Inhibition Of Platelet Responses Research Articles

Dual antiplatelet therapy is associated with high α-tubulin acetylation in circulating platelets from coronary artery disease patients

Platelet inhibition is the main treatment strategy to prevent atherothrombotic complications after acute coronary syndrome or percutaneous coronary intervention. Despite dual antiplatelet therapy (DAPT) combining aspirin and a P2Y12 receptor inhibitor, high on-treatment platelet reactivity (HPR) persists in some patients due to poor response to treatment and is associated with ischemic risk. Tubulin acetylation has been pointed out as a hallmark of stable microtubules responsible for the discoid shape of resting platelets. However, the impact of antiplatelet treatments on this post-translational modification has never been studied. This study investigated whether tubulin acetylation differs according to antiplatelet therapy and on-treatment platelet reactivity. Platelets were isolated from arterial blood samples of 240 patients admitted for coronary angiography, and levels of α-tubulin acetylation on lysine 40 (α-tubulin K40 acetylation) were assessed by western blot. We show that platelet α-tubulin K40 acetylation was significantly increased in DAPT-treated patients. In addition, the proportion of patients with high levels of α-tubulin K40 acetylation was drastically reduced among DAPT-treated patients with HPR. Multivariate logistic regression confirmed that DAPT resulting in adequate platelet inhibition was strongly associated with elevated α-tubulin K40 acetylation. In conclusion, our study highlights the role of elevated platelet α-tubulin K40 acetylation as a marker of platelet inhibition in response to DAPT. Clinical trial registration: https://clinicaltrials.gov - NCT03034148.

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.

Antithrombotic Effects of Fostamatinib in Combination with Conventional Antiplatelet Drugs.

New antithrombotic medications with less effect on haemostasis are needed for the long-term treatment of acute coronary syndromes (ACS). The platelet receptor glycoprotein VI (GPVI) is critical in atherothrombosis, mediating platelet activation at atherosclerotic plaque. The inhibition of spleen tyrosine kinase (Syk) has been shown to block GPVI-mediated platelet function. The aim of our study was to investigate if the Syk inhibitor fostamatinib could be repurposed as an antiplatelet drug, either alone or in combination with conventional antiplatelet therapy. The effect of the active metabolite of fostamatinib (R406) was assessed on platelet activation and function induced by atherosclerotic plaque and a range of agonists in the presence and absence of the commonly used antiplatelet agents aspirin and ticagrelor. The effects were determined ex vivo using blood from healthy volunteers and aspirin- and ticagrelor-treated patients with ACS. Fostamatinib was also assessed in murine models of thrombosis. R406 mildly inhibited platelet responses induced by atherosclerotic plaque homogenate, likely due to GPVI inhibition. The anti-GPVI effects of R406 were amplified by the commonly-used antiplatelet medications aspirin and ticagrelor; however, the effects of R406 were concentration-dependent and diminished in the presence of plasma proteins, which may explain why fostamatinib did not significantly inhibit thrombosis in murine models. For the first time, we demonstrate that the Syk inhibitor R406 provides mild inhibition of platelet responses induced by atherosclerotic plaque and that this is mildly amplified by aspirin and ticagrelor.

Platelet Reactivity and Outcomes after Off-Pump Coronary Surgery in Acute Coronary Syndrome Patients

Ischemic and hemorrhagic complications are major determinants of survival in acute coronary syndrome (ACS) patients undergoing coronary surgery. We investigated the association of preoperative platelet reactivity to P2Y12 antagonists with ischemic and hemorrhagic complications after Off-Pump Coronary Artery Bypass surgery (OPCAB) in ACS patients who received dual anti-platelet therapy (DAPT) within 5 days prior to surgery. This prospective, observational study with 177 patients compared the incidence of perioperative major bleeding and major adverse cardiac events (MACEs) in relation to the tertile distribution of the % inhibitory response to P2Y12 antagonists, as measured by a thromboelastography platelet mapping assay. The incidences of perioperative major bleeding and MACEs were similar in relation to the tertile distribution of inhibitory response to P2Y12 antagonists. The % inhibitory responses to P2Y12 antagonists between patients who did or did not exhibit MACEs, and with or without major bleeding, were 58 ± 20% and 56 ± 20% (p = 0.578) and 57 ± 19% and 56 ± 21% (p = 0.923), respectively. In ACS patients who received DAPT close to OPCAB, the platelet inhibitory response to P2Y12 antagonists was not associated with ischemic or hemorrhagic complications. OPCAB may obviate the need for routine platelet function testing for ACS patients requiring DAPT and surgical revascularization. Clinical Registration Number: NCT02184884.

