Non-compliance is the predominant cause of aspirin resistance in chronic coronary arterial disease patients

Contemporary Antiplatelet and Anticoagulant Therapies for Secondary Stroke Prevention: A Narrative Review of Current Literature and Guidelines

PURPOSE OF REVIEW

Stroke is a leading cause of death and disability worldwide. The annual incidence of new or recurrent stroke is approximately 795,000 cases per year in the United States, of which 87% are ischemic in nature. In addition to the management of modifiable high-risk factors to reduce the risk of recurrent stroke, antithrombotic agents (antiplatelets and anticoagulants) play an important role in secondary stroke prevention. This review will discuss the published literature on the use of antiplatelets and anticoagulants in secondary prevention of acute ischemic stroke and transient ischemic attack (TIA), including their pharmacology, efficacy, and adverse effects. We will also highlight the role of dual antiplatelet therapy (DAPT) in secondary stroke prevention, along with supporting literature.

RECENT FINDINGS

Single antiplatelet therapy (SAPT) with aspirin or clopidogrel reduces the risk of recurrent ischemic stroke in patients with non-cardioembolic ischemic stroke or TIA. However, as shown in recent trials, short-term DAPT with aspirin and clopidogrel or ticagrelor for 21-30 days is more effective than SAPT in patients with minor acute non-cardioembolic stroke or high-risk TIA. Although short-term DAPT is highly effective in preventing recurrent stroke, a more prolonged course can increase bleeding risks without additional benefit. DAPT for 90 days, followed by aspirin monotherapy for patients with large vessel intracranial atherosclerotic disease, is suitable for secondary stroke prevention. However, patients need to be monitored for both minor (e.g., bruising) and major (e.g., intracranial) bleeding complications. Conversely, oral warfarin and newer direct oral anticoagulant (DOACs) such as dabigatran, rivaroxaban, apixaban, and edoxaban are the agents of choice for secondary stroke prevention in patients with non-valvular cardioembolic strokes. DOACs may be preferred over warfarin due to decreased bleeding risks, including ICH, lack of need for international normalized ratio monitoring, no dietary restrictions, and limited drug-drug interactions. The choice between different antiplatelets and anticoagulants for prevention of ischemic stroke depends on the underlying stroke mechanism, cytochrome P450 2C19 polymorphisms, bleeding risk profile, compliance, drug tolerance, and drug resistance. Physicians must carefully weigh each patient's relative benefits and bleeding risks before initiating an antiplatelet/anticoagulant treatment regimen. Further studies are warranted to study the optimal duration of DAPT in symptomatic intracranial atherosclerosis since the benefit is most pronounced in the short term while the bleeding risk remains high during the extended duration of therapy.

Antiplatelet Use in Ischemic Stroke

Objective:

A literature review of antiplatelet agents for primary and secondary stroke prevention, including mechanism of action, cost, and reasons for lack of benefit.

Data sources:

Articles were gathered from MEDLINE, Cochrane Reviews, and PubMed databases (1980-2021). Abstracts from scientific meetings were considered. Search terms included ischemic stroke, aspirin, clopidogrel, dipyridamole, ticagrelor, cilostazol, prasugrel, glycoprotein IIb/IIIa inhibitors.

Study selection and data extraction:

English-language original and review articles were evaluated. Guidelines from multiple countries were reviewed. Articles were evaluated independently by 2 authors.

Data synthesis:

An abundance of evidence supports aspirin and clopidogrel use for secondary stroke prevention. In the acute phase (first 21 days postinitial stroke), these medications have higher efficacy for preventing further stroke when combined, but long-term combination therapy is associated with higher hemorrhage rates. Antiplatelet treatment failure is influenced by poor adherence and genetic polymorphisms. Antiplatelet agents such as cilostazol may provide extra benefit over clopidogrel and aspirin, in certain racial groups, but further research in more diverse ethnic populations is needed.

Relevance to patient care and clinical practice:

This review presents the data available on the use of different antiplatelet agents poststroke. Dual therapy, recurrence after initiation of secondary preventative therapy, and areas for future research are discussed.

Conclusions:

Although good evidence exists for the use of certain antiplatelet agents postischemic stroke, there are considerable opportunities for future research to investigate personalized therapies. These include screening patients for platelet polymorphisms that confer antiplatelet resistance and for randomized trials including more racially diverse populations.

Aspirin Use and Transcatheter Pulmonary Valve Replacement, the Need for Consistency

Transcatheter pulmonary valve replacement (TPVR) is a staple in the pediatric cardiac catheterization lab. Despite the ubiquitous use of this procedure, guidelines for antithrombosis post pulmonary valve replacement are non-existent. A survey was sent out via email to the members of the Congenital Cardiovascular Interventional Study Consortium (CCISC) and the Pediatric and Adult Interventional Cardiac Symposium (PICS-AICS). Responses were received from 109 cardiologists who perform this procedure. Following TPVR 76.5% of respondents use only Aspirin, while the remainder prescribe a second antithrombotic agent at discharge. The majority (78%) of respondents do not educate patients about avoiding enteric formulations of aspirin, and another 86% do not educate patients about the need to avoid proton pump inhibitors (PPI). In addition, 67% do not advise against concomitant use of Non-Steroidal Anti-Inflammatory Drugs (NSAIDs). Lastly, the survey showed a wide discrepancy in prescribed dose with 56% choosing to always prescribe 70-100 mg regardless of weight, 28% choosing to do weight-based dosing, and 7.5% choosing 325 mg regardless of weight. In a survey sent out to pediatric cardiac interventionalists worldwide, a significant discrepancy was noted in antithrombotic regimens used following TPVR. We hypothesize that these discrepancies may contribute to early valve failure and suggest the need for further study and the development of unified antithrombosis guidelines following TPVR.

