Do asymptomatic clots in children matter?

Epidemiology of clinically unsuspected venous thromboembolism in children with cancer: A population-based study from Maritimes, Canada

Inconsistencies in the definition of clinically unsuspected venous thromboembolism (VTE) in pediatric patients recently led to the recommendation of standardizing this terminology. Clinically unsuspected VTE (cuVTE) is defined as the presence of VTE on diagnostic imaging performed for indications unrelated to VTE in a patient without symptoms or clinical history of VTE. The prevalence of cuVTE in pediatric cancer patients is unclear. Therefore, the main objective of our study was to determine the prevalence of cuVTE in pediatric cancer patients. All patients 0-18 years old, treated at the IWK in Halifax, Nova Scotia, from August 2005 through December 2019 with a known cancer diagnosis and at least one imaging study were eligible (n = 743). All radiology reports available for these patients were reviewed (n = 18,120). The VTE event was labeled a priori as cuVTE event for radiology reports that included descriptive texts indicating a diagnosis of thrombosis including thrombus, central venous catheter-related, thrombosed aneurysm, tumor thrombosis, non-occlusive thrombus, intraluminal filling defect, or small fragment clot for patients without documentation of clinical history and or signs of VTE. A total of 18,120 radiology reports were included in the review. The prevalence of cuVTE was 5.5% (41/743). Echocardiography and computed tomography had the highest rate of cuVTE detection, and the most common terminologies used to diagnose cuVTE were thrombus and non-occlusive thrombus. The diagnosis of cuVTE was not associated with age, sex, and type of cancer. Future efforts should focus on streamlining radiology reports to characterize thrombi. The clinical significance of these cuVTE findings and their application to management, post-thrombotic syndrome, and survival compared to cases with symptomatic VTE and patients without VTE should be further studied.

Risk factors and clinical impact of thrombosis during induction chemotherapy for pediatric acute lymphoblastic leukemia: A report from CYP-C

Thromboembolism (TE) is associated with reduced survival in pediatric acute lymphoblastic leukemia (ALL). It has been hypothesized that TE might signal leukemic aggressiveness. The objective was to determine risk factors for TE during ALL induction (TEind ) therapy and whether TEind is associated with treatment refractoriness. This retrospective cohort study using the population-based Cancer in Young People Canada (CYP-C) registry included children <15 years of age diagnosed with ALL (2000-2019) and treated at one of 12 Canadian pediatric centers outside of Ontario. Univariate and multivariable logistic regression models were used to determine risk factors for TEind and whether TEind predicted induction failure and ALL treatment intensification. The impact of TEind on overall and event-free survival was estimated using Cox proportional hazard regression models. The study included 2589 children, of which 45 (1.7%) developed a TEind . Age (<1 year and ≥10 years vs. 1-<10 years), T-cell phenotype, high-risk ALL, and central nervous system involvement were all associated with TEind in univariate analysis. Age and T-cell phenotype remained independent predictors of TEind in multivariable analysis. Induction failure occurred in 53 patients (2.1%). TEind was not associated with induction failure (OR: not estimable) or treatment intensification (adjusted OR [95% CI]: 0.66 [0.26-1.69]). TEind was independently associated with overall survival (adjusted HR [95% CI]: 2.54 [1.20-5.03]) but not event-free survival (adjusted HR [95% CI] 1.86 [0.98-3.51]). In this population-based study of children treated with contemporary chemotherapy protocols, TEind was associated with age and T-cell phenotype and mortality but did not predict induction failure.

Bedside Durable Tunneled Femoral Central Venous Catheter is Feasible and Safe in High-Risk Infants in the Pediatric Cardiac Intensive Care Unit

OBJECTIVE

Ultrasound (US)-guided durable tunneled femoral central venous catheters (TF-CVCs) are a safe central venous access option in infants and neonates. Studies have shown, however, that femoral central venous access has the potential for high central line-associated bloodstream infection (CLABSI) rates with a significant increase in risk for line-related thrombosis. Our aims were to describe the bedside insertion technique and evaluate the safety and complication rates of TF-CVCs in high-risk, young, pediatric cardiac intensive-care unit (PCICU) population.

DESIGN

A retrospective observational cohort study.

SETTING

University affiliated, tertiary-care hospital, PCICU.

