Aspirin and clopidogrel resistance

Anti-thrombotics and major adverse cardiovascular events in anti-phospholipid syndrome: a cross-sectional study using the 2016-2018 National Inpatient Sample database

OBJECTIVE

This study assessed the relationship between anti-thrombotics and major adverse cardiovascular events (MACE) in patients with anti-phospholipid syndrome (APS).

METHOD

We included 13 947 subjects with APS from the National (Nationwide) Inpatient Sample (NIS) database for 2016-2018, and collected relevant covariates and demographic data using ICD-10 codes. Our two primary outcomes were MACE and death. We performed multivariate logistic regression analysis to assess the impact of various anti-thrombotic regimens on MACE/death in our primary cohort and high-risk subgroups.

RESULTS

Patients on anti-coagulants had significantly reduced odds of MACE [odds ratio (OR) 0.68, 95% confidence interval (CI) 0.62-0.76, p < 0.001] as well as each of its subcomponents. Those not on any anti-coagulants had significantly increased odds of MACE (OR 1.47, 95% CI 1.24-1.72, p < 0.001). No significant association was found between anti-platelet use and the odds of MACE (p > 0.05). Patients on anti-coagulants were the only class that appeared to have a mortality benefit with reduced odds for death (OR 0.64, 95% CI 0.49-0.84, p = 0.001). In the subgroups at higher risk for MACE (those with atrial fibrillation and thrombocytopenia), full anti-coagulation therapy was also the only anti-thrombotic class that significantly affected the odds of MACE, with a protective effect on MACE, but had no mortality benefit.

CONCLUSION

Patients with APS are most likely to benefit from anti-coagulant therapy in reducing MACE. Furthermore, anti-platelets alone or in combination with anti-coagulants are probably not beneficial in MACE reduction and may even increase risk.

Ilaprazole and Clopidogrel Resistance in Acute Stroke Patients

Clopidogrel, an antiplatelet agent used for secondary prevention of cerebrovascular diseases, is often taken with proton pump inhibitors (PPIs). Generally, the combined use of clopidogrel and PPIs causes adverse drug–drug interactions. VerifyNow is a quick and convenient method to confirm clopidogrel resistance (CR), which compromises adequate antithrombotic effects. We aimed to confirm CR, identify its factors, and determine the influence of the combination of ilaprazole and clopidogrel on clopidogrel using VerifyNow. In this retrospective study, we examined patients who were receiving clopidogrel after three months, starting within one week from the onset of cerebral infarction symptoms. Clinical records, imaging records, and diagnostic laboratory results, including P2Y12 reaction units (PRU), were compared and analyzed to check for CR. Additionally, the groups treated with either both ilaprazole and clopidogrel or with medications other than ilaprazole were comparatively analyzed. CR was defined as a PRU ≥240 after clopidogrel for three months. Among factors influencing CR by affecting clopidogrel metabolism, positive statistical correlations with age and alcohol consumption were confirmed. The diagnostic tests revealed a lower glomerular filtration rate and platelet count of the CR-positive group. This finding proved that the combination therapy of ilaprazole and clopidogrel is safe, as it does not interfere with the metabolism of clopidogrel.

Antiplatelet therapy for standalone coiling of ruptured intracranial aneurysms: a systematic review and meta-analysis

BACKGROUND

Endovascular embolization using standalone coils is the preferred treatment option for ruptured cerebral aneurysms to avoid the use of dual antiplatelet therapy with stent coiling or endoluminal flow diversion devices. However, it has been reported that patients undergoing the standalone coiling approach are at risk for periprocedural thromboembolism. Therefore, this systematic review and meta-analysis was performed to clarify the risks and benefits of antiplatelet therapy (AT) during coiling procedures performed to treat ruptured aneurysms, including the incidence of early thromboembolic events, hemorrhagic and delayed ischemic events, as well as clinical outcomes.

METHODS

A comprehensive search of three databases was performed for articles from inception to June 2021. After fulfilling the inclusion criteria, five studies were included in this meta-analysis and 462 patients with aneurysmal subarachnoid hemorrhage (aSAH) were identified who underwent endovascular standalone coiling treatment. Aneurysm location, patient characteristics, and aSAH grades were comparable between the AT and non-AT groups.

RESULTS

AT significantly decreased the incidence of thromboembolic events immediately after the coiling procedures compared with non-AT (OR 3.42; 95% CI 1.77 to 6.61, p<0.001). The incidences of hemorrhage, delayed ischemia, and clinical outcomes with or without AT were not significantly different between groups.

CONCLUSIONS

Although this study showed no beneficial effect of AT on clinical outcomes, the results suggest that AT could be combined with standalone coiling to avoid thromboembolism during the perioperative period. A large prospective study and/or an additional meta-analysis would be required to further investigate how AT benefits standalone coil embolization in aSAH.

