Intraoperative management of patients with heparin-induced thrombocytopenia

Prostacyclins in Cardiac Surgery: Coming of Age

Prostacyclin (prostaglandin I2 [PGI2]) is an eicosanoid lipid mediator produced by the endothelial cells. It plays pivotal roles in vascular homeostasis by virtue of its potent vasodilatory and antithrombotic effects. Stable pharmacological analogues of PGI2 are used for treatment of pulmonary hypertension and right ventricular failure. PGI2 dose dependently inhibits platelet activation induced by adenosine-5′-diphosphate, arachidonic acid, collagen, and low-dose thrombin. This property has led to its use as an alternative to direct thrombin inhibitors in patients with type II heparin-induced thrombocytopenia (HIT) undergoing cardiac surgery. The aims of this review are the following: (1) to review the pharmacology of PGI2 and its derivatives, (2) to present the evidence for their use in pulmonary hypertension and right heart failure, and (3) to discuss their utility in the management of HIT in cardiac surgery.

Management of Heparin-Induced Thrombocytopenia and Heparin-Induced Thrombocytopenia and Thrombosis Syndrome

Summary: Heparin-induced thrombocytopenia (HIT) is an immune mediated response to heparin in which antibody driven thrombosis can have a dramatic life-threatening expression. There is much interest on this subject including studies on the pathophysiologic mechanism, the clinical managements of the initial stages of HIT versus the HIT-positive patient requiring continued anticoagulation versus the HIT patient with thrombosis, the pros and cons of available alterr~aci~~ anticoagulants, and the laboratory assays to aid in the diagnosis of HIT with particular reference to the sensitivity/specificity of the new heparin-platelet factor 4 antibody titer assay. A comprehensive account of these timely issues is given in this article.

New Anticoagulants for the Cardiovascular Patient

Manuscript received May 9, 1994; accepted July 7, 1994. Address correspondence and reprint requests to Dr. Jeanine M. Walenga, Department of Pathology, Loyola University Med ical Center, 2160 South First Avenue, Maywood, IL 60153, U.S.A. Summary: Invasive cardiac procedures and cardiac sur gery, which have become a significant component of health care, provide a particular case scenario where there are special considerations given to control bleeding and to have available alternative anticoagulants for pa tients unable to tolerate heparin (e.g., heparin-induced thrombocytopenia). We describe a comprehensive proto col for blood preservation in cardiac surgery incorporat ing the patient's medical history, autologous transfusions, and intraoperative techniques of heparin and protamine titration and dosing. Furthermore, various new anticoag ulants under clinical development are discussed, particu larly hirudin, hirulog, iloprost, ancrod, Lomoparan, low- molecular-weight heparins, 1-deamino-8-D-arginine- vasopressin (DDAVP), and aprotinin. These approaches should benefit the patient with difficult to control periop erative bleeding, heparin-induced thrombocytopenia, al lergic reactions to protamine, platelet dysfunction, and poor response to heparin (e.g., due to antithrombin III deficiency).

Perioperative use of iloprost in cardiac surgery patients diagnosed with heparin-induced thrombocytopenia-reactive antibodies or with true HIT (HIT-reactive antibodies plus thrombocytopenia): An 11-year experience

Thrombocytopenia and thromboembolism(s) may develop in heparin immune-mediated thrombocytopenia (HIT) patients after reexposure to heparin. At the Onassis Cardiac Surgery Center, 530 out of 17,000 patients requiring heart surgery over an 11-year period underwent preoperative HIT assessment by ELISA and a three-point heparin-induced platelet aggregation assay (HIPAG). The screening identified 110 patients with HIT-reactive antibodies, out of which 46 were also thrombocytopenic (true HIT). Cardiac surgery was performed in HIT-positive patients under heparin anticoagulation and iloprost infusion. A control group of 118 HIT-negative patients received heparin but no iloprost during surgery. For the first 20 patients, the dose of iloprost diminishing the HIPAG test to ≤5% was determined prior to surgery by in vitro titration using the patients' own plasma and donor platelets. In parallel, the iloprost "target dose" was also established for each patient intraoperatively, but before heparin administration. Iloprost was infused initially at 3 ng/kg/mL and further adjusted intraoperatively, until ex vivo aggregation reached ≤5%. As a close correlation was observed between the "target dose" identified before surgery and that established intraoperatively, the remaining 90 patients were administered iloprost starting at the presurgery identified "target dose." This process significantly reduced the number of intraoperative HIPAG reassessments needed to determine the iloprost target dose, and reduced surgical time, while maintaining similar primary clinical outcomes to controls. Therefore, infusion of iloprost throughout surgery, under continuous titration, allows cardiac surgery to be undertaken safely using heparin, while avoiding life-threatening iloprost-induced hypotension in patients diagnosed with HIT-reactive antibodies or true HIT.

