Aspirin-resistant platelet aggregation in a cohort of patients with coronary heart disease.

Aspirin resistance could be defined as thrombotic and embolic cardiovascular events despite regular aspirin therapy. The study aimed to determine the profile and prevalence of aspirin resistance in coronary artery disease patients. We evaluated the prevalence of aspirin resistance in a cohort of 505 patients with the diagnosis of coronary artery disease taking 80-300 mg regular aspirin daily. Platelet functions were analyzed by the Platelet Function Analyzer (PFA)-100 with collagen and epinephrine cartridges and collagen and ADP cartridges. A closure time of 186 s or less with the collagen and epinephrine cartridge was defined as aspirin resistance. Of the patients, 118 (23.4%) were aspirin resistant by the PFA-100. Aspirin-resistant patients were more likely to be older than aspirin-sensitive patients (P = 0.024). No statistically significant differences between the aspirin-resistant and aspirin-sensitive individuals were present in gender, major risk factors of coronary artery disease, number and localization of involved coronary vessels, serum lipid levels, and blood counts. According to the high prevalence of coronary heart disease, many people are affected by aspirin resistance, which may play a role in adverse cardiovascular events. Monitoring of platelet function in patients with coronary heart disease may support the optimization of antiplatelet therapy with additional and/or alternative agents.     

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 resistance on outcome in patients with acute coronary syndrome and the effect of clopidogrel therapy in the prevention of major cardiovascular events

Background: Aspirin resistance may increase up to more then threefold the risk of major cardiovascular events (MACE) in patients with stable coronary artery disease. Aim:The aim of our study was to determine; the prevalence of aspirin resistance in patients with acute coronary syndromes, the role of aspirin resistance on outcome in the follow-up and the effect of clopidogrel therapy in the prevention of MACE in aspirin resistant subjects. Material and methods: We detected the prevelance of aspirin resistance in 105 patients with acute coronary syndrome. Platelet functions were analyzed in Platelet Function Analyzer (PFA)-100 (Dade Behring, Germany) with collagen and/or epinephrine (Col/Epi) and collagen and/or ADP (Col/ADP) cartridges. Primary end points of the study were myocardial infarction, unstable angina, cardiac death. Results: 19% (n = 20) of patients were aspirin resistant by PFA-100. In the follow-up, MACE occured in 9 patients (45%) with aspirin resistance and in 10 patients (11.7%) with aspirin sensitive platelet aggregation (p = 0.001). Multivariate analysis showed that aspirin resistance was an independant predictor of MACE. The prevalence of MACE in patients who were on clopidogrel treatment for 12 months were lower compared to those who were on a clopidogrel treatment for the first six months (p = 0.040). Conclusions: We determined that the MACE risk in patients with acute coronary syndromes having detected aspirin resistance, was higher at statistically significant levels compared to patients having aspirin sensitive platelet aggregation. Our results showed that aspirin resistance, was an independant predictor of MACE in patients with acute coronary syndrome.     

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

Aspirin resistance may increase the risk of major adverse cardiac events (MACE) more than threefold in patients with stable coronary artery disease (CAD). This study aimed to determine the prevalence of aspirin resistance in patients with stable CAD, the role of aspirin resistance on outcome in the follow-up, and the effect of clopidogrel therapy in MACE prevention in aspirin-resistant individuals. We detected the prevalence of aspirin resistance in 234 patients with stable CAD. Platelet function was determined by PFA-100 with collagen and/or epinephrine and collagen and/or ADP cartridges. The mean follow-up time was 20.6 +/- 6.9 months. The primary endpoints of the study were occurrence of myocardial infarction, unstable angina, stroke and cardiac death. Of patients, 22.2% (n = 52) were aspirin resistant by PFA-100. During follow-up, MACE occurred in eight patients (15.4%) with aspirin resistance and in 20 patients (11.0%) with aspirin-sensitive platelet aggregation (P = 0.269). MACE increased in aspirin-resistant patients after termination of clopidogrel therapy. Eleven patients experienced MACE after cessation of clopidogrel therapy (P < 0.001). The MACE risk in patients with stable CAD having detected aspirin resistance was similar compared with patients having aspirin-sensitive platelet aggregation by PFA-100. The MACE prevalence increased during follow-up, however, just after cessation of clopidogrel therapy.     

