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.     

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.     

Leukocytes Can Enhance Platelet-mediated Aggregation and Thromboxane Release via Interaction of P-selectin Glycoprotein Ligand 1 with P-selectin

Background: Platelet-leukocyte conjugates have been observed in patients with unstable coronary syndromes and after cardiopulmonary bypass. In vitro, the binding of platelet P-selectin to leukocyte P-selectin glycoprotein ligand-1 (PSGL1) mediates conjugate formation; however, the hemostatic implications of these cell-cell interactions are unknown. The aims of this study were to determine the ability of leukocytes to modulate platelet agonist-induced aggregation and secretion in the blood milieu, and to investigate the role of P-selectin and PSGL-1 in mediating these responses.

Methods: Blood was drawn from healthy volunteers for in vitro analysis of platelet agonist-induced aggregation, secretion (adenosine triphosphate, [beta]-thromboglobulin, and thromboxane), and platelet-leukocyte conjugate formation. Experiments were performed on live cells in whole blood or plasma to simulate physiologic conditions. Whole-blood impedance and optical aggregometry, flow cytometry, and enzyme-linked immunosorbent assays were performed in the presence and absence of blocking antibodies to P-selectin and PSGL1. The platelet-specific agonists, thrombin receptor activating peptide and adenosine diphosphate, were used to elicit platelet activation responses.

Results: Inhibition of platelet-leukocyte adherence by P- selectin and PSGL1 antibodies decreased agonist-induced aggregation in whole blood. The presence of leukocytes in platelet-rich plasma increased aggregation, and this increase was attenuated by P-selectin blocking antibodies. Data from flow cytometry confirmed that platelet-leukocyte conjugate formation contributed to aggregation responses. Blocking antibodies reduced platelet agonist-induced thromboxane release but had no impact on adenosine triphosphate and [beta]-thomboglobulin secretion.     

Prevention of heparin-induced thrombocytopenia during open heart surgery with iloprost (ZK36374)

Recurrent thrombocytopenia, thrombosis, or sudden death may develop in patients with heparin-induced thrombocytopenia who are reexposed to heparin. Three patients came to us in whom a diagnosis of heparin-induced thrombocytopenia had been made on the basis of clinical and serologic evidence; these patients required reexposure to heparin because of urgent cardiac surgery. Therefore, we evaluated the ability of iloprost (ZK36374), a new analogue of prostacyclin, to prevent heparin-dependent activation of platelets and thereby permit obligatory heparinization for safe extracorporeal circulation. Before operation, we demonstrated that iloprost prevented both heparin-dependent platelet aggregation and tritiated (3H)-serotonin release in vitro. Therefore a continuous infusion of iloprost was begun 1 hour before heparinization and was continued throughout cardiopulmonary bypass and for an additional 15 minutes after protamine administration. The mean platelet count of 130,000/microliters before operation remained stable, and no spontaneous platelet aggregation was observed in samples of platelet-rich plasma obtained before cardiopulmonary bypass but after heparin administration. Similarly, after heparin administration but before bypass, platelet responsiveness to adenosine diphosphate remained unchanged when compared with preoperative values. Plasma levels of platelet factor 4 increased from 26 +/- 1 ng/ml (mean +/- standard error) to 843 +/- 383 ng/ml after heparin administration but actually decreased throughout cardiopulmonary bypass to 52 +/- 25 ng/ml. Beta-thromboglobulin levels increased from 103 +/- 16 to 244 +/- 94 ng/ml with heparinization. The mean bleeding time was 10.5 minutes preoperatively and 13.3 minutes postoperatively. The mean amount of postoperative chest tube drainage (duration: 12 hours) was 432 +/- 67 ml. Thus, despite the confirmed presence of heparin-dependent platelet-activating factor in the plasma of these three patients, iloprost prevented heparin-induced platelet activation during cardiopulmonary bypass while preserving platelet function, as would be desired for postoperative hemostasis.     

Modulation of platelet surface adhesion receptors during cardiopulmonary bypass.