Heparin-induced thrombocytopenia

Heparin is widely used for the prevention and treatment of thrombotic and particularly cardiovascular disorders. Unfortunately, 0.5 to 3.0% of patients given heparin develop an immune reaction, commonly termed Type II heparin-induced thrombocytopenia (HIT). This is characterized by a moderate thrombocytopenia and in some patients, a venous or arterial thrombosis. This frequently leads to disastrous sequelae, such as limb amputation and death. The pathophysiological basis of this serious adverse drug reaction is the production of an immunoglobulin G antibody that reacts with an antigenic complex consisting of heparin and platelet factor 4. A significant risk factor for the development of HIT is recent surgery, and the frequency of developing an antiheparin-platelet factor 4 or HIT antibody is particularly high in cardiac surgery patients, although surprisingly, only a few of these patients actually develop the clinical syndrome of HIT. This review will discuss the frequency, pathophysiology, clinical features, diagnosis and management of HIT.

Iloprost for additional anticoagulation in continuous renal replacement therapy--a pilot study

PURPOSE

The aim of this pilot study was to compare the effect of heparin anticoagulation with and without iloprost administration during continuous renal replacement therapy (CRRT) in critically ill patients.

MATERIAL AND METHODS

In a prospective, randomized, controlled pilot study at an intensive care unit at a university hospital, 20 patients requiring CRRT were investigated. Patients were allocated into two groups: group 1, the heparin group; and group 2, the heparin plus 1 ng/kg/min iloprost. In both groups, activated partial thromboplastin time (aPTT) was adjusted to 40-50 sec. Observation time was a maximum of 7 days.

RESULTS

Median filter run time was significantly prolonged by iloprost administration to a median of 14 h (13-26 h) compared to 10 h (4-12 h) in the heparin group (p = 0.004). A decrease in platelet count was attenuated by iloprost administration (p = 0.012). There were no bleeding complications in either group. Hemofiltration efficiency did not differ significantly between the groups.

CONCLUSION

Additional administration of iloprost prolonged the filter run time of continuous veno-venous hemofiltration (CVVH) in this setting and attenuated the fall in platelet count during CRRT.

Delayed thrombin generation is not associated with fibrinopeptide formation during prolonged cardiopulmonary bypass with hirudin anticoagulation

Patients with heparin-induced thrombocytopenia urgently requiring surgery with cardiopulmonary bypass (CPB) present a unique management challenge that must be addressed by the use of alternative anticoagulants. Although clinical success with the direct thrombin inhibitor hirudin has been reported, there is sparse information in the literature supporting the efficacy of this drug as an anti-thrombotic to prevent fibrin formation during CPB. In this report, we describe the efficacy of this drug to prevent thrombin-mediated fibrin formation during CPB.

Unfractionated Heparin, Low Molecular Weight Heparins, and Pentasaccharide: Basic Mechanism of Actions, Pharmacology, and Clinical Use

During the past decade, a large number of new anticoagulant and antithrombotic drugs have been developed. These agents represent a wide variety of substances that are derived using natural sources, biotechnology-based methods, and synthetic approaches. Because of the structural and molecular characteristics, these agents exhibit physicochemical and functional diversities. Thus, each of these classes of drugs controls thrombogenesis by way of distinct mechanisms. The main classes of these new drugs include peptides, peptidomimetics, heparinomimetics, and recombinant proteins. Despite these significant developments, heparin and heparin-derived drugs have continued to play a major role in the management of thrombotic and cardiovascular disorders.

Delayed Thrombin Generation With Hirudin Anticoagulation During Prolonged Cardiopulmonary Bypass

Patients with heparin-induced thrombocytopenia requiring urgent cardiac surgery present a unique challenge that must be addressed by the use of nonheparin alternatives for anticoagulation during cardiopulmonary bypass. Although isolated cases have been presented involving the use of antithrombin III independent thrombin inhibitor hirudin in this situation, its ability to completely inhibit thrombin activity has not been demonstrated. In this report we describe the efficacy of this drug in inhibiting thrombin during a case requiring prolonged cardiopulmonary bypass.

Preoperative detection and management of immune heparin-induced thrombocytopenia in patients undergoing heart surgery with iloprost

OBJECTIVE

The objective of this study was to evaluate our protocol for the identification and management of patients with immune heparin-induced thrombocytopenia undergoing cardiac surgery.

