Aspirin resistance measured by cationic propyl gallate platelet aggregometry and recurrent cardiovascular events during 4 years of follow-up

Personalized allocation of acetylsalicylic acid therapy for secondary prevention of coronary artery disease

Background

A single-daily dose of 75 mg of acetylsalicylic acid inhibits 100% of thromboxane-B2 synthesis within 30–60 min. Thromboxane-B2 synthesis then recovers slowly as new platelets are released from the bone marrow. Normally, only 10% of the platelets are replaced daily by new platelets entering circulation. Hence, 24 h after a dose of acetylsalicylic acid, thromboxane-B2 synthesis is still suppressed by more than 90%. Hence, there is an adequate anti-platelet effect even after 24 h of acetylsalicylic acid intake. However, some patients treated with once-daily acetylsalicylic acid may have an incomplete 24-h suppression of thromboxane-B2 synthesis due to increased platelet turnover. The response could be improved in such patients by twice-daily acetylsalicylic acid administration. This study aimed to identify such a group of patients who would benefit from a twice-daily dose of acetylsalicylic acid.

Materials and methods

Serum thromboxane-B2 levels were measured in 79 patients with coronary artery disease receiving 75 mg of acetylsalicylic acid for secondary prophylaxis. Serum levels of thromboxane-B2 were measured after 4 and 24 h of acetylsalicylic acid intake. Patients were then classified into three groups: steady suppression group (serum thromboxane B2 is adequately suppressed at 4 and 24 h), i.e., adequate response to acetylsalicylic acid; fast recovery group (more than 10% rise in serum thromboxane-B2 levels at 24-h when compared to at 4-h) and non-responders (serum thromboxane-B2 levels of >3,100 pg/ml after 4 h of acetylsalicylic acid intake). Patients in the fast recovery group were given twice-daily acetylsalicylic acid and thromboxane-B2 levels were re-measured.

Results

A total of 20 patients (24.3%) had steady suppression of thromboxane-B2 and 11 patients (13.9%) belonged to the fast recovery group, i.e., thromboxane-B2 levels were adequately suppressed at 4 h but had recovered by more than 10% at 24 h; which was adequately suppressed by twice-daily acetylsalicylic acid (p 0.004). A total of 48 patients (60.8%) were non-responders.

Conclusion

Twice-daily acetylsalicylic acid may be beneficial if serum thromboxane-B2 levels at 4 h are <3,100 and >3,100 pg/ml at 24 h. If thromboxane-B2 levels at 4 and 24 h is <3100 pg/ml but if there is a >10% rise in serum thromboxane B2 at 24 h as compared to that at 4 h, then twice-daily acetylsalicylic acid should be considered. However, if thromboxane-B2 at 4 and 24 h is >3,100 pg/ml consider switching over to a P2Y12 inhibitor.

Platelet function in stroke/transient ischemic attack patients treated with tocotrienol

The purpose of this study was to characterize the effects of tocotrienol form of vitamin E (TCT) on platelet function in patients with stroke or transient ischemic attack (TIA). A double blind, randomized, single center phase II clinical trial was conducted comparing placebo (PBO) and 400 and 800 mg TCT daily for a year in 150 patients with a sentinel ischemic stroke or TIA event in the prior 6 months. Platelet function was measured at baseline and then, at 3 month intervals for a year, using light transmission aggregometry. The incidence of aspirin resistance in aspirin-treated patients or platelet inhibition in patients on clopidogrel alone was compared between the three treatment groups. Results showed that in patients taking aspirin and clopidogrel, the incidence of aspirin resistance was significantly decreased from 40% in PBO-treated patients to 9% in the 400 mg TCT group and 25% in the TCT 800 mg group (P = .03). In conclusion, patients on aspirin and clopidogrel had a higher incidence of aspirin resistance than all patients treated with aspirin alone and TCT decreased the frequency of aspirin resistance in this group.

Metabolomic Analysis of Platelets of Patients With Aspirin Non-Response

Background: Aspirin is the most commonly used antiplatelet agent for the prevention of cardiovascular diseases. However, a certain proportion of patients do not respond to aspirin therapy. The mechanisms of aspirin non-response remain unknown. The unique metabolomes in platelets of patients with coronary artery disease (CAD) with aspirin non-response may be one of the causes of aspirin resistance.

