Antithrombin supplementation attenuates heparin resistance in plasma spiked with Gla-domainless factor Xa S195A in vitro

BACKGROUND

Andexanet alfa is a Gla-domainless mutant (S195A) factor Xa (GDXa) approved for acute reversal of oral factor Xa inhibitors. Cardiac surgery patients exposed to andexanet before cardiopulmonary bypass often exhibit severe heparin resistance. There is a paucity of data on the effectiveness and optimal dosage of antithrombin use in this setting. The objective of this study was to evaluate the in vitro effect of increased heparin with antithrombin levels on attenuating heparin resistance induced by GDXa.

METHODS

Heparinised normal pooled plasma and cardiopulmonary bypass plasma were spiked with GDXa 4 μM. Tissue factor-activated thrombin generation was used to assess heparin reversal effects of GDXa and restoration of anticoagulation with additional heparin with and without antithrombin. Serum thrombin-antithrombin complex, antithrombin activity, and tissue factor pathway inhibitor were also measured in tissue factor-activated, recalcified cardiopulmonary bypass plasma spiked with GDXa.

RESULTS

In normal pooled plasma, GDXa-induced heparin reversal was mitigated by maintaining a high heparin concentration (12 U ml-1) and supplementing antithrombin (1.5-4.5 μM) based on peak and velocity of thrombin generation. Heparin reversal by GDXa was also demonstrated in cardiopulmonary bypass plasma, but supplementing both heparin (8 U ml-1) and antithrombin (3 μM) attenuated GDXa-induced changes in peak and velocity of thrombin generation by 72.5% and 72.2%, respectively. High heparin and antithrombin levels attenuated thrombin-antithrombin complex formation in tissue factor-activated, GDXa-spiked cardiopulmonary bypass plasma by 85.7%, but tissue factor pathway inhibitor remained depleted compared with control cardiopulmonary bypass plasma.

CONCLUSIONS

Simultaneous supplementation of heparin and antithrombin mitigate GDXa-induced heparin resistance by compensating for the loss of tissue factor pathway inhibitor.

Evaluation of the use of a heparin dose-response test in dogs to determine the optimal heparin dose during intravascular procedures and assessment of the in vitro heparin response in healthy dogs

BACKGROUND

No guidelines for administering and monitoring anticoagulants intraprocedurally are currently available in dogs, despite the prevalence of procedures necessitating systemic anticoagulation with heparin.

OBJECTIVES

To evaluate an activated clotting time (ACT)-based heparin dose-response (HDR) test to predict the individual required heparin dose in dogs during intravascular procedures, and to investigate both the in vitro heparin - ACT and in vitro heparin - factor anti-Xa activity (anti-Xa) relationships in dogs.

METHODS

Blood was collected from eight healthy beagles undergoing a cardiac procedure and utilised to establish baseline ACT and for in vitro evaluation. Subsequently, 100 IU/kg heparin was administered intravenously (IV) and ACT was remeasured (HDR test). The required heparin dose for an ACT target response ≥300 s was calculated for each individual and ACT was remeasured after administration of this dose. For in vitro testing, a serial heparin blood dilution (0-0.5-1-2-4 international unit (IU)/mL) was prepared and ACT and anti-Xa were determined using whole blood and frozen plasma, respectively.

RESULTS

The HDR test overestimated the required heparin dose in 3/7 dogs. In vitro, ACT and anti-Xa increased significantly with increasing blood heparin concentration. Heparin - ACT was nonlinear in 4/8 dogs at heparin concentrations >2 IU/mL, whereas heparin - anti-Xa remained linear throughout the tested range.

CONCLUSIONS

The HDR test poorly estimated the required heparin dose in dogs. This is most likely attributed to a nonlinear heparin - ACT relationship, as observed in vitro. Anti-Xa is a promising alternative for ACT; however, unavailability as a point-of-care test and lack of in vivo target values restrict its current use.

A Case of Andexanet Alfa Induced Heparin Resistance in Emergent Aortic Surgery: Successful Anticoagulation Management Using Antithrombin Administration

Andexanet alfa (AnAl) is utilized for the urgent reversal of direct oral anticoagulants (DOACs) in cases of severe bleeding. While the guidelines from the Society of Thoracic Surgeons recommend AnAl for urgent cardiac surgery in patients treated with DOACs, concerns persist regarding the potential of AnAl to induce heparin resistance. This report details the case of an 85-year-old woman diagnosed with acute type A aortic dissection, who received AnAl due to prior edoxaban use. During the emergent aortic surgery, she exhibited heparin resistance following the administration of unfractionated heparin (UFH). The administration of antithrombin III (ATIII) significantly influenced activated clotting times, facilitating successful surgery while maintaining adequate anticoagulation. This case underscores the importance of cautious management of AnAl-induced heparin resistance during critical surgeries, emphasizing the role of ATIII supplementation for effective anticoagulation.

Anti-Factor-Xa and Activated Partial Thromboplastin Time Concordance and Outcomes in Adults Undergoing Extracorporeal Membrane Oxygenation: A Secondary Analysis of the Pilot Low-Dose Heparin in Critically Ill Patients Undergoing Extracorporeal Membrane Oxygenation Randomized Trial

OBJECTIVES

To determine the concordance between activated partial thromboplastin time (aPTT) and anti-factor-Xa (anti-Xa) in adults undergoing extracorporeal membrane oxygenation (ECMO) and to identify the factors associated with discordant paired aPTT/anti-Xa.

