Antiplatelet drug response variability and the role of platelet function testing: A practical guide for interventional cardiologists

Diabetes and atherothrombosis: The circadian rhythm and role of melatonin in vascular protection

Obesity-related euglycaemic insulin resistance clusters with cardiometabolic risk factors, contributing to the development of both type 2 diabetes and cardiovascular disease. An increased thrombotic tendency in diabetes stems from platelet hyperactivity, enhanced activity of prothrombotic coagulation factors and impaired fibrinolysis. Furthermore, a low-grade inflammatory response and increased oxidative stress accelerate the atherosclerotic process and, together with an enhanced thrombotic environment, result in premature and more severe cardiovascular disease. The disruption of circadian cycles in man secondary to chronic obesity and loss of circadian cues is implicated in the increased risk of developing diabetes and cardiovascular disease. Levels of melatonin, the endogenous synchronizer of circadian rhythm, are reduced in individuals with vascular disease and those with deranged glucose metabolism. The anti-inflammatory, antihypertensive, antioxidative and antithrombotic activities of melatonin make it a potential therapeutic agent to reduce the risk of vascular occlusive disease in diabetes. The mechanisms behind melatonin-associated reduction in procoagulant response are not fully known. Current evidence suggests that melatonin inhibits platelet aggregation and might affect the coagulation cascade, altering fibrin clot structure and/or resistance to fibrinolysis. Large-scale clinical trials are warranted to investigate the effects of modulating the circadian clock on insulin resistance, glycaemia and cardiovascular outcome.

ABCC3 Polymorphisms and mRNA Expression Influence the Concentration of a Carboxylic Acid Metabolite in Patients on Clopidogrel and Aspirin Therapy

Acetylsalicylic acid (ASA) and clopidogrel combined therapy has been reported to be beneficial in patients with acute coronary syndrome (ACS). Antiplatelet drug resistance, especially to clopidogrel, is a multifactorial phenomenon that affects a large number of ACS patients. The genetic contribution to this drug response is not fully elucidated. We investigated the relationship of ABC-type efflux subfamily C member 3 (ABCC3) polymorphisms and mRNA expression with plasma concentrations of clopidogrel, salicylic acid (SA) and a carboxylic acid metabolite (CAM). Clopidogrel, CAM and SA plasma concentrations were measured simultaneously by liquid chromatography-tandem mass spectrometry (LCMS/MS) from 83 ACS patients undergoing percutaneous coronary intervention. ABCC3 (rs757421, rs733392 and rs739923) and CYP2C19*2 (rs4244285) polymorphisms as well as mRNA expression were evaluated. A positive correlation was found between CAM concentrations and ABCC3 mRNA expression (r = 0.494, p < 0.0001). Patients carrying genotype AA (rs757421 variant) had higher CAM concentrations and ABCC3 mRNA expression as compared to those of GG + GA carriers (p = 0.017). A multiple linear regression analysis revealed that ABCC3 mRNA expression (p = 0.017), rs757421 AA genotype (p = 0.001), blood collection time (p = 0.018) and clopidogrel dose (p = 0.001) contributed to the concentration of CAM. No associations were observed for the CYP2C19*2 polymorphism. These results suggest that up-regulation of ABCC3 mRNA expression leads to increased plasma CAM levels through MRP3-mediated cell efflux. The ABCC3 rs757421 polymorphism may contribute to gene expression. Therefore, ABCC3 may be a potential biomarker for the response to clopidogrel.

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

BACKGROUND

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

OBJECTIVE

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Clopidogrel Resistance Increases Rate of Recurrent Stroke and Other Vascular Events in Chinese Population

BACKGROUND

Research regarding clopidogrel resistance (CR) and ischemic stroke (IS) recurrence related to IS is scanty. The aim of the present study was to determine the incidence of CR and the association between CR and IS recurrence and other vascular events in patients with IS receiving clopidogrel.

