Prospective Exploratory Experience With Bivalirudin Anticoagulation in Pediatric Extracorporeal Membrane Oxygenation.

OBJECTIVES: Objective of this study was to determine if bivalirudin resulted in less circuit interventions than unfractionated heparin. A secondary objective was to examine associations between bivalirudin dose and partial thromboplastin time, international normalized ratio, and activated clotting time. DESIGN: Prospective observational. SETTING: Medical-surgical and cardiac PICUs. PATIENTS: Neonatal and pediatric extracorporeal membrane oxygenation patients who received bivalirudin anticoagulation. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Twenty extracorporeal membrane oxygenation runs in 18 patients used bivalirudin; 90% were venoarterial. Median (interquartile range) age was 4.5 months (1.6-35 mo). Thirteen patients (72%) had an underlying cardiac diagnosis. Of the 20 runs using bivalirudin, 16 (80%) were initially started on unfractionated heparin and transitioned to bivalirudin due to ongoing circuit thrombosis despite therapeutic anti-Xa levels (n = 13), ongoing circuit thrombosis with unfractionated heparin greater than or equal to 40 U/kg/hr (n = 2), or absence of increase in ACT after bolus of 100 U/kg of unfractionated heparin and escalation of unfractionated heparin infusion (n = 1). Initial bivalirudin dose ranged from 0.2 to 0.5 mg/kg/hr; no bolus doses were used. Median (range) bivalirudin dose was 0.9 mg/kg/hr (0.15-1.6 mg/kg/hr). Median (interquartile range) time on extracorporeal membrane oxygenation was 226.5 hours (150.5-393.0 hr) including 84 hours (47-335 hr) on bivalirudin. Nonparametric results are as follows: the rate of circuit intervention was significantly lower in patients on bivalirudin than on unfractionated heparin (median [interquartile range]: 0 [0-1] and 1 [1-2], respectively; Wilcoxon p = 0.0126). Bivalirudin dose was correlated to PTT (rs = 0.4760; p < 0.0001), INR (rs = 0.6833; p < 0.0001), and ACT (rs = 0.6161; p < 0.0001). Four patients had a significant bleeding complication on bivalirudin. Survival to hospital discharge was 56%. CONCLUSIONS: Bivalirudin appears to be a viable option for systemic anticoagulation in pediatric extracorporeal membrane oxygenation patients who have failed unfractionated heparin, but questions remain namely its optimal monitoring strategy. This pilot study supports the need for larger prospective studies of bivalirudin in pediatric extracorporeal membrane oxygenation, particularly focusing on meaningful monitoring variables.

Improving evidence on anticoagulant therapies for venous thromboembolism in children: key challenges and opportunities.

Venous thromboembolism (VTE) is increasingly diagnosed in pediatric patients, and anticoagulant use in this population has become common, despite the absence of US Food and Drug Administration (FDA) approval for this indication. Guidelines for the use of anticoagulants in pediatrics are largely extrapolated from large randomized controlled trials (RCTs) in adults, smaller dose-finding and observational studies in children, and expert opinion. The recently FDA-approved direct oral anticoagulants (DOACs), such as dabigatran, rivaroxaban, apixaban, and edoxaban, provide potential advantages over oral vitamin K antagonists and subcutaneous low-molecular-weight heparins (LMWHs). However, key questions arise regarding their potential off-label clinical application in pediatric thromboembolic disease. In this Perspective, we provide background on the use of LMWHs such as enoxaparin as the mainstay of treatment of pediatric provoked VTE; identify key questions and challenges with regard to DOAC trials and future DOAC therapy in pediatric VTE; and discuss applicable lessons learned from the recent pilot/feasibility phase of a large multicenter RCT of anticoagulant duration in pediatric VTE. The challenges and lessons learned present opportunities to improve evidence for anticoagulant therapies in pediatric VTE through future clinical trials.

