Clinical relevance of aspirin resistance in patients with stable coronary artery disease: a prospective follow-up study (PROSPECTAR)

vWF/ADAMTS13 is associated with on-aspirin residual platelet reactivity and clinical outcome in patients with stable coronary artery disease

Background

The mechanisms behind residual platelet reactivity (RPR) despite aspirin treatment are not established. It has been shown that coronary artery disease (CAD) patients with high on-aspirin RPR have elevated levels of von Willebrand factor (vWF). ADAMTS13 is a metalloprotease cleaving ultra large vWF multimers into less active fragments.

Our aim was to investigate whether ADAMTS13 and vWF/ADAMTS13 ratio were associated with high RPR, and further with clinical endpoints after 2 years.

Methods

Stable aspirin-treated CAD patients (n = 999) from the ASCET trial. RPR was assessed by PFA-100. ADAMTS13 antigen and activity were analysed using chromogenic assays. Endpoints were a composite of acute myocardial infarction, stroke and death.

Results

The number of patients with high RPR was 258 (25.8%). Their serum thromboxane B₂ (TxB₂) levels were low, indicating inhibition of COX-1. They had significantly lower levels of ADAMTS13 antigen compared to patients with low RPR (517 vs 544 ng/mL, p = 0.001) and significantly lower ADAMTS13 activity (0.99 vs 1.04 IU/mL, p = 0.020). The differences were more pronounced when relating RPR to ratios of vWF/ADAMTS13 antigen and vWF/ADAMTS13 activity (p < 0.001, both). We found an inverse correlation between vWF and ADAMTS13 antigen (r = −0.14, p < 0.001) and ADAMTS13 activity (r = −0.11, p < 0.001). No correlations between TxB₂ and ADAMTS13 antigen or activity, were observed, implying that ADAMTS13 is not involved in TxB2 production. Patients who experienced endpoints (n = 73) had higher vWF level (113 vs 105%, p = 0.032) and vWF/ADAMTS13 antigen ratio (0.23 vs 0.20, p = 0.012) compared to patients without. When dichotomizing vWF/ADAMTS13 antigen at median level we observed that patients above median had higher risk for suffering endpoints, with an adjusted OR of 1.86 (95% CI 1.45, 2.82).

Conclusion

These results indicate that ADAMTS13 is of importance for RPR, and that it in combination with vWF also is associated with clinical endpoints in stable CAD patients on aspirin.

Trial registration

Clinicaltrials.gov NCT00222261. Registered 13.09.2005. Retrospectively registered.

Electronic supplementary material

The online version of this article (10.1186/s12959-017-0151-3) contains supplementary material, which is available to authorized users.

The Prevalence and Clinical Relevance of ASA Nonresponse After Cardiac Surgery: A Prospective Bicentric Study

We aimed to identify the prevalence of acetylsalicylic acid (ASA) nonresponse in patients after coronary artery bypass graft (CABG) surgery and the possible consequences for the rate of major cardiovascular events. This prospective, observational, bicentric cohort study was conducted in two German University hospitals. A total of 400 patients (200 in each study center) undergoing elective CABG surgery were enrolled after written informed consent. Platelet function was analyzed on day 3 (d3) and day 5 (d5) postoperatively following stimulation with arachidonic acid (ASPItest) and with thrombin receptor-activating peptide 6 (TRAPtest) using multiple electrode aggregometry (Multiplate). Individuals with an ASPItest ≥40 AU·min were categorized as ASA nonresponders. A 1-year follow-up recorded the combined end point of cardiovascular events, hospital admissions, or deaths related to cardiovascular disease. The prevalence of ASA nonresponse was 51.5% on d3, and it significantly increased to 71.3% on d5 ( P = .0049). The area under the aggregation curve in the TRAPtest ( P < .0001), the platelet count on d5 ( P = .009), and the cardiopulmonary bypass time ( P = .01) were identified as independent predictors of an ASA nonresponse. A 1-year follow-up recorded 54 events fulfilling criteria for the combined end point with no difference between ASA responders and nonresponders. This study indicates a high incidence of perioperative ASA nonresponse in patients following CABG. No effect on the incidence of cardiovascular events was recorded in the 1-year follow-up. Therefore, a randomized dosage adjustment trial should elucidate whether a tailored ASA treatment after CABG surgery represents a useful concept.

