Catheter-related thrombosis in children with hemophilia A: evidence of a multifactorial disease

Paradigm shift for the treatment of hereditary haemophilia: Towards precision medicine

Patients with haemophilia A (HA) or B (HB) experience spontaneous limb- or life-threatening bleedings which are prevented by regular prophylactic intravenous infusions of the deficient coagulation factor (FVIII or FIX). Prophylaxis with subcutaneous long-acting non-factor products that improve in vivo thrombin generation is now under intensive investigation (concizumab, fitusiran) or successfully employed (emicizumab) in haemophilia patients. Both haemophilia patients with/without inhibitors take advantage of non-factor products employed alone. In those who also need bypassing agents (or FVIII concentrates) for breakthrough bleeds, thromboembolic events and/or thrombotic microangiopathy may occur. By enhancing thrombin generation, prothrombotic mutations co-segregating with FVIII/FIX gene mutations may trigger thrombotic episodes in HA patients carrying acquired thrombogenic factors (e.g. venous catheters). A thorough knowledge of individual needs increasingly contributed to improve comprehensive care and personalize treatments in haemophilia. Integrating genomics, lifestyle and environmental data is expected to be key to: 1) identify which haemophilia patients are less likely to benefit from a given intervention; 2) define optimal dosing and scheduling of bypassing agents (or FVIII) to employ in combination with non-factor products; 3) establish tests to monitor in vivo thrombin generation; 4) improve communication and deliver results to individuals. As individual outcomes will be improved and the risk of adverse events minimized, non-factor products will come into wider use within the haemophilia community, and patients will hopefully have no more risks of breakthrough bleeds. The risks of a normal life for a "former haemophilia patient" is likely to change the treatment landscape and the structure of haemophilia Centers.

Prophylactic versus on-demand treatments for hemophilia: advantages and drawbacks

INTRODUCTION

Early long-term prophylaxis is the standard of care to prevent joint bleeding and chronic arthropathy in patients with severe hemophilia. Areas covered: Despite the obvious prophylaxis advantages upon the clinical outcomes, there are still several drawbacks to be addressed for the optimal patients' compliance. Frequency of treatment due to short half-life of conventional FVIII and FIX concentrates, difficult venous access, adherence to the prescribed therapy and costs may represent significant critical issues. The development of inhibitors also makes replacement therapy ineffective, preventing patients from receiving long-term prophylaxis. This paper will review these drawbacks and the tools to overcome these limitations, mainly thanks to the use of extended half-life products and the development of novel non-conventional therapeutic approaches. Expert commentary: The use of extended half-life products may help in reducing the burden of the frequent intravenous administration and in better tailoring an individualized prophylaxis. The development of novel therapeutic approaches, like the bi-specific antibody mimicking the coagulation function of FVIII or inhibition of anticoagulant proteins may facilitate prophylaxis treatment not only in patients with inhibitors, but also in severe hemophilia patients without inhibitors. Exciting opportunities are emerging for improving prophylaxis in hemophilia.

Modifiers of clinical phenotype in severe congenital hemophilia

Patients with inherited hemophilia A and B usually exhibit a bleeding tendency of a severity proportional to the degree of plasmatic deficiency of the coagulant activity of factor VIII (FVIII:C) and factor IX (FIX:C). Although patients with severe hemophilia (i.e., with FVIII:C and FIX:C levels <1IU/dL) are generally those with the most severe bleeding phenotype, it is common experience that a variable proportion of them experiences a milder bleeding tendency. In this review, we summarize the current knowledge on the possible mechanisms at the basis of the phenotypic heterogeneity of severe hemophilia, focusing in particular on the role of FVIII/FIX gene mutations and thrombophilic polymorphisms. Finally, the possible therapeutic implications of such modifiers will be analyzed.

The incidence of catheter-associated venous thrombosis in noncritically ill children

OBJECTIVE

Previous studies estimated the incidence of catheter-associated venous thrombosis to be between 2% and 81%. Our goals were to define the incidence rate of catheter-related thrombosis in a hospitalized, noncritically ill, pediatric population and to determine modifiable factors that alter the risk of thrombosis.

