One-year experience with the platelet glycoprotein IIb/IIIa antagonist tirofiban and heparin during cardiopulmonary bypass in patients with heparin-induced thrombocytopenia type II

Novel Knowledge about Molecular Mechanisms of Heparin-Induced Thrombocytopenia Type II and Treatment Targets

Heparin-induced thrombocytopenia type II (HIT II), as stated in the literature, occurs in about 3% of all patients and in 0.1-5% of surgical patients. Thrombosis develops in 20-64% of patients with HIT. The mortality rate in HIT II has not decreased using non-heparin treatment with anticoagulants such as argatroban and lepirudin. An improved understanding of the pathophysiology of HIT may help identify targeted therapies to prevent thrombosis without subjecting patients to the risk of intense anticoagulation. The review will summarize the current knowledge about the pathogenesis of HIT II, potential new therapeutic targets related to it, and new treatments being developed. HIT II pathogenesis involves multi-step immune-mediated pathways dependent on the ratio of PF4/heparin and platelet, monocyte, neutrophil, and endothelium activation. For years, only platelets were known to take part in HIT II development. A few years ago, specific receptors and signal-induced pathways in monocytes, neutrophils and endothelium were revealed. It had been shown that the cells that had become active realised different newly formed compounds (platelet-released TF, TNFα, NAP2, CXCL-7, ENA-78, platelet-derived microparticles; monocytes-TF-MPs; neutrophils-NETs), leading to additional cell activation and consequently thrombin generation, resulting in thrombosis. Knowledge about FcγIIa receptors on platelets, monocytes, neutrophils and FcγIIIa on endothelium, chemokine (CXCR-2), and PSGL-1 receptors on neutrophils could allow for the development of a new non-anticoagulant treatment for HIT II. IgG degradation, Syk kinase and NETosis inhibition are in the field of developing new treatment possibilities too. Accordingly, IdeS and DNases-related pathways should be investigated for better understanding of HIT pathogenesis and the possibilities of being the HIT II treatment targets.

How to Solve the Conundrum of Heparin-Induced Thrombocytopenia during Cardiopulmonary Bypass

Heparin-induced thrombocytopenia (HIT) is a major issue in cardiac surgery requiring cardiopulmonary bypass (CPB). HIT represents a severe adverse drug reaction after heparin administration. It consists of immune-mediated thrombocytopenia paradoxically leading to thrombotic events. Detection of antibodies against platelets factor 4/heparin (anti-PF4/H) and aggregation of platelets in the presence of heparin in functional in vitro tests confirm the diagnosis. Patients suffering from HIT and requiring cardiac surgery are at high risk of lethal complications and present specific challenges. Four distinct phases are described in the usual HIT timeline, and the anticoagulation strategy chosen for CPB depends on the phase in which the patient is categorized. In this sense, we developed an institutional protocol covering each phase. It consisted of the use of a non-heparin anticoagulant such as bivalirudin, or the association of unfractionated heparin (UFH) with a potent antiplatelet drug such as tirofiban or cangrelor. Temporary reduction of anti-PF4 with intravenous immunoglobulins (IvIg) has recently been described as a complementary strategy. In this article, we briefly described the pathophysiology of HIT and focused on the various strategies that can be applied to safely manage CPB in these patients.

Management of heparin-induced thrombocytopenia: systematic reviews and meta-analyses

Heparin-induced thrombocytopenia (HIT) is a prothrombotic adverse drug reaction occurring in <0.1% to 7% of patients receiving heparin products depending on the patient population and type of heparin. Management of HIT is highly dependent on a sequence of tests for which clinicians may or may not have the results when care decisions need to be made. We conducted systematic reviews of the effects of management strategies in persons with acute HIT, subacute HIT A or B, and remote HIT. We searched Medline, EMBASE, and the Cochrane Database through July 2019 for previously published systematic reviews and primary studies. Two investigators independently screened and extracted data and assessed the certainty of the evidence using the Grading of Recommendations Assessment, Development and Evaluation approach. We found primarily noncomparative studies and case series assessing effects of treatments, which led to low to very low certainty evidence. There may be little to no difference in the effects between nonheparin parenteral anticoagulants and direct oral anticoagulants in acute HIT. The benefits of therapeutic-intensity may be greater than prophylactic-intensity anticoagulation. Using inferior vena cava filters or platelet transfusion may result in greater harm than not using these approaches. Evidence for management in special situations, such as for patients undergoing cardiovascular interventions or renal replacement therapy, was also low to very low certainty. Additional research to evaluate nonheparin anticoagulants is urgently needed, and the development of novel treatments that reduce thrombosis without increasing hemorrhage should be a priority.

GTH 2021 State of the Art-Cardiac Surgery: The Perioperative Management of Heparin-Induced Thrombocytopenia in Cardiac Surgery

Heparin-induced thrombocytopenia (HIT) is a severe, immune-mediated, adverse drug reaction that paradoxically induces a prothrombotic state. Particularly in the setting of cardiac surgery, where full anticoagulation is required during cardiopulmonary bypass, the management of HIT can be highly challenging, and requires a multidisciplinary approach. In this short review, the different perioperative strategies to run cardiopulmonary bypass will be summarized.

