Multiple Electrode Platelet Aggregometry Research Articles

Prospective evaluation of platelet function and fibrinolysis in 20 dogs with trauma.

To determine platelet function and assess fibrinolysis in dogs following trauma using multiple electrical impedance aggregometry and a modified thromboelastographic (TEG) technique. To determine if the severity of trauma, as assessed by the Animal Trauma Triage (ATT) score and clinicopathological markers of shock, is associated with a greater degree of platelet dysfunction and fibrinolysis. University teaching hospital. Twenty client-owned dogs with trauma (occurring <24h prior to admission and blood sampling) and ATT score of >4 were prospectively recruited. A control group of 10 healthy dogs was included. None. Platelet function was measured using multiple electrode platelet aggregometry (MEPA) utilizing arachidonic acid, ADP, and collagen agonists. Fibrinolysis was assessed in citrated whole blood with the addition of tissue plasminogen activator (tPA; 50U/mL) using kaolin-activated TEG. Conventional statistical analysis was performed to compare coagulation parameters between the groups and assess linear correlations. Median (interquartile range) ATT score was 5 (5-7), and 65% (n=13) of dogs suffered polytrauma. Mean(±SD) time from trauma to blood sampling was 9hours (±6). Median (interquartile range) shock index and plasma lactate concentration were 1.1 (0.7-2.0, n=16) and 2.9mmol/L (0.9-16.0, n=18), respectively. Four dogs did not survive to discharge (20%). There were no differences between the trauma and control group coagulation variables. A moderate negative correlation between ATT score and area under the curve for ADP was found (P=0.043, r2 =-0.496). Preliminary evaluation of platelet function measured by MEPA, and fibrinolysis measured by tPA-modified TEG, is not significantly different in this population of dogs with traumatic injury compared to healthy dogs.

Protease-activated receptor-mediated platelet aggregation in patients with type 2 diabetes on potent P2Y12 inhibitors.

BackgroundAntiplatelet therapy is a cornerstone in the secondary prevention of ischemic events following percutaneous coronary intervention (PCI). The new P2Y12 receptor inhibitors prasugrel and ticagrelor have been shown to improve patients' outcomes. Whether or not these drugs have equal efficacy in individuals with or without diabetes is disputed. Furthermore, platelets can be activated by thrombin, which is, at least in part, independent of P2Y12‐mediated platelet activation. Protease‐activated receptor (PAR)‐1 and −4 are thrombin receptors on human platelets. We sought to compare the in vitro efficacy of prasugrel (n = 121) and ticagrelor (n = 99) to inhibit PAR‐mediated platelet aggregation in individuals with type 2 diabetes (prasugrel n = 26, ticagrelor n = 29).Materials and MethodsWe compared P2Y12‐, PAR‐1‐ and PAR‐4‐mediated platelet aggregation as assessed by multiple electrode platelet aggregometry between prasugrel‐ and ticagrelor‐treated patients without and with type 2 diabetes who underwent acute PCI.ResultsOverall, there were no differences of P2Y12‐, PAR‐1‐ and PAR‐4‐mediated platelet aggregation between prasugrel‐ and ticagrelor‐treated patients. However, both drugs inhibited P2Y12‐mediated platelet aggregation stronger, and thereby to a similar extent in patients with type 2 diabetes than in those without diabetes. There was no correlation between either P2Y12‐, or PAR‐1‐ or PAR‐4‐mediated platelet aggregation and levels of HbA1c or the body mass index (BMI). However, we observed patients with high residual platelet reactivity in response to PAR‐1 and PAR‐4 stimulation in all cohorts.ConclusionPrasugrel and ticagrelor inhibit P2Y12‐ and PAR‐mediated platelet aggregation in individuals with diabetes to a similar extent, irrespective of HbA1c levels and BMI.

