Comparison of VerifyNow-P2Y12 test and Flow Cytometry for monitoring individual platelet response to clopidogrel. What is the cut-off value for identifying patients who are low responders to clopidogrel therapy?

Early detection of resistance to dual antiplatelet therapy in patients who have undergone percutaneous coronary intervention using the VerifyNow test and associated factors

Resistance to dual antiplatelet therapy (DAPT), including aspirin and clopidogrel, in patients who have undergone percutaneous coronary intervention (PCI) leads to the inability to prevent thrombotic complications. The present study aimed to evaluate early resistance to aspirin and clopidogrel in patients following PCI using the VerifyNow test and associated factors. A total of 50 patients diagnosed with acute coronary syndromes (ACS) who underwent emergency PCI and received DAPT were recruited in the present study. The detection of resistance to aspirin and clopidogrel was performed using the VerifyNow system. Resistance to aspirin was determined with VerifyNow Aspirin >550 aspirin reaction units (ARU). Resistance to clopidogrel was determined with VerifyNow P2Y12 >208 P2Y12 reaction units (PRU). The resistance rate to aspirin was 14%, while the resistance rate to clopidogrel was higher, at 34%. There were 2 patients with resistance to aspirin and clopidogrel (4%). Univariable logistic regression analysis revealed that diabetes, the use of β-blockers, and low levels of hemoglobin and hematocrit were associated with resistance to clopidogrel. Following multivariable logistic regression analysis, only the use of β-blockers was truly associated with resistance to clopidogrel. On the whole, the results of the present study may also prove to be helpful in the selection of therapeutic drugs for patients undergoing PCI and who are diagnosed with ACS.

Racial differences in P2Y12 inhibitor responsiveness in patients undergoing neuro-endovascular procedures: A cohort from the Middle East

BACKGROUND

Data on P2Y12 inhibitors responsiveness from the middle east is scarce. We sought to investigate patient responsiveness to P2Y12 inhibitors within a cohort of major races that characterize the UAE population. The secondary objective was to assess risk factors for hyper and hypo-responsiveness in this population.

METHODS

We conducted a cross-sectional study on adults who received either clopidogrel or ticagrelor treatments and had platelet responsiveness testing before undergoing neuro-endovascular interventions at our quaternary care hospital between March 2015 and April 2019.

RESULTS

During the study period, 249 subjects met the inclusion criteria. Overall, 17.3 % were hyper-responsive and 25.7 % were hypo-responsive to P2Y12 inhibitors. When comparing between the P2Y12 inhibitors, rates of hyper-responsiveness were significantly higher to ticagrelor when compared to clopidogrel (11 versus 6 %, p = 0.02 respectively). Contrarily, hypo-responsiveness rates were significantly higher in clopidogrel treated patients compared to their ticagrelor treated counterparts (23 versus 2 %, p < .001 respectively). Patients of Middle-Eastern origin showed a significantly higher rate of hypo-responsiveness to both clopidogrel and ticagrelor when compared to other races (41.1 % and 26.7 %, P < 0.001 respectively). Asians showed the highest rates of hyper-responsiveness for both agents. Multivariate logistic regression analysis showed that proton pump inhibitors and statin combination, (OR: 6.39, 95 %CI [1.60, 25.392]), and Middle East vs. Indian subcontinent patients (OR: 4.67, 95 %CI [1.79-12.14]) were independent predictors of hypo-responsiveness to both P2Y12 inhibitors.

CONCLUSION

This study demonstrated a high rate of hypo-responsiveness to P2Y12 inhibitors in a UAE cohort of patients undergoing neuro-endovascular procedures. In addition, therapeutic responsiveness to P2Y12 inhibitors varied markedly based on the racial background. Future larger studies are needed to evaluate genetic variations that may contribute to this rate of hypo-responsiveness in our population.

Clopidogrel hyper-response increases peripheral hemorrhagic complications without increasing intracranial complications in endovascular aneurysm treatments requiring dual antiplatelet therapy

Clinical significance of increased clopidogrel response measured by VerifyNow P2Y12 assay is unclear; management guidelines are lacking in the context of neuroendovascular intervention. Our objective was to assess whether increased clopidogrel response predicts complications from endovascular aneurysm treatment requiring dual antiplatelet therapy. A single-institution, 9-year retrospective study of patients undergoing endovascular treatments for ruptured and unruptured aneurysms requiring aspirin and clopidogrel was conducted. Patients were grouped according to preoperative platelet inhibition in response to clopidogrel measured by the VerifyNow P2Y12 assay (VNP; P2Y12 reactivity units, PRU). Demographic and clinical features were compared across groups. Hemorrhagic complication rates (intracranial, major extracranial, minor extracranial) and thromboembolic complications (in-stent stenosis, stroke/transient ischemic attack) were compared, controlling for potential confounders and multiple comparisons. Data were collected from 284 patients across 317 procedures. Pre-operative VNP assays identified 9 % Extreme Responders (PRU ≤ 15), 13 % Hyper-Responders (PRU 16-60), 62 % Therapeutic Responders (PRU 61-214), 16 % Hypo-Responders (PRU ≥ 215). Increased response to clopidogrel was associated with increased risk of any hemorrhagic complication (≤60 PRU vs > 60 PRU; 39 % vs 24 %, P = 0.050); all intracranial hemorrhages occurred in patients with PRU > 60. Thromboembolic complications were similar between therapeutic and subtherapeutic patients (<215 PRU vs ≥ 215 PRU; 15 % vs 16 %, P = 0.835). Increased preoperative clopidogrel response is associated with increased rate of extracranial hemorrhagic complications in endovascular aneurysm treatments. Hyper-responders (16-60 PRU) and Extreme Responders (≤15 PRU) were not associated with intracranial hemorrhagic or thrombotic complications. Hypo-responders who underwent adjustment of antiplatelet therapy and neurointerventions did not experience higher rates of complications.