Abstract P526: PON1 Q192R Alters Clopidogrel Efficacy in Patients With Coiling of Intracranial Aneurysm but Not Carotid Artery Stenting

Introduction: The impact of the paraoxonase-1 ( PON1 ) polymorphism, Q192R (rs662; c.575A&gt;G or p.Gln192Arg), on platelet inhibition in response to clopidogrel remains controversial. We investigated the impact of PON1 Q192R on post-clopidogrel platelet reactivity in patients undergoing coil embolization for intracranial aneurysm (IA) and carotid artery stenting (CAS). Methods: Between May 2010 and September 2015, 567 patients undergoing elective neurointervention with dual antiplatelet therapy were registered. On-treatment platelet reactivity was measured using a VerifyNow P2Y12 assay in P2Y12 reaction units (PRUs). High platelet reactivity (HPR) was defined as a PRU of ≥208. Genotype testing was performed for PON1 Q192R and CYP2C19*2 and *3 (loss of function alleles), and *17 . Consequently, 473 patients were eligible for further analysis. For patients undergoing coil embolization for IA or CAS, associations between ≥1 PON1 192R allele and HPR were investigated. Results: HPR was observed in 59.4% of 276 patients undergoing coil embolization for IA (78 male; median age, 62 years) and 47.7% of 197 patients undergoing CAS (153 male; median age, 72 years). Among patients undergoing coil embolization for IA, carriers of ≥1 PON1 192R allele demonstrated HPR more frequently compared with non-carriers (92.1% vs. 83.0%, respectively; P = 0.021). Carrying ≥1 PON1 192R allele was associated with HPR (adjusted odds ratio [aOR] 3.43, 95% confidence interval [CI] 1.45-8.42). In contrast, among patients undergoing CAS, the frequency of HPR was similar between carriers of ≥1 PON1 192R allele compared with non-carriers (90.4% vs. 87.4%, respectively; P = 0.652). Carrying ≥1 PON1 192R allele was not associated with HPR (aOR 0.95, 95% CI 0.34-2.60). Conclusions: PON1 Q192R is associated with HPR of clopidogrel in patients undergoing coil embolization for IA but not in patients undergoing CAS. PON1 metabolizes clopidogrel into the inactive endo isomer. By contrast, PON1 protects against low-density lipoprotein oxidation. High PON1 activity may cancel the disadvantage in clopidogrel metabolism through its antioxidant and atheroprotective effects in patients carrying ≥1 PON1 192R allele with carotid artery stenosis representing advanced systemic atherosclerosis.

De-escalation strategy with half-dose prasugrel or ticagrelor on pharmacodynamics and outcome in East Asians patients with acute coronary syndrome

Abstract Background East Asians treated with potent P2Y12 inhibitors (prasugrel or ticagrelor) are exposed to more potent platelet inhibitory response. Whether half-dose de-escalation strategy would be benefit for chronic antiplatelet strategy in East Asian patients with acute coronary syndrome (ACS) remain uncertain. Method In half-dose de-escalation strategy, 129 Korean ACS patients were assigned to receive standard-dose potent P2Y12 inhibitors (n=86, prasugrel [n=38], ticagrelor [n=48]), followed by half-dose reduction at 1 month for maintenance, and was compared to clopidogrel (n=43) as control. The primary safety outcome was any clinically significant bleeding according to BARC (Bleeding Academic Research Consortium) criteria at 12 months. The pharmacodynamic response is accessed by VerifyNow P2Y12 reaction unit (PRU) at 1 month and 3 months post PCI. Results Ticagrelor achieved significantly lower PRU (7 [4–32] vs. 11 [5–76] vs. 167 [97–212]) than prasugrel and clopidogrel, resulting OPR rate 0% vs. 21.6% vs. 58.5%, respectively at 1 month post PCI. Similar results were observed at 3 months (PRU 12 [6–43] in ticagrelor vs. 88 [58–148] in prasugrel vs. 169 [107–199] in clopidogrel), with OPR rate 7.1% vs. 51.5% vs. 65.9%, respectively. At 12 months, the incidence of BARC type-1 or -2 bleeding was significantly higher in potent P2Y12 inhibitors (37.5% in ticagrelor, 34.2% in prasugrel) than in clopidogrel (36.0 vs. 14.0%; HR, 2.86; 95% CI, 1.19–6.87; p=0.018). Conclusion In Korean ACS patients, pharmacodynamic response (OPR rate) with half-dose prasugrel appears comparable to that with clopidogrel, whereas ticagrelor still exhibit potent platelet inhibition either standard or half doses. De-escalation strategy with half-dose potent P2Y12 inhibitor was associated with higher incidence of clinically insignificant bleeding compared with clopidogrel. Optimal dose reduction strategies in potent P2Y12 inhibitors to balance safety and effectiveness remain uncertain, and require further studies. Pharmcodynamics to oral P2Y12 inhibitors Funding Acknowledgement Type of funding source: Private grant(s) and/or Sponsorship. Main funding source(s): National Research Foundation of Korea