[Evaluation of treatment adaptation for low response to ASA in vascular surgery]

Hintergrund

Eine verminderte antithrombozytäre Prophylaxe („Low-Response [LR]“/„high on-treatment platelet reactivity [HPR]“) mit Acetylsalicylsäure (ASS) ist mit einem erhöhten Risiko für thrombembolische Ereignisse assoziiert. Die Prävalenz einer Low-Response ist mit ca. 20 % häufig und ein Therapieregime wurde bisher noch nicht etabliert. Das Ziel dieser prospektiven Studie war es, die Effektivität eines Therapieschemas zur Therapieanpassung bei detektierter LR/HPR bei gefäßchirurgischen Patienten zu evaluieren.

Methodik

Insgesamt wurden 36 gefäßchirurgischen Patienten mit einer antithrombozytären Dauermedikation mit ASS 100 mg/Tag und einer nachgewiesenen ASS-Low-Response (ALR) in die Studie eingeschlossen. Entsprechend dem festgelegten Therapieplan wurde bei diesen Patienten eine Therapieanpassung durchgeführt und eine Kontrollaggregometrie zur Erfolgskontrolle durchgeführt. Das verwendete Therapieschema folgte dem Test-and-treat-Prinzip. Zur Beurteilung der Wirkung von ASS diente die Impedanzaggregometrie mittels Mehrelektrodenaggregometer (Multiplate).

Ergebnisse

Insgesamt konnten alle 36 Patienten erfolgreich in eine Response überführt werden. Bei 32 (88,89 %) Patienten erfolgte eine Dosiserhöhung auf 300 mg ASS, 2 (5,56 %) Patienten wurden von ASS auf Clopidogrel umgestellt. Bei weiteren 2 (5,56 %) Patienten wurde auf eine orale Antikoagulation mit Phenprocoumon aufgrund anderer Indikationen umgestellt. Blutungskomplikationen oder Nebenwirkungen traten nicht auf.

Schlussfolgerung

Das gewählte Therapieschema zur Behandlung einer Low-Response erwies sich als effektiv und sicher bei gefäßchirurgischen Patienten. Überwiegend führte eine leitliniengerechte Dosiserhöhung der Prophylaxe von 100 mg auf 300 mg ASS zu einer effektiven Thrombozytenaggregationshemmung in der Aggregometrie.

Perioperative changes of response to antiplatelet medication in vascular surgery patients

Introduction

Reduced antiplatelet activity of aspirin (ALR) or clopidogrel (CLR) is associated with an increased risk of thromboembolic events. The reported prevalence data for low-responders vary widely and there have been few investigations in vascular surgery patients even though they are at high risk for thromb-embolic complications. The aim of this prospective observational monocentric study was to elucidate possible changes in ALR or CLR after common vascular procedures.

Methods

Activity of aspirin and clopidogrel was measured by impedance aggregometry using a multiple electrode aggregometer (Multiplate®). Possible risk factors for ALR or CLR were identified by demographical, clinical data and laboratory parameters. In addition, a follow-up aggregometry was performed after completion of the vascular procedure to identify changes in antiplatelet response.

Results

A total of 176 patients taking antiplatelet medications aspirin and/or clopidogrel with peripheral artery disease (PAD) and/or carotid stenosis (CS) were included in the study. The prevalence of ALR was 13.1% and the prevalence of CLR was 32% in the aggregometry before vascular treatment. Potential risk factors identified in the aspirin group were concomitant insulin medication (p = 0.0006) and elevated C-reactive protein (CRP) (p = 0.0021). The overall ALR increased significantly postoperatively to 27.5% (p = 0.0006); however, there was no significant change in CLR that was detected. In a subgroup analysis elevation of the platelet count was associated with a post-procedure increase of ALR incidence.

Conclusion

The incidence of ALR in vascular surgery patients increases after vascular procedures. An elevated platelet count was detected as a risk factor. Further studies are necessary to analyse this potential influence on patency rates of vascular reconstructions.

Clinical Influence of Nonadherence With Prophylactic Aspirin in Preventing Preeclampsia in High-Risk Pregnancies

Aspirin nonadherence and its associated increase in cardiovascular and cerebrovascular events is well described; however, the prevalence of aspirin nonadherence among high-risk pregnant women at risk of preeclampsia and its influence on clinical outcomes remains unclear. Our study examined the prevalence of aspirin nonadherence and resistance among high-risk pregnant women quantitatively (platelet function analyzer 100 and plasma salicylic acid) and clinical outcomes relative to adherence. High-risk pregnant women were recruited across 3 centers in the South West Sydney Local Health District. Simultaneous clinic data, blood sample, and self-reported adherence assessment were prospectively collected at 4-week intervals from 12 to 36 weeks of gestation. Nonadherence was defined as normal platelet function analyzer 100 and nondetectable plasma salicylic acid in <90% of time points. Value of <90% is based on current data. Two hundred twenty women were recruited over 25 months. No woman was aspirin resistant, and 63 (44%) women demonstrated inadequate adherence. Women with inadequate adherence had higher incidence of early-onset preeclampsia (17% versus 2%; odds ratio [OR], 1.9 [95% CI, 1.1–8.7]; P =0.04), late-onset preeclampsia (41% versus 5%; OR, 4.2 [95% CI, 1.4–19.8]; P =0.04), intrauterine growth restriction (29% versus 5%; OR, 5.8; [95% CI, 1.2–8.3]; P =0.001), preterm delivery (27% versus 10%; OR, 5.2 [95% CI, 1.5–8.7]; P =0.008), and higher likelihood of increase in antihypertensives antenatally (60% versus 10%; OR, 4.6 [95% CI, 1.2–10.5]; P =0.003). Kaplan-Meier analysis demonstrated lower incidence of premature delivery in the ≥90% adherent group (HR, 0.3 [95% CI, 0.2–0.5]; P <0.001).Kappa coefficient agreement between qualitative and quantitative assessment of adherence was moderate (κ=0.48; SE=0.029; P <0.0001). Our data demonstrates that aspirin is an effective prophylactic agent with an absolute risk reduction of 51% (number needed to treat, 2) when adherence is ≥90%, compared with women with inadequate adherence. Women who were <90% adherent had higher rates of preeclampsia, intrauterine growth restriction, preterm delivery, and increase in antenatal antihypertensive requirements. Self-reported adherence does not accurately reflect actual adherence.

