Measuring aspirin resistance, clopidogrel responsiveness, and postprocedural markers of myonecrosis in patients undergoing percutaneous coronary intervention

Time-dependent changes in P2Y12 reaction unit values for predicting the different types of cardiovascular events in patients with ischemic heart disease

Several studies have investigated the association between P2Y12 reaction unit (PRU) value and major adverse cardiovascular events (MACEs) in patients with ischemic heart disease, but there is no well-established consensus on the utility of PRU value. Furthermore, the optimal PRU cut-off value varied with studies. One reason may be that the endpoints and observation periods differed, depending on the study. This study aimed to investigate the optimal cut-off and predictive ability of the PRU value for predicting cardiovascular events, while considering different endpoints and observation periods. We surveyed a total of 338 patients receiving P2Y12 inhibitors and measured PRU during cardiac catheterization. Using time-dependent receiver operating characteristic analysis, we evaluated the cut-off and area under curve (AUC) of the PRU value for two MACEs (MACE ①: composite of death, myocardial infarction, stent thrombosis, and cerebral infarction; MACE ②: composite of MACE ① and target vessel revascularization) at 6, 12, 24 and 36 months after cardiac catheterization. MACE ① occurred in 18 cases and MACE ② in 32 cases. The PRU cut-off values at 6, 12, 24, and 36 months were 257, 238, 217, and 216, respectively, for MACE ① and 250, 238, 209, and 204, respectively, for MACE ②. The AUCs at 6, 12, 24, and 36 months were 0.753, 0.832, 0.718, and 0.717, respectively, for MACE ① and 0.724, 0.722, 0.664, and 0.682, respectively, for MACE ②. The optimal cut-off and predictive ability of PRU values for cardiovascular events varied depending on different endpoints and duration of the observation periods. A relatively high PRU value is effective for short-term event suppression, but a low value is required for long-term event suppression.

The Association between Multi-Vessel Coronary Artery Disease and High On-Aspirin Platelet Reactivity

BACKGROUND

Multi-vessel coronary artery disease (MV-CAD) is correlated with worse clinical outcomes compared with single-vessel CAD (SV-CAD). The aim of this study was to evaluate the association between MV-CAD and high on-aspirin platelet reactivity (HAPR) in patients with stable CAD treated with aspirin.

METHODS

The current study is an analysis of prospectively enrolled randomly selected patients with known stable CAD, who were taking aspirin (75-100 mg qd) regularly for at least one month, and had undergone coronary angiography at least 3 months prior to the enrollment to the study.

EXCLUSION CRITERIA

acute coronary syndrome at the time of platelet function testing, active malignancy, acute infection, active inflammatory/rheumatic disease, major surgery in the past 6 months, chronic liver failure, treatment with oral anticoagulation, non-adherence with Aspirin and thrombocytopenia (<100 K/micl). Blood was drawn from the participants and sent for platelet function testing (VerifyNow, Instrumentation Laboratory Company, Bedford, Massachusetts, United States). MV-CAD was defined as >50% stenosis in ≥2 separate major coronary territories per coronary angiography. HAPR was defined as aspirin reaction units (ARU) >550.

RESULTS

Overall, 507 patients were analyzed; age 66.7 ± 11.2, 17.9% women, 223 (44%) had MV-CAD. The rate of HAPR was significantly higher among patients with MV-CAD vs. SV-CAD (14.8% vs. 3.5%, p < 0.001, respectively). Furthermore, a "dose response"-like association was found between the number of stenotic coronary arteries and the rate of HAPR (3.5%, 13.5 and 17.3% for SV-CAD, 2-vessel and 3-vessel disease, respectively). In a multivariate analysis adjusted for potential confounders, MV-CAD was found to be a strong independent predictor of HAPR [OR = 1.8 (95%CI: 1.05-4.7), p = 0.014].

CONCLUSIONS

A significant association between MV-CAD and HAPR was found. Additional studies designed to investigate the mechanisms of HAPR and different therapeutic options for this subset of patients are warranted.