Secondary Prevention Beyond Hospital Discharge for Acute Coronary Syndrome: Evidence-Based Recommendations

In the past 3 decades, a better understanding of the pathophysiology of cardiovascular disease has resulted in innovations in the treatment and prevention of its clinical manifestations such as death, myocardial infarction, or stroke. After an acute coronary syndrome there are short- and long-term risks of subsequent cardiovascular events. This leads to opportunities to initiate strategies to reduce complications resulting from myocardial injury (cardiac protection) and to prevent recurrent acute coronary events (vascular protection). The results from clinical trials inform best practice and guidelines for patient management. Despite clear and consistent guidelines, an important number of patients are not receiving these treatments. Moreover, many others do not receive treatment that follows the strategy proven in the clinical trial and this is associated with a significant loss of opportunities to improve outcomes. The Canadian Heart Research Centre has therefore assembled a panel of experts to provide a review of available data and distill it to specific evidence-based recommendations that can be used by specialists and primary care physicians as a platform for secondary prevention. The therapeutic recommendations are conveniently divided into vascular protection (dual antiplatelet therapy, lipid-lowering, and renin angiotensin system inhibition) which should be considered in all patients; cardiac protection (addition of β-blocker therapy) in patients with left ventricular dysfunction including consideration for management of heart failure; and continuing management of risk factors and comorbid conditions on the basis of the specific patient profile. These recommendations are intended as a decision support tool and a quick reference for Canadian physicians.

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.

Platelet function testing: state of the art

Platelet function testing has evolved from crude tests, such as the bleeding time, to tests that permit a relatively sophisticated evaluation of platelet activity. Nonetheless, these tests are hampered by lack of specificity and sensitivity, and poor standardization of methods and techniques. The bleeding time, which has long been a staple of hemostasis testing, has been dropped from the test menu at many laboratories. In its place, tests such as the Platelet Function Analyzer-100 are increasingly used to screen patients with possible bleeding disorders. Older tests, such as platelet aggregometry and lumiaggregometry, are still used frequently because they provide insight into receptor, signaling pathway and granule release mechanisms. Flow cytometry is available in some specialized laboratories and allows for quantitative and qualitative assessment of some platelet functions, although the expense of testing is often prohibitive. Finally, the wider availability of platelet function testing has stimulated interest and demand for monitoring the effect of platelet inhibitory drugs, such as aspirin and clopidogrel. As platelet function pathways become better understood, the demand for these type of monitoring tests is likely to increase.

Aspirin treatment failure: is this a real phenomenon? A review of the aetiology and how to treat it

Multiple clinical trials have shown that aspirin can reduce all cardiovascular events in primary and secondary prevention and yet there is a large population in whom aspirin fails. This review brings together the evidence and controversies surrounding the definition of ‘aspirin treatment failure’, its clinical significance and the possible approaches to managing such patients. Several different assays have been developed to measure the biochemical action of aspirin. At present there is no ‘gold standard’ and there is massive disparity between methods. Studies thus far have shown inconsistent results and to date the treatment of aspirin therapy failure is left to the discretion of the leading physician.

