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Introduction: Thrombo-inflammatory syndrome (TIS) characterized by a pathophysiological state of hypercoagulability, heightened platelet function, and inflammation has been observed in patients with acute myocardial infarction, and HIV. Hypothesis: The incidence of TIS is observed at a high rate in COVID-19 patients and worsens with symptom severity Methods: Blood samples from COVID-19 positive hospitalized patients (n=24) was collected for coagulation and platelet function analysis using point-of-care thromboelastography, TEG6s (Haemonetics, Corp) and routine labs were collected to measure markers of inflammation, coagulation, and organ damage (Table). Disease severity was grouped according to oxygen supplementation requirements and comparisons were made using unpaired t-test and chi-squared tests. Thrombo-inflammation was defined as the presence of both hypercoagulability by TEG [Clot initiation (R) < 4.6, fibrin clot strength (FCS) >32mm, and platelet fibrin clot strength (PFCS) >69] and D-dimer >ULN. Results: Ninety- five percent of COVID positive patients had at least one co-morbidity with the incidence of hypertension (71%), diabetes (50%), and obesity (42%) being the most frequent. A total of 63% (16/24) of patients had TIS, the incidence was significantly increased with escalating disease severity (p=0.03). A significant stepwise (p Conclusions: Thrombo-inflammatory is observed with most COVID patients, importantly heightened platelet function is a component of the syndrome and raises the question if antiplatelet therapy is needed in select COVID patients. Selective assessments with TEG6s may facilitate antithrombotic personalization.

Up to 11% of patients presenting with acute coronary syndromes undergo coronary artery bypass grafting. Guidelines largely recommend a one-size-fits-all preoperative discontinuation period for P2Y 12 receptor blockers to avoid bleeding. These recommendations do not account for highly variable pharmacodynamic responsiveness and for variable recovery of platelet reactivity following discontinuation of P2Y 12 receptor blockers. Several observational studies have demonstrated that an objective measurement of platelet function among these patients may reduce the waiting period while mitigating the risk of bleeding. Based on these findings, 2 recent guidelines included a Class IIa and IIb recommendation for platelet function testing in patients undergoing cardiac surgery. The following review article describes the rationale for discontinuation of dual antiplatelet therapy before cardiac surgery and the limitations with this approach, available platelet function assays to assess pharmacodynamic effects, and the association between platelet inhibition and other clinical factors with surgery-related bleeding. The information will assist the reader in determining which patients undergoing cardiac surgery might benefit from preoperative platelet function monitoring.

Dual antiplatelet therapy with aspirin and a P2Y

Article, see p 1708 Greater protection against ischemic event occurrences has been associated with lower levels of platelet reactivity to adenosine diphosphate in patients with high-risk coronary artery disease.1–3 The latter observations serve as the basis of the platelet hypothesis, ie, greater inhibition of P2Y12 equals less thrombotic event occurrence.4 Ticagrelor, a cyclopentyl-triazolo-pyrimidine, is indisputably a more potent P2Y12 inhibitor than clopidogrel5 and, when administered to patients with acute coronary syndrome in the PLATO trial (Platelet Inhibition and Patient Outcomes), it resulted in a reduction not only in myocardial infarction, but also vascular death in comparison with clopidogrel.6 The observed reduction in vascular death has provided a strong impetus to search for mechanisms of benefit beyond greater P2Y12 inhibition that are not shared by other P2Y12 inhibitors: the non–P2Y12-mediated hypothesis of ticagrelor. The latter hypothesis is largely based on the property of ticagrelor to inhibit adenosine reuptake, thereby increasing systemic and tissue adenosine levels.7 Most of the subsequent beneficial effects proceed downstream for this pivotal step, because adenosine has been proposed as an important molecule that attenuates ischemia-reperfusion injury. Indeed, there has already been significant exploration in the ticagrelor-adenosine area. 1. Ticagrelor has been shown to inhibit adenosine reuptake in erythrocytes by inhibition of the sodium-independent equilibrative nucleoside transporter-1. Dipyridamole has 16-fold greater affinity for equilibrative nucleoside transporter-1.7 2. No direct effect of ticagrelor on adenosine receptors has been reported, and ticagrelor is not metabolized to adenosine.7 3. In an in vitro study, the antiplatelet effect of ticagrelor was mediated in part by increased extracellular adenosine levels and adenosine-mediated platelet inhibition via the A2A receptor.7 4. In a canine coronary artery ligation model using 1 minute of left anterior descending coronary artery occlusion, ticagrelor and dipyridamole dose-dependently …