Periprocedural Variability of Platelet Functions in Carotid Artery Stenting: An Analysis Using VerifyNow

Objective

The assessment of platelet functions is necessary to prevent both thromboembolic and hemorrhagic complications under dual antiplatelet therapy (DAPT). Using the VerifyNow (Accumetrics, Inc., San Diego, CA, USA) assay, this study aimed to reveal time-dependent changes in platelet functions after carotid artery stenting (CAS).

Methods

We enrolled retrospectively 43 patients who underwent CAS under DAPT. Aspirin reaction unit (ARU) and P2Y12 reaction unit (PRU) values were determined on the day before and on days 1, 3, and 7 after the procedure. Multiple comparison tests (MCTs) were performed among ARU and PRU measurement points, and the proportions of hypo- and hyper-responses were compared.

Results

The median ARU values were 408 (interquartile range: 392-497) before CAS and 418 (405-470) on day 1, 405 (393.0-460.5) on day 3, and 402 (388.5-477.5) on day 7 (not significant in MCTs). The percentages of hypo-responses were 16.3%, 7.0%, 2.3%, and 7.0%, respectively (p = 0.11). The significantly different median PRU values were 173 (116.5-209.5), 233 (166.5-273.5), 139 (70.5-205.5), and 51 (9.0-79.5), respectively. The median PRU was before the procedure within the therapeutic range but exceeded the upper cutoff on day 1 and was below the lower cutoff on day 7. The percentages of hypo-responses were 14.0%, 51.2%, 18.6%, and 11.6%, respectively (p <0.001) and the percentages of hyper-responses were 9.3%, 2.3%, 23.3%, and 62.8%, respectively (p <0.001).

Conclusion

In the periprocedural CAS period, ARU values were stable, but PRU values showed time-dependent changes. PRU values were above the therapeutic range the day after CAS but decreased below this range on day 7.

Variability of Platelet Reactivity on Antiplatelet Therapy in Neurointervention Procedure

As more intracranial aneurysms and other cerebrovascular pathologies are treated with neurointervention procedure, thromboembolic events that frequently lead to serious neurological deficit or fatal outcomes are increasing. In order to prevent the thromboembolic events, antiplatelet therapy is used in most procedures including coil embolization, stenting, and flow diversion. However, because of variable individual pharmacodynamics responses to antiplatelet drugs, especially clopidogrel, it is difficult for clinicians to select the adequate antiplatelet regimen and its optimal dose. This article reviews the neurointervention literature related to antiplatelet therapy and suggests a strategy for tailoring antiplatelet therapy in individual patients undergoing neurointervention based on the results of platelet function testing.

Platelet-to-lymphocyte ratio but not neutrophil-to-lymphocyte ratio predicts high on-treatment platelet reactivity in clopidogrel-treated patients with acute coronary syndrome

OBJECTIVES

Dual antiplatelet therapy (DAPT), consisting of clopidogrel and aspirin, is the main-stay treatment of acute coronary syndromes (ACS). However, major adverse cardiovascular events may occur even in patients undergoing DAPT, and this has been related to the variable pharmacodynamic efficacy of these drugs, especially clopidogrel. Platelet-to-lymphocyte ratio (PLR) and neutrophil-to-lymphocyte ratio (NLR) are novel inflammatory markers for cardiovascular risk stratification, which may reflect an inflammatory state and thus high on-treatment platelet reactivity (HPR).

METHODS

We investigated the usefulness of PLR and NLR in predicting HPR in clopidogrel-treated patients with ACS. A total of 244 patients were enrolled in this study, and 43 of them were nonresponsive to clopidogrel.

RESULTS

Logistic regression analysis indicated that PLR was significantly associated with HPR (P < 0.001). Using a cutoff level of 331, PLR predicted HPR with a sensitivity of 73% and a specificity of 69% (odds ratio: 376.15, 95% confidence interval = 37.813-3741.728 P < 0.001, receiver operating characteristic curve: 0.885).