[Prevalence of acetylsalicylic acid (ASA) - low response in vascular surgery]

BACKGROUND

Research has revealed that a decreased antiplatelet effect (low response [LR]/high on-treatment platelet reactivity [HPR]) of acetylsalicylic acid (ASA) and clopidogrel is associated with an increased risk of thromboembolic events. There are extensive ASA low response (ALR) and clopidogrel low response (CLR) prevalence data in the literature, but there are only a few studies concerning vascular surgical patients. The aim of this study was to examine the prevalence and risk factors of ALR and CLR in vascular surgical patients.

MATERIALS AND METHODS

We examined n = 154 patients with an antiplatelet long-term therapy, who were treated due to peripheral artery occlusive disease (PAD) and/or arteria carotis interna stenosis (CVD). To detect an ALR or CLR, we examined full blood probes with impedance aggregometry (ChronoLog® Aggregometer model 590). Risk factors were examined by acquisition of concomitant disease, severity of vascular disease, laboratory test results and medication.

RESULTS

We found a prevalence of 19.3 % in the ALR group and of 21.1 % in the CLR group. Risk factors for ALR were an increased platelet and leucocyte count and co-medication with pantoprazole. We found no significant risk factors for a decreased antiplatelet effect of clopidogrel treatment.

CONCLUSION

The investigated prevalence for ALR and CLR are in the range of other studies, particularly based on cardiological patients. More investigations are needed to gain a better evaluation of the risk factors for HPR and to develop an effective antiplatelet therapy regime to prevent cardiovascular complications.

How important is aspirin adherence when evaluating effectiveness of low-dose aspirin?

Low-dose aspirin (LDA) is advocated for women at high-risk of pre-eclampsia, providing a modest, 10%, reduction in risk. Cardiology meta-analyses demonstrate 18% reduction in serious vascular events with LDA. Non-responsiveness to aspirin (sometimes termed aspirin resistance) and variable clinical effectiveness are often attributed to suboptimal adherence. The aim of this review was to identify the scope of adherence assessments in RCTs evaluating aspirin effectiveness in cardiology and obstetrics and discuss the quality of information provided by current methods. We searched MEDLINE, EMBASE and the Cochrane Library, limited to humans and English language, for RCTs evaluating aspirin in cardiology; 14/03/13-13/03/16 and pregnancy 1957-13/03/16. Search terms; 'aspirin', 'acetylsalicylic acid' appearing adjacent to 'myocardial infarction' or 'pregnancy', 'pregnant', 'obstetric' were used. 38% (25/68) of obstetric and 32% (20/62) of cardiology RCTs assessed aspirin adherence and 24% (6/25) and 29% (6/21) of obstetric and cardiology RCTs, respectively, defined acceptable adherence. Semi-quantitative methods (pill counts, medication weighing) prevailed in obstetric RCTs (93%), qualitative methods (interviews, questionnaires) were more frequent in obstetrics (67%). Two obstetric RCTs quantified serum thromboxane B₂ and salicylic acid, but no quantitative methods were used in cardiology Aspirin has proven efficacy, but suboptimal adherence is widespread and difficult to accurately quantify. Little is currently known about aspirin adherence in pregnancy. RCTs evaluating aspirin effectiveness show over-reliance on qualitative adherence assessments vulnerable to inherent inaccuracies. Reliable adherence data is important to assess and optimise the clinical effectiveness of LDA. We propose that adherence should be formally assessed in future trials and that development of quantitative assessments may prove valuable for trial protocols.

A brief review on the mechanisms of aspirin resistance

Aspirin is the most widely prescribed drug for the primary and secondary prevention of cardiovascular and cerebrovascular diseases. However, a large number of patients continue to experience thromboembolic events despite aspirin therapy, a phenomenon referred to as aspirin resistance or treatment failure. Aspirin resistance is often observed along with a high incidence of unstable plaque, cardiovascular events and cerebrovascular accident. Studies have shown that aspirin reduces the production of TXA2, but not totally inhibits the activation of platelets. In this review, we analyze current and past research on aspirin resistance, presenting important summaries of results regarding the potential contributive roles of single nucleotide polymorphisms, inflammation, metabolic syndrome and miRNAs. The aim of this article is to provide a brief review on aspirin resistance and platelet function, which will provide important insights into the research of aspirin resistance.

The lack of aspirin resistance in patients with coronary artery disease

Background

Aspirin resistance established by different laboratory methods is still a debated problem. Using COX1 specific methods no aspirin resistance was detected among healthy volunteers. Here we tested the effect of chronic aspirin treatment on platelets from patients with stable coronary artery disease. The expression of COX2 mRNA in platelets and its influences on the effect of aspirin was also investigated.

Methods

One hundred and forty four patients were enrolled in the study. The direct measurement of COX1 acetylation was carried out by monoclonal antibodies specific to acetylated and non-acetylated COX1 (acCOX1 and nacCOX1) using Western blotting technique. Arachidonic acid (AA) induced TXB₂ production by platelets was measured by competitive immunoassay. AA induced platelet aggregation, ATP secretion and VerifyNow Aspirin Assay were also performed. COX2 and COX1 mRNA expression in platelets were measured in 56 patients by RT-qPCR.

Results

In 138 patients only acCOX1 was detected, in the remaining six patients nacCOX1 disappeared after a compliance period. AA induced TXB₂ production by platelets was very low in all patients including the 6 patients after compliance. AA induced platelet aggregation, secretion and with a few exceptions the VerifyNow Assay also demonstrated the effect of aspirin. Smoking, diabetes mellitus and inflammatory conditions did not influence the results. The very low amount of COX2 mRNA detected in 39 % of the investigated platelets did not influence the effect of aspirin.