DESIGN

Pre-planned secondary analysis of the Low-Dose Heparin in Critically Ill Patients Undergoing Extracorporeal Membrane Oxygenation pilot randomized unblinded, parallel-group controlled trial.

SETTING

Two ICUs in two university hospitals.

PATIENTS

Thirty-two critically ill patients who underwent ECMO and who had at least one paired aPTT and anti-Xa assay performed at the same time.

INTERVENTIONS

We analyzed the concordance between aPTT and anti-Xa and identified factors associated with discordant paired aPTT/anti-Xa based on their respective therapeutic ranges. We also compared biological parameters between heparin resistance episode and no heparin resistance.

MEASUREMENTS AND MAIN RESULTS

Of the 32 patients who were included in this study, 24 (75%) had at least one discordant paired aPTT/anti-Xa. Of the 581 paired aPTT/anti-Xa that were analyzed, 202 were discordant. The aPTT was relatively lower than anti-Xa in 66 cases (32.7%) or relatively higher than anti-Xa in 136 cases (67.3%). Thirty-three heparin resistance episodes were identified in six patients (19%).

CONCLUSIONS

In these critically ill patients undergoing ECMO, one third of paired aPTT/anti-Xa measures was discordant. Coagulopathy and heparin resistance might be the reasons for discordance. Our results support the potential importance of routinely monitoring both tests in this setting.

Intraoperative Heparin Resistance after Administration of Andexanet Alfa to Manage an Internal Iliac Artery Aneurysm Rupture: A Case Report

Antithrombotic agents are increasingly prescribed to older adults; however, they are associated with bleeding-related complications. We describe a case of intraoperative heparin resistance after administration of andexanet alfa (AA). An 81-year-old man was diagnosed with a ruptured internal iliac artery aneurysm. The patient required emergency endovascular aneurysm repair and was treated with AA because he was receiving apixaban. Despite high-dose intraoperative heparin administration, his activated coagulation time was not prolonged. Our findings suggest that AA should be administered with caution in patients experiencing potentially fatal bleeding (requiring surgical intervention) who are also receiving direct oral anticoagulants.

Antithrombin Deficiency and Thrombosis: A Wide Clinical Scenario Reported in a Single Institution

Congenital antithrombin (AT) deficiency represents the form of thrombophilia with the highest thrombotic risk. It is characterized by a heterogeneous clinical presentation, depending mostly on the family history of thrombosis and type of genetic mutation. Inherited AT deficiency promotes idiopathic thrombosis at an early age (even in the pediatric population) and at atypical sites. Therefore, a positive family background necessitates ruling out this high-risk thrombophilia at a young age. Studying first-degree relatives, even if they are asymptomatic, is essential to establish thromboprophylaxis and a proper therapeutic approach in case of thrombosis. Patients with congenital AT deficiency require indefinite anticoagulation owing to the high thrombotic recurrence rate. Here, we present four unrelated cases reported in our institution who were diagnosed with hereditary AT deficiency, with a contrasting clinical evolution.

Paraprotein associated heparin resistance during cardiopulmonary bypass

INTRODUCTION

Heparin resistance during cardiopulmonary bypass poses a significant intraoperative dilemma. Antithrombin deficiency related heparin resistance is well described, but less common causes are still poorly understood and inadequately managed.

CASE REPORT

We present a case of heparin resistance during cardiopulmonary bypass in a gentleman with no previous haematological history or thrombotic risk factors. The patient required three times the regular dose of unfractionated heparin to achieve acceptable conditions to initiate and maintain bypass. The patient was found to have elevated serum immunoglobulin M (IgM) kappa paraprotein on post-operative investigation.

DISCUSSION

Paraproteins may exhibit non-specific binding to long polymeric chains of unfractionated heparin and inhibits the interaction between heparin and antithrombin. As a result, excessive doses of heparin are required to overcome this, which increases the risk of perioperative bleeding and other complications.

CONCLUSION

Elevated serum paraprotein levels should be recognised as a cause of heparin resistance during cardiopulmonary bypass.

Successful Nafamostat Mesilate Administration for Andexanet Alfa-Induced Heparin Resistance

Andexanet alfa is an analog of activated factor X and is used as an antagonist of anti-activated factor X agents. Andexanet alfa is useful for hemostasis in emergent bleeding during direct oral anticoagulant administration, which contributes to safety. In patients undergoing surgery with cardiopulmonary bypass because of heparin resistance, anesthesiologists are faced with a choice of anticoagulants. Herein, we experienced anesthesia for vascular prostheses with cardiopulmonary bypass for acute aortic dissection in a patient who had received andexanet alfa preoperatively. Heparin was initially used as the anticoagulant during cardiopulmonary bypass; however, despite the administration of large doses and antithrombin III preparations, anticoagulation was insufficient. Therefore, nafamostat mesilate was administered and sufficient anticoagulation was attained. The patient completed surgery under cardiopulmonary bypass, coagulation function was recovered shortly after withdrawal, and no obvious adverse effects were observed.

