Antithrombotic therapy for ventricular assist devices in children: do we really know what to do?

Hemostatic and Thrombotic Considerations in the Diagnosis and Management of Childhood Arterial Ischemic Stroke: A Narrative Review

Although rare in children, arterial ischemic stroke (AIS) is associated with increased mortality and neurological morbidity. The incidence of AIS after the neonatal period is approximately 1-2/100,000/year, with an estimated mortality of 3-7%. A significant proportion of children surviving AIS experience life-long neurological deficits including hemiparesis, epilepsy, and cognitive delays. The low incidence of childhood AIS coupled with atypical clinical-presentation and lack of awareness contribute to delay in diagnosis and consequently, the early initiation of treatment. While randomized-clinical trials have demonstrated the efficacy and safety of reperfusion therapies including thrombolysis and endovascular thrombectomy in appropriately-selected adult patients, similar data for children are unavailable. Consequently, clinical decisions surrounding reperfusion therapy in childhood AIS are either extrapolated from adult data or based on local experience. The etiology of childhood AIS is multifactorial, often occurring in the setting of both acquired and congenital risk-factors including thrombophilia. While multiple studies have investigated the association of thrombophilia with incident childhood AIS, its impact on stroke recurrence and therefore duration and intensity of antithrombotic therapy is less clear. Despite these limitations, a significant progress has been made over the last decade in the management of childhood AIS. This progress can be attributed to international consortiums, and in selected cohorts to federally-funded clinical trials. In this narrative review, the authors have systematically appraised the literature and summarize the hemostatic and thrombotic considerations in the diagnosis and management of childhood AIS focusing on the evidence supporting reperfusion therapies, relevance of thrombophilia testing, and duration and drug choices for secondary-prophylaxis.

Clinical course and outcome after treatment with ventricular assist devices in paediatric patients: A single-centre experience

BACKGROUND

Heart failure is a rare condition in the paediatric population, associated with high morbidity and mortality. When medical therapy is no longer sufficient, mechanical circulatory support such as a ventricular assist device can be used to bridge these children to transplant or recovery. Coagulation-related complications such as thrombi, embolism and bleeding events represent the greatest challenge in paediatric patients on mechanical support. We aimed to describe the outcomes and coagulation-related complications in this patient population at our institution.

METHODS

A total of 20 patients with either Berlin Heart EXCOR® or HeartWare® implantation were reviewed in this retrospective study. Study endpoints were survival to heart transplant, weaning due to recovery or death. Thrombotic events were defined as thrombus formation in the device or in the patient, or cardioembolic strokes. Bleeding events were defined as events requiring interventional surgery or transfusion of red blood cells.

RESULTS

The aetiology of heart failure included cardiomyopathy (n = 12), end-stage congenital heart disease (n = 6) and myocarditis (n = 2). Of the 20 patients, 12 were bridged to transplant, 7 recovered and could be weaned and 1 died. The median duration of mechanical support was 84 days (range: 20-524 days). At least one major or minor bleeding event occurred in 45% of the patients. Thrombotic events occurred 21 times in 10 patients. Four of the patients (20%) had no bleeding or thromboembolic event.

CONCLUSION

In all, 95% of the patients were successfully bridged to transplant or recovery. Bleeding events and thrombotic events were common.

Kidney replacement therapy in pediatric patients on mechanical circulatory support: challenges for the pediatric nephrologist

The use of mechanical circulatory support (MCS) therapies in children with medically refractory cardiac failure has increased over the past two decades. With the growing experience and expertise, MCS is currently offered as a bridge to recovery or heart transplantation and in some cases even as destination therapy. Acute kidney injury (AKI) is common in patients with end-stage heart failure (ESHF). When severe AKI develops requiring kidney replacement therapy (KRT), these patients present unique challenges for the pediatric nephrology team. The use of KRT has not been adequately described in children with ESHF on the newer MCS. We also present original case series data from our center experience. The purpose of this review is to familiarize the reader with the current MCS technologies, approach to their selection, how they interact when combined with current KRT circuits, and distinguish similarities and differences. We will attempt to highlight the distinctive features of each technology, specifically focusing on growing trends in use of continuous-flow ventricular assist devices (CF-VAD) as it poses additional challenges to the pediatric nephrologist.