Influence of Sex on Platelet Reactivity in Response to Aspirin.

BackgroundThere are sex differences in the efficacy and safety of aspirin for the prevention of myocardial infarction and stroke. Whether this is explained by underlying differences in platelet reactivity and aspirin response remains poorly understood.Methods and ResultsHealthy volunteers (n=378 208 women) and patients with coronary artery disease or coronary artery disease risk factors (n=217 112 women) took aspirin for 4 weeks. Light transmittance aggregometry using platelet‐rich plasma was used to measure platelet reactivity in response to epinephrine, collagen, and ADP at baseline, 3 hours after the first aspirin dose, and after 4 weeks of daily aspirin therapy. A subset of patients underwent pharmacokinetic and pharmacodynamic assessment with levels of salicylate and cyclooxygenase‐1–derived prostaglandin metabolites and light transmittance aggregometry in response to arachidonic acid and after ex vivo exposure to aspirin. At baseline, women had increased platelet aggregation in response to ADP and collagen. Innate platelet response to aspirin, assessed with ex vivo aspirin exposure of baseline platelets, did not differ by sex. Three hours after the first oral aspirin dose, platelet aggregation was inhibited in women to a greater degree in response to epinephrine and to a lesser degree with collagen. After 4 weeks of daily therapy, despite higher salicylate concentrations and greater cyclooxygenase‐1 inhibition, women exhibited an attenuation of platelet inhibition in response to epinephrine and ADP.ConclusionsWe observed agonist‐dependent sex differences in platelet responses to aspirin. Despite higher cyclooxygenase‐1 inhibition, daily aspirin exposure resulted in a paradoxical attenuation of platelet inhibition in response to epinephrine and ADP over time in women but not in men.

Pharmacodynamic study of prasugrel or clopidogrel in non-ST-elevation acute coronary syndrome with CYP2C19 genetic variants undergoing percutaneous coronary intervention (PRAISE-GENE trial)

BackgroundThe CYP2C19*2 or *3 loss-of-function (LOF) allele is associated with high platelet reactivity (HPR) on clopidogrel treatment. East Asians may benefit from a lower dose of prasugrel due to their more potent platelet inhibitory response. The impact of LOF alleles on the pharmacodynamic response to half-dose prasugrel in patients with non-ST-elevation acute coronary syndrome (NSTE-ACS) undergoing percutaneous coronary intervention (PCI) is unknown. MethodsSeventy patients with the LOF alleles were assigned to half-dose prasugrel (n = 35, 30-mg load followed by 5 mg daily) or clopidogrel (n = 35, 600-mg load followed by 75 mg daily). The primary endpoint was the rate of HPR, defined as VerifyNow-P2Y12 reaction unit (PRU) >235, at 24 h post loading. ResultsPrasugrel achieved a lower PRU compared to clopidogrel after loading (119 [56–175] vs. 245 [189–299]), at 24 h (34 [8–58] vs. 196 [122–244]), and at 30 days (134 [98–189] vs. 203 [144–248]). Prasugrel had a lower rate of HPR after loading (5.7% vs. 57.1%, p <0.001), at 24 h (2.9% vs. 28.6%, p=0.006), and at 30 days (11.4% vs. 34.3%, p=0.004). Prasugrel had a similar rate of optimal platelet reactivity at 30 days (71.4% vs. 60.0%, p=0.450). There was no significant difference in the occurrence of periprocedural myonecrosis within 48 h after PCI with clopidogrel and prasugrel (22.9% vs. 17.1%, p>0.960). ConclusionsHalf-dose prasugrel provided potent platelet inhibition in NSTE-ACS patients that were carriers of the CYP2C19*2 or *3 allele, with a lower rate of HPR. Periprocedural myonecrosis was not significantly different in the 2 groups.