Conclusions

No aspirin resistance was detected among patients with stable coronary artery disease. COX2 expression in platelets did not influence the effect of aspirin.

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 effects of aspirin in chronic kidney disease patients

ESSENTIALS: Chronic kidney disease (CKD) patients have a high risk of cardiovascular events. A pharmacodynamic evaluation of the effects of aspirin in 116 patients was carried out. The antiplatelet effects of aspirin are associated with impaired renal function. The optimal antithrombotic regimen in CKD patients must be investigated on a larger scale.

BACKGROUND

The pharmacodynamic response to aspirin varies significantly between individuals. Insufficient antiplatelet effects of aspirin are associated with increased risk of ischemic events. Chronic kidney disease (CKD) is suggested to affect the pharmacodynamic response to antiplatelet medication. High on-treatment platelet reactivity (HTPR) to clopidogrel has been reported to partially account for the enhanced risk of death and cardiovascular events in CKD patients. Objective To investigate the antiplatelet effects of aspirin in patients with CKD.

METHODS

We conducted a cross-sectional study in 116 patients on permanent aspirin medication. The pharmacodynamic response to aspirin was determined by arachidonic acid-induced thromboxane formation.

RESULTS

HTPR to aspirin was more frequent in patients with impaired renal function (47% vs. 22%; odds ratio, 3.16; 95% confidence interval [CI], 1.34-7.41; P = 0.008). The pharmacodynamic response to aspirin was impaired in patients with moderate/severe CKD (92; interquartile range [IQR], 282 ng mL(-1) ) as compared to patients with normal/mildly reduced renal function (36; IQR, 100 ng mL(-1) ; difference in medians, 57; CI, 5-110 ng mL(-1) ; P = 0.013). Bivariate Pearson analysis showed residual thromboxane formation to be correlated with glomerular filtration rate (R = -0.303; R(2) = 0.092; P = 0.001). Patients with CKD were older and more frequently female. Multivariate linear regression analysis revealed that the correlation was independent of age (R = -0.314; R(2) = 0.082; P = 0.002) and gender (R = -0.305; R(2) = 0.077; P = 0.006).

CONCLUSION

Renal function is correlated with pharmacodynamic response to aspirin. Patients with CKD have an increased risk of impaired antiplatelet effects of aspirin. Larger trials are needed to assess the clinical impact of this finding and investigate the optimal antithrombotic regimen in CKD patients.

Anti-platelet Therapy Resistance - Concept, Mechanisms and Platelet Function Tests in Intensive Care Facilities

It is well known that critically ill patients require special attention and additional consideration during their treatment and management. The multiple systems and organ dysfunctions, typical of the critical patient, often results in different patterns of enteral absorption in these patients. Anti-platelet drugs are the cornerstone in treating patients with coronary and cerebrovascular disease. Dual anti-platelet therapy with aspirin and clopidogrel is the treatment of choice in patients undergoing elective percutaneous coronary interventions and is still widely used in patients with acute coronary syndromes. However, despite the use of dual anti-platelet therapy, some patients continue to experience cardiovascular ischemic events. Recurrence of ischemic events is partly attributed to the fact that some patients have poor inhibition of platelet reactivity despite treatment. These patients are considered low- or non-responders to therapy. The underlying mechanisms leading to resistance are not yet fully elucidated and are probably multifactorial, cellular, genetic and clinical factors being implicated. Several methods have been developed to asses platelet function and can be used to identify patients with persistent platelet reactivity, which have an increased risk of thrombosis. In this paper, the concept of anti-platelet therapy resistance, the underlying mechanisms and the methods used to identify patients with low responsiveness to anti-platelet therapy will be highlighted with a focus on aspirin and clopidogrel therapy and addressing especially critically ill patients.

Searching for factors associated with resistance to acetylsalicylic acid used for secondary prevention of stroke

INTRODUCTION

The aim of the study was to evaluate the prevalence of resistance to acetylsalicylic acid (ASA), used for secondary prevention of stroke, including the assessment of risk factors associated with the lack of ASA anti-aggregatory action.

MATERIAL AND METHODS

Patients after a transient ischaemic attack (TIA) or ischaemic stroke in the acute (n = 111) and chronic phase (n = 87) were enrolled in the study. The assessment of platelet function was performed by whole blood impedance aggregometry using a multi-channel platelet function analyser (Multiplate).

RESULTS

A proper response to ASA was found in 121 patients (61.1%) (ASA responders), a partial response to ASA in 59 patients (29.8%) (ASA partial responders), and ASA resistance in 18 patients (9.1%) (ASA non-responders). Acetylsalicylic acid resistance was observed more frequently in the chronic phase. The mean low-density lipoprotein (LDL) concentration was higher in ASA non-responders (p = 0.02). The mean heart rate (p = 0.03) and the mean haematocrit (p = 0.03) were higher in the group of ASA partial responders and ASA non-responders. Angiotensin II receptor antagonists were more often used in the group of ASA partial responders and ASA non-responders (p = 0.04). Diuretics were more rarely used by ASA non-responders, whereas fibrates were more rarely used by ASA partial responders.

CONCLUSIONS

The method enabled the detection of ASA resistance in some patients with cerebrovascular disease. The study revealed some possible risk factors of ASA resistance: long ASA therapy, increased heart rate, higher LDL concentration, and higher haematocrit value. The relationship between the effect of ASA and other medications (angiotensin II receptor blockers, fibrates, diuretics) requires further study. Platelet function monitoring should be considered in patients at a greater risk of ASA resistance.