Why Me? To Be an Ultra-Responder to Antiplatelet Therapy: A Case Report

Background: Platelet function testing is a valid tool to investigate the clinical response to antiplatelet therapy in different clinical settings; in particular, it might supply helpful information in patients with cerebrovascular disease. Oral antiplatelet treatment, such as Aspirin (ASA) and Clopidogrel, is the gold standard in secondary stroke prevention of non-cardiogenic ischemic stroke; conversely, its application as a primary prevention therapy is not routinely recommended in patients with vascular risk factors. Multiple electrode platelet aggregometry (MEA) impedance aggregometer is a validated device to test platelet inhibition induced by ASA or Clopidogrel.Case Report: We report the case of a 78-year-old patient without relevant clinical history, taking ASA as primary prevention strategy, who was admitted for sudden onset of dysarthria and left facial hyposthenia during physical effort. Brain CT revealed two small subcortical bilateral spontaneous intracranial hemorrhages. Platelet aggregometry with MEA performed upon admission revealed a very strong platelet inhibition induced by ASA (result of the ASPI Test was 5 U, consistent with an ultra-responsiveness to ASA, and the cutoff value of correct responsiveness is <40 U). MRI at longitudinal follow-up revealed the presence of two small cavernous angioma underlying hemorrhagic spots.Conclusion: The evaluation of platelet reactivity in stroke patients undergoing antiplatelet therapies, not commonly performed in clinical practice, could be useful to optimize prevention strategies; the verification of the biological effectiveness of ASA or Clopidogrel could be a valid tool in the definition of each patient's risk profile, particularly in patients with cerebrovascular disease known to be at increased risk for both hemorrhagic and thrombotic complications.

Good Platelets Gone Bad: The Effects of Trauma Patient Plasma on Healthy Platelet Aggregation.

Altered postinjury platelet behavior is recognized in the pathophysiology of trauma-induced coagulopathy (TIC), but the mechanisms remain largely undefined. Studies suggest that soluble factors released by injury may inhibit signaling pathways and induce structural changes in circulating platelets. Given this, we sought to examine the impact of treating healthy platelets with plasma from injured patients. We hypothesized that healthy platelets treated ex-vivo with plasma from injured patients with shock would impair platelet aggregation, while treatment with plasma from injured patients with significant injury burden, but without shock, would enhance platelet aggregation. Plasma samples were isolated from injured patients (pretransfusion) and healthy donors at a Level I trauma center and stored at -80°C. Plasma samples from four separate patients in each of the following stratified clinical groups were used: mild injury/no shock (injury severity score [ISS] 2-15, base excess [BE]>-6), mild injury/with shock (ISS 2-15, BE≤-6), severe injury/no shock (ISS>25, BE>-6), severe injury/with shock (ISS>25, BE≤-6), minimal injury (ISS 0/1, BE>-6), and healthy. Platelets were isolated from three healthy adult males and were treated with plasma for 30 min. Aggregation was stimulated with a thrombin receptor agonist and measured via multiple-electrode platelet aggregometry. Data were normalized to HEPES Tyrode's (HT) buffer-only treated platelets. Associations of plasma treatment groups with platelet aggregation measures were tested with Mann-Whitney U tests. Platelets treated with plasma from patients with shock (regardless of degree of injury) had significantly impaired thrombin-stimulated aggregation compared with platelets treated with plasma from patients without shock (P = 0.002). Conversely, platelets treated with plasma from patients with severe injury, but without shock, had amplified thrombin-stimulated aggregation (P = 0.030). Shock-mediated soluble factors impair platelet aggregation, and tissue injury-mediated soluble factors amplify platelet aggregation. Future characterization of these soluble factors will support development of novel treatments of TIC.

Low Response to Clopidogrel in Coronary Artery Disease.

In patients with coronary artery disease, cardiovascular mortality and other acute events showed a clear correlation with risk factors and biomarkers including platelet activation. Which was the incidence of low response to clopidogrel and its correlation with risk factors and biomarkers in coronary artery disease? Four hundred patients (pts) with coronary artery disease-stable angina (SA) and acute coronary syndrome-were divided into 8 groups of study, consistent with low response to clopidogrel and the type of coronary artery disease. Low response to clopidogrel-defined as adenosine diphosphate test-ADP-test of >46 U by multiple electrode platelet aggregometry was evaluated in correlation with cardiovascular risk factors and biomarkers of oxidative stress, endothelial dysfunction, hypercoagulability, high platelet reactivity. In coronary artery disease, low response to clopidogrel significantly correlated with older than 65 years, smoking, hypertension, diabetes mellitus, body mass index of >25, previous aspirin treatment (P < 0.05), high value of total and low-density lipoprotein cholesterol, low value of high-density lipoprotein cholesterol, low response to aspirin, high mean platelets volume and von Willebrand factor activity, low flow-mediated vasodilatation, total antioxidant status (P < 0.01) and only in patients with SA of male gender (P < 0.01). The incidence of other hypercoagulability biomarkers, such as reduced values of S protein, C protein, antithrombin III, and V Factor Leiden resistance to activated protein C, was very low and not correlated with low response to clopidogrel. In coronary artery disease, low response to clopidogrel significantly correlated with the most of old cardiovascular risk factors, with previous aspirin treatment, low response to aspirin, higher mean platelets volume, higher von Willebrand factor activity, lower flow-mediated vasodilatation, and lower total antioxidant status values and only in patients with SA of male gender.