CONCLUSIONS

We suggest that more attention should be paid to the PLR values of these patients on admission to identify individuals who may not benefit from clopidogrel during the course of ACS.

The prognostic utility of tests of platelet function for the detection of 'aspirin resistance' in patients with established cardiovascular or cerebrovascular disease: a systematic review and economic evaluation

BACKGROUND

The use of aspirin is well established for secondary prevention of cardiovascular disease. However, a proportion of patients suffer repeat cardiovascular events despite being prescribed aspirin treatment. It is uncertain whether or not this is due to an inherent inability of aspirin to sufficiently modify platelet activity. This report aims to investigate whether or not insufficient platelet function inhibition by aspirin ('aspirin resistance'), as defined using platelet function tests (PFTs), is linked to the occurrence of adverse clinical outcomes, and further, whether or not patients at risk of future adverse clinical events can be identified through PFTs.

OBJECTIVES

To review systematically the clinical effectiveness and cost-effectiveness evidence regarding the association between PFT designation of 'aspirin resistance' and the risk of adverse clinical outcome(s) in patients prescribed aspirin therapy. To undertake exploratory model-based cost-effectiveness analysis on the use of PFTs.

DATA SOURCES

Bibliographic databases (e.g. MEDLINE from inception and EMBASE from 1980), conference proceedings and ongoing trial registries up to April 2012.

METHODS

Standard systematic review methods were used for identifying clinical and cost studies. A risk-of-bias assessment tool was adapted from checklists for prognostic and diagnostic studies. (Un)adjusted odds and hazard ratios for the association between 'aspirin resistance', for different PFTs, and clinical outcomes are presented; however, heterogeneity between studies precluded pooling of results. A speculative economic model of a PFT and change of therapy strategy was developed.

RESULTS

One hundred and eight relevant studies using a variety of PFTs, 58 in patients on aspirin monotherapy, were analysed in detail. Results indicated that some PFTs may have some prognostic utility, i.e. a trend for more clinical events to be associated with groups classified as 'aspirin resistant'. Methodological and clinical heterogeneity prevented a quantitative summary of prognostic effect. Study-level effect sizes were generally small and absolute outcome risk was not substantially different between 'aspirin resistant' and 'aspirin sensitive' designations. No studies on the cost-effectiveness of PFTs for 'aspirin resistance' were identified. Based on assumptions of PFTs being able to accurately identify patients at high risk of clinical events and such patients benefiting from treatment modification, the economic model found that a test-treat strategy was likely to be cost-effective. However, neither assumption is currently evidence based.

LIMITATIONS

Poor or incomplete reporting of studies suggests a potentially large volume of inaccessible data. Analyses were confined to studies on patients prescribed aspirin as sole antiplatelet therapy at the time of PFT. Clinical and methodological heterogeneity across studies precluded meta-analysis. Given the lack of robust data the economic modelling was speculative.

CONCLUSIONS

Although evidence indicates that some PFTs may have some prognostic value, methodological and clinical heterogeneity between studies and different approaches to analyses create confusion and inconsistency in prognostic results, and prevented a quantitative summary of their prognostic effect. Protocol-driven and adequately powered primary studies are needed, using standardised methods of measurements to evaluate the prognostic ability of each test in the same population(s), and ideally presenting individual patient data. For any PFT to inform individual risk prediction, it will likely need to be considered in combination with other prognostic factors, within a prognostic model.

STUDY REGISTRATION

This study is registered as PROSPERO 2012:CRD42012002151.

FUNDING

The National Institute for Health Research Health Technology Assessment programme.

Clopidogrel resistance response in patients with coronary artery disease and metabolic syndrome: the role of hyperglycemia and obesity

BACKGROUND

Despite the proven benefits of clopidogrel combined aspirin therapy for coronary artery disease (CAD), CAD patients with metabolic syndrome (MS) still tend to have coronary thrombotic events. We aimed to investigate the influence of metabolic risk factors on the efficacy of clopidogrel treatment in patients with CAD undergoing percutaneous coronary intervention (PCI).