P2Y12 antagonists: Approved drugs, potential naturally isolated and synthesised compounds, and related in-silico studies

P2Y₁₂ is a platelet surface protein which is responsible for the amplification of P2Y₁ response. It plays a crucial role in platelet aggregation and thrombus formation through an ADP-induced platelet activation mechanism. Despite that P2Y₁₂ platelets' receptor is an excellent target for developing antiplatelet agents, only five approved medications are currently in clinical use which are classified into thienopyridines and nucleoside-nucleotide derivatives. In the past years, many attempts for developing new candidates as P2Y₁₂ inhibitors have been made. This review highlights the importance and the role of P2Y₁₂ receptor as part of the coagulation cascade, its reported congenital defects, and the type of assays which are used to verify and measure its activity. Furthermore, an overview is given of the clinically approved medications, the potential naturally isolated inhibitors, and the synthesised candidates which were tested either in-vitro, in-vivo and/or clinically. Finally, we outline the in-silico attempts which were carried out using virtual screening, molecular docking and dynamics simulations in efforts of designing novel P2Y₁₂ antagonists. Various phytochemical classes might be considered as a corner stone for the discovery of novel P2Y₁₂ inhibitors, whereas a wide range of ring systems can be deliberated as leading scaffolds in that area synthetically and theoretically.

The inhibition rate estimated using VerifyNow can help to predict the thromboembolic risk of coil embolization for unruptured intracranial aneurysms

BACKGROUND

The role of the inhibition rate of VerifyNow in assessing the thromboembolic risk of coil embolization for unruptured intracranial aneurysms is unclear.

OBJECTIVE

To carry out a retrospective study to determine whether the inhibition rate could provide additional help in predicting thromboembolic events when it was used for patients with a P2Y12 reaction unit (PRU) level of 220 or lower.

METHODS

Patients who underwent coil embolization for unruptured aneurysms with an appropriate PRU level (PRU 220 or lower) between January 1, 2015 and December 31, 2018 were analyzed. A total of 954 patients with 1020 aneurysms were included in this study. The primary outcome was the thromboembolic events occurring within 30 days after coil embolization. The receiver operating characteristic (ROC) curve and the area under the curve (AUC) were obtained to determine the quantitative predictive ability of the inhibition rate. The optimal cut-off value was derived using the Youden index.

RESULTS

Thromboembolic events developed in 11 patients (1.08% of 1020 procedures). The AUC of the ROC curve was 0.83. The optimal cut-off value of the inhibition rate derived using the maximum Youden index was 22.0%. A sensitivity test using a multiple logistic regression analysis demonstrated that the inhibition rate was a significant variable for predicting thromboembolic events.

CONCLUSIONS

The inhibition rate can be used to determine high thromboembolic risks for patients with PRU levels of 220 or lower. The optimal cut-off value of the inhibition rate was 22.0% when the PRU level was 220 or less.

Platelet dysfunction in patients with traumatic intracranial hemorrhage: Do desmopressin and platelet therapy help or harm?

BACKGROUND

Pre-injury anti-platelet use has been associated with increased risk of progression of traumatic intracranial hemorrhage (TICH) and worse outcomes. VerifyNow® assays assess platelet inhibition due to aspirin/clopidogrel. This study assesses the outcomes of patients with TICH and platelet dysfunction treated with desmopressin and/or platelets.

METHODS

We performed a retrospective chart review of patients with mild TICH at a level 1 trauma center 1/1/2013-6/1/2016. Patients with documented platelet dysfunction who received desmopressin and/or platelets were compared to those who were untreated. Primary outcomes were progression of TICH and neurologic outcomes at discharge.

RESULTS

Of 565 patients with a mild TICH, 200 patients had evidence of platelet dysfunction (a positive VerifyNow® assay). Patients had similar baseline demographics, injury characteristics, and rate of TICH progression; but patients who received desmopressin and/or platelets had worse Glasgow Outcomes Score at discharge.

CONCLUSION

Treatment of patients with mild TICH and platelet dysfunction with desmopressin and/or platelets did not affect TICH progression but correlated with worse neurologic status at discharge.

Assessment of therapeutic platelet inhibition in cardiac patients: Comparative study between VerifyNow-P2Y12 and Anysis-P2Y12 assay

BACKGROUND

Analyzing responsiveness to P2Y12 therapy is vital to preventing thrombotic and hemorrhagic complications in patients with cardiovascular diseases.

OBJECTIVE

This study evaluates a new Anysis-P2Y12 assay system against VerifyNow-P2Y12 in cardiac patients and analyzes the P2Y12 low-response rates of the two devices with various cutoff values.

METHODS

In total, 125 citrated blood samples were collected from cardiac patients referred for a P2Y12 antiplatelet response test. In the Anysis assay, the test result was the migration distance (MD) until the blood flow stops, which is comparable to both P2Y12 reaction units and percent inhibition obtained using VerifyNow.

RESULTS

The MDs without and with P2Y12 were 182±30 and 264±12 mm, respectively (p <  0.0001). Compared to VerifyNow-P2Y12, the sensitivity and specificity of Anysis-200 were 96.8%and 88.7%, respectively. Cohen's kappa coefficient between the two devices was 0.761, indicating a high agreement. However, there was an apparent difference in the low-response rate to P2Y12, which was 36.5%for VerifyNow and 5.9%for Anysis.

CONCLUSIONS

The performance of the newly developed platelet function assay, Anysis-P2Y12 was equivalent to that of VerifyNow-P2Y12 in terms of sensitivity and specificity. The Anysis-P2Y12 assay may help screen patients with abnormal P2Y12 non-responsiveness.

Pharmacokinetic, pharmacodynamic, and pharmacogenetic assays to monitor clopidogrel therapy

Clopidogrel is the most common and widely used antiplatelet agent for patients with coronary artery disease following confirmation by electrocardiographic studies. The nonresponsiveness of patients to clopidogrel and the possibility of testing for clopidogrel resistance by platelet function assays (PFA) are contentious issues. Light transmission aggregometry (LTA) is considered as the gold standard test among all PFA. In this review, the most commonly used PFA used for monitoring the effect of clopidogrel, LTA, vasodilator-stimulated phosphoprotein assay phosphorylation, rotational thromboelastometry (ROTEM) delta and ROTEM platelet, thromboelastography, PFA-100, VerifyNow P2Y12 assay, Multiplate analyzer, Plateletworks assay and pharmacogenetic studies, are comparatively discussed including their principles of action, advantages, and disadvantages. VerifyNow P2Y12 assay can be accepted as the ideal point of care test out of the discussed assays. However, modified assays are required which could overcome the limitations associated with currently available assays.