Correlation of Cardiovascular Risk Factors and Biomarkers With Platelet Reactivity in Coronary Artery Disease.

Low response to aspirin, aspirin resistance, and high platelet reactivity on aspirin treatment are similar names for lack of response to block arachidonic acid-induced aggregation with aspirin therapy and have an important role in the evolution of coronary artery disease (CAD) with thromboembolic events. Was to evaluate the correlation between cardiovascular risk factors, biomarkers, and low response to aspirin in patients (pts) with CAD. Four hundred pts with CAD were divided into 8 groups of study, consistent with the type of CAD and low response to aspirin. Cardiovascular risk factors and biomarkers-including some of high platelet reactivity, endothelial dysfunction, hypercoagulability, and oxidative stress-were evaluated in correlation with low response to aspirin, defined as on treatment aspirin test (ASPItest) >30U by multiple electrode platelet aggregometry. In patients with CAD, low response to aspirin was significantly correlated with age older than 65 years, smoking, presence of diabetes mellitus, body mass index >25, hypertension, previous aspirin treatment, low response to clopidogrel, high mean platelets volume and von Willebrand factor activity, low flow-mediated vasodilation, and total antioxidant status (P < 0.01). In unstable angina patients, low response to aspirin was significantly correlated with male sex (P < 0.03). Incidence of other hypercoagulability biomarkers-S Protein, C Protein, Antithrombin III, and V Factor Leiden resistance to activated protein C-was low and not correlated with low response to aspirin. In CAD, low response to aspirin was significantly correlated with age older than 65 years, smoking, presence of diabetes mellitus, body mass index I >25, hypertension, previous aspirin treatment, and only in unstable angina with male sex. Low response to aspirin was also statistically associated with low response to clopidogrel, high mean platelets volume, high von Willebrand factor activity, low flow-mediated vasodilation, and low total antioxidant status values.

Physical inactivity and platelet function in humans and brown bears: A comparative study

Physical inactivity increases the risk of thromboembolism. However, good standardized human models on inactivity are in short supply and experimental models are few.Our objective was to investigate how standardized bed rest affects platelet aggregation in humans and to investigate if aggregation is altered in a translational model system – the hibernating brown bear (Ursus arctos). We collected blood from (1) healthy male volunteers participating in a 21-day bed rest study in head-down tilt position (−6°) 24 h a day; (2) free-ranging brown bears captured during winter hibernation and again during active state in summer. We analyzed platelet function using multiple electrode platelet aggregometry. In total, 9 healthy male volunteers (age 31.0 ± 6.4 years) and 13 brown bears (7 females and 6 males, age 2.8 ± 0.6 years) were included. In hibernating bears adenosine diphosphate, arachidonic acid, thrombin receptor activating peptide, and collagen impedance aggregometry tests were all halved compared to summer active state. In human volunteers no statistically significant changes were found between baseline and the end of bed rest. In human male volunteers 3 weeks of bed rest did not affect platelet function. In hibernating brown bears platelet aggregation was halved compared to summer and we hypothesize that this is a protective measure to avoid formation of thrombi under periods of low blood flow.

A laboratory association between hemoglobin and VerifyNow P2Y12 reaction unit: A systematic review and meta-analysis

VerifyNow P2Y12 assay is used widely to evaluate residual platelet reactivity in patients taking P2Y12 receptor antagonists. However, a laboratory association between VerifyNow P2Y12 reaction unit (PRU) and hemoglobin, which might lead to wrong interpretation of the data, is reported. We performed these systematic review and meta-analysis to clearly define the relationship between PRU and hemoglobin and to elucidate whether the relationship, if any, is a true biological association or is just a laboratory error. Through a comprehensive electronic and manual search, 10 studies were selected for the cohort level meta-analysis. Among 10 studies, we were able to retrieve the raw data of 5 studies, and a patient-level meta-analysis was performed. Potential publication bias was searched by funnel plot analysis and was actively adjusted, if present, by trim and fill method. The pooled analysis revealed a significant inverse correlation between PRU and hemoglobin (r=-0.349; P<.001; 10 studies with 4,793 patients). VerifyNow P2Y12 base unit, which reflects off-drug platelet reactivity, was also inversely correlated with hemoglobin (r=-0.526; P<.001; 8 studies with 4,395 patients). % Inhibition (r=0.081; P=.059; 6 studies with 3,832 patients) and ΔPRU (r=-0.037; P=.188; 5 studies with 3,521 patients) were not associated with hemoglobin. A significant inverse association between PRU and hemoglobin was also observed in the patient-level meta-analysis (3,533 patients pooled from 5 studies; r=-0.335; P<.001). Light transmission aggregometry (r=0.160; P=.072; 4 studies with 1,144 patients) and multiple electrode platelet aggregometry (r=-0.029; P=.394; 3 studies with 7,645 patients) showed no significant association with hemoglobin. A significant inverse association was observed between PRU and hemoglobin which is likely to be a laboratory error. Clinicians should be aware that this association might lead to wrong interpretation of the data.

