Platelet activation with unfractionated heparin at therapeutic concentrations and comparisons with a low-molecular-weight heparin and with a direct thrombin inhibitor

Translating proof-of-concept for platelet slip into improved antithrombotic therapeutic regimens

Platelets are central to thrombosis. Research at the intersection of biological and physical sciences provides proof-of-concept for shear rate-dependent platelet slip at vascular stenosis and near device surfaces. Platelet slip extends the observed biological "slip-bonds" to the boundary of functional gliding without contact. As a result, there is diminished engagement of the coagulation cascade by platelets at these surfaces. Comprehending platelet slip would more precisely direct antithrombotic regimens for different shear environments, including for percutaneous coronary intervention (PCI). In this brief report we promote translation of the proof-of-concept for platelet slip into improved antithrombotic regimens by: (1) reviewing new supporting basic biological science and clinical research for platelet slip; (2) hypothesizing the principal variables that affect platelet slip; (3) applying the consequent construct model in support of-and in some cases to challenge-relevant contemporary guidelines and their foundations (including for urgent, higher-risk PCI); and (4) suggesting future research pathways (both basic and clinical). Should future research demonstrate, explain and control platelet slip, then a paradigm shift for choosing and recommending antithrombotic regimens based on predicted shear rate should follow. Improved clinical outcomes with decreased complications accompanying this paradigm shift for higher-risk PCI would also result in substantive cost savings.

Mean Activated Clotting Time of Patients Receiving Intravenous Heparin and Undergoing Primary Percutaneous Coronary Intervention for ST Elevation Myocardial Infarction

Introduction The most prevalent cause of death is acute myocardial infarction (AMI). Primary percutaneous coronary intervention (PPCI) has replaced thrombolysis as the recommended therapeutic option for individuals with ST-segment elevation myocardial infarction (STEMI). However, more effective anticoagulation regimes are required for PCI due to the limitations of unfractionated heparin. Objective This study aimed to ascertain the connection between the mean activated clotting time and the risk of bleeding and infarcts in individuals receiving intravenous heparin during PPCI for STEMI. Methods This was a one-year prospective observational study carried out at the National Institute of Cardiovascular Diseases (NICVD), Karachi, Pakistan. Results The majority (70.15%) were male, with a mean age of 56.08 ± 8.92 years. Following PPCI, the average active clotting time (ACT) was 350.56 ± 39.62 seconds (range 255 to 453), compared to the pre-PPCI mean of 504.15 ± 38.98 seconds. ACT was considerably higher in female patients, smokers, and overweight patients. The mean ACT was not significantly higher in patients with hypertension (HTN) and dyslipidemia (DLD). Conclusion The ACT range in this investigation was 255 to 453 seconds, and there was no discernible relationship between ACT readings and problems related to bleeding and ischemia. To determine who is more at risk, bleeding risk models should be used and improved further before catheterization.

Feasibility and safety values of activated clotting time-guided systemic heparinization in coil embolization for unruptured intracranial aneurysms

OBJECTIVE

This study aimed to evaluate the feasibility and safety values of activated clotting time (ACT)-guided systemic heparinization in reducing periprocedural thrombosis and bleeding complications during coil embolization of unruptured intracranial aneurysms.

METHODS

A total of 228 procedures performed on 213 patients between 2016 and 2021 were included in the retrospective analysis. The target ACT was set at 250 s. Logistic regression was performed to assess predictors for the occurrence of thrombosis and bleeding. Receiver operating characteristic (ROC) analyses were employed to determine the optimal cut-off values for ACT, heparinization, and procedure time.

RESULTS

Most (85.1%) of procedures were stent-assisted embolization. The mean baseline ACT was 128.8 ± 45.7 s. The mean ACT at 20 min after the initial intravenous heparin loading of 78.2 ± 18.8 IU/kg was 185 ± 46.4 s. The mean peak ACT was 255.6 ± 63.8 s with 51.3% (117 cases) achieving the target ACT level. Peak ACT was associated with symptomatic thrombosis (OR per second, 1.008; 95% CI, 1.000-1.016; P = 0.035) (cut-off value, 275 s; area under ROC (AUROC), 0.7624). Total administered heparin dose per body weight was negatively associated with symptomatic thrombosis (OR per IU/kg, 0.972; 95% CI, 0.949-0995; P = 0.018) (cut-off value, 294 IU/kg; AUROC, 0.7426) but positively associated with significant bleeding (OR, 1.008 per IU/kg; 95% CI, 1.005-1.012; P <0 .001) (cut-off value, 242 IU/kg; AUROC, 0.7391). Procedure time was significantly associated with symptomatic thrombosis (OR per minute, 1.05; 95% CI, 1.017-1.084; P value = 0.002) (cut-off value, 158 min; area under ROC, 0.8338).

CONCLUSION

This study demonstrated that ACT-guided systemic heparinization was feasible to achieve the target ACT value and proposes probable safety thresholds to prevent periprocedural complications through reducing procedure time during coil embolization of unruptured intracranial aneurysms in the stent era.

The medicinal panorama of benzimidazoles and their scaffolds as anticancer and antithrombotic agents: A review

Nitrogen-containing heterocyclic scaffolds have become a prospective pharmacophore with therapeutic importance due to their biological similarities with natural and synthetic drugs. Among all nitrogen heterocyclic compounds, benzimidazoles and their derivatives are privileged molecules structurally akin to naturally available nucleotides, enabling them to intercommunicate with numerous biopolymers in biological systems. This reason enlightens modern researchers worldwide to assess their potential significance in the context of synthetic and biological chemistry. Therefore, it is crucial to merge the latest data with the prior documentation to apprehend the ongoing situation of the benzimidazole moiety in various therapeutic zones of research. The current work displays that the benzimidazole center is a versatile nucleus that offers the necessary data of synthetic alterations for pre-existing compounds to provide new scaffolds to resist numerous therapeutic sectors, including those associated with anticancer and antithrombosis. Due to the potential significance of benzimidazoles, this review aims to emphasize the latest innovations in synthesizing several other notable benzimidazole substrates and their significant pharmacological prospects for the future, including anticancer and antithrombosis.

Assessment of Selected Immune Parameters in Patients Undergoing Cardiac Surgery with the Use of Cardiopulmonary Bypass: Aspects of Age and Sex-A Pilot Study

The present study aimed to assess the changes in the immunological parameters of patients undergoing cardiac surgery with cardiopulmonary bypass (CPB). The serum or plasma samples of patients were assessed to determine the concentrations of IL-6, one of the major proinflammatory cytokines (seven females and six males), and selected classes of immunoglobulins (six females and seven males). The samples for ELISA (enzyme-linked immunosorbent assay) were collected from patients before the use of CPB, at 60 min of the use of CPB, and at 24 h after the surgery. After 24 h of the surgery, IL-6, IgM, and IgG concentrations were higher in the serum of female patients than in the serum of male patients. However, compared to female patients, male patients showed a significant increase in IgG3 concentration after 24 h of the surgery. Regardless of age, the levels of the analyzed classes of immunoglobulins were similar in all patients. Additionally, in both age groups, a significant increase in the serum IL-6 concentration was observed after the first postoperative day, and this increase was more pronounced in patients diagnosed to have postoperative infections. The serum IL-6 concentration can serve as a potential marker of pathogenic infections in patients undergoing cardiac surgery with CPB and is thus useful for the early diagnosis of postoperative infections.

The Evolution of Anticoagulation for Percutaneous Coronary Intervention: A 40-Year Journey

The selection of antithrombotic strategies continue to be of utmost importance during percutaneous coronary intervention (PCI) and have evolved over the past 40 years. Although the backbone of therapy during PCI continues to be a combination of oral antiplatelets and parenteral anticoagulants, a variety of different approaches have been tested over time. In particular, different choices of anticoagulation management have been tested in the stable ischemic heart disease and acute coronary syndrome setting. Evaluation of alternative regimens in the quest to balance ischemic and bleeding risk have undoubtedly improved patient care with PCI. In the current review we highlight the evolution of evidence-based therapeutic options over the past 40 years from the beginning of coronary angioplasty to contemporary PCI. We provide insight into future therapeutic options and provide a contemporary overview of anticoagulation choices for patients who require PCI on the basis of up-to-date evidence balancing ischemic and bleeding risk and according to clinical presentation.