PATIENTS

All PCICU patients that underwent bedside TF-CVC insertion were enrolled. Data was collected from the electronic medical record system.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

During April 2016 to October 2021, 103 TF-CVC lines were inserted into 94 pediatric cardiac critical care patients, at the bedside. Patients' characteristics were median (IQR) age of 47.5 days (22.6, 120.5), weight 3.3 kg (2.9, 4.3), 33% prevalence of genetic anomalies, need for ECMO support in 20.4%, and STAT category 4-5 in 53.4%. All procedures were performed by intensivists. There were no immediate procedure-related complications. TF-CVCs were inserted on average on post-operative day (POD) 14, median line indwell duration was 25 days (16.3, 42.3) and total TF-CVC dwell duration for the entire cohort of 3442.7 days. During the study period eight CLABSI events were recorded (2.3/1000 line-days). Line obstruction rate was 1.16/1000 line-days and six lines were dislodged in the intermediate-care unit. There was no symptomatic line-related thrombosis.

CONCLUSIONS

We show that US-guided durable tunneled femoral central venous catheter (TF-CVC) insertion by an intensivist at the bedside is a technically feasible and safe prolonged central venous access option in critically ill, high-risk infants and neonates in the PCICU.

Hemostatic and thrombotic disorders in the pediatric patient

This review focuses on significant advances in the field of pediatric hemostasis and thrombosis, with a focus on published studies within the past decade. The evaluation and management of patients with excessive bleeding remain cornerstones of consultative hematology. We will describe the development of validated bleeding assessment tools relevant to pediatric practice, laboratory advances in the evaluation of von Willebrand disease, and a shift in clinical practice regarding the interpretation of normal coagulation studies in patients with significant bleeding phenotypes. There have also been critical advances in the management of hemostatic disorders. This review highlights new treatment paradigms in hemophilia and the rise of multidisciplinary medical homes for women living with bleeding disorders. Given the continued increase in the incidence of thrombosis, particularly in the hospital setting, a full call to arms against pediatric venous thromboembolism is now essential. We will describe recently completed clinical trials of direct oral anticoagulants in children and adolescents and ongoing work to elucidate the appropriate duration of therapy for children with provoked thrombosis. Recent work regarding the prevention of pediatric venous thromboembolism is highlighted, including studies of thromboprophylaxis and the development of risk prediction models for hospital-acquired thrombosis. Finally, we review advances in our understanding of thrombotic sequelae and the need for continued refinement of our evaluation tools. Despite the significant advances in pediatric hemostasis and thrombosis over the past decade, many unanswered questions remain for the next generation of investigators.

Recommendations for standardized definitions, clinical assessment, and future research in pediatric clinically unsuspected venous thromboembolism: Communication from the ISTH SSC subcommittee on pediatric and neonatal thrombosis and hemostasis

Clinically unsuspected venous thromboembolism (VTE) in children is defined as a VTE diagnosed via imaging test performed for surveillance (i.e., with an intent to identify clinically silent VTEs) or incidentally found (most often via imaging performed for evaluation of regional pathology unrelated to VTE) in the absence of any VTE-associated signs or symptoms. Our understanding of the clinical significance of these events in children is limited by a paucity of data on the epidemiology and outcomes of this complication. There is an urgent need for further research in this area to inform optimal management. Recognizing this knowledge gap, this Task Force has previously published a systematic review of the literature in this topic. We now provide guidance recommendations for standardization of definitions and identify future research needs on clinically unsuspected VTE in children. These recommendations will serve to enhance the quantity and quality of evidence on the topic and facilitate the design and execution of cooperative observational studies, and interventional trials of risk-stratified management approaches aimed at preventing and optimizing long-term outcomes of clinically unsuspected VTE in children.

Anticoagulation in Pediatric Patients

Special aspects of anticoagulation in children include the different epidemiology of thrombosis, developmental changes in the coagulation system, age-dependent pharmacokinetics of anticoagulants, risk of bleeding, and practical hurdles to anticoagulation. The classical anticoagulants so far used in children have several limitations, resulting in the need for regular monitoring. The pharmacological properties of direct oral anticoagulants (DOACs) and the special challenges of anticoagulation in children make the DOACs particularly attractive for children. All DOACs have pediatric development programs, targeting various indications for prevention and treatment of thrombosis. Child-appropriate formulations have been developed, age-specific dosing information generated, and safety and efficacy evaluated in ongoing phase 3 trials. Rivaroxaban and dabigatran have already been authorized for children for treatment of acute venous thrombosis and for extended secondary prevention. Their safety and efficacy have been demonstrated comparable to that of standard-of-care anticoagulants, without need for monitoring. Further studies are ongoing, which are expected to lead to pediatric authorizations of DOACs for primary venous thromboembolic event prevention in some high-risk settings. More real-life data will be necessary from postmarketing studies and registries to complement the evidence base for DOAC use in children, particularly in the youngest age groups and special disease populations.

Efficacy of Early Prophylaxis Against Catheter-Associated Thrombosis in Critically Ill Children: A Bayesian Phase 2b Randomized Clinical Trial

OBJECTIVES

We obtained preliminary evidence on the efficacy of early prophylaxis on the risk of central venous catheter-associated deep venous thrombosis and its effect on thrombin generation in critically ill children.