Assessment of platelet function in patients with stroke using multiple electrode platelet aggregometry: a prospective observational study.

BackgroundThere is a link between high on-treatment platelet reactivity (HPR) and adverse vascular events in stroke. This study aimed to compare multiple electrode platelet aggregometry (MEA), in healthy subjects and ischaemic stroke patients, and between patients naive to antiplatelet drugs (AP) and those on regular low dose AP. We also aimed to determine prevalence of HPR at baseline and at 3–5 days after loading doses of aspirin.MethodsPatients with first ever ischaemic stroke were age and sex-matched to a healthy control group. Three venous blood samples were collected: on admission before any treatment given (baseline); at 24 h and 3–5 days after standard treatment. MEA was determined using a Mutliplate® analyser and agonists tested were arachidonic acid (ASPI), adenosine diphosphate (ADP) and collagen (COL).ResultsSeventy patients (mean age 73 years [SD 13]; 42 men, 28 women) were age and sex-matched to 72 healthy subjects. Thirty-three patients were on antiplatelet drugs (AP) prior to stroke onset and 37 were AP-naive. MEA results for all agonists were significantly increased in AP-naive patients compared to healthy subjects: ADP 98 ± 31 vs 81 ± 24, p < 0.005; ASPI 117 ± 31 vs 98 ± 27, p < 0.005; COL 100 ± 25 vs 82 ± 20, p < 0.005. For patients on long term AP, 33% (10/30) of patients were considered aspirin-resistant. At 3–5 days following loading doses of aspirin, only 11.1% were aspirin resistant based on an ASPI cut-off value of 40 AU*min.ConclusionsMany patients receiving low dose aspirin met the criteria of aspirin resistance but this was much lower at 3–5 days following loading doses of aspirin. Future studies are needed to establish the causes of HPR and potential benefits of individualizing AP treatment based on platelet function testing.

Underlying mechanism and specific prevention of hemolysis-induced platelet activation

Thromboembolic complications significantly impair the outcome of hemolytic disorders. We hypothesized that red cell adenosine diphosphate (ADP) release results in significant platelet activation in hemolysis and that this prothrombotic state can be prevented by inhibition of the ADP P2Y12 receptor. In the current study, we therefore sought to investigate the mechanism and inhibition of hemolysis-induced platelet activation. The expression of activated integrin αIIbß3 was determined by flow cytometry, and platelet aggregation was assessed by multiple electrode platelet aggregometry. We demonstrate platelet activation and increased platelet aggregation by adding hemolytic blood (lysates) to whole blood, similarly to that achieved by the platelet agonist ADP. Enhanced platelet activation and reactivity in the presence of hemolytic blood were significantly abolished by apyrase, which catalyzes ADP degradation, and inhibited by blockade of the platelet ADP P2Y12 receptor with cangrelor. Platelets from patients treated with the ADP P2Y12 receptor antagonist clopidogrel showed a reduced response to lysates compared to platelets from healthy controls without antiplatelet treatment. Further, in vitro blood group ABO incompatibility induced hemolysis and led to increased platelet activation. Finally, “spontaneous” platelet aggregation seen in patients with cold agglutinin disease was completely abolished by cangrelor. In conclusion, hemolysis is associated with increased platelet activation and aggregation due to red cell derived ADP, which can be prevented by ADP receptor blockade.

Comparison of Three Tests to Distinguish Platelet Reactivity in Patients with Renal Impairment during Dual Antiplatelet Therapy