Genetic determinants of on-aspirin platelet reactivity: focus on the influence of PEAR1

Background

Platelet aggregation during aspirin treatment displays considerable inter-individual variability. A genetic etiology likely exists, but it remains unclear to what extent genetic polymorphisms determine platelet aggregation in aspirin-treated individuals.

Aim

To identify platelet-related single nucleotide polymorphisms (SNPs) influencing platelet aggregation during aspirin treatment. Furthermore, we explored to what extent changes in cyclooxygenase-1 activity and platelet activation may explain such influence.

Methods

We included 985 Danish patients with stable coronary artery disease treated with aspirin 75 mg/day mono antiplatelet therapy. Patients were genotyped for 16 common SNPs in platelet-related genes using standard PCR-based methods (TaqMan). Platelet aggregation was evaluated by whole blood platelet aggregometry employing Multiplate Analyzer (agonists: arachidonic acid and collagen) and VerifyNow Aspirin. Serum thromboxane B₂ was measured to confirm aspirin adherence and was used as a marker of cyclooxygenase-1 activity. Soluble P-selectin was used as marker of platelet activation. Platelet aggregation, cyclooxygenase-1 activity, and platelet activation were compared across genotypes in adjusted analyses.

Results

The A-allele of the rs12041331 SNP in the platelet endothelial aggregation receptor-1 (PEAR1) gene was associated with reduced platelet aggregation and increased platelet activation, but not with cyclooxygenase-1 activity. Platelet aggregation was unaffected by the other SNPs analyzed.

Conclusion

A common genetic variant in PEAR1 (rs12041331) reproducibly influenced platelet aggregation in aspirin-treated patients with coronary artery disease. The exact biological mechanism remains elusive, but the effect of this polymorphism may be related to changes in platelet activation. Furthermore, 14 SNPs previously suggested to influence aspirin efficacy were not associated with on-aspirin platelet aggregation.

Clinical Trial Registration

ClinicalTrials.gov NCT01383304

High prevalence of aspirin resistance in elderly patients with cardiovascular disease (CVD) and hyperhomocysteinaemia

Although aspirin resistance is well reported in CVD, little is known about aspirin response in elderly patients with hyperhomocysteinaemia. The aim of the present study was to explore the prevalence of aspirin resistance in elderly patients with CVD and hyperhomocysteinaemia. A total of 370 elderly patients with CVD were recruited. The study included 216 patients with hyperhomocysteinaemia and 154 patients with normohomocysteinaemia receiving daily aspirin therapy (≥ 75 mg) over 1 month. The effect of aspirin was assessed using by light transmission aggregometry (LTA). Aspirin resistance was defined as ≥ 20% arachidonic acid induced aggregation according to LTA. Aspirin resistance was defined in 48 (13.0%) of 370 patients. The prevalence of aspirin resistance was higher in hyperhomocysteinaemic patients than normohomocysteinaemic patients (16.7% vs. 7.8%, odds ratio (OR)=2.367; 95% confidence interval (CI)=1.188-4.715, p=0.012). In the multivariate logistic regression analysis, hyperhomocysteinaemia (OR=2.406, 95% CI=1.201-4.820, p=0.013) was a significant risk factor for aspirin resistance. A significant number of CVD patients with hyperhomocysteinemia are resistant to aspirin therapy. Hyperhomocysteinemia is a significant risk factor for aspirin resistance in elderly patients with CVD.

Resistance to acetylsalicylic acid in patients with type 2 diabetes mellitus is associated with lipid disorders and history of current smoking

BACKGROUND

Diabetes mellitus (DM) is an important risk factor for stroke. Acetylsalicylic acid (ASA) is the most frequently used medication for prevention of cardio-cerebral vascular diseases. However, some patients experience ischaemic vascular events despite the use of ASA. This phenomenon is known as "aspirin resistance" (AR). The aim of this study was to assess the prevalence of AR in diabetic patients and search for factors associated with it.

MATERIALS AND METHODS

The examined group consisted of 96 subjects with diagnosed type 2 DM. Platelet function test was performed by the method of whole blood impedance aggregometry.

RESULTS

Among examined subjects, 51 patients (53.1 %) were sensitive to ASA action (ASA responders) and 45 patients (46.9 %) were resistant to ASA action (ASA non-responders). No association was found between platelet aggregation and gender, age, dose of ASA, known duration of diabetes, BMI, heart rate, mean systolic and diastolic blood pressure, and risk factors except for current smoking (p = 0.030). ASA non-responders were treated shorter with ASA than ASA responders (p = 0.010). The mean total cholesterol (p = 0.020), LDL concentration (p = 0.005), HCT (p = 0.010), WBC (p = 0.030), and PLT (p = 0.050) were significantly higher in ASA non-responders. No association was found between AR and results of other laboratory tests and medications. Multiple logistic regression analysis revealed factors associated with AR: current smoking and LDL concentration higher than 3.5 mmol/l.

CONCLUSIONS

Results of our study did not confirm the association between poor glycaemic control in the diabetic patients and AR. Resistance to ASA in diabetic patients is associated with lipid disorders and history of current smoking.

Monitoring aspirin and clopidogrel response: testing controversies and recommendations

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

Evaluation of laboratory methods routinely used to detect the effect of aspirin against new reference methods

BACKGROUND

Aspirin, a commonly used antiplatelet agent, blocks platelet thromboxane A₂ (TXA₂) formation from arachidonic acid (AA) by acetylating platelet cyclooxygenase-1 (COX-1). Laboratory methods currently used to detect this antiplatelet effect of aspirin provide variable results. We have reported three methods that assess platelet COX-1 acetylation (inactivation) by aspirin and its direct consequences. The first and second assays use monoclonal anti-human-COX-1 antibodies that only detect acetylated (inactivated) COX-1 and active (non-acetylated) COX-1, respectively. The third method measures platelet production of TXB₂ (the stable metabolite of TXA₂) in vitro in response to AA. We compared the results of these three reference methods with other routinely used methods for assessing the functional consequences aspirin treatment.

