Expert position paper on the role of platelet function testing in patients undergoing percutaneous coronary intervention

Optimizing outcomes after percutaneous coronary intervention (PCI) requires balancing between the risks of thrombotic and bleeding events in individual patients.1–3 However, finding the optimal balance is not always straightforward since the risks of thrombotic and bleeding complications may differ extremely between individuals. In addition, the individual effects of anticoagulant and antiplatelet drugs are not uniform in patients.4 Recent European guidelines1,3 recommend the use of prasugrel or ticagrelor instead of clopidogrel in all PCI-treated acute coronary syndrome (ACS) patients without contraindication, acknowledging that laboratory assessment of P2Y12-receptor inhibition may be considered only in selected cases when clopidogrel is used.1 However, there is no guidance with respect to the appropriate methodology and the suggested interpretation of results. The Working Group on Thrombosis of the European Society of Cardiology aimed to review the available evidence and the clinical relevance of platelet function testing in order to reach a consensus regarding the methodology, evaluation, and clinical interpretation of platelet function in patients undergoing PCI. Regarding the choice between available P2Y12-inhibitors, the 2011 ESC guidelines on non-ST segment elevation acute coronary syndromes (NSTE-ACS)1 and the 2012 guidelines on ST-segment elevation myocardial infarction3 recommend prasugrel and ticagrelor for all ACS patients without contraindication, and clopidogrel is only recommended if these agents are not available. Despite the restrictive recommendations for clopidogrel, it still holds a class I indication in ACS due to the large differences in the availability of the new-generation P2Y12-inhibitors among European countries. According to the 2011 ACCF/AHA/SCAI guidelines for PCI,5 a P2Y12-inhibitor should be given for ACS patients without preferring novel P2Y12-inhibitors over clopidogrel. Similarly, the 2012 ACCF/AHA unstable angina/non-ST-segment elevation myocardial infarction guidelines6 and the 2013 ACCF/AHA ST-elevation myocardial infarction guidelines7 do not explicitly endorse one of the P2Y12-inhibitors over the other, acknowledging that large-scale, randomized clinical data on the use of prasugrel and ticagrelor are still limited. The 2011 ESC guidelines on NSTE-ACS1 issued a class IIb indication for platelet function testing stating that it may be considered in selected cases when clopidogrel is used. However, routine use of platelet function testing is not recommended because dose adaptation of clopidogrel according to residual platelet reactivity failed to show any clinical benefit.8–10 According to the 2011 ACCF/AHA/SCAI guidelines for PCI,5 platelet function testing may be considered in patients at high risk for poor clinical outcomes after PCI. If results reveal high on-treatment platelet reactivity (HPR), alternative agents, such as prasugrel or ticagrelor, may be considered. (Supplementary material online, Table S1) There are a wide variety of methods for monitoring platelet reactivity (Supplementary material online, Table S2). The global aggregation measure approach (platelet aggregation) is usually less specific to the drug action while analysis of the drug effect with high specificity at subcellular levels [such as vasodilator-stimulated phosphoprotein (VASP) phosphorylation] gives less information regarding the overall state of the activation-aggregation cascade. Testing the efficacy of aspirin is methodologically more complicated and less reliable than measuring the effects of P2Y12-receptor inhibitors.11,12 Monitoring the serum levels of thromboxane B2 (TxB2), the stable metabolite of TXA2, after aspirin administration is complex.13 As a surrogate, its urinary-excreted stable metabolite (11-dehydro-thromboxane B2, dTXB2) can be determined.11 However, these compounds can be generated via COX-1-independent, COX-2-dependent pathways, which may reflect the overall inflammatory status rather than platelet inhibition by aspirin ‘per se’.13 Therefore, the antiplatelet efficacy of aspirin is preferentially assessed via the indirect effect of TXA2-induced platelet aggregation by adding arachidonic acid to blood samples.11 Many non-COX-specific agonists (ADP, epinephrine, and collagen) are also used to evaluate ‘aspirin response’ with a common drawback of overestimation of true aspirin resistance.12,14 Therefore, most of the available methods are not specific for the effect of aspirin, but also reflect the overall inflammatory and hyper-reactive state of patients.13 Residual platelet reactivity during P2Y12-inhibitor treatment is evaluated via stimulating platelets with ADP.15 Results can be assessed at the stage of intracellular signalling pathways (VASP) or at the level of the subsequent aggregation process.16 Compared with the poor inter-assay correlation in case of aspirin testing, ADP-stimulated assays have better agreement among themselves.17,18 However, there are substantial methodological differences between ADP-stimulated assays that explain why this agreement is still far from perfect, resulting