Materials and Methods: We enrolled 29 patients with CAD who were aspirin non-responders, defined as a study subject who were taking aspirin with a platelet aggregation time less than 193 s by PFA-100, and 31 age- and sex-matched patients with CAD who were responders. All subjects had been taking 100 mg of aspirin per day for more than 1 month. Hydrophilic metabolites from the platelet samples were extracted and analyzed by nuclear magnetic resonance (NMR). Both 1D ¹H and 2D J-resolved NMR spectra were obtained followed by spectral processing and multivariate statistical analysis, such as partial least squares discriminant analysis (PLS-DA).

Results: Eleven metabolites were identified. The PLS-DA model could not distinguish aspirin non-responders from responders. Those with low serum glycine level had significantly shorter platelet aggregation time (mean, 175.0 s) compared with those with high serum glycine level (259.5 s). However, this association became non-significant after correction for multiple tests.

Conclusions: The hydrophilic metabolic profile of platelets was not different between aspirin non-responders and responders. An association between lower glycine levels and higher platelet activity in patients younger than 65 years suggests an important role of glycine in the pathophysiology of aspirin non-response.

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.

Antiplatelet resistance and the role of associated variables in stable patients treated with stenting

Introduction

Nowadays, clopidogrel and acetylsalicylic acid (ASA) have become routinely applied therapies in percutaneous coronary interventions (PCI) with stenting.

Aim

Numerous variables can interfere with antiplatelet responsiveness, so we aimed to investigate the role of different variables associated with ASA or clopidogrel resistance in stable coronary artery disease.

Material and methods

A total of 207 patients undergoing elective PCI were included in the analysis. All patients received a loading dose of clopidogrel and ASA during PCI procedure and followed by dual antiplatelet therapy. Clopidogrel and ASA resistance were measured by impedance aggregometry method.

Results

Of the patients, 19.8% had clopidogrel resistance, 18.8% had ASA resistance, 9.2% had both clopidogrel and ASA resistance, and 71.5% were responsive to both drugs. In multivariate analysis, platelet count, angiotensin receptor blocker (ARB) use, and ASA resistance were independent variables associated with clopidogrel resistance, and clopidogrel resistance was the only variable associated with ASA resistance. In differentiating whether clopidogrel resistance exists or not, optimum ASA aggregometry response cut-off values were specified, and in differentiating whether ASA resistance exists or not, optimum clopidogrel aggregometry response cut-off values were specified.

Conclusions

In this study, there was a higher incidence of low responsiveness to ASA when there was a low response to clopidogrel, and vice versa. Angiotensin receptor blocker use, platelet count, and ASA resistance were independent variables associated with clopidogrel resistance. Clopidogrel resistance was the only independent variable associated with ASA resistance. Angiotensin receptor blocker use seems to an independent risk factor for clopidogrel resistance in this study, but this result needs to be verified in other studies.

Prevalence of and risk factors for aspirin resistance in elderly patients with coronary artery disease

Objective

To assess the prevalence of and related risk factors for aspirin resistance in elderly patients with coronary artery disease (CAD).

Methods

Two hundred and forty-six elderly patients (75.9 ± 7.4 years) with CAD who received daily aspirin therapy (≥ 75 mg) over one month were recruited. The effect of aspirin was assessed using light transmission aggregometry (LTA) and thrombelastography platelet mapping assay (TEG). Aspirin resistance was defined as ≥ 20% arachidonic acid (AA)-induced aggregation and ≥ 70% adenosine diphosphate (ADP)-induced aggregation in the LTA assay. An aspirin semi-responder was defined as meeting one (but not both) of the criteria described above. Based on the results of TEG, aspirin resistance was defined as ≥ 50% aggregation induced by AA.

Results

As determined by LTA, 23 (9.3%) of the elderly CAD patients were resistant to aspirin therapy; 91 (37.0%) were semi-responders. As determined by TEG, 61 patients (24.8%) were aspirin resistant. Of the 61 patients who were aspirin resistant by TEG, 19 were aspirin resistant according to LTA results. Twenty-four of 91 semi-responders by LTA were aspirin resistant by TEG. Multivariate logistic regression analysis revealed that elevated fasting serum glucose level (Odds ratio: 1.517; 95% CI: 1.176–1.957; P = 0.001) was a significant risk factor for aspirin resistance as determined by TEG.