In Vitro Antithrombotic, Hematological Toxicity, and Inhibitor Studies of Protocatechuic, Isovanillic, and p-Hydroxybenzoic Acids from Maclura Tricuspidata (Carr.) Bur

In blood coagulation, circulating platelets and coagulation factors are crucial for the primary process because thrombi are generated by fibrin clotting with fibrinogen, thrombin, FXIIIa, and platelet activation. Therefore, strategies to reduce the activity of key coagulation factors, or interfere with their functions and delay the activation of platelets can be used as important tools to suppress excessive blood clot formation and platelet hyperactivation. This study examined the antithrombotic activity and hematological toxicity of PA, IVA, and 4-HA isolated from M. tricuspidata (Carr.) Bur in several in vitro experiments and inhibitor assays. We found that PA, IVA, and 4-HA attenuated the formation of fibrin polymers/clots and degraded the blood clots. These compounds inhibited the activities of procoagulant proteases and fibrinoligase, and prolonged the coagulation time. There was a significant reduction in platelet function and ATP or serotonin levels in thrombin-activated platelets. An inhibitor study showed that PA exhibited a mixed inhibition type for thrombin, an uncompetitive inhibition type for FXa, and a non-competitive inhibition type for FXIIIa and IVA, while 4-HA exhibited an uncompetitive inhibition type for thrombin and non-competitive inhibition type for FXa and FXIIIa. These three compounds (up to 50 μg/mL) were not toxic to blood cells.

Comparison of Bivalirudin Versus Heparin for Maintenance Systemic Anticoagulation During Adult and Pediatric Extracorporeal Membrane Oxygenation

OBJECTIVES

To provide a comparative analysis of conventional heparin-versus bivalirudin-based systemic anticoagulation in adult and pediatric patients supported on extracorporeal membrane oxygenation.

DESIGN

Retrospective chart review study of adult and pediatric patients receiving extracorporeal membrane oxygenation from January 1, 2014, to October 1, 2019.

SETTING

A large, high-volume tertiary referral adult and pediatric extracorporeal membrane oxygenation center.

PATIENTS

Four hundred twenty-four individuals requiring extracorporeal membrane oxygenation support and systemically anticoagulated with either unfractionated heparin (223 adult and 65 pediatric patients) or bivalirudin (110 adult and 24 pediatric patients) were included.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Digital data abstraction was used to retrospectively collect patient details. The majority of both groups were cannulated centrally (67%), and the extracorporeal membrane oxygenation type was predominantly venoarterial (84%). The adult bivalirudin group had a greater occurrence of heparin-induced thrombocytopenia (12% vs 1%; p < 0.01) and was more likely to require postcardiotomy extracorporeal membrane oxygenation (36% vs 55%; p < 0.01). There were no statistical differences between the groups in regards to age, sex, and extracorporeal membrane oxygenation initiation location. The main finding was a reduced mortality in the adult bivalirudin group (odds ratio, 0.39; p < 0.01), whereas no difference was noted in the pediatric group. A significant reduction in the composite transfusion requirement in the first 24 hours was noted in the pediatric bivaluridin group with an odds ratio of 0.28 (p = 0.02). Groups did not differ in regard to laboratories per day, anticoagulant dose adjustments, or ischemic complications.

CONCLUSIONS

When compared with heparin-based systemic anticoagulation, bivalirudin demonstrated feasibility and safety as established by the absence of increases in identifiable adverse outcomes while manifesting substantial improvements in hospital mortality in adult patients. Further studies are necessary to corroborate these findings and further elucidate the role of bivalirudin during extracorporeal membrane oxygenation support.

The effectiveness and safety of LMWH for preventing thrombosis in patients with spinal cord injury: a meta-analysis

BACKGROUND

Unfractionated heparin (UFH) and low molecular weight heparin (LMWH) are commonly used for preventing venous thrombosis of the lower extremity in patients with traumatic spinal cord injury. Although, LMWH is the most commonly used drug, it has yet to be established whether it is more effective and safer than UFH. Further, a comparison of the effectiveness of LMWH in preventing thrombosis at different locations and different degrees of spinal cord injury has also not been clearly defined.

MATERIALS AND METHODS

Cohort studies comparing the use of LMWH and UFH in the prevention of lower limb venous thrombosis in patients with spinal cord injury were identified using PubMed. The risk of bias and clinical relevance of the included studies were assessed using forest plots. The Newcastle-Ottawa quality assessment scale was used to evaluate the quality of the included studies. The main results of the study were analyzed using Review Manager 5.3.

RESULTS

A total of five studies were included in this meta-analysis. Four studies compared the effectiveness and safety of LMWH and UFH in preventing thrombosis in patients with spinal cord injury. No significant differences were found between the therapeutic effects of the two drugs, and the summary RR was 1.33 (95% CI 0.42-4.16; P = 0.63). There was also no significant difference in the risk of bleeding between the two medications, and the aggregate RR was 0.78 (95% CI 0.55-1.12; P = 0.18). When comparing the efficacy of LMWH in preventing thrombosis in different segments and different degrees of spinal cord injury, no significant differences were found.

CONCLUSIONS

The results of this analysis show that compared with UFH, LMWH has no obvious advantages in efficacy nor risk prevention, and there is no evident difference in the prevention of thrombosis for patients with injuries at different spinal cord segments.

Complex formation of anti-VEGF-C with VEGF-C released during blood coagulation resulted in an artifact in its serum pharmacokinetics

A phage‐derived human monoclonal antibody against VEGF‐C was developed as a potential anti‐tumor therapeutic and exhibited fast clearance in preclinical species, with notably faster clearance in serum than in plasma. The purpose of this work was to understand the factors contributing to its fast clearance. In vitro incubations in animal and human blood, plasma, and serum were conducted with radiolabeled anti‐VEGF‐C to determine potential protein and cell‐based interactions with the antibody as well as any matrix‐dependent recovery dependent upon the matrix. A tissue distribution study was conducted in mice with and without heparin infusion in order to identify a tissue sink and determine whether heparin could affect antibody recovery from serum and/or plasma. Incubation of radiolabeled anti‐VEGF‐C in human and animal blood, plasma, or serum revealed that the antibody formed a complex with an endogenous protein, likely VEGF‐C. This complex was trapped within the blood clot during serum preparation from blood, but not within the blood cell pellet during plasma preparation. Low level heparin infusion in mice slowed down clot formation during serum preparation and allowed for better recovery of the radiolabeled antibody in serum. No tissue sink was found in mice. Thus, during this characterization, we determined that the blood sampling matrix greatly impacted the amount of antibody recovered in the samples, therefore, altering its derived pharmacokinetic parameters. Target biology should be considered when selecting appropriate sampling matrices for PK analysis.

Variability of Activated Clotting Time by Site of Sample Draw During Percutaneous Coronary Intervention: A Prospective Single-Center Study

The activated clotting time (ACT) assay is used to monitor and titrate anticoagulation therapy with unfractionated heparin during percutaneous coronary intervention (PCI). Observations at our institution suggested a considerable difference between ACT values drawn from varying arterial sites, prompting the current study. Patients undergoing PCI with unfractionated heparin therapy were prospectively enrolled. Simultaneous arterial blood samples were drawn from the access sheath and the coronary guide catheter. Differences between Hemochron ACT values were determined, and potential interactions with clinical variables were analyzed. Immediately postprocedure, the simultaneous mean guide and sheath ACTs were 327 ± 62 seconds and 257 ± 44 seconds, respectively, with a mean difference of 70 ± 60 seconds (P < .001). Nearly all (90%) ACT values obtained via the guide catheter were higher than the concurrent ACT drawn from the sheath. Logistic regression analysis demonstrated that lower weight-adjusted heparin doses and absence of diabetes were associated with a greater difference between the ACT values. We conclude that the ACT value is substantially greater when assessed via the guide catheter versus the access sheath. Although the biological mechanisms require further study, this difference should be considered when managing anticoagulation during PCI and when reporting ACT as part of research protocols.