METHODS

Among 1518 patients who underwent cardiac surgery between June 1998 and May 2001, 32 (2.1%) presented with platelet counts less than 150,000/mm3 preoperatively or a history of prolonged (>3 days) intravenous exposure to heparin or both. These 32 patients were evaluated with an enzyme-linked immunosorbent assay for antibodies against heparin-platelet factor 4 complex. Platelets of patients with detected antibodies were tested with the prostacyclin analog iloprost for inhibition of heparin aggregation and determination of the inhibiting concentration and corresponding intravenous infusion rate of iloprost. Patients with antibodies received heparin after complete platelet inhibition with iloprost infusion. Hypotension was prevented or treated with intravenous noradrenaline. Ten randomly selected patients with similar preoperative characteristics, no previous extended exposure to heparin, and normal platelet counts served as controls.

RESULTS

Ten of the 32 patients (group A, 31.3%) and none of the controls had antibodies against heparin-platelet factor 4 complex. Patients in group A underwent surgery with iloprost (6-24 ng.kg(-1).min(-1)) and had their blood pressure maintained at greater than 95 mm Hg with norepinephrine infusion (1-4 microg.kg(-1).min(-1)). Operative mortality was zero. There were no thrombotic complications or bleeding requiring exploration. One patient in group A bled 1310 mL/6 hours but did not need exploration. There was no difference in postoperative blood loss and morbidity between groups. Platelet counts were reduced by 12.5% +/- 8.7% (group A) and 38.1% +/- 15.2% (control) (P <.001) 1 hour postoperatively and reached preoperative values by the fifth postoperative day.

CONCLUSIONS

Immune heparin-induced thrombocytopenia can be detected preoperatively among patients with a low platelet count or a history of prolonged heparin exposure or both. Cardiac surgery can be safely undertaken using iloprost-induced platelet inhibition during heparinization.

[Heparin-induced thrombocytopenia. Pathogenesis, diagnosis and treatment]

INTRODUCTION

Heparin-induced thrombocytopenia is due to the development of IgG antibodies specific to platelet factor 4. More frequently observed after administration of unfractionated heparin, this complication is characterized by a delayed decrease in platelet count (after the 5th day of treatment) associated with venous and/or arterial thromboses.

CURRENT KNOWLEDGE AND KEY POINTS

It is often difficult to discard another potential cause for thrombocytopenia and to demonstrate by Elisa or platelet activation tests the presence of heparin-dependent antibodies is therefore mandatory in every patient. Withdrawal of heparin treatment is always necessary as well as the administration of an alternative antithrombotic agent. Danaparoid sodium (mixture of glycosaminoglycanes mainly with anti-Xa activity) or lepirudin (a recombinant hirudin with only antithrombin activity) are both recommended but these two drugs are associated with a significant risk of bleeding in case of renal failure. Oral anticoagulants such as coumadin can only be given when platelet count is normalized and if the clinical evolution is favorable. Potent antiplatelet agents (ilomedine or tirofiban) can be used in specific situations necessitating heparin such as extracorporeal circulation.

FUTURE PROSPECTS AND PROJECTS

Early administration of coumadin for the treatment of venous thromboembolic disease efficiently prevent the occurrence of heparin-induced thrombocytopenia, which could disappear in the future with a wider use of the new antithrombotic agents, fondaparinux and ximelagatran.

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.

Heparin-induced thrombocytopenia, paradoxical thromboembolism, and other adverse effects of heparin-type therapy

This article discusses the common and uncommon side effects of heparin and heparin-like therapy. Most attention is devoted to heparin-induced thrombocytopenia, as it is the most clinically aggressive adverse reaction. Additionally, less common and several newly reported side effects are discussed.

Use of plasma exchange and heparin during cardiopulmonary bypass for a patient with heparin induced thrombocytopenia: a case report

Patients with documented history of heparin-induced thrombocytopenia (HIT) pose a difficult problem during surgery using cardiopulmonary bypass (CPB). Several alternatives to heparin exist, but these products either are not approved for use in the United States or have more side effects than heparin. We report on a patient with documented heparin-induced antibody and left main coronary artery disease who underwent uneventful coronary artery bypass surgery and recovery by using preoperative plasmaphresis and limited use of porcine intestinal heparin during CPB.

[Extracorporeal circulation with danaparoid sodium for valve replacement in thrombocytopenia induced by type II heparin]

A type II heparin-induced thrombocytopenia (HIT) was diagnosed in a 64-year-old woman at day 20 of intravenous unfractionated heparin (UFH) therapy, given after myocardial infarction treated by angioplasty and intracoronary stent. The infarction was complicated by a mitral insufficiency that led to a mitral valve replacement. Cardiopulmonary bypass was successfully performed with sodium danaparoid (Orgaran), as an alternative to UFH, without thrombotic or haemorrhagic complications and the follow-up was uneventful.