Conclusions

A significant number of elderly patients with CAD are resistant to aspirin therapy. Fasting blood glucose level is closely associated with aspirin resistance in elderly CAD patients.

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.

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.

Dose-related effect of aspirin on laboratory-defined platelet aggregation and clinical outcome after coronary stenting

BACKGROUND

Acetylsalicylic acid (aspirin) is widely used in the secondary prevention of coronary artery disease. There is controversy regarding the prevalence of aspirin resistance in patients with coronary artery disease and the effect of dose on resistance. Our primary aims were to determine the degree of platelet responsiveness to aspirin, and to study the influence of dose on platelet inhibition and clinical outcomes after coronary stenting.

METHODS AND RESULTS

We prospectively studied the effect of aspirin on platelet function in 106 stable outpatients 6 months after successful percutaneous coronary angioplasty. Participants were randomized in a double-blind, double-crossover study (80 or 500 mg per day for 6 months). The platelet response to aspirin was determined by 10 micromol/L adenosine-5-diphosphate-induced aggregation with light transmission aggregometry. The clinical outcome was determined by single photon emission computed tomography with Tc-99m, and major adverse cardiac events were recorded (myocardial infarction, death, unstable angina or need for revascularization). In both groups 30.2% of the participants were resistant to aspirin. There was no significant difference between the dose of 80 mg compared to 500 mg aspirin in the incidence of aspirin resistance (P= 0.3). No correlation was found between aspirin resistance and clinical outcome (P= 0.4). Female sex and smoking were strongly associated with aspirin resistance.

CONCLUSION

The frequency of aspirin resistance is not dependent on the dose of aspirin. Female sex and smoking were the strongest predictors of aspirin resistance. Aspirin resistance is not a predictor of poor clinical outcome in patients who received double antiplatelet therapy.

Significance of mean platelet volume on prognosis of patients with and without aspirin resistance in settings of non-ST-segment elevated acute coronary syndromes

Platelet volume is a marker of platelet function and activation. An elevated mean platelet volume (MPV) is associated with acute coronary syndromes (ACS). Recurrent cardiovascular events were found to be higher in patients with aspirin resistance. In this study, we investigated the effect of MPV on prognosis of patients with and without aspirin resistance by PFA-100 in settings of non-ST-segment elevated ACS. Two hundred and twenty patients with ACS were followed for an average of 14.86 +/- 5.93 months for the occurrence of death, myocardial infarction (MI) and revascularization. Aspirin effect on platelet function was assessed by PFA-100. According to MPV value and aspirin resistance status, patients were divided into four groups. Group 4 (with an elevated MPV and aspirin resistance) was significantly associated with worse prognosis for composite endpoint (death, MI and revascularization), death and MI (for all, log-rank P < 0.0001). Multivariate analysis showed that presence of an elevated MPV and aspirin resistance was an independent predictor of composite endpoint [hazard ratio 8.21, 95% confidence interval (CI) 3.48-19.35, P < 0.0001], death (hazard ratio 5.48, 95% CI 1.62-18.53, P = 0.006) and MI (hazard ratio 4.44, 95% CI 1.57-12.58, P = 0.005). Presence of an elevated MPV and aspirin resistance was significantly associated with death, MI and the composite endpoint, due to the lack of beneficial effect of aspirin on activated platelets. Patients with ACS, especially in the presence of an elevated MPV may benefit from the evaluation of aspirin resistance for risk stratification.

Aspirin resistance and compliance with therapy

INTRODUCTION

Aspirin resistance is associated with increased cardiovascular risk in aspirin-treated patients. Poor compliance may explain many cases of "resistance," yet few clinical studies have used objective measurement of therapy compliance. We did so in a case-controlled study.

METHODS

We enrolled patients within 24 h of ischemic stroke and a group of controls taking aspirin who had never suffered a vascular event on therapy. All claimed to be compliant. We assessed platelet function using platelet function analyser (PFA)-100 and rapid platelet function analyser (RPFA) devices, applying standard definitions of resistance. We used high-performance liquid chromatography for levels of aspirin metabolites in the urine to confirm compliance with therapy. We compared rates of resistance in stroke patients and controls, and performed subgroup analysis restricted to patients with objective confirmation of recent aspirin ingestion.