Negatively charged nanoparticles of multiple materials inhibit shear-induced platelet accumulation

Platelet accumulation by VWF under high shear rates at the site of atherosclerotic plaque rupture leads to myocardial infarction and stroke. Current anti-platelet therapies remain ineffective for a large percentage of the population, while presenting significant risks for bleeding. We explore a novel way to inhibit arterial thrombus formation. Theoretically, a negative charge may influence the tertiary structure of VWF to favor the globular configuration by biophysical means without the use of platelet inactivating drugs. We tested this hypothesis experimentally for charged nanoparticles (CNPs) to inhibit thrombus formation in a microfluidic thrombosis assay (MTA). Several different CNPs demonstrated the ability to retard thrombotic occlusion in the MTA. A preliminary study in mice shows that thrombus stability is weaker with CNP administration and bleeding times are not markedly prolonged. The CNPs tested here show promise as a new class of antithrombotic therapies that act by biophysical means rather than biochemical pathways.

Platelet Dysfunction after Traumatic Brain Injury: A Review

Coagulopathy is a known sequela of traumatic brain injury (TBI) and can lead to increased morbidity and mortality. Platelet dysfunction has been identified as one of several etiologies of coagulopathy following TBI and has been associated with poor outcomes. Regardless of whether the platelet dysfunction occurs as a direct consequence of the injury or because of pre-existing medical comorbidities or medication use, accurate detection and monitoring of response to therapy is key to optimal patient care. Platelet transfusion has been proposed as a potential therapeutic intervention to treat platelet dysfunction, with several studies using platelet function assays to monitor response. The development of increasingly precise diagnostic testing is providing enhanced understanding of the specific derangement in the hemostatic process, allowing clinicians to provide patient-specific treatment plans. There is wide variability in the currently available literature on the incidence and clinical significance of platelet dysfunction following TBI, which creates challenges with developing evidence-based management guidelines. The relatively high prevalence of platelet inhibitor therapy serves as an additional confounding factor. In addition, the data are largely retrospective in nature. We performed a literature review to provide clarity on this clinical issue. We reviewed 348 abstracts, and included 97 manuscripts in our final literature review. Based on the currently available research, platelet dysfunction has been consistently demonstrated in patients with moderate-severe TBI. We recommend the use of platelet functional assays to evaluate patients with TBI. Platelet transfusion directed at platelet dysfunction may lead to improved clinical outcome. A randomized trial guided by implementation science could improve the applicability of these practices.

Microfluidic assay of antiplatelet agents for inhibition of shear-induced platelet adhesion and activation

We have developed a microfluidic system to perfuse whole blood through a flow channel with an upstream stenotic region and a downstream protein capture region. This flow-based system was used to assay how effectively antiplatelet agents suppress shear-induced platelet adhesion and activation downstream of the stenotic region. Microcontact printing was used to covalently attach one of three platelet binding proteins [fibrinogen, collagen, or von Willebrand factor (vWf)] to the surface of the downstream capture region. Whole blood with an antiplatelet agent was transiently exposed to an upstream high wall shear rate (either 4860 s-1 or 11 560 s-1), and subsequently flowed over the downstream capture region where the platelet adhesion was measured. Several antiplatelet agents (acetylsalicylic acid, tirofiban, eptifibatide, anti-vWf, and anti-GPIbα) were evaluated for their efficacy in attenuating downstream adhesion. Following antibody blocking of vWf or GPIbα, downstream platelet activation was also assessed in perfused blood by flow cytometry using two activation markers (active GPIIb/IIIa and P-selectin). Acetylsalicylic acid demonstrated its inability to diminish shear-induced platelet adhesion to all three binding proteins. GPIIb/IIIa inhibitors (tirofiban and eptifibatide) significantly reduced platelet adhesion to fibrinogen. Antibody blocking of vWf or GPIbα effectively diminished platelet adhesion to all three capture proteins as well as platelet activation in perfused blood, indicating an essential role of vWf-GPIbα interaction in mediating shear-induced platelet aggregation.

Pharmacokinetic, pharmacodynamic, and pharmacogenetic assays to monitor clopidogrel therapy

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

Evolving Approaches to Antithrombotics in Stroke Prevention and Treatment

The optimization of antithrombotic therapy for acute stroke treatment and secondary prevention is an evolving process based on an increasing array of studies that provide an evidence-based approach. Options have increased dramatically with the release of the non-vitamin K oral anticoagulants and with the results of recent randomized clinical trials designed to assess potential benefits versus risks for patients in an individualized fashion. Recent studies have provided important information to guide choice and dosing of antiplatelet agents as well as the length of treatment. Anticoagulant use is particularly pertinent for stroke prevention in patients at higher risk of atrial fibrillation and may have a place in certain other stroke mechanisms. One important focus of study is the potential benefit of combined antiplatelet and anticoagulant therapy. Options for our patients, when the initial choice of therapy does not demonstrate benefit or is not well tolerated, clearly, are valuable. For example, short-term dual antiplatelet therapy for minor stroke and transient ischemic attack is being adopted, but with the recognition that longer-term combined therapy is not worth the increased risk of bleeding. Alternative antiplatelet choices, such as cilostazol and possibly ticagrelor, may be of benefit for refractory patients and this could affect the decision-making process. This review represents an effort to incorporate the information from more recent stroke prevention and treatment studies with information gleaned from prior studies.