2018 update of expert consensus statement on antiplatelet therapy in East Asian patients with ACS or undergoing PCI

East Asians are the most populous race in the world and their health status is an important global issue. Compared with Caucasian populations, East Asian patients have a different benefit/risk ratio when using antithrombotic treatment. Despite this observation, treatment strategies in East Asian patients are mostly based on the American and European guidelines. Despite a lower platelet inhibitory response to clopidogrel, East Asian patients show a similar or even a lower rate of ischemic event occurrence and higher bleeding risk compared with Caucasian patients. For potent P2Y12 inhibitors (ticagrelor and prasugrel), East Asian patients have shown less favorable net clinical benefits compared with Caucasian patients, which may be related to differences in pharmacokinetic/pharmacodynamic profiles and therapeutic zone of antiplatelet effect. This updated consensus mainly focuses on state-of-the-art and current controversies in the East Asian population. In addition, when East Asian patients are administered potent P2Y12 receptor inhibitors, the strategies and ongoing trials to overcome the related hurdles are discussed.

Obesity and Inflammation and Altered Clopidogrel Pharmacokinetics and Pharmacodynamics.

Clopidogrel is a key antiplatelet drug that has substantial interpatient variability in pharmacodynamic response. Patients with lesser degrees of platelet inhibition in response to clopidogrel appear to be at increased risk of cardiovascular events. Obesity is an independent risk factor for cardiovascular morbidity and mortality due to atherothrombotic events and represents a group of patients who are in need of optimized antithrombotic therapy. Central to the obesity-related risk of atherothrombosis is a pro-thrombotic state characterized by increased levels of coagulation factors, impaired fibrinolysis and platelet hyper-reactivity, which results from the interaction among the features clustering in obesity: insulin resistance, inflammation, oxidative stress, and endothelial dysfunction. A number of reports have demonstrated that obesity is a risk factor for a reduced clopidogrel pharmacodynamic response. The inflammatory state associated with obesity, particularly a metabolic endotoxemia, may set in motion, a number of mechanisms that increase platelet reactivity, suppress cytochrome P450 enzyme activity, and increase platelet turnover, all contributing to a poor clopidogrel response. Comprehensive understanding of the mechanisms underlying obesity-related high onclopidogrel platelet reactivity will help in the optimization of antithrombotic therapy in this patient population.

Induction of Diabetes Abolishes the Antithrombotic Effect of Clopidogrel in Apolipoprotein E–Deficient Mice

Patients with acute coronary syndrome with diabetes mellitus (DM) exhibit an impaired platelet inhibitory response to clopidogrel which is only partially understood. DM was induced by the administration of streptozotocin (STZ) to 9-week-old mice. The antithrombotic effects of clopidogrel (10 mg/kg/d, orally × 5 days) were determined using a FeCl 3 -induced thrombosis model employing wild-type (WT), apolipoprotein E (apoE)-deficient, and diabetic apoE-deficient mice at 21 weeks. Antiplatelet effects were determined using flow cytometry. The antithrombotic effects of clopidogrel were similar in WT and apoE-deficient mice but were attenuated in diabetic apoE-deficient mice with the percent inhibition of thrombus area (µm 2 ) by clopidogrel being 85.5% (WT mice), 75.0% (apoE-deficient mice), and 1.9% (diabetic apoE-deficient mice). The time to first occlusion and lumen stenosis also reflected a significant loss of the antithrombotic effects of clopidogrel in diabetic apoE-deficient mice. Ex vivo platelet activation, which was assessed using ADP-induced expression of activated glycoprotein IIb/IIIa, was completely inhibited by clopidogrel in these three groups of mice. In contrast, the effect of clopidogrel on the ex vivo expression of platelet P-selectin induced by protease-activated receptor 4–activating peptide was diminished in diabetic apoE-deficient mice compared with that in WT and apoE-deficient mice. These data suggest that diabetic apoE-deficient mice may serve as a useful model to better understand the impaired responses to clopidogrel in patients with DM, which may partially reflect a reduction of the effect of clopidogrel on thrombin-induced platelet activation.