Alterations in platelet receptors critical to adhesion may play a role in the pathogenesis of the qualitative platelet defect associated with cardiopulmonary bypass. Using flow cytometry, we measured changes in the following platelet surface adhesive proteins: the von Willebrand factor receptor, glycoprotein Ib; the fibrinogen receptor, glycoprotein IIb/IIIa; the thrombospondin receptor, glycoprotein IV; the adhesive glycoprotein granule membrane protein 140, whose expression also reflects platelet activation and alpha-granule release; and, as a control, the nonreceptor protein HLA, A,B,C. Glycoprotein Ib decreased during cardiopulmonary bypass (P less than 0.05) and reached a nadir at 72% (P less than 0.05) of its baseline value at 2-4 h after bypass. This decrease correlated (r = 0.76) with the magnitude of platelet activation (alpha-granule release) in any given patient, but even platelets that were not activated demonstrated a decrease in glycoprotein Ib expression. Glycoprotein IIb/IIIa also decreased in both the activated (47% of baseline, P less than 0.01) and unactivated (63% of baseline, P less than 0.01) subsets of platelets at the end of cardiopulmonary bypass. Glycoprotein IV and HLA A,B,C did not decrease, but instead increased 2-4 h after cardiopulmonary bypass (P less than 0.05). We conclude that cardiopulmonary bypass produces selective decreases in surface glycoproteins Ib and IIb/IIIa as well as in platelet activation; that these two alterations are temporally but not necessarily mechanistically linked; and that these changes have the potential to adversely affect platelet function.     

Leukocytes can enhance platelet-mediated aggregation and thromboxane release via interaction of P-selectin glycoprotein ligand 1 with P-selectin

BACKGROUND: Platelet--leukocyte conjugates have been observed in patients with unstable coronary syndromes and after cardiopulmonary bypass. In vitro, the binding of platelet P-selectin to leukocyte P-selectin glycoprotein ligand-1 (PSGL1) mediates conjugate formation; however, the hemostatic implications of these cell--cell interactions are unknown. The aims of this study were to determine the ability of leukocytes to modulate platelet agonist--induced aggregation and secretion in the blood milieu, and to investigate the role of P-selectin and PSGL-1 in mediating these responses. METHODS: Blood was drawn from healthy volunteers for in vitro analysis of platelet agonist--induced aggregation, secretion (adenosine triphosphate, beta-thromboglobulin, and thromboxane), and platelet-leukocyte conjugate formation. Experiments were performed on live cells in whole blood or plasma to simulate physiologic conditions. Whole-blood impedance and optical aggregometry, flow cytometry, and enzyme-linked immunosorbent assays were performed in the presence and absence of blocking antibodies to P-selectin and PSGL1. The platelet-specific agonists, thrombin receptor activating peptide and adenosine diphosphate, were used to elicit platelet activation responses. RESULTS: Inhibition of platelet--leukocyte adherence by P- selectin and PSGL1 antibodies decreased agonist--induced aggregation in whole blood. The presence of leukocytes in platelet-rich plasma increased aggregation, and this increase was attenuated by P-selectin blocking antibodies. Data from flow cytometry confirmed that platelet-leukocyte conjugate formation contributed to aggregation responses. Blocking antibodies reduced platelet agonist--induced thromboxane release but had no impact on adenosine triphosphate and beta-thomboglobulin secretion. CONCLUSIONS: Leukocytes can enhance platelet agonist--induced aggregation and thromboxane release in whole blood and platelet-rich plasma under shear conditions in vitro. Interaction of platelet P-selectin with leukocyte PSGL1 contributes substantially to these effects.     

The effects of aprotonin on platelets in vitro using whole blood flow cytometry

We sought to evaluate the effects of aprotinin on the number and function of the platelet glycoprotein (GP) IIb-IIIa receptor and on the expression of P-selectin in vitro in order to gain insight into the potential mechanisms involved in the platelet-protective action of aprotinin during cardiopulmonary bypass. Aprotinin at 50 to 200 kallikrein inhibiting units/mL decreased the expression of activated GP IIb-IIIa complex in response to adenosine diphosphate or thrombin receptor activator peptide 6 in a dose-dependent manner in both citrated and heparinized whole blood experiments. Aprotinin inhibited adenosine diphosphate-induced platelet aggregation, but it exhibited no effect on the expression of GP IIIa and P-selectin. These results indicate that aprotinin interferes with the platelet fibrinogen receptor function during pharmacological activation. Reduced aggregability and platelet adhesion to fibrinogen adsorbed to synthetic surfaces in the presence of aprotinin may prevent platelet consumption during clinical cardiopulmonary bypass. This in vitro study demonstrates that aprotinin decreases the agonist-induced expression of activated GP IIb-IIIa receptors that play a major role in platelet aggregation and adhesion to biomaterial surfaces. IMPLICATIONS: This in vitro study demonstrates that aprotinin decreases the agonist-induced expression of activated glycoprotein IIb-IIIa receptors that play a major role in platelet aggregation and adhesion to biomaterial surfaces.     