Variability of non-response to aspirin in patients with peripheral arterial occlusive disease during long-term follow-up

Non-responsiveness to aspirin as detected by laboratory tests may identify patients at high risk for future vascular events. The aim of this prospective study was to evaluate whether non-responsiveness to aspirin is stable over time. Ninety-eight patients with stable peripheral arterial occlusive disease (PAOD) treated with 100 mg/d aspirin were followed over a median timeframe of 17 months. Platelet function tests were performed initially and at follow-up using arachidonic acid-induced light transmittance aggregometry (LTA) in native platelet-rich plasma with the Behring Coagulation Timer® and by measuring the collagen?epinephrine closure time (CT) on a Platelet Function Analyzer (PFA-100®). When determining platelet function using LTA, four patients (4.1%) had residual platelet function (i.e., MaxAggr ≥78%) despite aspirin treatment, whereas, according to the PFA-100® results, 12 patients (12.2%) were identified as non-responders (i.e., CT <192 s). Fifty-seven patients who were still under treatment with 100 mg/d aspirin at the time of follow-up provided a second blood sample. Further platelet function tests with the PFA-100® system identified a persistent non-responsiveness to aspirin over time in three patients (5.3%) whereas four (7.0%) and 15 (26.3%) patients had changes in response status when platelet function was assessed by LTA and on the PFA-100®, respectively. We conclude that true non-responsiveness to aspirin is a rare phenomenon in stable PAOD patients. Furthermore, we conclude that in a number of patients, aspirin non-responsiveness is not stable over time.     

Overestimation of platelet aspirin resistance detection by thrombelastograph platelet mapping and validation by conventional aggregometry using arachidonic acid stimulation.

OBJECTIVES: This study sought to determine the prevalence of platelet aspirin resistance using methods that directly indicate the degree of platelet cyclooxygenase inhibition. BACKGROUND: Aspirin resistance in platelets may be overestimated by nonspecific laboratory measurements that do not isolate cyclooxygenase activity. METHODS: Arachidonic acid (AA)-induced light-transmittance platelet aggregation (LTA) and thrombelastography (TEG) platelet mapping were performed on the blood of healthy subjects (n = 6) before and 24 h after receiving 325 mg aspirin, and on 223 patients reporting compliance with long-term daily aspirin treatment (n = 203 undergoing percutaneous intervention [PCI] and n = 20 with a history of stent thrombosis). Aspirin resistance was defined as >20% aggregation by LTA or >50% aggregation by TEG. RESULTS: In healthy subjects, AA-induced aggregation by LTA was 82 +/- 10% before and 2 +/- 1% at 24 h after aspirin (p < 0.001), and aggregation by TEG was 86 +/- 14% before and 5 +/- 7% at 24 h after aspirin (p < 0.001). In compliant patients, AA-induced aggregation by LTA was 3 +/- 2% before PCI and 3 +/- 2% after PCI (p = NS), and aggregation by TEG was 5 +/- 9% before PCI and 6 +/- 14% after PCI (p = NS). Seven PCI patients were noncompliant, and all were aspirin sensitive after in-hospital aspirin treatment. Among 223 patients, only one patient ( approximately 0.4%) was resistant to aspirin treatment. CONCLUSIONS: Platelet aspirin resistance assessed by methods that directly indicate inhibition of cyclooxygenase is rare in compliant patients with coronary artery disease.     