Abdominal Aortic Aneurysm with Essential Thrombocythemia: A Case Report Describing Perioperative Management in Open Surgery

We report perioperative management and open surgery to treat a case of infrarenal abdominal aortic aneurysm with essential thrombocythemia (ET), a chronic myeloproliferative disorder associated with arterial or venous thrombosis, idiopathic bleeding, and heparin-resistant diathesis. Following careful preoperative management, including assessment of heparin resistance, open surgery was successfully performed to treat the aortic aneurysm of our patient. This report shows that optimal preparation for surgery is important to safely perform abdominal aortic aneurysm repair and prevent perioperative thrombosis and bleeding in patients with abdominal aortic aneurysm with ET.

The efficacy of low molecular weight heparin is reduced in COVID-19

BACKGROUND

A significant degree of mortality and morbidity in COVID-19 is through thromboembolic complications, only partially mitigated by anticoagulant therapy. Reliable markers of infection severity are not fully established.

OBJECTIVES

This study investigated whether visco-elastic biomarkers predict disease severity on presentation to the Emergency Department (ED) and how they measure response to anticoagulationMETHODS:Patients testing positive for COVID-19 at a large University Teaching Hospital ED were recruited at presentation. Multiple blood samples were taken throughout hospital admission to monitor disease progression with end outcome recorded. Visco-elastic markers, fractal dimension (df) and Time to Gel Point (TGP) which measure the properties of the incipient clot were compared in patients with and without anticoagulation by Low Molecular Weight Heparin (LMWH).

RESULTS

TGP and df did not predict severity of infection with COVID-19. Although LMWH prolonged TGP, there was no change in df indicating LMWH did not change clot microstructure.

CONCLUSIONS

Therapeutic efficacy of LMWH appears blunted in COVID-19 infection. This may be due to the inflammatory state creating a resistance to LMWH activity, which may explain why LMWH appears less effective in COVID-19 compared to other disease states. COVID-19 was not predicted by visco-elastic testing at the time of ED presentation.

A Case of Intraprocedural Thrombotic Events During Percutaneous Coronary Intervention Due to Acquired Antithrombin Deficiency-related Heparin Resistance Successfully Treated with Antithrombin Gamma Supplementation

A 75-year-old man receiving treatment for necrotizing pancreatitis developed septic disseminated intravascular coagulation and acute coronary syndrome (ACS). During percutaneous coronary intervention (PCI), a large amount of fresh thrombi appeared after balloon dilatation for the ACS-culprit lesion. Given the low plasma AT activity and poorly prolonged activated clotting time (ACT), we suspected that acquired AT deficiency-related heparin resistance (HR) was responsible for the thrombus formation. Administration of AT gamma markedly improved ACT, and we successfully completed PCI. We suggest that AT gamma be considered a treatment option for AT deficiency-related HR and subsequent intraprocedural thrombotic events.

Use of nafamostat mesilate for anticoagulation during extracorporeal membrane oxygenation: A systematic review

BACKGROUND

Extracorporeal membrane oxygenation (ECMO) represents an advanced option for supporting refractory respiratory and/or cardiac failure. Systemic anticoagulation with unfractionated heparin (UFH) is routinely used. However, patients with bleeding risk and/or heparin-related side effects may necessitate alternative strategies: among these, nafamostat mesilate (NM) has been reported.

METHODS

We conducted a systematic literature search (PubMed and EMBASE, updated 12/08/2021), including all studies reporting NM anticoagulation for ECMO. We focused on reasons for starting NM, its dose and the anticoagulation monitoring approach, the incidence of bleeding/thrombosis complications, the NM-related side effects, ECMO weaning, and mortality.

RESULTS

The search revealed 11 relevant findings, all with retrospective design. Of these, three large studies reported a control group receiving UFH, the other were case series (n = 3) or case reports (n = 5). The main reason reported for NM use was an ongoing or high risk of bleeding. The NM dose varied largely as did the anticoagulation monitoring approach. The average NM dose ranged from 0.46 to 0.67 mg/kg/h, but two groups of authors reported larger doses when monitoring anticoagulation with ACT. Conflicting findings were found on bleeding and thrombosis. The only NM-related side effect was hyperkalemia (n = 2 studies) with an incidence of 15%-18% in patients anticoagulated with NM. Weaning and survival varied across studies.

CONCLUSION

Anticoagulation with NM in ECMO has not been prospectively studied. While several centers have experience with this approach in high-risk patients, prospective studies are warranted to establish the optimal space of this approach in ECMO.

Management of heparin resistance due to antithrombin deficiency in a Chinese pregnant woman: a case report

Untreated individuals with antithrombin (AT) deficiency are at higher risk of thrombosis and adverse pregnancy outcomes. The present recommendations are mostly empirical for treating patients with AT deficiency during pregnancy because of the absence of guidelines. We report a rare case of heparin resistance due to AT deficiency in a pregnant 32-year-old Chinese woman. We also reviewed the English medical literature for AT deficiency and its association with thromboembolism and treatment. This patient suffered two early miscarriages because of thrombosis due to AT deficiency. The patient was administered the combination of adequate low molecular weight heparin with fresh frozen plasma and warfarin because of her heparin resistance. She delivered a healthy female newborn without any adverse effects of the anticoagulation therapy. Our findings suggest that the combination of adequate low molecular weight heparin with fresh frozen plasma and warfarin is effective for preventing thrombus during pregnancy.