The only reason P2Y12 inhibitors are administered in addition to aspirin is to improve the prevention of thrombosis. The clinical efficacy of adding clopidogrel to aspirin as a secondary prevention strategy in patients with high-risk coronary artery disease is well established.1 There are no effects of clopidogrel on any receptor other than P2Y12 to explain the magnitude of the clinical benefit. All of the established clinical effects are attributed to reduced platelet responsiveness to ADP.2 Therefore, the patient with inadequate P2Y12 inhibition determined by ex vivo testing logically has an increased risk for thrombosis. Persistent ischemic event occurrence and the irrefutable demonstration of clopidogrel antiplatelet response variability are 2 potent arguments against the widely practiced nonselective or one-size-fits-all strategy of administering clopidogrel therapy. Observational studies conducted in thousands of patients have led to an international consensus that high on-treatment platelet reactivity (HPR) to ADP is a major risk factor for post–percutaneous coronary intervention (PCI) ischemic event occurrence.3,4 Moreover, the recent 2011 American and European guidelines have given a Class IIb recommendation for platelet function testing or genotyping if the results of testing may alter management.5–7 Furthermore, the Society of Thoracic Surgeons gave a Class IIb recommendation for platelet function testing to determine the timing of surgery in patients on clopidogrel therapy (Level of Evidence C).8 These recommendations for personalizing antiplatelet therapy are unprecedented and acknowledge that a large body of data has accrued demonstrating the relation of HPR to ischemic risk in the PCI-treated patient. Finally, the evidence of diminished effectiveness of clopidogrel in poor metabolizers (those having 2 loss-of-function [LoF] cytochrome P450 [ CYP ] 2C19 alleles) has been recognized by the Food and Drug Administration (FDA) boxed warning about treatment with clopidogrel.9 Response by Krishna …

Background: PZ-128 is a first-in-class cell penetrating lipopeptide pepducin that inhibits PAR-1-G protein signaling by forming a structure highly similar to the corresponding off-state juxtamembrane region of the GPCR. PZ-128 inhibited PAR-1 and thrombosis in non-human primates. Its effects in humans are unknown. Methods and Results: PZ-128 was administered by continuous intravenous infusion (0.01 mg/kg to 2 mg/kg) to patients with multiple cardiovascular risk factors (n=31). Safety, tolerability, and pharmacokinetic (PK) effects were assessed. Platelet receptor function was assessed by conventional aggregation at baseline and 0.5, 1, 2, 6, 24 h and 8-11 d post-dosing. There were no effects on ECG, hematologic or clinical chemistry parameters. At 0.5 mg/kg given over 2 h there was 40 % and 50 % inhibition (8 μM SFLLRN) at 0.5 and 2 h, respectively. At 1-2 mg/kg, there was 25% and 75% inhibition at 0.5 h and 95-100% inhibition at 1-2 h (p Conclusion: PZ-128 is a promising parenteral antiplatelet agent that provided rapid, specific, dose-dependent, and reversible inhibition of platelet PAR-1 through a novel mechanism.

Background: High platelet turnover (HPT) is implicated in incomplete platelet inhibition and high platelet reactivity (HPR) during immediate release aspirin therapy in type II diabetes patients (T2DM). Durlaza is a new, extended-release orally administered aspirin formulation developed to provide 24-hour antithrombotic effects with once-daily dosing. Methods: In this open-label, single-center study, T2DM patients (n=40) and a history of cardiovascular disease (CVD) or multiple CVD risk factors were treated with daily 162.5 mg Durlaza for 14±4 days and adverse events were collected. Antiplatelet effects were determined by conventional aggregation (LTA), Multiplate analyzer, thrombelastography with PlateletMapping, PlateletWorks ,VerifyNow Assay, and serum thromboxane B2 (TxB2) at 1, 12, 16, and 24 hrs after the last dose. HPT was defined as immature platelet fraction of ≥3.0% or MPV≥11.0 fl. Patients exhibiting HPT and/or HPR (based on previously published cutpoints in ≥2 assays) were treated with Durlaza at 325mg for 14± 4 days and platelet function testing was repeated. Results: Prevalence of HPT and HPR was 47% and 27%, respectively. There was no loss of antiplatelet effect at 12, 16 and 24 h versus 1 h by all assays (Table 1). All patients responded to 162.5mg Durlaza as measured by arachidonic acid-induced aggregation with LTA and platelet reactivity levels were low at all timepoints (Table). Serum TxB2 was lower at 12 h (p Conclusion: In this first comprehensive assessment, a new, extended-release 162.5 Durlaza provided sustained antiplatelet effects over 24 h in T2DM patients with a favorable safety profile. Doubling the dose further lowered serum TxB2 in pts with HPT and/or HPR.

