Failure of argatroban anticoagulation during off-pump coronary artery bypass surgery

Quantitative and Qualitative Platelet Derangements in Cardiac Surgery and Extracorporeal Life Support

Thrombocytopenia and impaired platelet function are known as intrinsic drawbacks of cardiac surgery and extracorporeal life supports (ECLS). A number of different factors influence platelet count and function including the inflammatory response to a cardiopulmonary bypass (CPB) or to ECLS, hemodilution, hypothermia, mechanical damage and preoperative treatment with platelet-inhibiting agents. Moreover, although underestimated, heparin-induced thrombocytopenia is still a hiccup in the perioperative management of cardiac surgical and, above all, ECLS patients. Moreover, recent investigations have highlighted how platelet disorders also affect patients undergoing biological prosthesis implantation. Though many hypotheses have been suggested, the mechanism underlying thrombocytopenia and platelet disorders is still to be cleared. This narrative review aims to offer clinicians a summary of their major causes in the cardiac surgery setting.

Heparin-induced thrombocytopenia in cardiac surgery and critically ill patients

Thrombocytopenia as well as anti-platelet factor 4/heparin (PF4/H) antibodies are common in cardiac surgery patients and those treated in the intensive care unit. In contrast, heparin-induced thrombocytopenia (HIT) is uncommon in these populations (∼1 % and ∼0.5 %, respectively). A stepwise approach where testing for anti-PF4/H antibodies is performed only in patients with typical clinical symptoms of HIT improves diagnostic specificity of the laboratory assays without losing sensitivity, thereby helping to avoid overdiagnosis and resulting HIT overtreatment. Short-term re-exposure to heparin, especially given intraoperatively for cardiovascular surgery, is a reasonable therapeutic option in patients with a history of HIT who subsequently test negative for HIT antibodies. Organ failure(s), enhanced bleeding risks, and other characteristics require special considerations regarding non-heparin anticoagulation: Argatroban is the alternative anticoagulant with pharmacokinetics independent of renal function, but it has a prolonged half-life in case of impaired liver function. For bivalirudin, protocols during cardiopulmonary bypass surgery are established, and it is suitable for patients with liver insufficiency. A major issue of direct thrombin inhibitors are false high activated partial thromboplastin time values in patients with comorbidities affecting prothrombin, which can result in systematic underdosing of the drugs. This is not the case for danaparoid and fondaparinux, which can be monitored by anti-factor Xa assays, but have long half-lives and no suitable antidote. This review includes also information on management of on- and off-pump cardiac surgery, ventricular assist devices, percutaneous interventions, continuous renal replacement therapy, and extracorporeal membrane oxygenation in patients with HIT.

Difficulty in the management of anticoagulation with argatroban during off-pump coronary artery bypass grafting

Heparin-induced thrombocytopenia (HIT) can often result in devastating thromboembolic outcomes. Argatroban is frequently administered as an alternative anticoagulant to heparin. We present a complicated case of HIT in which off-pump coronary artery bypass grafting was performed using anticoagulation with argatroban. Although the active clotting time was maintained between 220 and 270 s using argatroban, intraoperative thrombotic complications and postoperative prolonged coagulopathy were encountered. <Learning objective: The use of argatroban involves a potential risk of inadequate anticoagulation or life-threatening postoperative bleeding depending on the dose. We recommend that the target ACT during off-pump coronary artery bypass grafting with argatroban should be strictly maintained over 250 s, although an ACT exceeding 300 s may cause prolonged coagulopathy>.

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.

Prolonged elevation of plasma argatroban in a cardiac transplant patient with a suspected history of heparin-induced thrombocytopenia with thrombosis

BACKGROUND

Direct thrombin inhibitors (DTIs) provide an alternative method of anticoagulation for patients with a history of heparin-induced thrombocytopenia (HIT) or HIT with thrombosis (HITT) undergoing cardiopulmonary bypass (CPB). In the following report, a 65-year-old critically ill patient with a suspected history of HITT was administered argatroban for anticoagulation on bypass during heart transplantation. The patient required massive transfusion support (55 units of red blood cells, 42 units of fresh-frozen plasma, 40 units of cryoprecipitate, 40 units of platelets, and three doses of recombinant Factor VIIa) for severe intraoperative and postoperative bleeding.

STUDY DESIGN AND METHODS

Plasma samples from before and after CPB were analyzed postoperatively for argatroban concentration using a modified ecarin clotting time (ECT) assay.

RESULTS

Unexpectedly high concentrations of argatroban were measured in these samples (range, 0-32 microg/mL), and a prolonged plasma argatroban half life (t(1/2)) of 514 minutes was observed (published elimination t(1/2) is 39-51 minutes [< or = 181 minutes with hepatic impairment]).