Non-cardiac surgery in patients with coronary artery disease: risk evaluation and periprocedural management

Perioperative cardiovascular complications are important causes of morbidity and mortality associated with non-cardiac surgery, particularly in patients with coronary artery disease (CAD). Although preoperative cardiac risk assessment can facilitate the identification of vulnerable patients and implementation of adequate preventive measures, excessive evaluation might lead to undue resource utilization and surgical delay. Owing to conflicting data, there remains some uncertainty regarding the most beneficial perioperative strategy for patients with CAD. Antithrombotic agents are the cornerstone of secondary prevention of ischaemic events but substantially increase the risk of bleeding. Given that 5-25% of patients undergoing coronary stent implantation require non-cardiac surgery within 2 years, surgery is the most common reason for premature cessation of dual antiplatelet therapy. Perioperative management of antiplatelet therapy, which necessitates concomitant evaluation of the individual thrombotic and bleeding risks related to both clinical and procedural factors, poses a recurring dilemma in clinical practice. Current guidelines do not provide detailed recommendations on this topic, and the optimal approach in these patients is yet to be determined. This Review summarizes the current data guiding preoperative risk stratification as well as periprocedural management of patients with CAD undergoing non-cardiac surgery, including those treated with stents.

Antithrombotic therapy in patients with acute coronary syndrome complicated by cardiogenic shock or out-of-hospital cardiac arrest: a joint position paper from the European Society of Cardiology (ESC) Working Group on Thrombosis, in association with the Acute Cardiovascular Care Association (ACCA) and European Association of Percutaneous Cardiovascular Interventions (EAPCI)

Timely and effective antithrombotic therapy is critical to improving outcome, including survival, in patients with acute coronary syndrome (ACS). Achieving effective platelet inhibition and anticoagulation, with minimal risk, is particularly important in high-risk ACS patients, especially those with cardiogenic shock (CS) or those successfully resuscitated following out-of-hospital cardiac arrest (OHCA), who have a 30-50% risk of death or a recurrent ischaemic event over the subsequent 30 days. There are unique challenges to achieving effective and safe antithrombotic treatment in this cohort of patients that are not encountered in most other ACS patients. This position paper focuses on patients presenting with CS or immediately post-OHCA, of presumed ischaemic aetiology, and examines issues related to thrombosis and bleeding risk. Both the physical and pharmacological impacts of CS, namely impaired drug absorption, metabolism, altered distribution and/or excretion, associated multiorgan failure, co-morbidities and co-administered treatments such as opiates, targeted temperature management, renal replacement therapy and circulatory or left ventricular assist devices, can have major impact on the effectiveness and safety of antithrombotic drugs. Careful attention to the choice of antithrombotic agent(s), route of administration, drug-drug interactions, therapeutic drug monitoring and factors that affect drug efficacy and safety, may reduce the risk of sub- or supra-therapeutic dosing and associated adverse events. This paper provides expert opinion, based on best available evidence, and consensus statements on optimising antithrombotic therapy in these very high-risk patients, in whom minimising the risk of thrombosis and bleeding is critical to improving outcome.

Influence of Direct Thrombin Inhibitor and Low Molecular Weight Heparin on Platelet Function in Patients with Coronary Artery Disease: A Prospective Interventional Trial

INTRODUCTION

The interaction between anticoagulants and platelet function is complex. Previous publications showed mixed results regarding the role of heparins in platelet aggregation. On the other hand, the direct thrombin inhibitor (DTI) dabigatran might enhance the risk of myocardial infarction in patients with atrial fibrillation, which could be related to increased platelet aggregability.

METHODS

This was a prospective, interventional study of patients with chronic coronary artery disease (CAD) taking low-dose aspirin. The objective of the current study was to compare the effects of dabigatran versus enoxaparin on platelet aggregability. Subjects initially were on orally administered dabigatran for 5 days followed by subcutaneously administered enoxaparin after a 30-day washout period. Platelet function was assessed at baseline and after each intervention by multiple electrode aggregometry (MEA-ASPI) (primary endpoint), serum thromboxane B2 (TXB2), VerifyNow Aspirin™, and coagulation tests (secondary endpoints).

RESULTS

Compared to baseline MEA-ASPI values, dabigatran increased platelet aggregation while enoxaparin decreased platelet aggregation (+ 5 U ± 24.1 vs - 6 U ± 22.2, respectively, p = 0.012). The TXB2 assay showed the same pattern (+ 2 pg/ml for dabigatran vs - 13 pg/ml for enoxaparin, p = 0.011). None of the additional tests showed significant differences between the groups. Individually, compared to baseline TXB2 results, enoxaparin significantly decreased platelet activation [33 (16.5-95) pg/mL vs 20 (10-52) pg/mL, respectively, p = 0.026], but no significant differences were observed with dabigatran.

CONCLUSIONS

DTI and anti-Xa drugs exert opposite effects on platelet function. A significant decrease in platelet activation through COX1 (also known as prostaglandin G/H synthase 1) was observed with enoxaparin, but no significant differences in platelet function were observed with dabigatran.

TRIAL REGISTRATION

ClinicalTrials.gov identifier, NCT02389582.

Association of Anti-Factor Xa-Guided Dosing of Enoxaparin With Venous Thromboembolism After Trauma

Importance

The efficacy of anti-factor Xa (anti-Xa)-guided dosing of thromboprophylaxis after trauma remains controversial.

Objective

To assess whether dosing of enoxaparin sodium based on peak anti-Xa levels is associated with the venous thromboembolism (VTE) rate after trauma.

Design, Setting, and Participants

Retrospective review of 950 consecutive adults admitted to a single level I trauma intensive care unit for more than 48 hours from December 1, 2014, through March 31, 2017. Within 24 hours of admission, these trauma patients were screened with the Greenfield Risk Assessment Profile (RAP) (possible score range, 0-46). Patients younger than 18 years and those with VTE on admission were excluded, resulting in a study population of 792 patients.

Exposures

The control group received fixed doses of either heparin sodium, 5000 U 3 times a day, or enoxaparin sodium, 30 mg twice a day. The adjustment cohort initially received enoxaparin sodium, 30 mg twice a day. A peak anti-Xa level was drawn 4 hours after the third dose. If the anti-Xa level was 0.2 IU/mL or higher, no adjustment was made. If the anti-Xa level was less than 0.2 IU/mL, each dose was increased by 10 mg. The process was repeated up to a maximum dose of 60 mg twice a day.

Main Outcomes and Measures

Rates of VTE were measured. Venous duplex ultrasonography and computed tomographic angiography were used for diagnosis.

Results

The study population comprised 792 patients with a mean (SD) age of 46 (19) years and was composed of 598 men (75.5%). The control group comprised 570 patients, was older, and had a longer time to thromboprophylaxis initiation. The adjustment group consisted of 222 patients, was more severely injured, and had a longer hospital length of stay. The mean (SD) RAP scores were 9 (4) for the control group and 9 (5) for the adjustment group (P = .28). The VTE rates were similar for both groups (34 patients [6.0%] vs 15 [6.8%]; P = .68). Prophylactic anti-Xa levels were reached in 119 patients (53.6%) in the adjustment group. No difference in VTE rates was observed between those who became prophylactic and those who did not (7 patients [5.9%] vs 8 [7.8%]; P = .58). To control for confounders, 132 patients receiving standard fixed-dose enoxaparin were propensity matched to 84 patients receiving dose-adjusted enoxaparin. The VTE rates remained similar between the control and adjustment groups (3 patients [2.3%] vs 3 [3.6%]; P = .57).

Conclusions and Relevance

Rates of VTE were not reduced with anti-Xa-guided dosing, and almost half of the patients never reached prophylactic anti-Xa levels; achieving those levels did not decrease VTE rates. Thus, other targets, such as platelets, may be necessary to optimize thromboprophylaxis after trauma.

Platelet Function During Extracorporeal Membrane Oxygenation in Adult Patients

Objective: Hemorrhagic and thromboembolic complications are common during support with extracorporeal membrane oxygenation (ECMO). As platelets play a pivotal role in hemostasis, we aimed to clarify how ECMO support affects platelet function.