The use of lepirudin for anticoagulation in patients with heparin-induced thrombocytopenia during major vascular surgery

The method of anticoagulation in patients undergoing major vascular surgery with a history of heparin-induced thrombocytopenia (HIT) is controversial. We present two cases in which a bolus only technique using recombinant hirudin (Lepirudin or Refludan) was used successfully in patients with HIT scheduled for vascular surgery.

Cardiac surgery with cardiopulmonary bypass in patients with type II heparin-induced thrombocytopenia

BACKGROUND

The use of cardiopulmonary bypass (CPB) in patients with a history of type II heparin-induced thrombocytopenia (HIT) may be associated with complications related to their anticoagulation management.

METHODS

Between January 1997 and December 1999, among 4,850 adults patients who underwent cardiac surgery in our institution, 10 patients presented with preoperative type II HIT. In 4 patients, anticoagulation during CPB was achieved with danaparoid sodium. In 6 other patients, heparin sodium was used after pretreatment with epoprostenol sodium.

RESULTS

No significant change in platelet count occurred in any patient. No intraoperative thrombotic complication was encountered. Total postoperative chest drainage ranged from 250 to 1,100 ml in patients pretreated with epoprostenol and 1,700 to 2,470 ml in patients who received danaparoid sodium during CPB (p < 0.05, Mann-Whitney U test).

CONCLUSIONS

During CPB, inhibition of platelet aggregation by prostacyclin may be a safe anticoagulation approach in patients with type II HIT.

Cardiopulmonary bypass in patients with heparin-induced thrombocytopenia and thrombosis

Heparin-induced thrombocytopenia and thrombosis (HITT) is an immunomediated disorder induced by the administration of heparin for therapeutic purposes. The presence of this condition in patients requiring full heparinization for cardiopulmonary bypass constitutes a formidable challenge for the cardiac surgeon. In this review, the clinical and experimental experience described in the literature are discussed in the perspective of the normal coagulation and the pathophysiology of HITT and in the light of a variety of old and new alternative anticoagulants.

Heparin-induced thrombocytopenia and thrombosis

Heparin remains the most commonly used parenteral medication in hospitalized patients. Heparin induced thrombocytopenia (HIT) and heparin induced thrombocytopenia with thrombosis syndrome or the white clot syndrome are important complications of heparin use. This article provides an in-depth review of the etiopathogenesis, clinical manifestations, diagnosis, and management options in patients with HIT. Clinical problems associated with HIT such as antiphospholipid antibody syndrome and venous gangrene are described. The management options of HIT patients during cardiac interventional procedures and coronary surgery as well as recent advances in therapeutic options are summarized.

Clinical aspects of heparin-induced thrombocytopenia and thrombosis and other side effects of heparin therapy

Heparin, first used to prevent the clotting of blood in vitro, has been clinically used to treat thrombosis for more than 50 years. Although several new anticoagulant drugs are in development, heparin remains the anticoagulant of choice to treat acute thrombotic episodes. The clinical effects of heparin are meritorious, but side effects do exist. Bleeding is the primary untoward effect of heparin. Major bleeding is of primary concern in patients receiving heparin therapy. However, additional important untoward effects of heparin therapy include heparin-induced thrombocytopenia, heparin-associated osteoporosis, eosinophilia, skin reactions, allergic reactions other than thrombocytopenia, alopecia, transaminasemia, hyperkalemia, hypoaldosteronism, and priapism. These side effects are relatively rare in a given individual, but given the extremely widespread use of heparin, some are quite common, particularly HITT and osteoporosis. Although reasonable incidences of many of these side effects can be "softly" deduced from current reports dealing with unfractionated heparin, at present the incidences of these side effects with newer low molecular weight heparins appear to be much less common. However, only longer experience will more clearly define the incidence of each side effect with low molecular weight preparations.

Heparin-induced thrombocytopenia: a ten-year retrospective

The past decade has seen many important advances in the pathogenesis, clinical and laboratory diagnosis, and management of heparin-induced thrombocytopenia (HIT), one of the most common immune-mediated adverse drug reactions. HIT is caused by IgG antibodies that recognize complexes of heparin and platelet factor 4, leading to platelet activation via platelet Fc gamma IIa receptors. Formation of procoagulant, platelet-derived microparticles, and, possibly, activation of endothelium generate thrombin in vivo. Thrombin generation helps to explain the strong association between HIT and thrombosis, including the newly recognized syndrome of warfarin-induced venous limb gangrene. This syndrome occurs when acquired protein C deficiency during warfarin treatment of HIT and deep venous thrombosis leads to the inability to regulate thrombin generation in the microvasculature. The central role of HIT antibodies in causing HIT, as well as refinements in laboratory assays to detect these antibodies, means that HIT should be considered a clinicopathologic syndrome. The diagnosis can be made confidently when one or more typical clinical events (most frequently, thrombocytopenia with or without thrombosis) occur in a patient with detectable HIT antibodies. The central role of thrombin generation in this syndrome provides a rationale for the use of anticoagulants that reduce thrombin generation (danaparoid) or inhibit thrombin (lepirudin).