Heparin-Induced Thrombocytopenia: A Review of New Concepts in Pathogenesis, Diagnosis, and Management

Knowledge on heparin-induced thrombocytopenia keeps increasing. Recent progress on diagnosis and management as well as several discoveries concerning its pathogenesis have been made. However, many aspects of heparin-induced thrombocytopenia remain partly unknown, and exact application of these new insights still need to be addressed. This article reviews the main new concepts in pathogenesis, diagnosis, and management of heparin-induced thrombocytopenia.

How would we treat our own heparin-induced thrombocytopenia during cardiac surgery?

The aim of this article is to provide a comprehensive review of the current state of knowledge on heparin-induced thrombocytopenia (HIT) in cardiac surgery. The management of HIT patients undergoing cardiac surgery with cardiopulmonary bypass is complex and requires an interdisciplinary and patient-tailored approach because available evidence is limited and current anticoagulation strategies have potential risks. An index case is used to discuss both the established and new perioperative therapeutic options in HIT patients undergoing urgent cardiac surgery with cardiopulmonary bypass.

Potential and Limitations of the New P2Y12 Inhibitor, Cangrelor, in Preventing Heparin-Induced Platelet Aggregation During Cardiac Surgery: An In Vitro Study

BACKGROUND

Heparin-induced thrombocytopenia (HIT) can put cardiac surgery patients at a high risk of lethal complications. If anti-PF4/heparin antibodies (anti-PF4/Hep Abs) are present, 2 strategies exist to prevent intraoperative aggregation during bypass surgery: first, using an alternative anticoagulant, and second, using heparin combined with an antiaggregant. The new P2Y12 inhibitor, cangrelor, could be an attractive candidate for the latter strategy; several authors have reported its successful use. The present in vitro study evaluated cangrelor's ability to inhibit heparin-induced platelet aggregation in the presence of anti-PF4/Hep Abs.

METHODS

Platelet-poor plasma (PPP) from 30 patients with functional anti-PF4/Hep Abs was mixed with platelet-rich plasma (PRP) from 5 healthy donors.Light transmission aggregometry was used to measure platelet aggregation after adding 0.5 IU·mL of heparin (HIT) to the plasma, and this was compared with samples spiked with normal saline (control) and samples spiked with cangrelor 500 ng·mL and heparin 0.5 IU·mL (treatment). Friedman test with post hoc Dunn-Bonferroni test was used for between-group comparisons.

RESULTS

Heparin 0.5 IU·mL triggered aggregation in 22 of 44 PPP-PRP mixtures, with a median aggregation of 86% (interquartile range [IQR], 69-91). The median aggregation of these 22 positive samples' respective control tests was 22% (IQR, 16-30) (P < .001). Median aggregation in the cangrelor-treated samples was 29% (IQR, 19-54) and significantly lower than the HIT samples (P < .001). Cangrelor inhibited heparin-induced aggregation by a median of 91% (IQR, 52-100). Cangrelor only reduced heparin-induced aggregation by >95% in 10 of the 22 positive samples (45%). Cangrelor inhibited heparin-induced aggregation by <50% in 5 of the 22 positive samples (22%) and by <10% in 3 samples (14%).

CONCLUSIONS

This in vitro study found that cangrelor was an unreliable inhibitor of heparin-induced aggregation in the presence of anti-PF4/Hep Abs. We conclude that cangrelor should not be used as a standard antiaggregant for cardiac patients affected by HIT during surgery. Unless cangrelor's efficacy in a particular patient has been confirmed in a presurgery aggregation test, other strategies should be chosen.

Successful Use of Cangrelor and Heparin for Cardiopulmonary Bypass in a Patient With Heparin-Induced Thrombocytopenia and End-Stage Renal Disease: A Case Report

Heparin is the only well-established anticoagulant medication for cardiopulmonary bypass making selecting an alternative anticoagulant challenging in patients with heparin-induced thrombocytopenia. Other anticoagulant medications can cause significant postoperative bleeding, especially in patients with end-stage renal disease. We present a case of a 63-year-old woman requiring aortic valve replacement with a history of heparin-induced thrombocytopenia and end-stage renal disease. Cangrelor and heparin were successfully used during cardiopulmonary bypass, offering an option for anticoagulation management for a uniquely challenging patient population.

Cardiac Surgery Successfully Managed With Cangrelor in a Patient With Persistent Anti-PF4/Heparin Antibodies 8 Years After Heparin-Induced Thrombocytopenia

A 66-YEAR-OLD female requiring cardiac surgery had persisting anti-platelet factor 4 (PF4)/heparin antibodies (HIT-abs) 8 years after heparin-induced thrombocytopenia (HIT). In 2010, she developed thrombotic thrombocytopenic purpura (TTP) (ADAMTS-13 <5%, inhibitor at 1.0 BU/mL), which was treated successfully with corticotherapy, plasmapheresis, and intravenous heparin. While taking heparin, she developed HIT, as evidenced by a positive functional test. Her platelet count fully resolved without thrombotic complications with danaparoid treatment. In 2018, the preoperative titer of HIT-abs was still 0.38 U/mL by chemoluminescent immunoassay (CLIA), and positive by particle-gel agglutination immunoassay (PaGIA) with a titer of 2 and was strongly positive on an enzyme-linked immunosorbent assay (ELISA). The authors of the case report chose to use cangrelor combined with heparin during cardiopulmonary bypass (CPB). Cangrelor was used without increased postoperative bleeding or thrombotic complications. Postoperatively she exhibited a huge rise in HIT-abs (14.22 U/mL on postoperative day 11) with a positive functional assay. There was no recurrence of HIT, however. This case illustrates the importance of excluding the presence of persisting HIT-abs before CPB and ensuring close medical follow-up after even a single exposure to heparin.