Atherothrombosis is the major pathophysiological process responsible for the occurrence of severe ischemic events in patients with cardiovascular diseases. In the United States, atherothrombosis strongly influenced mortality in 2004: One in 2.8 deaths was due to CVD, 1 in 5 deaths to coronary heart disease, and 1 in 17 deaths to stroke.1 Because cardiovascular disease is a progressive and systemic disease, long-term antithrombotic therapies that effectively target the entire arterial vasculature and modulate the key components responsible for thrombus generation are essential to improve patient outcomes. Because platelet activation is determined by multiple receptor-mediated signaling pathways, clinical studies have evaluated the efficacy of multidrug administration in the prevention of atherothrombotic complications.2,3 The major concern with these therapies is the critical balance between anti-ischemic effect and bleeding risk. This review summarizes our understanding of the role of combination antiplatelet therapies in the treatment and prevention of atherothrombosis. Platelet activation and aggregation play a pivotal role in the generation of occlusive thrombus at the site of coronary arterial plaque rupture. In addition, platelets influence various endothelial and inflammatory responses during the initiation and progression of atherosclerosis. Under normal conditions, anucleate circulating platelets are in a quiescent state. Healthy vascular endothelium prevents adhesion and activation of platelets by producing antithrombotic factors such as CD39 (ectoADPase), prostaglandin I2, nitric oxide, heparin, matrix metalloproteinase-9, protein S, and thrombomodulin.3,4 Endothelial activation and denudation and frank atherosclerotic plaque rupture expose the subendothelial matrix and release prothrombotic factors during acute coronary syndromes (ACS) and percutaneous interventions. These processes result in localized platelet adhesion and platelet activation. After adhesion to the exposed subendothelial matrix, platelets are activated by shear and the soluble agonists thromboxane A2 (TxA2), ADP, and thrombin. TxA2 is produced from arachidonic acid, which originates from membrane phospholipids and …

Background— Ticagrelor is the first reversibly binding oral P2Y 12 receptor antagonist. This is the first study to compare the onset and offset of platelet inhibition (IPA) with ticagrelor using the PLATO (PLATelet inhibition and patient Outcomes) trial loading dose (180 mg) with a high loading dose (600 mg) of clopidogrel. Methods and Results— In a multicenter, randomized, double-blind study, 123 patients with stable coronary artery disease who were taking aspirin therapy (75 to 100 mg/d) received ticagrelor (180-mg load, 90-mg BID maintenance dose [n=57]), clopidogrel (600-mg load, 75-mg/d maintenance dose [n=54]), or placebo (n=12) for 6 weeks. Greater IPA (20 μmol/L ADP, final extent) occurred with ticagrelor than with clopidogrel at 0.5, 1, 2, 4, 8, and 24 hours after loading and at 6 weeks ( P 50% IPA (98% versus 31%, P 70% IPA (90% versus 16%, P P P =NS). IPA for ticagrelor on day 3 after the last dose was comparable to clopidogrel at day 5; IPA on day 5 for ticagrelor was similar to clopidogrel on day 7 and did not differ from placebo ( P =NS). Conclusions— Ticagrelor achieved more rapid and greater platelet inhibition than high-loading-dose clopidogrel; this was sustained during the maintenance phase and was faster in offset after drug discontinuation. Clinical Trial Registration Information— URL: http://www.clinicaltrials.gov. Unique identifier: NCT00528411.

Background—The antiplatelet effect of aspirin is attributed to platelet cyclooxygenase-1 inhibition. Controversy exists on the prevalence of platelet resistance to aspirin in patients with coronary artery disease and effects of aspirin dose on inhibition. Our primary aim was to determine the degree of platelet aspirin responsiveness in patients, as measured by commonly used methods, and to study the relation of aspirin dose to platelet inhibition.Methods and Results—We prospectively studied the effect of aspirin dosing on platelet function in 125 stable outpatients with coronary artery disease randomized in a double-blind, double-crossover investigation (81, 162, and 325 mg/d for 4 weeks each over a 12-week period). At all doses of aspirin, platelet function was low as indicated by arachidonic acid (AA)-induced light transmittance aggregation, thrombelastography, and VerifyNow. At any 1 dose, resistance to aspirin was 0% to 6% in the overall group when AA was used as the agonist, whereas it was 1% to 27% by other methods [collagen and ADP-induced light transmittance aggregation, platelet function analyzer (PFA-100)]. Platelet response to aspirin as measured by collagen-induced light transmittance aggregation, ADP-induced light transmittance aggregation, PFA-100 (81 mg versus 162 mg,P≤0.05), and urinary 11-dehydrothromboxane B2was dose-related (81 mg versus 325 mg,P=0.003). No carryover effects were observed.Conclusions—The assessment of aspirin resistance is highly assay-dependent; aspirin is an effective blocker of AA-induced platelet function at all doses, whereas higher estimates of resistance were observed with methods that do not use AA as the stimulus. The observation of dose-dependent effects despite nearly complete inhibition of AA-induced aggregation suggests that aspirin may exert antiplatelet properties through non–cyclooxygenase-1 pathways and deserves further investigation.