Aspirin and clopidogrel in acute coronary syndromes: therapeutic insights from the CURE study

Platelet adhesion, activation, and aggregation are central to thrombus formation, which follows atherosclerotic plaque disruption and causes acute coronary syndromes. Aspirin and clopidogrel exert their antiplatelet effects by inhibiting thromboxane A2 production and adenosine diphosphate-induced platelet aggregation pathways, respectively. Aspirin has proven benefits in primary and secondary prevention of coronary artery disease. Clopidogrel, an alternative antiplatelet agent used in patients with aspirin intolerance, is especially useful in combination with aspirin after coronary stent procedures. The CURE (Clopidogrel in Unstable Angina to Prevent Recurrent Events) study demonstrates for the first time the benefit of adding clopidogrel to aspirin rather than using aspirin alone in patients having acute coronary syndromes without ST-segment elevation myocardial infarction. Patients who are resistant to aspirin (up to 10%) have higher rates of cardiovascular events and may derive special benefit from the combination therapy. Aspirin resistance can be assessed through platelet aggregometry testing, measurement of urinary thromboxane metabolites, and, possibly, genomic testing in the future.     

Platelet function measured by VerifyNow identifies generalized high platelet reactivity in aspirin treated patients

Selected aspirin treated patients may exhibit high platelet reactivity to agonists other than arachidonic acid. This study aimed to determine whether the VerifyNow identifies generalized high platelet reactivity supported by correlations with other established methods that stimulate platelets with various agonists. Stable outpatients with coronary artery disease (n = 110) were treated with aspirin in a two 3 x 3 Latin square design (81, 162 and 325 mg/day for 4 weeks each). VerifyNow (arachidonic acid (AA) cartridge); light transmittance aggregometry; thrombelastography; PFA-100; flow cytometry; PlateletWorks; and urinary 11- dehydro thromboxane levels were measured. Multianalyte profiling measured fibrinogen and von Willebrand factor (vWF). Patients with >or=550 ARU by VerifyNow had increased 5 mM AA-, 5 microM ADP-, and 2 microg/mL collagen-induced platelet aggregation compared to patients with <550 ARU (p 相似文献   

Hypersensitivity of platelets to adenosine diphosphate in patients with stable cardiovascular disease predicts major adverse events despite antiplatelet therapy

Enhanced platelet activity correlates with early markers of myocardial damage in patients with cardiovascular disease. However, the extent to which enhanced platelet function signals subsequent adverse clinical outcomes in patients with cardiovascular disease is unknown. Blood from patients with stable cardiovascular disease receiving aspirin (325 mg/day) as the only antiplatelet therapy was tested for closure time (CT) with the Dade PFA-100 Platelet Function Analyzer system collagen/adenosine diphosphate (ADP) [CADP] cartridge and platelet aggregometry using 10 microM ADP. This study intentionally focused on those patients defined as aspirin sensitive by previously established criteria of arachidonic acid- and ADP-induced platelet aggregometry, and separately by collagen/epinephrine (CEPI) CT using the PFA-100. Follow up averaged 22 months for the adverse clinical events of death, myocardial infarction or cerebrovascular accident. For aspirin sensitivity determined by aggregometry, patients with CADP CT < 90 seconds (125/296 = 42.2%) had a composite endpoint rate of 19.2% (24/125), while those with CADP CT 90 seconds (171/296 = 57.8%) had an endpoint rate of 5.3% (9/171). Patients with CADP CT <90 seconds had a relative risk (RR) of 3.65 (95% CI.: 1.76-7.57) for recurrent events and 6.56 (95% CI.: 1.93-22.35) for death compared to patients with CADP CT 90s. Nearly identical results were obtained when patients were categorized as aspirin sensitive by CEPI CT. Platelet aggregometry with 10 microM ADP yielded no significant RR for the selected outcomes. Platelet function testing using the PFA-100 system appears to identify a subgroup of stable cardiovascular disease patients with increased risk of major adverse events that is associated with hypersensitivity to ADP, regardless of apparently effective aspirin therapy.     