A Case of COVID-19 Related Coagulopathy Complications and Heparin Resistance

Mechanisms of COVID-19 coagulopathy have been speculated and are not definitively understood; the current speculation is that there is elaborate crosstalk between the inflammatory and hemostatic systems which contributes to the overall increased thrombotic risk in the setting of COVID-19 resulting in a hypercoagulable state. A few documented reports regarding cases of apparent heparin resistance in patients with COVID-19 with complications of thromboembolic events occurring in the setting of heparin anticoagulation have been described. This phenomenon of heparin resistance has been observed in patients with active, severe COVID-19 infection. However, we describe a unique case of a patient who had recovered from a recent, mild COVID-19 infection that did not require hospitalization and presented with acute limb ischemia and demonstrated heparin resistance. The patient was managed by specialists in vascular surgery, intensivists, cardiologists, hematology, and physical medicine and rehabilitation (PMR). We present the case of a patient who had successfully recovered from COVID-19 yet demonstrated post-COVID-19 complications related to coagulopathy and heparin resistance. 

Heparin Resistance Is Common in Patients Undergoing Extracorporeal Membrane Oxygenation but Is Not Associated with Worse Clinical Outcomes

Extracorporeal membrane oxygenation (ECMO) protocols generally require systemic anticoagulation with heparin to prevent circuit thrombosis. The prevalence, risk factors, and outcomes of heparin resistance in this setting are ill-defined. To better understand the prevalence and clinical consequences of heparin resistance in this population, we conducted a retrospective analysis of all patients treated with ECMO at a single academic medical center between 2016 and 2019. Univariate and multivariate analyses were used to evaluate predictors and outcomes of heparin resistance. Of 67 patients in our study, 50.7% met the threshold for heparin resistance for at least 1 day, which was managed in all cases with increases in heparin dose. Patients with heparin resistance were more likely to be male (82.4% vs. 48.5%, p = 0.005) and to have a higher mean platelet count (132 vs. 104 × 103/mL, p = 0.027) compared with those without heparin resistance. Multivariate logistic regression found no significant association between the development of heparin resistance and rates of thrombosis, hemorrhage, or overall survival. Additional prospective studies are required to clarify the clinical implications of heparin resistance in this population.

Infective Endocarditis Is a Risk Factor for Heparin Resistance in Adult Cardiovascular Surgical Procedures: A Retrospective Study

OBJECTIVES

Heparin resistance (HR), defined as a decrease in heparin responsiveness, can result in adverse events with prolonged duration of surgery. Although some clinical risk factors have been suggested, the relationship with the surgical diagnosis is unclear. The aim of present study was to elucidate the clinical predictors of HR including the surgical diagnosis.

DESIGN

This retrospective cohort study determined the incidence of HR (defined as activated clotting time [ACT] <400 seconds after 250-350 IU/kg of heparin administration) and heparin sensitivity index (HSI) was calculated from the rate of change in ACT per heparin dose. Preoperative demographic data, medication history, and laboratory data also were analyzed.

SETTING

Single institution, tertiary care hospital.

PARTICIPANTS

Adult patients who underwent cardiovascular surgery with cardiopulmonary bypass between January 2012 and September 2018.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Of 287 patients, 88 (30.7%) were classified as HR. In univariate analysis, infective endocarditis (IE), platelet count, and serum fibrinogen and albumin levels were associated with HR. After adjustment for baseline ACT and initial heparin dose, IE (odds ratio 4.57, [95% CI: 1.10-19.1]; p = 0.037) and albumin ≤3.5 g/dL (3.17, [1.46-6.93]; p = 0.004) were associated independently with HR. Patients with IE had significantly lower HSI than those with other diseases. All HR patients were treated with additional heparin, and 17 of them received human antithrombin-III concentrate.

CONCLUSIONS

Infective endocarditis and preoperative hypoalbuminemia were associated independently with HR. The optimal anticoagulation strategy for patients with these risk factors requires further investigations based on the authors' findings.

Heparin dosage, level, and resistance in SARS-CoV2 infected patients in intensive care unit

Introduction

Patients with COVID‐19 frequently exhibit a hypercoagulable state with high thrombotic risk, particularly those admitted to intensive care units (ICU). Thromboprophylaxis is mandatory in these patients; nevertheless, thrombosis still occurs in many cases. Thus, the problem of assessing an adequate level of anticoagulation in ICU patients becomes evident during the COVID‐19 pandemic. The aim of this study was to evaluate the heparin resistance and the efficacy of heparin monitoring using an anti‐Xa activity assay.

Methods

Thirty‐seven heparin‐treated patients admitted to ICU for SARS‐CoV‐2 pneumonia were retrospectively studied for antifactor Xa activity (anti‐Xa), activated partial thromboplastin time (APTT), Antithrombin, Fibrinogen, D‐Dimer, Factor VIII, von Willebrand Factor, and the total daily amount of heparin administered. The correlation between APTT and anti‐Xa was evaluated for unfractionated heparins (UFH). The correlations between the daily dose of UFH or the dosage expressed as IU/kg b.w. for low molecular weight heparin (LMWH) and anti‐Xa were also evaluated.