Impact of Boosted Antiretroviral Therapy on the Pharmacokinetics and Efficacy of Clopidogrel and Prasugrel Active Metabolites

BACKGROUND AND OBJECTIVES

Prasugrel and clopidogrel are inhibitors of the ADP-P₂Y₁₂ platelet receptor used in acute coronary syndrome patients. They require bioactivation via isoenzymes such as cytochrome P450 (CYP) 3A4, CYP2C19 and CYP2B6. Ritonavir and cobicistat are potent CYP3A inhibitors, prescribed as pharmacokinetic (PK) enhancers in the treatment of human immunodeficiency virus (HIV) infection.

METHODS

In this study, the impact of boosted antiretroviral therapies (ARTs) on the PK of clopidogrel and prasugrel active metabolites (AMs), and on the efficacy of prasugrel and clopidogrel, were evaluated in a randomized crossover clinical trial.

RESULTS

A significantly lower exposure to clopidogrel AM [3.2-fold lower area under the concentration-time curve (AUC) and maximum plasma concentration (C_max)] and prasugrel AM (2.1-fold and 1.7-fold lower AUC and C_max) were demonstrated in HIV-infected patients treated with boosted ARTs compared with healthy controls; however, a differential impact was observed on platelet inhibition between clopidogrel and prasugrel. Clopidogrel 300 mg induced adequate (although modest) platelet inhibition in all healthy subjects, while platelet inhibition was insufficient in 44% of HIV patients. On the contrary, prasugrel 60 mg induced a potent platelet inhibition in both healthy and HIV-infected subjects.

CONCLUSION

Prasugrel appears to remain an adequate antiplatelet agent in HIV-infected patients and could be preferred to clopidogrel in this context, regardless of the metabolic interaction and inhibition of its bioactivation pathways.

Monitoring of biological response to clopidogrel after treatment for non-cardioembolic ischemic stroke or transient ischemic attack

BACKGROUND AND PURPOSE

Biological response to clopidogrel prescribed after a non-cardioembolic ischemic stroke or transient ischemic attack (TIA) has been little studied. The aim of our study (AAPIX) was to assess this response and investigate the agreement between different biological assays in revealing poor responders.

METHODS

Patients hospitalized following a non-cardioembolic ischemic stroke or transient ischemic attack (TIA) and prescribed clopidogrel were consecutively included from September 2013 to November 2015 in the Stroke Center of Saint-Etienne Hospital. Blood was drawn after 5 to 8 days of standard-dose clopidogrel. Light transmission aggregometry (LTA) and flow cytometric assays, using vasodilator-stimulated phosphoprotein [VASP] and CD62P, were accomplished for all patients. Transmission electron microscopy (TEM) was performed for a poor clopidogrel-responder and for a patient with discordant platelet assay results (platelet reactivity index (PRI) >50% and maximum platelet aggregation <70%), after activation with adenosine diphosphate (ADP) 10 µM.

RESULTS

72 patients were included. According to LTA, VASP assay and CD62P test results, 65%, 71% and 0% of patients, respectively, had a low response to clopidogrel, indicating poor agreement between these assays. Images of ADP-activated platelet samples from a patient manifesting a low response to clopidogrel and from a patient with discordant platelet assay results showed an ultrastructural pattern typical of activation and a state of slight activation, respectively.

CONCLUSIONS

Platelet function results obtained using different assays for patients having experienced a non-cardioembolic ischemic stroke or TIA were discordant. Transmission electron microscopy could be useful in certain clinical contexts when platelet function assay results disagree.

Variability of Platelet Reactivity on Antiplatelet Therapy in Neurointervention Procedure

As more intracranial aneurysms and other cerebrovascular pathologies are treated with neurointervention procedure, thromboembolic events that frequently lead to serious neurological deficit or fatal outcomes are increasing. In order to prevent the thromboembolic events, antiplatelet therapy is used in most procedures including coil embolization, stenting, and flow diversion. However, because of variable individual pharmacodynamics responses to antiplatelet drugs, especially clopidogrel, it is difficult for clinicians to select the adequate antiplatelet regimen and its optimal dose. This article reviews the neurointervention literature related to antiplatelet therapy and suggests a strategy for tailoring antiplatelet therapy in individual patients undergoing neurointervention based on the results of platelet function testing.

Prevalence of poor biological response to clopidogrel

The existence of poor biological response to clopidogrel has been shown in some patients. Despite the increasing number of studies, this phenomenon remains difficult to quantify. We performed a systematic review to estimate the prevalence of poor biological response to clopidogrel and investigate the factors known to modulate this. An exhaustive search was performed. Altogether 171 publications were identified, providing data for a total of 45,664 subjects. The estimated prevalence of poor biological response to clopidogrel ranged from 15.9% to 49.5% according to the platelet function assay employed. The assays most frequently used were light transmittance aggregometry (LTA), the vasodilator-stimulated phosphoprotein (VASP) assay and the Verify -now® assay. For all these assays, higher cut-off values were associated with a lower prevalence of poor biological response to clopidogrel. However, when choosing a fixed cut-off point for each assay, the prevalence of poor biological response to clopidogrel was highly variable suggesting that other factors could modulate poor biological response to clopidogrel. Finally, none of the studied factors could apparently explain the variability of poor biological response to clopidogrel. This meta-analysis shows that the prevalence of poor biological response depends on the assay employed, the cut-off value and on various unidentified additional factors.

Influence of CYP2C19 genetic polymorphisms on clinical outcomes of intracranial aneurysms treated with stent-assisted coiling

OBJECTIVE

To investigate the influence of CYP2C19 genetic polymorphisms on clinical outcomes of intracranial aneurysms treated with stent-assisted coiling.

METHODS

Between September 2014 and October 2015, we prospectively recruited 215 patients with intracranial aneurysms who were treated with stent-assisted coiling. CYP2C19 genotypes were determined and clopidogrel response was tested. The primary endpoints included symptomatic or silent ischemic events, and bleeding events. The secondary endpoint was clinical outcome at 3 months.