Prospective Side by Side Comparison of Outcomes and Complications With a Simple Versus Intensive Anticoagulation Monitoring Strategy in Pediatric Extracorporeal Life Support Patients.

OBJECTIVES: A continuous infusion of unfractionated heparin is the most common anticoagulant used for pediatric patients on extracorporeal life support. The objective of this study was to compare extracorporeal life support complications and outcomes between two large-volume pediatric extracorporeal life support centers that use different anticoagulation strategies. DESIGN: Prospective, observational cohort study. SETTING: The University of Michigan used simple anticoagulation monitoring, whereas the University of Alberta used an intensive anticoagulation monitoring strategy. PATIENTS: Pediatric patients on extracorporeal life support. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The primary outcome measure was major bleeding per extracorporeal life support run defined as bleeding that was retroperitoneal, pulmonary, or involved the CNS; bleeding greater than 20 mL/kg over 24 hours; or bleeding that required surgical intervention. Secondary outcomes measured were patient thrombosis per run, circuit thrombosis per run, and survival to hospital discharge per patient. Eighty-eight patients (95 runs) less than 18 years old were enrolled at the two centers over 2 years. The two centers enrolled different extracorporeal life support populations; University of Alberta enrolled more postcardiac surgical patients (74% vs 47%; p = 0.005). The indication for extracorporeal life support support also varied by center (p = 0.04). The two centers used similar proportions of VA extracorporeal life support (p = 0.3). Median (interquartile range) unfractionated heparin doses were similar between University of Michigan and University of Alberta, 30 (21-34) U/kg/hr and 26 (22-31) U/kg/hr, p value equals to 0.3, respectively. Median (interquartile range) antifactor Xa was lower in the University of Michigan cohort (0.23 [0.19-0.28] vs 0.41 [0.36-0.46] U/mL; p < 0.001). There was no significant difference in major bleeding (15% University of Michigan vs 21% University of Alberta; p = 0.6) or in patient thromboses (18% University of Michigan vs 13% University of Alberta; p = 0.5). There was no significant difference in survival to hospital discharge (University of Michigan 63% vs University of Alberta 73%; p = 0.1). CONCLUSIONS: Although this prospective cohort study compared different pediatric extracorporeal life support populations, the results did not identify a significant difference in outcomes between simple and intensive anticoagulation monitoring strategies.

Closing in on the PumpKIN Trial of the Jarvik 2015 Ventricular Assist Device.

The Infant Jarvik ventricular assist device (VAD; Jarvik Heart, Inc., New York, NY) has been developed to support the circulation of infants and children with advanced heart failure. The first version of the device was determined to have elevated hemolysis under certain conditions. The objective of this work was to determine appropriate modifications to the Infant Jarvik VAD that would result in acceptably low hemolysis levels. In vitro hemolysis testing revealed that hemolysis was related to the shape of the pump blade tips and a critical speed over which hemolysis would occur. Various design modifications were tested and a final design was selected that met the hemolysis performance goal. The new version was named the Jarvik 2015 VAD. Chronic in vivo tests, virtual fit studies, and a series of other performance tests were carried out to assess the device's performance characteristics. In vivo test results revealed acceptable hemolysis levels in a series of animals and virtual fit studies showed that the device would fit into children 8 kg and above, but could fit in smaller children as well. Additional FDA-required testing has been completed and all of the data are being submitted to the FDA so that a clinical trial of the Jarvik 2015 VAD can begin. Development of a Jarvik VAD for use in young children has been challenging for various reasons. However, with the hemolysis issue addressed in the Jarvik 2015 VAD, the device is well-poised for the start of the PumpKIN clinical trial in the near future.

Prospective trial of a pediatric ventricular assist device.

