Tirofiban provides "platelet anesthesia" during cardiopulmonary bypass in baboons

Progress in platelet blockers: the target is the P2Y12 receptor

The considerable progress in P2Y12-platelet blockers has important perioperative implications due to a family of novel agents beyond clopidogrel. Although prasugrel is more potent than clopidogrel due to more efficient hepatic metabolism, it is limited clinically by its irreversibility and bleeding risks. Ticagrelor, as the first approved direct and reversible oral P2Y12 blocker, still is limited clinically by its novel side-effect profile. Intravenous reversible P2Y12 blockade is possible now with both cangrelor and elinogrel, although both agents are still in clinical development. Furthermore, elinogrel offers the possibility of both oral and parenteral P2Y12 blockade with a single agent. Future trials likely will continue to evaluate and compare the safety and efficacy of these agents in multiple clinical settings, including the perioperative period.

Combined blockade of ADP receptors and PI3-kinase p110β fully prevents platelet and leukocyte activation during hypothermic extracorporeal circulation

Extracorporeal circulation (ECC) and hypothermia are used to maintain stable circulatory parameters and improve the ischemia tolerance of patients in cardiac surgery. However, ECC and hypothermia induce activation mechanisms in platelets and leukocytes, which are mediated by the platelet agonist ADP and the phosphoinositide-3-kinase (PI3K) p110β. Under clinical conditions these processes are associated with life-threatening complications including thromboembolism and inflammation. This study analyzes effects of ADP receptor P₂Y₁₂ and P₂Y₁ blockade and PI3K p110β inhibition on platelets and granulocytes during hypothermic ECC. Human blood was treated with the P₂Y₁₂ antagonist 2-MeSAMP, the P₂Y₁ antagonist MRS2179, the PI3K p110β inhibitor TGX-221, combinations thereof, or PBS and propylene glycol (controls). Under static in vitro conditions a concentration-dependent effect regarding the inhibition of ADP-induced platelet activation was found using 2-MeSAMP or TGX-221. Further inhibition of ADP-mediated effects was achieved with MRS2179. Next, blood was circulated in an ex vivo ECC model at 28°C for 30 minutes and various platelet and granulocyte markers were investigated using flow cytometry, ELISA and platelet count analysis. GPIIb/IIIa activation induced by hypothermic ECC was inhibited using TGX-221 alone or in combination with P₂Y blockers (p<0.05), while no effect of hypothermic ECC or antiplatelet agents on GPIIb/IIIa and GPIbα expression and von Willebrand factor binding was observed. Sole P₂Y and PI3K blockade or a combination thereof inhibited P-selectin expression on platelets and platelet-derived microparticles during hypothermic ECC (p<0.05). P₂Y blockade alone or combined with TGX-221 prevented ECC-induced platelet-granulocyte aggregate formation (p<0.05). Platelet adhesion to the ECC surface, platelet loss and Mac-1 expression on granulocytes were inhibited by combined P₂Y and PI3K blockade (p<0.05). Combined blockade of P₂Y₁₂, P₂Y₁ and PI3K p110β completely inhibits hypothermic ECC-induced activation processes. This novel finding warrants further studies and the development of suitable pharmacological agents to decrease ECC- and hypothermia-associated complications in clinical applications.

Platelet function in stored heparinised autologous blood is not superior to in patient platelet function during routine cardiopulmonary bypass

Background

In cardiac surgery, cardiopulmonary bypass (CPB) and unfractionated heparin have negative effects on blood platelet function. In acute normovolemic haemodilution autologous unfractionated heparinised blood is stored ex-vivo and retransfused at the end of the procedure to reduce (allogeneic) transfusion requirements. In this observational study we assessed whether platelet function is better preserved in ex vivo stored autologous blood compared to platelet function in the patient during CPB.

Methodology/Principal Finding

We measured platelet aggregation responses pre-CPB, 5 min after the start of CPB, at the end of CPB, and after unfractionated heparin reversal, using multiple electrode aggregometry (Multiplate®) with adenosine diphosphate (ADP), thrombin receptor activating peptide (TRAP) and ristocetin activated test cells. We compared blood samples taken from the patient with samples taken from 100 ml ex-vivo stored blood, which we took to mimick blood storage during normovolemic haemodilution. Platelet function declined both in ex-vivo stored blood as well as in blood taken from the patient. At the end of CPB there were no differences in platelet aggregation responses between samples from the ex vivo stored blood and the patient.

Conclusion/Significance

Ex vivo preservation of autologous blood in unfractionated heparin does not seem to be profitable to preserve platelet function.

Short-acting P2Y12 blockade to reduce platelet dysfunction and coagulopathy during experimental extracorporeal circulation and hypothermia

BACKGROUND

Extracorporeal circulation (ECC) and hypothermia are routinely used in cardiac surgery to maintain stable circulatory parameters and to increase the ischaemic tolerance of the patient. However, ECC and hypothermia cause platelet activation and dysfunction possibly followed by a devastating coagulopathy. Stimulation of the adenosinediphosphate (ADP) receptor P(2)Y(12) plays a pivotal role in platelet activation. This experimental study tested P(2)Y(12) receptor blockade as an approach to protect platelets during ECC.

METHODS

Human blood was treated with the short-acting P(2)Y(12) blocker cangrelor (1 µM, t(1/2)<5 min) or the P(2)Y(12) inhibitor 2-MeSAMP (100 µM) and circulated in an ex vivo ECC model at normothermia (37°C) and hypothermia (28°C). Before and after circulation, markers of platelet activation and of coagulation (thrombin-antithrombin complex generation) were analysed. During hypothermic ECC in pigs, the effect of reversible P(2)Y(12) blockade on platelet function was evaluated by cangrelor infusion (0.075 µg kg(-1) min(-1)).