in heterogeneity in identification of subjects at risk for thrombotic events15 (Figure 1). According to the available evidence, there are currently four ADP-stimulated assays [VASP, Multiplate, VerifyNow, and light transmission aggregometry (LTA)] that were shown to predict clinical outcomes in large numbers of patients after PCI.15,19–24 Although the methodology of assessment in three of these tests is fairly standardized, LTA lacks standardization for sample collection, preparation, and processing.15 Most important advantages and disadvantages of these assays are discussed in detail in the Supplementary material online (Supplementary Data). Inter-individual variability in platelet reactivity after 600 mg clopidogrel loading dose. Inter-individual variation in platelet reactivity values in consecutive stable angina patients tested 6–24 h after a 600 mg clopidogrel loading dose with four different platelet function assays. Notably, each platelet function plot represents a unique stable angina patient population after a 600 mg clopidogrel loading dose. Patients in (A) were recruited for light transmission aggregometry, vasodilator-stimulated phosphoprotein phosphorylation (VASP-PRI) and Multiplate testing in the Heart Institute, University of Pécs, Hungary, while those in (B) represent a similar patient population enrolled in Institut de Cardiologie, Pitié-Salpêtrière Hospital, Paris, France. LTA, light transmission aggregometry; VASP-PRI, vasodilator-stimulated phosphoprotein phosphorylation index. Monitoring platelet reactivity during clopidogrel treatment with ADP-stimulated platelet assays is more specific to the drug action and more predictive for thrombotic events than the assessment of aspirin responsiveness.23 Based on the currently available evidence, the recommended assays for monitoring platelet inhibition during P2Y12-inhibitors are the VerifyNow P2Y12 assay, the Multiplate device with the ADP kit and the VASP assay. Although the optimal thresholds to define a higher risk for thrombotic events may depend on the clinical situation and are still under investigation, available evidence suggests 208 PRU with the VerifyNow,23,25 46 U with the Multiplate assay22 and 50% with the VASP assay.19,21 (Supplementary material online, Table S2) LTA is only recommended when no standardized assays are available. Measurement of response to aspirin therapy is not recommended. Numerous prospective, observational studies, including large patient populations, demonstrated that HPR to ADP is an independent and strong predictor of post-PCI ischaemic events.22–24,26–31 High on-treatment platelet reactivity has been associated with a significant increase in non-fatal myocardial infarction, definite/probable stent thrombosis, or cardiovascular mortality by four independent meta-analyses.32–35 The prospective, multicentre, large-scale ADAPT-DES registry involving 8583 patients demonstrated that HPR identified with the VerifyNow assay was an independent predictor of both early (HR: 3.00, 95% CI:1.39–6.49, P = 0.005) and 1-year ST (HR: 2.49, 95% CI:1.43–4.31, P = 0.001).23 Notably, the hazard associated with HPR was greater in patients with ACS than in patients undergoing PCI for stable angina.36 High on-treatment platelet reactivity to ADP explained almost 60% of the early ST events.23 Owing to the very low incidence of ST observed with new-generation drug-eluting stents, the positive predictive value of HPR remains low (<10%), with a large proportion of patients who tolerate HPR without any adverse events.15,23 However, HPR should not be viewed as a diagnostic marker for ST (such as troponin for myocardial infarction) but rather as a risk factor for the patient (such as diabetes or high cholesterol for myocardial infarction).37 Therefore, diagnostic tests (such as ROC curve analysis, positive, and negative predictive value) are not appropriate to judge the utility of platelet function estimates; instead, the associated relative risk (hazard or odds ratio) should be used to determine the clinical usefulness of platelet function testing.37 It is also important to know that platelet reactivity values during clopidogrel treatment are not only a measure of drug response, but rather a global integrator of response to P2Y12-inhibitiors and co-existing patient comorbidities that highly interfere with platelet activation (such as advanced age, diabetes, renal insufficiency).24,38,39 In contrast to the independent predictive value of HPR to ADP for thrombotic events, clinical relevance of platelet function testing reflecting the response to aspirin remains unclear. Although the ‘aspirin resistant’ phenotype was associated with higher risk of ischaemic events in a few studies,40 it is important to note that most of these results were gained from patients treated with aspirin monotherapy, not double anti-platelet therapy (DAPT). Moreover, many of these studies included non-specific platelet assays to determine ‘aspirin resistance’ that rather reflect the overall ‘hyper-reactive platelet phenotype’ than the specific effects of aspirin.13,14,41 The ADAPT-DES registry found no difference in response to aspirin between patients with and without stent thrombosis.23 Similar to