Background: Thrombelastography (TEG) is an established but labor intensive method for assessing global hemostasis for the management of bleeding and thrombotic risk in surgical, cardiovascular, and trauma patients. We performed the initial validation study of the first true point-of-care TEG, the CORA® (COagulation Resonance Analyzer or TEG-6S system). CORA uses resonance-frequency viscoelasticity measurements and a disposable multi-channel microfluidic cartridge to assess hemostasis and response to antiplatelet therapy. Methods: TEG assays (n=5,100) were performed from the blood of healthy volunteers (n=160) and patients undergoing coronary revascularization (n=300) collected at 3 hospitals. Quality controls were also assayed. The performance of the TEG-6S system was compared with the conventional TEG 5000 system in accordance with Clinical Laboratory Standards Institute Guidelines. Results: Regression analysis demonstrated a strong correlation (R) between the two systems by all standard measures and a lower coefficient of variation (CV %) with the CORA system at all hospitals (Table). Receiver operating characteristic (ROC) curve analysis showed an excellent correlation between platelet mapping methods (AUC≥0.90, p Conclusion: The new point-of-care TEG-6S system is associated with improved precision, greater ease of use, and a strong correlation as compared to the conventional TEG 5000 system. The TEG-6S will facilitate future trials of personalized antiplatelet therapy and improve the assessment of bleeding and thrombotic risk in cardiovascular, surgical, and trauma patients.

To the Editor: We read with interest the article by Sibbing et al on the activating CYP2C19*17 variant that unveils a more complicated picture of the CYP2C19 locus. The work by Sibbing et al complements investigations showing the opposite effect of the inactivating CYP2C19*2 variant, which accounts for 12% of clopidogrel response variability.2 The *2 and *17 variants, 19 959 base pairs apart and in linkage disequilibrium, are not independent of one another. Therefore, individuals heterozygous or homozygous for the *17 allele are less likely …

A major goal of any antithrombotic regimen administered during percutaneous coronary intervention (PCI) is the preservation of coronary microvascular perfusion, which is critical for myocardial survival. In addition to macrovascular thrombosis, microembolization into the downstream coronary artery bed that occurs during spontaneous plaque rupture and PCI plays a prominent role in the development of microvascular dysfunction that leads to myocardial infarction. In addition to physical obstruction of the lumen by the embolus, vasoconstriction and edema due to inflammation also impair microvascular flow.1 These events likely occur more frequently during PCI performed in the setting of unstable coronary syndromes.2 With Doppler guidewire technology, it was estimated that an average of 25 embolic events occurred during primary PCI for ST-segment elevation myocardial infarction.3 Article see p 784 Platelet aggregates are important components of coronary microemboli, along with leukocytes, erythrocytes, platelet-leukocyte aggregates, cholesterol crystals, and hyalin. Platelets and leukocytes within microemboli play a particularly important role in the pathophysiological changes of blood flow by promoting in situ microvascular thrombosis, vasoconstriction, and inflammation. Interestingly, the composition of the embolized material is similar in the settings of spontaneous and catheter-induced plaque rupture.1 In animal models, distal microembolization of inert microspheres is associated with an immediate reduction in flow due to vessel occlusion, followed by enhanced blood flow due to the effects of adenosine released from the embolized myocardium into the adjacent noninvolved myocardium.4 Microembolization results in overall reduced flow reserve and the progressive loss of contractile function, which often reverses within weeks. The degree of myocardial contractile dysfunction is disproportionate to the degree of infarction and is the result of inflammation.5 However, in the clinical condition, a more complex pathophysiology exists due to the influence of multiple components of the emboli. Platelets aggregate when fibrinogen binds to the active …