The Influence of Inflammation on Fibrinogen Turnover and Redistribution of the Hemostatic Balance to a Prothrombotic State in High On-Treatment Platelet Reactivity-Dual Poor Responder (HTPR-DPR) Patients

Knowledge about the influence of inflammation on platelet function and relocation of hemostatic balance to hypercoagulable state is still unclear. We compared two groups of patients who suffer from acute vs. chronic inflammatory process and additionally present high on-treatment platelet reactivity-dual platelet resistance. We did not found any differences in platelet aggregation between both investigated groups, but patients who suffer from chronic inflammation presented stronger relocation of the hemostatic balance to the hypercoagulability. A high concentration of prothrombin fragment F1+2 together with higher activity of von Willebrand factor in critical limb ischemia shows more exaggerated fibrinogen turnover although the blood concentration of this factor was in normal range. We concluded that high on-treatment platelet reactivity-dual platelet resistance and intensified inflammation are linked with elevated platelet and fibrinogen turnover to counteract proper hemostatic balance in favor of a prothrombotic state.

Effects of Aspirin on Growth Factor Release From Freshly Isolated Leukocyte-Rich Platelet-Rich Plasma in Healthy Men: A Prospective Fixed-Sequence Controlled Laboratory Study

BACKGROUND

The benefits of platelet-rich plasma (PRP) are believed to be in part dependent on growth factor release after platelet activation. Platelet activation is complex and involves multiple mechanisms. One important mechanism is driven by cyclooxygenase 1 (COX-1)-mediated conversion of arachidonic acid (AA) to precursor prostaglandins that then mediate proinflammatory responses that trigger growth factor release. Acetylsalicylic acid (ASA; also known as aspirin) is known to irreversibly inhibit COX-1, thereby blocking AA-mediated signaling; however, it is unclear whether ASA use alters growth factor release from freshly isolated PRP.

PURPOSE

To assess the effects of low-dose ASA use on activation of growth factor release from freshly isolated human PRP via AA and thrombin (TBN).

STUDY DESIGN

Controlled laboratory study.

METHODS

Twelve healthy men underwent blood collection and leukocyte-rich PRP (LR-PRP) preparation through a double-spin protocol to obtain baseline whole blood and PRP counts the same day. PRP was aliquoted into 3 groups: nonactivated, AA activated, and TBN activated. Immediately after activation, the concentrations of transforming growth factor β1 (TGF-β1), vascular endothelial growth factor (VEGF), and platelet-derived growth factor AB (PDGF-AB) were measured using enzyme-linked immunosorbent assays (ELISAs). The same 12 participants were then placed on an 81-mg daily dose of oral ASA for 14 days. Repeat characterization of whole blood and PRP analyses was done on day 14, followed by repeat ELISAs of growth factors under the same nonactivated and activated settings as previously stated.

RESULTS

Fourteen days of daily ASA had no effect on the number of platelets and leukocytes measured in whole blood and LR-PRP. Compared with nonactivated LR-PRP, AA- and TBN-mediated activation led to significant release of VEGF and PDGF-AB. In contrast, release of TGF-β1 from LR-PRP was observed only with activation by AA, not with TBN. Consistent with its inhibitory role in AA signaling, ASA significantly inhibited AA-mediated release of all 3 growth factors measured in this study. Although ASA had no effect on TBN-mediated release of VEGF and TGF-β1 from LR-PRP, ASA did partially block TBN-mediated release of PDGF-AB, although the mechanism remains unclear.

CONCLUSION

Daily use of low-dose ASA reduces VEGF, PDGF-AB, and TGF-β1 expression in freshly isolated human LR-PRP when activated with AA.

CLINICAL RELEVANCE

Reduction in growth factor release attributed to daily use of low-dose ASA or other COX inhibitors can be mitigated when PRP samples are activated with TBN. Clinical studies are needed to determine whether activation before PRP injection is needed in all applications where ASA is in use and to what extent ASA may inhibit growth factor release in vivo at the site of injury.