Variations of circulating miRNA in paediatric patients with Heart Failure supported with Ventricular Assist Device: a pilot study

Circulating miRNAs (c-miRNAs) are promising biomarkers for HF diagnosis and prognosis. There are no studies on HF pediatric patients undergoing VAD-implantation. Aims of this study were: to examine the c-miRNAs profile in HF children; to evaluate the effects of VAD on c-miRNAs levels; to in vitro validate putative c-miRNA targets. c-miRNA profile was determined in serum of HF children by NGS before and one month after VAD-implant. The c-miRNA differentially expressed were analyzed by real time-PCR, before and at 4 hrs,1,3,7,14,30 days after VAD-implant. A miRNA mimic transfection study in HepG2 cells was performed to validate putative miRNA targets selected through miRWalk database. Thirteen c-miRNAs were modified at 30 days after VAD-implant compared to pre-VAD at NSG, and, among them, six c-miRNAs were confirmed by Real-TimePCR. Putative targets of the validated c-miRNAs are involved in the hemostatic process. The in vitro study confirmed a down-regulatory effect of hsa-miR-409-3p towards coagulation factor 7 (F7) and F2. Of note, all patients had thrombotic events requiring pump change. In conclusion, in HF children, the level of six c-miRNAs involved in the regulation of hemostatic events changed after 30 days of VAD-treatment. In particular, the lowering of c-miR-409-3p regulating both F7 and F2 could reflect a pro-thrombotic state after VAD-implant.

Monitoring of Antiplatelet Therapy in Children on Ventricular Assist Device Support: Comparison of Multiplate and Thromboelastography Platelet Mapping

The optimal method for monitoring antiplatelet therapy in children supported with ventricular assist devices (VADs) is unknown. We conducted a retrospective study to compare Thromboelastography Platelet Mapping (TEG/PM) with multiple electrode platelet aggregometry (MEA) on a Multiplate analyzer (Roche Diagnostics, Mannheim, Germany). We analyzed data from 66 paired blood samples from 9 patients <16 years of age on VAD where platelet function was simultaneously measured with TEG/PM and MEA. Antiplatelet dose-response relationships and intraindividual variability during steady state therapy were determined. Agreement in determination of therapeutic antiplatelet therapy was poor (arachidonic acid, κ 0.23; adenosine diphosphate [ADP], κ 0.13). Rate of aspirin and clopidogrel resistance was much higher when determined using TEG/PM than MEA. In patients receiving ≥5 mg/kg/day aspirin, 72% of TEG/PM measurements showed subtherapeutic response compared with 11% of MEA measurements. There was evidence of a dose-response relationship with clopidogrel and MEA ADP-induced aggregation (R2 = 0.56; p < 0.0001); however, there was no association between dose and TEG/PM% ADP inhibition (p = 0.15). Intraindividual variability in platelet reactivity was far greater when measured by TEG/PM during steady state therapy. Multiple electrode platelet aggregometry appears to be more reliable than TEG/PM for monitoring antiplatelet therapy in children supported with VAD.

Antithrombin Population Pharmacokinetics in Pediatric Ventricular Assist Device Patients

OBJECTIVES

Describe the pharmacokinetics of antithrombin in pediatric patients undergoing ventricular assist device therapy and provide dosing recommendations for antithrombin in this population.

DESIGN

A retrospective population pharmacokinetic study was designed.

SETTING

Large tertiary care children's hospital Subject inclusion criteria consisted of less than 19 years old.

PATIENTS

Subjects less than 19 years old undergoing therapy with a HeartWare ventricular assist device (HeartWare, Framingham, MA) or Berlin EXCOR ventricular assist device (Berlin GmbH, Berlin, Germany), who received a dose of antithrombin with a postdose antithrombin activity level from January 1, 2011, to June 30, 2017.