CONCLUSIONS

Correlation of plasma argatroban concentration versus the patient's coagulation variables and clinical course suggest that prolonged elevated levels of plasma argatroban may have contributed to the patient's extended coagulopathy. Because DTIs do not have reversal agents, surgical teams and transfusion services should remain aware of the possibility of massive transfusion events during anticoagulation with these agents. This is the first report to measure plasma argatroban concentration in the context of CPB and extended coagulopathy.

Heparin-Induced Thrombocytopenia: Treatment Options and Special Considerations

Heparin-induced thrombocytopenia (HIT) is an immune-mediated adverse effect that typically manifests several days after the start of heparin therapy, although both rapid- and delayed-onset HIT have been described. Its most serious complication is thrombosis. Although not all patients develop thrombosis, it can be life threatening. The risk of developing HIT is related to many factors, including the type of heparin product administered, route of administration, duration of therapy, patient population, and previous exposure to heparin. The diagnosis of HIT is typically based on clinical presentation, exposure to heparin, and presence of thrombocytopenia with or without thrombosis. Antigen and activation laboratory assays are available to support the diagnosis of HIT. However, because of the limited sensitivity and specificity of these assays, bedside probability scales for HIT were developed. When HIT is suspected, prompt cessation of all heparin therapy is necessary, along with initiation of alternative anticoagulant therapy. Two direct thrombin inhibitors--argatroban and lepirudin--are approved for the management of HIT in the United States, and bivalirudin is approved for use in patients with HIT who are undergoing percutaneous coronary intervention. Other agents, although not approved to manage HIT, have also been used; however, their role in therapy requires further evaluation. A comprehensive HIT management strategy involves the evaluation of numerous factors. Many patients, including those undergoing coronary artery bypass surgery, those with acute coronary syndromes, those with hepatic or renal insufficiency, and children, require special attention. Clinicians must become familiar with the available information on this serious adverse effect and its treatment so that optimum patient management strategies may be formulated.

Argatroban for anticoagulation during cardiac surgery

BACKGROUND

The aim of this study was to report our experience and review the published data on argatroban administration during adult cardiac surgery.

METHODS

The information on all reported cases of argatroban use in adults, during cardiac surgery was reviewed, including that of the patient described here. This analysis focused on patient characteristics, type of surgery, argatroban dosing schedule, monitoring of anticoagulation and outcomes.

RESULTS

Twenty-one cases have been reported. Fifteen patients underwent off-pump surgical procedures with the argatroban dose adjusted to maintain an activated clotting time (ACT) range between 200 and 300 s. Three intraoperative thrombi occurred in two patients when the ACT was <280 s. None had coagulopathy. Six cases reported the use of argatroban during on-pump cardiac surgery dosed to keep the ACT >400 s. Intraoperative thrombotic complications were not reported in this group; however, one clot in the pump was noted after the procedure when the ACT was between 300 and 350 s. All six cases required larger volumes of perioperative blood products and three had severe coagulopathy. Of the 21 cases, seven had an indication for continued anticoagulation following surgery. Four cases did not report further use of argatroban after surgery. Three patients received argatroban after surgery without complications. Recommendations for how to use argatroban during cardiac surgery are proposed.

CONCLUSIONS

Argatroban, with ACT monitoring, might be safely used for anticoagulation during cardiac surgery.

Recombinant factor VIIa for refractory bleeding after cardiac surgery secondary to anticoagulation with the direct thrombin inhibitor lepirudin

A 56-year-old man with heparin-induced thrombocytopenia with thrombosis syndrome (HITTS) received anticoagulation with recombinant hirudin (lepirudin) for emergency coronary artery bypass graft (CABG) surgery and aortic valve replacement. The patient experienced life-threatening refractory bleeding that was successfully treated with recombinant factor VIIa. He had a history of infective endocarditis that resulted in severe aortic insufficiency, three-vessel coronary artery disease, and acute renal failure requiring hemodialysis. The patient was transferred from another hospital for the emergency surgery, but before his transfer, he developed HITTS secondary to therapeutic heparin for a deep vein thrombosis of the lower extremity. The presence of HITTS, the urgent nature of the case, and the availability of the direct thrombin inhibitor led the surgical team to select lepirudin for anticoagulation to facilitate cardiopulmonary bypass. After separation from cardiopulmonary bypass, the patient was in a coagulopathic state due to the inability to reverse the lepirudin and the slowed elimination of the drug secondary to inadequate renal function. As a result, the patient experienced excessive generalized oozing that was unresponsive to traditional therapies and blood product transfusions. Recombinant factor VIIa 35 microg/kg was given as rescue therapy. The bleeding slowed, which allowed placement of chest tubes and closing of the sternum. The patient was transferred to the intensive care unit in stable condition with no evidence of thrombosis in the freshly placed bypass grafts or on the bioprosthetic valve. Recombinant factor VIIa appears to be a suitable option as salvage therapy in patients with refractory bleeding secondary to anticoagulation with a direct thrombin inhibitor during cardiac surgery.