Correlation between light transmission aggregometry, VerifyNow P2Y12, and VASP-P platelet reactivity assays following percutaneous coronary intervention

BACKGROUND: High on-treatment platelet reactivity is an established risk factor for adverse cardiac events in patients taking clopidogrel following percutaneous coronary intervention (PCI). Methods: Two hundred patients underwent platelet reactivity testing with VerifyNow P2Y12, vasodilator-stimulated phosphoprotein phosphorylation (VASP), and light transmission aggregometry (LTA) with both 5 and 20 μM of adenosine diphosphate (ADP) following PCI. High on-treatment platelet reactivity was defined as a maximum platelet aggregation ≥46% for LTA ADP 5 μM or ≥60% for 20 μM; platelet reactivity index (PRI) ≥50% for VASP; and platelet reactivity units ≥235 for VerifyNow. Correlation between assays was tested using Spearman coefficients (ρ); agreement among tests in regards to high on-treatment platelet reactivity was evaluated with Kappa statistics (κ). Results: All Spearman correlations had P values <0.001, although ρ ranged from 0.60-0.86. The incidence of high on-treatment platelet reactivity was 39.3% with VASP, 27.3% with VerifyNow, 23.1% with LTA ADP 5 μM, and 16.2% with LTA ADP 20 μM. The strongest correlation was between LTA ADP 5 μM and LTA ADP 20 μM (κ= 0.53, 95% CI 0.37-0.68); the weakest was between VASP and LTA ADP 5 μM (κ= 0.33, 95% CI 0.19-0.47). Overall, the level of agreement between assays was in the moderate to poor range. CONCLUSION: Despite evidence that the most commonly used tests are correlated, agreement among tests is modest at best and demonstrates they are not interchangeable.     

Comparison of nine platelet function tests used to determine responses to different aspirin dosages in people with type 2 diabetes

The antiplatelet efficacy of aspirin (ASA) is reduced in type 2 diabetes (T2D). As the best ex vivo method of measuring ASA efficacy remains uncertain, we compared nine platelet function tests to assess responsiveness to three ASA dosing regimens in 24 T2D patients randomized in a three-treatment crossover design to ASA 100 mg/day, 200 mg/day, or 100 mg twice daily for 2-week treatment periods. Platelet function tests compared were as follows: light transmission aggregometry (LTA)–0.5 mg/mL of arachidonic acid (AA) and 10 µM adenosine diphosphate (ADP); multiplate whole blood aggregometry (WBA)–0.5 mM AA and 6.5 µM ADP; platelet function analyzer (PFA)-100?–collagen and ADP (CADP) and collagen and epinephrine (CEPI); VerifyNow?–ASA; and urinary 11-dehydro-thromboxane B2 (TxB₂) and serum TxB₂. All cyclo-oxygenase (COX-1)-dependent tests and some COX-1-independent tests (PFA-CEPI, LTA-ADP) demonstrated significant reductions in platelet reactivity with all ASA doses. Two COX-1-independent tests (WBA-ADP and PFA-CADP) showed no overall reduction in platelet reactivity. Overall classifications for detecting all ASA doses, compared to baseline, were as follows: very good–LTA-AA (k = 0.95) and VerifyNow?-ASA (k = 0.85); good–serum TxB₂ (k = 0.79); moderate–LTA-ADP (k = 0.59), PFA-100?-CEPI (k = 0.56), urinary TxB₂ (k = 0.55), WBA-AA (k = 0.47); and poor–PFA-100?-CADP (k = –0.02) and WBA-ADP (k = –0.07). No significant kappa statistic differences were seen for each test for each ASA dose. Correlations for each test with serum TxB₂ measurements were as follows: very good–VerifyNow?-ASA (k = 0.81, R² = 0.56) and LTA-AA (k = 0.85, R² = 0.65); good–PFA-100^TM-CEPI (k = 0.62, R² = 0.30); moderate–urinary TxB₂ (k = 0.57, R² = 0.51) and LTA-ADP (k = 0.47, R² = 0.56); fair–WBA-AA (k = 0.31, R² = 0.31); and poor–PFA-100?-CADP (k = 0.04, R² = 0.003) and WBA-ADP (k = –0.04, R² = 0.0005). The platelet function tests we assessed were not equally effective in measuring the antiplatelet effect of ASA and correlated poorly amongst themselves, but COX-1-dependent tests performed better than non-COX-1-dependent tests.     

