Variability in aggregometry response before and after initiation of clopidogrel therapy

Abstract

Background: Evaluation of clopidogrel therapy by in vitro methods has limitations which may be of clinical importance. We wanted to explore the variability in aggregometry response in aspirin sensitive patients before and after initiation of clopidogrel therapy. Methods: ADP 9.37 μM, AA 1.2mM and TRAP 25mM stimulated light transmissions aggregometry (LTA) were performed twice before (Exams 1 and 2; 3 weeks apart)-and within one year after-initiation of clopidogrel therapy (Exam 3) in 79 patients treated with PCI. Repeated ADP aggregometry was also performed in 16 healthy volunteers in order to estimate LTA measurement error. Result:. Inter-individual differences in ADP aggregation e.g. at Exam 1 were substantial (range 17–77%, SD 15.8%). Intra-individual changes between Exams 1 and 2 were significant (?27 to +36%, SD 14.6%, p<0.05). Inter-individual differences at Exam 3 (on clopidogrel treatment) were larger than expected from Exams 1 and 2 (p<0.01). AA aggregation was the same before and during clopidogrel treatment. In controls, inter-individual differences were smaller at ADP 10 than at ADP 5μM. Conclusions. Inter-individual differences in ADP aggregation were significant both before and during clopidogrel therapy, and there were significant intra-individual variations over time. Therefore, prediction of aggregometry response before or during clopidogrel therapy based on single tests may be unreliable. Inter-individual differences in healthy controls are smaller at high concentrations of ADP, and comparisons of aggregometry response should be performed with caution unless ADP concentrations are standardized.     

Standardization of light transmittance aggregometry for monitoring antiplatelet therapy: an adjustment for platelet count is not necessary

Summary. Background: Light transmittance aggregometry (LTA) is considered to be the ‘gold standard’ of platelet function testing. As LTA has been poorly standardized, we analyzed the results of LTA in healthy subjects and patients with antiplatelet therapy using different concentrations of agonists and performing tests in non‐adjusted and platelet count‐adjusted platelet‐rich plasma (PRP). Methods: LTA was performed in 20 healthy subjects and in patients treated with aspirin (n = 30) or clopidogrel (n = 30) monotherapy, as well as in patients on combination therapy (n = 20), using arachidonic acid (ARA 0.25 and 0.5 mg mL⁻¹) and adenosine diphosphate (ADP 2 and 5 μm ) as agonists and performing platelet function tests in non‐adjusted and platelet count (250 nL⁻¹ ± 10%)‐adjusted PRP. Results: The overall platelet aggregation response is decreased after adjusting the PRP for platelet count compared with measurements in unadjusted PRP. The variability of aggregation results is high in adjusted PRP in the subgroup of healthy subjects, ranging from 9.2–95.3% (5th–95th percentile) relative to 77.6–95.5% in non‐adjusted PRP when determining maximum aggregation to ARA 0.5 mg mL⁻¹. Late aggregation using ADP 2 μm ranges from 3.8–89.9% in adjusted PRP compared with 42.9–92.5% in non‐adjusted PRP. Maximum aggregation using ARA 0.5 mg mL⁻¹ in non‐adjusted PRP differentiates between aspirin‐treated patients and healthy controls well, whereas late aggregation using ADP 2 μm in non‐adjusted PRP offers the best discrimination between clopidogrel‐treated patients and healthy controls. Conclusion: Adjustment of PRP for platelet count does not provide any advantage and therefore the time‐consuming process of platelet count adjustment is not necessary.     

Microvesicles from patients with acute coronary syndrome enhance platelet aggregation

Abstract

Microvesicles (MVs) released from leukocytes, platelets and endothelial cells are elevated in patients with acute coronary syndrome (ACS). In the present study, we assessed the potential pro-aggregatory properties of MVs obtained from ACS patients. Thus, we divided the patients into two groups based on clopidogrel-responsiveness, i.e. high on-treatment platelet reactivity (HPR; n?=?16), and low or normal on-treatment platelet reactivity (non-HPR; n?=?14), respectively. MVs from patients were obtained by high-speed centrifugation, and the pro-aggregatory effect of MVs added to fresh isolated platelets from healthy subjects were analyzed by 96-well microplate aggregometry. MVs from HPR patients significantly enhanced spontaneous platelet aggregation around two times more than MVs from non-HPR patients. The pro-aggregatory effect of three out of four MV phenotypes correlated to MV-concentrations as determined by flow cytometry. Furthermore, MVs from patients with diabetes mellitus (n?=?9) had a stronger pro-aggregatory effect compared to MVs from those without diabetes (n?=?21; p?=?.025 between groups). In conclusion, MVs from ACS patients with clopidogrel non-responsiveness enhance platelet aggregation, as do MVs from ACS patients with diabetes. Thus, MVs from patients with hyperreactive platelets boost platelet aggregation. Blocking MV-formation may reduce platelet hyperreactivity.     