this, another large study found that high platelet reactivity to arachidonic acid is not associated with adverse clinical events.42 Therefore, current evidence does not support the prognostic utility of screening for aspirin response in patients after PCI. In the Targeted Platelet Inhibition to Clarify the Optimal Strategy to Medically Manage Acute Coronary Syndromes (TRILOGY-ACS) randomized controlled clinical trial,43 stabilized ACS patients managed without revascularization were randomized to either prasugrel or clopidogrel treatment.44 Although prasugrel demonstrated stronger and more consistent P2Y12-receptor inhibition with significantly lower rate of HPR compared with clopidogrel, the benefit achieved in platelet inhibition did not translate into a significant clinical improvement.43,44 According to the platelet function substudy, HPR was a univariate predictor of adverse clinical events, but not an independent predictor of the composite of cardiovascular death, myocardial infarction, or stroke.44 In addition to this trial, another prospective study investigated the link between platelet function results and clinical outcome in stable outpatients with coronary artery disease.45 In the Antiplatelet Drug Resistances and Ischemic Events (ADRIE) study, platelet function estimates were not associated with major ischaemic events.45 Overall, in contrast to patients undergoing PCI, HPR seems to carry less prognostic information in patients managed without revascularization, decreasing the value of platelet function testing in this subset. Genetic variability related to the steps of clopidogrel metabolism is responsible for the variable efficiency of generation of the active metabolite of clopidogrel and consequential variable platelet inhibition15,16,46 (Figure 2). The hepatic two-step oxidative process is of particular importance, as it is dependent on a highly polymorphic family of mono-oxygenases of the cytochrome P450 (CYP) enzymes.15,16 Pharmacogenomic analyses have identified CYP2C19 as the predominant isoenzyme in catalysing both oxidative steps;47 however, both loss-of-function (mainly *2) and gain-of-function (*17) variant alleles of CYP2C19 are common in the population resulting in variable active metabolite generation.48–51 Carriers of the have been shown to have lower levels of active less platelet inhibition and an risk for thrombotic events in patients after The however, for only of the variability of response to clopidogrel and is only one of the many and clinical in high platelet Despite the large of platelet inhibition with clopidogrel, the after is to explain why in hepatic the active metabolite and associated platelet inhibition with but do not have substantial on platelet inhibition after or (Figure 2). between the of clopidogrel, prasugrel and show while show active of cytochrome P450 it does not a in the activation process of and tests have available and P2Y12-inhibitor on was shown to the of However, clinical data are still treatment on is to clinical High on-treatment platelet reactivity to ADP is a strong and independent predictor of adverse thrombotic events, early stent in patients on clopidogrel after The is stronger in patients with while less in patients with stable angina.36 Although the for only a of the variability with clopidogrel, patients CYP2C19 alleles are at higher risk for stent Inter-individual differences in response to aspirin are not associated with stent in patients treated with testing the response to aspirin be recommended. In patients managed without revascularization, HPR is not an independent predictor of ischaemic platelet function testing to antiplatelet is not recommended in this It is still HPR is a marker of higher risk or a risk factor that can be used to treatment in patients after there are to platelet inhibition in patients with the dose of aspirin or clopidogrel, from clopidogrel to a new-generation of P2Y12-receptor or adding a antiplatelet on of therapy (Supplementary material online, Table Although there is no that has evaluated the clinical relevance of dose of aspirin on platelet reactivity testing, from a large and aspirin in patients with ACS without platelet function testing no benefit for high of The of Optimal and in Patients with ACS an Strategy with PCI compared and aspirin in patients with ACS and found no difference in the risk of cardiovascular death, myocardial infarction, or in both the overall ACS (HR: 95% P = and in the of patients who (HR: 95% P = There was a higher rate of bleeding in the aspirin P = Similarly, higher risk of bleeding with aspirin was observed in the analysis of the and in Acute analysis of the inhibition and patient trial, by differences between and in the of the trial, suggested a between ticagrelor and suggested that the use of aspirin explain the for an risk of cardiovascular death, myocardial infarction, or in patients randomized to ticagrelor, treated with aspirin and ticagrelor a significant benefit over However, since this and from a analysis, it should be Although of platelet activation reflecting response to aspirin be by a dose measuring aspirin is not recommended since these platelet activation are not associated with thrombotic events after