Heparin-induced thrombocytopenia in coronary bypass surgery

[Argatroban, a new antithrombotic treatment for heparin-induced thrombocytopenia application in cardiac surgery and in intensive care]

OBJECTIVES

Although heparin-induced thrombocytopemia (HIT) is uncommon, its thromboembolic complications are potentially life-threatening. The low-molecular weight heparins are less responsible of HIT than unfractionated heparin (UFH) but this latter is still indicated in some circumstances such as cardiac surgery. Argatroban, a selective thrombin inhibitor, recently available, has been indicated in HIT treatment. This review presents the main pharmacological characteristics, its indications and uses in the context of cardiac surgery and in intensive care medicine.

METHODS

Review of the literature in Medline database over the past 15 years using the following keywords: argatroban, cardiac surgery, circulatory assistance, cardiopulmonary bypass.

RESULTS

Despite its short-acting pharmacokinetic, argatroban cannot be recommended during cardiopulmonary bypass. On the contrary, argatroban is indicated in many circumstances in postoperative period of various cardiac surgeries (on-pump, off-pump, circulatory assistance). Nevertheless, after cardiac surgery, doses have to be adapted according to coagulation laboratory testing (ACT), particularly in patients presenting acute organ failure (kidney injury, heart failure, liver failure). This compound has no antagonist and is excluded during severe hepatic failure. The continuous intravenous administration is a drawback.

CONCLUSION

Argatroban is a new direct competitive thrombin inhibitor well evaluated as treatment of HIT after cardiac surgery. In HIT management, argatroban is an interesting alternative to lepirudin that is not anymore available and danaparoid because of supply disturbances.

Pharmacology of argatroban

Argatroban is a synthetic, small-molecule direct thrombin inhibitor that is approved in the USA, the EU and Japan for prophylaxis or treatment of thrombosis in patients with heparin-induced thrombocytopenia (HIT), and for anticoagulation of HIT patients undergoing PCI. Argatroban binds reversibly to, and inhibits both soluble and clot-bound thrombin. Argatroban does not generate antibodies, is not susceptible to degradation by proteases and is cleared hepatically. It has a predictable anticoagulant effect and there is a good correlation between dose, plasma concentration and pharmacodynamic effect. Initial clinical studies suggest that further investigations to establish the use of argatroban in ischemic stroke, acute coronary syndrome, hemodialysis, blood oxygenation, off-pump cardiac surgery and other clinical indications are warranted.

Mitigation of Coagulation by Removing Clotting Factors Part 1: In Vitro Feasibility Study

Heparin is associated with adverse effects in some patients during extracorporeal circulation. A potential alternate anticoagulation strategy explored in this investigation involved mitigation of coagulation by removing clotting factors from blood by adsorption on a protamine-immobilized Sepharose matrix (PSM). Human or porcine plasmas treated with PSM in vitro were tested for clotting factors I (fibrinogen), II (prothrombin), VIII, and X, and proteins C and S, and for prothrombin time (PT), activated partial thromboplastin time (APTT), and total protein concentration. Bovine blood treated with PSM was also perfused through a hollow-fiber cartridge to assess thrombogenic potential in a shear flow system. PT increased with increasing protamine-Sepharose-to-plasma ratios and with increasing mixing time. When the PT and APTT of treated plasma were prolonged three to six times the baseline, Factors II and X were significantly removed (>90%), Factors I and VIII were partly removed (<35%), and total protein concentration remained >80% of the initial value. When blood depleted of clotting factors was perfused through hollow-fiber cartridges without an anticoagulant, cartridge patency was prolonged compared with cartridges perfused with untreated blood. This investigation demonstrated that inhibition of blood coagulation by removal of key clotting proteins is feasible.

[Heparin-induced thrombocytopenia]

Heparins are in widespread use as anticoagulants for the prophylaxis and therapy of thromboembolisms. A dangerous side-effect is heparin-induced thrombocytopenia type II (HIT type II) with the paradox of thromboembolic venous and arterial vascular occlusions. HIT type II is an immunological disease which results in activation of platelets and plasma coagulation. The main symptom is an acute onset of thrombocytopenia with a fall in thrombocytes to less than 50% of the initial value with or without newly arising thromboembolic complications between days 5 and 14 after the start of heparin therapy. Surgery patients are more often affected by subclinical antibody formation as well as by symptomatic HIT type II than clinical patients. In this review we will discuss the difficult diagnosis and the differential diagnosis with special emphasis on postoperative intensive care patients, as well as preventive measures and management on occurrence of HIT type II and associated thrombotic complications.