INTERVENTIONS

Population pharmacokinetic analysis and simulation using NONMEM v.7.4 (Icon, PLC, Dublin, Ireland).

MEASUREMENTS AND MAIN RESULTS

A total of 41 patients met study criteria (median age, 5.8 years [interquartile range, 1.6-9.9 yr]), and 53.7% underwent therapy with the pulsatile Berlin EXCOR pediatric ventricular assist device (Berlin Heart GmbH, Berlin, Germany). All patients received unfractionated heparin continuous infusion at a mean ± SD dose of 29 ± 14 U/kg/hr. A total of 181 antithrombin doses (44.1 ± 24.6 U/kg/dose) were included, and baseline antithrombin activity levels were 77 ± 12 U/dL. Antithrombin activity levels were drawn a median 19.9 hours (interquartile range, 8.8-41.6 hr) after antithrombin dose. A one-compartment proportional error model best fit the data, with allometric scaling of fat-free mass providing a better model fit than actual body weight. Unfractionated heparin and baseline antithrombin were identified as significant covariates. A 50 U/kg dose of antithrombin had a simulated half-life 13.2 ± 6.6 hours.

CONCLUSIONS

Antithrombin should be dosed on fat-free mass in pediatric ventricular assist device patients. Unfractionated heparin dose and baseline antithrombin activity level should be considered when dosing antithrombin in pediatric ventricular assist device patients.

A Quality Bundle to Support High-Risk Pediatric Ventricular Assist Device Implantation

Pediatric ventricular assist device (VAD) implantation outcomes are increasingly promising for children with dilated cardiomyopathy and advanced decompensated heart failure (ADHF). VAD placement in patients with clinical features such as complex congenital cardiac anatomy, small body size, or major comorbidities remains problematic. These comorbidities have been traditionally prohibitive for VAD consideration leaving these children as a treatment-orphaned population. Here we describe the quality bundle surrounding these patients with ADHF considered high risk for VAD implantation at our institution. Over a 7-year period, a quality bundle aimed at the peri-operative care for children with high-risk features undergoing VAD implantation was incrementally implemented at a tertiary children's hospital. Patients were considered high risk if they were neonates (< 30 days), had single-ventricle physiology, non-dilated cardiomyopathy, biventricular dysfunction, or significant comorbidities. The quality improvement bundle evolved to include (1) structured team-based peri-operative evaluation, (2) weekly VAD rounds addressing post-operative device performance, (3) standardized anticoagulation strategies, and (4) a multidisciplinary system for management challenges. These measures aimed to improve communication, standardize management, allow for ongoing process improvement, and incorporate principles of a high-reliability organization. Between January 2010 and December 2017, 98 patients underwent VAD implantation, 48 (49%) of which had high-risk comorbidities and a resultant cohort survival-to-transplant rate of 65%. We report on the evolution of a quality improvement program to expand the scope of VAD implantation to patients with high-risk clinical profiles. This quality bundle can serve as a template for future large-scale collaborations to improve outcomes in these treatment-orphaned subgroups.

Aspirin in childhood acute ischemic stroke: The evidence for treatment and efficacy testing

Aspirin is the most commonly prescribed antiplatelet agent worldwide, but evidence supporting its use varies by age and disease process. Despite its frequent use in childhood acute ischemic stroke prevention and management, major knowledge gaps exist about optimal pediatric aspirin use, particularly in this setting, where high-quality clinical trials are urgently needed. This review focuses upon the evidence for aspirin use in childhood acute ischemic stroke, includes a summary of aspirin pharmacology to highlight misconceptions and common clinical situations which may limit its efficacy, and discusses the techniques and potential role of laboratory monitoring of aspirin efficacy in children.