Lack of reproducibility of assessment of aspirin responsiveness by optical aggregometry and two platelet function tests

The term aspirin-resistance describes the failure of aspirin to inhibit thromboxane A(2) production. Many new tests have become available for potentially measuring aspirin responses but some are non-specific and do not isolate COX-1 activity. We previously demonstrated that agreement between two tests (PFA-100 and VerifyNow-ASA) and light transmission aggregation (LTA) was no greater than would be expected by chance. In this study we re-tested the same patients using identical methods after 1 year to determine whether poor agreement might have been due to assessment in the acute phase and whether the results of the individual tests are consistent over time. Platelet function by all three tests was re-tested in the 72 patients who were alive and still receiving low dose ASA therapy one year after the first tests were performed. On re-testing the prevalence of ASA non-responsiveness compared with baseline was 10% vs 17% by the VerifyNow-ASA test, 25% vs 22% by the PFA-100(R), and 1% vs 5% by LTA. Agreement between the tests at 1 year remained poor (kappas: 0.02-0.17) and only one patient was identified as a non-responder by all three tests, in keeping with the theoretical differences between the tests. Within test comparisons of baseline vs 1 year showed moderate agreement for the PFA-100(R) (kappa = 0.44, 95% CI 0.19-0.68, p = 0.0006), a fair agreement for VerifyNow-ASA (kappa = 0.34, 0.04-0.64, p = 0.12) and poor agreement for LTA (kappa = 0.14, -0.11 -0.39, p = 0.24 for ADP; kappa = 0.09, -0.21-0.39, p = 0.41 for arachidonic acid). Agreement between the three tests in identifying aspirin non-responsiveness remained poor in patients who had been taking aspirin for at least 1 year follow-up. Reproducibility over time was no greater than chance for LTA and only moderate for VerifyNow-ASA and PFA-100(R). Lack of consistency over time in identification of apparently non-responsiveness individuals is likely to substantially undermine any ability of these tests to predict risk of recurrent vascular events.     

Hypersensitivity of platelets to adenosine diphosphate in patients with stable cardiovascular disease predicts major adverse events despite antiplatelet therapy

Enhanced platelet activity correlates with early markers of myocardial damage in patients with cardiovascular disease. However, the extent to which enhanced platelet function signals subsequent adverse clinical outcomes in patients with cardiovascular disease is unknown. Blood from patients with stable cardiovascular disease receiving aspirin (325 mg/day) as the only antiplatelet therapy was tested for closure time (CT) with the Dade® PFA-100® Platelet Function Analyzer system collagen/adenosine diphosphate (ADP) [CADP] cartridge and platelet aggregometry using 10 µM ADP. This study intentionally focused on those patients defined as aspirin sensitive by previously established criteria of arachidonic acid- and ADP-induced platelet aggregometry, and separately by collagen/epinephrine (CEPI) CT using the PFA-100®. Follow up averaged 22 months for the adverse clinical events of death, myocardial infarction or cerebrovascular accident. For aspirin sensitivity determined by aggregometry, patients with CADP CT < 90 seconds (125/296 = 42.2%) had a composite endpoint rate of 19.2% (24/125), while those with CADP CT ≥90 seconds (171/296 = 57.8%) had an endpoint rate of 5.3% (9/171). Patients with CADP CT <90 seconds had a relative risk (RR) of 3.65 (95% CI.: 1.76–7.57) for recurrent events and 6.56 (95% CI.: 1.93–22.35) for death compared to patients with CADP CT ≥ 90s. Nearly identical results were obtained when patients were categorized as aspirin sensitive by CEPI CT. Platelet aggregometry with 10 µM ADP yielded no significant RR for the selected outcomes. Platelet function testing using the PFA-100® system appears to identify a subgroup of stable cardiovascular disease patients with increased risk of major adverse events that is associated with hypersensitivity to ADP, regardless of apparently effective aspirin therapy.     

Prevalence and Risk Factors for Aspirin Resistance in Elderly Patients With Type 2 Diabetes

Background

Aspirin resistance in patients with diabetes is recognized. However, the prevalence and related risk factors for aspirin resistance in elderly patients with Type 2 diabetes have not been reported, which is why we undertook this study.