Results

Twenty‐one patients received calcium heparin, 8 sodium heparin, and 8 LMWH. A moderate correlation was found between APTT and anti‐Xa for UFH. APTT did not correlate with coagulation parameters. 62% of UFH and 75% of LMWH treated patients were under the therapeutic range. About 75% of patients could be considered resistant to heparin.

Conclusions

SARS‐COV2 pneumonia patients in ICU have frequently heparin resistance. Anti‐Xa seems a more reliable method to monitor heparin treatment than APTT in acute patients, also because the assay is insensitive to the increased levels of fibrinogen, FVIII, and LAC that are common during the COVID‐19 inflammatory state.

Effective use of fondaparinux in patient with unresponsiveness to nadroparin

WHAT IS KNOWN AND OBJECTIVE

Fondaparinux exhibits a similar mechanism of action as LMWH. Since both of these drugs bind to antithrombin and increase its affinity to factor Xa, fondaparinux is not expected to be an effective alternative anticoagulant to LMWH in case of LMWH resistance.

CASE SUMMARY

We report on a case of effective anticoagulation using fondaparinux following total unresponsiveness to high doses of nadroparin administered twice daily, as confirmed via repeated anti-Xa measurements. The antithrombin levels were within the normal range.

WHAT IS NEW AND CONCLUSION

To the best of our knowledge, this is the first report of the effective use of fondaparinux in the case of unresponsiveness to LMWH.

Surgical Revascularization With Cardiopulmonary Bypass on a Patient With Severe COVID-19

The coronavirus disease 2019 (COVID-19) may lead to an acute respiratory distress syndrome by an inappropriate cytokine response and may predispose to a prothrombotic state through multiple pathways. Both can complicate the management of cardiac surgery with cardiopulmonary bypass, which is known to activate the hemostatic system and to exacerbate systemic inflammatory response. Little is known about the impact of cardiac surgery with cardiopulmonary bypass on viral pneumonia, particularly with the new coronavirus. In this article, we describe the case of a diabetic patient with COVID-19 and a concomitant 3-vessel disease with a formal indication for surgical revascularization, who unexpectedly presented with a high heparin resistance during cardiopulmonary bypass. Emphasis is placed on the importance of multidisciplinary team discussions before surgery, on the thorough preoperative assessment, and on the perioperative management, particularly regarding mechanical ventilation and anticoagulation.

Monitoring of Unfractionated Heparin in Severe COVID-19: An Observational Study of Patients on CRRT and ECMO

Objective  Severe cases of coronavirus disease 2019 (COVID-19) can require continuous renal replacement therapy (CRRT) and/or extracorporeal membrane oxygenation (ECMO). Unfractionated heparin (UFH) to prevent circuit clotting is mandatory but monitoring is complicated by (pseudo)-heparin resistance. In this observational study, we compared two different activated partial thromboplastin time (aPTT) assays and a chromogenic anti-Xa assay in COVID-19 patients on CRRT or ECMO in relation to their UFH dosages and acute phase reactants. Materials and Methods  The aPTT (optical [aPTT-CS] and/or mechanical [aPTT-STA] clot detection methods were used), anti-Xa, factor VIII (FVIII), antithrombin III (ATIII), and fibrinogen were measured in 342 samples from 7 COVID-19 patients on CRRT or ECMO during their UFH treatment. Dosage of UFH was primarily based on the aPTT-CS with a heparin therapeutic range (HTR) of 50-80s. Associations between different variables were made using linear regression and Bland-Altman analysis. Results  Dosage of UFH was above 35,000IU/24 hours in all patients. aPTT-CS and aPTT-STA were predominantly within the HTR. Anti-Xa was predominantly above the HTR (0.3-0.7 IU/mL) and ATIII concentration was >70% for all patients; mean FVIII and fibrinogen were 606% and 7.5 g/L, respectively. aPTT-CS correlated with aPTT-STA ( r 2  = 0.68) with a bias of 39.3%. Correlation between aPTT and anti-Xa was better for aPTT-CS (0.78 ≤  r 2  ≤ 0.94) than for aPTT-STA (0.34 ≤  r 2  ≤ 0.81). There was no general correlation between the aPTT-CS and ATIII, FVIII, fibrinogen, thrombocytes, C-reactive protein, or ferritin. Conclusion  All included COVID-19 patients on CRRT or ECMO conformed to the definition of heparin resistance. A patient-specific association was found between aPTT and anti-Xa. This association could not be explained by FVIII or fibrinogen.