BACKGROUND: Options for mechanical circulatory support as a bridge to heart transplantation in children with severe heart failure are limited. METHODS: We conducted a prospective, single-group trial of a ventricular assist device designed specifically for children as a bridge to heart transplantation. Patients 16 years of age or younger were divided into two cohorts according to body-surface area (cohort 1, <0.7 m(2); cohort 2, 0.7 to <1.5 m(2)), with 24 patients in each group. Survival in the two cohorts receiving mechanical support (with data censored at the time of transplantation or weaning from the device owing to recovery) was compared with survival in two propensity-score-matched historical control groups (one for each cohort) undergoing extracorporeal membrane oxygenation (ECMO). RESULTS: For participants in cohort 1, the median survival time had not been reached at 174 days, whereas in the matched ECMO group, the median survival was 13 days (P<0.001 by the log-rank test). For participants in cohort 2 and the matched ECMO group, the median survival was 144 days and 10 days, respectively (P<0.001 by the log-rank test). Serious adverse events in cohort 1 and cohort 2 included major bleeding (in 42% and 50% of patients, respectively), infection (in 63% and 50%), and stroke (in 29% and 29%). CONCLUSIONS: Our trial showed that survival rates were significantly higher with the ventricular assist device than with ECMO. Serious adverse events, including infection, stroke, and bleeding, occurred in a majority of study participants. (Funded by Berlin Heart and the Food and Drug Administration Office of Orphan Product Development; ClinicalTrials.gov number, NCT00583661.).

Berlin Heart EXCOR pediatric ventricular assist device for bridge to heart transplantation in US children.

BACKGROUND: Recent data suggest that the Berlin Heart EXCOR Pediatric ventricular assist device is superior to extracorporeal membrane oxygenation for bridge to heart transplantation. Published data are limited to 1 in 4 children who received the device as part of the US clinical trial. We analyzed outcomes for all US children who received the EXCOR to characterize device outcomes in an unselected cohort and to identify risk factors for mortality to facilitate patient selection. METHODS AND RESULTS: This multicenter, prospective cohort study involved all children implanted with the Berlin Heart EXCOR Pediatric ventricular assist device at 47 centers from May 2007 through December 2010. Multiphase nonproportional hazards modeling was used to identify risk factors for early (<2 months) and late mortality. Of 204 children supported with the EXCOR, the median duration of support was 40 days (range, 1-435 days). Survival at 12 months was 75%, including 64% who reached transplantation, 6% who recovered, and 5% who were alive on the device. Multivariable analysis identified lower weight, biventricular assist device support, and elevated bilirubin as risk factors for early mortality and bilirubin extremes and renal dysfunction as risk factors for late mortality. Neurological dysfunction occurred in 29% and was the leading cause of death. CONCLUSIONS: Use of the Berlin Heart EXCOR has risen dramatically over the past decade. The EXCOR has emerged as a new treatment standard in the United States for pediatric bridge to transplantation. Three-quarters of children survived to transplantation or recovery; an important fraction experienced neurological dysfunction. Smaller patient size, renal dysfunction, hepatic dysfunction, and biventricular assist device use were associated with mortality, whereas extracorporeal membrane oxygenation before implantation and congenital heart disease were not.

Thrombophilia screening: whom to test?

In this issue of Blood, Holzhauer et al have determined a novel method of identifying patients with protein C, protein S, and antithrombin deficiency who are at increased risk of developing venous thromboembolism (VTE; see figure). Children with VTE and their relatives were screened for inherited thrombophilia including proteins C and S and antithrombin deficiency; and Factor (F)V G1691A and FII G20210A. Their study demonstrates that relatives with proteins C and S and antithrombin deficiency are at a significantly higher risk of developing VTE compared with those without inherited thrombophilia.

Antithrombin concentrate in pediatric patients requiring unfractionated heparin anticoagulation: a retrospective cohort study.