American Society of Hematology 2018 guidelines for management of venous thromboembolism: heparin-induced thrombocytopenia

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is an adverse drug reaction mediated by platelet-activating antibodies that target complexes of platelet factor 4 and heparin. Patients are at markedly increased risk of thromboembolism.

OBJECTIVE

These evidence-based guidelines of the American Society of Hematology (ASH) are intended to support patients, clinicians, and other health care professionals in their decisions about diagnosis and management of HIT.

METHODS

ASH formed a multidisciplinary guideline panel balanced to minimize potential bias from conflicts of interest. The McMaster University GRADE Centre supported the guideline development process, including updating or performing systematic evidence reviews. The panel prioritized clinical questions and outcomes according to their importance for clinicians and patients. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach was used to assess evidence and make recommendations, which were subject to public comment.

RESULTS

The panel agreed on 33 recommendations. The recommendations address screening of asymptomatic patients for HIT, diagnosis and initial management of patients with suspected HIT, treatment of acute HIT, and special situations in patients with acute HIT or a history of HIT, including cardiovascular surgery, percutaneous cardiovascular intervention, renal replacement therapy, and venous thromboembolism prophylaxis.

CONCLUSIONS

Strong recommendations include use of the 4Ts score rather than a gestalt approach for estimating the pretest probability of HIT and avoidance of HIT laboratory testing and empiric treatment of HIT in patients with a low-probability 4Ts score. Conditional recommendations include the choice among non-heparin anticoagulants (argatroban, bivalirudin, danaparoid, fondaparinux, direct oral anticoagulants) for treatment of acute HIT.

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.

Management of Patients with Heparin-Induced Thrombocytopenia During Cardiac Surgery

The role of heparin-induced thrombocytopenia and its possibly severe complications in patients undergoing cardiac surgery is increasingly appreciated. Increasing evidence indicates that in patients without the presence of antibodies, unfractionated heparins can be safely used during cardiopulmonary bypass, if their employment is restricted to this short period. This strategy is the first choice in patients with a current negative status of antibodies and in patients in whom surgery can be delayed until antibodies cannot be detected by laboratory tests. To date, however, no alternative anticoagulant to heparin during cardiopulmonary bypass has been approved. With the introduction of the class of direct thrombin inhibitors, effective anticoagulants have become available; however, they have no antidote and require specific monitoring. The availability of direct thrombin inhibitors is currently restricted. The administration of unfractionated heparin with anti-platelet agents such as prostaglandins or the short-acting platelet glycoprotein llb/Illa antagonist tirofiban is another option. Despite successful use of these strategies in fairly large numbers of patients, recent information suggests that in the case of tirofiban, renal failure may cause persistence of the agent with subsequent severe hemorrhage. If surgery is restricted to coronary artery bypass grafting, recent data show that off-pump strategies with use of the direct thrombin inhibitor bivalirudin appear to be a promising option. Therefore, if surgery cannot be postponed, the anticoagulation protocol and the surgical strategy must be adjusted to the condition of the patient and the experience of the center in order to reduce the risk of these “offlabel” strategies.

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.

A Novel Direct Factor Xa Inhibitory Peptide with Anti-Platelet Aggregation Activity from Agkistrodon acutus Venom Hydrolysates

Snake venom is a natural substance that contains numerous bioactive proteins and peptides, nearly all of which have been identified over the last several decades. In this study, we subjected snake venom to enzymatic hydrolysis to identify previously unreported bioactive peptides. The novel peptide ACH-11 with the sequence LTFPRIVFVLG was identified with both FXa inhibition and anti-platelet aggregation activities. ACH-11 inhibited the catalytic function of FXa towards its substrate S-2222 via a mixed model with a K_i value of 9.02 μM and inhibited platelet aggregation induced by ADP and U46619 in a dose-dependent manner. Furthermore, ACH-11 exhibited potent antithrombotic activity in vivo. It reduced paralysis and death in an acute pulmonary thrombosis model by 90% and attenuated thrombosis weight in an arterio-venous shunt thrombosis model by 57.91%, both at a dose of 3 mg/kg. Additionally, a tail cutting bleeding time assay revealed that ACH-11 did not prolong bleeding time in mice at a dose of 3 mg/kg. Together, our results reveal that ACH-11 is a novel antithrombotic peptide exhibiting both FXa inhibition and anti-platelet aggregation activities, with a low bleeding risk. We believe that it could be a candidate or lead compound for new antithrombotic drug development.

Heparin Reexposure in Patients With a History of Heparin-Induced Thrombocytopenia

Objectives:

Patients with a history of heparin-induced thrombocytopenia (HIT), who require subsequent anticoagulation, have limited options. Rechallenge with unfractionated heparin (UFH) has been reported but may be associated with a risk of recurrence of HIT. The objective of this study was to determine the safety of heparin reexposure in patients with a history of HIT.

Methods:

Using several search terms, all cases of heparin reexposure in patients with HIT indexed in MEDLINE (English language only) by June 2014 were reviewed. The bibliography of each relevant article was searched for additional reports. In cases of multiple reexposures, each reexposure was identified as a separate instance of reexposure during analysis.