METHODS

CR was assessed by platelet aggregation assay in 535 IS patients receiving clopidogrel. All patients continued taking clopidogrel after discharge and were followed up for 6 months. The primary outcome was a composite of recurrent ischemic stroke (RIS), myocardial infarction, and death. The secondary outcome was the degree of disability as measured by modified Rankin Scale (mRS).

RESULTS

Out of 535 IS patients, 208 (38.88%) were CR and 327 (61.12%) were clopidogrel sensitive (CS). Diabetes was independently associated with risk of CR (odds ratio: 2.42, 95% confidence interval [CI], 1.22-4.97, P <.01). During the follow-up period, the incidence of ischemic vascular events was higher in the CR group than in the CS group; the proportion of patients with mRS score of 0-2 points at 6 months was significantly lower in CR group than in CS group. CR (hazard ratio [HR]: 2.82, 95% CI, 1.23-6.94, P <.01), diabetes (HR: 1.61, 95% CI, 1.01-3.49, P = .02), and hypertension (HR: 1.84, 95% CI, 1.12-4.72, P = .03) were independent risk factors for ischemic vascular events.

CONCLUSION

The incidence of CR in IS patients taking clopidogrel is relatively high in the Chinese population. CR is associated with ischemic vascular events, including RIS, and poor neurological recovery.

Prevalence of aspirin resistance in Asian-Indian patients with stable coronary artery disease

OBJECTIVE

To evaluate the prevalence of pharmacological resistance to aspirin therapy by measuring platelet functions using the technique of light transmission aggregometry.

BACKGROUND

Aspirin is the cornerstone of antiplatelet therapy in patients with coronary artery disease (CAD). However, a substantial proportion of patients manifest breakthrough thrombotic events despite regular intake of aspirin suggesting therapeutic resistance to aspirin.

METHODS

We prospectively studied 126 patients with stable coronary artery disease at a tertiary center, who were recruited after ensuring compliance with a single formulation of aspirin (enteric coated aspirin 150 mg). Platelet aggregation was measured using light transmission aggregometry with ADP (10 µM) and Arachidonic acid (0.5 mg/mL). Pharmacological aspirin resistance was defined as the combined demonstration of mean platelet aggregation of ≥70% with 10 µM ADP and a mean aggregation of ≥20% with 0.5 mg/mL A.A. Patients satisfying either one of the above criteria were defined as semi-responders. Patients satisfying neither criterion were defined as "aspirin responders".

RESULTS

Out of 126 patients with stable CAD, 64 % were responders, 36% were non responders (semi-responders = 34% and resistant = 2%). Of the laboratory parameters, only the total leukocyte count was significantly associated with the presence of aspirin resistance (P < 0.03).

CONCLUSION

Pharmacological resistance to aspirin is noted in 36% (semi-responders = 34% and resistant = 2%) of Asian Indian patients with stable CAD. Long-term follow up of these patients will assist in determining the clinical importance of this phenomenon. © 2014 Wiley Periodicals, Inc.

VASP phosphorylation and genetic polymorphism for clopidogrel resistance in Chinese patients with non-cardioembolic ischemic stroke

BACKGROUND

Clopidogrel resistance(CR)is found in non-cardioembolic ischemic stroke (NCIS) patients. However, it is still largely unknown how to identify CR in NCIS patients by laboratory and genetic characteristics.

METHODS

A total of 95 patients with acute NCIS were recruited. Phosphorylation of the vasodilator stimulated phosphoprotein (VASP) was detected using flow cytometry, and genes(CYP2C19,CYP3A4) were detected using the Sanger method. The baseline of platelet reactivity index (BPRI) before clopidogrel treatment and the platelet reactivity index with clopidogrel treatment (CPRI) for 7 days were measured. Laboratory clopidogrel resistance (LCR) was defined as CPRI of ≥ 50%. Clinical clopidogrel resistance (CCR) was defined as the presence of progressive stroke during hospitalization, stroke recurrence or occurrence of other ischemic vascular events within 6 months.