Methods: We included 33 adult patients undergoing ECMO support at a tertiary ECMO referral center at Aarhus University Hospital, Denmark. Blood samples were collected on the first morning following ECMO initiation, and subsequently every morning until the 7th (±1) day. Platelet aggregation was evaluated by whole blood impedance aggregometry (Multiplate^® Analyzer) using adenosine diphosphate (ADPtest), arachidonic acid (ASPItest), and thrombin-receptor-agonist-peptide-6 (TRAPtest) as agonists. A new model was applied, taking platelet count into consideration in interpretation of impedance aggregometry analyses. On the 1st and 3rd day, platelet activation was assessed by flow cytometry (Navios) using collagen-related peptide, ADP, TRAP, and arachidonic acid as agonists.

Results: Blood samples from all 33 patients were analyzed on day 1 of ECMO support; 24 patients were still receiving ECMO and analyzed on day 3; 12 patients were analyzed on day 7 (±1). After ECMO initiation, platelet counts decreased significantly (p < 0.002) and remained low during ECMO support. ECMO patients demonstrated significantly reduced platelet aggregation on day 1 compared with healthy controls (all p < 0.001). However, when taking platelet count into consideration, platelet aggregation relative to platelet count did not differ from healthy controls. Flow cytometry analyses demonstrated impaired platelet activation in ECMO patients on day 1 compared with healthy controls (all p < 0.03). No substantial difference was found in platelet activation from day 1 to day 3 on ECMO support.

Conclusions: Employing impedance aggregometry and flow cytometry, we found both impaired platelet aggregation and decreased platelet activation on day 1 of ECMO support compared with healthy controls. However, platelet aggregation was not impaired, when interpreted relative to the low platelet counts. Furthermore, levels of bound fibrinogen, on the surface of activated platelets in ECMO patients, were higher than in healthy controls. Together, these findings suggestively oppose that platelets are universally impaired during ECMO support. No marked difference in activation from day 1 to day 3 was seen during ECMO support.

Zwitterionic poly-carboxybetaine coating reduces artificial lung thrombosis in sheep and rabbits

Current artificial lungs fail in 1-4 weeks due to surface-induced thrombosis. Biomaterial coatings may be applied to anticoagulate artificial surfaces, but none have shown marked long-term effectiveness. Poly-carboxybetaine (pCB) coatings have shown promising results in reducing protein and platelet-fouling in vitro. However, in vivo hemocompatibility remains to be investigated. Thus, three different pCB-grafting approaches to artificial lung surfaces were first investigated: 1) graft-to approach using 3,4-dihydroxyphenylalanine (DOPA) conjugated with pCB (DOPA-pCB); 2) graft-from approach using the Activators ReGenerated by Electron Transfer method of atom transfer radical polymerization (ARGET-ATRP); and 3) graft-to approach using pCB randomly copolymerized with hydrophobic moieties. One device coated with each of these methods and one uncoated device were attached in parallel within a veno-venous sheep extracorporeal circuit with no continuous anticoagulation (N = 5 circuits). The DOPA-pCB approach showed the least increase in blood flow resistance and the lowest incidence of device failure over 36-hours. Next, we further investigated the impact of tip-to-tip DOPA-pCB coating in a 4-hour rabbit study with veno-venous micro-artificial lung circuit at a higher activated clotting time of 220-300 s (N ≥ 5). Here, DOPA-pCB reduced fibrin formation (p = 0.06) and gross thrombus formation by 59% (p < 0.05). Therefore, DOPA-pCB is a promising material for improving the anticoagulation of artificial lungs. STATEMENT OF SIGNIFICANCE: Chronic lung diseases lead to 168,000 deaths each year in America, but only 2300 lung transplantations happen each year. Hollow fiber membrane oxygenators are clinically used as artificial lungs to provide respiratory support for patients, but their long-term viability is hindered by surface-induced clot formation that leads to premature device failure. Among different coatings investigated for blood-contacting applications, poly-carboxybetaine (pCB) coatings have shown remarkable reduction in protein adsorption in vitro. However, their efficacy in vivo remains unclear. This is the first work that investigates various pCB-coating methods on artificial lung surfaces and their biocompatibility in sheep and rabbit studies. This work highlights the promise of applying pCB coatings on artificial lungs to extend its durability and enable long-term respiratory support for lung disease patients.

Drug-induced activation of integrin alpha IIb beta 3 leads to minor localized structural changes

Integrins are transmembrane proteins involved in hemostasis, wound healing, immunity and cancer. In response to intracellular signals and ligand binding, integrins adopt different conformations: the bent (resting) form; the intermediate extended form; and the ligand-occupied active form. An integrin undergoing such conformational dynamics is the heterodimeric platelet receptor αIIbβ3. Although the dramatic rearrangement of the overall structure of αIIbβ3 during the activation process is potentially related to changes in the protein secondary structure, this has not been investigated so far in a membrane environment. Here we examine the Mn2+- and drug-induced activation of αIIbβ3 and the impact on the structure of this protein reconstituted into liposomes. By quartz crystal microbalance with dissipation monitoring and activation assays we show that Mn2+ induces binding of the conformation-specific antibody PAC-1, which only recognizes the extended, active integrin. Circular dichroism spectroscopy reveals, however, that Mn2+-treatment does not induce major secondary structural changes of αIIbβ3. Similarly, we found that treatment with clinically relevant drugs (e.g. quinine) led to the activation of αIIbβ3 without significant changes in protein secondary structure. Molecular dynamics simulation studies revealed minor local changes in the beta-sheet probability of several extracellular domains of the integrin. Our experimental setup represents a new approach to study transmembrane proteins, especially integrins, in a membrane environment and opens a new way for testing drug binding to integrins under clinically relevant conditions.

American College of Veterinary Emergency and Critical Care (ACVECC) Consensus on the Rational Use of Antithrombotics in Veterinary Critical Care (CURATIVE) guidelines: Small animal

OBJECTIVES

To systematically review available evidence and establish guidelines related to the risk of developing thrombosis and the management of small animals with antithrombotics.

DESIGN

Standardized, systematic evaluation of the literature (identified by searching Medline via PubMed and CAB abstracts) was carried out in 5 domains (Defining populations at risk; Defining rational therapeutic use; Defining evidence-based protocols; Refining and monitoring antithrombotic therapies; and Discontinuing antithrombotic therapies). Evidence evaluation was carried out using Population, Intervention, Comparison, Outcome generated within each domain questions to address specific aims. This was followed by categorization of relevant articles according to level of evidence and quality (Good, Fair, or Poor). Synthesis of these data led to the development of a series of statements. Consensus on the final guidelines was achieved via Delphi-style surveys. Draft recommendations were presented at 2 international veterinary conferences and made available for community assessment, review, and comment prior to final revisions and publication.

SETTINGS

Academic and referral veterinary medical centers.

RESULTS

Over 500 studies were reviewed in detail. Worksheets from all 5 domains generated 59 statements with 83 guideline recommendations that were refined during 3 rounds of Delphi surveys. A high degree of consensus was reached across all guideline recommendations.

CONCLUSIONS

Overall, systematic evidence evaluations yielded more than 80 recommendations for the treatment of small animals with or at risk of developing thrombosis. Numerous significant knowledge gaps were highlighted by the evidence reviews undertaken, indicating the need for substantial additional research in this field.

Consensus on the Rational Use of Antithrombotics in Veterinary Critical Care (CURATIVE): Domain 5-Discontinuation of anticoagulant therapy in small animals

OBJECTIVES

To systematically evaluate the evidence supporting the timing and mechanisms of permanent or temporary discontinuation of antiplatelet or anticoagulant medications in small animals DESIGN: Standardized, systematic evaluation of the literature, categorization of relevant articles according to level of evidence and quality (poor, fair, or good), and development of consensus on conclusions via a Delphi-style survey for application of the concepts to clinical practice.

SETTINGS

Academic and referral veterinary medical centers.

