Pediatric mechanical circulatory support

Developments and Challenges in Durable Ventricular Assist Device Technology: A Comprehensive Review with a Focus on Advancements in China

Heart transplantation is currently the most effective treatment for end-stage heart failure; however, the shortage in donor hearts constrains the undertaking of transplantation. Mechanical circulatory support (MCS) technology has made rapid progress in recent years, providing diverse therapeutic options and alleviating the dilemma of donor heart shortage. The ventricular assist device (VAD), as an important category of MCS, demonstrates promising applications in bridging heart transplantation, destination therapy, and bridge-to-decision. VADs can be categorized as durable VADs (dVADs) and temporary VADs (tVADs), according to the duration of assistance. With the technological advancement and clinical application experience accumulated, VADs have been developed in biocompatible, lightweight, bionic, and intelligent ways. In this review, we summarize the development history of VADs, focusing on the mechanism and application status of dVADs in detail, and further discuss the research progress and use of VADs in China.

Development of Inspired Therapeutics Pediatric VAD: Benchtop Evaluation of Impeller Performance and Torques for MagLev Motor Design

PURPOSE

Despite the availability of first-generation extracorporeal mechanical circulatory support (MCS) systems that are widely used throughout the world, there is a need for the next generation of smaller, more portable devices (designed without cables and a minimal number of connectors) that can be used in all in-hospital and transport settings to support patients in heart failure. Moreover, a system that can be universally used for all indications for use including cardiopulmonary bypass (CPB), uni- or biventricular support (VAD), extracorporeal membrane oxygenation (ECMO) and respiratory assist that is suitable for use for adult, neonate, and pediatric patients is desirable. Providing a single, well designed, universal technology could reduce the incidence of human errors by limiting the need for training of hospital staff on a single system for a variety of indications throughout the hospital rather than having to train on multiple complex systems. The objective of this manuscript is to describe preliminary research to develop the first prototype pump for use as a ventricular assist device for pediatric patients with the Inspired Universal MCS technology. The Inspired VAD Universal System is an innovative extracorporeal blood pumping system utilizing novel MagLev technology in a single portable integrated motor/controller unit which can power a variety of different disposable pump modules intended for neonate, pediatric, and adult ventricular and respiratory assistance.

METHODS

A prototype of the Inspired Pediatric VAD was constructed to determine the hemodynamic requirements for pediatric applications. The magnitude/range of hydraulic torque of the internal impeller was quantified. The hydrodynamic performance of the prototype pump was benchmarked using a static mock flow loop model containing a heated blood analogue solution to test the pump over a range of rotational speeds (500-6000 RPM), flow rates (0-3.5 L/min), and pressures (0 to ~ 420 mmHg). The device was initially powered by a shaft-driven DC motor in lieu of a full MagLev design, which was also used to calculate the fluid torque acting on the impeller.

RESULTS

The pediatric VAD produced flows as high as 4.27 L/min against a pressure of 127 mmHg at 6000 RPM and the generated pressure and flow values fell within the desired design specifications.

CONCLUSIONS

The empirically determined performance and torque values establish the requirements for the magnetically levitated motor design to be used in the Inspired Universal MagLev System. This next step in our research and development is to fabricate a fully integrated and functional magnetically levitated pump, motor and controller system that meets the product requirement specifications and achieves a state of readiness for acute ovine animal studies to verify safety and performance of the system.

Advanced Heart Failure in Special Population-Pediatric Age

Heart failure (HF) is an important health care issue in children because of its considerable morbidity and mortality. Advanced HF encompasses patients who remained symptomatic despite optimal medical treatment and includes patients who require special management, such as continuous inotropic therapy, mechanical circulatory support, or heart transplantation (HT). HT is the gold standard for children with advanced HF; nonetheless, the number of suitable donors has not increased for decades, leading to prolonged waitlist times and increased mortality rates. Therefore, the role of pediatric mechanic circulatory support has been assessed as an alternative treatment in patients in whom heart transplant could not be performed. The authors discuss the epidemiology, causes, pathophysiology, clinical manifestation, medical treatment, device therapy, and HT in pediatric HF, and a particular emphasis was posed on patients with advanced HF.