Randomized,double‐blind comparison of effects of abiciximab bolus only vs. on‐label regimen on ex vivo inhibition of platelet aggregation in responders to clopidogrel undergoing coronary stenting

Summary. Background: On top of aspirin, an abciximab bolus‐only regimen results in a 30% drop in platelet inhibition at 6 h as compared with the on‐label regimen. The concomitant administration of high loading dose clopidogrel, by bridging with abciximab bolus, may sustain suppression of platelet activity over time. Objectives: To investigate the non‐inferiority of abciximab bolus‐only and concomitant high loading dose clopidogrel vs. abciximab bolus + infusion with respect to the inhibition of platelet aggregation (IPA) as determined by light transmission aggregometry. Patients/Methods: Seventy‐three patients with non‐ST segment elevation acute coronary syndromes underwent double‐blind randomization to abciximab bolus followed by a 12‐h placebo infusion and concomitant 600‐mg clopidogrel vs. abciximab bolus + a 12‐h infusion and 300 mg of clopidogrel. IPA was determined by light transmission aggregometry throughout 24 h. Clopidogrel poor responsiveness was defined as ≥ 50% 5 μmol L^?1 ADP‐induced maximum platelet aggregation. Results: In clopidogrel responders (n = 68), IPA after 20 μmol L^?1 ADP at 4 h was 89% ± 13% in the bolus‐only arm vs. 92% ± 14% in the bolus + infusion arm (P = 0.011 for non‐inferiority). IPA after 5 or 20 μmol L^?1 ADP and 5 or 15 μmol L^?1 TRAP and the proportion of patients showing ≥ 80% IPA did not differ at any time point, irrespective of clopidogrel responsiveness status. Thirty‐day outcomes were similar, whereas hemoglobin (0.91 ± 0.8 vs. 0.5 ± 0.7 g dL^?1; P = 0.01) and platelet count mean drop (41.7 ± 57 vs. 18.6 ± 34 10⁹ L^?1; P = 0.042) were significantly reduced in the bolus‐only arm. Conclusions: Withholding abciximab post‐bolus infusion in patients receiving high loading dose clopidogrel does not impair platelet inhibition throughout 24 h, and has the potential to improve the safety profile of the drug at reduced costs.     

Clopidogrel discontinuation and platelet reactivity following coronary stenting

See also Lordkipanidzé M, Harrison P. Beware of being caught on the rebound. This issue, pp 21–3. Summary. Aims: Antiplatelet therapy with aspirin and clopidogrel is recommended for 1 year after drug‐eluting stent (DES) implantation or myocardial infarction. However, the discontinuation of antiplatelet therapy has become an important issue as recent studies have suggested a clustering of ischemic events within 90 days of clopidogrel withdrawal. The objective of this investigation was to explore the hypothesis that there is a transient ‘rebound’ increase in platelet reactivity within 3 months of clopidogrel discontinuation. Methods and Results: In this prospective study, platelet function was assessed in patients taking aspirin and clopidogrel for at least 1 year following DES implantation. Platelet aggregation was measured using a modification of light transmission aggregometry in response to multiple concentrations of adenosine diphosphate (ADP), epinephrine, arachidonic acid, thrombin receptor activating peptide and collagen. Clopidogrel was stopped and platelet function was reassessed 1 week, 1 month and 3 months later. Thirty‐two patients on dual antiplatelet therapy were recruited. Discontinuation of clopidogrel increased platelet aggregation to all agonists, except arachidonic acid. Platelet aggregation in response to ADP (2.5, 5, 10, and 20 μm ) and epinephrine (5 and 20 μm ) was significantly increased at 1 month compared with 3 months following clopidogrel withdrawal. Thus, a transient period of increased platelet reactivity to both ADP and epinephrine was observed 1 month after clopidogrel discontinuation. Conclusions: This study demonstrates a transient increase in platelet reactivity 1 month after clopidogrel withdrawal. This phenomenon may, in part, explain the known clustering of thrombotic events observed after clopidogrel discontinuation. This observation requires confirmation in larger populations.     