METHODS

Cohorts of 168 MS and 168 non-MS subjects with CAD identified by coronary angiography (CAG) were enrolled in our study. MS was defined by modified Adult Treatment Panel III criteria. All subjects had taken 100 mg aspirin and 75 mg clopidogrel daily for more than 1 month, and administered loading doses of 600 mg clopidogrel and 300 mg aspirin before PCI. Blood samples were taken 24 h after the loading doses of clopidogrel and aspirin. Platelet aggregation was measured using light transmittance aggregometry (LTA) and thrombelastography (TEG). Clopidogrel resistance was defined as more than 50% adenosine diphosphate (ADP) induced platelet aggregation as measured by TEG.

RESULTS

Platelet aggregation inhibition rate by ADP was significantly lower in patients with MS as measured both by TEG (55% ± 31% vs. 68% ± 32%; P < 0.001) and LTA (29% ± 23% vs. 42% ± 29%; P < 0.001). In the multivariate analysis, elderly [OR (95% CI): 1.483 (1.047-6.248); P = 0.002], obesity [OR (95% CI): 3.608 (1.241-10.488); P = 0.018], high fasting plasma glucose level [OR (95% CI): 2.717 (1.176-6.277); P = 0.019] and hyperuricemia [OR (95% CI): 2.583 (1.095-6.094); P = 0.030] were all statistically risk factors for clopidogrel resistance. CAD patients with diabetes and obesity were more likely to have clopidogrel resistance than the CAD patients without diabetes and obesity [75% (61/81) vs. 43% (67/156); P < 0.001].

CONCLUSIONS

CAD patients with MS appeared to have poorer antiplatelet response to clopidogrel compared to those without MS. Obesity, diabetes and hyperuricemia were all significantly associated with clopidogrel resistance.

Antiplatelet strategies for secondary prevention of stroke and TIA

Stroke is a major public health issue, and stroke recurrence accounts for a quarter of all events. Antiplatelet therapy has been extensively studied for secondary stroke prevention and is established as effective in this high-risk population. Several agents have been evaluated in this setting, both in isolation and combination. The most widely used antiplatelet medications are aspirin, clopidogrel, and aspirin plus extended-release dipyridamole. However, new agents and combinations continue to be evaluated. A detailed review of the evidence supporting various antiplatelet regimens for secondary stroke prevention is outlined with special focus on recent developments that may impact clinical management of patients with stroke or TIA.

Lack of association between clopidogrel responsiveness tested using point-of-care assay and prognosis of patients with coronary artery disease

Dual antiplatelet therapy is important treatment modality across the spectrum of coronary artery disease manifestations. However, a significant number of patients do not have a completely effective response to clopidogrel. This study assessed the impact of response after clopidogrel with Verify Now device on prognosis on patients undergoing coronary interventions. Consecutive patients following percutaneous coronary intervention were prospectively enrolled. A loading dose of 600 mg of clopidogrel was administered before or during PCI. Blood samples were drawn within 24 h after clopidogrel administration. The effect of clopidogrel was measured using VerifyNow. All patients were evaluated at 6 months. The primary end-point was the combination of death, MI and stroke. 378 patients (69.3 % men and 30.7 % women) were enrolled. The mean age was 67.2 ± 12.8 years, BMI 28.9 ± 17.7, and 116 patients had diabetes (30.7 %). During the 6-months follow-up 30 patients (7.94 %) experienced a monitored end-point: 12 patients (3.17 %) had MI; five patients (1.32 %) strokes and 15 patients (3.97 %) died. The remaining 248 patients (71.26 %) were end-point free. Factors associated with a poor prognosis were: leukocytes (OR 1.7 [1.2-2.4], p < 0.01), creatinine (OR 1.4 [1.1-2.5], p < 0.05) and at a borderline level the presence of AA allele of gene CYP2C19*2 (OR 2.5 [0.99-4.1], p = 0.052). The results using VerifyNow were similar between both groups (Group End-point: 208.5 ± 85.5, group No end-point 203.1 ± 91.3) and failed to show any prognostic value (OR 1.00 [0.992-1.007], p = 0.9). The measurement of clopidogrel efficacy using VerifyNow had no prognostic value for our unselected cohort of patients after PCI.