Update on the clinical applications of argatroban

The small molecule, arginomimetic drug argatroban is the first synthetic direct antithrombin to be approved for clinical use. Argatroban reversibly binds to and inhibits both soluble and clot-bound thrombin. In contrast to other direct thrombin inhibitors, argatroban upregulates nitric oxide, enhancing its antithrombotic effect, does not generate antibodies, is not susceptible to degradation by proteases and is hepatically cleared. It has a predictable anticoagulant effect. Argatroban has proven efficacy and safety for prophylaxis and treatment of patients with thrombosis associated with heparin-induced thrombocytopenia (HIT), and for percutaneous coronary intervention in HIT and non-HIT patients. Pilot studies suggest that further investigations to establish the use of argatroban in ischemic stroke, acute coronary syndrome, hemodialysis, blood oxygenation, off-pump cardiac surgery and other clinical indications are warranted.

Alternative parenteral anticoagulation with argatroban, a direct thrombin inhibitor

Argatroban, a direct thrombin inhibitor, effectively inhibits free and clot-bound thrombin without the need of a cofactor and exerts dose-dependent anticoagulant effects that are rapidly active and rapidly reversible (elimination half-life: 39-51 min). Argatroban provides predictable parenteral anticoagulation and is well tolerated with an acceptably low bleeding risk in a variety of clinical settings, including heparin-induced thrombocytopenia, acute ischemic stroke, percutaneous coronary intervention and hemodialysis. This review will discuss the clinical pharmacology and utility of argatroban; in particular, clinical trial experiences will be discussed in patients with, or at risk of, heparin-induced thrombocytopenia (where heparins must be avoided) including those requiring hemodialysis or percutaneous coronary intervention, and in patients with acute ischemic stroke (where heparins are not generally recommended).

The Management of Patients With Heparin-Induced Thrombocytopenia Who Require Anticoagulant Therapy

For patients with heparin-induced thrombocytopenia (HIT), reexposure to heparin is generally not recommended. However, these patients are likely to require anticoagulation therapy at some point in the future. During acute HIT, when thrombocytopenia and anti-heparin-platelet factor 4 antibodies (or HIT antibodies) are present, therapy with heparin must be avoided. In patients with subacute HIT, when platelets have recovered but HIT antibodies are still present, therapy with heparin should be avoided. In patients with a remote history of HIT, when HIT antibodies have cleared, heparin reexposure may be safe, although recurrent HIT has been described in some patients. For all of these patients, the use of alternate anticoagulant agents, including direct thrombin inhibitors and anti-Xa agents, is preferable. There is an increasing amount of data supporting the use of these alternative agents in a wide variety of clinical circumstances, including thromboprophylaxis and treatment of acute thrombosis. Except for a few clinical situations, it is generally possible to avoid heparin reexposure in patients with a history of HIT.

Argatroban anticoagulation in patients with a history of heparin-induced thrombocytopenia

INTRODUCTION

Heparin therapy is not recommended for patients with a history of heparin-induced thrombocytopenia (HIT), except in specialized situations, because this treatment can lead to severe reactions including thrombocytopenia and thrombosis. However, the optimal management of patients with a history of HIT requiring acute anticoagulation has not yet been clarified because of the lack of prospective studies. We evaluated the safety and efficacy of argatroban, a direct thrombin inhibitor, as an anticoagulant in patients with a history of HIT needing acute anticoagulation.

METHODS

Thirty-six patients with a history of serologically confirmed HIT were treated prospectively with argatroban [median (5th-95th percentile) dose of 2.0 (1.0-4.3) microg/kg/min for 4.0 (0.7-8.4) days]. Prospectively defined endpoints included successful anticoagulation (therapeutic activated partial thromboplastin time), and bleeding, new thromboembolic events, or other adverse effects during therapy or within 30 days following its cessation.