RESULTS

Databases searched included Medline via PubMed and CAB abstracts. Two specific courses of inquiry were pursued, one focused on appropriate approaches to use for small animal patients receiving antiplatelet or anticoagulant drugs and requiring temporary discontinuation of this therapy for the purposes of invasive procedures (eg, surgery), and the other aimed at decision-making for the complete discontinuation of anticoagulant medications. In addition, the most appropriate methodology for discontinuation of heparins was addressed.

CONCLUSIONS

To better define specific patient groups, a risk stratification characterization was developed. It is recommended to continue anticoagulant therapy through invasive procedures in patients at high risk for thrombosis that are receiving anticoagulant therapy, while consideration for discontinuation in patients with low to moderate risk of thrombosis is reasonable. In patients with thrombosis in whom the underlying cause for thrombosis has resolved, indefinite treatment with anticoagulant medication is not recommended. If the underlying cause is unknown or untreatable, anticoagulant medication should be continued indefinitely. Unfractionated heparin therapy should be slowly tapered rather than discontinued abruptly.

Bivalirudin during percutaneous coronary intervention in acute coronary syndromes

INTRODUCTION

Anticoagulant therapy is critical to prevent ischemic recurrences and complications in acute coronary syndrome (ACS) patients undergoing percutaneous coronary intervention (PCI). Unfractionated heparin (UFH), an injectable anticoagulant has several limitations: lack of predictability of its biological efficacy, platelets activation, heparin-induced thrombopenia and bleedings. Bivalirudin, a synthetic direct thrombin inhibitor has biological properties that promised better clinical outcome in ACS patients undergoing PCI.

AREAS COVERED

The present review aimed to summarize two decades of randomized clinical trials that compared bivalirudin to UFH in ACS patients treated with PCI. Early trials highlighted a reduction of bleedings with bivalirudin compared to UFH in combination with glycoprotein inhibitors (GPI). Recent studies questioned this reduction given that GPI are less and less used during PCI. Further, trials raised concerns about the risk of stent thrombosis in patients treated with bivalirudin. In light of this data, bivalirudin has been downgraded in international guidelines and appears as a second line anticoagulant agent after UFH.

EXPERT OPINION

The highly questioned reduction of bleedings under bivalirudin and the potential risk of stent thrombosis are unwarranted. Based on clinical trials, UFH has no equivalent in terms of anticoagulation in ACS patients undergoing PCI.

Pharmacodynamic Effects of a 6-Hour Regimen of Enoxaparin in Patients Undergoing Primary Percutaneous Coronary Intervention (PENNY PCI Study)

Delayed onset of action of oral P2Y ₁₂ inhibitors in ST-elevation myocardial infarction (STEMI) patients may increase the risk of acute stent thrombosis. Available parenteral anti-thrombotic strategies, to deal with this issue, are limited by added cost and increased risk of bleeding. We investigated the pharmacodynamic effects of a novel regimen of enoxaparin in STEMI patients undergoing primary percutaneous coronary intervention (PPCI). Twenty patients were recruited to receive 0.75 mg/kg bolus of enoxaparin (pre-PPCI) followed by infusion of enoxaparin 0.75 mg/kg/6 h. At four time points (pre-anti-coagulation, end of PPCI, 2–3 hours into infusion and at the end of infusion), anti-Xa levels were determined using chromogenic assays, fibrin clots were assessed by turbidimetric analysis and platelet P2Y ₁₂ inhibition was determined by VerifyNow P2Y12 assay. Clinical outcomes were determined 14 hours after enoxaparin initiation. Nineteen of 20 patients completed the enoxaparin regimen; one patient, who developed no-reflow phenomenon, was switched to tirofiban after the enoxaparin bolus. All received ticagrelor 180 mg before angiography. Mean (± standard error of the mean) anti-Xa levels were sustained during enoxaparin infusion (1.17 ± 0.06 IU/mL at the end of PPCI and 1.003 ± 0.06 IU/mL at 6 hours), resulting in prolonged fibrin clot lag time and increased lysis potential. Onset of platelet P2Y ₁₂ inhibition was delayed in opiate-treated patients. No patients had thrombotic or bleeding complications. In conclusion, enoxaparin 0.75 mg/kg bolus followed by 0.75 mg/kg/6 h provides sustained anti-Xa levels in PPCI patients. This may protect from acute stent thrombosis in opiate-treated PPCI patients who frequently have delayed onset of oral P2Y ₁₂ inhibition.

Low-molecular-weight heparin venous thromboprophylaxis in critically ill patients with renal dysfunction: A subgroup analysis of the PROTECT trial

Introduction

There is concern about excessive bleeding when low-molecular-weight heparins (LMWHs) are used for venous thromboembolism (VTE) prophylaxis in renal dysfunction. Our objective was to evaluate whether LMWH VTE prophylaxis was safe and effective in critically ill patients with renal dysfunction by conducting a subgroup analysis of PROTECT, a randomized blinded trial.

Methods

We studied intensive care unit (ICU) patients with pre-ICU dialysis-dependent end-stage renal disease (ESRD; pre-specified subgroup; n = 118), or severe renal dysfunction at ICU admission (defined as ESRD or non-dialysis dependent with creatinine clearance [CrCl] <30 ml/min; post hoc subgroup; n = 590). We compared dalteparin, 5000 IU daily, with unfractionated heparin (UFH), 5000 IU twice daily, and considered outcomes of proximal leg deep vein thrombosis (DVT); pulmonary embolism (PE); any VTE; and major bleeding. Adjusted hazard ratios [HR] were calculated using Cox regression.

Results

In patients with ESRD, there was no significant difference in DVT (8.3% vs. 5.2%, p = 0.76), any VTE (10.0% vs. 6.9%; p = 0.39) or major bleeding (5.0% vs. 8.6%; p = 0.32) between UFH and dalteparin. In patients with severe renal dysfunction, there was no significant difference in any VTE (10.0% vs. 6.4%; p = 0.07) or major bleeding (8.9% vs. 11.0%; p = 0.66) but an increase in DVT with dalteparin (7.6% vs. 3.7%; p = 0.04). Interaction p-values for comparisons of HRs (ESRD versus not) were non-significant.

Conclusions

In critically ill patients with ESRD, or severe renal dysfunction, there was no significant difference in any VTE or major bleeding between UFH and dalteparin. Patients with severe renal dysfunction who received dalteparin had more proximal DVTs than those on UFH; this finding did not hold in patients with ESRD alone.

Is It Reliable to Take the Molecular Docking Top Scoring Position as the Best Solution without Considering Available Structural Data?

Molecular docking is the most frequently used computational method for studying the interactions between organic molecules and biological macromolecules. In this context, docking allows predicting the preferred pose of a ligand inside a receptor binding site. However, the selection of the “best” solution is not a trivial task, despite the widely accepted selection criterion that the best pose corresponds to the best energy score. Here, several rigid-target docking methods were evaluated on the same dataset with respect to their ability to reproduce crystallographic binding orientations, to test if the best energy score is a reliable criterion for selecting the best solution. For this, two experiments were performed: (A) to reconstruct the ligand-receptor complex by performing docking of the ligand in its own crystal structure receptor (defined as self-docking), and (B) to reconstruct the ligand-receptor complex by performing docking of the ligand in a crystal structure receptor that contains other ligand (defined as cross-docking). Root-mean square deviation (RMSD) was used to evaluate how different the obtained docking orientation is from the corresponding co-crystallized pose of the same ligand molecule. We found that docking score function is capable of predicting crystallographic binding orientations, but the best ranked solution according to the docking energy is not always the pose that reproduces the experimental binding orientation. This happened when self-docking was achieved, but it was critical in cross-docking. Taking into account that docking is typically used with predictive purposes, during cross-docking experiments, our results indicate that the best energy score is not a reliable criterion to select the best solution in common docking applications. It is strongly recommended to choose the best docking solution according to the scoring function along with additional structural criteria described for analogue ligands to assure the selection of a correct docking solution.