RESULTS

We recruited 90 cases and 90 controls. Complete platelet function tests were available in 177. Resistance rates seen in cases and controls, respectively, were: resistance on one or more test, 30 (34%) versus 21 (25%), P= 0.19; on PFA-100 testing only, 28 (32%) versus 15 (18%), P= 0.031; on RPFA testing only, 16 (18%) versus 12 (14%), P= 0.54; resistance on both tests, 12 (14%) versus 5 (6%), P= 0.037. When only patients with objective evidence of recent aspirin ingestion were considered (n = 71), rates were similar regardless of definition of resistance used.

CONCLUSION

Aspirin resistance is common but poor compliance accounted for nearly half of cases of apparent aspirin "failure." Objective measures to assess compliance are essential in studies of aspirin resistance.

Hostility and platelet reactivity in individuals without a history of cardiovascular disease events

OBJECTIVE

To examine the association between hostility and platelet reactivity in individuals without a prior history of cardiovascular disease (CVD) events. Hostility is associated with incident CVD events, independent of traditional risk factors. Increased platelet reactivity and thrombus formation over a disrupted coronary plaque are fundamental for CVD event onset.

METHODS

Hypertensive patients (n = 42) without concomitant CVD event history completed the 50-item Cook-Medley Hostility Scale, and a subset score of 27 items (Barefoot Ho) was derived. We examined the relationship between Barefoot Ho scores and platelet aggregation. We also examined individual components of Barefoot Ho (aggressive responding, cynicism, and hostile affect) and their associations with platelet aggregation. Platelet reactivity, induced by adenosine diphosphate (ADP), was assessed by standard light transmission aggregometry, the current gold standard method of platelet aggregation assessment.

RESULTS

Barefoot Ho scores were related significantly to increased rate of platelet aggregation in response to ADP. Of the three Barefoot Ho components, only aggressive responding was associated independently with increased platelet aggregation rate. The strength of these relationships did not diminish after adjusting for several standard CVD risk factors.

CONCLUSIONS

These data demonstrate that hostility, particularly the aggressive responding subtype, is associated with platelet reactivity-a key pathophysiological pathway in the onset of CVD events.

Antiplatelet drug 'resistance'. Part 1: mechanisms and clinical measurements

Antiplatelet drug therapy has become one of the cornerstones of treatment for patients with cardiovascular disease. Large clinical trials have shown that antiplatelet medications have important clinical benefits and prevent adverse outcomes in patients with coronary artery disease. Recurrent adverse cardiovascular events still occur in a substantial proportion of patients on standard dual antiplatelet therapy, however, which has been attributed to nonresponsiveness to this treatment. Both pharmacological and pharmacokinetic mechanisms are involved in variability in responsiveness to antiplatelet agents, and include drug bioavailability, medication noncompliance, drug-drug interactions, cytochrome P450 activity, and genetic polymorphisms. Numerous observational studies have consistently shown an association between antiplatelet drug nonresponsiveness and adverse clinical outcomes. However, these studies are limited by varying antiplatelet drug dosing regimens, heterogeneous laboratory assessments for ex vivo platelet function, and wide interindividual variation in platelet responses. Only within the last 2 years have randomized clinical trials indicated that increased dosing with antiplatelet drugs could reduce adverse clinical outcomes. Nonetheless, large clinical trials with standardized laboratory methods and well-defined protocols are needed that will definitively determine the association between antiplatelet drug nonresponsiveness and clinical events, and establish therapeutic strategies to overcome blunted antiplatelet effects.

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.

Variability in responsiveness to oral antiplatelet therapy

Patients who have acute coronary syndromes or are undergoing percutaneous coronary intervention receive antiplatelet therapy to reduce the risk of atherothrombotic complications. Current guidelines favor the use of aspirin in combination with clopidogrel based on the results of a number of large-scale clinical trials. Aspirin alone is a relatively weak antiplatelet agent because it inhibits only one of many paths to platelet activation. By blockade of an adjunctive signaling pathway, the addition of clopidogrel to aspirin leads to synergistic platelet inhibitory effects. Dual antiplatelet therapy reduces the number of patients who experience adverse cardiovascular outcomes by 20% over aspirin alone. Nevertheless, approximately 10% of patients experience further atherothrombotic events, even while receiving dual antiplatelet therapy. Variability in individual responsiveness, including "resistance," has been attributed to the occurrence of these events. This article discusses variability in individual responses to oral antiplatelet therapy and its implications for clinical outcomes.