OBJECTIVE: To describe antithrombin levels, altered unfractionated heparin effect (anti-factor Xa activity and activated partial thromboplastin time), and adverse effects post administration of a single high dose of antithrombin concentrate. DESIGN: Retrospective review. PATIENTS: Infants and children with antithrombin levels less than 50% and a subtherapeutic unfractionated heparin effect. SETTING: Quaternary care children's hospital with a dedicated anticoagulation program. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: A single high dose of antithrombin concentrate was administered. Antithrombin level, anti-factor Xa, and activated partial thromboplastin times were measured post antithrombin concentrate infusion and daily until stable. One hundred twenty-one patients received 246 doses of antithrombin. Patients were described using two cohorts based on the ability to obtain exact heparin doses. Cohort 1 included all patients between January 2004 and May 2008 when complete heparin dosing was unavailable. Cohort 2 included patients from May 2008 to May 2011 when heparin dose was available. Median age and weight were 3.7 months and 4.1 kg. Mean antithrombin concentrate dose was 222 IU/kg. Mean antithrombin level increased from 0.39 to 1.20 U/mL following antithrombin concentrate administration. In cohort 2, unfractionated heparin doses to achieve a target anti-factor Xa activity pre-post antithrombin concentrate were 28 and 19 U/kg/hr, respectively, for children 12 months old or younger and 25 and 19 U/kg/hr, respectively, for children older than 12 months. There were no hemorrhagic, thrombotic, or allergic events within 1 week of antithrombin concentrate administration. CONCLUSIONS: This is the largest study of antithrombin concentrate evaluation in children. Administration of antithrombin concentrate increases anti-factor Xa activity with lower administered unfractionated heparin doses.

Right pulmonary artery thrombosis after hybrid stage 1 palliation: resolution after direct tissue plasminogen activator infusion.

A patient with unbalanced right ventricular dominant atrioventricular septal defect with ascending and transverse arch hypoplasia underwent hybrid stage 1 palliation. On postoperative day 7, he experienced irritability and acute cyanosis. Echocardiography demonstrated a thrombus occluding the right pulmonary artery band. Emergency cardiac catheterization confirmed thrombosis of the right pulmonary artery at the site of the band. Direct infusion of tissue plasminogen activator successfully lysed the thrombus.

Evaluation of a Video-Based Education Intervention for Parents of Children Undergoing Fontan Surgery: A Cluster Randomized Controlled Trial.

Background: Fontan surgery is performed at 2-4 years of age and is the third planned surgical intervention for children with a univentricular heart. Major challenges for children and parents after Fontan include (a) psychological distress, (b) prolonged pleural drainage, and (c) the need for postoperative anticoagulation. The aim of this study was to evaluate a pre-Fontan video-based intervention for parents to address these challenges. Methods: This study is a single-centre mixed-methods cluster randomized controlled trial. The intervention consisted of 3 brief whiteboard videos offered online from preadmission clinic to 1 month postoperatively. The parent's State Trait Anxiety Inventory score and the child's Post Hospital Behaviour Questionnaire score were measured 1 week and 1 month postoperatively. Semistructured interviews were conducted to obtain parental feedback on the videos. Results: We enrolled 26 children (13 female patients; 16 intervention group) and 1 parent per child. Mean State Trait Anxiety Inventory scores were similar between groups at both 1 week (52.8 vs 55.5, P = 0.25) and 1 month postoperatively (50.9 vs 53.9, P = 0.25). Post Hospital Behaviour Questionnaire scores were in the maladaptive range but did not differ between groups. Parents agreed or strongly agreed that the videos were helpful but should be provided earlier in the preoperative process. The main value of the videos was recognized as being a method for standardizing information provided to parents. Conclusions: A video-based education intervention did not impact State Trait Anxiety Inventory or Post Hospital Behaviour Questionnaire scores. However, the majority of parents agreed that the videos were helpful.