Background: Clopidogrel and aspirin combination remains a cornerstone for modern dual antiplatelet therapy (DAPT) following coronary stenting. Although monitoring is not currently recommended, certain high-risk cohorts may benefit from tailoring antiplatelet options to reduce thrombotic or/and hemorrhagic risks. Patients with diminished estimated glomerular filtration rate (eGFR) are prone to both vascular occlusions and bleeding events in whom monitoring may be especially advantageous. We compared the residual platelet reactivity assessed by 3 conventional tests during the maintenance antiplatelet therapy dependent on eGFR. Methods: Post-stenting patients (n = 701) receiving aspirin 100 mg/daily and clopidogrel 75 mg/daily were prospectively enrolled in the cross-sectional single-center study. Patients were dichotomized into 5 groups: eGFR >90, 60-89, 30-59, <30 ml/min/1.73 m², and dialysis. Platelet reactivity by VerifyNow™, light transmittance aggregometry (LTA), and Multiplate analyzer by multiple electrode platelet aggregometry (MEA) assays together with eGFR calculations were done simultaneously at 1 month after coronary stenting. Results: VerifyNow assay distinguished residual platelet reactivity dependent on eGFR deterioration (191 ± 72 vs. 216 ± 78 vs. 248 ± 80 vs. 264 ± 70 vs. 317 ± 96 PRU; p < 0.001). In contrast, LTA (34.3 ± 18.1 vs. 34.7 ± 18.1 vs. 38.0 ± 16.6 vs. 33.0 ± 17.3 vs. 34.1 ± 29.3%; p = 0.242), or MEA (37.2 ± 19.6 vs. 33.8 ± 18.4 vs. 38.6 ± 21.4 vs. 36.5 ± 20.5 vs. 38.3 ± 28.3 AU/min; p = 0.086) failed to triage platelet reactivity in renal patients. Agreement among assays to identify patients with impaired platelet reactivity and eGFR during antiplatelet therapy was low. The multivariable regression analyses confirmed the VerifyNow advantage, since the differences in the platelet reactivity were highly significant for all renal impairment (RI) groups. In contrast, LTA did not distinguish RI patients, and for the MEA, only RI5 (dialysis) cohort exhibit borderline significant decline of residual platelet reactivity. Conclusion: Among 3 assays, VerifyNow was capable to reliably triage residual platelet reactivity in post-stenting DAPT patients dependent on the gradual decline of eGFR during therapy with clopidogrel and aspirin. These data should be confirmed in a large validation longitudinal trial, and may justify future platelet activity monitoring for potential regimen/dose adjustment in high-risk patients. The clinical implications of these data are still unclear, but may give an indication as to whether or when DAPT dose adjustment will become a reality.

Clopidogrel pharmacokinetics and pharmacodynamics in out-of-hospital cardiac arrest patients with acute coronary syndrome undergoing target temperature management

BackgroundTarget temperature management (TTM) after cardiac arrest (CA) improves outcome in patients with acute coronary syndrome (ACS). Previous data point to an interaction between hypothermia and drug metabolism, potentially impacting on platelet function in patients on antiplatelet therapy. PurposeTo compare clopidogrel metabolism and platelet function in clopidogrel naïve ACS patients treated with TTM (33°C, n=15) and in ACS patients (troponin positive) without TTM (n=18). MethodsPlatelet function was measured by multiple electrode platelet aggregometry (MEA), light transmittance aggregometry (LTA) and VASP analysis before and after administration of a 600mg clopidogrel loading dose. Plasma levels of clopidogrel and its metabolites were measured. All patients were screened for CYP2C19*2 polymorphism and scheduled for PCI. TTM was carried out for 24h at a target temperature of 33°C using a computer feedback surface cooling device in cardiac arrest patients. ResultsPlasma concentration of clopidogrel and metabolites was lower in the TTM group after 2 and 4h, respectively (all p<0.005 vs. controls), and platelet function tests revealed an attenuated response to clopidogrel with respect to baseline platelet activity in the TTM group. This was significant for MEA, LTA and VASP analysis (all p<0.05). Moreover, there was no significant difference in genotype and platelet function determined ex vivo at 33 or 37°C, respectively. ConclusionInhibition of platelet function is significantly lessened in TTM at 33°C, likely due to reduced clopidogrel absorption. Patients with TTM might thus have a higher risk for further cardiovascular events despite antiplatelet therapy with clopidogrel.

The predictive value of multiple electrode platelet aggregometry for postoperative bleeding complications in patients undergoing coronary artery bypass graft surgery.