In aspirin treatment does not clinical but patients to higher risk of Therefore, a low dose of aspirin is recommended with P2Y12-inhibitors and dose increase is when on platelet function results. Many studies have shown that the loading or dose of clopidogrel significantly platelet however, this is rather and highly dependent on the The large-scale, randomized study to the clinical of 600 mg loading dose and mg clopidogrel for patients with HPR identified by the VerifyNow P2Y12 assay was the with VerifyNow on Thrombosis In the study, of the patients were found to have HPR h after PCI for stable angina or due to ST-elevation patients were and only of patients on The of cardiovascular death, myocardial infarction, or stent at was between and (HR: 95% P = bleeding events were also not significantly lower in the analysis of the suggested that patients PRU values at or a significant clinical benefit in the that the and variable effect of clopidogrel be one for the negative and the achieved level of platelet reactivity be important when clopidogrel is The to and Thrombosis observational registry evaluated the clinical of the dose of clopidogrel or to in ACS patients with HPR after According to the patients with HPR at significantly higher risk for adverse ischaemic events the treatment with clopidogrel or when compared with patients without including a higher risk for the by a of a Antiplatelet Strategy a Strategy for and of after multicentre, randomized study to determine a on VerifyNow testing to antiplatelet therapy is to in patients with stable angina or undergoing In contrast to the this study randomized the use of platelet function testing with treatment intervention of according to without platelet function In the monitoring platelet function tests stent and during the and treatment a treatment clopidogrel, aspirin, and were prasugrel available after study it was used in the study in both In addition to treatment patients were also from prasugrel to clopidogrel after PCI if low on-treatment platelet reactivity was observed on The of death, myocardial infarction, stent thrombosis, or revascularization was similar after between treatment (HR: 95% P = there was a for more stent but less major bleeding in the monitoring a finding that and is also available to clopidogrel with antiplatelet therapy in patients with Although the analysis included many studies and treatment was highly in the included loading of clopidogrel, mg dose of clopidogrel, or the results a significantly risk in definite/probable ST and in cardiovascular mortality without a significant increase in bleeding complications antiplatelet therapy in patients with Notably, the analysis a significant between the risk of stent and the clinical benefit achieved after antiplatelet the that not only the platelet function but also the clinical and risk for stent be into when the optimal antiplatelet is patients at high risk for stent more from treatment than at low risk for stent The only randomized that aimed to the clinical of a new-generation P2Y12-inhibitor for patients with HPR was due to In the Testing platelet In patients stent on clopidogrel to alternative with study, stable angina patients with HPR by the VerifyNow P2Y12 assay after PCI with were randomized to clopidogrel or mg of Although the was to a significant in cardiovascular and myocardial infarction with prasugrel during an analysis after patients demonstrated that only one to an incidence of the there were three major bleeding events in the prasugrel and one in the clopidogrel the of randomized The low rate of ischaemic events the study to the for results of a prospective, registry were on the clinical effects of P2Y12-inhibitors on platelet function testing in ACS patients undergoing Platelet reactivity to ADP was with the Multiplate device after 600 mg loading dose of clopidogrel in subjects with HPR the choice of prasugrel or clopidogrel was compared in a while platelet inhibition clopidogrel. of prasugrel was significantly more than clopidogrel in the risk of mortality or definite/probable stent in patients with while on clopidogrel low risk to thrombotic events as those treated with controlled clinical demonstrated that adding either or to during PCI of patients with HPR the risk of However, the of this on clinical including major bleeding is as these studies were not to these Although the study also used for PCI to antiplatelet therapy in patients with there was no of any benefit in the in the compared with the In patients with acute coronary syndrome undergoing PCI, prasugrel and ticagrelor should be the over clopidogrel (Supplementary material online, Table Although clinical data are platelet function testing may be considered in selected ACS patients with a of major bleeding or at low risk for thrombotic events (such as troponin negative patients without clinical to the choice between available the availability of prasugrel and ticagrelor is or to in a significant of platelet function testing may be considered in these to patients with who are at risk for thrombotic complications on clopidogrel and a P2Y12-inhibitor or of clopidogrel in ACS patients with HPR is not In stable angina patients after PCI, clopidogrel should