The effect of intravenously administered magnesium on platelet function in patients after cardiac surgery.

After cardiac surgery, magnesium is often administered for prophylaxis and treatment of cardiac arrhythmias. Magnesium, however, inhibits platelet function in vitro and in healthy volunteers. We performed a randomized, blinded, and placebo-controlled study to investigate the effect of magnesium on platelet function in patients after cardiac surgery. We studied patients who underwent uneventful coronary revascularization with cardiopulmonary bypass on the first postoperative day. Before and after an infusion of either 5.4 mmol magnesium (n = 19) or saline (n = 20), platelet function was investigated by means of in vitro bleeding time, platelet aggregation, and flow-cytometric assays. In addition, to investigate platelet function in vitro, 1, 5, and 10 mM magnesium were added to platelet-rich plasma before and 24 h after surgery in 30 patients. Compared with the control group, magnesium prolonged the in vitro bleeding time (22%) and inhibited ADP- and collagen-induced platelet aggregation (13% and 17%), platelet P-selectin expression (18%), and the binding of fibrinogen to the platelet glycoprotein IIb/IIIa receptor (10%). Magnesium also led to significant dose-dependent inhibition of platelet aggregation (19%), P-selectin expression (14%), and fibrinogen binding (11%) before and after surgery in vitro. Although the antithrombotic effect of magnesium may be beneficial in patients after coronary revascularization, large-dose magnesium therapy should be carefully considered in patients with impaired platelet function and co-existing bleeding disorders. IMPLICATIONS: In a randomized, blinded, placebo-controlled study of patients 24 h after coronary artery bypass grafting, IV administered magnesium inhibited platelet function in vitro and in vivo.     

Cardiopulmonary bypass in a patient with heparin-induced thrombocytopenia II and impaired renal function using heparin and the platelet GP IIb/IIIa inhibitor tirofiban as anticoagulant

In a patient with heparin-induced thrombocytopenia II and impaired renal function, anticoagulation during cardiopulmonary bypass was successfully performed by the use of unfractionated heparin and the platelet glycoprotein IIb/IIIa inhibitor tirofiban. Postoperative antithrombotic therapy with recombinant hirudin was immediately initiated. This regimen for anticoagulation for cardiopulmonary bypass in patients with heparin-induced thrombocytopenia II appears to be particularly appropriate for patients with impaired renal function or for hospitals without special experience with other alternative anticoagulation strategies.     

The effect of nitric oxide on platelets when delivered to the cardiopulmonary bypass circuit

Nitric oxide (NO) decreases platelet adhesion to foreign surfaces in the in vitro models of cardiopulmonary bypass (CPB). We hypothesized that NO, delivered into the membrane oxygenator (MO), would exert a platelet-sparing effect after CPB. Forty-seven patients scheduled for coronary artery surgery were randomized to either a NO group, in which NO (100 ppm) was delivered into the MO, or a control group, in which CPB was conducted without NO. Platelet numbers, platelet aggregation response to 2.5-20 microM adenosine diphosphate, and beta-thromboglobulin levels were measured after induction of anesthesia, after 1 h on CPB and 2 h after the end of CPB. Met-hemoglobin levels were measured during CPB. The amount of blood products administered and chest tube drainage were measured in the first postoperative 18 h. NO delivered into the MO for up to 180 min did not increase met-hemoglobin levels above 4%. NO inhibited the platelet aggregation response to 2.5 microM ADP during CPB, otherwise NO had no other detectable effect on the aggregation responses or the levels of beta-thromboglobulin. Platelet numbers were not significantly altered by NO. NO did not alter the use of blood products or chest tube drainage. In conclusion, this study suggests that NO delivered into the MO of the CPB circuit does not significantly alter platelet aggregation and numbers, and does not affect bleeding. IMPLICATIONS: Nitric oxide affects platelet function. We demonstrated that nitric oxide delivered into the gas inflow of the cardiopulmonary bypass circuit membrane oxygenator does not significantly alter platelet numbers or function.     

