Andexanet Alfa-Induced Heparin Resistance Missing From SCA Blood Management in Cardiac Surgery Guidelines

Andexanet alfa-associated heparin resistance in cardiac surgery: mechanism and in vitro perspectives

Background

Andexanet alfa (andexanet) is the only FDA-approved antidote for direct factor Xa (FXa) inhibitors but has been reported to cause resistance to unfractionated heparin (UFH). This has delayed anticoagulation for procedures requiring cardiopulmonary bypass (CPB). The mechanism, andexanet and UFH dose dependence, and thrombotic risk of andexanet-associated heparin resistance are unknown.

Methods

The effect of andexanet in vitro was determined using activated clotting times (ACT) and thromboelastography (TEG). Ex vivo CPB circuits were used to determine whether andexanet impaired anticoagulation for extracorporeal circulation. Kinetics of antithrombin (AT) inhibition of FXa and thrombin were measured in the presence of andexanet. Equilibrium modeling and thrombin generation assay (TGA) validation were used to predict the role of andexanet, AT, and UFH concentrations in andexanet-associated heparin resistance.

Results

Andexanet prevented UFH-mediated prolongation of ACT and TEG times. At lower concentrations of andexanet, heparin resistance could be overcome with suprapharmacologic doses of UFH, but not at higher andexanet concentrations. Andexanet rendered standard doses of UFH inadequate to prevent circuit thrombosis, and suprapharmacologic UFH doses were only partially able to overcome this. Scanning electron microscopy demonstrated coagulation activation in circuits. Andexanet prevented UFH enhancement of AT-mediated inhibition of FXa and thrombin. Equilibrium modeling and TGA validation demonstrated that andexanet creates a triphasic equilibrium with UFH and AT: initial UFH unresponsiveness, normal UFH responsiveness when andexanet is depleted, and finally AT depletion. Sufficient CPB heparinization can only occur at low therapeutic andexanet doses and normal AT levels. Higher andexanet doses or AT deficiency may require both AT supplementation and very high UFH doses.

Conclusions

Andexanet causes heparin resistance due to redistribution of UFH-bound AT. If andexanet cannot be avoided prior to heparinization and direct thrombin inhibitors are undesirable, our in vitro study suggests excess UFH should be considered as a potential strategy prior to AT supplementation.

Highlights

Andexanet alfa causes heparin resistance not by depleting antithrombin, but rather by sequestering heparin-bound antithrombin such that it cannot act as an anticoagulant.Heparin responsiveness in the presence of Andexanet alfa is triphasic such that the effect of a dose of heparin can now be predicted in vitro based on the relative concentrations of andexanet, heparin, and antithrombin.The in vitro insights provided by this work provide a rational starting point for further clinical elucidation of the problem and management of andexanet-associated heparin resistance.

[Use of specific antidotes in DOAC-associated severe gastrointestinal bleeding - an expert consensus - Antagonozation of direct oral anticoagulants in gastrointestinal hemorrhages]

Gastrointestinal (GI) bleeding is one of the most common complications associated with the use of direct oral anticoagulants (DOAC). Clear algorithms exist for the emergency measures in (suspected) GI bleeding, including assessing the medication history regarding anti-platelet drugs and anticoagulants as well as simple coagulation tests during pre-endoscopic management. Platelet transfusions, fresh frozen plasma (FFP), or prothrombin complex concentrate (4F-PCC) are commonly used for optimizing the coagulation status. For severe bleeding under the thrombin inhibitor dabigatran, idarucizumab is available, and for bleeding under the factor Xa inhibitors rivaroxaban or apixaban, andexanet alfa is available as specific antidotes for DOAC antagonization. These antidotes represent emergency drugs that are typically used only after performing guideline-compliant multimodal measures including emergency endoscopy. Antagonization of oral anticoagulants should be considered for severe gastrointestinal bleeding in the following situations: (1) refractory hemorrhagic shock, (2) endoscopically unstoppable bleeding, or (3) nonavoidable delays until emergency endoscopy for life-threatening bleeding. After successful (endoscopic) hemostasis, anticoagulation (DOACs, vitamin K antagonist, heparin) should be resumed timely (i.e. usually within a week), taking into account individual bleeding and thromboembolic risk.

Effective application of a direct-acting oral anticoagulants reversal agent in acute type A aortic dissection repair: A case report

There are insufficient reports on the use of andexanet alfa in cardiac surgery. A 67-year-old man was diagnosed with type A aortic dissection and performed emergent surgery. His medical history included atrial fibrillation treated with Edoxaban. We performed total arch replacement. Despite administration of enough protamine, fresh frozen plasma, and platelet administration, controlling bleeding was difficult. Thus, Andexanet Alfa was initiated after CPB withdrawal. Surgical bleeding was dramatically controlled after its administration. There were no findings suggestive of an embolic event. In conclusion, administration of Andexanet Alfa is safe after cardiopulmonary bypass withdrawal.

Andexanet alpha-induced heparin resistance treated by nafamostat mesylate in a patient undergoing total aortic arch repair for Stanford type A acute aortic dissection: a case report

BACKGROUND

Andexanet alfa, an anti-Xa inhibitor antagonist, induces heparin resistance. Here, we report a case of successful management of cardiopulmonary bypass with andexanet alfa-induced heparin resistance using nafamostat mesylate.

CASE PRESENTATION

An 84-year-old female, with Stanford type A acute aortic dissection, underwent an emergency surgery for total aortic arch replacement. Andexanet alfa 400 mg was administered preoperatively to antagonize edoxaban, an oral Xa inhibitor. Heparin 300 IU/kg was administered before cardiopulmonary bypass, and the activated clotting time (ACT) was 291 s. The ACT was 361 s after another administration of heparin 200 IU/kg. According to our routine therapy for heparin resistance, an initial dose of nafamostat mesylate 10 mg was administered intravenously, followed by a continuous infusion of 20-30 mg/h. The ACT was prolonged to 500 s, and cardiopulmonary bypass was successfully established thereafter.

CONCLUSIONS

This case report presents the successful management of cardiopulmonary bypass with andexanet alfa-induced heparin resistance using nafamostat mesilate. This report presents the successful management of cardiopulmonary bypass with andexanet alfa-induced heparin resistance using nafamostat mesilate.

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.