Continuous-flow ventricular assist device support in children: A paradigm change

An Up-to-Date Literature Review on Ventricular Assist Devices Experience in Pediatric Hearts

Ventricular assist devices (VAD) have gained popularity in the pediatric population during recent years, as more and more children require a heart transplant due to improved palliation methods, allowing congenital heart defect patients and children with cardiomyopathies to live longer. Eventually, these children may require heart transplantation, and ventricular assist devices provide a bridge to transplantation in these cases. The FDA has so far approved two types of device: pulsatile and continuous flow (non-pulsatile), which can be axial and centrifugal. Potential eligible studies were searched in three databases: Medline, Embase, and ScienceDirect. Our endeavor retrieved 16 eligible studies focusing on five ventricular assist devices in children. We critically reviewed ventricular assist devices approved for pediatric use in terms of implant indication, main adverse effects, and outcomes. The main adverse effects associated with these devices have been noted to be thromboembolism, infection, bleeding, and hemolysis. However, utilizing left VAD early on, before end-organ dysfunction and deterioration of heart function, may give the patient enough time to recuperate before considering a more long-term solution for ventricular support.

Relationship of ventricular assist device support duration with pediatric heart transplant outcomes

BACKGROUND

There is wide variability in the timing of heart transplant (HTx) after pediatric VAD implant. While some centers wait months before listing for HTx, others accept donor heart offers within days of VAD surgery. We sought to determine if HTx within 30 days versus ≥ 30 after VAD impacts post-HTx outcomes.

METHODS

Children on VAD pre-HTx were extracted from the Pediatric Heart Transplant Study database. The primary endpoints were post-HTx length of hospital stay (LOS) and one-year survival. Confounding was addressed by propensity score weighting using inverse probability of treatment. Propensity scores were calculated based on age, blood type, primary cardiac diagnosis, decade, VAD type, and allosensitization status.

RESULTS

A total of 1064 children underwent VAD prior to HTx between 2000 to 2018. Most underwent HTx ≥ 30 days post-VAD (70%). Infants made up 22% of both groups. Patients ≥ 12 years old were 42% of the < 30 days group and children 1 to 11 years comprised 47% of the ≥ 30 days group (p < 0.001). There was no difference in the prevalence of congenital heart disease vs. cardiomyopathy (p = 0.8) or high allosensitization status (p = 0.9) between groups. Post-HTx LOS was similar between groups (p = 0.11). One-year survival was lower in the < 30 days group (adjusted mortality HR 1.76, 95% CI 1.11-2.78, p = 0.016).

CONCLUSIONS

A longer duration of VAD support prior to HTx is associated with a one-year survival benefit in children, although questions of patient complexity, post-VAD complications and the impact on causality remain. Additional studies using linked databases to understand these factors will be needed to fully assess the optimal timing for post-VAD HTx.

Variability in clinical decision-making for ventricular assist device implantation in pediatrics

BACKGROUND

Minimal data exist on clinical decision-making in VAD implantation in pediatrics. This study aims to identify areas of consensus/variability among pediatric VAD physicians in determining eligibility and factors that guide decision-making.

METHODS

An 88-item survey with clinical vignettes was sent to 132 pediatric HT cardiologists and surgeons at 37 centers. Summary statistics are presented for the variables assessed.

RESULTS

Total respondents were 65 (72% cardiologists, 28% surgeons) whose centers implanted 1-5 (34%), 6-10 (40%), or >10 (26%) VADs in the past year. Consensus varied by patients' age, diagnosis, and Pedimacs profile. Highest agreement to offer VAD (97%) was a mechanically ventilated teenager with dilated cardiomyopathy. Patients stable on inotropes were less likely offered VAD (11%-25%). SV infant with Pedimacs profile 2 had the most varied responses: 37% offered VAD; estimated survival ranged from 15% to 90%. Variables considered for VAD eligibility included mild developmental delays (100% offered VAD), moderate-severe behavioral concerns (46%), cancer in remission >2 years (100%), active malignancy with good prognosis (68%) or uncertain prognosis (36%), and BMI >35 (74%) or <15 (69%). Most respondents (91%) would consider destination therapy VADs in pediatrics, though not currently feasible at 1/3 of centers. Factors with greatest influence on decision-making included HT candidacy, families' goals of care, and risks of complications.