The mechanisms of sulfated polysaccharide drug of propylene glycol alginate sodium sulfate (PSS) on bleeding side effect

Propylene glycol alginate sodium sulfate (PSS), a sulfated polysaccharide derivative, has been used as a heparinoid drug to prevent and treat hyperlipidemia and ischemic cardio-cerebrovascular diseases in China for 30 years. But its bleeding risk should not be overlooked. Here we clarified the reasons and mechanism leading to bleeding side effect of PSS. It was found that PSS fractions with low mannuronic acid (M)/guluronic acid (G) ratio and high molecular weight (Mw) can excessively extend activated partial thromboplastin time (APTT) and thrombin time (TT), over-inhibit the thrombin (FIIa) activity mediated by anti-thrombin III (ATIII) to induce bleeding risk. In addition, the fraction of low M/G ratio can suppress platelet aggregation mediated by adenosine diphosphate (ADP) and induce platelet reduction by improving platelet antibody (PA)-IgA/G in serum and by inhibiting or damaging the bone marrow hematopoietic function. And the fraction of high Mw can restrain the reticulated platelet (RP) production, then reduce mean platelet volume (MPV) and platelet-large cell counts or ratio, and finally decrease platelet amount by inhibiting or damaging the bone marrow hematopoietic function. In brief, PSS fractions with low M/G ratio and high Mw were the main reasons to bring about bleeding by excessively suppressing coagulant factors activities and weakening platelet function. Our results suggested that it is very necessary to control the M/G ratio and the range of Mw of PSS to guarantee its safety and effectiveness in clinical.

Relation of antifactor-Xa peak levels and venous thromboembolism after trauma

BACKGROUND

No previous studies have established the optimal antifactor Xa (anti-Xa) level to guide thromboprophylaxis (TPX) dosing with enoxaparin in trauma patients. We hypothesize that achieving 0.2-0.4 IU/mL anti-Xa will decrease venous thromboembolism (VTE) rates after trauma.

METHODS

This was a retrospective review of 194 intensive care unit patients sustaining blunt or penetrating trauma from January 2015 to March 2017. All received initial enoxaparin (30 mg BID subcutaneous) and mechanical devices for TPX. Peak anti-Xa levels were drawn after each third dose. The enoxaparin dose was adjusted up to a maximum of 60 mg BID subcutaneous until a peak level of 0.2-0.4 IU/mL was achieved. Data are expressed as mean ± SD if parametric or median (IQR) if not.

RESULTS

The Greenfield Risk Assessment Profile score was 9 ± 4, Injury Severity Score 23 ± 14, and hospital length of stay 19 (11-38) days. The overall VTE rate was 7.2% (n = 14), with 10 deep venous thromboses (DVT) and 5 pulmonary emboli (PE). One patient had both a DVT and PE. The median time to VTE diagnosis was 14 (7-17) days. In those diagnosed with a VTE, 50.0% (n = 7) never reached 0.2-0.4 IU/mL anti-Xa and 42.8% (n = 6) were diagnosed with a VTE after achieving these levels. Prophylactic levels were achieved initially in 64 (33.0%) patients, and achieved later in 38 (19.6%) additional patients, giving an overall prophylactic rate of 52.6% (n = 102). There were no differences in VTE (6.9% vs. 7.6%, p = 0.841), DVT (3.9% vs. 6.5%, p = 0.413), or PE (3.9% vs. 1.1%, p = 0.213) rates between those who became prophylactic and those who did not.

CONCLUSIONS

There was no difference in VTE incidence between those achieving anti-Xa peak levels of 0.2-0.4 IU/mL and those who did not. Furthermore, these levels were never achieved in some trauma patients despite repeated dosing over a >10-day period.

LEVEL OF EVIDENCE

Therapeutic study, level IV.

Outcomes in elderly and young patients with ST-segment elevation myocardial infarction undergoing primary percutaneous coronary intervention with bivalirudin versus heparin: Pooled analysis from the EUROMAX and HORIZONS-AMI trials

BACKGROUND

Since older age is a strong predictor of not only bleeding but also of ischemic events, understanding the risk:benefit profile of bivalirudin in the elderly undergoing primary percutaneous coronary intervention (pPCI) for ST-segment elevation (STEMI) is important. For this, we aim to compare elderly with young patients, who all underwent pPCI for STEMI and randomly received either bivalirudin or heparin.

METHODS

We performed a patient-level pooled analysis (n=5800) of two large randomized trials. A total of 2149 (37.1%) elderly patients (>65 years of age) with STEMI were enrolled and randomly assigned to either bivalirudin or heparin with or without a GPI (control group) before pPCI. Clinical outcomes at 30 days were analyzed.

RESULTS

In elderly patients, bivalirudin significantly reduced non-CABG major bleeding (7.1% vs 10.4%; P<.01), subacute ST (0.4% vs 1.5%; P<.01), and net adverse clinical events (NACE; composite of all-cause mortality, reinfarction, IDR, stroke or protocol-defined non-CABG major bleeding [13.7% vs 17.2%; P=.03]) with comparable rates of stroke, MI, acute ST, or all-cause death, when compared with heparin with or without GPI.

CONCLUSIONS

In a large group of elderly patients enrolled in the EUROMAX and HORIZONS-AMI trials, bivalirudin was associated with lower 30-day rates of non-CABG major bleeding, subacute ST and NACE, with similar 30-day rates of acute ST and mortality.

Impact of Test Conditions on ADP-Induced Platelet Function Results With the Multiplate Assay: Is Further Standardization Required?

BACKGROUND

Platelet function testing was suggested to help tailor P2Y₁₂-inhibitor therapy; however, the lack of proper standardization is still a limitation.

METHODS

In a prospective study, we enrolled clopidogrel-treated and P2Y₁₂-inhibitor naive patients to investigate the influence of (1) time from blood collection, (2) stability of the stored Adenosine diphosphate (ADP) reagent, and (3) the use of enoxaparin on results of the Multiplate assay. Measurements were performed from samples kept for 0, 30, 60, 120, and 240 minutes at room temperature before processing. To determine the impact of the reagent stability, freshly thawed ADP was compared with ADP kept for 3 to 5 or 8 to 13 days at 2°C to 8°C. Finally, samples containing enoxaparin at therapeutic or prophylactic doses were compared with enoxaparin-free blood.

RESULTS

A total of 180 measurements were performed. ADP-stimulated platelet reactivity values decreased significantly over time (67 ± 40 U to 68 ± 37 U to 58 ± 37 U to 45 ± 33 U to 35 ± 33 U; P < .0001). Consequently, a dramatic reduction was observed in the proportion of patients with high platelet reactivity ( P < .0001). A significant drop in platelet reactivity was observed with ADP stored for 8 to 13 days as compared to freshly thawed ADP ( P = .011). Enoxaparin triggered a slight, concentration-dependent increase in platelet reactivity ( P < .05).

CONCLUSION

Test conditions may have profound impacts on the obtained results with the Multiplate assay. Our findings highlight the large influence of the time from sample collection until testing, suggesting that measurements should be performed within an hour of blood collection.

Perioperative management and monitoring of antiplatelet agents: a focused review on aspirin and P2Y12 inhibitors

Platelets play pivotal roles in hemostasis as well as pathological arterial thrombosis. The combination of aspirin and a P2Y₁₂ inhibitor has become the mainstay therapy in the ageing population with cardiovascular conditions, particularly during and after percutaneous coronary intervention. A number of novel P2Y₁₂ inhibitors has become available in the recent years, and they markedly vary in pharmacokinetic and pharmacodynamic properties. Perioperative physicians today face a challenge of preventing hemorrhage due to platelet inhibitors, while minimizing thrombotic risks. There are several point-of-care platelet function tests available in the peri-procedural assessment of residual platelet aggregation. However, these platelet function tests are not standardized in terms of sample processing, agonist type and potency as well as methods of detecting platelet activity. Understanding the differences in pharmacological properties of antiplatelet agents, principles of platelet function tests, and pertinent hemostatic strategies may be useful to anesthesiologists and intensivists who manage perioperative issues associated with antiplatelet agents. The objectives of this review are: 1) to discuss clinical data on aspirin and P2Y₁₂ inhibitors relating to perioperative bleeding, 2) to outline different features of point-of-care platelet function tests, and 3) to discuss therapeutic options for the prevention and treatment of bleeding associated with antiplatelet agents.