Methods

One hundred and forty elderly patients (age, 73.84 ± 8.02 years) with Type 2 diabetes receiving daily aspirin therapy (≥75 mg) over 1 month were recruited. Platelet aggregation was measured by light transmission aggregometry (LTA) and thrombelastography (TEG) platelet mapping assay. The definitions of aspirin resistance were 20% or greater arachidonic acid-induced and 70% or greater adenosine diphosphate-induced aggregation by LTA. Aspirin semiresponders were defined as meeting one (but not both) of these criteria. Aspirin resistance by TEG was defined as 50% or greater aggregation induced by arachidonic acid.

Results

By LTA, 6 (4.3%) patients with Type 2 diabetes were found to be resistant to aspirin therapy; 44 (31.4%) patients were semiresponders. By TEG, 31 patients (22.1%) were aspirin resistant. Of the 31 patients who were aspirin-resistant by TEG, 3 were aspirin-resistant by LTA. Eight of 44 semiresponders by LTA were aspirin-resistant by TEG. In the multivariate logistic regression analysis, being female (odds ratio: 5.54, 95% confidence interval: 1.17–27.47, p = 0.036) and homocysteine levels (odds ratio: 1.15, 95% confidence interval: 1.00–1.31, p = 0.043) were significant risk factors for aspirin resistance by TEG.

Conclusion

The prevalence of aspirin resistance in elderly patients with Type 2 diabetes was considerably higher in female patients and in patients with higher serum levels of homocysteine.     

Major clinical vascular events and aspirin-resistance status as determined by the PFA-100 method among patients with stable coronary artery disease: a prospective study.

Aspirin inhibits platelet activation and reduces major vascular events in patients with stable coronary artery disease. The extent of platelet inhibition, denoted as aspirin resistance, however, is not always sufficient. A correlation between aspirin resistance as measured by aggregometry and adverse clinical events has been demonstrated. The point-of-care platelet function analyzer PFA-100 is usually used to detect aspirin resistance, but the relation between PFA-100 results and the vascular prognosis is not assessed. We prospectively enrolled 97 patients with stable coronary artery disease who were on aspirin (160 mg per day since 1 month or longer). Aspirin resistance was measured by the PFA-100 analyzer. Median follow-up was 2.5 years and the primary outcome was the composite of death, myocardial infarction, and ischemic cerebral infarction or acute limb ischemia. In our study, 29 patients (29.9%) showed resistance to aspirin, with a higher percentage of female patients (38 vs. 15%; P=0.01). During the follow-up, aspirin resistance was not associated with an increased risk of death, myocardial infarction, or ischemic vascular event compared with the aspirin-sensitive patients (17 vs. 13%; P>0.60). In this cohort of stable coronary artery disease, patients on aspirin dose of 160 mg per day, the aspirin-resistance status based on the PFA-100 results is not associated with a significant increase in major vascular clinical events.     

Lack of reproducibility of assessment of aspirin responsiveness by optical aggregometry and two platelet function tests

The term aspirin-resistance describes the failure of aspirin to inhibit thromboxane A₂ production. Many new tests have become available for potentially measuring aspirin responses but some are non-specific and do not isolate COX-1 activity. We previously demonstrated that agreement between two tests (PFA-100® and VerifyNow®-ASA) and light transmission aggregation (LTA) was no greater than would be expected by chance. In this study we re-tested the same patients using identical methods after 1 year to determine whether poor agreement might have been due to assessment in the acute phase and whether the results of the individual tests are consistent over time. Platelet function by all three tests was re-tested in the 72 patients who were alive and still receiving low dose ASA therapy one year after the first tests were performed. On re-testing the prevalence of ASA non-responsiveness compared with baseline was 10% vs 17% by the VerifyNow®-ASA test, 25% vs 22% by the PFA-100®, and 1% vs 5% by LTA. Agreement between the tests at 1 year remained poor (kappas: 0.02–0.17) and only one patient was identified as a non-responder by all three tests, in keeping with the theoretical differences between the tests. Within test comparisons of baseline vs 1 year showed moderate agreement for the PFA-100® (kappa = 0.44, 95% CI 0.19–0.68, p = 0.0006), a fair agreement for VerifyNow®-ASA (kappa = 0.34, 0.04–0.64, p = 0.12) and poor agreement for LTA (kappa = 0.14, ?0.11 ?0.39, p = 0.24 for ADP; kappa = 0.09, ?0.21–0.39, p = 0.41 for arachidonic acid). Agreement between the three tests in identifying aspirin non-responsiveness remained poor in patients who had been taking aspirin for at least 1 year follow-up. Reproducibility over time was no greater than chance for LTA and only moderate for VerifyNow®-ASA and PFA-100®. Lack of consistency over time in identification of apparently non-responsiveness individuals is likely to substantially undermine any ability of these tests to predict risk of recurrent vascular events.     