Assessment of platelet inhibition by point-of-care testing in neuroendovascular procedures

Antiplatelet agents are an important component of the preventive strategies currently used in clinical practice to minimize the risk of thromboembolic events during and after endovascular procedures. Because of the variability in the response to antiplatelet agents, measuring the degree of platelet inhibition may help identify and properly treat poor responders. POC testing is defined as diagnostic testing at or near the site of patient care. Knowledge of the specifics of these devices among practicing neurointerventionalists is relatively limited. In this article, the different POC devices available are presented, and their clinical utility in relation to endovascular procedures is discussed.

Impact of platelet reactivity on long-term clinical outcomes and bleeding events in Japanese patients receiving antiplatelet therapy with aspirin

AIM

Aspirin is an antiplatelet drug widely used for the prevention of cardiovascular disease; however, it is known to increase bleeding events. A low response to aspirin was reported to correlate with poor prognosis in patients undergoing antiplatelet therapy with aspirin. The aim of this study was to evaluate the impact of the antiplatelet activity of aspirin on cardiovascular and bleeding events in Japanese patients.

METHODS

We analyzed the clinical course of 239 Japanese patients undergoing antiplatelet therapy with aspirin for a median of 64 months in this study. Their residual platelet reactivity was examined at enrollment and after 2 years. The co-primary endpoints were the occurrence of major adverse cardiac and cerebrovascular events (MACCEs) and bleeding events.

RESULTS

The annual incidence of MACCEs and major bleeding events was 3.7% and 0.48%, respectively. With defined criteria, 67 patients (28%) were classified as low responders based on the platelet aggregability measured at enrollment. Low response to aspirin was not associated with increased MACCEs, while it clearly increased MACCEs in patients less than 70 years old (low responders 36.9% vs. responders 14.8%, log rank p=0.008). Five major types of bleeding occurred in the responders, but not in low responders, although the difference was not statistically significant (p= 0.07).

CONCLUSION

Low response to aspirin was not associated with the increase of long-term MACCEs, while it increased MACCEs in patients less than 70 years old; however, it tended to decrease major bleeding events in Japanese patients.

A randomized study assessing the effects of pretreatment with cilostazol on periprocedural myonecrosis after percutaneous coronary intervention

PURPOSE

It is unknown whether cilostazol pretreatment reduces postprocedural myonecrosis (PPMN). Cilostazol pretreatment reduces PPMN after percutaneous coronary intervention (PCI).

MATERIALS AND METHODS

A total of 120 patients with stable angina scheduled for elective PCI were randomly assigned to a 7-day pretreatment with Cilostazol (200 mg/day) or to a control group. Creatine kinase-MB (CK-MB) and cardiac troponin I (cTnI) levels were measured at baseline and at 6 and 24 hours after PCI. The primary end-point was the occurrence of PPMN, defined as any CK-MB elevation above the upper normal limit (UNL). Aspirin and clopidogrel were co-administered for 7 days before PCI, and resistance to these agents was then assayed using the VerifyNow System.

RESULTS

There was no difference in baseline characteristics between the final analyzable cilostazol (n=54) and the control group (n=56). Despite a significantly greater % inhibition of clopidogrel in the cilostazol group (39±23% versus 25±22%, p=0.003), the incidence of PPMN was similar between the cilostazol group (24%) and the control group (25%, p=1.000). The rate of CK-MB elevation at ≥3 times UNL was also similar between the two groups (6% versus 5%, p=0.583). The incidence of cTnI increase over the UNL or to 3 times the UNL was not different between the two groups. There was no significant difference in terms of the rate of adverse events during follow- up, although the cilostazol group showed a tendency to have a slightly higher incidence of entry site hematoma.