Aprotinin administration in the pericardial cavity does not prevent platelet activation

OBJECTIVES: Aprotinin is frequently administered systemically to patients undergoing cardiopulmonary bypass to inhibit activation of platelets and plasma protein systems and thus reduce postoperative blood loss. Two reports on local aprotinin administration, that is, into the pericardial cavity, also indicated improvement in postoperative blood loss, but the underlying mechanism was not investigated. We previously reported the disappearance of glycoprotein Ib from the platelet surface and the appearance of platelet-derived microparticles in the pericardial cavity of patients undergoing cardiopulmonary bypass as signs of platelet activation. Here, we investigated whether such local aprotinin administration reduced platelet activation. METHODS: In a double-blind study, 6 patients received aprotinin (500,000 KIU) into the pericardial cavity during the operation and 7 patients received a placebo. Platelet surface glycoprotein Ib expression, concentration of microparticles, and concentration of complexes of platelets with leukocytes, erythrocytes, or each other, were measured by flow cytometry. RESULTS: We confirmed the reduced glycoprotein Ib expression and the increased concentration of microparticles in the pericardial cavity, as previously reported, and found no increased concentration of platelet complexes. However, no differences between aprotinin and placebo treatments were observed in these platelet activation parameters in the pericardial cavity or the systemic circulation. CONCLUSION: We conclude that administration of aprotinin into the pericardial cavity during cardiopulmonary bypass and at concentrations similar to the systemic application does not reduce platelet activation in that compartment or the systemic circulation.     

Profound drug-induced thrombocytopenia before urgent cardiopulmonary bypass

A patient with acute coronary syndrome scheduled for urgent coronary artery bypass grafting developed a profound thrombocytopenia during therapy with intravenous heparin and the glycoprotein IIb/IIIa inhibitor tirofiban. Heparin-induced thrombocytopenia and all other possible aetiologies were unlikely and the low platelet count had to be attributed to tirofiban. Anticoagulation during cardiopulmonary bypass was successfully managed with standard heparin. Implications for the diagnosis of coagulation disorders and the management of perioperative anticoagulation are discussed.     

Efficacy of FK633, an ultra-short acting glycoprotein IIb/IIIa antagonist on platelet preservation during and after cardiopulmonary bypass.

OBJECTIVE: Temporary pharmacologic inhibition of platelet function during and after cardiopulmonary bypass (CPB) (platelet anesthesia) is an attractive strategy for preserving platelets during CPB. We examined the efficacy of FK633, an ultra-short acting glycoprotein IIb/IIIa antagonist. METHODS: The study was carried out in six mongrel dogs that received an intravenous bolus of 0.1 mg/kg of FK633 at the time of administration of heparin (group F), and six control dogs (group C). All animals underwent 60 min of normothermic CPB followed by a 2-h observation period. Blood samples for platelet count, platelet aggregation to adenosine diphosphate and parameters concerning the coagulation system were obtained at eight time points. Hemodynamics, bleeding time, and postoperative blood loss were assessed serially. Scanning electron micrograph of the oxygenator's membrane was investigated. RESULTS: FK633 significantly protected platelet number (group F, 59+/-10% versus group C, 38+/-15% of the pre-CPB value; P < 0.01), and inhibited platelet aggregation to adenosine diphosphate (group F, 13+/-12% versus group C, 35+/-9% of the pre-CPB value; P < 0.01) during CPB. Postoperative blood loss did not significantly differ between the two groups, but there was a tendency of less bleeding in group F (group F, 73+/-23 ml versus group C, 111+/-44 ml; P = 0.09). In group F, scanning electron micrograph of the oxygenator's membrane showed that its surface was free from platelets. There were no significant differences between the groups in hemodynamics. CONCLUSIONS: An ultra-short acting glycoprotein IIb/IIIa antagonist, FK633, is effective in preventing both platelet aggregation and thrombocytopenia during CPB, and may be effective for minimizing postoperative bleeding.     