RXR Ligands Negatively Regulate Thrombosis and Hemostasis.

Platelets have been found to express intracellular nuclear receptors including the retinoid X receptors (RXRα and RXRβ). Treatment of platelets with ligands of RXR has been shown to inhibit platelet responses to ADP and thromboxane A2; however, the effects on responses to other platelet agonists and the underlying mechanism have not been fully characterized. The effect of 9-cis-retinoic acid, docosahexaenoic acid and methoprene acid on collagen receptor (glycoprotein VI [GPVI]) agonists and thrombin-stimulated platelet function; including aggregation, granule secretion, integrin activation, calcium mobilization, integrin αIIbβ3 outside-in signaling and thrombus formation in vitro and in vivo were determined. Treatment of platelets with RXR ligands resulted in attenuation of platelet functional responses after stimulation by GPVI agonists or thrombin and inhibition of integrin αIIbβ3 outside-in signaling. Treatment with 9-cis-retinoic acid caused inhibition of thrombus formation in vitro and an impairment of thrombosis and hemostasis in vivo. Both RXR ligands stimulated protein kinase A activation, measured by VASP S157 phosphorylation, that was found to be dependent on both cAMP and nuclear factor κ-light-chain-enhancer of activated B cell activity. This study identifies a widespread, negative regulatory role for RXR in the regulation of platelet functional responses and thrombus formation and describes novel events that lead to the upregulation of protein kinase A, a known negative regulator of many aspects of platelet function. This mechanism may offer a possible explanation for the cardioprotective effects described in vivo after treatment with RXR ligands.

Escitalopram Impairs Thrombin-Induced Platelet Response, Cytoskeletal Assembly and Activation of Associated Signalling Pathways.

Background Serotonin reuptake inhibitors (SSRIs) may impair platelet function. Thrombin is a strong platelet agonist causing irreversible aggregation, release of granules' contents, cytoskeletal rearrangement and activation of signalling pathways. We investigated the effects of the SSRI escitalopram (SCIT) on thrombin-induced platelet response. Methods Isolated platelets were exposed to SCIT and activated with thrombin. We evaluated (1) platelet response by aggregometry and flow cytometry; (2) modifications in cytoskeleton proteins and signalling pathways by electrophoresis and Western blot; and (3) ultrastructural changes in platelets by electron microscopy. Results SCIT inhibited platelet response to thrombin, measured as platelet aggregation and expression of activation markers CD62-P and CD63 from platelet granules. Platelet aggregation decreased in a dose-dependent manner, reaching statistical significance with SCIT ≥32 µg/mL (65.4 ± 6.8% vs. 77.7 ± 2.5% for controls; p < 0.05). Expression of activation markers was statistically reduced with SCIT ≥20 µg/mL (p < 0.05). SCIT impaired the polymerization of the actin cytoskeleton and association of contractile proteins during activation with thrombin (p < 0.05 with SCIT ≥50 µg/mL). Resting platelets incubated with SCIT became most spherical, with increased platelet roundness (p < 0.01, SCIT 50 µg/mL vs. control). SCIT interfered with signalling pathways modulated by thrombin (RhoA, PKC, Erk1/2 and PI3K/AKT). Conclusions Our data indicate that SCIT inhibits thrombin-induced platelet response and interferes with cytoskeletal assembly and related signalling pathways, thus resulting in compromised release of granules' contents, reduced platelet activation and aggregation. These mechanisms may explain the antithrombotic benefits observed in patients treated with this SSRI, and could become new therapeutic targets for future antithrombotic strategies.

Insufficient platelet inhibition and thromboembolic complications in patients with intracranial aneurysms after stent placement.