CONCLUSION

This trial demonstrated that adjunctive cilostazol pretreatment might not significantly reduce PPMN after elective PCI in patients with stable angina.

Functional testing methods for the antiplatelet effects of aspirin

At antiplatelet doses of 75–325 mg/day, aspirin irreversibly inhibits the platelet cyclooxygenase (COX)-1-dependent thromboxane A2 (TXA2) formation. This is the pharmacological mode of action of aspirin, and it can be predicted that if aspirin does not inhibit COX-1 sufficiently, patients will not benefit from its antiplatelet effects. A pharmacodynamic failure of aspirin occurs in 1–2% of patients. The vast majority of atherothrombotic events in patients treated with aspirin result from mechanisms that are dependent on residual (non-COX-1-dependent) platelet reactivity. Global tests of platelet activation in vitro may identify patients with high residual platelet reactivity but are not sufficiently specific to test the pharmacological effect of aspirin. A further problem is the absence of standardized normal ranges for many assays and the fact that different equipment measures different signals, which are also influenced by the agonist and the anticoagulant used. Similar considerations apply for the determination of platelet-derived biomarkers such as circulating P-selectin, soluble CD40 ligand and others. The direct measurement of inhibition of thromboxane-forming capacity is the most specific pharmacological assay for aspirin. However, there is no linear correlation between inhibition of TXA2 formation and inhibition of platelet function. Measurement of urinary levels of the TXB2 metabolite, 11-dehydro-thromboxane B2, represents an index of TXA2 biosynthesis in vivo, but is also sensitive to other cellular sources of TXA2. One general problem of all assays is the relationship with clinical outcome, which is still unclear. Monitoring aspirin treatment by testing platelet function or measuring biomarkers in clinical practice should not be recommended until a clear relationship for the predictive value of these assays for clinical outcome has been established.

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.

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.

Developments in antiplatelet therapy for acute coronary syndromes and considerations for long-term management

OBJECTIVE

This article reviews the currently available antiplatelet therapies and emerging investigational drugs in the treatment of acutecoronary syndrome (ACS), and considerations for primary and secondary prevention in the long-term management of ACS patients undergoing percutaneous coronary intervention (PCI).

RESEARCH DESIGN AND METHODS

Primary studies and reviews in the peer-reviewed, English-language literature were identified through searches of MEDLINE (1966-2008) using the terms 'acute coronary syndrome', 'antiplatelet', 'aspirin', 'long-term management', 'P2Y(12) receptor', and 'thienopyridine'. Additional references were obtained by searching the reference lists of the identified articles. Articles were included if they were recently published and pertinent, patient-focused, and authors were recognized as leaders in the field. Current review is limited by literature search on single database.

RESULTS

Platelets play a major role in atherogenesis and the formation of thrombi, the main events in the pathogenesis of ACS. Although aspirin is an effective antiplatelet agent, efficacy and safety data from a number of randomized clinical trials on atherothrombotic disease support the use of dual antiplatelet therapies such as aspirin and thienopyridines over single antiplatelet therapy for ACS and up to 1 year following ACS. Antiplatelet agents reduce, but do not eliminate, ischemic events after ACS due, in part, to variable individual response (or resistance) in antiplatelet agents, non-compliance, progression of atherosclerosis, modest inhibition of platelet aggregation (IPA) levels and other factors. Several antiplatelet agents, including novel P2Y(12)-receptor antagonists and thrombin-receptor antagonists, are currently under investigation for ACS and primary and secondary prevention in the long-term management of patients undergoing PCI.

CONCLUSIONS

Current antiplatelet therapies have clinical benefits such as reducing immediate and long-term cardiovascular risk, but substantial residual risk remains indicating a need for new therapeutic agents. Additional large randomized trials are necessary to determine the most appropriate treatment regimens for ACS patients.