Profile and prevalence of aspirin resistance in patients with cardiovascular disease

We determined the prevalence and clinical predictors of aspirin resistance by prospectively studying 325 patients with stable cardiovascular disease who were receiving aspirin (325 mg/day for > or =7 days) but no other antiplatelet agents. We also compared the detection of aspirin resistance with optical platelet aggregation, a widely accepted method, with a newer, more rapid method, the platelet function analyzer (PFA)-100, a whole blood test that measures platelet adhesion and aggregation ex vivo. Blood samples were analyzed in a blinded fashion for aspirin resistance by optical aggregation using adenosine diphosphate (ADP) and arachidonic acid, and by PFA-100 using collagen and/or epinephrine and collagen and/or ADP cartridges to measure aperture closure time. Aspirin resistance was defined as a mean aggregation of > or =70% with 10 microM ADP and a mean aggregation of > or =20% with 0.5 mg/ml arachidonic acid. Aspirin semiresponders were defined as meeting one, but not both of the above criteria. Aspirin resistance by PFA-100 was defined as having a normal collagen and/or epinephrine closure time (< or =193 seconds). By optical aggregation, 5.5% of the patients were aspirin resistant and 23.8% were aspirin semiresponders. By PFA-100, 9.5% of patients were aspirin resistant. Of the 18 patients who were aspirin resistant by aggregation, 4 were also aspirin resistant by PFA-100. Patients who were either aspirin resistant or aspirin semiresponders were more likely to be women (34.4% vs 17.3%, p = 0.001) and less likely to be smokers (0% vs 8.3%, p = 0.004) compared with aspirin-sensitive patients. There was a trend toward increased age in patients with aspirin resistance or aspirin semiresponders (65.7 vs 61.3 years, p = 0.06). There were no differences in aspirin sensitivity by race, diabetes, platelet count, renal disease, or liver disease.     

Relationship between the serum sCD40L level and aspirin-resistant platelet aggregation in patients with stable coronary artery disease

BACKGROUND: Current evidence supports the central role of inflammation in all phases of the atherosclerotic process, including its thrombotic complications. Increased serum sCD40L may trigger platelet activation, so the aim of the present study was to determine the relation between sCD40L levels and aspirin-resistant platelet aggregation in patients with coronary atherosclerosis. METHODS AND RESULTS: A total of 167 consecutive patients (39-85 years old, 35.9% women) with stable coronary artery disease was enrolled in the study. Platelet function was evaluated by a Platelet Function Analyzer 100 device (PFA-100) with collagen and epinephrine (Col/Epi) and collagen and adenosine diphosphate (ADP) (Col/ADP) cartridges. Aspirin resistance was defined as a closure time (CT) <186 s with Col/Epi cartridges, despite regular aspirin therapy. Serum sCD40L level was determined quantitatively with an ELISA method. Fifty-seven (34.1%) patients had aspirin resistance according to the PFA-100. Mean CT measured with the Col/ADP cartridges was 83+/-18 s (65-101 s). Mean serum sCD40L was 157 pg/ml (6-700 pg/ml) in the entire cohort. Patients with aspirin resistance had a mean serum sCD40L level of 166 pg/ml and patients with aspirin-sensitive platelet aggregation had an sCD40L level of 152 pg/ml (p=0.582). CONCLUSION: The sCD40L level is similar in patients with aspirin-resistant and aspirin-sensitive platelet aggregation according to the PFA-100. There is still need for further studies to elucidate the relationship between aspirin-resistant platelet aggregation and sCD40L, which is now known to be prothrombotic, proinflammatory and to be a risk factor for cardiovascular events.     