Results:

A total of 136 patients with a history of HIT had 141 instances of heparin reexposure. Cardiac (76%) and vascular surgeries (11%) were the most common indications. Antiplatelet factor 4/heparin antibodies were positive in 63% of evaluable cases before reexposure. Preexposure plasma exchange (11%) and postexposure nonheparin anticoagulants (63%) were frequently utilized. Complications with heparin reexposure included recurrence of HIT (2.1%, 95% confidence interval 0.73%-6.07%) and bleeding (2.1%).

Conclusion:

Intraoperative heparin reexposure in patients with a history of HIT has a small risk of developing HIT recurrence. The use of preexposure plasma exchange in patients with positive antiplatelet factor 4/heparin antibody and postexposure nonheparin anticoagulants arguably may have reduced the risk of recurrence of HIT.

[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.

Pulmonary Endarterectomy

Chronic thromboembolic pulmonary hypertension (CTEPH) results from recurrent or incomplete resolution of pulmonary embolism. CTEPH is much more common than generally appreciated. Although pulmonary embolism (PE) affects a large number of Americans, chronic pulmonary thromboembolic hypertension remains underdiagnosed. It is imperative that all patients with pulmonary hypertension (PH) be screened for the presence of CTEPH since this form of PH is potentially curable with pulmonary endarterectomy (PEA) surgery. The success of this procedure depends greatly on the collaboration of a multidisciplinary team approach that includes pulmonary medicine, cardiothoracic surgery, and cardiac anesthesiology. This review, based on the experience of more than 3000 pulmonary endarterectomy surgeries, is divided into 2 parts. Part I focuses on the clinical history and pathophysiology, diagnostic workup, and intraoperative echocardiography. Part II focuses on the surgical approach, anesthetic management, postoperative care, and complications.

Systemic infusion and local irrigation with argatroban effective in preventing clot formation during carotid endarterectomy in a patient with heparin-induced thrombocytopenia

BACKGROUND

A therapeutic dilemma exists when patients with symptomatic carotid stenosis and concomitant heparin-induced thrombocytopenia (HIT) are advised to urgently undergo carotid endarterectomy (CEA) with heparin therapy.

METHODS

After a 63-year-old man with HIT and multiple medical comorbidities underwent emergent coronary artery bypass grafting, postoperative imaging revealed plaque at the origin of the left internal carotid artery with 80%-99% stenosis and minimal contralateral internal carotid artery disease. During the patient's evaluation to undergo CEA for symptomatic high-grade carotid stenosis, enzyme-linked immunosorbent assay revealed persistent platelet factor 4 antibodies.

RESULTS

The endarterectomy was successfully performed while the patient received argatroban, both as a continuous infusion and intermittent irrigation during dissection of the plaque. Postoperatively, the drip was continued for 24 hours, and the patient was discharged day 2 on a daily dose of 325 mg of aspirin. At the 6-month examination, Doppler ultrasound revealed normal anterograde velocities with no evidence of stenosis, and the patient noted no subsequent ischemic events.

CONCLUSIONS

We now recommend systemic intravenous and local argatroban irrigation to prevent thromboembolic complications in CEA cases with HIT and renal insufficiency. Bivalirudin for both systemic intravenous use and local irrigation may be safer in patients without renal insufficiency because of its shorter half-life.

Heparin-induced thrombocytopenia associated with massive intracardiac thrombosis: a case report

A 60-years old patient was admitted to a community hospital with septic arthritis. He was treated with antibiotics and subcutaneous unfractionated heparin (UH) was used for venous thromboprophylaxis. After three days, he developed leg deep venous thrombosis and was treated with IV heparin. One day later, the patient developed pulmonary emboli, which was found using ventilation/perfusion scan. He was transferred to the University Hospital for further management. Upon arrival, antibiotic and intravenous UH were continued. Trans-Esophageal Echocardiogram showed a thrombus in the right atrium, a small portion of which extended to the left atrium through a patent foramen ovale. Another large thrombus was noted in the right ventricle, which extended to the pulmonary artery. Review of the patient's medical records revealed a halving of his platelet count three days following the heparin administration. Therefore, HIT seemed very likely. Intravenous UH was stopped and an emergency thrombectomy was performed. ELISA testing of HIT antibodies came negative. This made HIT diagnosis unlikely and the patient received dalteparin. A week later, as the platelet count declined again, HIT antibodies' testing using ELISA and C-14 serotonin release was repeated, and both assays were positive. Argatroban was restarted and the platelet count normalized.

[Direct thrombin inhibitors: pharmacology and application in cardiovascular anesthesia]

The options for drug-controlled anticoagulation are becoming noticeably more manifold. In the area of anaesthesiology and intensive care, there are furthermore special disease patterns, such as heparin-induced thrombocytopenia (HIT) to be known, diagnosed and treated. This article gives a review of the substance groups of the direct thrombin inhibitors (DTI) as alternative anticoagulants for HIT in combination with cardiovascular diseases. For the administration of DTIs, experience and the correct dose are the keys to success and are the deciding factors for the two sides of haemostasis: thrombosis and haemorrhage.