Inhibition of high shear arterial thrombosis by charged nanoparticles

Platelet accumulation under high shear rates at the site of atherosclerotic plaque rupture leads to myocardial infarction and stroke. Current antiplatelet therapies remain ineffective within a large percentage of the population, while presenting significant risks for bleeding. We explore a novel way to inhibit arterial thrombus formation by biophysical means without the use of platelet inactivating drugs. Our computational multi-scale dynamics model has predicted that charged particles of a specific size may entangle von Willebrand Factor (vWF) polymers and reduce the amount of elongation at high shear rates. We tested this hypothesis experimentally for negatively charged nanoparticles (CNP) to inhibit arterial thrombus formation. CNP of a particular size and charge inhibited thrombus formation, with a 10-fold peak inhibition over control conditions of thrombotic occlusion. Particles of differing material composition, size, and charge had little effect as predicted by computational studies. Surprisingly, the dose response curve was not sigmoidal, but exhibited a peak at 1.5 CNP:vWF proteins, which was not predicted by the model. This study describes a new antithrombotic agent that may have a different mechanism of action than current pharmaceutical therapies.

Predictors of thromboxane levels in patients with non-ST-elevation acute coronary syndromes on chronic aspirin therapy

High levels of thromboxane A2 (TxA2), a key mediator of platelet activation and aggregation, are associated with an increased risk of cardiovascular events. We aimed at assessing the predictors of higher plasma levels of TxB2, the stable metabolite of TxA2, in consecutive patients presenting with non-ST-elevation acute coronary syndrome (NSTE-ACS) on previous aspirin (ASA) treatment undergoing coronary angiography. Ninety-eight consecutive patients (age 61 ± 11, 75% males) with NSTE-ACS, on previous chronic ASA treatment, were prospectively enrolled in this study. Coronary disease extent was assessed by angiography according to the Bogaty score. In all patients, admission plasma levels of TxB2 (pg/ml) were measured by enzyme-linked immunosorbent assay, and patients showing TxB2 levels in the fourth quartile were compared to patients showing TxB2 levels in the lower quartiles. Multivariable logistic regression analysis showed that platelet count (odds ratio [OR] 1.18, 95% confidence interval [CI] 1.02–1.63, p=0.04), multivessel coronary disease (OR 1.37, 95% CI 1.13–3.67, p=0.03), and coronary atherosclerosis extent index (OR 1.91, 95% CI 1.45–6.79, p=0.001) were independent predictors of TxB2 level upper quartile. Of note, C-reactive protein serum levels were similar in patients with TxB2 levels in the upper quartile as compared to those in the lower quartiles (p=0.49). In conclusion, NSTE-ACS patients with severe coronary atherosclerosis may have incomplete suppression of TxA2 production despite chronic ASA therapy. This finding suggests that additional efforts should be made to lower TxA2 levels in patients with widespread coronary artery disease.

Review of aspirin and clopidogrel resistance in peripheral arterial disease

OBJECTIVE

Aspirin resistance (AR) and clopidogrel resistance (CR) are terms used to describe a reduction in the medication's efficacy in inhibiting platelet aggregation despite regular dosing. This review gives context to the clinical role and implications of antiplatelet resistance in peripheral arterial disease (PAD).

METHODS

A review of English-language literature on AR and CR in PAD involving human subjects using PubMed and MEDLINE databases was performed in April 2017. A total of 2075 patients in 22 relevant studies were identified. To give this issue context, a review of the larger, more established literature on antiplatelet resistance in coronary disease was undertaken, identifying significant research associating resistance to major adverse cardiovascular events (MACEs).

RESULTS

Studies in the coronary arterial disease literature have strongly associated antiplatelet resistance with increased MACE. Prevalence of AR or CR in coronary disease appears to be >55% for each in some studies. Meta-analyses of >50 studies revealed that AR and CR are significantly associated with MACE (relative risk of 2.09 and 2.8, respectively). This adds further weight to the literature reporting antiplatelet resistance as an independent predictor of and a threefold risk factor for major adverse cardiovascular events. The prevalence of resistance in PAD in this review was comparable to that in the coronary disease literature, with AR and CR prevalence up to 60% and 65%, respectively. There is evidence that the adverse effects of antiplatelet resistance are significant in PAD. In fact, research directly studying stent thrombosis populations with either coronary arterial disease or PAD revealed more significantly impaired platelet responsiveness to clopidogrel and aspirin in PAD compared with similar individuals with coronary disease. AR in PAD was found in studies to be a significant risk factor for iliofemoral stent reocclusion (P = .0093) and stroke in patients with symptomatic carotid disease (P = .018). CR was found to be a significant, independent risk factor in predicting ischemic outcomes in several recent PAD studies (P < .0001). Loss-of-function carriers of enzyme CYP2C19, important in clopidogrel metabolism, have a 30% greater risk of ischemic events (P < .001). Importantly, less antiplatelet drug resistance may be encountered with newer antiplatelet agents, including ticagrelor and prasugrel, because of reduced enzymatic polymorphisms.

CONCLUSIONS

The limited research addressing AR and CR in PAD suggests that further research is required to clarify the role of platelet assays and potential for individualized antiplatelet therapy.