Preoperative aspirin resistance does not increase myocardial injury during off-pump coronary artery bypass surgery

We performed a prospective cohort trial on 220 patients undergoing elective off-pump coronary artery bypass surgery and taking aspirin to evaluate the effect of aspirin resistance on myocardial injury. The patients were divided into aspirin responders and aspirin non-responders by the value of the aspirin reaction units obtained preoperatively using the VerifyNow™ Aspirin Assay. The serum levels of troponin I were measured before surgery and 1, 6, 24, 48 and 72 hr after surgery. In-hospital major adverse cardiac and cerebrovascular events, graft occlusion, the postoperative blood loss and reexploration for bleeding were recorded. Of the 220 patients, 181 aspirin responders (82.3%) and 39 aspirin non-responders (17.7%) were defined. There were no significant differences in troponin I levels (ng/mL) between aspirin responders and aspirin non-responders: preoperative (0.04 ± 0.08 vs 0.03 ± 0.06; P = 0.56), postoperative 1 hr (0.72 ± 0.87 vs 0.86 ± 1.10; P = 0.54), 6 hr (2.92 ± 8.76 vs 1.50 ± 2.40; P = 0.94), 24 hr (4.16 ± 13.44 vs 1.25 ± 1.95; P = 0.52), 48 hr (2.15 ± 7.06 vs 0.65 ± 0.95; P = 0.64) and 72 hr (1.20 ± 4.63 vs 0.38 ± 0.56; P = 0.47). Moreover, no significant differences were observed with regard to in-hospital outcomes. In conclusion, preoperative aspirin resistance does not increase myocardial injury in patients undergoing off-pump coronary artery bypass surgery. Postoperative dual antiplatelet therapy might have protected aspirin resistant patients.

Clinical importance of aspirin and clopidogrel resistance

Aspirin and clopidogrel are important components of medical therapy for patients with acute coronary syndromes, for those who received coronary artery stents and in the secondary prevention of ischaemic stroke. Despite their use, a significant number of patients experience recurrent adverse ischaemic events. Interindividual variability of platelet aggregation in response to these antiplatelet agents may be an explanation for some of these recurrent events, and small trials have linked "aspirin and/or clopidogrel resistance", as measured by platelet function tests, to adverse events. We systematically reviewed all available evidence on the prevalence of aspirin/clopidogrel resistance, their possible risk factors and their association with clinical outcomes. We also identified articles showing possible treatments. After analyzing the data on different laboratory methods, we found that aspirin/clopidogrel resistance seems to be associated with poor clinical outcomes and there is currently no standardized or widely accepted definition of clopidogrel resistance. Therefore, we conclude that specific treatment recommendations are not established for patients who exhibit high platelet reactivity during aspirin/clopidogrel therapy or who have poor platelet inhibition by clopidogrel.

Effects of clopidogrel on "aspirin specific" pathways of platelet inhibition

The most widely accepted methods of assessing response to clopidogrel involve isolated ADP-induced platelet aggregation. Whilst poor response determined by these assays correlates with adverse clinical events, the number of "poor responders" is far higher than the number of events attributed to treatment failure. Clopidogrel may have effects that cannot be assessed using isolated ADP-induced aggregation. We have investigated the effect of clopidogrel on Arachidonic Acid (AA) induced platelet activation-an "aspirin specific" pathway using a novel near patient assay. Thirty four volunteers on no medication and 36 patients, on maintenance therapy with aspirin 75 mg daily, were recruited. Blood tests for Thrombelastogram PlateletMapping were taken immediately prior to and 6 hours after administration of a 600 mg clopidogrel loading dose. Changes in the area under the response curve at 15 minutes (AUC15) with both ADP- and AA-stimulation were calculated as were the corresponding percentage platelet and percentage clotting inhibition (%PIn and %CIn). There were predictable and significant changes in the AUC15 of the ADP channel in response to clopidogrel and the corresponding %PIn and %CIn in both volunteers and patients. There were also significant reductions in the AUC15 of the AA channel (presented as Mean +/- 95%CI), by 27.2 +/- 11.8%, p = 0.005 in volunteers and 35.0 +/- 8.2%, p < 0.001 in patients) and increases in the %PIn and %CIn calculated using the AA channel in volunteers (by 20.0 +/- 11.4%, p + 0.02 and 32.3 +/- 12.8%, p < 0.001 respectively) and patients (by 24.2 +/- 8.6%, p < 0.001 and by 18.0 +/- 8.6, p < 0.001 respectively). Clopidogrel has both independent and aspirin-synergistic effects on AA-induced platelet activation suggesting potentiation of the antiplatelet activity of aspirin. This effect may be clinically important and is not detected by current "gold standard" methods of assessing response to clopidogrel.