Combined use of Orgaran and Reopro during coronary angioplasty in patients unable to receive heparin

Orgaran, a heparinoid, has been used successfully in patients with heparin-induced thrombocytopenia. We report three cases in which Orgaran was combined with the glycoprotein IIbIIa receptor antagonist Reopro during coronary angioplasty. Orgaran was given as a single intravenous bolus of 1500 anti-factor Xa units. No ischemic or hemorrhagic complications occurred during or following the procedure.

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.

Heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is a potentially serious complication of heparin therapy and is being encountered more frequently in patients with cardiovascular disease as use of anticoagulant therapy becomes more widespread. Our understanding of the pathophysiology of this immune-mediated condition has improved in recent years, with heparin-platelet factor 4 complex as the culprit antigen in most patients. New sensitive laboratory assays for the pathogenic antibody are now available and should permit an earlier, more reliable diagnosis, but their optimal application remains to be defined. For patients in whom HIT is diagnosed, immediate discontinuation of heparin infusions and elimination of heparin from all flushes and ports are mandatory. Further management of patients with HIT is problematic at present, as there are no readily available alternative anticoagulant agents in the United States with proven efficacy in acute coronary disease. The direct thrombin inhibitors appear to be the most promising alternatives to heparin, when continued use of heparin is contraindicated, and the results of several multicenter trials evaluating their application in patients with HIT are awaited.

Heparin-induced thrombocytopenia, paradoxical thromboembolism, and other side effects of heparin therapy

Although several new anticoagulant drugs are in development, heparin remains the drug of choice for most anticoagulation needs. The clinical effects of heparin are meritorious, but side effects do exist. Important untoward effects of heparin therapy including heparin-induced thrombocytopenia, heparin-associated osteoporosis, eosinophilia, skin reactions, allergic reactions other than thrombocytopenia and alopecia will be discussed in this article.

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.

Tirofiban provides "platelet anesthesia" during cardiopulmonary bypass in baboons

OBJECTIVE

Tirofiban (Aggrastat) is a reversible, nonpeptide inhibitor of platelet glycoprotein II/IIIa receptors. We tested the hypothesis that tirofiban preserves platelet number and function and shortens postoperative bleeding times in baboons after cardiopulmonary bypass.

METHODS

Four groups were studied: control, n = 12; low-dose tirofiban (0.1 microg/kg per minute), n = 7; high-dose tirofiban (0.3 microg/kg per minute), n = 7; and bolus tirofiban (15 microg/kg) followed by 0.1 microg/kg per minute during cardiopulmonary bypass, n = 7. After heparin, animals were perfused for 60 minutes at 50 ml/kg per minute and 37 degrees C with a bubble oxygenator, roller pump, and peripheral cannulation. Hemodynamics, platelet count, platelet aggregation to adenosine diphosphate, and release of beta-thromboglobulin were measured before tirofiban infusion, before heparin, after heparin before bypass, after 5 and 55 minutes of bypass, after protamine, and 60 minutes after protamine. Template bleeding times were measured at the same times except during cardiopulmonary bypass and 120 and 180 minutes after protamine administration. Platelet glycoprotein IIIa antigen was measured in Triton X-100 washes (Sigma Chemical Company) of the perfusion circuit after bypass.

RESULTS

High-dose tirofiban completely prevents platelet loss during cardiopulmonary bypass. beta-Thromboglobulin release and sensitivity to adenosine diphosphate are significantly less than control at the end of bypass in all tirofiban groups. Template bleeding times return to preoperative values in both the low- and high-dose tirofiban groups 180 minutes after protamine administration and are significantly less than control bleeding times at both 120 and 180 minutes after protamine. Surface glycoprotein IIIa antigen does not significantly differ between groups.

CONCLUSION

High-dose tirofiban completely preserves platelet number and improves platelet function during cardiopulmonary bypass in baboons and significantly accelerates restoration of normal template bleeding times after bypass.

The glycoprotein IIb/IIIa antagonist c7E3 inhibits platelet aggregation in the presence of heparin-associated antibodies

PURPOSE

Heparin-associated antibodies (HAAb), in the presence of heparin, can cause platelet activation and aggregation. The purpose of this study was to assess whether a platelet glycoprotein (GP) IIb/IIIa receptor antagonist, c7E3, would inhibit platelet aggregation in the presence of HAAb. If aggregation is inhibited by c7E3, enzyme-linked immunosorbent assays (ELISA) would be done to determine whether c7E3 interfered with the binding of heparin and the HAAb.