Treatment and prevention of heparin-induced thrombocytopenia: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition)

This chapter about the recognition, treatment, and prevention of heparin-induced thrombocytopenia (HIT) is part of the Antithrombotic and Thrombolytic Therapy: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition). Grade 1 recommendations are strong and indicate that the benefits do, or do not, outweigh risks, burden, and costs. Grade 2 suggests that individual patient values may lead to different choices. Among the key recommendations in this chapter are the following: For patients receiving heparin in whom the clinician considers the risk of HIT to be > 1.0%, we recommend platelet count monitoring over no platelet count monitoring (Grade 1C). For patients who are receiving heparin or have received heparin within the previous 2 weeks, we recommend investigating for a diagnosis of HIT if the platelet count falls by >/= 50%, and/or a thrombotic event occurs, between days 5 and 14 (inclusive) following initiation of heparin, even if the patient is no longer receiving heparin therapy when thrombosis or thrombocytopenia has occurred (Grade 1C). For patients with strongly suspected (or confirmed) HIT, whether or not complicated by thrombosis, we recommend use of an alternative, nonheparin anticoagulant (danaparoid [Grade 1B], lepirudin [Grade 1C], argatroban [Grade 1C], fondaparinux [Grade 2C], or bivalirudin [Grade 2C]) over the further use of unfractionated heparin (UFH) or low-molecular-weight heparin (LMWH) therapy or initiation/continuation of vitamin K antagonists (VKAs) [Grade 1B]. The guidelines include specific recommendations for nonheparin anticoagulant dosing that differ from the package inserts. For patients with strongly suspected or confirmed HIT, we recommend against the use of vitamin K antagonist (VKA) [coumarin] therapy until after the platelet count has substantially recovered (usually, to at least 150 x 10(9)/L) over starting VKA therapy at a lower platelet count (Grade 1B); that VKA therapy be started only with low maintenance doses (maximum, 5 mg of warfarin or 6 mg of phenprocoumon) over higher initial doses (Grade 1B); and that the nonheparin anticoagulant (eg, lepirudin, argatroban, danaparoid) be continued until the platelet count has reached a stable plateau, the international normalized ratio (INR) has reached the intended target range, and after a minimum overlap of at least 5 days between nonheparin anticoagulation and VKA therapy rather than a shorter overlap (Grade 1B). For patients receiving VKAs at the time of diagnosis of HIT, we recommend use of vitamin K (10 mg po or 5 to 10 mg IV) [Grade 1C].

Focus on Thrombin: Alternative Anticoagulants

Unfractionated heparin and protamine have been integral to cardiopulmonary bypass since cardiac surgery was first undertaken. These drugs are inexpensive and well understood but are contraindicated in some individuals, and resistance to heparin can be problematic in others. The interplay between the endothelium, anticoagulants, the coagulation cascade, and the inflammatory response that characterizes cardiac surgery may contribute to some of the complications associated with cardiopulmonary bypass. Various alternative drugs and strategies have been used to manage patients unsuitable for heparin or protamine, but each has its own disadvantages. At present, direct thrombin inhibitors may offer the best available alternative to heparin in cardiac surgery, particularly the short-acting bivalirudin, but this class of anticoagulants is relatively expensive and has no reversal agent. Balanced anticoagulation using combinations of drugs that act at different stages in the coagulation system may improve the management of coagulation in cardiac surgery, but careful investigation of this concept is needed.

Off-Pump Coronary Artery Bypass With Bivalirudin for Patients With Heparin-Induced Thrombocytopenia or Antiplatelet Factor Four/Heparin Antibodies

BACKGROUND

This study assessed the use of bivalirudin as an alternative anticoagulant in patients with heparin-induced thrombocytopenia-thrombotic syndrome (HIT/TS) or antiplatelet factor four-heparin (anti-PF4/H) antibodies undergoing off-pump coronary artery bypass (OPCAB).

METHODS

In a prospective, open-label, multicenter study, fifty-one patients with documented anti-PF4/H antibodies and (or) HIT/TS underwent OPCAB with bivalirudin anticoagulation (0.75 mg/kg i.v. bolus, 1.75 mg/kg/hour infusion). Procedural success (absence of death, Q-wave myocardial infarction, repeat revascularization, and stroke), bleeding, and transfusion at day seven/discharge, thirty days, and twelve weeks were assessed.

RESULTS

Thirty-five patients (67%) were included with positive anti-PF4/H antibodies and no thrombocytopenia or thrombosis, eleven patients (22%) had thrombocytopenia, and five patients had clinical HIT/TS (10%). Procedural success at seven days/discharge was achieved in forty-seven patients (92%), while procedural success at thirty days and twelve weeks was 88%. There were no deaths. Chest tube output over the first twenty-four hours was 936 +/- 525 mL and twenty-five patients received a red blood cell transfusion during their hospitalization. Two patients required reexploration for persistent postoperative hemorrhage.

CONCLUSIONS

Bivalirudin was an effective alternative anticoagulant for patients with HIT/TS or circulating anti-PF4/H antibodies undergoing OPCAB, with high rates of procedural success and an acceptable incidence of bleeding or transfusions.

Heparin-Induced Thrombocytopenia in Left Ventricular Assist Device Bridge-to-Transplant Patients

BACKGROUND

The presence of heparin-induced thrombocytopenia (HIT) increases the risk for thromboembolic events in ventricular assist device (VAD) patients undergoing transplantation. However, cardiopulmonary bypass with alternative anticoagulants is often complicated by bleeding. Owing to this concern, we compared outcomes of HIT-positive versus control bridge-to-transplantation VAD patients; both groups were reexposed to heparin for cardiopulmonary bypass during transplant.