OBJECT Insufficient platelet inhibition has been associated with an increased incidence of thromboembolic complications in cardiology patients undergoing percutaneous coronary intervention. Data regarding the relationship between insufficient platelet inhibition and thromboembolic complications in patients undergoing neurovascular procedures remain controversial. The purpose of this study was to assess the relationship of insufficient platelet inhibition and thromboembolic complications in patients with intracranial aneurysm undergoing stent treatment. METHODS The authors prospectively recruited patients with intracranial aneurysms undergoing stent treatment and maintained the data in a database. MRI with diffusion-weighted sequences was performed within 24 hours of stent insertion to identify acute ischemic lesions. The authors used thromboelastography to assess the degree of platelet inhibition in response to clopidogrel and aspirin. Univariate and multivariate logistic regression analysis was used to identify potential risk factors of thromboembolic complications. RESULTS One hundred sixty-eight patients with 193 aneurysms were enrolled in this study. Ninety-one of 168 (54.2%) patients with acute cerebral ischemic lesions were identified by diffusion-weighted MRI. In 9 (5.4%) patients with ischemic lesions, transient ischemic attack or stroke was found at discharge, and these complications were found in 11 (6.5%) patients during the follow-up period. The incidence of periprocedural thromboembolic complications increased with resistance to antiplatelet agents, hypertension, hyperlipidemia, complete occlusion, and aneurysm of the anterior circulation. The multivariate regression analysis demonstrated that the anterior circulation and adenosine diphosphate (ADP) inhibition percentage were independent risk factors of perioperative thromboembolic complications. The maximum amplitude and ADP inhibition percentage were independent risk factors for thromboembolic complications during the follow-up period. CONCLUSIONS The ADP inhibition percentage is related to thromboembolic complications after stent placement for intracranial aneurysms. The increase of the ADP inhibition may decrease the risk of thromboembolic complications.

Development of a concept for a personalized approach in the perioperative antiplatelet therapy administration/discontinuation management based on multiple electrode aggregometry in patients undergoing coronary artery surgery.

In patients undergoing coronary artery surgery, improvements in clinical outcomes currently rely on continued refinements of the surgical technique and modulation of adjuvant pharmacotherapy. Despite medical and technological advances, negligible rate of bleeding and ischemic events still persist necessitating further improvements in patient management. Platelet function testing (PFT) might play an important role in meticulous balancing between the risk of bleeding and thrombotic events. A suitable balance can be achieved by implementing a personalized, PFT based approach in antiplatelet therapy (APT) administration/discontinuation management. Despite emerging evidence on the widespread variability in platelet inhibitory response to APT, numerous PFT devices and heterogeneity in reporting study results hamper pooling of the evidence which in turn results with a lack of consensus in "on treatment" platelet reactivity associated with ischemic and bleeding events in perioperative phase. The literature on multiple electrode aggregometry (Multiplate(®); Roche Diagnostics, Mannheim, Germany) in coronary artery disease patients was reviewed systematically. Based on the evidence evaluating the relationship between "drug specific" PFT and bleeding or adverse ischemic events, we sought to define therapeutic window for the most commonly administered antiplatelet drugs such as aspirin (ASPI test) and adenosine-diphosphate receptor blockers (ADP test). Preoperatively, APT administration was primarily focused to avoid bleeding complications. ASPI test value of 20 AUC and ADP test value of <73 AUC were set as cut-off values that delineate bleeding tendency. Postoperatively, "therapeutic window" was set to avoid both bleeding and adverse ischemic events. Therapeutic ranges were as follows: 20 AUC < ASPItest ≤ 30 AUC and 19AUC < ADP ≤ 46AUC, respectively. This is the first attempt to define PFT based "therapeutic window" according to, perioperative APT administration/discontinuation management would be targeted. It seems that the "one-size-fits-all" concept of perioperative APT administration management is outdated and further development of PFT based, personalized APT administration/discontinuation management is desirable. This concept therefore presents a possible step forward in patient care and provides a platform for further interventional trials whereby the impact of its application on clinical outcomes would be validated.

Impact of aspirin resistance on outcomes among patients following coronary artery bypass grafting: exploratory analysis from randomized controlled trial (NCT01159639).

