Ventricular Assist Devices in Children

In-Vivo Evaluation of a Novel Integrated Pediatric Pump Lung in a 30-Day Ovine Animal Model

Recently there has been increased use of mechanical circulatory support in pediatric patients as a bridge to cardiopulmonary recovery or transplantation. However, there are few devices that are optimized and approved for use in pediatric patients. We designed and prototyped a novel integrated pediatric pump lung (PPL) that underwent 30 day in-vivo testing in seven juvenile Dorset Hybrid sheep. Devices were implanted in a right atrial to pulmonary artery configuration. Six of seven sheep survived with a device functioning for 25-35 days. The device flow rate was maintained at 2.08 ± 0.34 to 2.54 ± 0.16 L/min with oxygen transfer of 109.8 ± 24.8 to 151.2 ± 26.2 ml/min over the study duration. Aside from a postoperative drop in hematocrit, all hematologic and blood chemistry test values returned to normal ranges after 1-2 weeks postoperatively. Similarly, lactate dehydrogenase increased postoperatively and returned to baseline. In two sheep, there were early device failures due to oxygenator thrombosis on postoperative days zero and five; they then had oxygenator exchanges with subsequent devices performing stably for 30 days. This study demonstrated that the integrated PPL device exhibited stable performance and acceptable biocompatibility in a 30 day ovine model.

Computed Tomography-Derived Normative Values of Right Ventricular Outflow Tract Structures in the Pediatric Population

Recent advances in available percutaneous device technology require accurate measurements and quantification of relationships between right ventricular outflow tract (RVOT) structures in children with and without congenital heart disease to determine device suitability. To date, no population study has described normal reference ranges of these measurements by computed tomography (CT). We aimed to establish normative values for four CT-derived measurements between RVOT structures from a heterogeneous population without heart disease and develop z scores useful for clinical practice. Patients without heart disease who underwent cardiac CT between April 2014 and February 2021 at Children's Hospital Colorado were included. Distance between the right ventricular (RV) apex to pulmonary valve (PV), PV to pulmonary trunk bifurcation, and bifurcation to the right and left pulmonary artery was measured. Previously validated models were used to normalize the measurements and calculate Z scores. Each measurement was plotted against BSA and Z scores distributions were used as reference lines. Three-hundred and sixty-four healthy patients with a mean age of 8.8 years (range 1-21), 58% male, and BSA of 1 m2 (range 0.4-2.1) were analyzed. The Haycock formula was used to present data as predicted values for a given BSA and within equations relating each measurement to BSA. Predicted values and Z-score boundaries for all measurements are presented.We report CT-derived normative data for four measurements between RVOT structures from a heterogeneous cohort of healthy children. Knowledge of this normative data will be useful in both determining device fit and customizing future devices to accommodate the diverse pediatric size range.

Outcomes of pediatric patients supported with ventricular assist devices single center experience

BACKGROUND

There has been a remarkable increase in the number of pediatric ventricular assist device (VAD) implanted over the past decade. Asian pediatric heart centers had not participated in the multicenter registries among the Western countries. This article aimed to report the outcomes of pediatric VAD in our hospital.

METHODS

The study enrolled all patients aged <18 years at the time of VAD implantation in our institution between 2008 and 2021.

RESULTS

There were 33 patients with diagnosis of acute fulminant myocarditis (n = 9), congenital heart disease (n = 5), dilated cardiomyopathy (n = 16), and others. Paracorporeal continuous-flow pump was the most frequently implanted (n = 27). Most of the devices were implanted in patients with INTERMACS profile 1 (n = 24). The median duration on VAD was 22 days (range 2-254). The proportion of patients attaining positive outcomes (alive on device, bridge to transplantation or recovery) was 72.7% at 1 month, 67.7% at 3 months, and 67.7% at 6 months. Most of the deaths on device occurred within the first month post-implant (n = 9), with neurological complications being the most frequent cause of death. All recovered cases were successfully weaned off the device within the first month of implantation.

CONCLUSION

We demonstrated a favorable outcome in pediatric patients supported with VAD at our institution.

Channel impeller design for centrifugal blood pump in hybrid pediatric total artificial heart: Modeling, magnet integration, and hydraulic experiments

BACKGROUND

The purpose of this research is to address ongoing device shortfalls for pediatric patients by developing a novel pediatric hybrid total artificial heart (TAH). The valveless magnetically-levitated MCS device (Dragon Heart) has only two moving parts, integrates an axial and centrifugal blood pump into a single device, and will occupy a compact footprint within the chest for the pediatric patient population.

METHODS

Prior work on the Dragon Heart focused on the development of pump designs to achieve hemodynamic requirements. The impeller of these pumps was shaft-driven and thus could not be integrated for testing. The presented research leverages an existing magnetically levitated axial flow pump and focuses on centrifugal pump development. Using the axial pump diameter as a geometric constraint, a shaftless, magnetically supported centrifugal pump was designed for placement circumferentially around the axial pump domain. The new design process included the computational analysis of more than 50 potential centrifugal impeller geometries. The resulting centrifugal pump designs were prototyped and tested for levitation and no-load rotation, followed by in vitro testing using a blood analog. To meet physiologic demands, target performance goals were pressure rises exceeding 90 mm Hg for flow rates of 1-5 L/min with operating speeds of less than 5000 RPM.