Platelet-to-lymphocyte ratio but not neutrophil-to-lymphocyte ratio predicts high on-treatment platelet reactivity in clopidogrel-treated patients with acute coronary syndrome

OBJECTIVES

Dual antiplatelet therapy (DAPT), consisting of clopidogrel and aspirin, is the main-stay treatment of acute coronary syndromes (ACS). However, major adverse cardiovascular events may occur even in patients undergoing DAPT, and this has been related to the variable pharmacodynamic efficacy of these drugs, especially clopidogrel. Platelet-to-lymphocyte ratio (PLR) and neutrophil-to-lymphocyte ratio (NLR) are novel inflammatory markers for cardiovascular risk stratification, which may reflect an inflammatory state and thus high on-treatment platelet reactivity (HPR).

METHODS

We investigated the usefulness of PLR and NLR in predicting HPR in clopidogrel-treated patients with ACS. A total of 244 patients were enrolled in this study, and 43 of them were nonresponsive to clopidogrel.

RESULTS

Logistic regression analysis indicated that PLR was significantly associated with HPR (P < 0.001). Using a cutoff level of 331, PLR predicted HPR with a sensitivity of 73% and a specificity of 69% (odds ratio: 376.15, 95% confidence interval = 37.813-3741.728 P < 0.001, receiver operating characteristic curve: 0.885).

CONCLUSIONS

We suggest that more attention should be paid to the PLR values of these patients on admission to identify individuals who may not benefit from clopidogrel during the course of ACS.

Acetylsalicylic Acid Resistance After Simultaneous Pancreas-Kidney Transplantation

BACKGROUND

The most common conditions leading to death after simultaneous pancreas-kidney transplantations (SPKs) are cardiovascular diseases. The aim of this study was to test the platelet aggregation inhibitor acetylsalicylic acid (ASA) resistance in patients after SPKs, including investigations into the triggering factors.

METHODS

Thirty-two patients (22 men, 10 women; overall age, 47.4 ± 8.6 years) were involved in our study and took 100 mg ASA per day. We used optical platelet aggregometry to detect resistance.

RESULTS

Resistance occurred in 40.6% of the study group. However, with the use of logistic regression analysis, the examined 24 factors did not show any significant correspondence with resistance.

CONCLUSIONS

The incidence of ASA resistance seems to be higher compared with other groups, but the triggering effect is still unproved. Clarifying this question should be important regarding the mortality- and morbidity-reducing capacity of antiplatelet drugs in the management of cardiovascular conditions.

High on-treatment platelet reactivity: risk factors and 5-year outcomes in patients with acute myocardial infarction

Objective:

The aim of the present study was to assess long-term prognostic value of high on-treatment platelet reactivity (HTPR) in patients after acute myocardial infarction (MI) and its association with possible risk factors.

Methods:

This prospective, case-control study was an observation of 198 patients who had acute MI. Response to aspirin and clopidogrel was assessed using impedance aggregometry. Patients were divided into groups of adequate response, dual poor responsiveness (DPR), poor responsiveness to aspirin (PRA), and poor responsiveness to clopidogrel (PRC). Simultaneously, potential risk factors of HTPR development were recorded. After 5 years, MI recurrence and overall mortality were assessed.

Results:

HTPR was more frequent in New York Heart Association Class III and IV patients, and in patients with left ventricle systolic dysfunction. Five-year mortality rate was higher in all groups of patients with HTPR compared to patients with sufficient response to antiplatelet treatment: in PRA patients, 38.1% vs. 19.2%, p<0.01; in PRC patients, 45.2% vs. 17.3%, p<0.001; and in DPR patients, 50.0% vs. 19.9%, p<0.05. Risk of repeat MI also increased (hazard ratio [HR] 4.0, p<0.05 for DPR group; HR 4.37, p<0.01 for PRA group; and HR 3.25, p<0.05 for PRC group).

Conclusion:

PRA, PRC, and DPR are independent predictors of increased 5-year mortality and risk of repeat non-fatal MI. The study has demonstrated that HTPR is frequently observed in patients with severe heart failure and left ventricle systolic dysfunction.

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.

Percutaneous left atrial appendage occlusion - treatment outcomes and 6 months of follow-up - a single-center experience

Aim

To present the results of treatment and evaluate 6 months of follow-up in a group of patients with non-valvular atrial fibrillation, who underwent the procedure of percutaneous left atrial appendage occlusion (PLAAO).

Material and methods

Percutaneous left atrial appendage occlusion was performed in 34 patients with non-valvular atrial fibrillation and contraindications for oral anticoagulation therapy. The risk of thromboembolic and bleeding complications was determined based on the CHA₂DS₂VASc and HAS-BLED scales. The Amplatzer Amulet system from St. Jude Medical was used. On the first postoperative day, all patients were started on double antiplatelet therapy with 75 mg/day of acetylsalicylic acid (ASA) and 75 mg/day of clopidogrel (CLO). On the 30^th postoperative day, the efficacy of the antiplatelet therapy was assessed with impedance aggregometry using a Multiplate analyzer (Roche). Echocardiographic examinations were performed intraoperatively and on the first postoperative day; subsequently, follow-up examinations were conducted 1 and 6 months after the implantation.