Contexte: L'opération de Fontan est réalisée à l'âge de 2 à 4 ans et constitue la troisième intervention chirurgicale planifiée chez les enfants qui présentent un ventricule unique. Les enfants et leurs parents font face à des défis importants après une opération de Fontan, dont a) la détresse psychologique, b) le drainage pleural prolongé et c) la nécessité de recourir à une anticoagulothérapie après la chirurgie. Notre étude visait à évaluer une intervention éducative préopératoire sous forme de vidéos présentées aux parents afin de leur permettre de mieux relever ces défis. Méthodologie: Nous avons mené un essai monocentrique à méthodes mixtes et à répartition aléatoire par grappes avec groupe témoin. L'intervention éducative consistait en une série de trois courtes vidéos sur tableau blanc disponibles en ligne à partir de la consultation clinique de préadmission et jusqu'à un mois après la chirurgie. Les scores des parents à l'inventaire d'anxiété situationnelle et de trait d'anxiété (State Trait Anxiety Inventory) et les scores des enfants à l'évaluation du comportement suivant l'hospitalisation (Post Hospital Behaviour Questionnaire) ont été mesurés une semaine et un mois après l'opération. Des entrevues semi-dirigées ont été réalisées afin de recueillir les commentaires des parents au sujet des vidéos. Résultats: Nous avons recruté 26 enfants (dont 13 filles; 16 enfants ont été affectés au groupe d'intervention éducative) et un parent pour chacun des enfants. Les scores moyens obtenus au State Trait Anxiety Inventory étaient comparables entre les deux groupes une semaine (52,8 vs 55,5, p = 0,25) et un mois (50,9 vs 53,9, p = 0,25) après l'opération. Les scores obtenus au Post Hospital Behaviour Questionnaire se situaient dans la fourchette des comportements mésadaptés, mais ne différaient pas entre les groupes. Les parents étaient d'accord ou fortement d'accord pour dire que les vidéos étaient utiles, mais qu'elles auraient dû être offertes plus tôt dans le processus préopératoire. La valeur principale des vidéos était selon eux qu'il s'agissait d'un moyen d'uniformiser l'information transmise aux parents. Conclusions: Une intervention éducative sous forme de vidéos n'a pas eu d'incidence sur les scores obtenus au State Trait Anxiety Inventory ou au Post Hospital Behaviour Questionnaire. Toutefois, la majorité des parents ont trouvé que les vidéos étaient utiles.

Consensus Statement: Hemostasis Trial Outcomes in Cardiac Surgery and Mechanical Support.

BACKGROUND: Research evaluating hemostatic agents for the treatment of clinically significant bleeding has been hampered by inconsistency and lack of standardized primary clinical trial outcomes. Clinical trials of hemostatic agents in both cardiac surgery and mechanical circulatory support, such as extracorporeal membrane oxygenation and ventricular assist devices, are examples of studies that lack implementation of universally accepted outcomes. METHODS: A subgroup of experts convened by the National Heart, Lung, and Blood Institute and the US Department of Defense developed consensus recommendations for primary outcomes in cardiac surgery and mechanical circulatory support. RESULTS: For cardiac surgery the primary efficacy endpoint of total allogeneic blood products (units vs mL/kg for pediatric patients) administered intraoperatively and postoperatively through day 5 or hospital discharge is recommended. For mechanical circulatory support outside the perioperative period the recommended primary outcome for extracorporeal membrane oxygenation is a 5-point ordinal score of thrombosis and bleeding severity adapted from the Common Terminology Criteria for Adverse Events version 5.0. The recommended primary endpoint for ventricular assist device is freedom from disabling stroke (Common Terminology Criteria for Adverse Events AE ≥ grade 3) through day 180. CONCLUSIONS: The proposed composite risk scores could impact the design of upcoming clinical trials and enable comparability of future investigations. Harmonizing and disseminating global consensus definitions and management guidelines can also reduce patient heterogeneity that would confound standardized primary outcomes in future research.

Quality of life in children requiring antithrombotic therapy: development of a measure.