Which platelet function test is suitable to monitor clopidogrel responsiveness? A pharmacokinetic analysis on the active metabolite of clopidogrel

Summary. Background: Multiple platelet function tests claim to be P2Y12‐pathway specific and capable of capturing the biological activity of clopidogrel. Objectives: The aim of the present study was to determine which platelet function test provides the best reflection of the in vivo plasma levels of the active metabolite of clopidogrel (AMC). Patients/methods: Clopidogrel‐naive patients scheduled for elective percutaneous coronary intervention (PCI) received a 600 mg loading dose of clopidogrel and 100 mg of aspirin. For pharmacokinetic analysis, blood was drawn at 0, 20, 40, 60, 90, 120, 180, 240 and 360 min after clopidogrel loading and peak plasma concentrations (C_max) of the AMC were quantified with liquid chromatography‐tandem mass spectrometry (LC‐MS/MS). Platelet function testing was performed at baseline and 360 min after the clopidogrel loading. Results: The VASP‐assay, the VerifyNow P2Y12‐assay and 20 μmol L^?1 adenosine diphosphate (ADP)‐induced light transmittance aggregometry (LTA) showed strong correlations with C_max of the AMC (VASP: R² = 0.56, P < 0.001; VerifyNow platelet reactivity units (PRU): R² = 0.48, P < 0.001; VerifyNow %inhibition: R² = 0.59, P < 0.001; 20 μmol L^?1 ADP‐induced LTA: R² = 0.47, P < 0.001). Agreement with C_max of the AMC was less evident for 5 μmol L^?1 ADP‐induced LTA or whole blood aggregometry (WBA), whereas the IMPACT‐R ADP test did not show any correlation with plasmalevels of the AMC. Conclusion: The flow cytometric VASP‐assay, the VerifyNow P2Y12 assay and, although to a lesser extent, 20 μmol L^?1 ADP‐induced LTA correlate best with the maximal plasma level of the AMC, suggesting these may be the preferred platelet function tests for monitoring the responsiveness to clopidogrel.     

Reversal of the anti‐platelet effects of aspirin and clopidogrel

Summary. Background: Guidelines recommend stopping aspirin and clopidogrel 7 to 10 days before surgery to allow time for replacement of permanently inhibited platelets by newly released uninhibited platelets.Objectives: The purpose of the present study was to determine the rate of offset of the anti‐platelet effects of aspirin and clopidogrel after stopping treatment and the proportion of untreated donor platelets that are required to reverse their anti‐platelet effects.Methods: Cohort 1 consisted of 15 healthy subjects who received aspirin 81 mg day^?1 or clopidogrel 75 mg day^?1 for 7 days and underwent serial blood sampling until platelet function testing results normalized. Cohort 2 consisted of 36 healthy subjects who received aspirin 325 mg day^?1, clopidogrel 75 mg day^?1, aspirin 81 mg day^?1 plus clopidogrel 75 mg day^?1 or no treatment for 7 days and underwent a single blood sampling.Results: In cohort 1, arachidonic acid (AA)‐induced light transmission aggregation (LTA) returned to baseline levels in all subjects within 4 days of stopping aspirin, coinciding with the partial recovery of plasma thromboxane B₂ concentrations. ADP‐induced LTA did not return to baseline levels until 10 days after stopping clopidogrel. In cohort 2, AA‐induced LTA in patient treated with aspirin reached control levels after mixing with 30% untreated donor platelets whereas ADP‐induced LTA in patients treated with clopidogrel reached control levels only after the addition of 90% or more donor platelets.Conclusions: Platelet aggregation recovers within 4 days of stopping aspirin but clopidogrel must be stopped for 10 days to achieve a normal aggregatory response.     