Aspirin resistance

The development of adverse cardiovascular events despite aspirin use has established an interest in a possible resistance to the drug. Several definitions have been set and various laboratory testing modalities are available. This has led to a wide range of prevalence reports in different clinical entities. The etiologic mechanism has been related to clinical, genetic, and other miscellaneous factors. The clinical implications of this phenomenon are significant and warrant concern. Management strategies are currently limited to dosing alteration and introduction of other anitplatelet agents. However, these measures have not met the expected efficacy or safety.

Responsiveness to aspirin in patients with unstable angina pectoris by whole blood aggregometry

AIMS

To evaluate aspirin responsiveness in patients with unstable angina pectoris (UAP) by whole blood aggregometry. Another goal was to differentiate aspirin-resistant patients into pharmacokinetic or pharmacodynamic type.

METHODS

We measured platelet aggregation by determining impedance values in 70 normal volunteers and 104 UAP patients on aspirin (100 mg/day > or = 7 days) in four inducing conditions [1 microg/ml collagen, 2 microg/ml collagen, 5 micromol/l adenosine diphosphate (ADP) and 10 micromol/l ADP]. We calculated a cut-off value based on data from normal volunteers to define aspirin responsiveness in cases. Then, the correlation and agreement between the results in the four conditions was analysed to choose a preferred inducing condition for identification of aspirin resistance. Aliquots from all samples were incubated with 0.1 mmol/l aspirin and measured again for aspirin-resistant classification.

RESULTS

Aspirin resistance was observed in 38 patients (36.5%), 51 patients (49.0%), 67 patients (64.4%) and 67 patients (64.4%), respectively, for 1 microg/ml collagen, 2 microg/ml collagen, 5 micromol/l ADP and 10 micromol/l ADP among 104 patients. Collagen at low concentration was suggested as a preferred agent for detecting aspirin inhibitory effect according to the coefficient of sensitivity. After incubation, only three among 38 aspirin-resistant patients showed normal platelet aggregation and were classified into pharmacodynamic type.

CONCLUSIONS

In the presence of collagen at low concentration (1 microg/ml), the prevalence of aspirin resistance is about 36.5% in UAP patients, and according to a classification specific for resistant patients, most of the aspirin 'resistance' is just because of pharmacokinetic issues.

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.

Aspirin resistance: what the cardiologist needs to know?

"Aspirin resistance" can be defined as the inability of aspirin to inhibit cyclooxygenase (COX)-1 dependent thromboxane (TX) A2 production, and consequently TX A2-dependent platelet functions. Several laboratory methods have been proposed, to evaluate platelets' resistance to antiplatelet treatment (bleeding time, light transmission aggregation, impedance aggregation, platelet function analyser, rapid platelet function assay, TXB2, flow cytometry). However, all these methods have their advantages intrinsic limitations. Although aspirin resistance appears to be linked to worse long-term outcomes in cardiovascular disease patients, clinical treatment of aspirin resistance, including an increased aspirin dose or the addition of other antiplatelet drugs, is not often effective. Further studies needed to elucidate the appropriate management of aspirin resistance.

Use of antiplatelet agents for prevention of ischemic stroke

Overall management to lower risk for ischemic stroke is multifaceted. Management includes measures to treat risk factors for accelerated atherosclerosis and stroke, antithrombotic therapies to lower the risk for thromboembolism, and surgery to treat a defined arterial or cardiac lesion. Treatment decisions are made on a case-by-case basis, with most patients receiving some combination of medication and recommendations for lifestyle modification. Some patients will also undergo surgical or endovascular interventions. This article discusses antithrombotic treatment for ischemic stroke prevention, placing major emphasis on the indications for and administration of antiplatelet therapy.