METHODS

HAAb-positive plasmas from 21 patients (determined by platelet aggregation assays) were studied. Normal donor platelet-rich plasmas (PRP) were incubated (1 minute) with either saline solution or 3 microg/ml of c7E3. Platelet-poor plasma from patients with HAAb and one of three sources of heparin (25 microl, 10 U/ml; porcine heparin, bovine heparin, and low molecular weight heparin [enoxaparin]) were added to the PRP mixture. Aggregation was determined using a platelet aggregometer by measuring time to aggregation, the slope of the aggregation curve, and the percent change in optical density.

RESULTS

Platelet aggregation occured in 100%, 100%, and 95% of the saline solution incubations exposed to porcine heparin, bovine heparin, and enoxaparin, respectively. Incubation with c7E3 caused 100% inhibition of platelet aggregation in plasma exposed to porcine heparin, bovine heparin, and enoxaparin. The optical density curves obtained from the ELISA, which were dependent on the binding of HAAb to heparin, were not significantly different when c7E3 was compared to buffer alone.

CONCLUSIONS

The GP IIb/IIIa receptor antagonist, c7E3, inhibits HAAb-induced platelet aggregation via a mechanism that does not appear to interfere with the binding between heparin and HAAb. Clinical trials are warranted to assess whether GP IIb/IIIa antagonists may allow patients with HAAb to safely receive heparin.

Cardiopulmonary bypass in patients with heparin-induced thrombocytopenia using Org 10172

BACKGROUND

In patients with heparin-induced thrombocytopenia undergoing cardiac operations, anticoagulation with heparin should be avoided. The low-molecular-weight glycosaminoglycan Orgaran has been used as an alternative, but the overall experience is limited.

METHODS

Two patients with heparin-induced thrombocytopenia underwent cardiopulmonary bypass using Orgaran for anticoagulation. A 30-year-old woman suffered from emboli to her brain through a secondary atrial septal defect, a 14-year-old boy from ischemia of his left leg due to recurrent embolism originating from the mitral valve. In both cases, cardiopulmonary bypass was performed in a routine manner, except for using low-dose Orgaran instead of heparin. Anticoagulation was monitored during cardiopulmonary bypass by measuring Orgaran plasma levels and activated clotting time.

RESULTS

No thromboembolic or bleeding complications occurred during and after atrial septal defect repair and mitral valve replacement, respectively. In the former case, thrombotic material from the inferior vena cava was removed during hypothermic circulatory arrest within the same procedure. Activated clotting time did not correlate with plasma levels of Orgaran.

CONCLUSIONS

Orgaran might be a useful alternative for anticoagulation during extracorporeal circulation. Adequate dosages and measurement of plasma levels are recommended for its use in cardiopulmonary bypass.

Lupus anticoagulant, heparin use, and thrombocytopenia in patients with chronic thromboembolic pulmonary hypertension: a preliminary report

PURPOSE

An increased occurrence of thrombotic events has been described in patients exhibiting a lupus anticoagulant (LA). In patients with chronic, major vessel thromboembolic pulmonary hypertension, not only has there been a relatively high frequency of the LA, but also an unexpected association with heparin-related thrombocytopenia. This retrospective report emphasizes the frequency of this association.

PATIENTS AND METHODS

We retrospectively reviewed the medical records of 216 patients admitted to the University of California, San Diego, Medical Center who were being considered for surgical correction of their chronic thromboembolic pulmonary hypertension. For each patient, the following information was sought: presence of an LA, variation in platelet numbers during the preoperative evaluation, and determination of whether an observed thrombocytopenia was related to heparin use.

RESULTS

An LA was found in 23 of the 216 patients (10.6%). Of the remaining patients, sufficient platelet data for comparison were available for 68 patients. These 68 patients constituted the control group. Within the LA group, platelet counts during the preoperative evaluation declined to 51.6% +/- 16.7% of baseline counts, a highly significant difference (P < 0.0001) compared with the non-LA control group, who underwent a comparable evaluation with similar heparin exposure. In addition, heparin-associated thrombocytopenia developed in 13 of the 23 LA patients (56.5%) and in none of the control patients. Heparin-induced arterial thrombosis was implicated as the cause of a myocardial infarction in 1 of the patients with heparin-associated thrombocytopenia.

CONCLUSIONS

In patients with chronic thromboembolic pulmonary hypertension, a high incidence of the LA and an accompanying association with heparin-related thrombocytopenia have been observed. Although further prospective studies of this relationship are needed, physicians should be alert to the possibility of thrombocytopenia when using heparin for patients exhibiting an LA.