RESULTS

The incidence of LCR was 41.05% and 18.95% developed CCR. The incidence of LCR was significantly higher in GA/AA patients with CYP2C19 (681G > A) (χ2 = 11.16, P = 0.001) and CYP2C19 (636G > A) (χ2 = 4.829, P = 0.028) than in wildtype GG patients. CYP2C19 (681G > A) (OR 6.272, 95%CI 2.162,18.199,P = 0.001) and CYP2C19 (636G > A) (OR: 5.625,95%CI 1.439, 21.583,P = 0.013) were risk factors for LCR. patients with LCR were more likely to develop CCR (χ2 = 6.021, P = 0.014). The probability of CCR was markedly increased in GA/AA patients with CYP2C19 (681G > A) (χ2 = 10.341, P = 0.001). We identified CYP2C19 (681G > A) (OR 7.814, 95%CI 1.816, 33.618 P = 0.006), Essen score (OR 8.351, 95%CI 1.848, 37.745 P = 0.006), and LCR (OR 5.881, 95%CI 1.373, 25.192, P = 0.017) as risk factors for CCR.

CONCLUSION

In clinical practice,LCR and CYP2C19 gene polymorphism should be assessed in NCIS patients receiving clopidogrel treatment.

Patients carrying CYP2C19 loss of function alleles have a reduced response to clopidogrel therapy and a greater risk of in-stent restenosis after endovascular treatment of lower extremity peripheral arterial disease

OBJECTIVE

This study evaluated the relationship between the cytochrome P450 (CYP) 2C19 genotype and the antiplatelet effect of clopidogrel therapy and investigated whether genotyping can predict the risk of ischemic events after endovascular treatment (ET) of lower extremity peripheral arterial disease.

METHODS

From January 2011 to July 2012, 120 consecutive patients with arteriosclerosis obliterans (TransAtlantic Inter-Society Consensus for the Management of Peripheral Arterial Disease [TASC II] A-C) in the superficial femoral artery were included in a prospectively maintained database. Patients received 75 mg clopidogrel and 100 mg aspirin daily for at least 5 days before TaqMan (Life Technologies, Grand Island, NY) of CYP2C19 single-nucleotide polymorphisms and thromboelastography of the clopidogrel response. ET was subsequently performed, and follow-up evaluations, including duplex ultrasound imaging and ankle-brachial index assessment, were performed at 1, 3, 6, and 12 months after ET. During the follow-up, stent patency was assessed by ultrasound imaging, computed tomography angiography, or digital subtraction angiography.

RESULTS

A total of 74 ET procedures were performed. Fifty of the enrolled patients (41.7%) completed the follow-up examinations and were included in the analysis. The mean duration of follow-up was 9.8 ± 2.1 months (range, 1-30 months). Carriers of at least one CYP2C19 loss-of-function (LOF) allele had a diminished pharmacodynamic response to clopidogrel (51.6 ± 20.1 vs. 39.8 ± 15.2 for patients without and with LOF alleles, respectively; P = .022). Carriers of one LOF allele had an increased incidence of ischemic events compared with patients without any LOF alleles (59.0% vs. 20.8%, respectively; P = .008). This trend was even more evident in patients with two LOF alleles compared with patients with no LOF alleles (100% vs. 20.8% ischemic events; P = .002). The cumulative primary patency rate at 12 months was 56.0%, with significant differences between groups (73.1% vs. 34.6% in patients without and with LOF alleles, respectively; P = .0.006). CYP2C19 LOF carrier status was associated with an increased rate of primary end points (P = .007). On the basis of their adenosine diphosphate-induced platelet aggregation, patients with high platelet reactivity had a significantly higher risk of ischemic events (P = .012). CYP2C19 genotypic classification (adjusted hazard ratio, 2.688; 95% confidence interval, 1.366-5.288; P = .004) and history of smoking (adjusted hazard ratio, 2.430; 95% confidence interval, 1.024-5.765; P = .044) were independent risk factors for ischemic events.