METHODS

A retrospective cohort study was performed at the North Carolina Children's Hospital from 2009 to 2012. Chart review was performed with extraction of patient characteristics and line-related variables. Presence of symptomatic catheter-associated venous thrombosis was the primary outcome. Bivariable analysis and multivariable logistic regression were used to explore associations between line-related variables and thrombosis.

RESULTS

A total of 1135 lines were placed in 815 patients for 118,023 catheter-days. Thirty-six were complicated by venous thrombosis (3.2%) yielding a rate of 0.3 events per 1000 catheter-days. In multivariable analysis, increasing age (odds ratio [OR] 1.08, 95% confidence interval [CI] 1.03-1.13; P=.002), renal dialysis (OR 3.2, 95% CI 1.09-9.66; P=.035), and a diagnosis of inflammatory bowel disease or short bowel syndrome (OR 4.3, 95% CI 1.2-15.0; P=.02) were associated with increased risk of thrombosis. Modifiable risk factors, such as line site, size, and lumens, were not significantly associated with thrombosis. No thromboembolic events were observed.

CONCLUSIONS

We observed a lower incidence rate of catheter-associated venous thrombosis than in most previous reports. No modifiable characteristics altered the risk of thrombosis. Additional investigation of measures to prevent thrombosis is warranted in higher-risk populations, such as patients undergoing dialysis or patients with inflammatory bowel disease.

Central venous access devices in patients with hemophilia

Hemophilia is a hereditary disorder in which the major clinical manifestation is bleeding into the joints, muscles, internal organs and the CNS, often without any obvious trauma. Bleeding can be fatal as in the case of CNS hemorrhage, or severely debilitating following repeated bleeding into joints that results in crippling arthritis. Treatment for hemophilia includes the intravenous administration of clotting factor concentrates to replace the missing or defective protein. Venous access is therefore critical to the treatment of hemophilia and the prevention of complications due to bleeding. According to the US Centers for Disease Control and Prevention, approximately half of patients less than 16 years of age and one-third of all patients with hemophilia receive regular prophylactic injections of clotting factor concentrates. Prophylaxis, or the regular scheduled administration of antihemophilic factor concentrate, is effective in preventing bleeding. Among those patients with severe disease, in the absence of prophylaxis, approximately 13 bleeds, including nine joint hemorrhages, occur annually. In contrast, when prophylaxis is administered, the annual number of total and joint bleeds decreases to five and three, respectively. One of the major barriers to the more wide-spread use of prophylaxis is venous access. While peripheral venipuncture remains the first choice for venous access, central venous access devices are frequently used to facilitate repeated and/or urgent administration of clotting factor concentrates. The advantages of central venous access devices are well recognized in certain treatment regimens such as prophylaxis and immune tolerance therapy, as well as certain patient groups such as young children in whom venipuncture is often difficult and traumatic, and adults with scarred veins. Central venous access devices also allow earlier commencement of both home treatment and prophylaxis. The goal of this review is to discuss the different types of central venous access devices and their role in the management of hemophilia to provide practitioners that care for patients with hemophilia with the necessary information to make sound therapeutic recommendations to their patients.

Haemophilia in the first years of life

Surgery in infants and young children with haemophilia, when preceded by accurate diagnosis and accompanied by safe and effective factor prophylaxis, is not associated with a significant risk of haemorrhage. Haemophilic newborns undergoing circumcision or major surgery prior to diagnosis and in the absence of appropriate haemostatic prophylaxis remain as a concern. Inhibitor development has replaced haemorrhage as the major surgical complication in the developed world, largely because of the intensity of treatment used to secure haemostasis. For that reason only, essential surgery should be performed. Intracranial haemorrhage (ICH) during the neonatal period affects 3.5-4.0% of all haemophilia boys in countries with a good standard of health care, which is considerably (40-80 times) higher than expected in the normal population. Because of the high frequency of sporadic cases, ICH in the neonatal period can only be partially prevented by improved carrier diagnosis and counselling. Infections and thrombosis are the major serious complications of central venous lines. Large differences are seen in the frequency of these complications, the most plausible explanations are probably related to the protocol used for device care, the quality of education and the compliance of the users, an issue addressed in an on-going study.