Design and Computational Evaluation of a Pediatric MagLev Rotary Blood Pump

Pediatric heart failure (HF) patients have been a historically underserved population for mechanical circulatory support (MCS) therapy. To address this clinical need, we are developing a low cost, universal magnetically levitated extracorporeal system with interchangeable pump heads for pediatric support. Two impeller and pump designs (pump V1 and V2) for the pediatric pump were developed using dimensional analysis techniques and classic pump theory based on defined performance criteria (generated flow, pressure, and impeller diameter). The designs were virtually constructed using computer-aided design (CAD) software and 3D flow and pressure features were analyzed using computational fluid dynamics (CFD) analysis. Simulated pump designs (V1, V2) were operated at higher rotational speeds (~5,000 revolutions per minute [RPM]) than initially estimated (4,255 RPM) to achieve the desired operational point (3.5 L/min flow at 150 mm Hg). Pump V2 outperformed V1 by generating approximately 30% higher pressures at all simulated rotational speeds and at 5% lower priming volume. Simulated hydrodynamic performance (achieved flow and pressure, hydraulic efficiency) of our pediatric pump design, featuring reduced impeller size and priming volume, compares favorably to current commercially available MCS devices.

Tipless transseptal cannula concept combines improved hemodynamic properties and risk-reduced placement: An in silico proof-of-concept

As a leading cause of death worldwide, heart failure is a serious medical condition in which many critically ill patients require temporary mechanical circulatory support (MCS) as a bridge-to-recovery or bridge-to-decision. In many cases, the TandemHeart system is used to unload the left heart by draining blood from the left atrium (LA) to the femoral artery via a transseptal multistage cannula. However, even though the correct positioning of the cannula is crucial for a safe treatment, the long cannula tip currently used in transseptal cannulas complicates positioning, making the cannula vulnerable to displacement during MCS. To overcome these limitations, we propose the development of a new tipless transseptal cannula with improved hemodynamic properties. We discuss the tipless cannula concept by comparing it to the common multistage cannula concept using computational fluid dynamics simulations and assess the flow field in the LA, the wall shear stresses (WSS), and the pressure loss. Across the two distinct time points of end-systole and end-diastole and two drainage flow rates of 3.5 and 5.0 L/min, we find a more homogeneous inlet flow pattern for the tipless cannula concept, accompanied by a remarkably reduced area of platelet-activating WSS (up to 10-times smaller area compared to the multistage cannula). Moreover, pressure loss is up to 14.5% lower in the tipless cannula concept, confirming overall improved hemodynamic properties of the tipless cannula concept. Finally, a diameter-dependent study reveals that lower WSS and pressure losses can be further reduced by large-lumen designs for any simulation setting. Overall, our results suggest that a tipless cannula concept remedies the crucial disadvantages of a long-tip multistage cannula by reducing the risk of misplacement, and it furthermore promotes optimized hemodynamics. With this successful proof-of-concept, we underscore the potential for and encourage the realization of further experimental investigations regarding the development of a tipless transseptal cannula for MCS.

Pediatric Ventricular Assist Device

There have been great advances in ventricular assist device (VAD) treatment for pediatric patients with advanced heart failure. VAD support provides more time for the patient in the heart transplant waiting list. Augmented cardiac output improves heart failure symptoms, end-organ function, and general condition, and consequently provides beneficial effects on post-transplant outcomes. Miniaturized continuous flow devices are more widely adopted for pediatric patient with promising results. For infants and small children, still paracorporeal pulsatile device is the only option for long-term support. Younger age, congenital heart disease, biventricular support, patient's status and end-organ dysfunction at the time of implantation are risks for poor outcomes. Patient selection, timing of implantation, and selection of device for each patient are critical for optimal clinical outcomes.

Eighteen years of paediatric extracorporeal membrane oxygenation and ventricular assist devices: insight regarding late outcomes

BACKGROUND

We reviewed all patients who were supported with extracorporeal membrane oxygenation and/or ventricular assist device at our institution in order to describe diagnostic characteristics and assess mortality.