Efficacy of iloprost (ZK36374) versus aspirin in preventing heparin-induced platelet activation during cardiac operations

For patients with heparin-induced platelet activation, reexposure to heparin can result in profound thrombocytopenia, intravascular thrombosis, and hemorrhage. We compared the ability of aspirin to that of iloprost (ZK36374), an analogue of prostacyclin, in preventing heparin-induced platelet activation and thus permitting a cardiac operation in a patient with heparin-induced platelet activation. Despite abolishing thromboxane A2 synthesis, aspirin (4 mmol/L) failed to prevent either in vitro heparin-induced platelet aggregation (65.0% without versus 59% with aspirin) or carbon 14-serotonin release (81.8% without versus 59.7% with aspirin). In contrast, iloprost (0.01 mumol/L) prevented both in vitro heparin-induced platelet aggregation (65% without versus 5.0% with iloprost) and release (81.8% without versus 0% with iloprost). Consequently, a continuous infusion of iloprost was begun before administration of heparin, continued throughout cardiopulmonary bypass, and discontinued 15 minutes after administration of protamine. The whole blood platelet count (209,000/microliter) remained stable after intraoperative administration of heparin (238,000/microliter) and was 115,000/microliter after the operation. No spontaneous platelet aggregates were observed in samples of platelet-rich plasma after heparin administration, and no platelet transfusions were required. Plasma levels of platelet factor 4 rose from 27 to 725 ng/ml after heparin administration but then declined during bypass to 50 ng/ml. Beta thromboglobulin levels only rose from 92 to 496 ng/ml with administration of heparin. Fibrinopeptide A levels fell from 72 to 22 ng/ml after heparin and remained stable throughout bypass. The template bleeding time was 7.5 minutes preoperatively and 8.0 minutes postoperatively. The postoperative chest tube drainage (12 hours) was 475 ml, and platelets responded normally to adenosine diphosphate. In conclusion, iloprost but not aspirin completely prevented heparin-induced platelet activation in vitro. Furthermore, iloprost effectively prevented this syndrome clinically, which permitted a safe cardiac operation in this patient with heparin-induced platelet activation.     

Supplemental nitric oxide and its effect on myocardial injury and function in patients undergoing cardiac surgery with extracorporeal circulation

BACKGROUND: Cardiopulmonary bypass induces a systemic inflammatory response that may contribute to clinical morbidity. Gaseous nitric oxide at relatively low concentrations may elicit peripheral anti-inflammatory effects in addition to a reduction of pulmonary resistances. We examined the effects of 20 ppm of inhaled nitric oxide administered for 8 hours during and after cardiopulmonary bypass. METHODS AND RESULTS: Twenty-nine consecutive patients undergoing aortic valve replacement combined with aortocoronary bypass were randomly allocated to either 20 ppm of inhaled nitric oxide (n = 14) or no additional inhalatory treatment (n = 15). Blood samples for total creatine kinase, creatine kinase MB fraction, and troponin I measurements were collected at 4, 12, 24, and 48 hours postsurgery. In addition, we collected perioperative blood samples for measurements of circulating nitric oxide by-products and brain natriuretic peptide. Soluble P-selectin was analyzed in blood samples withdrawn from the coronary sinus before and after aortic clamping. The area under the curve of creatine kinase MB fraction (P =.03), total creatine kinase (P =.04), and troponin I (P =.04) levels were significantly decreased in the nitric oxide-treated patients. Moreover, in the same group we observed blunted P-selectin and brain natriuretic peptide release (P =.01 and P =.02, respectively). Nitric oxide inhalation consistently enhanced nitric oxide metabolite levels (P =.01). CONCLUSIONS: Nitric oxide, when administered as a gas at low concentration, is able to blunt the release of markers of myocardial injury and to antagonize the left ventricular subclinical dysfunction during and immediately after cardiopulmonary bypass. The organ protection could be mediated, at least in part, by its anti-inflammatory properties.     