Tissue plasminogen activator to prevent central venous access device infections: a systematic review of central venous access catheter thrombosis, infection and thromboprophylaxis

The recent unequivocal demonstration that prophylaxis, three to four weekly factor infusions, is effective in preventing joint disease in children with haemophilia, has provided impetus to initiate prophylaxis early in such children. Yet, nearly a quarter (22%) of the 83% who required central venous access devices for factor infusion developed central venous access catheter (CVAD)-related infection. This limitation of CVAD use prevents many families from initiating prophylaxis. The frequent occurrence of local thrombosis accompanying CVAD-related infection in surgical patients and autopsy cases, the thrombogenic plastic CVAD surfaces, and local clot formation at the insertion site, suggest the potential role of thrombolytic agents in preventing these infections. Yet, correlation between CVAD-related infection and local thrombosis in children with haemophilia are lacking, and thromboprophylaxis to prevent CVAD-related infection is controversial. Tissue plasminogen activator (t-PA), a recombinant serine protease glycoprotein that lyses plasmin-bound fibrin and is safe and effective in the treatment of occluded catheters, has not been evaluated in the prevention of these infections. We performed a literature review of CVAD-related infection, CVAD-related thrombosis, and thromboprophylaxis studies to evaluate the role of t-PA in the prevention of these infections in children with haemophilia. Metanalysis of published thromboprophylaxis trials demonstrate current prophylaxis regimens do not prevent CVAD infection, and further, that thrombosis and infection do not necessarily occur simultaneously. Pilot data demonstrate CVAD infection reduction in haemophilic children by monthly t-PA in 18 haemophilic children, suggesting the potential role of t-PA in CVAD infection prevention. Clinical trials to evaluate t-PA in CVAD infection prevention are justified.

The risk associated with indwelling catheters in children with haemophilia

Infections are the most frequent complications associated with the use of central venous lines (CVLs) in children with haemophilia. Several retrospective studies that include data from a substantial number of patients have reported approximately 0.2-0.3 infections per 1000 catheter-days (mainly Port-A-Cath). Some studies have shown a much higher frequency of infections, 1-2/1000 catheter-days. The most plausible explanations, for the difference seen in frequency of infections with Port-A-Caths, are probably related to the protocol used for the device care and the quality of education and the compliance of the users, whether these are parents or health-care professionals. The figures are low for clinically apparent thrombosis in the larger series on record, but routine venograms were not performed in most of these series. In studies, where this has been performed, a high frequency of abnormalities (>50%) on venograms have been seen in some series but not in others. Despite obvious potential risks with CVLs, they are useful in many cases and facilitate the treatment of a serious disorder. With careful guidelines and surveillance protocols, the risk of complications should be reduced in the future.

Overview of the use of implantable venous access devices in the management of children with inherited bleeding disorders

Frequent infusion of factor concentrates may be challenging in young boys with haemophilia, especially if their disease is complicated by inhibitors. A central venous access device (CVAD) is often placed in young patients in need of repeated infusions for prophylaxis or immune tolerance induction. Although user friendly and capable of providing reliable venous access, these devices are associated with a high complication rate over time. In the haemophilia population, major complications include CVAD-associated infections and deep venous thrombosis, which is most often silent. Established risk factors for catheter-related infection include age less than 6 years at the time of CVAD placement and use of an external CVAD when compared with a totally implantable device such as a port. Avoidance of CVAD-related infections is facilitated by strict adherence to aseptic technique. The risk of deep venous thrombosis appears related to the duration for which the catheter is in place, with the risk increasing beyond 4 years. The promotion of a strict clinic policy in which CVADs are left in place for as short a time as possible should decrease the risk of complications. In rare cases where a totally implantable CVAD cannot be placed for technical reasons, an arteriovenous fistula may provide reliable venous access. In all cases, however, venous access via peripheral veins is preferred over CVADs.