RESULTS

Of the 215 patients, 108 (50.2%) were classified as intermediate metabolizers (IMs, CYP2C19*1/*2, *1/*3), 76 (35.3%) as extensive metabolizers (EMs, CYP2C19*1/*1) and 31 (14.4%) as poor metabolizers (PMs, CYP2C19*2/*2, *2/*3, *3/*3). Carriers of CYP2C19 loss-of-function (LOF) alleles (*2 or *3, p=0.001), especially PMs (p=0.004), had an increased risk for clopidogrel resistance. After the procedures, cerebral ischemic events occurred in 69 patients (32.1%) and bleeding was seen in 20 patients (9.3%). In comparison with IMs and PMs, EMs had a lower risk for ischemic events (21.1% vs 37.0% and 41.9%, p=0.02 and 0.027, respectively) and a relatively higher risk for bleeding events (18.4% vs 5.6% and 0%, p=0.006 and 0.01, respectively). Based on multivariate analysis, the carriage of CYP2C19 LOF alleles (p=0.032) and clopidogrel resistance (p=0.047) were considered as predictors of cerebral ischemic events, and EMs were significantly associated with bleeding (p=0.002). Posterior circulation aneurysms (p=0.038), hemorrhagic history (p=0.001) and poor metabolic genotypes (p=0.001) could result in poor clinical outcomes (modified Rankin Scale >2).

CONCLUSIONS

CYP2C19 genetic polymorphisms had significant influence on the antiplatelet effect of clopidogrel, and could be considered as risk factors of ischemic or bleeding events and even clinical outcomes of patients with intracranial aneurysms treated with stent-assisted coiling.

Application of a strain rate gradient microfluidic device to von Willebrand's disease screening

Von Willebrand's disease (VWD) is the most common inherited bleeding disorder caused by either quantitative or qualitative defects of von Willebrand factor (VWF). Current tests for VWD require relatively large blood volumes, have low throughput, are time-consuming, and do not incorporate the physiologically relevant effects of haemodynamic forces. We developed a microfluidic device incorporating micro-contractions that harnesses well-defined haemodynamic strain gradients to initiate platelet aggregation in citrated whole blood. The microchannel architecture has been specifically designed to allow for continuous real-time imaging of platelet aggregation dynamics. Subjects aged ≥18 years with previously diagnosed VWD or who presented for evaluation of a bleeding disorder, where the possible diagnosis included VWD, were tested. Samples were obtained for device characterization as well as for pathology-based testing. Platelet aggregation in the microfluidic device is independent of platelet amplification loops but dependent on low-level platelet activation, GPIb/IX/V and integrin α_IIbβ₃ engagement. Microfluidic output directly correlates with VWF antigen levels and is able to sensitively detect aggregation defects associated with VWD subtypes. Testing demonstrated a strong correlation with standard clinical laboratory-based tests. Head-to-head comparison with PFA100® demonstrated equivalent, if not improved, sensitivity for screening aggregation defects associated with VWD. This strain rate gradient microfluidic prototype has the potential to be a clinically useful, rapid and high throughput-screening tool for VWD as well as other strain-dependent platelet disorders. In addition, the microfluidic device represents a novel approach to examine the effects of high magnitude/short duration (ms) strain rate gradients on platelet function.

Malignant stroke in a ticagrelor non-responder as a complication following aneurysm treatment with the Pipeline Embolization Device™

The Pipeline Embolization Device™ (PED; Covidien Neurovascular Inc, Irvine, CA, USA) is a flow-diverting stent often used for the endovascular treatment of large or giant, wide-necked intracranial aneurysms of the internal carotid artery. Because of the inherent thrombogenicity of intracranial stents, dual-antiplatelet therapy is initiated after placement, which has been shown to decrease morbidity and mortality related to perioperative ischemic events in neurointerventional procedures. However, in some series, as much as 50% of patients demonstrate clopidogrel non-responsiveness. In these non-responders, alternate agents such as ticagrelor can be used to achieve adequate anticoagulation. Compared with clopidogrel, a prodrug requiring Cytochrome P450 enzymolysis for activation, ticagrelor directly and reversibly inhibits the P2Y12 ADP receptor. The absorption of the prodrug and the formation of its active metabolite is comparatively quicker ( t_max 1.3-2 hours; 1.5-3 hours, respectively). To date, there have been no documented cases of ticagrelor non-responsiveness involving patients undergoing placement of flow-diverting stents or other endovascular neuro-interventional procedures.

Contribution of whole platelet aggregometry to the endovascular management of unruptured aneurysms: an institutional experience

BACKGROUND

Stent-assisted coiling of intracranial aneurysms is an efficient alternative treatment to surgical clipping but requires prolonged antiplatelet therapy. Some patients are non-responsive to aspirin and/or clopidogrel.

OBJECTIVE

To analyze the implications of this assessment using the 'whole blood aggregometry (WBA) by impedance' technique.

MATERIALS AND METHODS

The Southwestern Tertiary Aneurysm Registry was reviewed between 2002 and 2012 for patients with unruptured aneurysms treated with stent-assisted coiling. The study population was divided into patients who were tested preoperatively for platelet responsiveness to aspirin and clopidogrel ('tested' patients) and those who were not ('non-tested'). Where necessary, tested patients received additional doses of antiplatelet drugs to achieve adequate platelet inhibition. Endpoints included the incidence of non-responsiveness, the rates of thrombotic and hemorrhagic complications, and the rates of permanent morbidity and mortality.

RESULTS

A total of 266 patients fulfilled our selection criteria: 114 non-tested patients who underwent 121 procedures, and 152 tested patients who underwent 171 procedures. The two groups did not vary significantly in patient age, gender, and aneurysms location. Aspirin non-responsiveness was detected in 3 patients (1.75%) and clopidogrel non-responsiveness in 21 patients (12.3%). Non-tested patients had an 11.6% rate of thrombotic complications with a 4.1% permanent morbidity or mortality rate versus 2.3% and 0.6% in tested patients (p=0.0013). The incidence of hemorrhagic complications was similar between the two groups.

CONCLUSIONS

Preoperative platelet inhibition testing using WBA can be useful to assess and correct antiaggregant non-responsiveness, and may reduce postoperative mortality and permanent morbidity.

Coadministration of ticagrelor and ritonavir: Toward prospective dose adjustment to maintain an optimal platelet inhibition using the PBPK approach

Ticagrelor is a potent antiplatelet drug metabolized by cytochrome (CYP)3A. It is contraindicated in patients with human immunodeficiency virus (HIV) because of the expected CYP3A inhibition by most protease inhibitors, such as ritonavir and an increased bleeding risk. In this study, a physiologically based pharmacokinetic (PBPK) model was created for ticagrelor and its active metabolite (AM). Based on the simulated interaction between ticagrelor 180 mg and ritonavir 100 mg, a lower dose of ticagrelor was calculated to obtain, when coadministered with ritonavir, the same pharmacokinetic (PK) and platelet inhibition as ticagrelor administered alone. A clinical study was thereafter conducted in healthy volunteers. Observed PK profiles of ticagrelor and its AM were successfully predicted with the model. Platelet inhibition was nearly complete in both sessions despite administration of a fourfold lower dose of ticagrelor in the second session. This PBPK model could be prospectively used to broaden the usage of ticagrelor in patients with ritonavir-treated HIV regardless of the CYP3A inhibition.