Individual variability in the response to aspirin, has been established by various platelet function assays, however, the clinical relevance of aspirin resistance (AR) in patients undergoing coronary artery bypass grafting (CABG) has to be evaluated. Our working group conducted a randomized controlled trial (NCT01159639) with the aim to assess impact of dual antiplatelet therapy (APT) on outcomes among patients with AR following CABG. Patients that were aspirin resistant on fourth postoperative day (POD 4) were randomly assigned to receive either dual APT with clopidogrel (75 mg) plus aspirin (300 mg)-intervention arm or monotherapy with aspirin (300 mg)-control arm. This exploratory analysis compares clinical outcomes between aspirin resistant patients allocated to control arm and patients that have had adequate platelet inhibitory response to aspirin at POD 4. Both groups were treated with 300 mg of aspirin per day following surgery. We sought to evaluate the impact of early postoperative AR on outcomes among patients following CABG. Exploratory analysis included a total number of 325 patients. Of those, 215 patients with adequate response to aspirin and 110 patients with AR allocated to aspirin monotherapy following randomization protocol. The primary efficacy end point (MACCEs-major adverse cardiac and cardiovascular events) occurred in 10 and 6 % of patients with AR and with adequate aspirin response, respectively (p = 0.27). Non-significant differences were observed in bleeding events occurrence. Subgroup analysis of the primary end point revealed that aspirin resistant patients with BMI > 30 kg/m(2) tend to have a higher occurrence of MACCEs 18 versus 5 % (relative risk 0.44 [95 % CI 0.16-1.16]; p = 0.05). This exploratory analysis did not reveal significant impact of aspirin resistance on outcomes among patients undergoing CABG. Further, sufficiently powered studies are needed in order to evaluate clinical relevance of AR in patients undergoing CABG.

Antiplatelet therapy at the time of coronary artery surgery: can a personalized approach improve outcomes?

We read with great interest the recently published multicentre cohort study by Kremke et al. [1]. Patients exposed to antiplatelet therapy (APT) at the time of coronary artery surgery (CAS) had greater postoperative bleeding volumes and greater transfusion requirements [1]. Exposure to clopidogrel, but not aspirin, was associated with greater reoperation rates and was an independent risk factor for severe postoperative bleeding, although mean bleeding volumes were not significantly different in the aspirin and clopidogrel subgroups [1]. Despite current guidelines, it is apparent that many patients are proceeding with CAS without the 5-day delay off clopidogrel. The efficacy of platelet inhibition with clopidogrel varies widely among patients, from intensive platelet inhibition to poor platelet response [2], and these variations could, to some degree, explain the non-significant differences in mean bleeding volumes in the aspirin and clopidogrel subgroups [1]. The effect of clopidogrel on bleeding mainly depends on two factors: (i) observed platelet inhibition, which depends on inherent platelet activity prior to clopidogrel administration and platelet inhibitory response to clopidogrel and (ii) newborn platelets ability to restore normal aggregation after clopidogrel discontinuation. Therefore, the use of suitable point-of-care platelet function analysers seems to be reasonable in this field. Recently, we found aspirin(P = 0.014) and clopidogrel(P = 0.003) sensitive platelet function tests to be predictive of excessive postoperative bleeding in patients following CAS [2]. Of note, 76.3% patients were transfused with no significant differences among the groups with regard to the preoperative APT administration regime (P = 0.636) [2]. However, transfused patients had significantly lower values of aspirin-sensitive platelet function tests (P = 0.002) [2]. In our opinion, the study cohort is somehow heterogeneous. Eligible procedures were either isolated CAS or CAS combined with aortic valve replacement (AVR) [1]. AVR certainly extends the duration of cardiopulmonary bypass, which was recently described as a predictor of transfusion requirements [3]. After matching, authors reported a slightly greater use of antifibrinolytic drugs in the APT group [1]. Both on-pump and off-pump procedures were included [1]. Authors reported that off-pump surgery and perioperative use of tranexamic acid were associated with a lower risk of severe postoperative bleeding [1]. The use of antifibrinolytic drugs should be equally balanced since there is evidence that antifibrinolytic therapy reduces bleeding and transfusion outcomes [4]. It would be interesting to see if exclusion of CAS + AVR and off-pump CAS patients would bring different results. During the study period, thromboelastometry-guided blood component therapy became available at two of three participating centres [1]. At the same time, multivariate analysis revealed that surgery at one of the participating centres was one of independent risk factors for severe postoperative bleeding [1]. Spiess et al. [5] reported thromboelastography-guided haemostatic management to have significantly reduced the incidence of overall transfusion and mediastinal re-exploration due to excessive bleeding. Thus, perhaps one could assume that one centre, which was found to be independent risk factor for severe postoperative bleeding, was in fact the one without thromboelastometry guided transfusion therapy available. The largest extent of chest tube output together with the greatest transfusion rates, was observed in the subgroup of patients exposed to dual APT [1]. Those results are in line with the results recently published by Miceli et al. [6]. Further incremental platelet inhibition may be observed in the group of patients receiving dual APT. Therefore, the role of aspirin and clopidogrel administration management should be separately assessed by drug-specific platelet function tests, thus facilitating an individual therapeutic approach for discontinuation management of each antiplatelet agent preoperatively.