METHODS

From February 2000 to January 2006, data were reviewed on 92 consecutive adult patients who underwent VAD placement as a bridge to transplantation. Patients in whom thrombocytopenia developed after heparin exposure were tested for HIT with an enzyme-linked immunosorbent assay for antiheparin/platelet factor-4 (HPF4) antibody (GTI Diagnostics, Waukesha, Wisconsin). During VAD support, heparin was avoided in HIT-positive patients, but all patients were reexposed to heparin during transplantation. Comparisons between HIT-positive and control patients for survival and freedom from thromboembolic events were determined using the Kaplan-Meier method and log-rank test. Continuous and categorical variables were compared using the Wilcoxon rank-sum and Student t test.

RESULTS

Twenty-four of the 92 patients (26.1%) were determined to be HIT positive by enzyme-linked immunosorbent assay. Survival to transplant was not different between the two groups. When compared with control patients, HIT-positive patients who were reexposed to heparin had a greater decrease in platelet counts immediately after transplant (postoperative days 1 to 4, p < 0.05). Despite this transient thrombocytopenia, there was no difference in posttransplant mortality or thromboembolism.

CONCLUSIONS

Heparin-induced thrombocytopenia-positive VAD patients did not experience increased thromboembolism or mortality after heparin reexposure. In light of the risks of using heparin alternatives, heparin reexposure is a safe management strategy for HIT-positive VAD patients.

Bivalirudin During Cardiopulmonary Bypass in Patients With Previous or Acute Heparin-Induced Thrombocytopenia and Heparin Antibodies: Results of the CHOOSE-ON Trial

BACKGROUND

The coronary artery bypass grafting (CABG) heparin-induced thrombocytopenia thrombosis syndrome (HITTS) on- and off-pump safety and efficacy (CHOOSE-ON) trial was designed as a safety and efficacy trial of bivalirudin for use in anticoagulation during cardiopulmonary bypass (CPB) in patients with confirmed or suspected HIT and (or) antiplatelet factor 4/heparin (anti-PF4/H) antibodies.

METHODS

In an open-label, multicenter trial, 50 patients were enrolled prospectively. The primary study endpoint was in-hospital acute procedural success, defined as the absence of death, Q-wave myocardial infarction (MI), repeat operation for coronary revascularization, and stroke at day seven after surgery or hospital discharge, whichever occurred first. The secondary study endpoints were procedural success, defined as the absence of death, Q-wave MI, repeat operation for coronary revascularization, and stroke, at 30 days and 12 weeks after surgery. Perioperative blood loss, transfusions, and the incidence of major bleeding events were also captured.

RESULTS

There were 49 patients treated with bivalirudin of which 43 had acute HIT and thrombosis syndrome (HITTS) with antibodies at time of surgery. Procedural success in-hospital or at 7 days was achieved in 46 (94%) patients. At day 30 procedural success was achieved in 42 (86%) patients, and after 12 weeks in 40 (82%) patients. Mean intraoperative blood loss was 575 +/- 524 mL, and mean 24-hour postoperative blood loss was 998 +/- 595 mL. Forty-one (84%) patients received transfusions before day 7 or discharge with a mean of 5.6 +/- 3.8 units of red blood cells, 8.6 +/- 7.2 units of platelets, and 6.0 +/- 4.7 units of fresh frozen plasma. No differences in outcome among bivalirudin-treated patients were observed between those in the overall group and those with moderately impaired renal function (n = 10).

CONCLUSIONS

The current investigation expands the experience of safe and effective anticoagulation with bivalirudin during CPB to patients with confirmed or suspected HIT and anti-PF4/H antibodies, including in the setting of impaired renal function.

Impact of Heparin-Induced Thrombocytopenia on Outcome in Patients with Ventricular Assist Device Support: Single-Institution Experience in 358 Consecutive Patients

BACKGROUND

Cardiac surgical patients are at an approximate 1% to 2% risk of experiencing heparin-induced thrombocytopenia (HIT), a severe immune-mediated disease that is associated with thromboembolic events. We assessed the occurrence of this disease and its influence on clinical outcome in patients after implantation of a ventricular assist device (VAD).

METHODS

This retrospective analysis assessed data from our adult patient VAD program between the years 2000 and 2005. Patients were divided into three groups: those without confirmed HIT ((non)HIT), those in whom the diagnosis of HIT was made before VAD implantation (HIT(pre)), and those who experienced HIT after VAD implantation (HIT(post)). End points assessed were procedural success, as defined by discharge from hospital or transplantation or recovery of the failing heart, as opposed to death before procedural success was achieved.

RESULTS

The data of 358 consecutive patients were analyzed. There were 330 (non)HIT patients (91.6%), 15 HIT(pre) patients (4.5%), and 13 HIT(post) patients (3.9%). Procedural success was observed in 50% of (non)HIT patients, 67% of HIT(pre) patients, and 31% of HIT(post) patients.

CONCLUSIONS

Heparin-induced thrombocytopenia is a frequent complication in VAD patients and is associated with detrimental outcome when occurring after implantation. Preoperative diagnosis of HIT and the implementation of alternative anticoagulation procedures appears to be associated with better results. Early detection of HIT antibodies before or shortly after VAD implantation and immediate implementation of an alternative anticoagulation regimen may be a strategy to improve outcome.