RESULTS

During ex vivo hypothermic ECC, P(2)Y(12) blockade inhibited platelet granule release (P<0.01), platelet-granulocyte binding (P<0.05), and platelet loss (P<0.001), whereas no effects on platelet-ECC binding, platelet CD42bα expression, glycoprotein IIb/IIIa activation, or thrombin-antithrombin complex generation were observed. During hypothermic ECC in pigs, cangrelor inhibited platelet-fibrinogen binding (P<0.05) and ADP-induced platelet aggregation (P<0.001). Platelet function was rapidly restored after termination of cangrelor infusion.

CONCLUSIONS

P(2)Y(12) blockade by cangrelor prevents platelet activation during ECC and hypothermia. Owing to its short half-life, platelet inhibition can be well controlled, thus potentially reducing bleeding complications. This novel pharmacological strategy has the potential to reduce complications associated with ECC and hypothermia.

Regulation of cardiac afferent excitability in ischemia

The heart at the time of Sir William Harvey originally was thought to be an insensate organ. Today, however, we know that this organ is innervated by sensory nerves that course centrally though mixed nerve pathways that also contain parasympathetic or sympathetic motor nerves. Angina or cardiac pain is now well recognized as a pressure-like pain that occurs during myocardial ischemia when coronary artery blood flow is interrupted. Sympathetic (or spinal) afferent fibers that are either finely myelinated or unmyelinated are responsible for the transmission of information to the brain that ultimately allows the perception of angina as well as activation of the sympathetic nervous system, resulting in tachycardia, hypertension, and sometimes arrhythmias. Although early studies defined the importance of the vagal and sympathetic cardiac afferent systems in reflex autonomic control, until recently there has been little appreciation of the mechanisms of activation of the sensory endings. This review examines the role of a number of chemical mediators and their sources that are activated by the ischemic process. In this regard, patients with ischemic syndromes, particularly myocardial infarction and unstable angina, are known to have platelet activation, which leads to release of a number of chemical mediators, including serotonin, histamine, and thromboxane A(2), all of which stimulate ischemically sensitive cardiac spinal afferent endings in the ventricles through specific receptor-mediated processes. Furthermore, protons from lactic acid, bradykinin, and reactive oxygen species, especially hydroxyl radicals, individually and frequently in combination, stimulate these endings during ischemia. Cyclooxygenase products appear to sensitize the endings to the action of bradykinin and histamine. These studies of the chemical mechanisms of activation of cardiac sympathetic afferent endings during ischemia have the potential to provide targeted therapies that can modify the angina and the deleterious reflex responses that have the potential to exacerbate ischemia and myocardial cell death.

Tirofiban preserves platelet loss during continuous renal replacement therapy in a randomised prospective open-blinded pilot study

Introduction

Approximately one third of all patients with cardiogenic shock suffer from acute kidney injury. Percutaneous coronary intervention, intra-aortic balloon pump, and continuous renal replacement therapy (CRRT) require effective antiplatelet therapy and anticoagulation, resulting in a high risk for platelet loss and bleeding events. The reversible platelet glycoprotein IIb/IIIa receptor inhibitor tirofiban was investigated to preserve platelet number and activation in a prospective open-blinded endpoint evaluation study.

Methods

Forty patients with cardiogenic shock and acute kidney injury requiring CRRT were randomly assigned to two groups receiving unfractioned heparin (UFH) (n = 20) or a combined anticoagulation with UFH and tirofiban (n = 20). The primary endpoint was platelet loss during CRRT. Secondary endpoints were urea reduction, haemofilter life span, bleeding events, and necessity for platelet transfusions.

Results

In UFH-treated patients, the percentage of platelet-monocyte aggregates significantly increased (P < 0.001) and consecutively platelet cell count significantly decreased (P < 0.001). In contrast, combined treatment with UFH and tirofiban significantly decreased platelet-monocyte aggregates and platelet numbers (P < 0.001).

Conclusions

This pilot study provides evidence that the use of tirofiban in addition to UFH prevents platelet loss and preserves platelet function in patients with cardiogenic shock and acute kidney injury requiring CRRT. The pathophysiological inhibition of platelet aggregation and platelet-monocyte interaction appears to be causally involved.

Platelet anaesthesia during extracorporeal circulation: differential effects of GP IIb/IIIa blockers on platelet activation marker P-selectin expression at hypothermia

INTRODUCTION

Blood contact with artificial surfaces of extracorporeal circulation (ECC) and hypothermia as applied in cardiac surgery cause platelet dysfunction possibly followed by bleeding complications. "Platelet anaesthesia" is a pharmacological strategy to protect platelets against ECC-induced damage using a GP IIb/IIIa blocker, which should be short acting to achieve maximal therapy control thereby avoiding post-ECC haemorrhage. However, GP IIb/IIIa blockers can paradoxically induce platelet activation, which may limit their efficiency as anti-platelet drugs. This in-vitro study investigated potentially platelet-activating effects of short-acting GP IIb/IIIa blockers during normothermic and hypothermic ECC.

MATERIALS AND METHODS

Control (untreated) and treated (using either FK633 [half-life: 0.52 h], tirofiban [half-life: 1.5-2 h], or eptifibatide [half-life: 1.5 h]) heparinized blood was circulated in an ECC-model at normothermia (37 degrees C) and hypothermia (18 degrees C). Percentages of platelet aggregates and P-selectin-expressing (activated) platelets, platelet-counts and Thrombin-Antithrombin (TAT) complex formation were determined before (baseline) and after ECC. Statistical analysis was performed using multifactorial ANOVA after log-transforming the data.

RESULTS

GP IIb/IIIa blockade inhibited ECC-induced platelet aggregation and platelet loss and decreased P-selectin expression at normothermia. During hypothermic ECC P-selectin was decreased by tirofiban but augmented by FK633 and eptifibatide. TAT formation was only decreased by FK633.