RLOAD: does sex mediate the effect of acute antiplatelet loading on stroke outcome.

BackgroundBiologic sex can influence response to pharmacologic therapy. The purpose of this proof-of-concept study was to evaluate the medicating effects of estrogen in the efficacy of acute antiplatelet loading therapy on stroke outcome in the rabbit small clot embolic model.MethodsFemale and male (20/group) New Zealand White rabbits were embolized to produce embolic stroke by injecting small blood clots into the middle cerebral artery via an internal carotid artery catheter. Two hours after embolization, rabbits were treated with standard dose antiplatelet loading (aspirin 10 mg/kg plus clopidogrel 10 mg/kg). Primary outcome measures were platelet inhibition, behavioral outcome P50 (the weight of microclots (mg) that produces neurologic dysfunction in 50% of a group of animals), and effect of endogenous estrogen on outcome.ResultsFor the first time in a non-rodent model of stroke, it was found that higher endogenous estrogen levels resulted in significantly better behavioral outcome in female subjects (rs −0.70, p < 0.011). Platelet inhibition in response to collagen, arachidonic acid, and adenosine diphosphate (ADP) was not significantly different in females with higher vs. lower estrogen levels.ConclusionsBehavioral outcomes are improved with females with higher endogenous estrogen levels treated with standard dose antiplatelet loading. This is the first non-rodent study to demonstrate that higher endogenous estrogen levels in female rabbits appear to be neuroprotective in ischemic stroke. This research supports the further study of the effect of endogenous estrogen levels on outcome with standard dose antiplatelet loading in stroke patients not eligible for revascularization therapies.

Implications of the VerifyNow P2Y12 Assay on Patient Outcomes

Background: The platelet inhibitory response of clopidogrel is substantially variable among patients, and numerous studies have shown that post-percutaneous intervention, patients with high on-treatment platelet reactivity have an increase in risk of major adverse cardiovascular events. No published studies to date have utilized platelet function monitoring assays prior to coronary artery bypass graft (CABG) surgery, but determination of patients’ antiplatelet effects prior to surgery may decrease time to surgery and length of hospital stay. The purpose of the study was to evaluate the clinical outcomes of non-elective CABG patients analyzed by the VerifyNow P2Y12 platelet-function monitoring assay prior to surgery compared to a similar set of patients not analyzed by the VerifyNow P2Y12 assay. Methods: This was a retrospective, single center, cohort study. The primary endpoints of this study were time to surgery and length of hospital stay. Results: From March 2013 to July 2013, 60 patient charts were reviewed and included in this study. 49 patients were analyzed by the VerfiyNow P2Y12 assay, and 16 of these patients underwent non-elective CABG surgery. Eleven patients underwent non-elective CABG surgery and were not analyzed by the VerifyNow P2Y12 assay. There was no difference between groups regarding time to surgery (p = 0.75) or length of stay (p = 0.42). Based on the assay’s P2Y12 reaction unit results, 69% of VerifyNow P2Y12 patients went to surgery sooner than the institution’s recommendations which generated more bleeding events, half of which were considered major bleeds. Conclusions: Utilization of the VerifyNow P2Y12 assay prior to non-elective CABG surgery does not shorten time to surgery or overall length of hospital stay. However, insufficient P2Y12 reaction units prior to surgery may lead to more bleeding events, thus the application of platelet function monitoring assays prior to procedures may be beneficial as a bleeding risk-assessment tool.

Perioperative use of point-of-care devices in cardiac surgery may improve bleeding and transfusion outcome

Background Hemostatic disorder and massive bleeding are common complications after cardiac surgery procedures, particularly in procedures requiring prolonged cardiopulmonary bypass. Conventional laboratory coagulation tests failed to predict hemostatic disorder and consequent proclivity to excessive bleeding. On the other hand there is evergrowing proportion of patients who need antiplatelet therapy (APT) in perioperative setting. Platelet inhibitory response to antiplatelet therapy varies widely among individuals, thus reflecting bleeding tendency as well as risk for adverse ischemic events. Bedside suitable devises for assessment of platelet function as well as assessment of viscoelastic blood properties are desired. Herein, we present our institutional experience in hemostatic and antiplatelet therapy administration management.