RESULTS

All patients required acute anticoagulation with the most common admission diagnoses being deep venous thrombosis or pulmonary embolism (n=13) and chest pain or acute coronary syndrome (n=12). Eleven patients had previously received argatroban therapy for HIT; one patient underwent two treatment courses of argatroban for a history of HIT. The median (5th-95th percentile) time between the past diagnosis of HIT and initiation of argatroban was 7.5 (0.4-114.6) months. All evaluable patients were successfully anticoagulated. No patient had major bleeding, new thromboembolic events, or other adverse effects. There were no adverse events related to reexposure.

CONCLUSIONS

Argatroban can provide safe and effective anticoagulation, on initial or repeat exposure, in patients with a history of HIT.

[Thrombocytopenia induced by type II heparin and myocardial infarct: 2 case reports]

Heparin-induced thrombocytopenia (HIT) type II is an acquired thrombophylic state and life-threatening immune complication of a heparin treatment mainly clinically manifested by marked thrombocytopenia, frequently by arterial and venous thrombosis, and sometimes by skin changes. Functional assay as heparin aggregation test and 14C-serotonin release assays are used in diagnostics as well as antigen assays of which detection tests for heparin-platelet factor 4 antibodies are most frequently used. Considering the fact that there is no single reliable assays for HIT II detection available, sometimes it is necessary to combine both of the above-mentioned types of assays. We present the case of a 57-year-old patient with an acute anterior myocardial infarction with cardiac insufficiency of III and IV degree according to Killip, recurrent ventricular fibrillation and diabetes mellitus type II developing thrombocytopenia to 37 x 10(9)/l accompanied with typical skin changes. The diagnosis was confirmed by the heparin aggregation test. The second patient aged 70 undergoing the treatment for anteroseptal myocardial infarction and reinfarction of the inferior wall complicated by a cardiogenic shock and acute right bundle branch block developed thrombocytopenia 59 x 10(9)/l on the third day of the heparin therapy, with the remark that he had received a heparin therapy during the first infarction as well. Antibodies against heparin-platelet factor 4 were detected by particle gel ID-HPF4 immuno-assay. In both patients, the disease had a lethal outcome despite all then available therapeutic measures applied. Further on we discuss advantages of certain types of tests, a therapy doctrine, need for urgent therapeutic measures, inclusive of the administration of antithrombins, avoidance of harmful procedures like low-molecular-weight heparins administration and prophylactic platelet transfusion as well as preventive measures.

[Heparin-induced type II thrombocytopenia--new views on diagnosis and therapy]

HEPARIN-INDUCED THROMBOCYTOPENIA (HIT): Management of heparin-induced thrombocytopenia (HIT) and treatment options have significantly changed recently. Heparin may induce two types of thrombocytopenia. Type I, occurring earlier with a much higher rate of incidence (5-30%), is characterized by mild thrombocytopenia without significant clinical manifestations. Type II, is less frequent (0.5-2%), life threatening immune type, develops following a period of minimum 5-7 days upon introduction of heparin therapy (patients earlier treated with heparin are excluded). Type II heparin-induced thrombocytopenia with severely reduced platelet count may be clinically manifested by thrombosis in 20-50% cases within the period of 30 days. HIT is suspected in persons resistant to heparin with relatively reduced platelet count, though HIT is described in person with normal platelet counts, as well. None of available assays used for HIT detection is completely reliable. Sensitivity of a highly specific platelet aggregation assay is only 36%, sensitivity and specificity of 14C-serotonin release assays amounts to 95%, while ELISA using a heparin/platelet factor-4 target has a sensitivity of 85%. Thus, it is sometimes necessary to combine functional and antigen assays. Furthermore, new classes of antigen assays, like antibody detection tests of complexes between heparin and neutrophil-activating peptide-2 as well as those between heparin and interleukin-8, have been used. CURRENT THERAPY OPTIONS: Current therapy options exclude formerly applied low-molecular-weight heparins due to the existing cross-reactivity of 80-100%. Danaparoid sodium exhibits in vitro cross-reactivity of 10-61%, clinically manifested in less than 5% of patients. Two drugs are drugs of choice in HIT type II treatment: lepirudin, especially in patients without renal failure, and argatroban, particularly in patients with renal failure. The following procedures and agents are also efficient: asmapheresis in the first four days, high-dose intravenous gammaglobulin, antiaggregans, especially ADP antagonists, aspirin, dipirydamole, dextran, prostacyclin analagoues, thrombolytic therapy as well as thromboembolectomy. Oral anticoagulants are not administered in active HIT type II, in deep vein thrombosis with high international normalized ratio (INR) and thrombin-antithrombin complexes, and low protein C levels to avoid the possibility of venous limb gangrene development. They can be administered in a stable phase, when the thrombin generation is controlled by previous administration of one of the above-mentioned alternative anticoagulants.