Association between Postprocedural Infarction and Antiplatelet Drug Resistance after Coiling for Unruptured Intracranial Aneurysms

BACKGROUND AND PURPOSE

Procedure-related thromboembolism is a major limitation of coil embolization, but the relationship between thromboembolic infarction and antiplatelet resistance is poorly understood. The purpose of this study was to verify the association between immediate postprocedural thromboembolic infarction and antiplatelet drug resistance after endovascular coil embolization for unruptured intracranial aneurysm.

MATERIALS AND METHODS

This study included 338 aneurysms between October 2012 and March 2015. All patients underwent postprocedural MR imaging within 48 hours after endovascular coil embolization. Antiplatelet drug resistance was checked a day before the procedure by using the VerifyNow system. Abnormal antiplatelet response was defined as >550 aspirin response units and >240 P2Y12 receptor reaction units. In addition, we explored the optimal cutoff values of aspirin response units and P2Y12 receptor reaction units. The primary outcome was radiologic infarction based on postprocedural MR imaging.

RESULTS

Among 338 unruptured intracranial aneurysms, 134 (39.6%) showed diffusion-positive lesions on postprocedural MR imaging, and 32 (9.5%) and 105 (31.1%) had abnormal aspirin response unit and P2Y12 receptor reaction unit values, respectively. Radiologic infarction was associated with advanced age (65 years and older, P = .024) only with defined abnormal antiplatelet response (aspirin response units ≥ 550, P2Y12 receptor reaction units ≥ 240). P2Y12 receptor reaction unit values in the top 10th percentile (>294) were associated with radiologic infarction (P = .003). With this cutoff value, age (adjusted odds ratio, 2.29; 95% confidence interval, 1.28-4.08), P2Y12 receptor reaction units (>294; OR, 3.43; 95% CI, 1.53-7.71), and hyperlipidemia (OR, 2.05; 95% CI, 1.04-4.02) were associated with radiologic infarction in multivariate analysis.

CONCLUSIONS

Radiologic infarction after coiling for unruptured aneurysm was closely associated with age. Only very high P2Y12 receptor reaction unit values (>294) predicted postprocedural infarction. Further controlled studies are needed to determine the precise cutoff values, which could provide information regarding the optimal antiplatelet regimen for aneurysm coiling.

Prevalence and risk factors of clopidogrel non-response among Saudi patients undergoing coronary angiography

OBJECTIVES

To estimate the prevalence of clopidogrel non-response and identify its risk factors among Saudi patients. 

METHODS

This cross-sectional study was conducted at Prince Sultan Cardiac Center, Riyadh, Kingdom of Saudi Arabia between January and June 2013, to assess the degree of platelet inhibition using the VerifyNow assay (Accumetrics, San Diego, CA, USA) after receiving clopidogrel standard loading dose. Clopidogrel resistance was defined as ≤15% platelet inhibition or greater than 213 P2Y12 reaction units (PRU). 

RESULTS

Three hundred and four patients were included in the study. The mean age was 60.3 ± 11.4 years, and 73% were males. Clopidogrel doses were 300 mg (57%), 600 mg (27%), and 75 mg (16%). All patients used aspirin (81 mg in 94%). Approximately 66% (200/304) showed in vitro clopidogrel non-response, 54% had low platelet inhibitions, and 61% had high post-loading PRU. Using multivariate regression analysis that included all significant characteristics; only diabetes (odds ratio [OR]: 2.36, 95% confidence interval [CI]: 1.30-4.27, p=0.005) and higher preloading PRU (OR: 2.39, 95% CI: 1.40-4.11, p=0.002) remained significantly associated with higher clopidogrel non-response while myocardial infarction (OR: 0.34, 95% CI: 0.15-0.81, p=0.014) remained significantly associated with lower clopidogrel non-response. The associations of morbid obesity and diuretics use with higher clopidogrel non-response were slightly attenuated.  

CONCLUSION

Our findings indicate a high rate of clopidogrel in-vitro non-response among Saudi patients undergoing coronary angiography.

Association between CYP2C19 Polymorphisms and Outcomes in Cerebral Endovascular Therapy

BACKGROUND AND PURPOSE

Differing responses to clopidogrel following endovascular treatment of cerebrovascular diseases may increase the risk of vascular complications. CYP2C19 gene polymorphisms influence clopidogrel activity. We aimed to study the clinical impact of CYP2C19 gene polymorphisms in patients undergoing endovascular treatment.

MATERIALS AND METHODS

This was a prospective, longitudinal, observational study. Information on demographics and cerebrovascular status was collected as baseline. Clopidogrel response was tested by the VerifyNow P2Y12 assay. CYP2C19 genotyping was undertaken by polymerase chain reaction-restriction fragment length polymorphism. Three-month follow-up data included vascular complications, mortality, and modified Rankin Scale score. Associations were investigated among CYP2C19 genotypes, clopidogrel responsiveness, and clinical outcomes.

RESULTS

One hundred and eight participants were included. Median age was 56 years (interquartile range, 48.8-65.0 years), and 35 (32.4%) were male. Forty-four participants were classified into group 1 (homozygous CYP2C19*1/*1); 31, into group 2 (25 with CYP2C19*1/*2, two with CYP2C19*1/*3, three with CYP2C19*3/*3, one with CYP2C19*2/*3); 28, into group 3 (24 with CYP2C19*1/*17, four with CYP2C19*17/*17); and 5, into group 4 (CYP2C19*2/*17). A significantly higher proportion of participants in group 3 experienced ischemic events (9 of 28, 32.1%) compared with group 1 (5 of 44, 11.4%; P = .04; odds ratio, 3.7; 95% confidence interval, 1.1-12.6). There was no significant difference in clopidogrel response among the 4 genotype groups.

CONCLUSIONS

Individuals with CYP2C19*17 may have increased risk of ischemic events following endovascular treatment, independent of clopidogrel responsiveness. Larger studies are required to confirm the influence of CYP2C19*17 on clinical outcomes and to understand the mechanisms for increased ischemic events.