Prophylactic factor replacement in hemophilia

Prophylaxis, the regular infusion of coagulation factor concentrates to severe hemophiliacs, has been an evolving therapeutic tool of management for the past three decades. Multiple clinical trials have and continue to be conducted in the field of prophylaxis in an attempt to determine ideal regimens of prophylaxis, its benefits, its risks and costs, and to address still unanswered questions; who to place on prophylaxis, when to start prophylaxis, when (if ever) to stop prophylaxis, etc. We present a detailed review and discussion of the evolution of prophylaxis as a tool in managing patients with hemophilia and we address the major issues and still unanswered questions.

Consensus recommendations for use of central venous access devices in haemophilia

Venous access is essential for delivery of haemophilia factor concentrate. Wherever possible, peripheral veins remain the route of choice, and the use of central venous access devices (CVADs) should be limited to cases of clear need in patients with caregivers able to exercise diligence in CVAD care and should continue no longer than necessary. CVADs are of recognized value for repeated administration of coagulation factors in haemophilia, particularly for prophylaxis and immune tolerance therapy and in young children. Evidence to guide best practices has been fragmentary, and standardized methods for CVAD usage have yet to be established. We have developed management recommendations based upon available published evidence as well as extensive clinical experience. These recommendations address patient and CVAD selection; CVAD placement, care and removal; caregiver/patient guidance; and complications, including infection and thrombosis. In the absence of inhibitors, ports are recommended, primarily because of fewer associated infections than with external catheters. For patients with inhibitors, ports also appear to be associated with fewer infections. Infection is the most frequent complication, and recommendations to prevent and treat infections are supported by extensive clinical data and experience. Strict adherence to handwashing and aseptic technique are essential elements of catheter care. Evidence-based data regarding the detection and treatment of CVAD-related thrombotic complications are limited. Caregiver education is an integral part of CVAD use and the procedural practices of users should be regularly re-assessed. These recommendations provide a basis for sound current CVAD practice and are expected to undergo further refinements as new evidence is compiled and clinical experience is gained.

Central venous catheters in children with haemophilia

Infections, thrombosis and technical problems are the most frequent complications when using implantable central venous access devices in patients with haemophilia. There seem to be two major experiences concerning infections in non-inhibitor patients, one is approx. 0.2 infections per 1000 days and the other approx. 1.0(0.7-1.6)/1000 days. Infections are more frequent in inhibitor patients and one can expect approx. one infection per 6-12 months of use. The figures are low for clinically apparent thrombosis in the larger series on record, but routine venograms were not done in most of these series. In studies where this has been done, a high frequency of abnormalities on venograms have been seen in some but not in others. The final decision to use a central line has to be a compromise between the medical goal, the patient's bleeding tendency, the social situation and the expected risk of complications at the particular haemophilia center. Some of the complications may be reduced by adequate aseptic measures both during implantation and in the subsequent use and clear basic routines for surveillance of the systems and repeated education of the users.

A prospective, longitudinal study of central venous catheter-related deep venous thrombosis in boys with hemophilia

BACKGROUND

Central venous catheters (CVCs) are often inserted into boys with hemophilia to secure venous access for factor prophylaxis and immune tolerance induction therapy. Complications associated with CVCs include catheter-related infections, local hemorrhage, and mechanical failure. Less frequently reported is CVC-related deep venous thrombosis (DVT). We conducted a prospective study to determine the frequency and outcome of this complication.

METHODS

All boys (n = 16) with congenital hemophilia A or B with a CVC in place who were registered in the pediatric comprehensive care program at the Hospital for Sick Children, Toronto, were included in the study. They were prospectively assessed by imaging studies and clinical examinations for CVC-related DVT at two time-points, 2 years apart. Each boy was evaluated for inherited hypercoagulability.