Human neutrophil cathepsin G is a potent platelet activator

Purpose: Neutrophil activation has been implicated in the pathophysiologic condition of ischemia-reperfusion injury, the formation of arterial aneurysms, the progression of myocardial ischemia, and the initiation of deep venous thrombosis. Activated neutrophils release cathepsin G, a serine protease, from their granules, which may cause platelet activation that leads to intravascular thrombosis, tissue infarction, and systemic release of the thrombogenic products of platelet granules. This study used flow cytometry to quantify the extent of cathepsin G–induced platelet activation and degranulation through changes in the expression of platelet surface glycoproteins.Methods: Increasing concentrations of human neutrophil–derived cathepsin G were incubated with washed platelets or whole blood from healthy human donors. The platelet surface expression of glycoproteins, including P-selectin, a platelet membrane glycoprotein only expressed after platelet alpha granule release, were determined by quantifying the platelet binding of a panel of fluorescently labeled monoclonal antibodies. Results were compared with the effect of a maximal dose of thrombin, the most potent known platelet activator.Results: In a washed platelet system, cathepsin G increased platelet surface expression of P-selectin (an activation-dependent neutrophil binding site), the glycoprotein IIb/IIIa complex (fibrinogen receptor), and glycoprotein IV (thrombospondin receptor), and decreased surface expression of glycoprotein Ib (von Willebrand factor receptor) to an extent comparable to maximal thrombin. However, these effects were not observed in a whole blood system. Further experiments revealed that preexposure to plasma completely inhibited cathepsin G–induced washed platelet activation and degranulation. Prostacyclin treatment of washed platelets markedly inhibited cathepsin G–induced platelet activation.Conclusions: Cathepsin G is a very potent platelet agonist and degranulator, comparable to maximal thrombin, which alters platelet surface glycoprotein expression for enhanced neutrophil binding and effective platelet aggregation. This study helps to elucidate a possible pathway through which neutrophils may directly activate platelets, leading to intravascular thrombosis, irreversible ischemia, and tissue death in cardiovascular disease states. Patients with diseased endothelium that is deficient in prostacyclin production may be particularly prone to the detrimental effects of neutrophil-derived cathepsin G platelet activation. (J VASC SURG 1994;19:306-19.)     

Anticoagulation during cardiopulmonary bypass in patients with heparin-induced thrombocytopenia type II and renal impairment using heparin and the platelet glycoprotein IIb-IIIa antagonist tirofiban

BACKGROUND: Patients with heparin-induced thrombocytopenia type II require an alternative to standard heparin anticoagulation. However, in patients with renal impairment, anticoagulation during cardiopulmonary bypass with agents such as danaparoid sodium or r-hirudin are associated with hemorrhage. Anticoagulation with unfractionated heparins combined with prostacyclin, a potent platelet aggregation inhibitor, is associated with severe hypotension. The authors investigated a new concept using unfractionated heparins after platelet inhibition with the short-acting platelet glycoprotein IIb-IIIa antagonist tirofiban. METHODS: Ten patients with heparin-induced thrombocytopenia type II and renal impairment were enrolled in the investigation. All had heparin-induced thrombocytopenia type II antibodies present as proved by the heparin-induced platelet aggregation assay, the heparin-platelet factor 4 enzyme-linked immunosorbent assay, or both. In all patients, preoperative anticoagulation to an activated partial thromboplastin time of 40-60 s was performed with r-hirudin. Anticoagulation during cardiopulmonary bypass was achieved with a bolus of 400 IU/kg unfractionated heparins after a bolus of tirofiban 10 microg/kg followed by an infusion of tirofiban at a rate of 0.15 microg x kg(-1) x min(-1) until 1 h before conclusion of cardiopulmonary bypass. Additional unfractionated heparins were only administered if activated clotting time decreased below 480 s. Coagulation was monitored by a abciximab-modified TEG and the adenosine diphosphate-stimulated (20 microm) platelet aggregometry. D-dimer concentrations, as a marker of venous thromboembolism, were measured before and 12, 24, and 48 h after surgery. Postoperative antithrombotic therapy was started immediately with r-hirudin to anticoagulation to an activated partial thromboplastin time of 40-60 s. RESULTS: The postoperative blood loss ranged from 110 to 520 ml. No patient needed reexploration. In no patient was there clinical evidence of thrombosis or embolism in the postoperative period or of a critical increase of the D-dimer concentrations, suggesting venous thromboembolism. Transfusion of platelets was necessary in only two patients. CONCLUSIONS: The protocol is easy to perform and no increased postoperative bleeding and no thromboembolic complications occurred. The combination of unfractionated heparins and tirofiban may be an alternative to other anticoagulation strategies in patients with heparin-induced thrombocytopenia.     