METHODS

A retrospective cohort study was performed including all patients supported with extracorporeal membrane oxygenation and/or ventricular assist device from our first case (8 October, 1998) through 25 July, 2016. The primary outcome of interest was mortality, which was modelled by the Kaplan-Meier method.

RESULTS

A total of 223 patients underwent 241 extracorporeal membrane oxygenation runs. Median support time was 4.0 days, ranging from 0.04 to 55.8 days, with a mean of 6.4±7.0 days. Mean (±SD) age at initiation was 727.4 days (±146.9 days). Indications for extracorporeal membrane oxygenation were stratified by primary indication: cardiac extracorporeal membrane oxygenation (n=175; 72.6%) or respiratory extracorporeal membrane oxygenation (n=66; 27.4%). The most frequent diagnosis for cardiac extracorporeal membrane oxygenation patients was hypoplastic left heart syndrome or hypoplastic left heart syndrome-related malformation (n=55 patients with HLHS who underwent 64 extracorporeal membrane oxygenation runs). For respiratory extracorporeal membrane oxygenation, the most frequent diagnosis was congenital diaphragmatic hernia (n=22). A total of 24 patients underwent 26 ventricular assist device runs. Median support time was 7 days, ranging from 0 to 75 days, with a mean of 15.3±18.8 days. Mean age at initiation of ventricular assist device was 2530.8±660.2 days (6.93±1.81 years). Cardiomyopathy/myocarditis was the most frequent indication for ventricular assist device placement (n=14; 53.8%). Survival to discharge was 42.2% for extracorporeal membrane oxygenation patients and 54.2% for ventricular assist device patients. Kaplan-Meier 1-year survival was as follows: all patients, 41.0%; extracorporeal membrane oxygenation patients, 41.0%; and ventricular assist device patients, 43.2%. Kaplan-Meier 5-year survival was as follows: all patients, 39.7%; extracorporeal membrane oxygenation patients, 39.7%; and ventricular assist device patients, 43.2%.

CONCLUSIONS

This single-institutional 18-year review documents the differential probability of survival for various sub-groups of patients who require support with extracorporeal membrane oxygenation or ventricular assist device. The indication for mechanical circulatory support, underlying diagnosis, age, and setting in which cannulation occurs may affect survival after extracorporeal membrane oxygenation and ventricular assist device. The Kaplan-Meier analyses in this study demonstrate that patients who survive to hospital discharge have an excellent chance of longer-term survival.

Feasibility of a Post-Auricle Wireless Power System for Pediatric Mechanical Circulatory Support Pumps

Heart failure (HF) affects approximately 12,000-35,000 children each year in the United States. The development of blood pumps has provided circulatory support for many adults suffering with HF until they receive a heart transplant. However, while the development of blood pumps for adults has led to fullyimplantable continuous flow devices, blood pump technology for children has lagged significantly behind. One area for improving blood pump implantability in children is the use of wireless powering transfer systems (WPTS). These systems eliminate the power cord connecting the implanted blood pump to the external power supply. In adults, WPTS have decreased the number of power cord-related infections and have improved patient outcomes after pump implantation. Unfortunately, the components of these wireless systems are too large for children. In this paper we describe the preliminary work to develop a fully implantable WPTS specifically designed to power the Jarvik 2000 Child. Specifically, we design planar coils 36 um in thickness to be implanted in behind-the-ear fashion. An amplifier and rectifier circuit were also built to provide 15.7V and 0.5A of voltage and current to the pump.