METHODS

108 healthy volunteers were treated with low-dose aspirin for 7 days. On day 7 following aspirin treatment COX-1 in the platelets was fully acetylated whereas only non-acetylated COX-1 was present in the day 0 platelets. Further, TXB2 production by day 7 platelets was completely blocked. The following tests were performed on the samples obtained from study participants before and after seven days of aspirin treatment: PFA-100 closure time with collagen/epinephrine cartridge, VerifyNow (VN) Aspirin Assay, platelet aggregation and ATP secretion using AA, ADP, epinephrine and collagen as agonists.

RESULTS

Comparing the pre-treatment and day 7 values, methods that use AA as platelet agonist (AA-induced platelet aggregation/secretion and VN Aspirin Assay) showed high discriminative power. In contrast, results of the other tests showed considerable overlap between day 7 and day 0 values.

CONCLUSIONS

Only assays that clearly distinguish between acetylated and non-acetylated platelet COX-1 are useful for establishing the antiplatelet effect of aspirin. The other tests are not suitable for this purpose.

Aspirin resistance: a clinical review focused on the most common cause, noncompliance

Aspirin is an inexpensive, readily available medication that reduces the risk of subsequent vascular disease by about 25% in patients with known occlusive vascular disease. Aspirin's beneficial effect is mediated via inhibition of arachidonic acid (AA) activation of platelets and is detected by demonstrating a decrease in platelet function and/or a decrease in prostaglandin metabolites. Patients who are assumed to be taking their aspirin, but who do not demonstrate an aspirin effect are labeled as, "aspirin resistant." This is an unfortunate designation as the vast majority of patients labeled as "aspirin resistant" are noncompliant. Noncompliance is demonstrated in multiple studies that use repeat testing for platelet inhibition in patients with an initial inadequate response to aspirin. When the test is repeated under condition where ingestion of the test aspirin is assured, the patients' platelets are inhibited. Instead of using the term "aspirin resistance," this review will use "inadequate response to aspirin." Patients with an inadequate aspirin response have an increased likelihood for subsequent vascular events. Detection and treatment of an inadequate aspirin response would be facilitated by the development of a bedside assay that uses whole blood, is technically simple, inexpensive, sensitive, specific, reproducible, and provides an answer in a few minutes. Future research in patients with an inadequate response to aspirin should focus on mechanisms to improve compliance, which should decrease their risk of future vascular events.

Microfluidic assay of platelet deposition on collagen by perfusion of whole blood from healthy individuals taking aspirin

BACKGROUND

Microfluidic devices can create hemodynamic conditions for platelet assays. We validated an 8-channel device in a study of interdonor response to acetylsalicylic acid (ASA, aspirin) with whole blood from 28 healthy individuals.

METHODS

Platelet deposition was assessed before treatment or 24 h after ingestion of 325 mg ASA. Whole blood (plus 100 μmol/L H-d-Phe-Pro-Arg-chloromethylketone to inhibit thrombin) was further treated ex vivo with ASA (0-500 μmol/L) and perfused over fibrillar collagen for 300 s at a venous wall shear rate (200 s(-1)).

RESULTS

Ex vivo ASA addition to blood drawn before aspirin ingestion caused a reduction in platelet deposition [half-maximal inhibitory concentration (IC50) approximately 10-20 μmol/L], especially between 150 and 300 s of perfusion, when secondary aggregation mediated by thromboxane was expected. Twenty-seven of 28 individuals displayed smaller deposits (45% mean reduction; range 10%-90%; P < 0.001) from blood obtained 24 h after ASA ingestion (no ASA added ex vivo). In replicate tests, an R value to score secondary aggregation [deposition rate from 150 to 300 s normalized by rate from 60 to 150 s] showed R < 1 in only 2 of 28 individuals without ASA ingestion, with R > 1 in only 3 of 28 individuals after 500 μmol/L ASA addition ex vivo. At 24 h after ASA ingestion, 21 of 28 individuals displayed poor secondary aggregation (R < 1) without ex vivo ASA addition, whereas the 7 individuals with residual secondary aggregation (R > 1) displayed insensitivity to ex vivo ASA addition. Platelet deposition was not correlated with platelet count. Ex vivo ASA addition caused similar inhibition at venous and arterial wall shear rates.

CONCLUSIONS

Microfluidic devices quantified platelet deposition after ingestion or ex vivo addition of aspirin.

Internal challenge to clinical trial project management: strategies for managing investigator compliance

BACKGROUND

Managing compliance in a clinical research, especially in a multi-centre randomized clinical trial (MRCT) is vital. We now feel the need to take a look at the once overlooked area of investigator compliance as it may provide resources necessary for producing satisfactory trial outcomes.

OBJECTIVES

To analyze investigator performance and examine their adherence behavior using data collected and information gained from the MISPS-TCM, a Chinese national research project.

METHODS

Four researchers were responsible for collecting relevant information and investigating the compliance behavior of participants in MISPS-TCM. The Data Management Committee of MISPS-TCM offered us the number of withdrawal at each site and other site information. Reports on investigator compliance events were provided by the Monitoring Committee. Records of any misconduct of or errors made by the investigator were collected from the Center's daily management diary. Other information sources included trial managers and investigators at the Center or at different sites of the study.

RESULTS

Investigator compliance can be an important determinant of trial outcomes and the degree of compliance may have detrimental effects on the reliability of findings of an MRCT, directly or indirectly.

CONCLUSIONS

Trial managers of future MRCTs should take a firm grip on investigator compliance from the following aspects. First, physicians should be provided with more opportunities. Second, we created and recommended the 'Five Step Method' for evaluating investigators. Third, measures must be taken to secure investigator compliance. Fourth, evaluation of investigator compliance in an MRCT needs to be made.