Introduction: The ADP receptor P2Y 12 plays a central role in platelet function. Clopidogrel therapy is associated with various limitations including irreversible inhibition, a delayed antiplatelet effect, wide response variability, and non-responsiveness that has been linked to adverse ischemic event occurrence. We report the first pharmacodynamic study of a single oral dose of PRT060128 (PRT128), a novel, direct-acting reversible P2Y 12 inhibitor in patients with high platelet reactivity while on maintenance dose clopidogrel therapy(75mg/d) and aspirin. Methods: Previously stented patients (n=27) on maintenance aspirin and clopidogrel therapy were screened for high platelet reactivity (HPR) defined as upper tertile 5μ M ADP-induced aggregation (>43%) based on prior studies conducted at our Center; 7/27 had HPR and were treated with a single oral dose (60 mg) of PRT128. Platelet function was assessed at baseline, 4 hours, 6 hours, and 24 hours post-dosing by light transmittance aggregometry (LTA) stimulated by 5μ M, 20 μ M ADP, and 4μ g/ml collagen; Thrombelastography PlateletMapping (MA ADP ), Accumetrics P2Y12 assay (PRU), platelet reactivity ratio (%) by vasodilator stimulated phosphoprotein phosphorylation (VASP), and Perfusion Chamber Assay (PCA). Results: Results shown in the Table represent means ± standard deviation for the 7 patients at each time point. Conclusion: Based on results using multiple pharmacodynamic assays, PRT060128 is a potent rapid-acting inhibitor of P2Y 12 that overcomes high platelet reactivity in patients non-responsive to clopidogrel therapy. The pharmacodynamic properties of this novel P2Y 12 antagonist warrant future large scale investigations to determine clinical efficacy.

Dr Klein appears concerned about the uniform inhibition of arachidonic acid–induced aggregation observed in the Aspirin-Induced Platelet Effect (ASPECT) trial. We would like to reassure Dr Klein that the compliance of the patients in ASPECT was meticulously recorded and, as reported in the manuscript, was overall 98%. Dr Klein should also be aware of the significance of results determined by double crossover studies such as the ASPECT study and the robust statistical analyses performed.1 Why were we not surprised by the results of the ASPECT study? In a previous study of 223 patients undergoing stenting who were treated with long-term aspirin therapy, only 1 compliant patient was …

Background: High on-treatment platelet reactivity to adenosine diphosphate (HPR-ADP) may be a risk factor for ischemic events after percutaneous coronary intervention (PCI). We determined whether a cutpoint of HPR-ADP, similar to the INR used to guide anticoagulant therapy, could predict ischemic event occurrence after PCI. Methods : Post-procedural platelet reactivity to ADP was measured by conventional aggregometry in 352 consecutive patients undergoing non-emergent PCI followed for up to 2 years for post-discharge ischemic events. All patients had received clopidogrel and aspirin therapy at the time of aggregation measurements. Results: Eighty-two patients (23%) suffered ischemic events and had higher 5 and 20 μM ADP-induced aggregation compared to patients without ischemic events (46 ± 14% and 60 ± 13% versus 30 ± 17% and 43 ± 19%, respectively, p Conclusions: High on-treatment platelet reactivity to ADP is an independent risk factor for ischemic events within 2 years of non-emergent PCI. These data are the first to support a therapeutic target for antiplatelet therapy based on an ex vivo platelet function test, similar to the INR used for anticoagulant therapy. The study is a step towards a personalized medicine approach to guide the intensity of antiplatelet therapy.

Background— Pretreatment is not the most common strategy practiced for clopidogrel administration in elective coronary stenting. Moreover, limited information is available on the antiplatelet pharmacodynamics of a 300-mg versus a 600-mg clopidogrel loading dose, and the comparative effect of eptifibatide with these regimens is unknown. Methods and Results— Patients undergoing elective stenting (n=120) were enrolled in a 2×2 factorial study (300 mg clopidogrel with or without eptifibatide; 600 mg clopidogrel with or without eptifibatide) (Clopidogrel Loading With Eptifibatide to Arrest the Reactivity of Platelets [CLEAR PLATELETS] Study). Clopidogrel was administered immediately after stenting. Aggregometry and flow cytometry were used to assess platelet reactivity. Eptifibatide added a ≥2-fold increase in platelet inhibition to 600 mg clopidogrel alone at 3, 8, and 18 to 24 hours after stenting as measured by 5 μmol/L ADP–induced aggregation ( P P P Conclusions— In elective stenting without clopidogrel pretreatment, use of a GPIIb/IIIa inhibitor produces superior platelet inhibition and lower myocardial necrosis compared with high-dose (600 mg) or standard-dose (300 mg) clopidogrel loading alone. In the absence of a GPIIb/IIIa inhibitor, 600 mg clopidogrel provides better platelet inhibition than the standard 300-mg dose. These results require confirmation in a large-scale clinical trial.