IntroductionPostoperative bleeding is one of the most serious complications of cardiac surgery and requires transfusion of blood or blood products. Acetylsalicylic acid (ASA) and clopidogrel (CLO) are the two most commonly used antiplatelet agents; when used in combination (i.e., as dual antiplatelet therapy [DAPT]), they exert a synergistic effect. Dual antiplatelet therapy, however, significantly increases the risk of postoperative bleeding. The effect of antiplatelet therapy can be monitored by platelet aggregation testing. One of the most commonly methods used for assessing platelet reactivity is multiple electrode aggregometry (MEA) which can be performed with the use of Multiplate analyzer. Although the method has long been used in interventional cardiology to assess the effect of antiplatelet therapy, it is not available at cardiac surgery departments as a standard diagnostic procedure. The aim of the study was to establish the frequency of bleeding complications following coronary artery bypass graft (CABG) surgery in patients on single antiplatelet therapy (SAPT) and patients on DAPT and to determine the usefulness of routine measurement of platelet responsiveness before CABG surgery in patients receiving antiplatelet therapy.Material and methodsA consecutive cohort of 200 patients referred for elective surgical treatment of stable coronary artery disease was enrolled (100 consecutive patients on SAPT [ASA 75 mg/day] and 100 consecutive patients on DAPT [ASA 75 mg/day + CLO 75 mg/day]). All subjects continued their antiplatelet therapy until the day before surgery. For each subject, platelet aggregation testing in the form of an ASPI test and an ADP test was performed on the Multiplate analyzer. Each subject underwent coronary artery bypass grafting surgery. For the primary and secondary endpoints in our study we adopted the definition provided in ‘Standardised Bleeding Definitions for Cardiovascular Clinical Trials: A Consensus Report from the Bleeding Academic Research Consortium’ (‘Circulation’, 2011) for BARC type 4 bleeding (i.e. CABG-related bleeding).ResultsAn ROC curve was constructed for the ASPI test and ADP test for a total of 200 patients. No significant correlations were demonstrated between the ASPI test results and either the primary endpoint or the secondary endpoints. A correlation was found between the ADP test results and the composite primary endpoint and each of the secondary endpoints. The primary endpoint of major postoperative bleeding occurred in 16 subjects. From the ROC curve, we established the optimal cut-off value for the ADP test of 26 U at sensitivity of 72%, specificity of 69%, positive predictive value of 69.90%, and negative predictive value of 71.13%.ConclusionsIn patients on antiplatelet therapy, an ADP test result of < 26 U is strongly predictive of serious bleeding complications after CABG surgery. The MEA ADP test allows to identify the group of patients at an increased risk of postoperative bleeding.

Abstract 17314: Impact of Mild Therapeutic Hypothermia on Platelet Inhibition in Acute Coronary Syndrome

Background: Mild therapeutic hypothermia (MTH) improves outcome for patients with acute coronary syndrome (ACS) after cardiac arrest (CA). Previous data point to an interaction between hypothermia and drug metabolism, thus potentially impacting on platelet function under antiplatelet therapy. Purpose: The aim of the study is to determine clopidogrel metabolism and platelet function in clopidogrel naïve ACS patients treated with mild hypothermia (33°C, n=12) compared with ACS patients (troponin positive) with normal body temperature (n=14). Methods: Platelet function was measured by light transmittance aggregometry (LTA), multiple electrode platelet aggregometry (MEA) and VASP phosphorylation analysis before, 2h, 4h and 24h after administration of a 600 mg clopidogrel loading dose. Furthermore, plasma concentrations of clopidogrel, the active thiol metabolite and the inactive carboxyl metabolite were determined. All patients were screened for CYP2C19*2 polymorphism and scheduled for PCI. Mild hypothermia was carried out according to current guidelines for 24 hours at a target temperature of 33°C. Results: Plasma concentration of clopidogrel and metabolites were lower in the MTH group after 2h and 4h, respectively (all p&lt;0.005). All platelet function tests showed an attenuated response to clopidogrel with respect to baseline platelet activity in the MTH group. This was significant for VASP analysis and LTA (p&lt;0.05). Moreover, there was no difference in genotype and platelet function determined ex vivo with 33°C and 37°C, respectively. Conclusion: Inhibition of platelet function is decreased under MTH, presumably due to a diminished clopidogrel absorption and metabolization. Thus, these patients might have a higher risk for cardiovascular events despite antiplatelet therapy.

Comparison of pharmacodynamics between low dose ticagrelor and clopidogrel after loading and maintenance doses in healthy Korean subjects