be and routine platelet function testing is not Platelet function testing may be considered if results may the P2Y12-inhibitor due to stent to risk for stent stent or in and or PCI involving the The on the P2Y12-inhibitor should both the platelet function and the bleeding risk of the In patients with for after PCI or therapy of and an anticoagulant or or should clopidogrel. Platelet function testing to dose of clopidogrel or to is not recommended in these The risk of bleeding is dependent on the clinical of the patient and on the and of antiplatelet and anticoagulant agents used in the specific In addition to the clinical and the large variability in response to P2Y12-inhibitors is also an important to bleeding In a study including patients undergoing PCI, the found that on clopidogrel were associated with a higher risk for major bleeding the 1-year results of the large-scale, ADAPT-DES registry in patients that platelet reactivity after PCI is an independent predictor of bleeding patients with a PRU less than 208 a significantly risk for major Compared with clopidogrel, P2Y12-receptor inhibition is more common with prasugrel and studies that patients with a higher risk for bleeding According to a study, these subjects from prasugrel to clopidogrel the risk of bleeding however, a of patients with HPR is during clopidogrel treatment with clinical with the predictive value of HPR in thrombotic the higher risk for bleeding in patients with suggests the relevance of a for P2Y12-receptor in that both thrombotic and bleeding complications be the Therefore, the approach of platelet function assays to the effect of P2Y12-inhibitors into a is both and but randomized studies should the benefit of such a Although evidence is (Supplementary material online, Table the link between and bleeding events in PCI patients to P2Y12-inhibitors is not as as for HPR and stent In addition, outcome studies are in patients with Therefore, the of evidence on the relevance of with the dose of or to clopidogrel on platelet function results be However, in selected patients who a major bleeding during P2Y12-inhibitor treatment and at risk for platelet function testing be considered to determine the of platelet inhibition and to the optimal P2Y12-inhibitor the bleeding platelet inhibition with double antiplatelet therapy the clinical benefit in should of aspirin and a given at low results in of thromboxane generation in the of higher increase bleeding complications without decreasing thrombotic Therefore, aspirin should be given at low and platelet function testing to is not recommended (Supplementary material online, Table the there are large differences in the achieved level of platelet inhibition during treatment with and HPR is associated with higher risk for stent In routine clinical and patient should the choice between available P2Y12-inhibitors during and after prasugrel or ticagrelor is for ACS while clopidogrel is recommended in PCI for stable In selected patients who have high clinical risk for adverse outcomes or with recommended P2Y12-inhibitors, platelet function testing may the by information on the level of platelet reactivity (Supplementary material online, Table should be that platelet function measure different of platelet are also by poor standardization and testing process the of the recommend the more standardized, assays and to during testing and of results. is important with respect to the (Supplementary material online, Table S2) recommended to predict thrombotic and bleeding However, it to be that platelet function results should only be in the clinical and of each platelet reactivity to ADP be one important of information that can the but be the only on which a clinical is The why platelet function testing has a of and a restrictive indication in current guidelines is the of positive, controlled studies to show an in clinical outcomes by these assays in patients undergoing PCI. the of demonstrated that should be large studies that are for ischaemic patients at high risk for stent use P2Y12-inhibitors such as prasugrel or ticagrelor instead of clopidogrel to platelet and the clinical value of platelet function assays that were not used in Based on current ACS patients are recommended to be treated with prasugrel or a among ACS patients with a clopidogrel is and Therefore, platelet and approach be according to for thrombotic events, and if is in bleeding and should be to and novel The are highly because the balance of the and the of platelet testing should be in an when clopidogrel is available in important for is the of platelet function assays to bleeding is important with novel P2Y12-inhibitors in ACS in the population and in patients in both antiplatelet drugs and are a class of antiplatelet agents has been tested in clinical Although the results of the are regarding the clinical of also on the between inhibition and clinical events, as platelet activation is a process in Supplementary material is available at European Heart of from and from from and from and from and from from and from from and from from and from from is a in from and from from and from to the or from de Cardiologie, de Institut de de Cardiologie, Thrombosis Institute, The from The