Evaluation of the role of the new INNOVANCE PFA P2Y test cartridge in detection of clopidogrel resistance

Light transmittance aggregometry (LTA) has been extensively used in monitoring clopidogrel therapy. However, the availability of simple and rapid point-of-care platelet function assays is of great clinical importance. Thus, the manufacturer of the Platelet Function Analyzer (PFA)-100 System has recently produced the INNOVANCE PFA P2Y test cartridge. We assessed the ability of this new test to reliably detect clopidogrel resistance. We enrolled 90 consecutive patients with coronary artery disease receiving chronic clopidogrel maintenance therapy in combination with aspirin. Twenty healthy volunteers served as controls. Clopidogrel resistance was simultaneously analysed by the INNOVANCE PFA P2Y test cartridge, ADP-induced LTA, the flow-cytometric vasodilator-stimulated phosphoprotein (VASP)-phosphorylation assay and the multiple electrode aggregometry (Multiplate). Agreement among the four platelet function methods by two was assessed using Cohen's kappa coefficient. According to the cut-off points for clopidogrel resistance proposed by the literature, agreement was fair between INNOVANCE PFA-100 P2Y and LTA (74.4%) and Multiplate (75.6%), while poor agreement was noticed in VASP assay (63.3%). Based on cut-off points indicating a higher thrombotic risk, agreement between the PFA-100 System and the other three methods did not significantly differ compared to the previous cut-offs (72.2%, 71.1% and 55.1%, respectively). The INNOVANCE PFA-100 P2Y test seems to be comparable to other established platelet function assays in detecting clopidogrel resistance. However, the modest agreement among platelet function methods makes the performance of platelet function testing crucial with more than one technique in order to reliably identify poor responders to clopidogrel treatment.     

The Role of Exercise on Platelet Aggregation in Patients with Stable Coronary Artery Disease: Exercise Induces Aspirin Resistant Platelet Activation

Objectives: The aim of our study was to determine the relation between exercise stress test and aspirin resistance in patients with stable coronary artery disease.Background: Clinically aspirin resistance is defined as having thrombotic and embolic cardiovascular events despite regular aspirin therapy.Methods: We studied platelet functions of 62 patients with stable coronary artery disease and 20 subjects with normal coronary arteries by Platelet Function Analyzer (PFA-100, Dade Behring, Germany) at rest and after exertion with collagen and/or epinephrine (Col/Epi) and collagen and/or ADP cartridges. Closure time (CT) < 186 seconds was defined as aspirin resistance with Col/Epi cartridges of PFA-100. Symptom limited treadmill stress test (protocol of Bruce) was performed with Oxford Streslink TD-1 system.Results: 8 (12.9%) patients were aspirin resistant by PFA-100 (CT < 186s despite regular aspirin therapy) at rest. At the first minute of the recovery period of exercise stress test 14 (22.5%) patients were aspirin resistant by PFA-100. CTs with Col/ADP were respectively 89 ± 6 s (83–100s) and 89 ± 5 s (82–104s) at rest and after exercise (p = 0.107). 20.3% (11/54) of patients known as in vitro aspirin sensitives at rest had shorter CTs and 11.1% (6/54) had aspirin resistance after exercise (p = 0.004). There was no statistically significiant difference in platelet functions in the control group after exertion.Conclusion: We conclude that 11.1% of in vitro aspirin sensitive subjects at rest had aspirin resistance after exercise by PFA-100. In some individuals, exercise induced platelet activation is aspirin insensitive at usual antiplatelet doses. We need further clinical trials to optimize antiplatelet therapy in patients with coronary artery disease.The main supporter of the study was Turkish Society of Cardiology (Istanbul, Turkey). The society is a non-profit association and a member of the European Society of Cardiology. The PFA-100 device and test cartridges are bought with the grant of this non-profit association.