Results

In all patients, proper occluder position was observed throughout the follow-up. No leakage or thrombi around the implants were found. No strokes or bleeding complications associated with the antiplatelet therapy were observed. Multiplate assessment of platelet activity was conducted in 20 out of 34 patients. The efficacy of ASA treatment was demonstrated in all patients; no response to clopidogrel treatment was observed in 5 out of 20 patients. One patient suffered from cardiac tamponade, which required the performance of full sternotomy. Local complications (hematomas of the inguinal region) were observed in 3 patients. One of the patients died for reasons unrelated to the procedure.

Conclusions

Percutaneous left atrial appendage occlusion is an effective procedure in patients with non-valvular atrial fibrillation and contraindications for chronic anticoagulation therapy. Further observation is necessary to evaluate the longterm results.

Influence of Different β-Blockers on Platelet Aggregation in Patients With Coronary Artery Disease on Dual Antiplatelet Therapy

INTRODUCTION

The use of β-blockers in the treatment of patients with coronary heart disease is associated with a decrease in the frequency of angina pectoris and mortality of patients. Due to the severity of the disease and previous cardiovascular interventions, many patients with coronary artery disease (CAD) use dual antiplatelet therapy to achieve greater inhibition of platelet aggregation. The influence of β-blockers on platelet aggregation in patients using antiplatelet therapy is not well understood.

OBJECTIVE

To examine the effect of different β-blockers on platelet aggregation in patients on dual antiplatelet therapy.

METHODOLOGY

The study included 331 patients who were treated at the Department of Cardiology, Clinical Center Kragujevac during 2011. Patients were divided into 4 groups depending on the type of β-blockers that were used (bisoprolol, nebivolol, metoprolol, and carvedilol). Platelet aggregation was measured using the multiplate analyzer and expressed through the value of adenosine diphosphate (ADP) test (to assess the effect of clopidogrel), ASPI test (to assess the effect of acetyl salicylic acid), TRAP test (to assess baseline platelet aggregation), and the ratio of ADP/TRAP and ASPI/TRAP ASPI/TRAP (ASPI - aranchidonic acid induced aggregation, TRAP - thrombin receptor activating peptide) representing the degree of inhibition of platelet aggregation compared to the basal value. In consideration were taken the representation of demographic, clinical characteristics, laboratory parameters, and cardiovascular medications between the groups.

RESULTS

Patients who used nebivolol had a significantly lower value of the ratio of ADP/TRAP (0.39 ± 0.30) compared to patients who used bisoprolol (0.48 ± 0.26; P = .038), and trend toward the lower values of ADP test (328.0 ± 197.3 vs 403.7 ± 213.2; P = .059), while there was no statistically significant difference in values of other laboratory parameters of platelet function between other groups.

CONCLUSION

Patients with CAD on dual antiplatelet therapy who used nebivolol had significantly lower levels of residual ADP-induced platelet aggregation compared to baseline than patients who used bisoprolol.

Pyrazole derivatives as inhibitors of arachidonic acid-induced platelet aggregation

Antiplatelet drugs are promising therapeutics to intervene with platelet aggregation in arterial thrombosis, most prominently in myocardial infarction and ischemic stroke. Here, we describe the synthesis and structure-activity relationships of potent inhibitors of platelet aggregation based on the 1,5-diarylpyrazol-3-carboxamide scaffold. Analogs from this series demonstrated potent anti-aggregatory activities against arachidonic acid-induced platelet aggregation, as measured by turbidimetric method of Born. 1,5-Diarylpyrazole-3-carboxamides obtained with small-basic amines (7, 8, 50, 51, 61, 62) displayed the strongest activity with IC50 values in low nanomolar range (5.7-83 nM). On the basis of their high potency in cellular environment, these straightforward pyrazole derivatives may possess potential in the design of more potent compounds for intervention with cardiovascular diseases.

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

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

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.

Stent thrombosis in real-world patients: a comparison of drug-eluting with bare metal stents

BACKGROUND

Although the introduction of drugeluting stents (DES) has been associated with an impressive reduction in target vessel revascularisation, there has been concern about the safety profile. The aim of this study was to determine the incidence of stent thrombosis in real-world patients and evaluate the contribution of drug-eluting stents.

METHODS

A prospective observational cohort study was conducted at a high-volume centre in Utrecht, the Netherlands. All patients who underwent a percutaneous coronary intervention (PCI) between 1 January and 31 December 2005 were evaluated. The patients were pretreated with aspirin and clopidogrel, which was continued for six months in bare metal stents (BMS) and 12 months in DES.