CONCLUSIONS

CYP2C19 LOF alleles were associated with a diminished platelet response to clopidogrel treatment. Patients carrying CYP2C19 LOF alleles who are treated with clopidogrel may trend toward a poor prognosis after ET.

Blunt cerebrovascular trauma

PURPOSE OF REVIEW

Blunt cerebrovascular injuries (BCVI) are a rare but potentially devastating injury with stroke rates up to 50%. Over the past decade, the recognition and subsequent management of these injuries has undergone a marked evolution. This review will focus on the rationale for BCVI screening, imaging options, and treatment modalities.

RECENT FINDINGS

There are no prospective randomized controlled trials evaluating the management of BCVI. Available studies support screening a high-risk patient population based upon injury mechanism and constellation of associated injuries using multidetector-row (16-slice or greater) computed tomographic angiography (CTA). Although the ideal regimen of antithrombotic therapy has yet to be determined, treatment with either anticoagulation or antiplatelet agents has been shown to reduce BCVI-related stroke rate.

SUMMARY

Cerebrovascular injuries (CVI) are now diagnosed in approximately 1% of blunt trauma patients. The recognition of a clinically silent period allows for injury screening based upon mechanism of trauma and the patient's injury pattern. Following identification of injuries in asymptomatic patients, prompt initiation of antithrombotic therapy reduces the incidence of stroke.

Pharmacogenomics of anti-platelet therapy focused on peripheral blood cells of coronary arterial disease patients

BACKGROUND

To investigate genes differentially expressed in peripheral blood cells (PBCs) from patients with coronary arterial disease (CAD) under double anti-platelet therapy.

METHODS

Twenty-six CAD patients that were submitted to percutaneous coronary intervention (PCI) were selected to participate in this study. These patients took 100mg/day of acetylsalicylic acid (ASA) and 75mg/day of clopidogrel. Blood samples were collected before PCI to evaluate platelet reactivity using VerifyNow ASA and P2Y12 assays (Accumetrics). The patients were stratified into 4 quartiles based on ASA reaction units (ARUs) and P2Y12 reaction units (PRUs). Quartile 1 (Q1) patients were classified as responders and quartile 4 (Q4) patients as non-responders. Global mRNA expression from Q1 to Q4 was analyzed by microarray using the GeneChip Exon 1.0 ST array (Affymetrix) and was confirmed by RT-qPCR.

RESULTS

Patients with ARU or PRU values within the first quartile (Q1, ARU<390 and PRU<151) were considered responders, while those who had ARU or PRU within the fourth quartile (Q4, ARU>467 and PRU>260) were considered nonresponders. The risk factors associated for CAD showed expected frequencies and no difference was found between Q1 and Q4. Microarray analysis identified 117 genes differentially expressed for ASA and 29 for clopidogrel between Q1 and Q4 groups (p<0.01, FC>1.2).

CONCLUSION

The variation in response to ASA may be related with an increased expression of IGF1 and IGF1R, as well as a response to clopidogrel can be affected by pharmacokinetic change related to the reverse transport pathway by increased expression of ABCC3.

Antiplatelet therapy in acute coronary syndromes: current agents and impact on patient outcomes

Platelets play a central role in atherothrombosis and subsequent development of acute coronary syndromes (ACS). The understanding of this process has driven a large body of evidence demonstrating the mortality and morbidity benefits of antiplatelet agents in the ACS population. As expected, however, these agents come with an intrinsically increased risk of bleeding which underlies the vast majority of their complications and adverse effects. In today’s setting of compounding comorbidities and broadening indications, finding the balance between thrombosis prevention and bleeding risk remains the challenge for all clinicians considering these medications. This article reviews the current main antiplatelet agents that are available for clinical use and outlines their impact on ACS outcome. We also outline factors which affect the response to these agents and discuss strategies to optimize clinical outcomes.