Comparison of collagen versus adenosine diphosphate in detecting antiplatelet effect in patients with coronary artery disease

Widely varying methods of assessing platelet aggregation have resulted in the absence of an established standard approach to assess the effects of antiplatelet drugs. The objective of this study was to compare the roles of collagen and adenosine diphosphate (ADP) in the assessment of effects of aspirin or clopidogrel on platelet aggregation. Sixty patients with documented coronary artery disease were assigned to receive aspirin alone (ASA 100 mg/d) (n=30) or aspirin-plus-clopidogrel (ASA 100 mg/d+C 75 mg/d) (n=30). Platelet aggregation assessment by the use of whole blood aggregation tests with collagen or ADP was performed in these patients and 30 age- and gender-matched normal volunteers. When compared with the control group, therapy with ASA or ASA+C resulted in significant inhibition of collagen-induced platelet aggregation (P<0.001 for each), but there was no statistically significant difference in the results between the ASA and ASA+C groups. When platelet aggregation was induced by ADP, the combined therapy with aspirin and clopidogrel decreased platelet aggregation significantly when compared with aspirin alone (P<0.001), and no significant difference in the results between the ASA and normal groups was observed. In conclusion, collagen may prove useful to study the effect of aspirin and ADP may be appropriate for assessing the inhibitory effect of clopidogrel.

Effects of aspirin and clopidogrel in healthy men measured by platelet aggregation and PFA-100

There are no generally accepted definitions for low-response (frequently called resistance) to the platelet inhibitors, aspirin and clopidogrel. Low-response may increase the risk of cardiovascular events in atherosclerotic patients. We aimed to define the normal drug responses in healthy men. Platelet function was measured in 20 healthy men during 11 days of aspirin or clopidogrel intake, using light transmission aggregometry (LTA) and the Platelet Function Analyzer 100 (PFA-100). The lower limits for LTA at baseline were 64% and 61%, using arachidonic acid and ADP as agonists, respectively. During aspirin intake the LTA results were stable from day to day, and an upper limit of 9% arachidonic acid stimulated aggregation was found. Clopidogrel intake was best shown by ADP induced aggregation. However, two out of 20 individuals exhibited low-response to clopidogrel. In the remaining 18 volunteers an upper limit of 48% aggregation was found. We found an upper limit for collagen-epinephrine stimulated PFA-100 results of 166 s at baseline. During aspirin intake, these results varied considerably from day to day in nine out of 20 men, resulting in an overlap between the reference ranges at baseline and during therapy. In conclusion, platelet inhibition by aspirin and clopidogrel assessed by aggregometry was stable during 11 days of treatment and reference ranges were established. The PFA-100 results varied greatly and low-response was not precisely defined by this method.

The role of aspirin in cardiovascular prevention: implications of aspirin resistance

Aspirin is well recognized as an effective antiplatelet drug for secondary prevention in subjects at high risk of cardiovascular events. However, most patients receiving long-term aspirin therapy still remain at substantial risk of thrombotic events due to insufficient inhibition of platelets, specifically via the thromboxane A2 pathway. Although the exact prevalence is unknown, estimates suggest that between 5.5% and 60% of patients using this drug may exhibit a degree of "aspirin resistance," depending upon the definition used and parameters measured. To date, only a limited number of clinical studies have convincingly investigated the importance of aspirin resistance. Of these, few are of a sufficient scale, well designed, and prospective, with aspirin used at standard doses. Also, most studies do not sufficiently address the issue of noncompliance to aspirin as a frequent, yet easily preventable cause of resistance to this antiplatelet drug. This review article provides a comprehensive overview of aspirin resistance, discussing its definition, prevalence, diagnosis, and therapeutic approaches. Moreover, the clinical implications of aspirin resistance are explored in various cardiovascular disease states, including diabetes mellitus, hypertension, heart failure, and other similar disorders where platelet reactivity is enhanced.