Off-pump right atrial thrombectomy for heparin-induced thrombocytopenia with thrombosis

This report describes a 72-year-old woman with atrial fibrillation who presented with lower extremity ischemia secondary to thromboembolism. After lower extremity thrombectomy, the patient developed heparin-induced thrombocytopenia with thrombosis (HITT). Her postoperative course was complicated by recurrent supraventricular and ventricular tachycardia, secondary to a mobile thrombus in the right atrium extending into the right ventricle. Because administration of heparin was contraindicated, the patient underwent off-pump right atrial thrombectomy during a brief period of inflow occlusion. Postoperatively, she was placed on lepirudin. Her platelet count normalized without any further thrombotic episodes, and she was discharged on warfarin.

Pharmacotherapy of heparin- induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is a life-and-limb threatening condition that is associated with the development of antibodies that activate platelets and the coagulation system in the presence of unfractionated heparin or low molecular weight heparin. The binding of antibody to heparin-PF-4 complexes can activate platelets, leading to an acute, often catastrophic, thrombotic diathesis. The most common laboratory finding is the development of thrombocytopenia 5 or more days after beginning heparin treatment, which occur in up to 1 - 5% of patients exposed to heparin, depending on type of heparin and indication for anticoagulation. The onset of thrombocytopenia can be immediate or delayed for several weeks after the exposure to heparin. Approximately 50 - 60% of patients who develop HIT manifest acute venous or arterial thrombosis and a significant percentage of these patients die or develop vascular gangrene of a limb that requires amputation. Given the severe sequelae associated with HIT, recognition and immediate medical management is essential. Treatment of a patient with HIT is complex, as there are several different anticoagulants now available which have been shown to be useful. Optimal management depends on each patient's individual clinical manifestations, as well as the need for ongoing anticoagulation therapy. No single agent or treatment approach can be considered to be 'standard practice' as very few clinical trials have been completed, compare different treatment options. The use of warfarin alone in a patient with HIT, must be avoided in order to avoid the possibility of further activating coagulation, which may hasten the development of venous limb gangrene. There are several different tests available that detect HIT antibodies and each has different sensitivity and specificity for HIT. In this review we discuss the epidemiology and natural history of HIT, risk factors associated with the development of HIT and the clinical and laboratory tests that aid in the diagnosis and treatment. Special emphasis is given to addressing the management of HIT in special populations, particularly patients with renal or liver disease, acute coronary syndromes, pregnancy, paediatrics and patients who require cardiopulmonary bypass surgery.

Hemostatic analysis of a patient undergoing off-pump coronary artery bypass surgery with argatroban anticoagulation

IMPLICATIONS

This case describes the impact of argatroban and off-pump coronary revascularization on hemostasis as assessed by conventional hemostatic measures and Thrombelastography in a patient with heparin-induced thrombocytopenia.

Diagnosis and treatment of heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is a major side effect secondary to the administration of heparin. This syndrome is serious and potentially life threatening. This response is the result of antibodies formed against the platelet factor 4 (PF4)/heparin complex. The incidence of this immune-mediated syndrome has been estimated to be 1-3% of all patients receiving heparin therapy. The occurrence of HIT in patients requiring full anticoagulation for cardiopulmonary bypass (CPB), therefore, presents a serious challenge to the cardiac surgery team. The diagnosis of HIT should be based on both clinical and laboratory evidence. While functional assays, platelet aggregation tests, and the serotonin release assay can be used to support the diagnosis, the negative predictive value of these tests is generally less than 50%. In contrast, although non-functional antibody detection assays are more sensitive, they have a low specificity. HIT can be treated in several ways, including cessation of all heparin and giving an alternative thrombin inhibitor, platelet inhibition followed by heparin infusion, and the use of low molecular weight heparins. In this presentation, the pathology and current diagnostic tests, as well as the successful management of patients with HIT undergoing CPB at New York Presbyterian Hospital, are reviewed.