HeartWare Ventricular Assist Device Implantation for Pediatric Heart Failure-A Single Center Approach

While pediatric HeartWare HVAD application has increased, determining candidacy and timing for initiation of pediatric VAD support has remained a challenge. We present our experience with a systematic approach to HVAD implantation as a bridge to pediatric heart transplantation. We performed a retrospective, single center review of pediatric patients (n = 11) who underwent HVAD implantation between September 2014 and January 2018. Primary endpoints evaluated were survival to heart transplantation, need for right ventricular assist device (RVAD) at any point, ongoing HVAD support, or death. Median patient age was 11 years (range: 3-16). Median BSA was 1.25 m² (range: 0.56-2.1). Heart failure etiologies requiring support were dilated cardiomyopathy (n = 8), myocarditis (n = 1), congenital mitral valve disease (n = 1), and single ventricle heart failure (n = 1). Median time from cardiac ICU admission for heart failure to HVAD placement was 15 days (range 3-55), based on standardized VAD implantation criteria involving imaging assessment and noncardiac organ evaluation. The majority of patients (91%) were INTERMACS Level 2 at time of implant. Three patients (27%) had CentriMag RVAD placement at time of HVAD implantation. Two of these three patients had successful RVAD explanation within 2 weeks. Median length of HVAD support was 60 days (range 6-405 days). Among the 11 patients, survival during HVAD therapy to date is 91% (10/11) with 9 (82%) bridged to heart transplantation and one (9%) continuing to receive support. Posttransplant survival has been 100%, with median follow-up of 573 days (range 152-1126). A systematic approach to HVAD implantation can provide excellent results in pediatric heart failure management for a variety of etiologies and broad BSA range.

Clinical pharmacology considerations for children supported with ventricular assist devices

The ventricular assist device is being increasingly used as a "bridge-to-transplant" option in children with heart failure who have failed medical management. Care for this medically complex population must be optimised, including through concomitant pharmacotherapy. Pharmacokinetic/pharmacodynamic alterations affecting pharmacotherapy are increasingly discovered in children supported with extracorporeal membrane oxygenation, another form of mechanical circulatory support. Similarities between extracorporeal membrane oxygenation and ventricular assist devices support the hypothesis that similar alterations may exist in ventricular assist device-supported patients. We conducted a literature review to assess the current data available on pharmacokinetics/pharmacodynamics in children with ventricular assist devices. We found two adult and no paediatric pharmacokinetic/pharmacodynamic studies in ventricular assist device-supported patients. While mechanisms may be partially extrapolated from children supported with extracorporeal membrane oxygenation, dedicated investigation of the paediatric ventricular assist device population is crucial given the inherent differences between the two forms of mechanical circulatory support, and pathophysiology that is unique to these patients. Commonly used drugs such as anticoagulants and antibiotics have narrow therapeutic windows with devastating consequences if under-dosed or over-dosed. Clinical studies are urgently needed to improve outcomes and maximise the potential of ventricular assist devices in this vulnerable population.

Pediatric ventricular assist devices: current challenges and future prospects

The field of mechanical circulatory support has made great strides in the preceding 2 decades. Although pediatric mechanical circulatory support has lagged behind that of adults, the gap between them is expected to close soon. The only device currently approved by the US Food and Drug Administration for use in children is the Berlin Heart EXCOR ventricular assist device (VAD). The prospective Berlin Heart Investigational Device Exemption Trial demonstrated good outcomes, such as bridge to transplantation or recovery, in ~90% of children supported with this device. However, a high incidence of hemorrhagic and thrombotic complications was also noted. As a result, pediatric centers have just started implanting adult intracorporeal continuous-flow devices in children. This paradigm shift has opened a new era in pediatric mechanical circulatory support. Whereas children on VAD were previously managed exclusively in hospital, therapeutic options such as outpatient management and even destination therapy have been becoming a reality. With continued miniaturization and technological refinements, devices currently in development will broaden the range of options available to children. The HeartMate 3 and HeartWare MVAD are two such compact VADs, which are anticipated to have great potential for pediatric use. Additionally, a pediatric-specific continuous-flow VAD, the newly redesigned Jarvik Infant 2015, is currently undergoing preclinical testing and is expected to undergo a randomized clinical trial in the near future. This review aims to discuss the challenges posed by the use of intracorporeal adult continuous-flow devices in children, as well as to provide our perspective on the future prospects of the field of pediatric VADs.