RESULTS

In 2005, 1309 patients underwent a percutaneous coronary intervention procedure with stent implantation. After a median follow-up of nine months, 1.8% (n=23) of the patients had suffered from stent thrombosis. Two cases could be attributed to incorrect use of antiplatelet agents. In 8/23 cases, a technical reason was found such as an unrecognised dissection or stent underexpansion. The timing of stent thrombosis was acute in 1/23 patients, subacute in 20/23 patients and late in 2/23 patients. In both cases of late stent thrombosis, a BMS had been used. There were no differences in stent thrombosis rates between DES and BMS (1.4 vs. 1.9%, ns.). This is remarkable since DES were used in more complex and longer lesions.

CONCLUSION

The use of DES in routine daily practice does not appear to be associated with a higher rate of stent thrombosis than BMS. (Neth Heart J 2007;15:382-6.Neth Heart J 2007;15:382-6).

Antithrombotic drug candidate ALX-0081 shows superior preclinical efficacy and safety compared with currently marketed antiplatelet drugs

Neutralizing the interaction of the platelet receptor gpIb with VWF is an attractive strategy to treat and prevent thrombotic complications. ALX-0081 is a bivalent Nanobody which specifically targets the gpIb-binding site of VWF and interacts avidly with VWF. Nanobodies are therapeutic proteins derived from naturally occurring heavy-chain-only Abs and combine a small molecular size with a high inherent stability. ALX-0081 exerts potent activity in vitro and in vivo. Perfusion experiments with blood from patients with acute coronary syndrome on standard antithrombotics demonstrated complete inhibition of platelet adhesion after addition of ALX-0081, while in the absence of ALX-0081 residual adhesion was observed. In a baboon efficacy and safety model measuring acute thrombosis and surgical bleeding, ALX-0081 showed a superior therapeutic window compared with marketed antithrombotics. Pharmacokinetic and biodistribution experiments demonstrated target-mediated clearance of ALX-0081, which leads to a self-regulating disposition behavior. In conclusion, these preclinical data demonstrate that ALX-0081 combines a high efficacy with an improved safety profile compared with currently marketed antithrombotics. ALX-0081 has entered clinical development.

The influence of bisoprolol dose on ADP-induced platelet aggregability in patients on dual antiplatelet therapy

PURPOSE

Dual antiplatelet therapy is recommended after acute coronary syndrome or after percutaneous coronary intervention with coronary stent implantation. Many of the patients on dual antiplatelet therapy receive β-blockers; some of them could have antiaggregatory effect. Bisoprolol is a highly selective adrenoceptor-blocker, which is often used in the settings of percutaneous coronary intervention or acute coronary syndrome in patients on dual antiplatelet therapy. Its antiaggregative effect has not been extensively studied. Therefore, the aim of this study is to investigate the effect of bisoprolol on ADP-induced platelet aggregation in patients on dual antiplatelet therapy.

METHODS

Platelet aggregability has been measured in 100 patients on dual antiplatelet therapy with multiplate analyzer using ADP test in blood samples anticoagulated with heparin. ADP test values have been expressed by arbitrary units/minute. In univariate and multivariate regression analyses, we have investigated the influence of bisoprolol and its dose and also different factors, such as risk factors, concomitant drugs and their dosage, laboratory findings, on ADP test values.

RESULTS

Univariate regression analysis showed significant correlation between the bisoprolol dose and the ADP test value (P=0.046, B=52.55, 95% confidence interval 0.87-104.23), which was also shown in the multivariate regression analysis (P=0.018; B=57.011; 95% confidence interval 10.455-103.567).

CONCLUSION

We have identified a positive correlation between bisoprolol dose and ADP-induced platelet aggregability in patients on dual antiplatelet therapy.

Measurement of antiplatelet inhibition during neurointerventional procedures: the effect of antithrombotic duration and loading dose

BACKGROUND/OBJECTIVE

Symptomatic thromboembolic events are the most common complications associated with aneurysm coiling, and carotid and intracranial stenting. Our objective is to assess the effect of aspirin (ASA) and clopidogrel dose and duration on platelet inhibition using a point of care assay in neurointerventional (NI) suite.

METHOD

The dose, duration, and point of care platelet function assay data for clopidogrel and aspirin therapy were prospectively collected between February 2006 and November 2007. Inadequate platelet inhibition for ASA was defined as >or=550 ASA reaction units (ARU), and for clopidogrel was defined as <or=50% inhibition of the P2Y12/ADP receptor

RESULTS

We collected data from 216 consecutive patients. Inadequate platelet inhibition was noted in 13% of patients on aspirin and 66% of patients on clopidogrel (P-value < .0001). Patients taking clopidogrel 75 mg for >or=7 days, 300 mg for 24 hours, and 600 mg same day load had a mean P2Y12/ADP inhibition of 45%, 35% (P-value = .09), and 16%, respectively (P-value = .005).