RESULTS

Eleven (69%) of the 16 boys had radiological evidence of DVT at the first evaluation and 13/16 (81%) at the second evaluation. In two boys there was improvement in the venogram findings at the second evaluation. None of the CVC-related DVTs completely resolved. Median age at the time of initial insertion of a CVC was 1.0 years (range 0.02-6.7 years). Median duration of CVC placement was 6.4 years (range 3.3-15.5 years). Only 4/13 boys with DVTs had clinical evidence of upper venous system obstruction. Only one boy, who did not develop a DVT, had a low protein C level.

CONCLUSIONS

CVC-related DVTs occur in the majority of boys with hemophilia who have CVCs inserted for a prolonged period of time. Annual screening with imaging is recommended for boys with CVCs in place for >/= 3 years. Consideration should be given to removing CVCs as soon as peripheral venous access is feasible.

Central venous access devices in haemophilia

Central venous access devices (CVADs) can facilitate repeated and/or urgent administration of coagulation factors in haemophilic patients. We conducted a systematic review and meta-analysis of complication rates and risk factors for poor outcome. Forty-eight studies with a total of 2704 patients and 2973 CVADs were included. The primary indications for CVADs were immune tolerance therapy (34.9% of patients), difficult venous access (31.8%) and prophylaxis (29.1%). Fully implanted CVADs were employed in 77.4% of cases and external CVADs in 22.6%. A total of 1190 infections were reported, and the pooled incidence of infection was 0.66 per 1000 CVAD days [confidence interval (CI), 0.44-0.97 per 1000 CVAD days]. Among patients developing infection, the pooled time to first infection was 295 days (CI, 181-479 days). Presence of inhibitors was an independent risk factor for infection with an incidence rate ratio (IRR) of 1.67 (CI, 1.15-2.43). Infection was less likely in patients >6 years of age (IRR, 0.46; CI, 0.27-0.79) and recipients of fully implanted CVADs (IRR, 0.31; CI, 0.12-0.86). Available information on thrombosis was limited, with only 55 cases being reported. Eventually, 31.3% of CVADs were removed, and infection was the reason for removal in 69.9% of cases and thrombosis in 4.1%. The pooled time period CVADs remained indwelling prior to removal or the expiration of the study observation period was 578 days per CVAD (CI, 456-733 days per CVAD). CVADs can confer major benefits in patients with haemophilia requiring long-term venous access, and serious complications are rare.

Long-term safety and feasibility of arteriovenous fistulae as vascular accesses in children with haemophilia: a prospective study

Infectious and thrombotic complications limit the long-term use of subcutaneous ports as venous accesses for children with haemophilia. This study has evaluated for the first time the safety and feasibility of internal arteriovenous fistulae (AVF) as alternative accesses. During the 3-year study period, 27 severe haemophiliacs, 14 with factor VIII inhibitors (52%), underwent the creation of 31 proximal AVF in the forearm. Mild forearm haematomas were observed after five procedures (16%) in five patients who had or developed inhibitors after surgery. Inadequate AVF maturation was observed after five of 31 procedures (16%) in four children. AVF were first accessed after a median of 42 d and regularly used at home by 26 patients (96%) for a median follow-up period of 29 months. Thrombosis of a venous branch occurred in one AVF (3%) after 9 months of uncomplicated use in a child with inhibitor who spontaneously recovered from the symptoms and still used AVF for nine additional months. Mild symptoms, referable to distal ischaemia, were transiently reported by two children (7%) who needed no remedial intervention. This study demonstrates that the use of AVF in haemophiliacs enabled long-term treatment at home in all patients but one.