CONCLUSIONS

Especially regarding its ultra-short half-life FK633 has the best properties for platelet protection during normothermic ECC. However, at hypothermia FK633 and eptifibatide induce platelet activation. In relation with "platelet anaesthesia" possible hypothermia-associated prothrombotic side effects of GP IIb/IIIa blockers should be considered.

Emergency coronary artery bypass grafting in patients with acute myocardial infarction treated with glycoprotein IIb/IIIa receptor inhibitors

Glycoprotein (GP) IIb/IIIa receptor inhibitors before primary angioplasty in patients with ST-elevation acute myocardial infarction (STEMI) are recommended by current guidelines. Thus, an increasing number of patients receive these drugs before coronary angiography, particularly if a between-hospital transfer is needed. However, when coronary anatomy is unsuitable for angioplasty, emergency coronary artery bypass grafting (CABG) under GP IIb/IIIa inhibitor treatment may be needed, with a potential increase in bleeding risk. Abciximab has a long duration of action, because of its high-affinity binding to GP IIb/IIIa receptors. Initial retrospective studies reported a higher incidence of major bleeding during emergency CABG after abciximab administration, leading to the recommendation of delaying surgery >12 h. However, data from the prospective trials on abciximab do not confirm the increase in bleeding risk, and current evidence shows that emergency surgery can be performed safely soon after abciximab cessation. Monitoring of activated clotting time during surgery and platelet transfusion in case of postoperative relevant bleeding are the only measures needed. No data are available on emergency surgery in patients with STEMI treated with eptifibatide or tirofiban. However, their short-lasting effects and the results of trials on non-ST-elevation acute coronary syndromes suggest that they could even reduce postoperative bleeding by preventing platelet consumption during cardiopulmonary bypass. In conclusion, the early administration of GP IIb/IIIa inhibitors, in particular of abciximab, in patients with STEMI in whom primary angioplasty is planned should not be discouraged because of the potential bleeding risk in case of emergency CABG.

Platelet function monitoring with the Sonoclot analyzer after in vitro tirofiban and heparin administration

OBJECTIVE

Reliable platelet function monitoring is desirable in patients treated with glycoprotein IIb/IIIa receptor inhibitors. The aim of the present laboratory-based study was to assess platelet function after administration of clinically relevant doses of the glycoprotein IIb/IIIa antagonist tirofiban with or without heparin by using Sonoclot (Sienco Inc) and platelet aggregometry.

METHODS

Tirofiban (0-100 ng x mL(-1)) and heparin (0 or 1 U x mL(-1)) were added to blood samples obtained from 20 healthy volunteers. Coagulation analysis was performed on citrated whole blood by using the Sonoclot analyzer. The glass bead-activated test and the new glass bead test with heparinase were used. The results were compared with adenosine-5'-diphosphate-activated platelet aggregometry.

RESULTS

Administration of tirofiban showed a similar increase of platelet inhibition detected with the Sonoclot glass bead-activated test and glass bead test with heparinase, as well as by means of aggregometry. Bias between the different techniques was comparable; Spearman rank correlation was strong (glass bead-activated test vs aggregometry: rho = 0.823, P < .001; glass bead test with heparinase vs aggregometry: rho = 0.856, P < .001). After additional administration of heparin, platelet inhibition was only comparable for the glass bead test with heparinase and aggregometry, and the correlation coefficient remained unchanged for the glass bead test with heparinase versus aggregometry (rho = 0.878, P < .001). By contrast, the glass bead-activated test showed a nearly complete platelet inhibition with a significant bias compared with the glass bead test with heparinase and aggregometry. Correlation was weak for the glass bead-activated test versus aggregometry (rho = 0.407, P = .004).

CONCLUSIONS

When compared with platelet aggregometry, the glass bead-activated test from Sonoclot reliably detects glycoprotein IIb/IIIa receptor inhibition with tirofiban in unheparinized whole blood. However, in heparinized blood the glass bead test with heparinase is essential to accurately assess platelet function.

Platelet Preservation With a Glycoprotein IIb/IIIa Inhibitor in a Porcine Cardiopulmonary Bypass Model

BACKGROUND

We tested whether administration of FK633, a short-acting glycoprotein IIb/IIIa inhibitor, before median sternotomy and cardiopulmonary bypass was able to interrupt the platelet activation loop and thereby preserve platelet number and function.

METHODS

This study investigated 16 pigs that underwent median sternotomy and 120 minutes of normothermic cardiopulmonary bypass (100 mL/kg) adding pericardial blood to the perfusate. FK633 was administered with heparin to one group (group F, n = 8), whereas only heparin was administered to the control group (group C, n = 8). Blood samples were obtained at several times, and complete blood count, platelet aggregation to adenosine diphosphate, thrombin-antithrombin complex, and bradykinin were evaluated. P-selectin expression and fibrinogen binding on platelet surfaces were measured by flow cytometry. Template bleeding times were measured before and after cardiopulmonary bypass. Chest tube drainage and hematocrit were determined at 2 and 6 hours after cardiopulmonary bypass.

RESULTS

In group F, platelet counts were preserved from 90 minutes of cardiopulmonary bypass. Platelet aggregation was inhibited at the beginning of cardiopulmonary bypass and showed no change at wound closure, and bleeding times were shortened at 2 hours after cardiopulmonary bypass. There were significant reductions in hematocrit of drainage. Flow cytometry showed no changes in P-selectin expression and fibrinogen binding in group F, whereas P-selectin expression and fibrinogen binding were elevated in group C.

CONCLUSIONS

Platelet inhibition with FK633 before invasive surgical procedure preserved platelet counts during and after cardiopulmonary bypass, and produced normal or near-normal bleeding times in the immediate postoperative period.

Preoperative use of enoxaparin increases the risk of postoperative bleeding and re-exploration in cardiac surgery patients

OBJECTIVE

The purpose of this study was to investigate if the preoperative use of new platelet inhibitors and low-molecular-weight heparins may contribute to bleeding after cardiac surgery.

DESIGN

Retrospective data review.