DESIGN

Bayesian phase 2b randomized clinical trial.

SETTING

Seven PICUs.

PATIENTS

Children less than 18 years old with a newly inserted central venous catheter and at low risk of bleeding.

INTERVENTION

Enoxaparin adjusted to anti-Xa level of 0.2-0.5 international units/mL started at less than 24 hours after insertion of central venous catheter (enoxaparin arm) versus usual care without placebo (usual care arm).

MEASUREMENTS AND MAIN RESULTS

At the interim analysis, the proportion of central venous catheter-associated deep venous thrombosis on ultrasonography in the usual care arm, which was 54.2% of 24 children, was significantly higher than that previously reported. This resulted in misspecification of the preapproved Bayesian analysis, reversal of direction of treatment effect, and early termination of the randomized clinical trial. Nevertheless, with 30.4% of 23 children with central venous catheter-associated deep venous thrombosis on ultrasonography in the enoxaparin arm, risk ratio of central venous catheter-associated deep venous thrombosis was 0.55 (95% credible interval, 0.24-1.11). Including children without ultrasonography, clinically relevant central venous catheter-associated deep venous thrombosis developed in one of 27 children (3.7%) in the enoxaparin arm and seven of 24 (29.2%) in the usual care arm (p = 0.02). Clinically relevant bleeding developed in one child randomized to the enoxaparin arm. Response profile of endogenous thrombin potential, a measure of thrombin generation, was not statistically different between trial arms.

CONCLUSIONS

These findings suggest the efficacy and safety of early prophylaxis that should be validated in a pivotal randomized clinical trial.

Thrombosis is associated with worse survival in children with acute lymphoblastic leukemia: A report from CYP-C

There are conflicting data about whether the development of cancer-associated thrombo-embolism (TE) negatively impacts survival in children. The objective was to determine whether TE during treatment was associated with overall survival (OS) and event-free survival (EFS) in children with acute lymphoblastic leukemia (ALL). We performed a population-based retrospective cohort study using the Cancer in Young People-Canada registry. Children <15 years of age were diagnosed with de novo ALL (2000-2016). The primary exposure variable was radiologically-confirmed thrombo-embolism requiring medical intervention. Multivariable Cox regression models were used to determine the impact of thrombo-embolism on survival, where TE was time-dependent. We included 2006 children (median age: 4 years, 88.5% precursor B-cell ALL). Thrombo-embolism occurred in 113 patients (5.6%), at a median time of 107 days (interquartile range: 35-184 days) after ALL diagnosis. Among standard/low-risk patients, 41/1165 (3.5%) developed TE while among high/very high-risk patients, 72/841 (8.6%) developed TE. Patients with TE had a significantly worse OS (adjusted HR [aHR] of death: 2.61, 95% CI: 1.62-4.22, p < 0.001) and EFS (aHR of an event [death, relapse, second malignancy]: 2.03, 95% CI: 1.35-3.05, p = 0.001), compared with patients without TE. No statistically significant difference was seen in standard/low risk ALL for OS and EFS, but TE was associated with a significantly lower OS and EFS in children with high/very high-risk ALL (aHR of death: 2.90, 95% CI: 1.79-4.72, p < 0.001; aHR of an event: 2.02, 95% CI: 1.30-3.12, p = 0.002). Thus, TE led to a statistically significant reduction in OS and EFS in children with high risk/very high-risk leukemia.

Venous Thromboembolism among Critically Ill Children: A Narrative Review

Venous thromboembolism (VTE) is a leading cause of morbidity and mortality among hospitalized patients, including children. In recent years, it has become clear that hospitalization and critical illness bestow an increased VTE risk in pediatrics and relate to mortality and life-limiting comorbidities. For critically ill children, reported rates of VTE vary by study sampling techniques, presence of inherited or acquired thrombophilia, acute and chronic immobility, underlying illness prompting hospitalization, and clinical factors related to illness severity such as central venous catheterization, length of stay, mechanical ventilation, and patient age. Accordingly, critically ill children with new signs of venous congestion, acute inflammation, or unexplained acute organ dysfunction should be routinely evaluated for VTE. This narrative review summarizes recent and historical literature regarding risk factors, prevention, presentation, treatment, and outcomes of VTE in critically ill children. In addition, we identify knowledge gaps and priorities for future collaborative research on this vital condition. Special attention is given to the clinical trial opportunities, challenges, and ongoing efforts in thromboprophylaxis in critically ill children, including those hospitalized for disease related to novel coronavirus (COVID-19) and multisystem inflammatory disease in children.