Measurement of quality of life (QOL) has been accepted as an important outcome measure in therapeutic clinical trials. Long-term antithrombotic therapy is hypothesized to induce treatment dissatisfaction and influence QOL. Health-related quality of life (HRQOL) can be measured by an inventory developed specific to the patient condition. Pediatric QOL inventory for children on long-term antithrombotic therapy should assess constructs salient for this population. Creation of an HRQOL measurement inventory requires rigor and methodological adherence. Identification and evaluation of QOL constructs is critical to improve care and is accepted as the "gold standard" measurement for patient-centered outcomes in clinical research. The use of a valid and reliable HRQOL inventory specific for the antithrombotic therapy is required for upcoming clinical trials as it will provide a method to measure change in HRQOL specific to the antithrombotic agent. In this way, it will be possible to provide the child/family with information to make safe and effective therapeutic choices, define future antithrombotic therapy research strategies, and inform decision makers to change policies to improve health care.

Hemostasis and platelet dysfunction in asphyxiated neonates.

Hemostasis is the balance between bleeding and clotting and includes coagulation and fibrinolysis with platelet interactions. Despite developmental hemostasis that describes the major differences between neonates and older children and adults, neonates do not have increased bleeding or clotting unless clinical situations disturb the "balance." Perinatal asphyxia alters the balance of hemostasis, resulting in abnormalities that may result in bleeding and thrombosis. The following discussion will describe normal hemostasis, laboratory measures of hemostasis, developmental hemostasis, and the effects of asphyxia on hemostasis.

Safety and efficacy of anticoagulant therapy in pediatric catheter-related venous thrombosis (EINSTEIN-Jr CVC-VTE).

Anticoagulant treatment of pediatric central venous catheter-related venous thromboembolism (CVC-VTE) has not been specifically evaluated. In EINSTEIN-Jr, 500 children with any VTE received rivaroxaban or standard anticoagulants. A predefined analysis of the CVC-VTE cohort was performed. Children with CVC-VTE (age, birth to 17 years) were administered rivaroxaban or standard anticoagulants during the 1-month (children <2 years) or 3-month (all other children) study period. Predefined outcomes were recurrent VTE, change in thrombotic burden on repeat imaging, and bleeding. Predictors for continuation of anticoagulant therapy beyond the study period were evaluated. One hundred twenty-six children with symptomatic (n = 76, 60%) or asymptomatic (n = 50, 40%) CVC-VTE received either rivaroxaban (n = 90) or standard anticoagulants (n = 36). There was no recurrent VTE (0%; 95% confidence interval [CI], 0.0%-2.8%). Three children had the principal safety outcome: none had major bleeding and 3 children had clinically relevant nonmajor bleeding (2.4%; 95% CI, 0.7%-6.5%), all in the rivaroxaban arm. Complete or partial vein recanalization occurred in 57 (55%) and 38 (37%) of 103 evaluable children, respectively. Results were similar for symptomatic and asymptomatic CVC-VTE. Continuation of anticoagulant therapy beyond the study period occurred in 61 (48%) of children and was associated with residual VTE but only in children <2 years (odds ratio [OR], 20.9; P = .003) and continued CVC use (OR, 6.7; P = .002). Anticoagulant therapy appeared safe and efficacious and was associated with reduced clot burden in most children with symptomatic or asymptomatic CVC-VTE. Residual VTE and continued CVC use were associated with extended anticoagulation. This trial was registered at www.clinicaltrials.gov as #NCT02234843.

Rivaroxaban for treatment of pediatric venous thromboembolism. An Einstein-Jr phase 3 dose-exposure-response evaluation.