Confirmation of reported aspirin use in community studies: utility of serum thromboxane B2 measurement

Aspirin (ASA) is recommended for the prevention of cardiovascular disease; however, the compliance is low. Reported use may not reflect actual use. Serum thromboxane B2 (STxB2) measurement was evaluated to validate reported ASA use. Males aged 45 to 79 years and females aged 55 to 79 years completed a survey and STxB2 measurement (Thromboxane B2 EIA Kit; Cayman Chemical, Ann Arbor, Michigan). The 107 patients were grouped by use of ASA (56 ASA+ and 51 ASA-) and possible interfering medications (INT) such as nonsteroidal anti-inflammatory drugs. The STxB2 levels (ng/mL) were significantly lower in ASA users: ASA+ INT- 3.0 (0.7, 8.4), ASA+ INT+ 2.0 (0.8, 4.9), ASA- INT+ 176 (75, 390), and ASA- INT- 271 (199, 366). The INT use did not cause a significant difference in STxB2 levels. A STxB2 cut point of 25 ng/mL had high sensitivity (94.1%) and specificity (91.1%) for ASA use. The STxB2 was a reliable marker of ASA use and could be used to confirm ASA exposure in population-based health studies.

Primary and secondary prevention of cardiovascular disease in diabetes with aspirin

Diabetes is associated with an increased cardiovascular risk. The role for aspirin in diabetes is of high clinical interest. Guidelines recommend that primary prevention of cardiovascular disease (CVD) in diabetes with aspirin should be based on the individual risk for CVD. New mechanistic studies suggest that enhanced platelet turnover may partly contribute to the fact the primary prevention studies found unequivocal results in diabetes. There is initial evidence that a potential future modification of dosages in diabetes may counteract the enhancement in platelet turnover in diabetes. The use of aspirin in diabetic patients for secondary prevention of CVD is supported by key evidence. The aim of the review is to present recent studies on aspirin for prevention of CVD in diabetes and to highlight its role also in view of new mechanistic and clinical studies with aspirin. Novel aspects of aspirin, e.g. its potential role for the prevention of cancer, are also presented.

Biological efficacy of twice daily aspirin in type 2 diabetic patients with coronary artery disease

BACKGROUND

Diabetes is associated with a high rate of events after acute coronary syndrome and percutaneous coronary intervention despite aspirin treatment. Once daily aspirin might not provide 24-hour stable biological efficacy in patients with diabetes. We compared the biological efficacy of the same daily dose of aspirin given either once (OPD) or divided twice per day in a population of diabetic patients with previous coronary artery disease.

METHODS

Ninety-two consecutive diabetic patients with at least 1 criteria of time-dependent aspirin efficacy, elevated high-sensibility C-reactive protein (hs-CRP), fibrinogen, platelet count, or active smoking were prospectively included. Consecutive patients were randomly treated with 150-mg aspirin daily given either OPD (150 mg in the morning) or twice per day (75 mg in the morning and 75 mg in the evening) in a crossover study. The main outcome was platelet reactivity to arachidonic acid (0.5 mg/mL) measured by light transmission aggregometry at trough level before morning aspirin intake.

RESULTS

Mean maximum aggregation intensity triggered by arachidonic acid was 19.7% ± 15.4% on OPD and 11.9% ± 10.4% on twice per day (P < .0001). Biological resistance (maximum aggregation intensity ≥20%) was observed in 42% of patients on OPD and 17% on twice per day (P < .001). Of the 39 patients with biological resistance on OPD, 24 (62%) overcame resistance on twice per day. Of the 16 resistant on twice per day, only 1 patient (6%) overcame resistance on OPD. Results were concordant with global evaluation of platelet reactivity by Platelet Function Analyzer-100. A better twice per day efficacy was independent of clopidogrel cotreatment.

CONCLUSION

In a population of diabetic patients with coronary artery disease and a high risk of time-dependent aspirin resistance, aspirin divided twice per day can significantly decrease the rate of biological loss of efficacy at trough level.

The prevalence, risk factors and prognosis of aspirin resistance in elderly male patients with cardiovascular disease

AIM

Aspirin resistance is recognized in different population. However, the prevalence and clinical events of aspirin resistance in elderly male patients with cardiovascular disease (CVD) have not been reported.

METHODS

We enrolled 304 elderly male patients with CVD receiving daily aspirin therapy (≥ 75 mg) more than 1 month. Platelet aggregation was measured by light transmission aggregometry (LTA) and thrombelastography platelet mapping assay (TEG). The median follow-up time was 1.8 years. The primary outcome was the composite of death, myocardial infarction, unstable angina, stroke and transient ischemic attack.

RESULTS

By LTA, 25 (8.2%) of elderly patients were aspirin resistant and 106 (34.9%) patients were semiresponders. According to TEG, 62 patients (20.4%) were found to be resistant to aspirin therapy. Of the 62 patients with aspirin resistance by TEG, 21 patients were aspirin resistant by LTA. Twenty-two of the 106 semiresponders by LTA were aspirin resistant by TEG. Patients with aspirin resistance or aspirin semiresponders were at increased risk of the composite outcome compared with aspirin-sensitive patients by LTA (18.3% vs 9.8%, Hazard ratio (HR) = 1.864, 95% confidence interval (CI): 1.046-3.324 p = 0.039). However, aspirin resistance was not associated with an increased risk of clinical vascular events compared to aspirin-sensitive patients by TEG (17.7% vs 10.9%, p = 0.452). In addition, Cox proportional hazard regression modeling demonstrated that aspirin resistance or semiresponders (HR = 3.050, 95% CI: 1.464-6.354, p = 0.003) and diabetes (HR = 2.055, 95% CI: 1.060-3.981, p = 0.033) were associated with major adverse long-term outcomes.

CONCLUSIONS

Aspirin resistance or semiresponders, defined by LTA, are associated with an increased risk of adverse clinical events in elderly male patients with CVD.

Antiplatelet therapy: aspirin resistance and all that jazz!