Clopidogrel resistance is associated with long-term thrombotic events in patients implanted with drug-eluting stents

BACKGROUND

There are limited prospective data on clopidogrel resistance and clinical outcome of patients with selective coronary drug-eluting stent (DES) implantation.

OBJECTIVE

To investigate whether clopidogrel resistance is associated with long-term thrombotic events in patients with selective coronary DES implantation.

METHODS

A total of 154 patients who underwent selective percutaneous coronary intervention (PCI) with DES were enrolled in this study. Platelet aggregation was measured using light transmittance aggregometry (LTA) before clopidogrel administration (baseline) and 24 hours after loading with clopidogrel 300 mg. Clopidogrel resistance was defined as ≤10% absolute difference between baseline aggregation and post-administration aggregation. All patients who received the same anti-platelet treatment were followed up for 1 year after discharge for the incidence of a composite endpoint consisting of cardiovascular death, myocardial infarction (MI) and revascularization, and secondly for the incidence of stent thrombosis.

RESULTS

The incidence of clopidogrel resistance is 20.28% in our study population. Patients who are complicated by diabetes mellitus, smoke, or have a higher body mass index (BMI) tend to have clopidogrel resistance. Patients in the clopidogrel-resistant group have significantly higher incidences of composite endpoints (21.88% vs 4.92%; p = 0.006) and stent thrombosis (12.5% vs 1.64%; p = 0.017) than patients in the clopidogrel-response group during 1-year follow-up.

CONCLUSIONS

Diabetes, smoking, and high BMI are associated with clopidogrel resistance, and clopidogrel resistance indicates an increased risk of long-term thrombotic events in patients implanted with DES.

Good short-term but not long-term reproducibility of the antiplatelet efficacy laboratory assessment

BACKGROUND

The antiplatelet effect of acetylsalicylic acid (ASA) varies among individual patients. We assessed the short-term reproducibility (STR) and long-term reproducibility (LTR) of light transmission aggregometry (LTA).

METHODS

Residual platelet reactivity was measured twice using LTA in a group of 207 consecutive patients (56 females, mean age 67 ± 9 years) on ASA therapy in 10 ± 6 months interval. The STR was assessed in 15 patients (6 females, mean age 61 ± 7 years) with 10 measurements on 2 consecutive days.

RESULTS

There was no correlation between both measurements in the long-term part of the study, and also Bland-Altman plot showed a diverging pattern. However, LTA STR was good with a correlation coefficient of .800 (P < .05) confirmed by Bland-Altman plot.

CONCLUSIONS

Although short-term intraindividual reproducibility of LTA assessment of platelet reactivity is very good, in the long-term perspective the antiplatelet ASA effectivity may be influenced by additional variables and repeated measurements are warranted.

2011 update to the Society of Thoracic Surgeons and the Society of Cardiovascular Anesthesiologists blood conservation clinical practice guidelines

BACKGROUND

Practice guidelines reflect published literature. Because of the ever changing literature base, it is necessary to update and revise guideline recommendations from time to time. The Society of Thoracic Surgeons recommends review and possible update of previously published guidelines at least every three years. This summary is an update of the blood conservation guideline published in 2007.

METHODS

The search methods used in the current version differ compared to the previously published guideline. Literature searches were conducted using standardized MeSH terms from the National Library of Medicine PUBMED database list of search terms. The following terms comprised the standard baseline search terms for all topics and were connected with the logical 'OR' connector--Extracorporeal circulation (MeSH number E04.292), cardiovascular surgical procedures (MeSH number E04.100), and vascular diseases (MeSH number C14.907). Use of these broad search terms allowed specific topics to be added to the search with the logical 'AND' connector.