Massive atrial myxoma requiring emergency cardiopulmonary bypass in a patient with heparin resistance

Heparin exhibits complex pharmacology with a wide variation in individual response. Despite this, heparin is the most commonly used anticoagulant during cardiopulmonary bypass. Heparin resistance in the context of a patient with severe cardiovascular compromise presents a potentially life-threatening challenge. A 31-year-old woman was listed for emergency excision of a massive left atrial myxoma. On induction of anaesthesia, she developed marked cardiovascular instability secondary to mitral inflow obstruction. An initial heparin dose of 600 units.kg^-1 produced an activated clotting time of 360 s; however, immediate cardiopulmonary bypass was required. Heparin resistance remained problematic throughout the procedure, with an inadequate response to antithrombin three supplementation. Despite a total dose of 120,000 units of heparin, anticoagulation was fully reversed with 500 mg protamine and there was no subsequent re-heparinisation. Heparin resistance, when coinciding with profound cardiovascular instability, requires a pragmatic response to expedite establishment of cardiopulmonary bypass whilst minimising potential harm. In this case, successful cardiopulmonary bypass was achieved with additional heparin boluses from an alternative batch administered both intravenously and via the bypass circuit. We therefore advocate consideration of this approach as one possible solution to achieving safe entry onto cardiopulmonary bypass in a crisis scenario.

Treatment with rivaroxaban and monitoring of coagulation profiles in two dogs with venous thromboembolism

Two dogs with immune-mediated hemolytic anemia complicated with thromboembolism were presented. Both of the dogs were initially treated with immunosuppressive therapy in conjunction with dalteparin and clopidogrel. Although the immunosuppressive therapy was effective, peritoneal effusion due to thromboembolism was observed during the course of the disease in these dogs. After initiation of rivaroxaban treatment, peritoneal effusion decreased immediately in parallel with the normalization of D-dimer, antithrombin (AT), and thrombin-antithrombin complex (TAT). Hematochezia, cutaneous hemorrhage, and hematuria were observed as adverse events after administration of rivaroxaban in one case. Rivaroxaban was effective for the control of thromboembolism secondary to immune-mediated hemolytic anemia, and D-dimer, AT, and TAT were useful to monitor the status of thromboembolic disease in dogs.

Application of goal-directed therapy for the use of concentrated antithrombin for heparin resistance during cardiac surgery

The maintenance of anticoagulation in adult patients undergoing cardiopulmonary bypass is dependent upon a number of factors, including heparin concentration and adequate antithrombin activity. Inadequate anticoagulation increases the risk of thrombosis and jeopardizes both vascular and extracorporeal circuit integrity. The purpose of this study was to evaluate a goal-directed approach for the use of antithrombin in patients who were resistant to heparin. Following institutional review board approval, data were obtained from quality improvement records. A goal-directed protocol for antithrombin was established based upon heparin dosing (400 IU kg^-1 body weight) and achieving an activated clotting time of ⩾500 seconds prior to cardiopulmonary bypass. Two groups of patients were identified as those receiving antithrombin and those not receiving antithrombin. Outcome measures included activated clotting time values and transfusion rates. Consecutive patients (n = 140) were included in the study with 10 (7.1%) in the antithrombin group. The average antithrombin dose was 1,029.0 ± 164.5 IU and all patients had restoration to the activated clotting time levels. Patients in the antithrombin group were on preoperative heparin therapy (80.0% vs. 24.6%, p = 0.001). Prior to cardiopulmonary bypass the activated clotting time values were lower in the antithrombin group (417.7 ± 56.1 seconds vs. 581.1 ± 169.8 seconds, p = 0.003). Antithrombin patients had a lower heparin sensitivity index (0.55 ± 0.17 vs. 1.05 ± 0.44 seconds heparin^-1 IU kg^-1, p = 0.001), received more total heparin (961.3 ± 158.5 IU kg^-1 vs. 677.5 ± 199.0 IU kg^-1, p = 0.001), more cardiopulmonary bypass heparin (22,500 ± 10,300 IU vs. 12,100 ± 13,200 IU, p = 0.016), and more protamine (5.4 ± 1.2 vs. 4.1 ± 1.1 mg kg^-1, p = 0.003). The intraoperative transfusion rate was higher in the antithrombin group (70.0% vs. 35.4%, p = 0.035), but no differences were seen postoperatively. Utilization of a goal-directed algorithm for the administration of antithrombin for the treatment of heparin resistance is effective in patients undergoing cardiac surgery.

Management of antithrombin deficiency: an update for clinicians

Introduction. Antithrombin is a serpin that inhibits multiple procoagulant serine proteases and acts as an endogenous anticoagulant. Thus, congenital antithrombin deficiency constitutes a major thrombophilic state, the most severe so far. Areas covered. In the present work, we globally review the biology, genetics, diagnosis, and management of congenital antithrombin deficiency, and also discuss puzzling questions and future perspectives regarding this severe inherited thrombophilia. Expert opinion. Although this disorder exerts high clinical heterogeneity, many carriers will need careful and long-term anticoagulation and/or thromboprophylaxis, especially in high-risk situations, such as surgery and pregnancy. Notably, antithrombin concentrates constitute a considerable arsenal for both treatment and prevention of acute venous thrombosis in subjects with antithrombin deficiency. Current evidences are based almost exclusively on retrospective case series, so an integrated functional, biochemical and molecular characterization will be of clinical relevance and guide hematologists' personalized decisions.