In vitro platelet function of platelet concentrates prepared using three different apheresis devices determined by impedance and optical aggregometry

BACKGROUND: Testing the functional capacity of platelets (PLTs) from platelet concentrates (PC) is a main issue in transfusion medicine. Therefore, the aim was to study agonist-inducible PLT aggregation of PLTs obtained by three apheresis devices. A semiautomated impedance aggregometry-based whole-blood method (multiplate electrode PLT aggregometry [MEA]) was modified for the use of PLTs from PC and data were compared with light transmission aggregometry (LTA).
STUDY DESIGN AND METHODS: PLT function was determined in 135 PCs without reconstitution with red blood cells (RBCs), obtained by three devices: Amicus, Trima Accel collection system, and MCS+. PLT function was assessed by the Multiplate TRAP test, and the area under the curve (AUC) was quantified. TRAP-6–inducible maximal PLT aggregation (MA%) by LTA was used for analyses.
RESULTS: The AUC was significantly lower in the Amicus PLTs compared to the Trima and MCS+ PLTs (Amicus versus Trima, p = 0.007; Amicus versus MCS+, p < 0.001). The Amicus PLTs were significantly less responsive to TRAP-6–inducible PLT aggregation than Trima (p = 0.002) or MCS+ PLTs (p < 0.001) by LTA, and Trima PLTs responded significantly less than MCS+ PLTs (p = 0.001). There was only a weak correlation between MEA and LTA (r = 0.29, p = 0.019).
CONCLUSION: PLTs obtained by the Amicus system show significantly less aggregation response to thrombin receptor stimulation compared to those obtained with other cell separators, examined by MEA and LTA. Testing PLT function in PCs by the MEA is a simple and rapid method without the need of adding RBCs. However, LTA and MEA appear to measure different aspects of PLT function.     

Results of a worldwide survey on the assessment of platelet function by light transmission aggregometry: a report from the platelet physiology subcommittee of the SSC of the ISTH

Background: Light transmission aggregometry (LTA) is the most common method used in clinical and research laboratories to assess platelet function. However, the method has never been standardized. Objectives: As the first step towards development of methodological guidelines, the Platelet Physiology Subcommittee of the Scientific and Standardization Committee of the International Society on Thrombosis and Haemostasis (ISTH) undertook a large, detailed, global survey of LTA practices. Methods: Members of ISTH and of External Quality Assurance in Thrombosis and Haemostasis organizations were invited to complete a 129 item, online questionnaire. Results were analyzed anonymously to participant identities. Results: The online supplement for this article ( http://www.isth.org/Publications/OfficialCommunications/PlateletPhysiology/LightTransmissionAggregometry/tabid/201/Default.aspx ) contains the full details of the study findings. 359 (244 clinical, 115 research) laboratories from 48 countries participated in the survey. LTA was widely used to assess inherited or acquired bleeding disorders. Common practices were identified in sample collection, processing and analysis and although some are generally considered acceptable, others are not ideal. The agonist concentrations used for LTA varied, and many laboratories used ADP, collagen, epinephrine and Ristocetin, at more than one concentration, in addition to arachidonic acid. The parameters commonly used to assess LTA responses were maximal amplitude or % aggregation, which was considered particularly important, in addition to the presence of a ‘secondary wave’, deaggregation, shape change and a measure of the lag phase. However, many laboratories did not have appropriate reference intervals. Conclusions: This is the largest and most detailed survey of LTA practices ever undertaken. It shows a very high variability in LTA practices worldwide, and, as a consequence, methodological standardization is necessary. The information gathered in this survey will be helpful in the development of ISTH methodological guidelines for LTA.     

Use of ISTH bleeding assessment tool to predict inherited platelet dysfunction in resource constrained settings

Background: The International Society of Thrombosis &; Hemostasis (ISTH) bleeding assessment tool (ISTH-BAT) is used to record bleeding symptoms in patients with possible bleeding disorders.

Aim: To investigate the utility of the ISTH-BAT in predicting platelet dysfunction in individuals with suspected inherited platelet function disorders.

Method: Individuals with clinical evidence of bleeding and suspected inherited platelet function disorder and healthy volunteers were included in the study. The ISTH-BAT questionnaire was applied prior to light transmission aggregometry (LTA).

Results: A total of 261 participants were included (100 healthy volunteers, and 161 with suspected inherited platelet function disorders). The ISTH-BAT score in participants with suspected inherited platelet function disorders (median 2; interquartile range [IQR] 5–1) was significantly higher than in healthy volunteers (median 0; IQR 2–0). There was also a significant difference between participants with suspected inherited platelet function disorders with a platelet defect detected by LTA (median 4; IQR 8–3) and those with normal platelet function (median 2; IQR 3–1) (p?p?=?p?=?< 0.001]).