Comparison of Aggregometry with Flow Cytometry for the Assessment of Agonists´-Induced Platelet Reactivity in Patients on Dual Antiplatelet Therapy

Data on the agreement between aggregometry and platelet activation by flow cytometry regarding the measurement of on-treatment platelet reactivity to arachidonic acid (AA) and adenosine diphosphate (ADP) are scarce. We therefore sought to compare three platelet aggregation tests with flow cytometry for the assessment of the response to antiplatelet therapy. Platelet aggregation in response to AA and ADP was determined by light transmission aggregometry (LTA), the VerifyNow assays, and multiple electrode aggregometry (MEA) in 316 patients receiving aspirin and clopidogrel therapy after angioplasty with stent implantation. AA- and ADP-induced P-selectin expression and activated glycoprotein (GP) IIb/IIIa were determined by flow cytometry. LTA, the VerifyNow P2Y₁₂ assay and MEA in response to ADP correlated significantly (all p<0.001), and the best correlation was observed between LTA and the VerifyNow P2Y₁₂ assay (r = 0.63). ADP-induced platelet reactivity by all aggregation tests correlated significantly with ADP-induced P-selectin expression and activated GPIIb/IIIa (all p<0.001). The best correlation was seen between the VerifyNow P2Y₁₂ assay and activated GPIIb/IIIa (r = 0.68). The platelet surface expressions of P-selectin and activated GPIIb/IIIa in response to ADP were significantly higher in patients with high on-treatment residual platelet reactivity (HRPR) to ADP by all test systems (all p<0.001). A rather poor correlation was observed between AA-induced platelet reactivity by LTA and the VerifyNow aspirin assay (r = 0.15, p = 0.007), while both methods did not correlate with MEA. AA-induced platelet reactivity by all aggregation tests correlated significantly, but rather poorly with AA-induced P-selectin expression (all p<0.05), while only AA-induced platelet reactivity by LTA correlated significantly with AA-induced activated GPIIb/IIIa (r = 0.21, p<0.001). The platelet surface expression of P-selectin in response to AA was significantly higher in patients with HRPR by LTA AA and MEA AA (both p<0.02). In contrast, P-selectin expression in response to AA was similar in patients without and with HRPR by the VerifyNow aspirin assay (p = 0.5), and platelet surface activated GPIIb/IIIa in response to AA did not differ significantly between patients without and with HRPR to AA by all test systems (all p>0.1). In conclusion, ADP-induced platelet reactivity by aggregometry translates partly into flow cytometry. In contrast, AA-induced platelet reactivity correlates poorly between different platelet aggregation tests, and between aggregometry and flow cytometry. Overall, both approaches capture different aspects of platelet function and are therefore not interchangeable in the assessment of agonists´-induced platelet reactivity. Clinical outcome data are needed to determine which test systems and settings are associated with different in vivo consequences.

Thrombotic and bleeding events after coronary stenting according to clopidogrel and aspirin platelet reactivity: VerifyNow French Registry (VERIFRENCHY)

BACKGROUND

Dual antiplatelet therapy, comprising aspirin and clopidogrel, is recommended in patients undergoing coronary stenting to avoid the occurrence of stent thrombosis and others ischaemic events. Interindividual response to clopidogrel varies, however, with poor response associated with an increased risk of ischaemic events. New assays are available for testing aspirin and clopidogrel response routinely at the bedside.

AIM

To evaluate the prognostic value of testing antiplatelet response in an intermediate-risk population undergoing stent implantation.

METHODS

We prospectively assessed clopidogrel and aspirin response using the VerifyNow assay at the time of coronary stenting in 1001 patients who presented with stable coronary disease or non-ST-segment elevation acute coronary syndrome. The main ischaemic endpoint was the composite of definite and probable stent thrombosis, cardiovascular death or spontaneous myocardial infarction at one year. The safety endpoint was major bleeding.

RESULTS

Overall, 36.0% of patients had high on-clopidogrel platelet reactivity (OCR) and 8.6% had high on-aspirin platelet reactivity (OAR). The main ischaemic composite endpoint occurred in 3.9% of patients with high vs. 2.3% of patients with normal OCR (hazard ratio 1.66, 95% confidence interval 0.78-3.54; P=0.18). Definite or probable stent thrombosis occurred in 1.1% of patients with high vs. 0.3% of patients with normal OCR (P=0.86). There was no significant difference in ischaemic endpoints according to OAR and there was no difference in rates of major bleeding between patients with high versus normal on-treatment platelet reactivity.

CONCLUSIONS

On-treatment platelet reactivity was not associated with 1-year ischaemic or bleeding events in an intermediate-risk population undergoing stent implantation.

[Cardiovascular pharmacogenomics]

Cardiovascular disease remains a major cause of morbidity and mortality worldwide. Current medical practice takes into account information based on population studies and benefits observed in large populations or cohorts. However, individual patients present great differences in both toxicity and clinical efficacy that can be explained by variations in adherence, unknown drug to drug interactions and genetic variability. The latter seems to explain from 20% up to 95% of patient to patient variability. Treating patients with cardiovascular disorders faces the clinician with the challenge to include genomic analysis into daily practice. There are several examples within cardiovascular disease of treatments that can vary in toxicity or clinical usefulness based on genetic changes. One of the main factors affecting the efficacy of Clopidogrel is the phenotype associated with polymorphisms in the gene CYP 2C9. Furthermore, regarding oral anticoagulants, changes in CYP2C9 and VKORC1 play an important role in changing the clinical response to anticoagulation. When analyzing statin treatment, one of their main toxicities (myopathy) can be predicted by the SLCO1B1 polymorphism. The potential for prediction of toxicity and clinical efficacy from the use of genetic analysis warrants further studies aiming towards its inclusion in daily clinical practice.