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.

Argatroban: update

Unfractionated heparin has historically been used as the anticoagulant of choice in the management of a number of thrombotic diseases. Recognition of the limitations of heparin has led to the development of a newer class of anticoagulants, the direct thrombin inhibitors. Argatroban is a synthetic small molecule that selectively inhibits thrombin at its active site. In preclinical studies, argatroban has been shown to be more effective than heparin in preventing arterial thrombosis and in promoting vessel patency in conjunction with thrombolysis in a number of animal models. In clinical trials, argatroban has been shown to be as effective as heparin in the management of ST-segment elevation myocardial infarction in conjunction with thrombolysis. It has been shown to be an effective anticoagulant in patients undergoing percutaneous coronary interventions. In patients with heparin-induced thrombocytopenia and heparin-induced thrombocytopenia complicated by thrombosis, argatroban significantly decreases the risk of thrombotic events. Small studies have demonstrated a potential role for its use in ischemic stroke and hemodialysis. Additional studies are warranted to confirm argatroban's efficacy in a wide variety of clinical settings.

Bivalirudin anticoagulation for cardiopulmonary bypass in a patient with heparin-induced thrombocytopenia

PURPOSE

To describe the perioperative management in a heparin-induced thrombocytopenia (HIT) positive patient who had prosthetic valve endocarditis and an aortic root abscess. The patient underwent high-risk cardiac re-operation with the use of the alternative anticoagulant, bivalirudin.

CLINICAL FEATURES

A 62-yr-old patient who underwent stentless tissue aortic valve replacement with a Toronto-SPV valve in 1998, was admitted to hospital with symptoms of stroke. A heparin infusion was started and further investigation revealed positive blood cultures. The patient developed HIT which was confirmed by laboratory tests. Echocardiographic examination performed one month later showed vegetations on the aortic tissue valve and a small aortic root abscess. The patient still tested positively for the presence of HIT antibodies and was treated conservatively with antibiotics. A repeat echocardiographic examination showed progression of the aortic root abscess and it was decided to proceed with urgent redo aortic valve surgery. Anticoagulation for cardiopulmonary bypass (CPB) was achieved with the use of a direct thrombin inhibitor (DTI), bivalirudin. Following an uneventful wean from CPB, hemostasis was achieved within 40 min. The postoperative course was uncomplicated and the patient was discharged from hospital on the seventh postoperative day.

CONCLUSION

Bivalirudin is a DTI, which can be used as an alternative anticoagulant for CPB in HIT positive patients. This case report showed a favourable outcome with bivalirudin for urgent complex redo cardiac surgery requiring CPB.

Update on Heparin-Induced Thrombocytopenia and Cardiovascular Interventions

Although heparin/protamine has been the standard anticoagulation regimen in cardiac surgery for decades, it induces negative reactions within the vasculature. Heparin-induced thrombocytopenia (HIT) is a highly prothrombotic immune reaction to heparin that may result in death, limb ischemia leading to amputation, graft occlusion, and other severe thrombotic events. Patients undergoing cardiac surgery are at high risk for HIT antibody seroconversion and at risk for clinical HIT. For patients with acute or subacute HIT and needing urgent cardiac surgery, accepted protocols for alternative, non-heparin anticoagulation are needed. The direct thrombin inhibitor bivalirudin offers promise in this area and is currently being evaluated in multicenter trials as an alternative for heparin/protamine in patients with HIT undergoing cardiac surgery.

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).

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.

Severe Argatroban-Induced Coagulopathy in a Patient With a History of Heparin-Induced Thrombocytopenia

Heparin-induced thrombocytopenia is a serious complication of heparin therapy, and it remains a therapeutic challenge in the subset of patients requiring cardiopulmonary bypass. Alternative anticoagulation strategies include lepirudin, danaparoid, bivalirudin, and argatroban, or a combination of unfractionated heparin with a platelet antagonist. Argatroban is eliminated by a hepatic route, making it a practical option for patients with renal insufficiency. However, the lack of an effective antidote poses a significant problem. We present a patient with a history of heparin-induced thrombocytopenia with thrombosis who underwent a redo aortic valve replacement. Although the level of anticoagulation achieved with argatroban was initially adequate, its persistence after the completion of cardiopulmonary bypass proved to be life threatening.