Conclusion: The ISTH-BAT is a useful tool for documenting bleeding symptoms and the score obtained is also predictive of the presence of a platelet defect on LTA in patients with suspected inherited platelet dysfunction.     

Adenosine diphosphate-inducible platelet reactivity shows a pronounced age dependency in the initial phase of antiplatelet therapy with clopidogrel

Summary.  Background:  Until recently, there were hardly any data on the antiplatelet effect of clopidogrel in advanced age. Like other metabolic processes, the conversion of clopidogrel to its active metabolite may be impaired in older patients, leading to high on-treatment residual ADP-inducible platelet reactivity. Objective:  To investigate the age dependency of clopidogrel-mediated platelet inhibition. Patients and methods:  This was a prospective observational study. We determined adenosine 5'-diphosphate (ADP)-inducible platelet reactivity using light transmission aggregometry (LTA) and the VerifyNow P2Y12 assay in 191 patients on dual antiplatelet therapy after angioplasty and stenting for cardiovascular disease. Results:  ADP-inducible platelet reactivity increased linearly with age after adjustment for cardiovascular risk factors, type of intervention, medication, C-reactive protein (CRP) and renal function [using LTA 0.36% of maximal aggregation per year, 95% CI 0.08–0.64%, P  = 0.013; using the VerifyNow P2Y12 assay 3.2 P2Y12 reaction units (PRU) per year, 95% CI 1.98–4.41 PRU, P  < 0.001]. ADP-inducible platelet reactivity was significantly higher in patients aged 75 years or older compared with younger patients ( P  = 0.003 for LTA and P  < 0.001 for the VerifyNow P2Y12 assay). Further, high on-treatment residual ADP-inducible platelet reactivity was significantly more common among patients aged 75 years or older ( P  = 0.02 for LTA and P  < 0.001 for the VerifyNow P2Y12 assay). Conclusion:  ADP-inducible platelet reactivity shows a pronounced age dependency in the initial phase of antiplatelet therapy with clopidogrel. The clinical implications of these findings need to be addressed in future trials.     

Investigation of drug–drug interactions between clopidogrel and fluoxetine

Drug–drug interactions may contribute to the variability of the response of clopidogrel. Several hypotheses have been proposed concerning the potential modification of clopidogrel pharmacokinetics and pharmacodynamics by fluoxetine. This open‐label crossover study assessed the effect of fluoxetine on the pharmacological activity of clopidogrel in healthy volunteers. Eight healthy male volunteers received a single 600‐mg loading dose of clopidogrel followed by 20 mg of fluoxetine on 4 days and then 20 mg of fluoxetine plus 600 mg of clopidogrel on the fifth day. Eleven blood samples were withdrawn after clopidogrel administration to determine plasma concentrations of clopidogrel active metabolite (CAM) and platelet function. Platelet aggregation was measured by light transmittance aggregometry (LTA) and platelet reactivity index by flow cytometric vasodilator‐stimulated phosphoprotein (VASP) analysis. The areas under the curve and maximum plasma concentrations of CAM were, respectively, 20.6 and 25.3% lower after co‐administration of fluoxetine compared with administration of clopidogrel alone. The percentage maximum platelet aggregation values in the presence of 5 μm and 10 μm adenosine diphosphate, measured by LTA, were, respectively, 13.9 and 22.4% lower after fluoxetine co‐administration. The platelet reactivity index measured by the flow cytometric VASP method was 36.8% lower when clopidogrel was administered in conjunction with fluoxetine.     