Plasma protein profiling in patients undergoing coronary artery bypass grafting surgery and clinical significance

This study was designed to identify the protein profiling in patients with triple vessel coronary artery disease (CAD) undergoing CABG, in order to detect CAD-related differential proteins in these patients. CABG patients with triple vessel disease with/without left main stenosis (n =160) were compared to normal coronary angiographic subjects (n =160). Plasma samples of 20 males and 20 females in each group were analyzed with iTRAQ technique. ELISA test was used to test the chosen proteins from iTRAQ results in plasma samples from a new cohort of the CABG group (n=120, male/femal=61/59) and control (n =120, male/female=60/60). iTRAQ detected 544 proteins with 35 up-regulated and 41 down-regulated (change fold > 1.2 or < 0.83, p < 0.05). Three proteins including platelet factor 4 (PF4), coagulation factor XIII B chain (F13B), and secreted frizzled-related protein 1 (sFRP1) were selected for validation by using ELISA that demonstrated significant up-regulation of PF4 and sFRP1 (p < 0.05). There was a positive correlation between these proteins and CAD (p < 0.05) and myocardial infarction history (p < 0.05). Thus, we for the first time have found 76 proteins differentially expressed in plasma of CABG patients. The thrombotic disease/inflammation progress-related protein PF4 and sFRP1, a member of the Wnt/fz signal-transduction pathway and related to myocardial repair, are significantly up-regulated in triple-vessel disease with/without left main stenosis. PF4 may be developed as a biomarker for the diagnosis of the severity of CAD requiring CABG procedure.

Bleeding Following Deep Hypothermia and Circulatory Arrest in Children

Deep hypothermic circulatory arrest (DHCA) is a technique of extracorporeal circulation commonly used in children with complex congenital heart defects undergoing surgical repairs. The use of profound cooling (20°C) and complete cessation of circulation allow adequate exposure and correction of these complex lesions, with enhanced cerebral protection. However, the profound physiologic state of DHCA results in significant derangement of the coagulation system and a high incidence of postoperative bleeding. This review examines the impact of DHCA on bleeding and transfusion requirements in children and the pathophysiology of DHCA-induced platelet dysfunction. It also focuses on possible pharmacologic interventions to decrease bleeding following DHCA in children.

Approach to the Assessment of Platelet Function: Comparison between Optical-based Platelet-rich Plasma and Impedance-based Whole Blood Platelet Aggregation Methods

Platelet aggregation studies play an important role in the assessment of hereditary and acquired platelet function defects. The first aggregation test introduced into laboratory practice used platelet-rich plasma (PRP) where aggregation was detected by an optical method. The assessment of platelet function using whole blood (WB) aggregation by an impedance method followed up nearly 20 years later. The WB impedance aggregation assay appears to be superior to the optical method because it 1) evaluates platelets in a physiologic milieu in the presence of red and white blood cells, which are known to modulate platelet function; 2) is faster; 3) has higher sensitivity; and 4) does not require centrifugation, thus avoiding injury to platelets and loss of giant thrombocytes. These two assays were compared. Clearly, the WB impedance aggregation methodology has many advantages over the optical PRP assay for the assessment of the hyperactive platelet syndrome and the effects of anti-platelet drugs.

Potential mechanism of acute stent thrombosis with bivalirudin following percutaneous coronary intervention in acute coronary syndromes

BACKGROUND

Clinical trials have demonstrated an excess of acute stent thrombosis (AST) in acute coronary syndromes patients (ACS) undergoing percutaneous coronary intervention (PCI) with bivalirudin compared to heparin. We aimed to investigate the potential mechanisms responsible for thrombus formation under bivalirudin.

METHODS

We compared heparin and bivalirudin during PCI for ACS in a prospective monocentre randomized study. Twenty patients were included after coronary angiography and received a loading dose (LD) of 180mg of ticagrelor at the time of PCI. They were randomly assigned to heparin (70UI/kg) intra-venous (IV) bolus or bivalirudin IV bolus of 0.75mg/kg followed by an infusion of 1.75mg/kg/h until the end of the PCI. The VASP index and thrombin generation test were used to assess the course of platelet reactivity (PR) and thrombin generation.

RESULTS

Thrombin generation and PR were identical in both groups at baseline. There was no difference in the course of PR following the LD over time. An optimal PR inhibition was reached 4h after the LD of ticagrelor. Heparin and bivalirudin infusion effectively inhibited thrombin generation during PCI. However, 4h after the end of bivalirudin infusion, thrombin generation had returned to its baseline value whereas in the heparin group it remained significantly inhibited compared to baseline and to the bivalirudin group 4h after the end of the infusion (p<0.01 and p<0.02 respectively).

CONCLUSIONS

The present study suggests that the short half-life of bivalirudin and the quick restoration of thrombin activity at a time when optimal PR is not reached may be responsible for acute stent thrombosis. Clinicaltrial.gov: NCT02428725.

Peripheral Atherectomy: Applications and Techniques

Peripheral atherectomy is a class of procedures that is rapidly increasing in volume. Multiple classes of devices exist, and newer variants are added to the market annually. The devices see wide application for de novo lesions, in-stent restenosis, and adjunctive therapy for drug-coated balloons. The body of evidence supporting atherectomy is less robust than for many other peripheral therapies. The frequency and severity of complications from atherectomy can be significant compared with angioplasty and stenting, and familiarity with preventative and bailout techniques is essential for the interventionalist.

Unfractionated Heparin during the Interruption of Antiplatelet Therapy for Non-cardiac Surgery after Drug-eluting Stent Implantation

OBJECTIVE

Heparin is not recommended to be administered during the interruption of antiplatelet therapy for non-cardiac surgery. However, there are insufficient data to determine the value. The purpose of the present study was to evaluate the clinical results of the administration of unfractionated heparin during the interruption of antiplatelet therapy in non-cardiac surgery patients who had previously undergone drug-eluting stent (DES) implantation.

METHODS

We retrospectively identified 210 elective non-cardiac surgical procedures that were performed with the administration of unfractionated heparin during interruption of all antiplatelet therapies in patients who had previously undergone DES implantation. Heparin was administered during the perioperative period in accordance with the local practice guideline at out institution. We examined the clinical outcomes within 30 days of surgery.

RESULTS

The mean number of implanted DESs was 2.1±1.3. No major adverse cardiac events (including cardiac death, definite stent thrombosis, and non-fatal myocardial infarction) occurred in any of the 210 cases within 30 days of surgery. Four of the 210 cases (1.9%) required reoperation for bleeding within 30 days of surgery.

CONCLUSION

Our data showed the potential for the perioperative management with unfractionated heparin administration in Japanese patients who had previously undergone DES implantation who required non-cardiac surgery with the interruption of all antiplatelet therapies.

Analysis of the influence of antithrombin on microvascular thrombosis: anti-inflammation is crucial for anticoagulation

Purpose

Microvascular thrombosis during septic conditions is of essential clinical relevance, but the pathomechanisms are not yet completely understood. The purpose of this study was to study the distinguished differentiation of the interactions of inflammation and coagulation using antithrombin (AT), a mediator of anticoagulation and anti-inflammation.

Methods

Using a thrombosis model in a cremaster muscle preparation of male C57Bl/6J mice (n = 83), we quantitatively assessed microvascular thrombus formation by using intravital fluorescence microscopy. Experimental groups consisted of animals treated with AT or with tryptophan⁴⁹-blocked AT (TrypAT), which exerts only anticoagulant but no anti-inflammatory effects. To further see whether endothelial glycosaminoglycan (GAG) binding with consecutive prostacyclin (PGI₂) release is mandatory for the anticoagulant process of AT, animals were administered heparin or indomethacin either alone or in combination with AT.

Results

The antithrombotic capacity of AT significantly differs in the experimental groups in which anti-inflammation was antagonized. This is given by the significantly prolonged occlusion times (p < 0.05) and higher patency rates in case of application of AT alone; while all other groups in which the anti-inflammatory action of AT was blocked by TrypAT, heparin or indomethacin revealed thrombus kinetics comparable to controls.