Platelets play a crucial role in the pathogenesis of atherosclerosis, thrombosis, and stroke. Aspirin used alone or in combination with other antiplatelet drugs has been shown to offer significant benefit to patients at high risk of vascular events. Resistance to the action of aspirin may decrease this benefit. Aspirin resistance has been defined by clinical and/or laboratory criteria; however, detection by laboratory methods prior to experiencing a clinical event will likely provide the greatest opportunity for intervention. Numerous laboratory methods with different cutoff points have been used to evaluate the resistance. Noncompliance with aspirin treatment has also confounded studies. A single assay is currently insufficient to establish resistance. Combinations of results to confirm compliance and platelet inhibition may identify "at-risk" individuals who truly have aspirin resistance. The most effective strategy for managing patients with aspirin resistance is unknown; however, studies are currently underway to address this issue.

Plasma proteome changes in cardiovascular disease patients: novel isoforms of apolipoprotein A1

Background

The aim of this proteomic study was to look for changes taking place in plasma proteomes of patients with acute myocardial infarction (AMI), unstable angina pectoris (UAP), and stable angina pectoris (SAP).

Methods

Depleted plasma proteins were separated by 2D SDS-PAGE (pI 4-7), and proteomes were compared using Progenesis SameSpots statistical software. Proteins were identified by nanoLC-MS/MS. Proteins were quantified using commercial kits. Apolipoprotein A1 was studied using 1D and 2D SDS-PAGE, together with western blotting.

Results

Reciprocal comparison revealed 46 unique, significantly different spots; proteins in 34 spots were successfully identified and corresponded to 38 different proteins. Discrete comparisons of patient groups showed 45, 41, and 8 significantly different spots when AMI, UAP, and SAP were compared with the control group. On the basis of our proteomic data, plasma levels of two of them, alpha-1 microglobulin and vitamin D-binding protein, were determined. The data, however, failed to prove the proteins to be suitable markers or risk factors in the studied groups. The plasma level and isoform representation of apolipoprotein A1 were also estimated. Using 1D and 2D SDS-PAGE, together with western blotting, we observed extra high-molecular weight apolipoprotein A1 fractions presented only in the patient groups, indicating that the novel high-molecular weight isoforms of apolipoprotein A1 may be potential new markers or possible risk factors of cardiovascular disease.

Conclusion

The reported data show plasma proteome changes in patients with AMI, UAP, and SAP. We propose some apolipoprotein A1 fractions as a possible new disease-associated marker of cardiovascular disorders.

Antiplatelet resistance in stroke

Although the exact prevalence of antiplatelet resistance in ischemic stroke is not known, estimates about the two most widely used antiplatelet agents - aspirin and clopidogrel - suggest that the resistance rate is high, irrespective of the definition used and parameters measured. Inadequate antiplatelet responsiveness correlates with an increased risk of recurrent ischemic vascular events in patients with stroke and acute coronary syndrome. It is not currently known whether tailoring antiplatelet therapy based on platelet function test results translates into a more effective strategy to prevent secondary vascular events after stroke. Large-scale clinical trials using a universally accepted definition and standardized measurement techniques for antiplatelet resistance are needed to demonstrate whether a 'platelet-function test-guided antiplatelet treatment' strategy translates into improved stroke care. This article gives an overview of the clinical importance of laboratory antiplatelet resistance, describes the challenges for platelet-function test-guided antiplatelet treatment and discusses practical issues about the management of patients with aspirin and/or clopidogrel resistance.

Laboratory evaluation of aspirin responsiveness

Aspirin is the most commonly used antiplatelet medication. Laboratory monitoring of aspirin response has recently become a topic of interest due to potential impacts on patient management and clinical outcomes. This article summarizes available laboratory testing of aspirin response with focus on technical issues, limitations, and current opinion on the utility of routine patient testing.

Aspirin and clopidogrel resistance: methodological challenges and opportunities

Antiplatelet drug resistance is one of the urgent issues in current cardiovascular medicine. Many platelet function tests have been used to define responsiveness of patients with cardiovascular disease to aspirin and clopidogrel. In most studies, cut-off values of platelet function tests for defining responsiveness to antiplatelets were chosen arbitrarily. Different tests provided wide-ranging figures of the prevalence of aspirin and clopidogrel resistance, suggesting poor correlation between currently available platelet function tests. Measurement of platelet size seems to be a promising approach for monitoring antiplatelet drug therapy. This commentary highlights some limitations of studies on aspirin and clopidogrel resistance in patients undergoing coronary interventions.

'Aspirin resistance' or treatment non-compliance: which is to blame for cardiovascular complications?

Aspirin is one of the 'cornerstone' drugs in our current management of cardiovascular disorders. However, despite the prescription of aspirin recurrent vascular events still occur in 10-20% of patients. These, data together with the observations of diminished antiaggregatory response to aspirin in some subjects have provided the basis of the current debate on the existence of so-called "aspirin resistance". Unfortunately, many of the tests employed to define 'aspirin resistance' lack sufficient sensitivity, specificity, and reproducibility. The prevalence of 'aspirin resistance' as defined by each test varies widely, and furthermore, the value of a single point estimate measure of aspirin resistance is questionable. The rate of 'aspirin resistance' is law if patients observed to ingest aspirin, with large proportion of patients to be pseudo-'aspirin resistant', due to non-compliance. What are the implications for clinical practice? Possible non-adherence to aspirin prescription should also be carefully considered before changing to higher aspirin doses, other antiplatelet drugs (e.g. clopidogrel) or even combination antiplatelet drug therapy. Given the multifactorial nature of atherothrombotic disease, it is not surprising that only about 25% of all cardiovascular complications can usually be prevented by any single medication. We would advocate against routine testing of platelet sensitivity to aspirin (as an attempt to look for 'aspirin resistance') but rather, to highlight the importance of clinicians and public attention to the problem of treatment non-compliance.