Chirurgie cardiaque effectuée avec une association héparine non fractionnée et inhibiteur des récepteurs GPIIbIIIa plaquettaire (tirofiban) pour suspicion de TIH

In a patient with heparin-induced thrombocytopenia few antithrombotic alternate treatments are proposed for cardiac surgery with or without cardiopulmonary bypass: danaparoid, lepirudine or powerful antiplatelet agent. Recently, the platelet GPIIbIIIa antagonist tirofiban (Aggrastat) was tested in humans. We reported two cases of patients operated upon for cardiac surgery with unfractionnated heparin (UFH) and tirofiban. The first patient underwent an off-pump coronary artery bypass graft and the second one a mitral valvular replacement under cardiopulmonary bypass. Tirofiban was associated with UFH and aprotinine. Postoperative bleeding was in the normal range for the two types of surgeries and haemodynamic tolerance was good. These two case reports support the possibility of secure cardiac surgery under efficient platelet inhibition with tirofiban. The management of cardiac surgery with tirofiban without monitoring of platelet aggregation appeared to be more simple than with the other alternate antithrombotic agents.

Bivalirudin Anticoagulation for a Patient with Hypercoagulable Immune Syndromes Undergoing Mitral Valve Surgery

Unfractionated heparin has been a near universal anticoagulant for cardiac surgery; however it is contraindicated in heparin-induced thrombocytopenia type II. Alternative anticoagulants such as bivalirudin (a direct thrombin inhibitor) are being utilized. Bivalirudin was successfully used in an immunologically complex patient (diagnoses of heparin-induced thrombocytopenia type II, systemic lupus erythematosus, antiphospholipid syndrome, and dialysis-dependent renal failure) requiring cardiopulmonary bypass. Thrombotic events are common in antiphospholipid syndrome patients undergoing cardiac surgery utilizing high-dose heparin. This may represent unrecognized heparin-induced thrombocytopenia type II. Our patient did not experience perioperative thrombotic or bleeding complications. The possible cross-reactivity between heparin induced thrombocytopenia type II and antiphospholipid syndrome has not been investigated.

Antithrombotic therapy in cardiac surgery

PURPOSE

To review the perioperative management of antithrombotic therapy in cardiac surgery, including the management of cardiopulmonary bypass (CPB) and off-pump surgery.

METHODS

A review of the relevant English literature over the period 1975-2005 was undertaken, in addition to a review of international practices in antithrombotic therapy in cardiac surgery.

PRINCIPAL FINDINGS

Cardiopulmonary bypass is required in most procedures and makes anticoagulation mandatory. Anticoagulation is, usually, achieved with unfractionnated heparin (UFH). Unfractionated heparin is monitored by point-of-care (POC) testing, such as the activated clotting time or the determination of heparin concentration. The target values of both tests remain empirical, with no clearly validated thresholds. The target value needs to be adjusted according to the POC test, given significant variations between devices and activators. After CABG, the need for antiplatelet therapy is well demonstrated, in order to limit the risk of postoperative death or ischemic events, and improve venous graft patency. Immediately after valvular surgery, antithrombotic therapy should take into account the specific risk carried by each patient and by each prosthetic device. The risk of venous thromboembolism, though poorly defined, is also present in the postoperative period and may require additional attention. Given the frequent exposure to UFH, occurrence of heparin-induced thrombocytopenia is not infrequent in these patients and requires careful individual management.

CONCLUSIONS

Antithrombotic therapy is an essential component of cardiac surgery. Yet, with the exception of antiplatelet agents in CABG patients, antithrombotic therapy is often based on the clinical experience of medical teams more than on an evidence-based assessment of the literature.

Anticoagulation management and cardiac surgery in patients with heparin-induced thrombocytopenia

Unfractionated heparin (UFH) is the gold standard for anticoagulation during cardiopulmonary bypass (CPB). Of patients undergoing CPB operations, 25% to 50% develop heparin-dependent antibodies during the postoperative period, typically between day 5 and 10, if UFH is continued during the postoperative course. In 1% to 3% of all patients undergoing CPB operation with UFH anticoagulation, these antibodies activate platelets causing a prothrombotic disorder, known as heparin-induced thrombocytopenia (HIT), which can lead to life-threatening thromboembolic complications. If urgent cardiac operation with the use of CPB in patients with positive antibody titer is required, different anticoagulatory approaches are available, such as lepirudin, bivalirudin, and danaparoid or UFH in combination with platelet antagonists, such as epoprostenol or tirofiban. In patients with previous HIT but no detectable antibodies, UFH alone can be used only during CPB, but alternative anticoagulation has to be used pre- and postoperatively.

Bidirectional Glenn Shunt Surgery Using Lepirudin Anticoagulation in an Infant with Heparin-Induced Thrombocytopenia with Thrombosis

There are few reports of the management of pediatric patients with heparin-induced thrombocytopenia (HIT) requiring cardiac surgery using currently available anticoagulants. We report a case of an infant with HIT requiring a bidirectional Glenn shunt who was successfully managed using lepirudin (r-hirudin, Refludan; Aventis, Bridgewater, NJ). Dosing and monitoring of anticoagulation were difficult, and we suggest caution in the use of lepirudin for cardiac surgery unless reliable monitoring of the degree of anticoagulation becomes available.

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.

Incidence of Heparin-Induced Thrombocytopenia and Therapeutic Strategies in Pediatric Cardiac Surgery

BACKGROUND

We identified the incidence of heparin-induced thrombocytopenia and the antiheparin-platelet factor 4 (PF4) antibody in pediatric patients undergoing cardiac surgery and documented the differences in the anticoagulation management for the extracorporeal circulation.