Case report and review of the literature: the utilisation of a ventricular assist device as bridge to recovery for anthracycline-induced ventricular dysfunction

Ventricular assist devices are used in children with heart failure as a bridge to myocardial recovery or cardiac transplantation. Anthracyclines cause cardiac toxicity and may result in acute or long-term cardiac failure. We describe the use of a ventricular assist device as a bridge to recovery in a child with severe acute anthracycline-induced cardiomyopathy, and we review the associated literature. A 6-year-old girl was treated for acute myeloblastic leukaemia with daunorubicin and mitoxantrone. After 2 weeks her final dose of chemotherapy, her Left Ventricular Ejection Fraction decreased to 21%. Despite initiation of medical therapy, she had continued deterioration of left ventricular function and developed evidence of poor end-organ perfusion. She was not a candidate for cardiac transplantation, as the post-transplant immune suppression therapy would put her at risk for recurrence of her malignancy. We placed her on a short-term ventricular assist device as a bridge to ultimately placing her on a long-term ventricular assist device versus continuing medical therapy. Her left ventricular ejection fraction improved to 55% 24 days after ventricular assist device insertion. She was separated from the ventricular assist device 26 days after its insertion. She was discharged home 29 days later and is now 28 months after ventricular assist device implantation with stable ventricular function, as documented by a left ventricular ejection fraction of 55%, and normal end organ function. This case is one of the only reports known describing successful use of a short-term ventricular assist device as a bridge to recovery in a child with severe acute anthracycline-induced cardiotoxicity.

Externally applied compression therapy for Fontan patients

BACKGROUND

Limited therapeutic options are available for Fontan patients with dysfunctional or failing single ventricle physiology. This study describes the evaluation of an alternative, non-invasive, at-home therapeutic compression treatment for Fontan patients. Our hypothesis is that routinely administered, externally applied compression treatments to the lower extremities will augment systemic venous return, improve ventricular preload, and thus enhance cardiac output in Fontan patients.

METHODS

To initially evaluate this hypothesis, we employed the NormaTec pneumatic compression device (PCD) in a pilot clinical study (n=2). This device is composed of inflatable trouser compartments that facilitate circumferentially and uniformly applied pressure to a patient's lower extremities. Following an initial health screening, test subjects were pre-evaluated with a modified-Bruce treadmill exercise stress test, and baseline data on cardiorespiratory health was collected. After training, test subjects conducted 6 days of external compression therapy at-home. Subjects were then re-evaluated with a final treadmill stress test and data acquisition of new cardiorespiratory parameters.

RESULTS

Both subjects demonstrated improvement in exercise duration time, peak oxygen volume, and ventilator threshold, as compared to the baseline evaluation.

CONCLUSIONS

These findings are promising and provide the foundation for future studies that will focus on increasing study participation (sample size) to better assess the clinical benefit of compression therapy for Fontan patients.

Ventricular assist device use in congenital heart disease with a comparison to heart transplant

Despite advances in medical and surgical therapies, some children with congenital heart disease (CHD) are not able to be adequately treated or palliated, leading them to develop progressive heart failure. As these patients progress to end-stage heart failure they pose a unique set of challenges. Heart transplant remains the standard of care; the donor pool, however, remains limited. Following the experience from the adult realm, the pediatric ventricular assist device (VAD) has emerged as a valid treatment option as a bridge to transplant. Due to the infrequent necessity and the uniqueness of each case, the pediatric VAD in the CHD population remains a topic with limited information. Given the experience in the adult realm, we were tasked with reviewing pediatric VADs and their use in patients with CHD and comparing this therapy to heart transplantation when possible.

Mechanical circulatory support for infants and small children

The number of children in need of mechanical circulatory support has increased substantially over the last two decades, due to the technological progress made in surgery and intensive care, leading to improved survival of patients with congenital heart disease. In addition, primary myocardial dysfunction related to myocarditis or dilated cardiomyopathy may cause end-stage cardiac failure in children or infants, although not as frequently as in adults. The need for mechanical circulatory support may be either temporary until spontaneous myocardial recovery, as in postcardiotomy cardiac failure, or prolonged until heart transplantation in the absence of recovery. Two types of mechanical circulatory devices are suitable for the paediatric population: extracorporeal membrane oxygenation for short-term support; and ventricular assist devices for long-term support as a bridge to transplantation. The aim of this review is to describe the specific issues related to paediatric mechanical circulatory support and the different types of devices available, to report on their rapidly growing use worldwide and on the outcomes for each indication and type of device, and to provide a perspective on the future developments and remaining challenges in this field.