00 per day was used and genetic testing was assumed to cost $500. Results: Base case analyses demonstrated little difference between treatment strategies. The genetic testing‐guided strategy yielded the most QALYs and was the least costly. Over 15 months, total costs were $18 lower with a gain of 0.004 QALY in the genotype‐guided strategy compared with empiric clopidogrel, and $899 lower with a gain of 0.0005 QALY compared with empiric prasugrel. The strongest predictor of the preferred strategy was the relative risk of thrombotic events in carriers compared with wild‐type individuals treated with clopidogrel. Above a 47% increased risk, a genotype‐guided strategy was the dominant strategy. Above a clopidogrel cost of $3.96 per day, genetic testing was no longer dominant but remained cost‐effective. Conclusions: Among ACS patients undergoing PCI, a genotype‐guided strategy yields similar outcomes to empiric approaches to treatment, but is marginally less costly and more effective.     

Antithrombotic therapy of acute coronary syndromes

Recent advances in the diagnosis and the treatment of acute coronary syndromes (ACS) have led to a substantial reduction of major coronary events, to an improvement in patient outcome and the definition of new guidelines. Current strategies for the treatment of patients with non-ST-elevation ACS recommend a combined antithrombotic therapy (including aspirin, clopidogrel, anticoagulation with low-molecular weight or unfractionated heparins or FXa-inhibitors or direct antithrombins and, eventually glycoprotein IIb/IIIa receptor antagonists). This combined antithrombotic therapy allows to increase the benefit of an early invasive strategy including coronary angiogram with stent percutaneous coronary angioplasty. The purpose of this review is to discuss and highlight the recommendations for the appropriate use of antithrombotic strategies in the setting of angioplasty in ACS patients.     

The role of cardiac markers in the emergency department.

The emergency department (ED) evaluation of patients with potential acute coronary syndromes (ACS) has traditionally included initial cardiac marker testing for suspected acute myocardial infarction (AMI). While ED management decisions for patients with ACS have largely been based on history, physical examination, and a presenting 12-lead electrocardiogram (ECG), there is ample evidence that markers impact treatment decisions and provide risk stratification. Newer, more sensitive markers of myocardial necrosis have blurred the distinction between patients with and without classically defined AMI, and have focused attention on the continuum of ACS from angina to transmural Q-wave MI. Newer antiplatelet agents, the glycoprotein IIb/IIIa receptor blockers, are likely to receive increased ED utilization. This use will be partially driven by ED cardiac marker determination. Bedside, point-of-care testing is reliable technology that may shorten time to diagnosis and treatment of ACS in the emergency setting. The ED-based chest pain center (CPC) has become a popular tool to evaluate patients at low- to moderate-risk for ACS and a non-diagnostic ECG. Such centers use serial cardiac marker testing as a mainstay for evaluation and risk stratification. Cost issues have driven many diagnostic patient evaluations from the inpatient setting to such ED observation units. As this becomes more common for low- to moderate-risk patients with chest pain, serial assessment of cardiac markers, and their interpretation by emergency physicians, will become essential.