Aspirin resistance: disparities and clinical implications

Abstract Aspirin is one of the most widely prescribed drugs for the prevention of thrombosis in patients with vascular disease. Yet, aspirin is unable to prevent thrombosis in all patients. The term "aspirin resistance" has been used to broadly define the failure of aspirin to prevent a thrombotic event. Whether this is directly related to aspirin itself through biochemical aspirin resistance or treatment failure, or if it is because of aspirin's inability to overcome the thrombogenic aspects of the disease process itself, has not been elucidated. This can have dramatic clinical implications for a variety of vascular disease subsets and is cause for concern, considering the high prevalence of aspirin use for both primary and secondary prevention. Disparities exist in the rates of aspirin resistance among certain patient populations, such as women, patients with diabetes mellitus, and those with heart failure, and across clinical conditions, such as cardiovascular and cerebrovascular disease. Clinical trial data from studies observing resistance have revealed that regardless of study size, dose of aspirin, control for drug interactions and adherence, or assay used to measure platelet function, aspirin resistance is associated with an increased risk for adverse events. Although the evidence is mounting, there has yet to be a consensus on the appropriate clinical response to aspirin resistance.

Aspirin resistance in atherosclerosis

Clinically, aspirin resistance is defined as the failure of aspirin therapy to prevent an acute vascular thrombotic event despite regular intake of appropriate doses. In the laboratory, aspirin resistance encompasses the drug's failure to attain a particular level of platelet inhibition. From a clinical standpoint, the inability of aspirin to prevent a thrombotic event, despite appropriate cyclooxygenase-1 inhibition, implies the involvement of other factors. Evidence is emerging that aspirin resistance, as defined by residual platelet activity, merely reflects an individual's enhanced basal platelet function and suggests a hereditary component. Due to the multifactorial nature of cardiovascular disease, it is likely that a single therapy like aspirin cannot fully treat and prevent all thrombotic complications in the setting of atherosclerosis.

The effect of acetylsalicylic acid resistance on prognosis of patients who have developed acute coronary syndrome during acetylsalicylic acid therapy

AIM

The relationships between clinical events and acetylsalicylic acid resistance (AR), as well as its frequency, have been established in stable patients with coronary artery disease (CAD). Although acute coronary syndrome (ACS) patients taking acetylsalicylic acid have been accepted as a high-risk population, the role of AR has not been investigated in these patient groups. Thus, in the present study, the impact of AR was investigated in patients with ACS who were taking acetylsalicylic acid.

METHODS

Between January 2001 and February 2003, 140 ACS patients were included in the present prospective study. All patients had ACS while taking acetylsalicylic acid. Coronary angiographic scores for severity and extent of CAD were determined for all patients. The effect of acetylsalicylic acid on platelet function was assessed by the platelet function analyzer PFA-100 (Dade Behring, USA). The primary end point was the composite of death, myocardial infarction, cerebrovascular accident and revascularization. The mean follow-up period was 20 months.

RESULTS

Patients with AR were older than patients without AR (63.8+/-10.8 years versus 58.3+/-11.2 years; P=0.005). Moreover, myocardial damage was higher in patients with AR according to cardiac troponin T values (1.11+/-1.3 mug/L versus 0.41+/-0.5 mug/L; P=0.01). The composite end point of death, myocardial infarction, cerebrovascular accident or revascularization was present in 16 of 45 patients (35%) with AR and in 13 of 79 patients (16%) without AR (hazard ratio 2.46, 95% CI 1.18 to 5.13; P=0.016). After adjustment for age, platelet count, cardiac troponin T value and CAD severity score, AR remained an independent predictor for long-term adverse events (hazard ratio 3.03, 95% CI 1.06 to 8.62; P=0.038).

CONCLUSIONS

The clinical event rate was found to be higher in ACS patients with AR than in those without AR. Thus, it may be concluded that there is a strong correlation between a worse prognosis and AR in these patients.