State-of-the-Art Review: Optimal Anticoagulation in Cardiovascular Surgery

Despite current developments in anticoagulant drugs, unfractionated heparin has remained the drug of choice for anticoagulation during cardiopulmonary bypass surgical procedures. The use of heparin has been associated with problems. Heparin-induced thrombocytopenia, intra- and postoperative bleeding, heparin resistance, and heparin rebound after heparin neutralization are the major complications. The complexity of hemostatic control during cardiopulmonary bypass (CPB) must be emphasized. The protocol for anticoagulation during CPB has varied greatly from institution to institution. With the use of the activated clotting time (ACT) and the heparin analyzer, control of anticoagulation has become more uniform and neutralization of heparin with protamine more accurate. The preferred initial dose of heparin is controversial. It varies from 200 U/kg to 450 U/kg. In our institution the initial dose used is 200 U/kg. During cardiopulmonary bypass the ACT is maintained above 400 s. Several doses of 2,000-3,000 U of heparin are added to the oxygenator, if needed, to maintain that level. Monitoring anticoagulation with the ACT and the heparin analyzer has convinced us that the lower dose is safe and the higher dose unnecessary. Once CPB is discontinued, the dose of protamine for heparin reversal is calculated with the use of the Hepcon heparin analyzer. The total dose is divided into two: 75% is given once the lines have been removed, and the other 25% is administered once the blood from the oxygenator and the cell saver has been reinfused into the patient. With this method heparin rebound is prevented. The large surface of the extracorporeal circulation apparatus acts as a massive thrombotic stimulus. The early reactions that lead to activation of the contact system of plasma proteins, white cells, fibrinolysis, platelets, and complement are not inhibited because heparin acts near the end of the coagulation cascade. The consequences of these early reactions are potential bleeding, thrombotic complications, and inflammatory reactions associated with cardiopulmonary bypass. The introduction of aprotinin has decreased perioperative bleeding by inhibiting the inflammatory cascades associated with contact activation and by acting as an antifibrinolytic agent. Newly developed anticoagulants, such as r-hirudin, peptides, plasma-derived agents, and glycoprotein targeting drugs, may be useful as a adjunct to or replacement for heparin.

Blood anesthesia for cardiopulmonary bypass

Cardiopulmonary bypass (CPB) causes bleeding and thrombotic complications, fluid retention and temporary dysfunction of every organ system. This morbidity of CPB is primarily do to activation of blood proteins and cells by contact with nonendothelial cell surfaces of the wound and biomaterials of the extracorporeal perfusion circuit. CPB is not possible without heparin, yet heparin is not an ideal anticoagulant and does not prevent activation of at least five plasma protein systems and five blood cells. Stimulation of these blood elements produces over 25 vasoactive substances that alter vascular tone, capillary permeability, and cardiac myocyte contractility. In addition, CPB produces showers of microemboli that pass filters to obstruct arterioles and precapillaries to produce necrosis of widely dispersed, small groups of cells. Attempts to develop nonthrombogenic synthetic materials have failed; only the endothelial cell is nonthrombogenic and achieves this property by active metabolic processes. Although some biomaterials are less thrombogenic than others, all activate blood elements to initiate clotting and the body's defense reaction. The concept of "blood anesthesia" envisions the use of reversible inhibitors of key blood reactions to temporarily prevent activation of blood elements during CPB. If the initial reactions of blood with nonendothelial surfaces are blocked, production of many vasoactive substances and microemboli by CPB is suppressed. This conserves blood elements that are normally consumed during CPB and makes them available after the inhibitor is reversed. Effective, reversible inhibitors of platelets are entering clinical trials; reversible inhibitors of other key blood relations are being developed and tested at a rapid rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Iloprost and echistatin protect platelets during simulated extracorporeal circulation

Temporary, reversible inhibition of platelets during cardiopulmonary bypass is an attractive strategy to protect platelets and normalize postoperative bleeding times. Iloprost, an analogue of prostacyclin, and the disintegrins reversibly inhibit platelets by different mechanisms. We tested the hypothesis that reduced doses of iloprost and either echistatin, a natural disintegrin, or RO43-5054, a peptidomimetic, in combination provide better platelet protection than any drug alone during simulated extracorporeal circulation. Thirty-five recirculation studies using fresh, heparinized human blood in an extracorporeal perfusion circuit that contained a 0.45-m2 spiral coil membrane oxygenator were performed. Iloprost, but neither echistatin nor RO43-5054, increased platelet cyclic adenosine monophosphate. Combinations of iloprost and either fibrinogen receptor antagonist at reduced doses submaximally increased platelet cyclic adenosine monophosphate. Platelet adhesion and release of beta-thromboglobulin antigen was completely inhibited by combinations of the two classes of drugs, but only partially inhibited by each drug alone. Combinations of drugs also completely inhibited platelet aggregation to adenosine diphosphate; these platelets retained full sensitivity to adenosine diphosphate after 90 minutes of recirculation when drugs were removed by gel filtration. We conclude that combinations of iloprost and a fibrinogen receptor antagonist at doses that are unlikely to produce clinical side effects completely inhibit platelet activation and preserve platelet function during in vitro extracorporeal circulation.