SETTING

University teaching hospital.

PARTICIPANTS

One hundred eleven patients divided in 5 groups.

INTERVENTIONS

Patients were grouped according to preoperative antithrombotic regimen: group 1, control, no agents (n=55); group 2, clopidogrel (n=9); group 3, enoxaparin (n=17); group 4, any GP IIb/IIIa inhibitor (n=14); and group 5, any drug combination (n=15). Data included cumulative mediastinal chest tube drainage, allogeneic blood transfusions, total blood donor exposures, and re-exploration.

MEASUREMENTS AND MAIN RESULTS

Use of any drug (groups 2-5) resulted in greater total blood transfusions and donor exposure (p=0.0003) than control, especially red cells (p=0.002) and platelets (p=0.006). A greater percentage of patients on enoxaparin required mediastinal re-exploration for nonsurgical bleeding versus control (3/17 v 0/55, p=0.001). The use of enoxaparin was associated with significantly higher chest tube output after the first 24 hours postoperatively (p=0.048).

CONCLUSION

Newer antithrombotic agents were associated with greater transfusion rates and total donor exposures. Enoxaparin use was associated with greater overall blood loss and with higher incidence of mediastinal re-exploration. The relative risk-benefit ratio of reduced periprocedure morbidity versus increased bleeding complications has yet to be determined.

The state of platelets preserved in extracorporeal circulation with a glycoprotein IIb/IIIa inhibitor

INTRODUCTION

Temporary inhibition of platelet function during extracorporeal circulation (platelet anesthesia) can preserve platelet count. We hypothesized that platelet anesthesia with a glycoprotein IIb/IIIa inhibitor could preserve activated platelets.

MATERIALS AND METHODS

Fresh human blood from donors was recirculated for 120 min in a simulated extracorporeal circuit. Heparin and FK633, a short-acting platelet glycoprotein IIb/IIIa inhibitor, were added to recirculated blood in one group (group F, n=5) whereas only heparin was used in controls (group C, n=5). Blood samples were obtained from the donors, and at 0, 5, 15, 30, 60, and 120 min of recirculation. Platelet counts, beta-thromboglobulin, thrombin-antithrombin complex, and aggregation to adenosine diphosphate were measured. Flow cytometry was performed for measurement of fibrinogen binding, platelet surface expression of P-selectin, and microparticles.

RESULTS AND CONCLUSIONS

In the FK633 group, platelet counts were preserved and beta-thromboglobulin levels remained unchanged, whereas in group C, platelet counts decreased significantly and beta-thromboglobulin increased significantly from 30 and 60 min, respectively. FK633 inhibited platelet aggregation and fibrinogen binding to platelets throughout recirculation. A significant difference between groups with respect to microparticle parameters and thrombin-antithrombin complex levels was evident by 120 min. P-selectin expression increased at 0 min in both groups, and was preserved significantly at 5 min and reduced at 120 min in group F. Platelet counts were preserved by platelet anesthesia during recirculation without platelet activation. These results suggest that FK633 inhibits the amplification loop by reducing the binding of fibrinogen to glycoprotein IIb/IIIa and platelet aggregation.

The effect of ASA on platelet activation during apheresis and on in-vitro properties of stored platelet concentrates

BACKGROUND

Preventing the activation of PLTs may ameliorate (or mitigate) the PLT storage lesion (PSL), which encloses all structural and biochemical changes caused by collection, processing, and storage of PLT concentrates (PCs). Partial inhibition of PLT function due to ingestion of aspirin (ASA) by blood donors reduces the functional activity of the collected PLTs, however, by preventing premature PLT activation, it might reduce the PSL as well.

STUDY DESIGN AND METHODS

In a randomized crossover study, 10 healthy donors donated two single-donor PCs (SDPCs) each, taking 500 mg ASA 12 hours before one of the aphereses (Group A) and taking no medication before the other donation (Group B). In-vitro tests of PLT function were performed in donors before and after apheresis and in SDPCs during storage (Days 1, 3, and 5).

RESULTS

ASA ingestion resulted in a significant decrease of induced PLT aggregation in donors (p < 0.005) and SDPCs on Day 1 (p < 0.01). TRAP-6-induced expression of p-selectin (CD62p) was significantly reduced in Group A SDPCs only on Day 1 (p < 0.02). There were no significant differences of in-vitro function (LDH, lactate, pH, morphology score, CD62p expression, fibrinogen binding) between Group A and B (SDPCs and donors). Apheresis did not result in a significant activation of PLTs in donors or SDPCs.

CONCLUSIONS

These limited data do not show a detectable beneficial effect of ASA ingestion on the PSL but do suggest that ASA ingestion before apheresis may not be detrimental to the clinical effectiveness of the stored product.

Effects of tirofiban on haemostatic activation in vitro

BACKGROUND

Thrombin plays a critical role in normal haemostasis and pathological thrombosis. Heparin has long been a mainstay choice of antithrombotic regimen in cardiac patients, but persistent thrombin generation seems to occur during heparin therapy. Because platelets are integral to primary haemostasis and clot formation, we evaluated the use of tirofiban (Aggrastat),a platelet inhibitor, as a therapy to improve heparin sensitivity and delay thrombin formation.

METHODS

Blood samples were obtained from healthy subjects (n=8) and cardiac surgical patients (n=34). Thrombin formation was measured in platelet-rich plasma with a Thrombogram-Ascent fluorescent plate reader system. Platelet inhibition by tirofiban was evaluated with Plateletworks, and the interaction of tirofiban and heparin (>1.5 U ml(-1)) on clot formation was evaluated with Sonoclot Analyzer or kaolin activated clotting times (ACTs).