Bivalirudin as an adjunctive anticoagulant to heparin in the treatment of heparin resistance during cardiopulmonary bypass-assisted cardiac surgery

Heparin resistance (unresponsiveness to heparin) is characterized by the inability to reach acceptable activated clotting time values following a calculated dose of heparin. Up to 20% of the patients undergoing cardiothoracic surgery with cardiopulmonary bypass using unfractionated heparin (UFH) for anticoagulation experience heparin resistance. Although UFH has been the "gold standard" for anticoagulation, it is not without its limitations. It is contraindicated in patients with confirmed heparin-induced thrombocytopenia (HIT) and heparin or protamine allergy. The safety and efficacy of the use of the direct thrombin inhibitor bivalirudin for anticoagulation during cardiac surgery has been reported. However, there have been no reports on the treatment of heparin resistance with bivalirudin during CPB. In this review, we report the favorable outcome of our single-center experience with the alternative use of bivalirudin in the management of anticoagulation of heparin unresponsive patients undergoing coronary artery bypass graft surgery.

Anticoagulation management associated with extracorporeal circulation

The use of extracorporeal circulation requires anticoagulation to maintain blood fluidity throughout the circuit, and to prevent thrombotic complications. Additionally, adequate suppression of hemostatic activation avoids the unnecessary consumption of coagulation factors caused by the contact of blood with foreign surfaces. Cardiopulmonary bypass represents the greatest challenge in this regard, necessitating profound levels of anticoagulation during its conduct, but also quick, efficient reversal of this state once the surgical procedure is completed. Although extracorporeal circulation has been around for more than half a century, many questions remain regarding how to best achieve anticoagulation for it. Although unfractionated heparin is the predominant agent used for cardiopulmonary bypass, the amount required and how best to monitor its effects are still unresolved. This review discusses the use of heparin, novel anticoagulants, and the monitoring of anticoagulation during the conduct of cardiopulmonary bypass.

Achievement of therapeutic anti-Xa levels in a proven heparin-resistant patient through the use of nontraditional high-dose enoxaparin

OBJECTIVE

To describe the successful use of high-dose enoxaparin therapy (1.5 mg/kg subcutaneously twice daily) to attain a therapeutic anti-factor Xa (anti-Xa) level in a cancer patient with heparin resistance.

CASE SUMMARY

A proven heparin-resistant patient with venous thromboembolism (VTE) and lung cancer who required approximately 66 000 units of unfractionated heparin daily was successfully transitioned to an off-label high-dose enoxaparin (OLHDE) 1.5 mg/kg subcutaneously twice daily. The patient was maintained on this same dose, and therapeutic levels were confirmed via use of the anti-Xa monitoring test. The patient was able to be discharged from the medical floor on this same dose with no further complications of VTE noted. No adverse events from this dosing were observed during the duration of therapy.

DISCUSSION

Options for overcoming heparin resistance are limited to case reports and small studies. The best course of treatment in the cancer patient is unclear. OLHDE allowed for the transition from intravenous to subcutaneous medication and transition off the medical floor. This case supports the use of OLHDE as a therapeutic option in heparin-resistant patients with cancer. Further study is needed to confirm the efficacy of OLHDE in this patient population.

CONCLUSION

High-dose enoxaparin may be an option to treat cancer patients with confirmed heparin resistance and venous thromboembolism.

Initial experience with recombinant antithrombin to treat antithrombin deficiency in patients on extracorporeal membrane oxygenation

Acquired antithrombin (AT) deficiency has been associated with patients on extracorporeal membrane oxygenation (ECMO) as a result of hemodilution, blood coagulation activation, and the use of heparin. Replacement of AT has been typically utilized through the use of fresh-frozen plasma or AT concentrate. Antithrombin alfa (ATryn) is a recombinant form of AT (rAT) with an identical amino acid sequence as that of plasma-derived antithrombin. The primary objective of this study is to examine the relationship of rAT dose to measured plasma antithrombin activity in a small series of patients who received rAT while on ECMO. A retrospective chart review was performed of all patients at Medical City Children's Hospital who received ATryn while supported on ECMO between December 2011 and April 2012. Five patients were identified and the patients' weight, bolus dose of ATryn, drip rate of ATryn, and AT blood levels were collected for analysis. The median age of these patients was 1 month (range, 1 day to 3.75 years). Because no dosing guidelines exist for pediatric ECMO, a starting dose of ATryn was chosen based on the manufacturer's labeled indication (prevention of thromboembolic events in patients with AT hereditary deficiency). The median dose of rAT was 368 IU/kg/day (range, 104-520 IU/kg/day) to obtain AT activity level of 80-120%. The average time to reach the targeted AT activity level (80-120%) was 12.7 hours (range, 11-17 hours). Our findings suggest that the published ATryn dose may be inadequate to reach desired AT activity concentrations for pediatric patients on ECMO. Difference in patient population, use of extracorporeal circuits, and the use of heparin are likely explanations for this finding. We would also recommend frequent checking of AT levels while delivering this drug because making timely adjustments is necessary for achieving and maintaining the target AT activity level.