The novel antiplatelet agent ticagrelor has been demonstrated to exert a faster and more powerful inhibition of platelet aggregation in comparison to clopidogrel in coronary artery disease patients. However, a ticagrelor dose of 90 mg twice daily might not be suitable for patients of East Asian ethnicity, and has not been fully investigated. The aim of this study was to assess the effects of low loading doses (LD, 90 mg) and maintenance doses (MD, 90 mg daily) of ticagrelor in comparison to clopidogrel (600 mg LD, 75 mg daily MD) in healthy Korean volunteers. Twelve subjects were randomized into two groups, receiving either clopidogrel (600 mg LD, followed by 75 mg MD daily for 5 days) or ticagrelor (90 mg LD, followed by 90 mg MD daily for 5 days). Following a 2-week washout period, the treatments were switched between the groups. Three platelet function assessment methods which included light transmission aggregometry (LTA), the VerifyNow assay and multiple electrode platelet aggregometry (MEA) were then used to serially measure platelet function at various time points (baseline, 0.5, 2, 6, 24, 26, 120 and 122 h). The mean IPA to 10 µM ADP in the ticagrelor group was significantly higher than that for the clopidogrel group at the 0.5, 2, 6, 26 and 122 h time points (p ≤ 0.001). However, there was no significant difference between the two groups at the 24- and 120-hour time points (p > 0.05). The assay results produced by the other two platelet function tests (VerifyNow and MEA) were similar to those obtained by LTA. The low loading and maintenance doses of ticagrelor (90 mg LD, 90 mg daily MD) cause a more rapid and potent inhibition of platelet function when compared to clopidogrel (600 mg LD and 75 mg MD). Additionally, at the lowest value of platelet inhibition strength, oral once-daily administration of ticagrelor was no less efficacious than clopidogrel at the 24- and 120-hour time points. Due to a large diurnal variation occurring with a single daily dose, a lower dose twice-daily could be a better option for patients of East Asian ethnicity.

Platelet Volume Indices are Associated with High Residual Platelet Reactivity after Antiplatelet Therapy in Patients Undergoing Percutaneous Coronary Intervention

It is well known that platelet volume indices are associated with adverse outcomes following percutaneous coronary intervention(PCI). In this study, we investigated the hypothesis whether the association between platelet size and clinical outcomes is the result of high residual platelet reactivity after antiplatelet therapy in patients with large platelets. Between February 2010 and December 2011, a total of 462 consecutive patients with coronary artery disease who were scheduled to undergo planned PCI were enrolled in this study. The degree of platelet aggregation induced by arachidonic acid(AA) and adenosine diphosphate(ADP) was assessed using the Multiple Electrode Platelet Aggregometry(Multiplate(®), Dynabyte, Munich, Germany)(MEA) test. We simultaneously measured the mean platelet volume(MPV) in the same period(Sysmex XE-2100, Mundelein, IL). The study population consisted of 462 consecutive patients, including 371 stable angina patients and 91 acute coronary syndrome patients. The patients with large platelets(upper quintile of MPV ≥10.6 fL) had significantly high residual platelet reactivity after both aspirin(MEA ASP 9 [5-14] Units vs. 13 [8-18.5] Units, p < 0.001) and clopidogrel(MEA ADP 21 [15-30] Units vs. 24 [18.5-40] Units, p=0.003) treatment. According to a multivariate analysis, having large platelets was independently associated with high residual platelet reactivity after both aspirin (OR 2.52, 95% CI 1.50-4.24, p < 0.001) and clopidogrel(OR 2.86, 95% CI 1.59-5.15, p < 0.001) treatment. Platelet volume indices were not associated with any differences in the incidence of major adverse cardiac events during follow-up. Platelets with a higher volume are associated with high residual platelet reactivity after conventional dual antiplatelet therapy.

Rotational thromboelastometry and multiple electrode platelet aggregometry in four patients with abnormal routine coagulation studies before removal of epidural catheters after major surgery: a case series and research study.

IntroductionRoutine coagulation tests have a low predictability for perioperative bleeding complications, and spinal hematoma after removal of epidural catheters is very infrequent. Thromboelastometry and point-of-care platelet aggregometry may improve hemostatic monitoring but have not been studied in the context of safety around epidural removal.MethodsTwenty patients who received an epidural catheter for major thoracoabdominal and abdominal surgery were included prospectively. In addition to routine coagulation tests, rotational thromboelastometry and multiple electrode platelet aggregometry were carried out.ResultsA coagulation deficit was suggested by routine coagulation tests on the intended day of epidural catheter removal in four out of 20 patients. Prothrombin time-international normalized ratio was elevated to 1.5 in one patient (normal range: 0.9 to 1.2) while rotational thromboelastometry and multiple electrode platelet aggregometry parameters were within normal limits. Activated partial thromboplastin time was elevated to 47 to 50 seconds in the remaining three patients (normal range 28 to 45 seconds). Rotational thromboelastometry showed that one of the patients’ results was due to heparin effect: the clotting time with the HEPTEM® activator was 154 seconds as compared to 261 seconds with INTEM. The three remaining patients with prolonged routine coagulation test results had all received over 1L of hydroxyethyl starch (Venofundin®) and thrombosis prophylaxis with low-molecular-weight heparin (enoxaparin). Rotational thromboelastometry and multiple electrode platelet aggregometrygave normal or hypercoagulative signals in most patients.ConclusionsThis case series is new in that it examines rotational thromboelastometry and multiple electrode platelet aggregometry postoperatively in the context of epidural analgesia and shows that they may be clinically useful. These methods should be validated before they can be used for standard patient care.

