Katharina Thom

Incidence and Diagnosis of Thrombosis in Children With Short-Term Central Venous Lines of the Upper Venous System

OBJECTIVES. Deep venous thrombosis in children is frequently related to central venous lines. Study objectives were to determine objectively the incidence of deep venous thrombosis in children with short-term central venous lines and to assess the diagnostic value of venography, venous ultrasonography, and echocardiography, in a prospective cohort study. METHODS. Consecutive children with congenital heart disease requiring short-term central venous lines in the upper venous system were screened systematically for deep venous thrombosis by using venography, venous ultrasonography, and echocardiography, according to standardized protocols. RESULTS. The study population consisted of 90 children (median age: 2.7 years; range: birth to 18 years). Most central venous lines (97%) were located in the jugular veins. The overall incidence of deep venous thrombosis was 25 cases (28%) among 90 children. Venography identified deep venous thrombosis located in the subclavian and central veins but missed most deep venous thrombosis in the jugular veins. Venous ultrasonography had good sensitivity in the jugular veins but did not detect deep venous thrombosis in central veins. Echocardiography detected only 1 case of central deep venous thrombosis. CONCLUSIONS. The incidence of central venous line-related deep venous thrombosis in children with short-term central venous lines is high and comparable to reports for children with long-term central venous lines. Sensitivities of venography, venous ultrasonography, and echocardiography in children vary depending on the affected venous segment. A combination of diagnostic tests is required for sensitive detection of central venous line-related deep venous thrombosis in the upper venous system.

Incidence of thrombotic and bleeding complications during cardiac catheterization in children: comparison of high-dose vs. low-dose heparin protocols.

Summary.  Background: During cardiac catheterization (CC) in children, unfractionated heparin (UFH) is used for primary prophylaxis of thrombotic events (TE). However, the optimal UFH dose to minimize TE and bleeding in children has yet to be established. Objectives: To (i) objectively assess the incidence of TE and bleeding during pediatric CC using clinical assessment and ultrasound; and (ii) compare a high‐dose vs. low‐dose UFH protocol for thromboprophylaxis. Methods: A randomized controlled trial (RCT) comparing high‐dose UFH (100 units kg−1 bolus, followed by 20 units kg h−1 continuous infusion) vs. low‐dose UFH (50 units kg−1 bolus) during CC. Outcome assessment was by clinical examination and vascular ultrasound, performed by blinded examiners before and within 48 h after CC. Children with no consent for randomization were followed in a cohort receiving standard‐of‐care UFH (parallel‐cohort RCT). Results: A total of 227 children were included; 137 were randomized and 90 followed in the cohort study. The overall incidence of TE was 4.6% and bleeding 6.6%. The RCT was stopped early for futility as there were no differences between the high‐dose and the low‐dose UFH in TE (5% vs. 3%; risk ratios [RR] 1.5, 95% confidence interval [CI] 0.3; 9) and bleeding (7% vs. 12%, RR 0.6, 95% CI 0.2; 2). There were also no differences when RCT and cohort study populations were combined. Conclusions: The incidences of TE and bleeding during CC in children were low. There were no differences between the high‐dose and the low‐dose UFH protocols studied. Although Heparin Anticoagulation Randomized Trial in Cardiac Catheterization (HEARTCAT) was not designed as non‐inferiority trial, low‐dose UFH (50 units kg−1 bolus) appears sufficient for thromboprophylaxis during CC.

Determinants of factor VIII plasma levels in carriers of haemophilia A and in control women.

Summary.  Factor VIII (FVIII) levels show a considerable variability in female carriers of haemophilia A. Presently, the reasons for this are poorly understood. The aim of the study was to elucidate the influence of genetic and non‐genetic parameters on FVIII plasma levels in carriers (n = 42). Results were compared with age‐matched healthy women without carriership of haemophilia A (n = 42). Each carrier was tested for the family‐specific mutation, ABO blood group, FVIII level, von Willebrand factor (VWF) antigen and activity and C‐reactive protein (CRP). FVIII levels were lower in carriers compared to non‐carriers [74% (51–103) vs. 142% (109–169), P < 0.001]. No statistically significant differences were observed between the two groups with respect to VWF activity, prothrombin–time, hs‐CRP, fibrinogen, body mass index (BMI), age and smoking status as well as the distribution of ABO blood groups. In non‐carriers, FVIII was statistically significantly correlated with BMI, activated partial thromboplastin time (APTT), VWF antigen, hs‐CRP and fibrinogen. In carriers, significant correlations between FVIII and APTT, VWF antigen and activity were found, whereas BMI, hs‐CRP or fibrinogen did not correlate with FVIII. In non‐carriers, the association of FVIII with ABO blood groups was statistically significant (P = 0.006), but not in carriers of haemophilia A (P = 0.234). The type of FVIII gene mutation did not influence FVIII levels. Carrier status is the major determinant of a carrier`s FVIII plasma level. Factors known to influence FVIII levels in the general population do not significantly affect FVIII activity in carriers, neither does the type of mutation influence FVIII levels.