Conclusions

The anti-inflammatory influence of AT is essentially linked to its anticoagulant effect in the microvascular system. Those specifications of the active profile of AT characterize the intimate interactions of the anticoagulant and anti-inflammatory pathways. This might be of relevance for AT as a therapeutic agent in critically diseased patients and the clinical understanding of microvascular thrombosis.

Aspirin and heparin in pregnancy

INTRODUCTION

A pro-coagulant state during pregnancy can be involved in the occurrence of gestational vascular complications (GVCs) and venous thromboembolism (VTE).

AREAS COVERED

Antithrombotic drugs are used to prevent GVCs and VTE. Aspirin is not efficacious to prevent recurrences in women with previous early loss, while it can prevent pre-eclampsia in some groups of women. Heparins are not effective in the prevention of early recurrent loss and there is uncertainty about their efficacy in women carrying inherited thrombophilias. They could be efficacious in the prevention of GVCs in carriers of inherited thrombophilias, as GVCs have heterogeneous causes, and future studies have to focus on more homogeneous groups of patients. Not enough data are available regarding prophylaxis with heparins to prevent pregnancy-related VTE, but an accurate risk stratification of women during pregnancy and puerperium is crucial for administering prophylaxis in moderate-/high-risk women. Aspirin does not improve live births after assisted reproductive technologies, while heparins increase the number of clinical pregnancies and live births.

EXPERT OPINION

Aspirin is efficacious in the prevention of GVCs in women at risk for pre-eclampsia and in those with antiphospholipid antibodies syndrome. Heparins could give benefit to women at risk for GVCs and/or pregnancy-related VTE.

Graz Critical Limb Ischemia Score: A Risk Score for Critical Limb Ischemia in Peripheral Arterial Occlusive Disease

Critical limb ischemia (CLI), a frequently encountered disorder, is associated with a high rate of limb amputation and mortality. To identify patients at high risk for CLI, we developed a simple risk score for peripheral arterial occlusive disease (PAOD).In our cross-sectional study, we first evaluated 1000 consecutive PAOD patients treated at our institution from 2005 to 2007, documenting clinical symptoms, comorbidities, and concomitant medication. We calculated odds ratios (OR) in a binary logistic regression model to find possible risk factors for CLI. We then verified the score in a second step that included the 1124 PAOD patients we treated between 2007 and 2011.In the first patient group, the greatest risk factors for CLI were age ≥75 years (OR 2.0), type 2 diabetes (OR 3.1), prior myocardial infarction (OR 2.5), and therapy with low molecular weight heparins (2.8). We scored 1 point for each of those conditions. One point was given for age between 65 and 75 years (OR 1.6) as well as for therapy with cardiac glycosides (OR 1.9) or loop diuretic therapy (OR 1.5). As statin therapy was protective for CLI with an OR of 0.5, we subtracted 1 point for those patients.In the second group, we could prove that frequency of CLI was significantly higher in patients with a high CLI score. The score correlated well with inflammatory parameters (c-reactive protein and fibrinogen). We were also able to define 3 different risk groups for low (score -1 to 1), intermediate (score 2-4), and high CLI risk (score >4).We developed a simple risk stratification scheme that is based on conditions that can be easily assessed from the medical history, without any laboratory parameters. This score should help to identify PAOD patients at high risk for CLI.

Anticoagulation management associated with extracorporeal circulation

The use of extracorporeal circulation requires anticoagulation to maintain blood fluidity throughout the circuit, and to prevent thrombotic complications. Additionally, adequate suppression of hemostatic activation avoids the unnecessary consumption of coagulation factors caused by the contact of blood with foreign surfaces. Cardiopulmonary bypass represents the greatest challenge in this regard, necessitating profound levels of anticoagulation during its conduct, but also quick, efficient reversal of this state once the surgical procedure is completed. Although extracorporeal circulation has been around for more than half a century, many questions remain regarding how to best achieve anticoagulation for it. Although unfractionated heparin is the predominant agent used for cardiopulmonary bypass, the amount required and how best to monitor its effects are still unresolved. This review discusses the use of heparin, novel anticoagulants, and the monitoring of anticoagulation during the conduct of cardiopulmonary bypass.

Prognostic value of angiographic lesion complexity in patients with acute coronary syndromes undergoing percutaneous coronary intervention (from the acute catheterization and urgent intervention triage strategy trial)

Although lesion complexity is predictive of outcomes after balloon angioplasty, it is unclear whether complex lesions continue to portend a worse prognosis in patients with acute coronary syndrome (ACS) undergoing percutaneous coronary intervention (PCI) with contemporary interventional therapies. We sought to assess the impact of angiographic lesion complexity, defined by the modified American College of Cardiology/American Heart Association classification, on clinical outcomes after PCI in patients with ACS and to determine whether an interaction exists between lesion complexity and antithrombin regimen outcomes after PCI. Among the 3,661 patients who underwent PCI in the Acute Catheterization and Urgent Intervention Triage strategy study, patients with type C lesions (n = 1,654 [45%]) had higher 30-day rates of mortality (1.2% vs 0.6%, p = 0.049), myocardial infarction (9.2% vs 6.3%, p = 0.0006), and unplanned revascularization (4.3% vs 3.1%, p = 0.04) compared with those without type C lesions. In multivariate analysis, type C lesions were independently associated with myocardial infarction (odds ratio [95% confidence interval] = 1.37 [1.04 to 1.80], p = 0.02) and composite ischemia (odds ratio [95% confidence interval] = 1.49 [1.17 to 1.88], p = 0.001) at 30 days. Bivalirudin monotherapy compared with heparin plus a glycoprotein IIb/IIIa inhibitor reduced major bleeding complications with similar rates of composite ischemic events, regardless of the presence of type C lesions. There were no interactions between antithrombotic regimens and lesion complexity in terms of composite ischemia and major bleeding (p [interaction] = 0.91 and 0.80, respectively). In conclusion, patients with ACS with type C lesion characteristics undergoing PCI have an adverse short-term prognosis. Treatment with bivalirudin monotherapy reduces major hemorrhagic complications irrespective of lesion complexity with comparable suppression of adverse ischemic events as heparin plus glycoprotein IIb/IIIa inhibitor.

Reference range determination for whole-blood platelet aggregation using the Multiplate analyzer

OBJECTIVES

To develop reference ranges for platelet aggregation using the Multiplate analyzer (Roche Diagnostics, Mannheim, Germany) in blood anticoagulated with sodium citrate (Na-citrate), lithium heparin (Li-heparin), or hirudin.

METHODS

The study was performed at three sites on consented, healthy adults (n = 193) not taking antiplatelet medication. Platelet aggregation was evaluated in response to adenosine-5'-diphosphate, arachidonic acid, collagen, thrombin receptor activating peptide, ristocetin, and adenosine-5'-diphosphate combined with prostaglandin E1. Precision testing was conducted using healthy donors and donors taking aspirin.

RESULTS

Whole-blood platelet aggregation showed anticoagulant-dependent differences in platelet responses to all agonists. Samples collected in Na-citrate demonstrated the lowest responses to all agonists. The highest responses were obtained using Li-heparin. Precision testing revealed high variability in platelet aggregation at lower agonist doses, regardless of anticoagulant. Highest platelet response variations occurred in response to arachidonic acid in blood anticoagulated with hirudin from participants taking aspirin.

CONCLUSIONS

These data demonstrate the importance of establishing locally relevant reference ranges.

An objective comparison between bivalirudin and heparin during peripheral vascular interventions

ABSTRACT 

Patients undergoing percutaneous peripheral interventions are at increased risk for thrombotic complications hence the routine use of periprocedural anticoagulants. There is currently no American College of Cardiology/American Heart Association guidelines for periprocedural anticoagulants use in percutaneous peripheral interventions. Historically, unfractionated heparin has been the most common periprocedural anticoagulant used during percutaneous peripheral interventions. There may be a role for more predictable periprocedural anticoagulants in percutaneous peripheral interventions as has been demonstrated in percutaneous coronary interventions. Our review focuses on the evidence supporting the use of bivalirudin in percutaneous peripheral interventions.