RESULTS

In this 2011 guideline update, areas of major revision include: 1) management of dual anti-platelet therapy before operation, 2) use of drugs that augment red blood cell volume or limit blood loss, 3) use of blood derivatives including fresh frozen plasma, Factor XIII, leukoreduced red blood cells, platelet plasmapheresis, recombinant Factor VII, antithrombin III, and Factor IX concentrates, 4) changes in management of blood salvage, 5) use of minimally invasive procedures to limit perioperative bleeding and blood transfusion, 6) recommendations for blood conservation related to extracorporeal membrane oxygenation and cardiopulmonary perfusion, 7) use of topical hemostatic agents, and 8) new insights into the value of team interventions in blood management.

CONCLUSIONS

Much has changed since the previously published 2007 STS blood management guidelines and this document contains new and revised recommendations.

Antiplatelet drug therapy: role of pharmacodynamic and genetic testing

Antiplatelet therapy represents the cornerstone of treatment for the short- and long-term prevention of atherothrombotic disease processes, in particular in high-risk settings such as in patients with acute coronary syndrome and those undergoing percutaneous coronary intervention. Currently, dual antiplatelet therapy with aspirin and clopidogrel represents the most commonly used treatment regimen in these settings. However, a considerable number of patients continue to experience adverse outcomes, including both bleeding and recurrent ischemic events. Numerous investigations have demonstrated that this phenomenon may be, in part, attributed to the broad variability in individual response profiles to this standard antiplatelet treatment regimen, as identified by various assays of platelet function testing. In addition, recent studies have demonstrated that genetic polymorphisms may also have an important role in determining levels of platelet inhibition and may be considered as a tool to identify patients at risk of adverse events. This article provides an overview on antiplatelet drug response variability, an update on definitions, including the role of pharmacodynamic testing, underlying mechanisms – with emphasis on recent understandings on pharmacogenetics and drug–drug interactions – and current and future perspectives on individualized antiplatelet therapy.

The case for routine genotyping in dual-antiplatelet therapy

Over 1 million coronary stent procedures are performed annually in the U.S., with dual-antiplatelet therapy, which includes the use of both aspirin and clopidogrel, being a cornerstone in the management of these patients after coronary intervention. Now, recent data have surfaced demonstrating altered active metabolite levels of clopidogrel in patients harboring hepatic cytochrome gene variants. These variants, which have been validated through genome-wide association as the dominant explanation for the marked heterogeneity of clopidogrel response, are linked to a significant increase in the risk for bleeding, stent thrombosis, myocardial infarction, and death. With viable alternatives to clopidogrel now available, including higher clopidogrel maintenance and loading doses, prasugrel, and ticagrelor, clinicians can now effectively guide therapy in those with at-risk gene variants by simple genotyping. Such an individualized approach can potentially prevent tens of thousands of adverse cardiovascular events in the over 30% of those with European ancestry and over 40% of those with Asian or African ancestry who harbor these important clopidogrel gain-of-function and loss-of-function alleles.

Cangrelor: a review on its mechanism of action and clinical development

In patients with acute coronary syndromes and undergoing percutaneous coronary intervention, numerous large-scale clinical trials have shown that adjunctive treatment with the P2Y(12) receptor antagonist clopidogrel in addition to aspirin reduces ischemic events. These studies underscore the importance of blockade of the P2Y(12) signaling pathway in these settings. However, recent findings have shown that clopidogrel therapy may have some shortcomings. These include its broad range of interindividual-response profiles, where patients with low P2Y(12) inhibitory effects have an increased risk of recurrent ischemic events, including stent thrombosis, and its irreversible mechanism of action. These observations underscore the need for novel antiplatelet agents overcoming these limitations. Cangrelor (AR-C69931MX) is an intravenous, direct-acting and reversible P2Y(12) receptor antagonist. Cangrelor has a rapid onset and offset of action and achieves significantly greater degrees of platelet inhibition compared with clopidogrel. This article provides an overview of the current status of knowledge on cangrelor, focusing on its pharmacologic properties, clinical development and potential future applications.