Complications from heparin-induced thrombocytopenia in patients undergoing cardiopulmonary bypass

The purpose of this study was to evaluate retrospectively the incidence and severity of heparin-induced thrombocytopenia (HIT)-related complications in patients undergoing cardiopulmonary bypass. We reviewed the records of 1,500 consecutive patients who underwent cardiopulmonary bypass between August 1987 and December 1991 at Thomas Jefferson University Hospital. During this period of time, there were 1,155 coronary artery bypass graft operations (77 percent); 225 valve replacements and repairs, or both (15 percent); 60 combination coronary artery bypass graft or valve operations, or both (4 percent); and 60 miscellaneous procedures (4 percent). Although not all patients with postoperative complications were tested for the HIT antibody, 11 patients (0.75 percent) were diagnosed with HIT. There were 17 complications in these 5 men and 6 women including 6 cases of ischemic limbs which required amputation, 4 strokes, 2 instances of saphenous vein graft occlusion with resulting myocardial infarction, 2 cases of pulmonary emboli, 1 case of phlegmasia cerulea dolens, and 2 deaths. The complications occurred an average of 3.6 days postoperatively, with a range of occurrence of 1 to 11 days postoperatively. The mean nadir platelet count at the time of recognition was 123,000/mm3 (range 32,000 to 193,000/mm3) with 9 of 11 patients (81.8 percent) having counts greater than 100,000/mm3. There was, however, a mean percent decrease in the platelet count of 50 percent (range, 31 to 75 percent) from the time of first exposure to heparin to the time of recognition of HIT. In our patients, HIT was not related to the type, duration of treatment with or amount of heparin, or to pretreatment with aspirin.

Blood-surface interactions during cardiopulmonary bypass

The interaction between blood and the synthetic surfaces of the heart-lung machine activates plasma protein systems and blood cells to produce a host of vasoactive substances that mediate the "whole body inflammatory response" associated with cardiopulmonary bypass (CPB). Plasma proteins are instantaneously adsorbed onto nonendothelial surfaces; plasma factor XII is cleaved into two serine proteases; and platelets are activated to aggregate, adhere to adsorbed fibrinogen, and release granule contents. Activation of factor XII initiates coagulation by the intrinsic coagulation pathway and activates complement. Complement stimulates neutrophils to release vasoactive and cytotoxic substances. Endothelial cells, perhaps stimulated by formation of minute quantities of thrombin, produce tissue plasminogen activator, which generates plasmin, a fibrolytic enzyme. Blood becomes a stew of powerful enzymes and chemicals that alters vascular smooth muscle and endothelial cell contraction. Capillary permeability increases, fluid is retained, and function of essentially every organ is temporarily impaired. Attempts to control the morbidity of CPB have focused on reversible inhibitors of specific reactions in blood. Prostanoids and new disintegrins are promising platelet inhibitors that are reversible. Aprotinin and other serine protease inhibitors partially control fibrinolysis and activation of neutrophils. Alternatives to heparin also show promise. Eventually control of the interaction of blood and synthetic surfaces will control the adverse reactions of the heart-lung machine and reduce the bleeding, thrombotic and inflammatory complications of open heart operations.

Dipyridamole in the Management of Severe Heparin-associated Thrombocytopenia

Severe heparin-associated thrombocytopenia (SHAT) is a rare, life-threatening condition. The aim of this prospective pilot study was to determine the safety and efficacy of dipyridamole-heparin infusion (DHI) in the management of the condition. We studied 6 patients (4 males and 2 females) aged 28 to 80 years (mean 50.5±14.2) with deep venous thrombosis and/or pulmonary embolism who developed SHAT a few days following heparin therapy. Heparin-dependent platelet aggregating factor was demonstrated ex vivo in the plasma of 4 patients. 240-300 mg of dipyridamole/day (4 mg/kg/day) was mixed with heparin in the same bag and given as a continuous intravenous infusion. Anticoagulation was continued successfully along with significant platelet recovery over a few days. This regimen was without side-effects. We conclude that DHI may provide an effective therapy for patients with SHAT.