Central venous catheter-related thrombosis presenting as superior vena cava syndrome in a haemophilic patient with inhibitors

We report the case of a 10.5-year-old boy with severe haemophilia A (SHA) and inhibitors who presented with superior vena cava (SVC) obstruction while on immune tolerance induction (ITI) with daily recombinant factor VIII (rFVIII) and factor eight bypassing activity (FEIBA) (75 U kg(-1)) twice a week. The boy had a right-sided implanted central venous catheter. Imaging revealed a large occlusive thrombus in the SVC with all upper venous system drainage occurring through the azygos and collateral veins. Despite initial success with local thrombolytic therapy using recombinant tissue plasminogen activator, the thrombus persisted. Mechanical thrombolysis and angioplasty resulted in the successful removal of the thrombus and resolution of the SVC syndrome. Unfractionated heparin was used to prevent thrombus reformation/propagation. A work-up did not reveal any underlying genetic prothrombotic risk factors. The occurrence of such a profoundly symptomatic thromboembolism (TE) in a boy with SHA with inhibitors is unusual. A combination of risk factors, including the ongoing infusion of high doses of FVIII in the context of a disappearance of inhibitors together with the infusion of clotting factors known to be potentially thrombogenic, may place haemophilic patients on ITI (immune tolerance induction) at risk for this rare, life-threatening complication. The appropriate management of TEs in such a setting is unknown.

Adverse events in the prophylaxis of haemophilia

Whilst prophylaxis undoubtedly offers many advantages, the potential for adverse effects must also be borne in mind. Modern plasma-derived products have an extremely good safety record with regard to transmission of pathogens, although continuous vigilance is required as new pathogens continue to emerge, eg new variant Creutzfeldt-Jakob disease. There is no evidence that prophylactic treatment is associated with an increased incidence of inhibitors, and it is now recognized that genetic factors are the most significant in conferring susceptibility. Although subtle immunological abnormalities have also been observed in patients with haemophilia, there is no evidence that these are of any clinical significance. There has been a growing trend to use indwelling venous catheters for prophylaxis. The risk of infection has been appreciated for some time, although it has only recently been possible to quantify this with more precision. The risk of catheter-associated thrombosis is now recognized to be higher than hitherto appreciated. Whilst sporting activities are to be encouraged, there is a potential for significant trauma in children with prophylaxis, as plasma coagulation factor levels remain far below normal with the usual regimens.

Central venous lines in haemophilia

Infections and technical problems are the most frequent complications when using implantable central venous access devices in patients with haemophilia. There are two major experiences reported concerning infections in noninhibitor patients: one is approximately 0.2 infections per 1000 days and the other approximately 1.0 (0.7-1.6) per 1000 days. Infections are more frequent in inhibitor patients and approximately one infection per 6-12 months of use can be expected. The figures are low for clinically apparent thrombosis in the larger series on record, but routine venograms were not carried out in most of these series. In studies where this has been done, a high frequency of abnormalities on venograms has been seen in some but not in others. The final decision to use a central line has to take into account the medical goal, the patient's bleeding tendency, the social situation and the expected risk of complications at the particular haemophilia centre. Some of the complications may be reduced by adequate aseptic measures both during implantation and in subsequent use, and by clear basic routines for surveillance of the systems and repeated education of the users.

Thromboembolism in children

Acquired and inherited prothrombotic risk factors increase the risk of thrombosis in children. This review is based on "milestone" pediatric reports and new literature data (January 2001-February 2002) on the presence of acquired and inherited prothrombotic risk factors, imaging methods, and treatment modalities in pediatric thromboembolism. After confirming clinically suspected thromboembolism with suitable imaging methods, pediatric patients should be screened for common gene mutations (factor V G1691A, prothrombin G20210A and MTHFR C677T genotypes), rare genetic deficiencies (protein C, protein S, antithrombin, and plasminogen), and new candidates for genetic thrombophilia causing elevated levels of lipoprotein(a), and homocysteine, and probable genetic risk factors (elevations in fibrinogen, factor IX, and factor VIIIC, and decreases in factor XII). Data interpretation is based on age-dependent reference ranges or the identification of causative gene mutations/polymorphisms with respect to individual ethnic backgrounds. Pediatric treatment protocols for acute thromboembolism, including thrombolytic and anticoagulant therapy, are mainly adapted from adult patient protocols.