CONCLUSION

Premedication with clopidogrel, in contrast to aspirin, does not achieve adequate platelet inhibition in about two-third of the patients. Same day antiplatelet loading may be insufficient to achieve adequate platelet inhibition and should be avoided if clinically feasible.

Diabetes, vascular complications and antiplatelet therapy: open problems

Diabetes mellitus is commonly associated with both microvascular and macrovascular complications (coronary artery disease, cerebrovascular events, severe peripheral vascular disease, nephropathy and retinopathy). There is wide evidence demonstrating that platelet degranulation and synthesis of TxA2 are increased in diabetic patients. For this reason, many studies on anti-platelet therapy have been made to reduce thrombotic complication of diabetes mellitus. Some diabetic patients, although treated with ASA, have a high prevalence of recurrent thrombotic events, which may presumably be due to an "ASA resistance". Nevertheless, this drug remains the one with the greatest benefit. To optimize its function, we should try to understand the causes of "aspirin resistance", try to find the most suitable dosage, recommending patients to comply constantly with the prescription given and to avoid interactions with other drugs. "Clopidogrel resistance" is a term not clearly defined. The clinical implications of "clopidogrel resistance" are unknown. An important consideration affecting the use of aspirin in diabetic patients is its interaction with ACE-inhibitors. Another question is antiplatelet therapy in nephropathic diabetic patients. Although these patients are at high thrombotic and haemorrhagic risk, they should nevertheless be considered eligible to undergo antithrombotic therapy, taking into account the individual's haemorrhagic risk.

A comparison of clopidogrel responsiveness in patients with versus without chronic renal failure

We sought to compare the platelet responsiveness to clopidogrel between patients with chronic renal failure and those with normal renal function. We conducted a prospective, randomized, open-label, single-center trial. A total of 23 patients with normal renal function received a usual daily dose of 75 mg of clopidogrel (group I, 61 +/- 7 years). Also, 36 patients with chronic renal failure (60 +/- 5 years) were divided into 2 groups according to their daily dose of clopidogrel: a daily dose of 75 mg of clopidogrel for 30 days (group II, n = 18) or a daily dose of 150 mg (group III, n = 18). The primary efficacy variables among the study groups using the VerifyNow P2Y12 assay were the P2Y12 reaction unit value and the percentage of inhibition. A significant difference was found in the P2Y12 reaction unit value among the 3 groups (239 +/- 87 in group I, 308 +/- 70 in group II, 302 +/- 81 in group III (p = 0.013) and in the percentage of inhibition (35 +/- 20 in group I, 21 +/- 16 in group II, 23 +/- 14 in group III, p = 0.026). No significant difference was found in the P2Y12 reaction units or percentage of inhibition between groups II and III. In conclusion, platelet responsiveness to clopidogrel decreased more in patients with chronic renal failure than in those with normal renal function, and this decreased platelet responsiveness to clopidogrel was not improved by an increase in the clopidogrel dosage.

Unmet needs in oral antiplatelet therapy with ADP receptor blocking agents

Antiplatelet agents like aspirin and clopidogrel are treatment cornerstones for acute coronary syndromes (ACS). Drawbacks of dual therapy with these agents include slow onset and offset of effect and wide response variability. Clopidogrel may provide little benefit if administered too close to percutaneous coronary intervention (PCI) and increase major bleeding risk if given too close to coronary artery bypass grafting (CABG) or other surgery. It may not provide sufficient antiplatelet coverage prior to CABG if stopped too long before intervention and leave patients without antiplatelet coverage due to hyporesponsiveness. Prasugrel has made steps towards addressing these limitations by exhibiting more efficient metabolism, more rapid onset of effect, and greater and more consistent platelet inhibition than clopidogrel. The TRITON-TIMI38 trial in ACS patients undergoing PCI showed prasugrel produced greater ischemic event protection than clopidogrel but significantly increased major bleeding risk. AZD6140, the first reversible oral P2Y(12) inhibitor, provides more rapid onset of effect and greater and more consistent platelet inhibition than clopidogrel. In DISPERSE2, a phase II trial in ACS patients, AZD6140 did not increase bleeding risk, reduced bleeding risk among CABG patients, and produced numerical reductions in myocardial infarction risk. AZD6140 is being compared with clopidogrel in PLATO, a phase III trial in approximately 18000 ACS patients.

Aspirin resistance: an update

Aspirin resistance (AR) still lacks a universally accepted definition, but it may be discussed as either a laboratory phenomenon or a clinical presentation. Laboratory resistance is mainly defined as abnormal platelet response to aspirin, whereas the clinical manifestation is the failure of aspirin to prevent cardiovascular events. Although there is evidence of an association, it appears that a laboratory abnormality in platelet function is not the only risk factor for the clinical manifestation of AR. Therapies for primary and secondary prevention of AR still need to be elucidated, but there are some data to suggest that in an acute episode of aspirin failure because of AR, different therapeutic interventions need to be considered.