Poor agreement between light transmission aggregometry, Verify Now P2Y₁₂ and vasodilatator-stimulated phosphoprotein for clopidogrel low-response assessment: a potential explanation of negative results of recent randomized trials

Clopidogrel low response as assessed by several different biological tests correlates with poor prognosis after percutaneous coronary intervention (PCI). However, recent randomized clinical trials (RCT) testing the strategy of individual antiplatelet therapy tailoring based on one sole test have all shown negative results. Poor correlation between the different tests may explain the difficulties of patient selection and identification of "true poor responders" to clopidogrel. In this prospective study, clopidogrel response was assessed in 100 consecutive patients between 18 and 24 hours after a 600 mg clopidogrel loading dose using three different tests: light transmission aggregometry with 10 μmol ADP (LTA, results expressed as platelet aggregation percentage: PAP), Verify Now P2Y12 (VN, results expressed as P2Y12 reaction unit: PRU) and vasodilatator-stimulated phosphoprotein (VASP, results expressed as platelet reactivity index: PRI). Patients under chronic clopidogrel therapy were excluded. The mean PAP, PRU and PRI values were 38.6%, 176.1 PRU and 52.4%, respectively. When clopidogrel response was analyzed as continuous variable, there was a good correlation between the different tests: LTA/VN (R(2 )= 0.642, p < 0.001), LTA/VASP (R(2 )= 0.409, p < 0.001) and VN/VASP (R(2 )= 0.616, p < 0.001). However, when clopidogrel response was analyzed as pre-specified cut-off points to define patients as "poor or good responders" (according to the literature: 50% PAP for LTA, 235 PRU for VN and 50% PRI for VASP), only 47% of the patients were defined as "good" or "poor responders" by the three tests. Altogether, 33% of the patients were defined as "poor responders" by only one test, 20% by two tests and only 16% by the three tests. The correlation between the different tests is good when clopidogrel response is analyzed as continuous variable. Each individual is however rarely (less than 50%) defined as "poor or good responder" by all the three tests when pre-specified cut-off values are used. A sole test might not be sufficient to manage antiplatelet therapy in an individual patient and these results may explain the results of recent RCT showing the lack of benefit of systematic antiplatelet therapy monitoring strategy.

Triple antiplatelet therapy with addition of cilostazol to aspirin and clopidogrel for Y-stent-assisted coil embolization of cerebral aneurysms

BACKGROUND

Dual antiplatelet therapy for stent-assisted coiling of cerebral aneurysms is essential to prevent thromboembolic complications. There is concern that Y-stent-assisted coiling may increase thromboembolic complications compared with coiling with a single stent. Several reports have demonstrated that cilostazol may improve clopidogrel responsiveness. We investigated whether triple antiplatelet therapy with addition of cilostazol to aspirin plus clopidogrel for Y-stents can prevent thromboembolic events.

METHODS

Between July 2010 and October 2012, we treated 40 consecutive aneurysms with coil embolization using Enterprise stents. At the peri-procedural period, dual antiplatelet agents (100 mg aspirin and 75 mg clopidogrel) were used for the single stent group (n = 36), and triple antiplatelet agents (addition of 200 mg cilostazol) were used for the Y-stent group (n = 4). We evaluated post-operative diffusion-weighted imaging (DWI) and any complications. We assessed the following for statistical analysis: age, sex, aneurysm location, shape, and size, neck size, size of parent vessels, and stent length.

RESULTS

We found two neurological peri-procedural complications: one transient ischemic attack and one infarction. Both complications belonged to the Y-stent group, which was a significant factor of thromboembolic events (P = 0.008). There were no other significant factors related to neurological complications or positive DWI. For subgroup analysis of the single stent group, stent length was significantly longer in positive DWI than negative DWI (P = 0.04). In the follow-up period of 20 ± 8.6 months, there were no symptomatic late complications in any patients.

CONCLUSIONS

Although the number of patients in the Y-stent group is small, this group had a significantly higher risk of thromboembolic complications. While our protocol of a routine dose of dual antiplatelet therapy may be sufficient for single stent therapy, our protocol of a routine dose of triple antiplatelet therapy for Y-stents may not prevent thromboembolic events. This suggests that evaluation of platelet function may be essential, especially for Y-stents.

Incidence of microemboli and correlation with platelet inhibition in aneurysmal flow diversion

Flow-diverting stents have been associated with embolic and hemorrhagic complications, but the rate of procedure-related microemboli is unknown. Using transcranial Doppler sonography, we measured the rate of microemboli in 23 patients treated with flow-diverting stents. Patients received preprocedural dual antiplatelet medications and intraprocedural heparinization. Point-of-care platelet reactivity testing was performed before the procedure, and nonresponders (>213 P2Y12/ADP receptor reactivity units) received additional thienopyridine. Transcranial Doppler sonography was performed within 12-24 hours. Microemboli were detected in 3 patients (13%), 2 of whom were initially nonresponders. There was no association between the presence of microemboli and procedural or neurologic complications, aneurysm size, number of stents, or procedure time. Eight procedures (34.8%) required additional thienopyridine for inadequate platelet inhibition, and 3 required further treatment for persistent nonresponse to point-of-care platelet reactivity testing. There were 6 technical and 2 postoperative complications; none were associated with inadequate platelet inhibition or microemboli. The combination of routine point-of-care platelet reactivity testing and postprocedural microembolic monitoring may help identify patients at risk for thromboembolic complications after flow-diverting stents.

The role of anticoagulants, antiplatelet agents, and their reversal strategies in the management of intracerebral hemorrhage

New anticoagulant and antiplatelet medications have been approved and are prescribed with increased frequency. Intracranial hemorrhage is associated with the use of these medications. Therefore, neurosurgeons need to be aware of these new medications, how they are different from their predecessors, and the strategies for the urgent reversal of their effects. Utilization of intraluminal stents by endovascular neurosurgeons has resulted in the need to have a thorough understanding of antiplatelet agents. Increased use of dabigatran, rivaroxaban, and apixaban as oral anticoagulants for the treatment of atrial fibrillation and acute deep venous thrombosis has increased despite the lack of known antidotes to these medications.

Pharmacotherapy for the reduction of stent thrombosis

The benefits of percutaneous coronary intervention (PCI) can be offset by periprocedural complications such as acute vessel closure and stent thrombosis in the absence of adequate antiplatelet and antithrombotic therapy. Additionally, conditions occurring after 30 days post-PCI, such as in-stent restenosis or late stent thrombosis can occur. Excess antithrombotic therapy, on the other hand, carries a risk of major gastrointestinal or intracranial bleeding as well as vascular access site bleeding complications. In this review, evidence related to the various pharmacological agents for reduction of stent thrombosis available to clinicians during and after PCI will be explored.