METHODS

Between January 2001 and September 2003, 559 cardiac procedures with extracorporeal circulation in 415 patients with congenital heart defects were performed in our institution. Because the development of heparin-induced thrombocytopenia requires previous exposition to heparin, only the 144 patients undergoing a scheduled second procedure on extracorporeal circulation were screened preoperatively. Of these 144 patients, 41 underwent also a third procedure and were screened before each procedure for presence of antiheparin-PF4 antibodies and for clinical signs of heparin-induced thrombocytopenia.

RESULTS

The incidence of antiheparin-PF4 antibodies during the study period was 1.4% (2 of 144 patients). Patients with clinically significant heparin-induced thrombocytopenia could not be identified. Outside the study protocol, 2 more patients with antiheparin-PF4 antibodies were found. In these 4 patients, surgery was performed using lepirudin (Schering, Berlin, Germany) instead of the usual heparin management for extracorporeal circulation. Three of these 4 patients had an uneventful procedure and postoperative course. In 1 patient after total cavopulmonary connection, a reoperation was necessary on the seventh postoperative day owing to partial thrombosis of the lateral tunnel.

CONCLUSIONS

The incidence of heparin-induced thrombocytopenia and of antiheparin-PF4 antibodies in patients undergoing repeated cardiac surgery is low. In antiheparin-PF4 antibody positive patients, the complete avoidance of heparin can be achieved and may account for an uneventful perioperative course.

Heparin-induced thrombocytopenia: recognition, treatment, and prevention: the Seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy

This chapter about the recognition, treatment, and prevention of heparin-induced thrombocytopenia (HIT) is part of the Seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy: Evidence Based Guidelines. Grade 1 recommendations are strong and indicate that the benefits do, or do not, outweigh risks, burden, and costs. Grade 2 suggests that individual patients' values may lead to different choices (for a full understanding of the grading, see Guyatt et al, CHEST 2004; 126:179S-187S). Among the key recommendations in this chapter are the following: For patients in whom the risk of HIT is considered to be > 0.1%, we recommend platelet count monitoring (Grade 1C). For patients who are receiving therapeutic-dose unfractionated heparin (UFH), we suggest at least every-other-day platelet count monitoring until day 14, or until UFH is stopped, whichever occurs first (Grade 2C). For patients who are receiving postoperative antithrombotic prophylaxis with UFH (HIT risk > 1%), we suggest at least every-other-day platelet count monitoring between postoperative days 4 to 14 (or until UFH is stopped, whichever occurs first) [Grade 2C]. For medical/obstetric patients who are receiving prophylactic-dose UFH, postoperative patients receiving prophylactic-dose low molecular weight heparin (LMWH), postoperative patients receiving intravascular catheter UFH "flushes," or medical/obstetrical patients receiving LMWH after first receiving UFH (risk, 0.1 to 1%), we suggest platelet count monitoring every 2 days or 3 days from day 4 to day 14, or until heparin is stopped, whichever occurs first (Grade 2C). For medical/obstetrical patients who are only receiving LMWH, or medical patients who are receiving only intravascular catheter UFH flushes (risk < 0.1%), we suggest clinicians do not use routine platelet count monitoring (Grade 2C). For patients with strongly suspected (or confirmed) HIT, whether or not complicated by thrombosis, we recommend use of an alternative anticoagulant, such as lepirudin (Grade 1C+), argatroban (Grade 1C), bivalirudin (Grade 2C), or danaparoid (Grade 1B). For patients with strongly suspected (or confirmed) HIT, we recommend routine ultrasonography of the lower-limb veins for investigation of deep venous thrombosis (Grade 1C); against the use of vitamin K antagonist (VKA) [coumarin] therapy until after the platelet count has substantially recovered; that the VKA antagonist be administered only during overlapping alternative anticoagulation (minimum 5-day overlap); and begun with low, maintenance doses (all Grade 2C). For patients receiving VKAs at the time of diagnosis of HIT, we recommend use of vitamin K (Grade 2C) [corrected] For patients with a history of HIT who are HIT antibody negative and require cardiac surgery, we recommend use of UFH (Grade 1C).

Extracorporeal Elimination of Large Concentrations of Tirofiban by Zero-Balanced Ultrafiltration During Cardiopulmonary Bypass: An In Vitro Investigation

The short-acting platelet glycoprotein IIb/IIIa antagonist tirofiban is beneficial when used in the context of cardiac surgery. Tirofiban has an elimination half-life of 2 h. Renal failure prolongs the half-life and continues inhibition of platelet aggregation refractory to transfusions of platelets. Extracorporeal elimination is necessary to prevent excessive hemorrhage in this condition. We assessed the elimination of tirofiban by hemofiltration in an in vitro model of cardiopulmonary bypass (CPB). Two hemofilters and one plasmapheresis filter were assessed. Three separate filters of each type were tested serially. The CPB circuit was primed with a total volume of 1000 mL. Tirofiban was added to a calculated concentration of 200 ng/mL. Portions of 50 mL of filtrate were retrieved from the dialyzer, and equal amounts of fluid were substituted in the circuit. After each filtration, the tirofiban blood level was analyzed. The procedure was repeated 16 times. Peak tirofiban concentrations ranged from 160 to 260 ng/mL. The elimination of tirofiban followed an exponential decay curve with fast clearance of the large therapeutic concentrations of 250 to 50 ng/mL. The subsidence coefficient b revealed no significant differences in elimination between the filter systems. These data suggest that ultrafiltration is an effective means for extracorporeal elimination of therapeutic levels of tirofiban.