Antiplatelet drug nonresponsiveness

The response to most medication, including antiplatelet drugs, is highly variable between individuals. Observational studies have shown that nonresponders to antiplatelet agents appear to have an increased incidence of vascular events. This review article reviews the background, mechanisms, and evidence in support of the clinical significance of this phenomenon.

Use of the PFA-100 closure time to predict cardiovascular events in aspirin-treated cardiovascular patients: a systematic review and meta-analysis

BACKGROUND

PFA-100 is a point-of-care assay that evaluates platelet reactivity in high-shear-stress conditions by measuring the closure time (CT) of a membrane aperture. When determined with a collagen/epinephrine cartridge (CEPI), the CT is usually prolonged by aspirin. Studies of the predictive value of a short PFA-100CT(CEPI) for ischemic events in aspirin-treated patients have given variable results.

OBJECTIVES

To conduct a systematic review and meta-analysis of studies on the clinical predictive value of a short PFA-100CT(CEPI) in aspirin-treated cardiovascular patients.

PATIENTS AND METHODS

Relevant studies were identified by scanning electronic databases. Studies were selected if they included aspirin-treated patients with symptomatic atherosclerosis, measured the PFA-100CT(CEPI), used a CT cut-off value to define aspirin 'responders' and 'non-responders', and reported ischemic events.

RESULTS

We selected seven non-prospective studies (1466 patients) and eight prospective studies (1227 patients). In non-prospective studies, the PFA-100CT(CEPI) was performed after the ischemic clinical endpoint, and a publication bias was identified. In prospective studies, the global odds ratio (OR) for the recurrence of an ischemic event in 'aspirin non-responders' relative to 'aspirin responders' was 2.1 [95% confidence interval (CI) 1.4-3.4, P < 0.001]. Pooled analysis with a random effect model revealed no heterogeneity (Q Cochran P = 0.36 and I(2) = 9.4%).

CONCLUSIONS

A short PFA-100CT(CEPI) is associated with increased recurrence of ischemic events in aspirin-treated cardiovascular patients. This finding needs to be confirmed in stable ischemic patients, and the PFA-100CT(CEPI) cut-off needs to be refined in these patients.

Abnormal PFA-100 closure time is associated with increased platelet aggregation in patients presenting with chest pain

BACKGROUND

Antiplatelet therapy has been proven to be effective for both primary and secondary prevention of myocardial infarction, stroke, and cardiovascular death. However, a significant proportion of patients treated with aspirin experience ischemic events. A number of prospective studies have demonstrated that decreased responsiveness to antiplatelet therapy as measured by various methods, is strongly associated with an increase in clinical events. Our objective was to characterize platelet function in patients presenting with chest pain using a point-of-care assay, PFA-100 and correlating results to traditional platelet aggregometry to determine if patients with aspirin non-responsiveness have increased clinical sequelae.

METHODS

Platelet function was assessed using PFA-100, flow cytometry, and optical aggregometry in 94 patients presenting to the emergency department with chest pain. All patients were on aspirin 81-325 mg daily. Clinical events occurring during the index hospitalization were documented.

RESULTS

Forty-seven patients (50%) were defined as aspirin non-responders by PFA-100 (collagen-epinephrine closure time <or= 193). Compared to aspirin responders, aspirin non-responders had higher levels of mean platelet aggregation to adenosine diphosphate (ADP) (P = 0.004) and high dose epinephrine (P = 0.03). Furthermore, expression of PAC-1 was significantly increased in patients with aspirin nonresponse as compared to aspirin responders (P = 0.003 and P = 0.0006 respectively). No significant difference in clinical events during the index hospitalization was noted between aspirin non-responders and aspirin responders.

CONCLUSION

Patients presenting with chest pain who have abnormal PFA-100 closure times have increased platelet aggregation and activation however this aspirin non-responsiveness does not correlate with increased clinical events in the index hospitalization.