RESULTS

Addition of tirofiban (70-280 ng ml(-1)) progressively delayed onset of thrombin generation triggered by adenosine diphosphate (ADP). Plateletworks showed platelet inhibition with tirofiban (>35 ng ml(-1)), whereas heparin per se failed to produce platelet inhibition at 7 U ml(-1). Heparin (1.5 U ml(-1)) slowed the onset and rate of fibrin formation on Sonoclot analyses, and this was further slowed after addition of tirofiban (70 ng ml(-1)) to heparin-containing blood samples. Significant increases in ACT at all heparin concentrations were observed with the addition of tirofiban (70 ng ml(-1)). The addition of antithrombin (0.2 units/ml) to heparinized blood samples further prolonged ACTs, but the difference was not statistically significant when compared with heparin alone.

CONCLUSION

Tirofiban delays platelet activation-mediated thrombin generation and prolongs ACT in heparinized blood.

Pharmacologic platelet anesthesia by glycoprotein IIb/IIIa complex antagonist and argatroban during in vitro extracorporeal circulation

OBJECTIVE

Contact between blood and the synthetic surfaces of a cardiopulmonary bypass circuit leads to platelet activation, and resultant platelet dysfunction contributes to postoperative bleeding. We compared the effects of various platelet inhibitors on preservation of platelet function during simulated cardiopulmonary bypass circulation.

METHODS

Fresh human blood was recirculated in an in vitro cardiopulmonary bypass model circuit. We measured various platelet activation markers including expressions of PAC-1 and P-selectin, annexin V binding, and microparticle formations by means of whole-blood flow cytometry.

RESULTS

Two types of glycoprotein IIb/IIIa complex antagonists, peptide-mimetic FK633 and abciximab and prostaglandin E(1), significantly prevented platelet loss and the increase in binding of PAC-1, an antibody specific for fibrinogen receptor on activated platelets, during extracorporeal circulation of heparinized blood. These antagonists significantly suppressed but did not abolish P-selectin expression, annexin V binding, and microparticle formation. Anti-von Willebrand factor monoclonal antibody and aurin tricarboxylic acid (an inhibitor of glycoprotein Ib) had no effect on platelet activation during simulated cardiopulmonary bypass circulation. These data suggest that inhibition of fibrinogen binding glycoprotein IIb/IIIa complex is partly effective in attenuating platelet activation in a heparinized cardiopulmonary bypass model circuit. The direct thrombin inhibitor argatroban prevented platelet loss and expression of P-selectin significantly more than did heparin. A combination of FK633 with argatroban as a substitute for heparin further prevented platelet loss and platelet secretion during simulated cardiopulmonary bypass circulation, although the inhibition of microparticle formation was less.

CONCLUSION

The inhibition of both platelet adhesion and thrombin may be effective to preserve platelet number and function during cardiopulmonary bypass circulation.

Activated platelets contribute to stimulation of cardiac afferents during ischaemia in cats: role of 5-HT(3) receptors

Myocardial ischaemia activates blood platelets and cardiac sympathetic afferents, which mediate chest pain and cardiovascular reflex responses. We have demonstrated that activated platelets stimulate ischaemically sensitive cardiac sympathetic afferents. Platelets absorb and release 5-hydroxytryptamine (5-HT) when they are activated. In the present study we hypothesized that, by releasing 5-HT, activated platelets stimulate cardiac afferents during ischaemia through a 5-HT(3) receptor mechanism. Platelet-rich plasma (PRP) and platelet-poor plasma (PPP) were obtained from cats. Activation of platelets in PRP was induced by thrombin (5 units ml(-1)) or collagen (2 mg kg(-1)). Using high-performance liquid chromatography, we observed that the concentration of 5-HT was increased significantly in suspensions of platelets activated with thrombin (PRP+thrombin, 28 +/- 1.7 microM) or collagen (PRP+collagen, 27 +/- 2.5 microM) compared with suspensions of unactivated platelets (PRP+saline, 2.3 +/- 0.8 microM) and PPP. During myocardial ischaemia and reperfusion, tirofiban, a specific inhibitor of platelet glycoprotein (GP) IIb-IIIa receptors (100 microg kg(-1), I.V., followed by 5 microg kg(-1) min(-1)), significantly reduced the increase in the concentration of 5-HT in cardiac venous plasma from ischaemic region. Nerve activity of single-unit cardiac afferents was recorded from the left sympathetic chain (T2-T5) in anaesthetized cats. Eighty ischaemically sensitive and seven ischaemically insensitive cardiac afferents were identified. Tirofiban reduced the ischaemia-related increase in activity of seven cardiac sympathetic afferents by 50 %. Injection of 1.5 ml of PRP+collagen or PRP+thrombin into the left atrium (LA) increased activity of 16 cardiac afferents. Tropisetron (300 microg kg(-1), I.V.), a selective 5-HT(3) receptor antagonist, eliminated the afferent's responses to platelets activated with collagen or thrombin. Moreover, LA injection of 5-HT (20-40 microg kg(-1)) and PBG (100 microg kg(-1)), a 5-HT(3) receptor agonist, stimulated nine ischaemically sensitive cardiac sympathetic afferents, significantly increasing the activity of these afferents. However, injection of alpha-M-5-HT (100 microg kg(-1), LA), a 5-HT(2) receptor agonist, stimulated only two of the nine ischaemically sensitive cardiac afferents, and thus did not significantly alter impulse activity of this group of afferents. Both the 5-HT(1) (5-CT, 100 microg kg(-1), LA) and 5-HT(4) receptor agonists (SC53116, 100 microg kg(-1), LA) did not stimulate any of the nine afferents tested. Tropisetron (300 microg kg(-1), I.V.) also eliminated the response of seven ischaemically sensitive cardiac afferents to exogenous 5-HT and attenuated the ischaemia-related increase in activity of nine cardiac sympathetic afferents by 41 %. Conversely, LA injection of 5-HT (40 microg kg(-1)) did not stimulate any of seven ischaemically insensitive cardiac afferents, although this group of afferents consistently responded to bradykinin (3 microg, LA). These data indicate that during myocardial ischaemia the activated platelets stimulate cardiac sympathetic afferents, at least in part, through a 5-HT(3) receptor mechanism.