Current Concepts in the Clinical Utility of Platelet Reactivity Testing

The pharmacodynamic effect of clopidogrel varies among individuals; approximately a third will have high on-treatment platelet reactivity (HTPR) to adenosine diphosphate and may benefit from more intensive antiplatelet therapy. Platelet reactivity testing has an important role in monitoring the therapeutic efficiency of clopidogrel and the safety of more potent drugs that confer an increased bleeding risk, because it provides a direct measure of the biological effect of these drugs. Numerous studies have demonstrated an association between HTPR and the risk of cardiac events in acute coronary syndrome (ACS) or after percutaneous coronary intervention (PCI). While the prognostic value of platelet reactivity testing following PCI has been demonstrated repeatedly in cohort studies and meta-analyses, randomised controlled studies investigating the clinical utility of the technique to guide treatment decisions failed to improve clinical outcomes of clopidogrel-treated patients undergoing stent implantation. Available data suggest that platelet function monitoring may be carried out in clopidogrel-treated patients with a higher risk of thrombotic events. These include patient risk factors such as body mass index (BMI), type 2 diabetes, and those prior unexpected ischemic events such as stent thrombosis, as well as procedural risk factors. As we move towards conclusively defining a therapeutic window associated with both cardiovascular (upper threshold) and bleeding risk (lower threshold) for antiplatelet agents, platelet reactivity testing will become a central tool in the practice of personalised strategies.

A Case of Three Consecutive Events of Acute Myocardial Infarctions in Three Different Vessels

A 51-year-old man was being admitted to the emergency department with chest pains. He had a history of acute myocardial infarction (MI) on two prior occasions and was successfully treated with drug eluting stents. He was diagnosed with 3 consecutive events of acute MI in 3 different vessels. The consecutive events of acute MI in different vessels are a very rare case. He did not have risk factors, such as coagulation abnormality, clopidogrel resistance, patient's compliance and vessel abnormality, except for his cigarette smoking. We reported the first case with 3 consecutive events of acute MI in each 3 vessels during a long-term interval.

Cytochrome P450 2C19 polymorphism is associated with reduced clopidogrel response in cerebrovascular disease

PURPOSE

Clopidogrel is a prodrug that requires transformation into an active metabolite by cytochrome P450 (CYP) in the liver in order to irreversibly inhibit the P2Y12 adenosine diphosphate platelet receptor. CYP2C19 polymorphism has been reported to correlate with reduced antiplatelet activity of clopidogrel in coronary artery disease. We assessed the association between CYP2C19 polymorphism and clopidogrel resistance in patients with cerebrovascular disease.

MATERIALS AND METHODS

We retrospectively gathered data from patients who experienced cerebrovascular disease, received clopidogrel, and were tested for clopidogrel resistance and CYP2C19 polymorphism. Clopidogrel resistance was tested by the VerifyNow P2Y12 system, and the CYP2C19 polymorphism was tested by the Seeplex CYP2C19 ACE Genotyping system. Clopidogrel resistance was expressed in P2Y12 reaction units (PRU) and percent inhibition. High PRU and low percent inhibition suggests clopidogrel resistance. CYP2C19 polymorphisms were expressed as extensive, intermediate, and poor metabolizers. Clopidogrel resistance was assessed according to the subgroup of CYP2C19 polymorphism.

RESULTS

A total of 166 patients were evaluated. The PRU values of extensive CYP2C19 metabolizers (195.0±84.9) were significantly lower than those of intermediate and poor metabolizers (237.9±88.0, 302.2±58.9). The percent inhibition of extensive metabolizers (44.6±21.8) was significantly higher than that of intermediate and poor metabolizers (30.5±21.5, 14.0±13.4).

CONCLUSION

Intermediate and poor metabolizing CYP2C19 polymorphism is associated with reduced clopidogrel antiplatelet activity in patients with cerebrovascular disease. The clinical implications of this finding require further investigation.

Blood management-issues: the panic of coagulopathic bleeding--is there a rational approach?

Blood management is an evolving field of reducing transfusions of allogeneic blood by maximizing multi-modality therapy to optimize red cell mass, reduce red cell loss, and harvest red cells that would have otherwise been discarded. These techniques are highly dependent upon teams working together. The programs are not just focused upon red cells but also on coagulation therapy. Coagulopathy is at times a difficult complex pathologic conundrum. In cardiac surgery the complexity is added to because of the inflammatory effects of anticoagulation, air/blood interfaces, and inflammation. Patients respond variably due to their own genetic and environmental factors. There can be a rational approach, thereby avoiding panic (a normal fear response) if the clinician utilizes not only the available laboratory technologies existing today but also follows published algorithms for treatment. These technologies with their coexisting algorithms have been widely shown to decrease blood usage, yet not to decrease bleeding. That finding suggests that therapy without such guidance wastes expensive pro-coagulant blood products and produces no advantage (a decrease in bleeding). When a therapy produces no advantage all that it leaves the patient with is the side effects or adverse outcomes. Adverse outcomes from coagulation products are real and sobering.

Clopidogrel resistance and the effect of combination cilostazol in patients with ischemic stroke or carotid artery stenting using the VerifyNow P2Y12 Assay

OBJECTIVE

The inhibitory response to clopidogrel considerably varies among individuals and clopidogrel resistance is a risk factor for thrombotic events in patients with cardiovascular disease. Based on the platelet aggregation evaluated by the VerifyNow P2Y12 Assay, the present study investigated clopidogrel resistance and the effect of cilostazol addition.

METHODS

We measured the ability of 20 µM ADP to aggregate platelets using the VerifyNow P2Y12 Assay. Clopidogrel resistance was defined as % inhibition of <20% in this assay.

PATIENTS

We examined 77 patients (53 men and 24 women, aged 65.8 ± 9.9 years) with ischemic stroke or carotid artery stenting who received clopidogrel (75 mg) for >7 days at our hospital between October 2009 and March 2010. For 62 patients (42 men and 20 women, aged 65.3 ± 9.9 years) 75 mg clopidogrel alone was administered (clopidogrel only group); the other 15 patients (11 men and 4 women, aged 67.9 ± 9.9 years) received 75 mg of clopidogrel plus 100 or 200 mg of cilostazol (cilostazol combination group).

RESULTS

Clopidogrel resistance was identified in 18 (29%) of the 62 patients in the clopidogrel only group. The percent inhibition was significantly higher in the cilostazol combination group than in the clopidogrel only group (41.7 ± 28.0% vs. 64.9 ± 22.7%, p=0.005). None of the patients in the cilostazol combination group had % inhibition of <20%.

CONCLUSION

Clopidogrel resistance developed in 29% of patients given clopidogrel alone. The addition of cilostazol to clopidogrel may have intensified platelet inhibition.