P257 Sustained Aspirin effects on platelets function over 24 hours in patients with untreated Obstructive Sleep Apnoea Syndrome (OSAS)

IntroductionPrevalence of OSAS in people with cardiovascular disease is much higher than in the general population. Many OSAS patients are prescribed Aspirin for secondary prevention of cardiovascular events but the...

Predictive values of post-clopidogrel platelet reactivity assessed by different platelet function tests on ischemic events in East Asian patients treated with PCI

An accumulating number of studies are revealing that platelet reactivity above specific cut-off scores leads to exponentially increased rates of post-percutaneous coronary intervention (PCI) ischemic events. To evaluate the optimal predictive values for three different platelet function measurement assays of platelet reactivity on early clinical outcomes in Korean patients undergoing PCI, we enrolled 228 patients receiving clopidogrel prior to PCI. Platelet reactivity was measured by light transmittance aggregometry (LTA), VerifyNow P2Y12 assay, and multiple electrode platelet aggregometry (MEA). The primary endpoint was the 30-day occurrence of ischemic events after PCI. MACE occurred in 36 patients (15.8%), including 35 patients (15.4%) with periprocedural MI and the death of one patient (0.4%). ADP-induced LTA and VerifyNow values (pre- and post-PCI) were significantly higher in patients with the subsequent occurrence of periprocedural MI, but the MEA assay data (PCI and post-PCI) displayed no significant differences (pre-PCI p = 0.25 and post-PCI p = 0.33). ROC curve analysis demonstrated HPR values for LTA (pre-PCI, >66% and post-PCI, >53 %, all p < 0.001), VerifyNow (pre-PCI, >347 PRU and post-PCI >272 PRU, all p < 0.001) and MEA (pre-PCI, >50 U and post-PCI >39 U, all p > 0.05). The platelet reactivity measurements by LTA and the VerifyNow assay can discriminate the risk of 30-day ischemic events after PCI. The predictive cut-off values for adverse events are dependent on sampling time.

CYP2C19 genotypes and their impact on clopidogrel responsiveness in percutaneous coronary intervention

Cytochrome P450 2C19 (CYP2C19) loss-of-function polymorphisms are more common in Asian populations and have been associated with diminished antiplatelet response to clopidogrel. In this era of 'personalised medicine', combining genotyping and phenotyping as a strategy to personalise antiplatelet therapy warrants further exploration. This study aimed to investigate the prevalence and impact of CYP2C19*2, *3 and *17 genotypes on clopidogrel responsiveness in a multiethnic Malaysian population planned for percutaneous coronary intervention. Between October 2010 and March 2011, a total of 118 consecutive patients planned for percutaneous coronary intervention were enrolled in Sarawak General Hospital, Borneo. All patients received at least 75 mg aspirin daily for at least 2 days and 75 mg clopidogrel daily for at least 4 days prior to angiography. Genotyping for CYP2C19*2 (rs4244285, 681G > A), *3 (rs4986893, 636G > A) and *17 (rs11188072, -3402C > T) alleles were performed by polymerase chain reaction-restriction fragment linked polymorphism method. Whole blood ADP-induced platelet aggregation was assessed with multiple electrode platelet aggregometry (MEA) using the Multiplate Analyzer. The distribution of CYP2C19*2, *3 and *17 among different ethnic groups and the association between genotype, clopidogrel responsiveness and clinical outcome were the main outcome measures. The highest prevalence of poor metabolisers (carriers of at least one copy of the *2 or *3 allele) was among the Chinese (53.7 %), followed by the Malays (26.9 %), Ibans (16.4 %) and other races (3.0 %). Poor metabolisers (PMs) had the highest mean MEA (303.6 AU*min), followed by normal metabolisers (NMs) with 270.5 AU*min and extensive metabolisers (EMs) with 264.1 AU*min (p = 0.518). Among poor responders to clopidogrel, 65.2 % were PMs and NMs, respectively, whereas none were EMs (p = 0.350). Two cardiac-related deaths were reported. There was a diverse inter-ethnic difference in the distribution of CYP2C19 polymorphism. The findings of this study echo that of other studies where genotype appears to have a limited impact on clopidogrel responsiveness and clinical outcome in low-risk patients.