The effect of clopidogrel in combination with aspirin when given before coronary artery bypass grafting

OBJECTIVES

This study was designed to evaluate the effect of preoperative clopidogrel on coronary artery bypass graft surgery (CABG) outcomes.

BACKGROUND

Clopidogrel in combination with aspirin, given before percutaneous coronary intervention, has become the standard for stent thrombosis prevention. Some premedicated patients, however, are found to have surgical disease on angiography, and irreversible platelet inhibition becomes a concern for upcoming CABG.

METHODS

We prospectively studied 224 consecutive patients undergoing nonemergent first-time CABG, and compared those with preoperative clopidogrel exposure within seven days (n = 59) to those without exposure (n = 165).

RESULTS

The groups were comparable in age, gender, body surface area, preoperative hematocrit, preoperative prothrombin time and prior myocardial infarction. The clopidogrel group had higher 24-h mean chest tube output (1,224 ml vs. 840 ml, p = 0.001), and more transfusions of red blood cells (2.51 U vs. 1.74 U, p = 0.036), platelets (0.86 U vs. 0.24 U, p = 0.001) and fresh frozen plasma (0.68 U vs. 0.24 U, p = 0.015). Moreover, reoperation for bleeding was 10-fold higher in the clopidogrel group (6.8% vs. 0.6%, p = 0.018). The clopidogrel group also had less extubation within 8 h (54.2% vs. 75.8%, p = 0.002) and a trend towards less hospital discharge within five days (33.9% vs. 46.7%, p = 0.094).

CONCLUSIONS

Clopidogrel in combination with aspirin before CABG is associated with higher postoperative bleeding and morbidity. These findings raise concern regarding the routine administration of clopidogrel before anticipated coronary stent implantation.

Perioperative use of tirofiban hydrochloride (Aggrastat) does not increase surgical bleeding after emergency or urgent coronary artery bypass grafting

BACKGROUND

The platelet glycoprotein IIb/IIIa inhibitor tirofiban hydrochloride improves outcome in patients with acute coronary syndrome. Nevertheless, a considerable number of patients require emergency or urgent coronary artery bypass grafting and may be at increased risk of postoperative bleeding after treatment with this molecule. The aim of this study is to evaluate the incidence of bleeding complications among patients undergoing bypass grafting after treatment with tirofiban.

METHODS

We investigated the influence of the molecule on postoperative bleeding after cardiac surgery, comparing 2 groups of patients undergoing emergency or urgent coronary artery bypass grafting: group A (n = 20) received tirofiban, and group B (n = 68) received conventional therapy with intravenous heparin up until the operation. A total of 88 patients underwent coronary artery bypass surgery within 2 hours of ceasing the hemodynamic study. Clinical outcome, chest tube outputs, bleeding complications, transfusion requirements, platelet and hemoglobin counts, and clinical complications were examined.

RESULTS

Bleeding differences were noted between the 2 groups at 8, 16, and 24 hours postoperatively. The incidence of blood, platelet, and fresh frozen plasma transfusions was higher in the control group. Postoperative thrombocytopenia was preserved in group A (199.5 +/- 70.4 vs 150.6 +/- 33.4 10(3)/mL, P <.01). No significant differences were noted between the 2 groups in the incidence of perioperative myocardial infarction, but significant differences were noted in enzyme levels, length of stay in the intensive care unit, and length of stay in the hospital. No deaths were observed. Hospital morbidity was increased in group B because of factors that were not apparently linked with tirofiban infusion.

CONCLUSIONS

Patients may safely undergo coronary artery bypass surgery after treatment with tirofiban hydrochloride. This molecule, administered in the immediate preoperative period, has no adverse clinical effects and does not seem to negatively influence the incidence of perioperative myocardial infarction. Although extracorporeal circulation can modify platelet numbers and function, our ongoing data could show significant reduction in the loss of platelets induced by cardiopulmonary bypass, minor postoperative bleeding, and a minor transfusion requirement in general.

Enhanced efficacy of eptifibatide administration in patients with acute coronary syndrome requiring in-hospital coronary artery bypass grafting. PURSUIT Investigators

BACKGROUND

Patients with a recent episode of non-ST-segment elevation acute coronary syndrome before CABG have higher rates of operative morbidity and mortality than patients with stable coronary syndromes. The efficacy of administering eptifibatide to these patients undergoing in-hospital CABG is unknown.

METHODS AND RESULTS

The Platelet Glycoprotein IIb-IIIa in Unstable Angina: Receptor Suppression Using Integrilin Therapy (PURSUIT) trial randomized 10 948 patients to receive either eptifibatide or placebo. There were 1558 study participants who underwent in-hospital CABG: 692 received placebo, and 866 received eptifibatide. The main substudy analysis end point was death or myocardial infarction (MI) rates at the 6-month follow-up. The 30-day death or MI rates were 30. 8% and 26.1% for the placebo and eptifibatide groups, respectively (P:=0.041). The benefit of eptifibatide administration persisted through 6-months of follow-up (32.7% versus 27.6% for placebo versus eptifibatide, respectively; P:=0.029). There was a greater reduction in the 6-month death or MI rate for patients who received eptifibatide within 72 hours of CABG (33.6% versus 23.8%; P:=0.002) compared with the >72-hour group (31.6% versus 32%; P:=1.0). The incidence of major bleeding was 56.6% for placebo-treated patients versus 58.2% for eptifibatide-treated patients (P:=0.7).

CONCLUSIONS

Eptifibatide administration in patients undergoing in-hospital CABG with a recent episode of a non-ST-segment elevation acute coronary syndrome results in a significant reduction in death or MI that is evident at 7 days and persists through the 6-month follow-up without a significant increase in perioperative bleeding rates.