Bivalirudin in venovenous extracorporeal membrane oxygenation

Optimal anticoagulation plays a pivotal role in successful outcome of extracorporeal membrane oxygenation (ECMO). Heparin has been the anticoagulant of choice owing to its advantages like easy monitoring and reversibility. However, if heparin resistance is encountered, one has to decide whether to treat heparin resistance with fresh-frozen plasma or antithrombin concentrates or to choose one of the heparin alternatives for anticoagulation. We report a case of heparin resistance resulting from antithrombin III deficiency in a patient on venovenous ECMO, in which anticoagulation was managed with bivalirudin. The dose of bivalirudin for anticoagulation in ECMO has not been standardized and different authors have reported different doses. We found a bivalirudin dose of .1-.2 mg/kg/h to be adequate to maintain a target activated clotting time of 200-220 seconds. Platelet counts were stable throughout and no major bleeding or thrombotic complications took place. We found bivalirudin to be a feasible and effective anticoagulant and safe to use for long durations in ECMO without any major complications.

The evaluations of frequency distribution heparin resistance during coronary artery bypass graft

BACKGROUND

Heparin is one of the most important medication that is used in coronary artery bypass graft (CABG) operations, but some patients demonstrate heparin resistance (HR) during CABG. Heparin resistance was defined as at least one activated clothing time <400 seconds after heparinization and/or the need for purified antithrombin III (AT-III) administration. The goal of this study was the investigation of HR prevalence in our country and relation between HR and post-operative CABG complications.

MATERIALS AND METHODS

One hundred patients that candidate for CABG were selected and surveyed for HR and complications. The data entered to computer and analyzed by SPSS soft ware. The Chi-square and student t-tests were used for data analysis.

RESULTS

The prevalence of heparin resistance in our study was 3%. There was no relation among bleeding, cardiac arrest and HR. Bleeding happened in 13 patients of which 1 person was in HR group (33.3%) and 12 in non HR group (12.4%) (P = 0.34). Cardiac arrest happened in 8 patients, 1 person was in HR group (33.3%) and 7 in non HR group (7.2%) (P = 0.22). According our data there were no relation among HR and gender and ventilator dependency time.

CONCLUSIONS

HR is a nearly prevalent complication among patients that undergone CABG that may led to some complications such as bleeding and cardiac arrest. In our study, we did not find significant relation among them, but in frequency these complications were higher in HR group.

Evidence-based algorithm for heparin dosing before cardiopulmonary bypass. Part 1: Development of the algorithm

The incidence of heparin resistance during adult cardiac surgery with cardiopulmonary bypass has been reported at 15%-20%. The consistent use of a clinical decision-making algorithm may increase the consistency of patient care and likely reduce the total required heparin dose and other problems associated with heparin dosing. After a directed survey of practicing perfusionists regarding treatment of heparin resistance and a literature search for high-level evidence regarding the diagnosis and treatment of heparin resistance, an evidence-based decision-making algorithm was constructed. The face validity of the algorithm decisive steps and logic was confirmed by a second survey of practicing perfusionists. The algorithm begins with review of the patient history to identify predictors for heparin resistance. The definition for heparin resistance contained in the algorithm is an activated clotting time < 450 seconds with > 450 IU/kg heparin loading dose. Based on the literature, the treatment for heparin resistance used in the algorithm is anti-thrombin III supplement. The algorithm seems to be valid and is supported by high-level evidence and clinician opinion. The next step is a human randomized clinical trial to test the clinical procedure guideline algorithm vs. current standard clinical practice.

Heparin sensitivity test for patients requiring cardiopulmonary bypass

Anticoagulation for the open heart surgery patient undergoing cardiopulmonary bypass (CPB) is achieved with the use of heparin. The industry standard of activated clotting time (ACT) was used to measure the effect of heparin. The commonly acceptable target time of anticoagulation adequacy is 480 seconds or greater. Some patients, however, exhibit resistance to standard dosing of heparin and do not reach target anticoagulation time (480 seconds). Antithrombin III deficiency has been previously cited as the cause of heparin resistance. Early detection of heparin resistance (HR) may avoid both the delayed start of CPB and inadequate anticoagulation, if emergency bypass is required. An anticoagulation sensitivity test (AST) was developed by adding 12 units of porcine mucosa heparin to the ACT tube (International Technidyne, celite type). Before anticoagulation, 4 mL of blood was drawn from the patient arterial line. Following the manufacturer's instructions, 2 mL of blood was added to each tube (ACT-baseline and ACT-AST). Three minutes after anticoagulation with 4 mg heparin/kg body weight, a second sample (ACT-CPB) was taken to determine anticoagulation adequacy. The ACT times of each sample were recorded for 300 procedures occurring during 2004 and were retrospectively reviewed. Heparin resistance occurred in approximately 20% of the patients (n = 61). In 54 patients, heparin resistance was predicted by the ACT-AST. This was determined by the presence of an ACT-AST time and an ACT-CPB that were both < 480 seconds. The positive predictive value was 90%, with a false positive rate of 3%. Heparin resistance occurs in patients undergoing CPB. We describe a simple and reliable test to avoid the delays of assessing anticoagulation for CPB (90% positive predictive value). Depending on program guidelines, patients can be given additional heparin or antithrombin III derivatives to aid in anticoagulation. An additional ACT must be performed and reach target times before CPB initiation. Testing of patient blood before the time of incision for sensitivity to heparin is a way to avoid a delay that can be critical in the care of the patient. Commercial tests are available, but efficacy data are limited, and they lead to added inventory expense. This method of titrating a diluted heparin additive, mixed with patient blood in a familiar ACT test, has proven to be an inexpensive and reliable test to predict patient's sensitivity to heparin.