Anticoagulation during Cardiopulmonary Bypass in Patients with Heparin-induced Thrombocytopenia Type II and Renal Impairment Using Heparin and the Platelet Glycoprotein IIb-IIIa Antagonist Tirofiban

Background: Patients with heparin-induced thrombocytopenia type II require an alternative to standard heparin anticoagulation. However, in patients with renal impairment, anticoagulation during cardiopulmonary bypass with agents such as danaparoid sodium or r-hirudin are associated with hemorrhage. Anticoagulation with unfractionated heparins combined with prostacyclin, a potent platelet aggregation inhibitor, is associated with severe hypotension. The authors investigated a new concept using unfractionated heparins after platelet inhibition with the short-acting platelet glycoprotein IIb-IIIa antagonist tirofiban.

Methods: Ten patients with heparin-induced thrombocytopenia type II and renal impairment were enrolled in the investigation. All had heparin-induced thrombocytopenia type II antibodies present as proved by the heparin-induced platelet aggregation assay, the heparin-platelet factor 4 enzyme-linked immunosorbent assay, or both. In all patients, preoperative anticoagulation to an activated partial thromboplastin time of 40-60 s was performed with r-hirudin. Anticoagulation during cardiopulmonary bypass was achieved with a bolus of 400 IU/kg unfractionated heparins after a bolus of tirofiban 10 [mu]g/kg followed by an infusion of tirofiban at a rate of 0.15 [mu]g [middle dot] kg-1 [middle dot] min-1 until 1 h before conclusion of cardiopulmonary bypass. Additional unfractionated heparins were only administered if activated clotting time decreased below 480 s. Coagulation was monitored by a abciximab-modified TEG(R) and the adenosine diphosphate-stimulated (20 [mu]m) platelet aggregometry. D-dimer concentrations, as a marker of venous thromboembolism, were measured before and 12, 24, and 48 h after surgery. Postoperative antithrombotic therapy was started immediately with r-hirudin to anticoagulation to an activated partial thromboplastin time of 40-60 s.

Results: The postoperative blood loss ranged from 110 to 520 ml. No patient needed reexploration. In no patient was there clinical evidence of thrombosis or embolism in the postoperative period or of a critical increase of the D-dimer concentrations, suggesting venous thromboembolism. Transfusion of platelets was necessary in only two patients.     

Perioperative management of a heterozygous carrier of Glanzmann's thrombasthenia submitted to coronary artery bypass grafting with cardiopulmonary bypass

Glanzmann's thrombasthenia is a congenital hemorrhagic disorder transmitted as an autosomal recessive trait and characterized by altered production and/or assembly of the platelet membrane glycoprotein IIb/IIIa receptor. We describe the perioperative management of a heterozygous carrier of Glanzmann's thrombasthenia submitted to cardiac surgery with cardiopulmonary bypass and the case was complicated by early excessive postoperative bleeding.     

Platelet-activated clotting time does not measure platelet reactivity during cardiac surgery.

BACKGROUND: Platelet dysfunction is a major contributor to bleeding after cardiopulmonary bypass (CPB), yet it remains difficult to diagnose. A point-of-care monitor, the platelet-activated clotting time (PACT), measures accelerated shortening of the kaolin-activated clotting time by addition of platelet activating factor. The authors sought to evaluate the clinical utility of the PACT by conducting serial measurements of PACT during cardiac surgery and correlating postoperative measurements with blood loss. METHODS: In 50 cardiac surgical patients, blood was sampled at 10 time points to measure PACT. Simultaneously, platelet reactivity was measured by the thrombin receptor agonist peptide-induced expression of P-selectin, using flow cytometry. These tests were temporally analyzed. PACT values, P-selectin expression, and other coagulation tests were analyzed for correlation with postoperative chest tube drainage. RESULTS: PACT and P-selectin expression were maximally reduced after protamine administration. Changes in PACT did not correlate with changes in P-selectin expression at any time interval. Total 8-h chest tube drainage did not correlate with any coagulation test at any time point except with P-selectin expression after protamine administration (r = -0.4; P = 0.03). CONCLUSIONS: The platelet dysfunction associated with CPB may be a result of depressed platelet reactivity, as shown by thrombin receptor activating peptide-induced P-selectin expression. Changes in PACT did not correlate with blood loss or with changes in P-selectin expression suggesting that PACT is not a specific measure of platelet reactivity.