Leukocyte-depleted blood cardioplegia reduces cardiac troponin T release in patients undergoing coronary artery bypass grafting

OBJECTIVE

Activated neutrophils have been implicated in reperfusion injury of the myocardium. Leukocyte depletion at reperfusion may contribute to better myocardial protection during cardiac surgery. We tested the efficacy of leukocyte-depleted blood cardioplegia in reducing myocardial injury during coronary artery bypass grafting.

METHODS

Subjects were 27 patients undergoing elective coronary artery bypass grafting divided into controls (perfused with nonfiltered blood cardioplegia, n = 12) and those undergoing leukocyte-depleted blood cardioplegia (n = 15). Oxygenated blood mixed with a potassium crystalloid cardioplegic solution was delivered through the aortic root at every 30 minutes during cardiac arrest and terminal warm blood was administered before aortic declamping in both groups. In leukocyte depletion, blood was filtered prior to the mixture with crystalloid solution in the cardioplegic reservoir.

RESULTS

Patient profiles did not differ significantly between groups, nor did systemic leukocyte count during or after surgery despite more than 81% removal of leukocytes in cardioplegic delivery. No consistent differences between groups in creatine kinase or creatine kinase-MB were seen up to 18 hours after surgery. Peak troponin T levels were significantly lower in the leukocyte-depleted blood cardioplegia group (0.52 +/- 0.13 ng/ml), however, than in controls (3.85 +/- 0.85 ng/ml).

CONCLUSION

We concluded that leukocyte-depleted blood cardioplegia reduces the release of cardiac troponin T in patients undergoing elective coronary artery bypass grafting and may produce better myocardial protection in patients with impaired cardiac function or a damaged myocardium.

The effects of heparin and extracorporeal circulation on platelet counts and platelet microaggregation during cardiopulmonary bypass

BACKGROUND

Cardiopulmonary bypass is associated with platelet activation and reduced platelet counts. Platelet activation may artifactually lower platelet counts by causing aggregation. In vivo platelet activation may increase existent platelet microaggregation ex vivo. We studied platelet counts and existent platelet microaggregation at different stages of cardiopulmonary bypass.

METHODS

Twenty-one patients were studied before and after heparinization (300 U. kg(-1)) and at the end of cardiopulmonary bypass. Unaggregated (or single) platelets were counted in hirudin-anticoagulated blood, and total platelets were counted in ethylenediaminetetraacetic acid-anticoagulated blood.

RESULTS

The total platelet count, 198 +/- 61 x 10(9). L(-1), was unaffected by heparin and stayed at 197 +/- 60 x 10(9). L(-1) (P =.7) but fell during extracorporeal circulation; the hemodilution-corrected count was 163 +/- 52 x 10(9). L(-1) (P =.0004). Heparinization reduced the unaggregated platelet count from (mean +/- 1 SD) 178 +/- 62 x 10(9). L(-1) to 155 +/- 60 x 10(9). L(-1) (P =.0001). Extracorporeal circulation had little additional effect. The hemodilution-corrected count was 142 +/- 48 x 10(9). L(-1) (P =.6).

CONCLUSIONS

Heparinization caused platelet activation and increased existent platelet microaggregation ex vivo. During extracorporeal circulation, there was a reduction in total platelets that was greater than could be explained by hemodilution alone, but the unaggregated platelet count did not change significantly when corrected for hemodilution. Furthermore, the increased platelet microaggregation observed after heparinization was no longer evident after this loss. These findings suggest that during extracorporeal circulation, the platelets that formed into microaggregates after heparinization were lost from the circulation in preference to single platelets.

Platelet inhibitors and bleeding in cardiac surgical patients

A variety of measures may affect bleeding and transfusion requirements in abciximab-treated patients. These measures include recognition of the risk factors for increased bleeding and transfusion requirements, use of proper transfusion practices, conservation or increasing of red cell mass, appropriate heparin dosing and protamine reversal, reversal of anticoagulation, awareness of factors that affect activated clotting time (ACT), and appropriate anticoagulation for cardiopulmonary bypass.

Comparative study of antiplatelet drugs in vitro: distinct effects of cAMP-elevating drugs and GPIIb/IIIa antagonists on thrombin-induced platelet responses

Among various categories of antiplatelet drugs, cAMP-elevating agents and GP IIb/IIIa antagonists have been reported to inhibit platelet aggregation stimulated by a wide variety of platelet agonists. To clarify the qualitative difference between these two agents, their effects on various platelet responses in washed platelets evoked by thrombin (0.05 U/mL) were compared in vitro. Two types of cAMP-elevating drugs, cilostazol (a phosphodiesterase III inhibitor) and prostaglandin E1 (an adenylate cyclase activator), both inhibited platelet aggregation, thromboxane A2 formation, and platelet factor 4 release in a concentration-dependent manner. In addition, both agents suppressed intracellular Ca++ elevation induced by thrombin. However, two classes of GP IIb/IIIa antagonists, abciximab (Fab fragment of antibody) and tirofiban (a synthetic compound), showed no inhibitory effects against thromboxane A2 formation and platelet factor 4 release, although these drugs inhibited platelet aggregation. Essentially the same results were obtained in platelet-rich plasma stimulated with high concentration (100 microM) of thrombin receptor activating peptide. In contrast to these different profiles on thromboxane A2 formation and release reaction, both cAMP-elevating agents and GP IIb/IIIa antagonists potently suppressed procoagulant activity in thrombin-stimulated platelets. These results suggest that the development of platelet procoagulant activity induced by thrombin is exclusively dependent on platelet aggregation or aggregation-dependent processes. These observations also indicate that cAMP-elevating agents possess wider inhibitory effects on platelet responses evoked by strong agonists than GP IIb/IIIa antagonists.

Platelet anesthesia with nitric oxide with or without eptifibatide during cardiopulmonary bypass in baboons

OBJECTIVE

This study tested the hypothesis that nitric oxide or nitric oxide and eptifibatide (Integrilin) reversibly inhibit platelet activation and consumption during cardiopulmonary bypass and rapidly restore platelet numbers and function after bypass.