CONCLUSIONS

Significant variation exists among pediatric VAD physicians when determining VAD eligibility and estimating survival, which can lead to differences in access to emerging technologies across institutions. Further work is needed to understand and mitigate these differences.

Bridge to Transplant with Ventricular Assist Device Support in Pediatric Patients with Single Ventricle Heart Disease

Ventricular assist device (VAD) support for children with single ventricle (SV) heart disease remains challenging. We performed a single-center retrospective review of SV patients on VAD support and examined survival to transplant using the Kaplan-Meier method. Patients transplanted were compared with those who died on support. Between 2009 and 2017, there were 14 SV patients with 1,112 patient-days of VAD support. Stages of palliation included pre-Glenn (n = 5), Glenn (n = 5), and Fontan (n = 4). Eight patients (57%) were successfully bridged to transplant at a median 107 days. Deaths occurred early (n = 6, median 16 days) and in smaller patients (10.1 vs. 28.3 kg, P = 0.04). All Fontan patients survived to transplant, whereas only 20% of Glenn patients survived to transplant. Adverse events occurred in 79% (n = 11). Five patients met hospital discharge criteria, with two patients (one pre-Glenn, one Glenn) discharged and transplanted after 219 and 174 days of VAD support. All transplanted patients were discharged at a median 21 days posttransplant. SV patients in various stages of palliation can be successfully bridged to transplant with VAD support. With use of intracorporeal continuous-flow devices, longer-term support and hospital discharge are possible.

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.

Pediatric ventricular assist devices: Bridge to a new era of perioperative care

Pediatric ventricular assist devices (VADs) are evolving as a standard therapy for end stage heart failure in children. Major recent developments include the increased use of continuous flow (CF) devices in children and increased experience with congenital heart disease (CHD) and outpatient management. In the current and future era anesthesiologists will encounter more children presenting for VAD implantation, subsequent procedures and heart transplantation. Successful perioperative management requires an understanding of the interaction between the patient's physiology and the device and a framework to troubleshoot problems. This review focuses on CF devices, VAD support for CHD and perioperative management of pulsatile and CF devices in the pediatric population.

Current status and future perspectives of the PumpKIN trial

Similar to the adult experience, the use of continuous-flow ventricular assist devices (VADs) has been increasing in the pediatric population. According to the PediMACS registry, continuous-flow VAD currently accounts for >60% of the durable device implantations in the U.S. Nonetheless, the continuous-flow VADs currently in use are designed for adults; this inevitably causes the patient-device size mismatch issue, especially when applied for small children. Pulsatile VADs, therefore, represent the only practical option for this group of patients despite the known risk profile of pulsatile VADs. To address such a frustrating reality, the National Heart, Lung, and Blood Institute (NHLBI) launched the Pediatric Circulatory Support Program in 2004, which is the predecessor of the so-called PumpKIN (Pump for Kids, Infants, and Neonates) program. The goal of this program was to develop mechanical circulatory support devices specifically designed for small children. As a result of extensive efforts of the multi-disciplinary team involving clinicians, scientists, manufactures, and federal agencies, the Infant Jarvik 2015, one of the original devices within the Pediatric Circulatory Support Program, has become the first continuous-flow VAD specifically designed for small children that obtained the Investigational Device Exemption (IDEs) from the U.S. Food and Drug Administration (FDA). This approval is a prerequisite to initiate a clinical trial (i.e., the PumpKIN trial). This article describes the history, current status, and future perspectives of this extremely challenging project, with a focus on the lessons we have learned over the decade.