Multiple electrode aggregometry predicts stent thrombosis better than the vasodilator‐stimulated phosphoprotein phosphorylation assay

Summary. Background and Aim: The prognostic value of the vasodilator‐stimulated phosphoprotein (VASP) phosphorylation assay and multiple electrode aggregometry (MEA) for thrombotic adverse events has been shown in independent studies. As no direct comparison between the two methods has been made so far, we investigated which laboratory approach has a better predictive value for stent thrombosis. Methods: The VASP phosphorylation assay and MEA were performed in 416 patients with coronary artery disease undergoing percutaneous coronary intervention. The rate of stent thrombosis was recorded during a 6‐month follow‐up. Results: Definite stent thrombosis occurred in three patients (0.7%) and probable stent thrombosis in four (1%). Receiver operating characteristic (ROC) analysis demonstrated that MEA distinguishes between patients with or without subsequent stent thrombosis better than the VASP phosphorylation assay: the area under the ROC curve was higher for MEA (0.92; P = 0.012) than for the VASP phosphorylation assay (0.60; P = 0.55). At equal levels of sensitivity (100%), the specificity was greater for MEA than for the VASP phosphorylation assay (86% vs. 37%). Stent thrombosis occurred in 9% of patients with platelet hyperreactivity in MEA, who were simultaneously clopidogrel non‐responders in the VASP phosphorylation assay. Interestingly, clopidogrel non‐responders in the VASP phosphorylation assay without platelet hyperreactivity in MEA did not suffer from stent thrombosis. Conclusions: Platelet hyperreactivity in MEA might be a better risk predictor for stent thrombosis than the assessment of the specific clopidogrel effect with the VASP phosphorylation assay.     

Phenotyping vs. genotyping for prediction of clopidogrel efficacy and safety: the PEGASUS‐PCI study

Summary. Background: Prognostic values of genotyping and phenotyping for assessment of clopidogrel responsiveness have been shown in independent studies.Objectives: To compare different assays for prediction of events during long‐term follow‐up.Methods: In this prospective cohort study polymorphisms of CYP2C19*2 and CYP2C19*17 alleles, vasodilator‐stimulated phosphoprotein phosphorylation (VASP) assay, multiple electrode aggregometry (MEA), cone and platelet analyser (CPA) and platelet function analyser (PFA‐100) were performed in 416 patients undergoing percutaneous coronary intervention. The rates of events were recorded during a 12‐month follow‐up.Results: Platelet aggregation by MEA predicted stent thrombosis (2.4%) better (c‐index = 0.90; P < 0.001; sensitivity = 90%; specificity = 83%) than the VASP assay, CPA or PFA‐100 (c‐index < 0.70; P > 0.05; sensitivity < 70%; specificity < 70% for all) or even the CYP2C19*2 polymorphism (c‐index < 0.56; P > 0.05; sensitivity = 30%; specificity = 71%). Survival analysis indicated that patients classified as poor responders by MEA had a substantially higher risk of developing stent thrombosis or MACE than clopidogrel responders (12.5% vs. 0.3%, P < 0.001, and 18.5% vs. 11.3%, P = 0.022, respectively), whereas poor metabolizers (CYP2C19*1/*2 or *2/*2 carriers) were not at increased risks (stent thrombosis, 2.7% vs. 2.5%, P > 0.05; MACE, 13.5% vs. 12.1%, P = 0.556). The incidence of major bleedings (2.6%) was numerically higher in patients with an enhanced vs. poor response to clopidogrel assessed by MEA (4% vs. 0%) or in ultra‐metabolizers vs. regular metabolizers (CYP2C19*17/*17 vs. CYP2C19*1/*1; 9.5% vs. 2%). The classification tree analysis demonstrated that acute coronary syndrome at hospitalization and diabetes mellitus were the best discriminators for clopidogrel responder status.Conclusions: Phenotyping of platelet response to clopidogrel was a better predictor of stent thrombosis than genotyping.     

High on‐aspirin platelet reactivity as measured with aggregation‐based,cyclooxygenase‐1 inhibition sensitive platelet function tests is associated with the occurrence of atherothrombotic events