METHODS

Nitric oxide, a short-acting, reversible platelet inhibitor, was studied with and without eptifibatide, a short-acting, reversible glycoprotein IIb/IIIa inhibitor, in 21 baboons that underwent 60 minutes of normothermic cardiopulmonary bypass with peripheral cannulas. A control group, a group that received 80 ppm nitric oxide, and a group that received both nitric oxide and eptifibatide were studied. Blood samples were obtained at several time points to determine platelet count, aggregation in response to adenosine diphosphate, and levels of beta-thromboglobulin, prothrombin fragment 1.2, and thrombin-antithrombin complex. Template bleeding times were measured before and at 4 intervals after cardiopulmonary bypass.

RESULTS

Both nitric oxide and the combination of the 2 drugs significantly attenuated platelet consumption, improved postbypass function, and reduced plasma beta-thromboglobulin release with respect to values in control animals. Both nitric oxide and the combination restored baseline bleeding times 55 minutes after cardiopulmonary bypass ended. No significant differences between nitric oxide and the combination were found for any measurement.

CONCLUSION

Nitric oxide with or without eptifibatide protects platelets during cardiopulmonary bypass and accelerates restoration of normal bleeding times after operation in a baboon model. Although nitric oxide and eptifibatide reversibly inhibit platelets by different mechanisms, in the absence of a wound no synergistic effect was demonstrated.

Integrilin prevents prolonged bleeding times after cardiopulmonary bypass

BACKGROUND

Cardiopulmonary bypass reduces platelet number and function, increases postoperative bleeding time, and is the major, unsolved cause of nonsurgical bleeding after open heart operations. Temporary inhibition of platelet function during cardiopulmonary bypass (platelet anesthesia) protects platelets and reduces postoperative bleeding time and bleeding.

METHODS

Integrilin, a short-acting, reversible platelet glycoprotein IIb/IIIa inhibitor was studied in 28 baboons that had 60 minutes of normothermic cardiopulmonary bypass using peripheral cannulas. A control group, two groups that received different doses of Integrilin, and a group that received a combination of Integrilin and low-dose Iloprost were studied. Blood samples for platelet count, aggregation to adenosine diphosphate, beta-thromboglobulin, prothrombin fragment F1.2, thrombin-antithrombin complex, and fibrinopeptide A were obtained at seven time points. Template bleeding times were measured before and at five intervals after cardiopulmonary bypass.

RESULTS

Both doses of Integrilin and the combination of Integrilin and Iloprost significantly protected platelet number, inhibited the response to adenosine diphosphate, and reduced postoperative bleeding times, but they did not reduce beta-thromboglobulin release except in the high-dose Integrilin group. Thrombin formation and activity were qualitatively, but not significantly, reduced in all treatment groups. Bleeding times were not significantly different from baseline at the time protamine was given in the combination group and 60 minutes after protamine administration in all treatment groups.

CONCLUSIONS

Integrilin alone or in combination with Iloprost significantly reduces platelet activation during cardiopulmonary bypass and produces normal or near-normal bleeding times at the time protamine is given.

Platelet protective effect of TAK-029, a novel glycoprotein IIb/IIIa antagonist: an in vitro study

Previous studies have indicated that exposure of fibrinogen receptors associated with the glycoprotein IIb/IIIa complex contributes to platelet loss during cardiopulmonary bypass. TAK-029 is a newly developed reversible, nonpeptide inhibitor of platelet glycoprotein IIb/IIIa receptors. In this study, we tested the platelet preserving effect of TAK-029 in an in vitro model. The methods included the comparison of the release of beta-thromboglobulin (beta-TG) between a TAK-029 group (n = 5) and a control group (n = 5) in a mock circulation under a shear force generated by a centrifugal pump. To evaluate the degree of beta-TG release, deltabeta-TG/deltaT was calculated where deltabeta-TG is the increase in beta-TG and deltaT is the time. The results showed that the value of deltabeta-TG/deltaT in the TAK-029 group was significantly lower than it was in the control group (4.22 +/- 0.27 x 10(2) ng/ml vs. 7.33 +/- 0.66 x 10(2) ng/ml, respectively). In conclusion, TAK-029 reduced the platelet activation under the shear forces of an in vitro model, suggesting that TAK-029 is a potential candidate for platelet protection during cardiopulmonary bypass.

A baboon model for hematologic studies of cardiopulmonary bypass

Objective investigation of new inhibitors of blood protein or cellular systems that are activated during cardiopulmonary bypass (CPB) is impeded by the absence of a satisfactory animal model. Because most baboon hematologic proteins immunologically cross-react with those used for human assays, we developed a robust, reusable baboon model of CPB. Blood samples were obtained from adult baboons at six time intervals before, during, and after 60 minutes of partial CPB at 37 degrees C with peripheral cannulas. Both membrane (n = 7) and bubble oxygenators (n = 7) were investigated. We measured platelet and white blood cell counts; platelet response to adenosine diphosphate and release of beta-thromboglobulin; fibrinopeptide A, prothrombin fragment F1.2, thrombin-antithrombin complex, D-dimer, and plasmin-antiplasmin complex; activated complement (C3b/c and C4b/c); elastase-alpha1 proteinase inhibitor complex; and bleeding times. Adherent glycoprotein IIIa antigen in Triton X-100 washes of the perfusion circuit was also measured. Markers of baboon platelet, complement, and neutrophil activation and thrombosis significantly increased during CPB with bubble oxygenator systems but did not change appreciably in membrane oxygenator circuits. Markers of fibrinolysis, D-dimer, and plasmin-antiplasmin complex did not change with either oxygenator. The baboon model of CPB, when a bubble oxygenator is used, is a robust, reusable animal model for evaluating inhibitors of platelet, complement, and neutrophil activation and thrombosis during and after CPB.