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?

Aspirin resistance: focus on clinical endpoints

INTRODUCTION

Via its antiplatelet effect, aspirin reduces the odds of an arterial thrombotic event in high-risk patients by approximately 25%. However, 10% to 20% of patients with an arterial thrombotic event who are treated with aspirin have a recurrent arterial thrombotic event during long-term follow-up. Nevertheless, the effectiveness of aspirin has been questioned by the emergence of the concept of aspirin resistance, which has been introduced as an explanation of the fact that a considerable proportion of patients treated with aspirin exhibit normal platelet function.

OBJECTIVES AND METHODS

We systematically reviewed all available evidence till March 2008 on prevalence of aspirin resistance and its association with clinical outcome. We also collected articles showing the possible way of treatment.

CONCLUSION

Analyzing the data of different laboratory methods aspirin resistance seems to be associated with poor clinical outcome, although currently no standardized or widely accepted definition of aspirin resistance exists. The widely used laboratory methods might not be comparable with each other; therefore, specific treatment recommendations for patients who exhibit high platelet reactivity during aspirin therapy or who have poor platelet inhibition by aspirin are not established.

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

Impaired responses to antiplatelet therapy assessed by laboratory tests are associated with an increased risk of recurrent ischemic events after percutaneous coronary intervention (PCI). This study was designed to determine the relation between responses to aspirin and clopidogrel as assessed by a point-of-care assay (Verify Now, Accumetrics, San Diego, California) and periprocedural myocardial infarction (PMI) in patients undergoing elective PCI for stable angina. One hundred twenty-two consecutive patients undergoing elective coronary stenting prospectively received aspirin 500 mg and clopidogrel 600 mg >or=12 hours before PCI. Clopidogrel response was measured with P2Y12 reaction units (PRUs) and percent inhibition P2Y12 from baseline (percent inhibition P2Y12) and aspirin response with aspirin reaction units (ARUs). Troponin T level was considered positive if it was >0.03 ng/ml. Responses to aspirin and clopidogrel were correlated (r=0.42, p <0.0001). PMI occurred in 27 patients (22%) who showed significantly lower percent inhibition P2Y12 (25.3+/-26 vs 38.3+/-25, p=0.01) and a trend toward higher PRU values (221+/-87 vs 193+/-94, p=0.21). We did not find any difference for aspirin response as assessed by ARUs in patients with or without PMI (460+/-82 vs 454+/-73, p = 0.82). Stratification of percent inhibition P2Y12 isolated a quartile of clopidogrel nonresponders (inhibition P2Y12 <15%) with significantly higher incidence of PMI (44% vs 15%, odds ratio 4.6, 95% confidence interval 1.9 to 11.5, p=0.001). In conclusion, point-of-care assessment of clopidogrel response reliably predicted PMI after low- to medium-risk elective PCI for stable angina.

Aspirin and clopidogrel resistance

Aspirin and clopidogrel provide significant clinical benefit in patients with cardiovascular disease. However, given the complexity of platelet activation, it is not surprising that aspirin or clopidogrel prevent a small proportion of cardiovascular events. Of late, the terms aspirin and clopidogrel "resistance" have entered the physicians' lexicon, and infer a lack of therapeutic response and a single underlying mechanism, which is misleading. The incidence of "resistance" detected in studies varies with the definition applied and assay used to measure response. Rather than true resistance, however, there is a variable response that reflects the unique pharmacology and pharmacokinetics of each drug, the clinical significance of which remains to be established. True "aspirin resistance" implies that cyclooxygenase-1 is less sensitive to inactivation by aspirin. Despite 95% inhibition of serum thromboxane B(2) by aspirin, residual platelet aggregation is detected in some cases, the clinical significance of which is unknown. Heritable factors directly and indirectly related to platelet cyclooxygenase may influence aspirin response. In contrast to aspirin, the response to clopidogrel is highly variable and reflects the bioavailability of the active metabolite and not "resistance" of the receptor to inhibition.