Summary. Background: High on‐aspirin platelet reactivity (HAPR) is associated with atherothrombotic events following percutaneous coronary intervention (PCI). The aim of the present study was to identify the platelet function test sensitive for platelet cyclooxygenase‐1 inhibition that best predicts atherothrombotic events. Methods and results: Nine hundred and fifty‐one consecutive patients on dual antiplatelet therapy undergoing elective PCI were enrolled. On‐aspirin platelet reactivity was measured in parallel by arachidonic acid (AA)‐induced light transmittance aggregometry (AA‐induced LTA), the VerifyNow® Aspirin Assay (VerifyNow® Aspirin Assay), the arachidonic acid prestimulated IMPACT‐R (IMPACT‐R AA) and the PFA‐100 collagen/epinephrine cartridge (PFA COL/EPI). Cut‐offs for HAPR were established by receiver‐operator characteristic curve analysis. At 1‐year follow‐up, the composite of all‐cause death, non‐fatal acute myocardial infarction, stent thrombosis and ischemic stroke occurred more frequently in patients with HAPR when assessed by LTA [10.1% vs. 6.0%, P = 0.020 (n = 925)] and VerifyNow^® [13.3% vs. 5.9%, P = 0.015 (n = 422)]. The VerifyNow^® ASA assay (AUC = 0.78) and, to a lesser extent, AA‐induced LTA (AUC = 0.73) added significantly to a model consisting of clinical and procedural risk factors in predicting atherothrombotic events. In contrast, the IMPACT‐R (n = 791) and the PFA Collagen/Epinephrine (n = 719) were unable to discriminate between patients with and without primary endpoint at 1‐year follow‐up. None of the platelet function tests was able to identify patients at risk for bleeding. Conclusions: AA‐induced LTA and the VerifyNow^® ASA test were able to identify aspirin‐treated patients undergoing PCI with stenting at risk for atherothrombotic events. The VerifyNow^® Aspirin Assay had the highest predictive accuracy. None of the tests was able to identify patients at higher risk of bleeding.     

On-treatment platelet reactivity in peripheral and coronary blood in patients undergoing primary PCI for ST-segment elevation myocardial infarction (STEMI)

Dual antiplatelet therapy is recommended in patients undergoing primary percutaneous coronary intervention (p-PCI) for ST-segment elevation myocardial infarction (STEMI). Pre-analytical variables may influence platelet function analysis results. Our aim was to evaluate the on-treatment platelet reactivity in peripheral artery vs coronary blood in patients with STEMI. We enrolled one hundred and nine patients who consecutively underwent p-PCI at Cardiology Unit of Padua University Hospital between June 2014 and June 2015. Before the procedure, all patients received intravenous aspirin 250?mg and either of the thienopyridines; clopidogrel 600?mg, prasugrel 60?mg or ticagrelor 180?mg. ASPI-test and ADP-test using multiple electrode aggregometry (MEA) were performed in samples collected from both a peripheral artery and the culprit coronary artery. ‘Low responders’ were patients with an ASPI-test or ADP-test value greater than or equal to a pre-established normal range. No significant differences were observed in ASPI-test values between peripheral (19 (median) [3–49 (10–90 percentiles)] U) vs coronary (12 [1–40] U, p?=?.06) blood and in ADP-test (40 [14–82] U vs 33 [7–79] U, p?=.68) blood. In peripheral blood, fifteen (14%) patients were ‘low aspirin’ and forty-one (38%) ‘low thienopyridines’ responders. The prevalence of ‘low clopidogrel’ responders was higher (45%) than prasugrel (36%) and ticagrelor (33%). Similar results were observed in coronary blood. In patients undergoing p-PCI for STEMI, MEA platelet function observed in coronary arteries was consistent with peripheral artery blood’s independently of the antiplatelet drug used. The clinical significance of peripheral and coronary on-aspirin/thienopyridines platelet reactivity needs further clarification.     

血栓弹力图法与光学比浊法监测冠心病患者阿司匹林抵抗的效果比较

目的：评价血栓弹力图法（TEG）与光学比浊法（LTA）监测冠心病患者阿司匹林抵抗的一致性。方法通过LTA法与TEG法检测70例冠心病患者的血小板聚集功能,并对两种方法的检测结果进行一致性比较。结果LTA法和TEG法检测阿司匹林抵抗的发生率分别为10．0％和11．4％;两种方法检测阿司匹林抵抗具有好的一致性（Kappa＝0．790）。结论TEG法与LTA法具有好的一致性,可用于评价阿司匹林的临床疗效,指导临床治疗。     

Randomized double‐blind placebo‐controlled crossover study to determine the effects of esomeprazole on inhibition of platelet function by clopidogrel