No impact of endogenous prothrombotic conditions on the risk of central venous line-related thrombotic events in children: results of the KIDCAT study (KIDs with Catheter Associated Thrombosis)

Central venous lines (CVLs) are the major exogenous risk factor for deep venous thrombosis (DVT) in children. The study objective was to assess whether endogenous prothrombotic conditions contribute to the risk of CVL‐related DVT in children.

Monitoring unfractionated heparin in children: a parallel-cohort randomized controlled trial comparing 2 dose protocols.

Monitoring unfractionated heparin (UFH) is crucial to prevent over- or under-anticoagulation. However, the optimal parameters for monitoring UFH in children are not well established. The study objectives were to investigate (1) the relationship between UFH dose and its anticoagulant effect as assessed by anti-Xa, activated partial thromboplastin time (aPTT) and activated clotting time (ACT); (2) other factors influencing UFH effect; (3) the agreement between the assays; and (4) the association between UFH effect and clinical outcome. HEARTCAT was a parallel-cohort randomized controlled trial comparing high-dose (100 U/kg bolus followed by age-based continuous infusion in randomized children) vs low-dose UFH (50 U/kg bolus) during cardiac catheterization in children. Blood samples were drawn before and after UFH administration at 30, 60, and 90 minutes. Four-hundred and two samples of 149 patients were evaluable. Anti-Xa, aPTT, and ACT all showed good discrimination between UFH doses. Regression models demonstrated the following determinants of UFH effect: UFH dose, age, baseline antithrombin (for anti-Xa), and baseline levels of aPTT and ACT, respectively. UFH effects were lower in infants compared with older children, which was more pronounced at low-dose than at high-dose UFH. Agreement between the 3 assays was poor. Most aPTT values were above therapeutic range or beyond measuring limit and thus of limited value for UFH monitoring. No association of UFH dose or effect with clinical outcome could be observed. In conclusion, all assays reflected a significant UFH dose-effect relationship, however, with poor agreement between the respective tests. The age-dependency of UFH effect was confirmed. Notably, the influence of age on UFH effect was dose-dependent.

Anti‐activated factor II assay for monitoring unfractionated heparin in children: results of the HEARTCAT study

Essentials Unfractionated heparin has variable effects in children and therefore, monitoring is essential. A randomized controlled trial substudy investigating an anti‐IIa assay in children was conducted. Anti‐IIa values are lower in younger children, an effect more pronounced at low‐dose heparin. Heparin effect on Xa and IIa is not equal, particularly in infants and after high‐dose heparin.

Direct oral anticoagulants: What will be their role in children?

Thrombotic events in children differ from those in adults in epidemiology, pathophysiology, and anatomical location. However, anticoagulation in children is mostly based on evidence from adults while scarce evidence exists from children. The classical anticoagulants currently used in children have several limitations, resulting in the need for regular monitoring. Several direct oral anticoagulants (DOACs) are now authorized for adults in whom they have established efficacy and safety without the need for monitoring. Given their pharmacological properties and the special characteristics of children requiring anticoagulation, the DOACs have the potential to be particularly suitable for children. All currently approved DOACs have paediatric development plans, targeting various indications for prevention and treatment of thrombosis. Paediatric formulations are being developed and systematic age-specific dosing information will be generated. Whether therapeutic drug monitoring will be necessary in certain situations in children remains to be elucidated. The results of ongoing clinical studies still need to demonstrate whether there is a positive benefit-risk balance in all targeted paediatric indications and age-groups, particularly in indications that have not been explored in adults, such as catheter-related thrombosis or congenital heart disease. If the advantages of DOACs bear out in the results of the current paediatric studies, they will likely be used widely in children. As of now, the DOACs should not be used routinely in children as there is still insufficient information on appropriate dosing, safety and efficacy. The paediatric community is encouraged to promote participation of children and adolescents into the multiple ongoing studies of DOACs.

Arteriovenous shunts as venous access in children with haemophilia

Venous access is essential in patients with haemophilia for administration of factor concentrates. Peripheral venipuncture may be challenging, particularly in young children or during immune tolerance induction (ITI). Central venous access devices (CVADs) carry a significant risk for complications. An alternative for venous access is peripheral arteriovenous shunts (AVSs), but there is sparse documentation in the literature. The aim of this study was to document our experience with AVS over 12 years in 27 boys with severe haemophilia.

Homozygous antithrombin deficiency type II causing neonatal thrombosis

We report four children from different families with homozygous antithrombin (AT) deficiency type II affecting the heparin binding site (p.Leu131Phe mutation). All children had severe spontaneous venous and/or arterial thromboembolic events shortly after birth. This report intends to raise awareness among clinicians about this rare but severe condition. When thrombosis occurs in an otherwise healthy newborn, a severe congenital thrombophilic disorder should be considered. In homozygous AT deficiency type II, AT activity is typically reduced but may also be in the normal range, posing a diagnostic challenge. Rapid diagnosis is important to initiate appropriate therapy. Standard anticoagulation with heparin may prove ineffective in severe AT deficiency, requiring substitution of AT concentrate and early switch to alternative anticoagulants such as vitamin K antagonists.