Objective The use of apixaban in the pediatric cardiac population is expanding. We describe our apixaban dosing and monitoring strategy in children and young adults awaiting heart transplantation, along with outcomes related to bleeding and thrombosis during wait-list and early post-transplant periods. Methods This study is a retrospective, single center analysis of all patients receiving apixaban while awaiting cardiac transplantation. Weight-based dosing was monitored with peak drug-specific anti-Xa chromogenic analysis. Significant post-operative bleeding defined by chest tube output or need for surgical intervention. Results From September 2020 through December 2022, 19 patients, median age 13.5 years (6.1, 15.8 years), weighing 48.9 kg (15.4, 67.6) received apixaban while awaiting transplant. Indication for apixaban was prophylaxis (n=18, 3 with ventricular assist devices) and treatment of thrombus (n=1). There were no clinically relevant non-major or major bleeding, nor thrombotic events while awaiting transplant. The median time from last apixaban dose to arrival in the operating room was 23.2 hours (15.6-33.8), with median random apixaban level of 37 ng/ml (28.3, 59), 6.3 hours (4.8, 8.4) prior to arrival in the operating room. 32% of patients had significant post-operative bleeding based on chest tube output post-transplant or need for intervention. No patients meeting criteria for significant postoperative bleeding were thought to be attributable to apixaban. Conclusion Careful use of apixaban can be safe and effective while awaiting heart transplant. There was no appreciable increase in perioperative bleeding. The use of apixaban is promising in providing safe, predictable and efficacious anticoagulation while avoiding additional patient stressors.

Objective: To characterize viscoelastic testing profiles of children with multisystem inflammatory syndrome in children (MIS-C). Methods: This single-center retrospective review included 30 patients diagnosed with MIS-C from January 1 to September 1, 2020. Thromboelastography (TEG) with platelet mapping was performed in 19 (63%) patients and compared to age- and gender- matched controls via Student’s t-test and Wilcoxon rank sum test. Pearson’s and Spearman correlation were used to assess relationships between TEG parameters and inflammatory markers. Results: Patients with MIS-C had abnormal TEG results compared to controls, including decreased K time (1.1 vs. 1.7 min, P<0.01), increased alpha angle (75.0 vs. 65.7 degrees, P<0.01), increased maximum amplitude (70.8 vs. 58.3 mm, P<0.01), and decreased Ly-30 (1.1 vs. 3.7%, P=0.03); consistent with increased clot formation rate and strength, and slower fibrinolysis. TEG maximum amplitude was moderately correlated with erythrocyte sedimentation rate (r=0.60, P=0.02), initial platelet count (r=0.67, P<0.01), and peak platelet count (r=0.51, P=0.03). TEG alpha angle was moderately correlated with peak platelet count (r=0.54, P=0.02). 17 (57%) patients received aspirin (ASA) and anticoagulation, 5 (17%) received only ASA, and 3 (10%) received only anticoagulation. No patients had a thrombotic event. 6 (20%) patients had a bleeding event, none of which was major. Conclusions: Patients with MIS-C had evidence of hypercoagulability on TEG. Increased erythrocyte sedimentation rate and platelets were associated with higher clot strength. Treatment with ASA or anticoagulation was well tolerated. Further multi-center study is required to characterize the rate of thrombosis and optimal thromboprophylaxis algorithm in this patient population.