Safety and efficacy of combined use of low molecular weight heparin (enoxaparin, lovenox) and glycoprotein IIb/IIIa receptor antagonist (eptifibatide, integrelin) during nonemergent coronary and peripheral vascular intervention

Coronary and peripheral intervention requires intraprocedural anticoagulation to prevent intraluminal thrombosis. Traditionally, unfractionated heparin (UFH) is administered during the procedure to achieve activated clotting time (ACT) of 300 to 400 seconds. When the intravenous IIb/IIIa antagonists are also used, the recommended ACT is 250 to 300 seconds because higher anticoagulation (ACT, 300-400 seconds) is accompanied by an unacceptable bleeding complication rate without added benefits. Because low molecular weight heparin has a more predictable anticoagulant effect and a higher anti-factor Xa/anti-factor IIa ratio, allows better bioavailability, is resistant to inhibition by activated platelets, and does not require routine monitoring using ACT, its use for intraprocedural anticoagulation (instead of UFH) has been an area of increasing interest. The safety and efficacy of coadministration of low molecular weight heparin with IIb/IIIa antagonists have not been adequately evaluated. We report a study of prospective evaluation of the safety and efficacy of combined use of intravenous enoxaparin and intravenous eptifibatide during nonemergent coronary and peripheral vascular intervention in 93 consecutive procedures performed on 56 patients. The procedural success rate was 99% (92/93 procedures), the acute clinical success rate was 98% (54/55 patients), the major bleeding complication rate was 2% (1/56 patients), and the vascular complication rate was 0.0%. In conclusion, the use of intravenous enoxaparin in conjunction with intravenous eptifibatide during nonemergent coronary and peripheral vascular intervention is safe and effective and eliminates the need for routine measurement of ACT during the procedure.

Treatment of heparin-induced thrombocytopenia

OBJECTIVE

To describe heparin-induced thrombocytopenia (HIT or HIT-2), an immune-mediated adverse reaction to heparin or low-molecular-weight heparin. Available treatment options and considerations in developing a therapy approach are discussed.

DATA SOURCES

A search of the National Library of Medicine (1992-June 2001) was done to identify pertinent literature. Additional references were reviewed from selected articles.

STUDY SELECTION

Articles related to laboratory recognition and treatment options of HIT, including the use of agents in selected clinical conditions, were reviewed and included.

CONCLUSIONS

HIT is a rare but potentially severe adverse reaction to heparin that was, until recently, poorly understood and had limited treatment options. Recent advances describing the recognition and clinical manifestations of immune-mediated HIT, including recently available antithrombotic treatment options, have dramatically changed outcomes for patients having this syndrome.

A synopsis of the clinical uses of argatroban

Argatroban, a direct thrombin inhibitor, has been used in Japan since the early 1980's and was recently approved for use in the United States for patients with heparin-induced thrombocytopenia. However, its use has been studied in other clinical settings including, myocardial infarction, percutaneous coronary intervention and cerebral thrombosis. The doses used in the different clinical situations vary, but argatroban offers the advantage of not requiring renal adjustment. Because of its small molecular weight, argatroban has the ability to inhibit both clot bound and soluble thrombin. This paper provides a comprehensive review of both indicated and off label uses of argatroban. Pharmacology, pharmacokinetics, adverse events and drug interactions with argatroban are also discussed.