Summary. Background: Pharmacokinetic studies suggest that clopidogrel and esomeprazole are metabolized by similar hepatic enzymes; however, previous studies have not identified a biochemical interaction. Objectives: To determine whether addition of esomeprazole to patients receiving aspirin and clopidogrel reduces the antiplatelet effects of clopidogrel. Patient/Methods: Patients with a history of an acute coronary syndrome who had previously received clopidogrel were recruited. Subjects were commenced on clopidogrel and randomized to one of two treatment arms (esomeprazole or placebo) for 6 weeks. Following a 2‐week washout period for study medications, patients were crossed over onto the alternative treatment arm for a further 6 weeks. Platelet function tests were undertaken at baseline, following the first treatment period, after washout and following the second treatment period. Results: Thirty‐one patients were enrolled. Significant attenuation of clopidogrel’s antiplatelet effects was seen with co‐administration of esomeprazole compared with placebo. Vasodilator stimulated phosphoprotein (VASP), platelet aggregometry (area under the curve (AUC)) and VerifyNow results were 54.7% ± 2.8 platelet reactivity index (PRI), 66.3 ± 2.6 AUC units and 213.1 ± 14.1 platelet reactivity units (PRU) with esomeprazole vs. 47% ± 2.7 PRI, 59.7 ± 3.7 AUC units and 181.4 ± 14.6 PRU with placebo (P < 0.01 esomeprazole vs. placebo for all measures). There was no significant difference in platelet aggregometry (maximal aggregation) between the esomeprazole group (68.9% ± 2.7 units) and placebo‐treated group (64.5% ± 4.1 units; P > 0.05). Conclusion: Esomeprazole when co‐administered with aspirin and clopidogrel results in a significant attenuation of clopidogrel’s antiplatelet effects.     

Effect of platelet turnover on whole blood platelet aggregation in patients with coronary artery disease

Summary. Background: Previous studies have demonstrated considerable variation in the antiplatelet effect of aspirin. Objectives: To investigate the impact of platelet turnover on the antiplatelet effect of aspirin in patients with stable coronary artery disease (CAD) and to identify determinants of platelet turnover. Methods: Platelet turnover was evaluated by measurements of immature platelets and thrombopoietin in 177 stable CAD patients on aspirin monotherapy, including 85 type 2 diabetics and 92 non‐diabetics. Whole blood platelet aggregation was determined using the VerifyNow^® Aspirin test and multiple electrode aggregometry (MEA, Multiplate^®) induced by arachidonic acid (AA) (1.0 mm ), adenosine diphosphate (ADP) (10 μm ) and collagen (1.0 μg mL^?1). Results: Immature platelet levels significantly correlated with MEA (r = 0.31–0.36, P‐values < 0.0001) and the platelet activation marker sP‐selectin (r = 0.19, P = 0.014). Contrary to the VerifyNow^® test, MEA significantly correlated with variations in platelet count (r = 0.45–0.68, P‐values < 0.0001). Among patients with residual platelet reactivity according to AA, there were significantly more diabetics (61% vs. 41%, P = 0.027) and higher levels of sP‐selectin (77.7 ± 29 vs. 70.2 ± 25 ng mL^?1, P = 0.070) and serum thromboxane B₂ (0.81 [0.46; 1.70] vs. 0.56 [0.31; 1.12] ng mL^?1, P = 0.034). In a multivariate regression analysis, immature platelet levels were determined by thrombopoietin levels (P < 0.001), smoking (P = 0.020) and type 2 diabetes (P = 0.042). Conclusions: The antiplatelet effect of aspirin was reduced in CAD patients with an increased platelet turnover. Once‐daily dosing of aspirin might not suffice to adequately inhibit platelet aggregation in patients with an increased platelet turnover.     

血栓弹力图法与光学比浊法监测氯吡格雷疗效的对比研究

目的：对比研究监测急性冠状动脉综合征患者氯吡格雷疗效的两种方法：血栓弹力图法（TEG）与光学比浊法（LTA）。方法用 LTA法与TEG法检测2013年2月～12月期间心内科68例急性冠状动脉综合征患者的血小板聚集功能,并对两种方法的检测结果进行比较。结果 TEG监测的血小板抑制率为（47.84±26.04）％,LTA监测的血小板聚集率为（45.64±20.92）％。患者组中 LTAADP与TEGADP存在负相关（r＝－0.752,P＜0.001）;LTAADP与 MAADP存在正相关（r＝0.789,P＜0.001）;TEGADP与 MAADP呈负相关（r＝－0.820,P＜0.001）。结论 TEG血小板图与 LTA监测氯吡格雷疗效具有较好的相关性。用 MAADP联合TEGADP监测氯吡格雷抗血小板治疗效果,可提供更高的临床预测价值。