BACKGROUND: Recently, the randomized EINSTEIN-Jr study showed similar efficacy and safety for rivaroxaban and standard anticoagulation for treatment of pediatric venous thromboembolism (VTE). The rivaroxaban dosing strategy was established based on phase 1 and 2 data in children and through pharmacokinetic (PK) modeling. METHODS: Rivaroxaban treatment with tablets or the newly developed granules-for-oral suspension formulation was bodyweight-adjusted and administered once-daily, twice-daily, or thrice-daily for children with bodyweights of ≥30, ≥12 to <30, and <12 kg, respectively. Previously, these regimens were confirmed for children weighing ≥20 kg but only predicted in those <20 kg. Based on sparse blood sampling, the daily area under the plasma concentration-time curve [AUC(0-24)ss ] and trough [Ctrough,ss ] and maximum [Cmax,ss ] steady-state plasma concentrations were derived using population PK modeling. Exposure-response graphs were generated to evaluate the potential relationship of individual PK parameters with recurrent VTE, repeat imaging outcomes, and bleeding or adverse events. A taste-and-texture questionnaire was collected for suspension-recipients. RESULTS: Of the 335 children (aged 0-17 years) allocated to rivaroxaban, 316 (94.3%) were evaluable for PK analyses. Rivaroxaban exposures were within the adult exposure range. No clustering was observed for any of the PK parameters with efficacy, bleeding, or adverse event outcomes. Results were similar for the tablet and suspension formulation. Acceptability and palatability of the suspension were favorable. DISCUSSION: Based on this analysis and the recently documented similar efficacy and safety of rivaroxaban compared with standard anticoagulation, we conclude that bodyweight-adjusted pediatric rivaroxaban regimens with either tablets or suspension are validated and provide for appropriate treatment of children with VTE.

Rivaroxaban compared with standard anticoagulants for the treatment of acute venous thromboembolism in children: a randomised, controlled, phase 3 trial.

BACKGROUND: Treatment of venous thromboembolism in children is based on data obtained in adults with little direct documentation of its efficacy and safety in children. The aim of our study was to compare the efficacy and safety of rivaroxaban versus standard anticoagulants in children with venous thromboembolism. METHODS: In a multicentre, parallel-group, open-label, randomised study, children (aged 0-17 years) attending 107 paediatric hospitals in 28 countries with documented acute venous thromboembolism who had started heparinisation were assigned (2:1) to bodyweight-adjusted rivaroxaban (tablets or suspension) in a 20-mg equivalent dose or standard anticoagulants (heparin or switched to vitamin K antagonist). Randomisation was stratified by age and venous thromboembolism site. The main treatment period was 3 months (1 month in children <2 years of age with catheter-related venous thromboembolism). The primary efficacy outcome, symptomatic recurrent venous thromboembolism (assessed by intention-to-treat), and the principal safety outcome, major or clinically relevant non-major bleeding (assessed in participants who received ≥1 dose), were centrally assessed by investigators who were unaware of treatment assignment. Repeat imaging was obtained at the end of the main treatment period and compared with baseline imaging tests. This trial is registered with ClinicalTrials.gov, number NCT02234843 and has been completed. FINDINGS: From Nov 14, 2014, to Sept 28, 2018, 500 (96%) of the 520 children screened for eligibility were enrolled. After a median follow-up of 91 days (IQR 87-95) in children who had a study treatment period of 3 months (n=463) and 31 days (IQR 29-35) in children who had a study treatment period of 1 month (n=37), symptomatic recurrent venous thromboembolism occurred in four (1%) of 335 children receiving rivaroxaban and five (3%) of 165 receiving standard anticoagulants (hazard ratio [HR] 0·40, 95% CI 0·11-1·41). Repeat imaging showed an improved effect of rivaroxaban on thrombotic burden as compared with standard anticoagulants (p=0·012). Major or clinically relevant non-major bleeding in participants who received ≥1 dose occurred in ten (3%) of 329 children (all non-major) receiving rivaroxaban and in three (2%) of 162 children (two major and one non-major) receiving standard anticoagulants (HR 1·58, 95% CI 0·51-6·27). Absolute and relative efficacy and safety estimates of rivaroxaban versus standard anticoagulation estimates were similar to those in rivaroxaban studies in adults. There were no treatment-related deaths. INTERPRETATION: In children with acute venous thromboembolism, treatment with rivaroxaban resulted in a similarly low recurrence risk and reduced thrombotic burden without increased bleeding, as compared with standard anticoagulants. FUNDING: Bayer AG and Janssen Research & Development.