Alternatives to unfractionated heparin for anticoagulation in cardiopulmonary bypass

Despite the progress made in the development of cardiopulmonary bypass (CPB) equipment, systemic anticoagulation with unfractionated heparin and post-bypass neutralization with protamine are still used in most perfusion procedures. However, there are a number of situations where unfractionated heparin, protamine or both cannot be used for various reasons. Intolerance of protamine can be addressed with extracorporeal heparin removal devices, perfusion with (no) low systemic heparinization and, to some degree, by perfusion with alternative anticoagulants. Various alternative anticoagulation regimens have been used in cases of intolerance to unfractionated heparin, including extreme hemodilution, low molecular weight heparins, danaparoid, ancrod, r-hirudin, abciximab, tirofiban, argatroban and others. In the presence of heparin-induced thrombocytopenia (HIT) and thrombosis, the use of r-hirudin appears to be an acceptable solution which has been well studied. The main issue with r-hirudin is the difficulty in monitoring its activity during CPB, despite the fact that ecarin coagulation time assessment is now available. A more recent approach is based on selective blockage of platelet aggregation by means of monoclonal antibodies directed to GPIIb/IIIa receptors (abciximab) or the use of a GPIIb/IIIa inhibitor (tirofiban). An 80% blockage of the GPIIb/IIIa receptors and suppression of platelet aggregation to less than 20% allows the giving of unfractionated heparin and running CPB in a standard fashion despite HIT and thrombosis. Likewise, at the end of the procedure, unfractionated heparin is neutralized with protamine as usual and donor platelets are transfused if necessary. GPIIb/IIIa inhibitors are frequently used in interventional cardiology and, therefore, are available in most hospitals.

Heparin-induced Thrombocytopenia

Treatment with heparin is associated with two types of thrombocytopenia. The most worrisome of these is the immune-mediated heparin-induced thrombocytopenia (HIT type II). Suspicion of HIT type II mandates immediate cessation of heparin administration and consideration of an alternative anticoagulation therapy. Hirudin and argatroban are approved alternative anticoagulants with no cross-reactivity with the HIT antibody. HIT type II is a clinicopathologic syndrome, and therefore diagnosis requires clinical and laboratory confirmation. The laboratory evaluation for HIT type II should also determine whether or not there is HIT-antibody cross-reactivity with danaparoid and low molecular weight heparin. Patients with HIT type II who require coronary artery bypass graft surgery present a particularly difficult situation, as there is no ideal alternative to heparin anticoagulation.

Argatroban: a direct thrombin inhibitor for heparin-induced thrombocytopenia and other clinical applications

Argatroban, a direct thrombin inhibitor derived from arginine, is an effective anticoagulant indicated for prophylaxis or treatment of thrombosis in patients with heparin-induced thrombocytopenia (HIT). Argatroban has been used as an alternative anticoagulant in patients with HIT in various clinical conditions including interventional cardiovascular procedures that require anticoagulation. Satisfactory clinical outcomes with acceptable complications have been reported in these patients. Whether argatroban offers additional clinical advantage over conventional heparin therapy in patients without HIT remains unclear. Argatroban has been evaluated as an alternative anticoagulant to replace heparin in various clinical studies, especially in patients with coronary artery disease or cerebral vascular disease. To date, it remains unclear if argatroban is more effective than heparin, although the agent seems to cause less bleeding complications. This article reviews the pharmacology of argatroban and its clinical application beyond the management of HIT, with particular emphasis on interventional cardiology procedure, acute myocardial infarction, unstable angina pectoris, cerebral thrombosis or ischemic stroke, peripheral obstructive arterial disease, and extracorporeal circulation.

Management strategies for heparin-induced thrombocytopenia in heart-transplant candidates: case report and review of the literature

Management of anticoagulation in patients with heparin-induced thrombocytopenia (HIT) undergoing surgery requiring cardiopulmonary bypass (CPB), such as cardiac transplantation, represents a difficult clinical problem and no clear management strategy exists. The cases of 2 patients with HIT who underwent cardiac transplantation using differing anticoagulation strategies are presented with a discussion of potential advantages and pitfalls of each approach used.

Gastrointestinal bleeding associated with myocardial infarction

Gastrointestinal (GI) bleeding associated with myocardial infarcation (MI) often presents as a distinct syndrome that differs from either disease alone. MI is frequently overlooked in the setting of severe GI bleeding because the symptoms and signs of MI are frequently overshadowed by the severe bleeding. GI bleeding, particularly when massive, may precipitate MI from hypovolemia, hemodynamic compromise, and myocardial hypoperfusion. Esophagogastroduodenoscopy is safe in relatively clinically stable patients after MI and is indicated to evaluate significant upper GI bleeding.