RESULTS

Three puck-shaped, channel impellers for the centrifugal blood pump were selected based on achieving performance and space requirements for magnetic integration. A quasi-steady flow analysis revealed that the impeller rotational position led to a pulsatile component in the pressure generation. After prototyping, the centrifugal prototypes (3, 4, and 5 channeled designs) demonstrated levitation and no-load rotation. Hydraulic experiments established pressure generation capabilities beyond target requirements. The pressure-flow performance of the prototypes followed expected trends with a dependence on rotational speed. Pulsatile blood flow was observed without pump-speed modulation due to rotating channel passage frequency.

CONCLUSION

The results are promising in the advancement of this pediatric TAH. The channeled impeller design creates pressure-flow curves that are decoupled from the flow rate, a benefit that could reduce the required controller inputs and improve treatment of hypertensive patients.

Design and Fabrication of Pneumatically Actuated Valveless Pumps

In this study, a valveless pump was successfully designed and fabricated for the purpose of medium transportation. Different from traditional pumps, the newly designed pump utilizes an actuated or a deflected membrane, and it serves as the function of a check valve at the same time. For achieving the valveless property, an inlet or outlet port positioned in an upper- or lower-layer thin membrane was designed to be connected to an entrance or exit channel. Theoretical analysis and numerical simulation were conducted simultaneously to investigate the large deformation characteristics of the membranes and to determine the proper location of the inlet or outlet port on the proposed pump. Then, the valveless pump was fabricated on the basis of the proposed design. In the experiment, the maximum flow rate of the proposed pump exceeded 12.47 mL/min at a driving frequency of 5.0 Hz and driving pressure of 68.95 kPa.

Integrated long-term multifunctional pediatric mechanical circulatory assist device

There continues to be limited, viable ventricular assist device technology options to support the dysfunctional states of pediatric heart failure. To address this need, we are developing a magnetically suspended, versatile pumping technology that uniquely integrates two blood pumps in a series configuration within a single device housing. This device enables operational switching from the usage of one pump to another as needed for clinical management or to support growth and development of the pediatric patient. Here, we present the initial design where we conducted a virtual fit study, the Taguchi Design Optimization Method, iterative design to develop pump geometries. Computational tools were used to estimate the pressure generation, capacity delivery, hydraulic efficiency, fluid stress levels, exposure time to stresses, blood damage index, and fluid forces on the impellers. Prototypes of the pumps were tested in a flow loop using a water-glycerin solution. Both designs demonstrated the capability to generate target pressures and flows. Blood damage estimations were below threshold levels and achieved design requirements; however, maximum scalar stress levels were above the target limit. Radial and axial forces were less than 1 N and 10 N, respectively. The performance data trends for physical prototypes correlated with theoretical expectations. The centrifugal prototype was able to generate slightly higher pressure rises than numerical predictions. In contrast, the axial prototype outperformed the computational studies. Experimental data were both repeatable and reproducible. The findings from this research are promising, and development will continue.

Destination-Therapy Ventricular Assist Device in Children: "The Future Is Now"

Durable ventricular assist devices (VADs) have significantly improved survival to transplantation among children with advanced stages of heart failure. The fundamental goals of VAD therapy include decreasing mortality, minimizing adverse events, and improving quality of life. As the pediatric VAD experience has evolved with reduced device related complications and improved survival, VAD therapy is being considered not only as a bridge to transplantation (BTT) but also as a bridge to decision (BTD) and as destination therapy (DT). Data regarding pediatric DT VAD are limited to anecdotal or case reports of children being supported for long periods with VADs and by default being classified as DT VAD. This article reviews current trends in the use of DT VAD and adverse events in children vs adults on VAD, and provides a framework for patient selection with the use of a multidisciplinary approach including palliative care. The general approach to determining DT VAD candidacy should include: 1) a reasonable success that the patient will survive the peri- and postoperative state; and 2) a high likelihood that the patient will be able to be discharged out of hospital and have adequate caregiver support. Patients with muscular dystrophy and failing Fontan physiology are examples of pediatric populations for whom DT VAD may be considered and which require unique considerations.

Evaluation and Management of the Child and Adult With Fontan Circulation: A Scientific Statement From the American Heart Association

It has been 50 years since Francis Fontan pioneered the operation that today bears his name. Initially designed for patients with tricuspid atresia, this procedure is now offered for a vast array of congenital cardiac lesions when a circulation with 2 ventricles cannot be achieved. As a result of technical advances and improvements in patient selection and perioperative management, survival has steadily increased, and it is estimated that patients operated on today may hope for a 30-year survival of >80%. Up to 70 000 patients may be alive worldwide today with Fontan circulation, and this population is expected to double in the next 20 years. In the absence of a subpulmonary ventricle, Fontan circulation is characterized by chronically elevated systemic venous pressures and decreased cardiac output. The addition of this acquired abnormal circulation to innate abnormalities associated with single-ventricle congenital heart disease exposes these patients to a variety of complications. Circulatory failure, ventricular dysfunction, atrioventricular valve regurgitation, arrhythmia, protein-losing enteropathy, and plastic bronchitis are potential complications of the Fontan circulation. Abnormalities in body composition, bone structure, and growth have been detected. Liver fibrosis and renal dysfunction are common and may progress over time. Cognitive, neuropsychological, and behavioral deficits are highly prevalent. As a testimony to the success of the current strategy of care, the proportion of adults with Fontan circulation is increasing. Healthcare providers are ill-prepared to tackle these challenges, as well as specific needs such as contraception and pregnancy in female patients. The role of therapies such as cardiovascular drugs to prevent and treat complications, heart transplantation, and mechanical circulatory support remains undetermined. There is a clear need for consensus on how best to follow up patients with Fontan circulation and to treat their complications. This American Heart Association statement summarizes the current state of knowledge on the Fontan circulation and its consequences. A proposed surveillance testing toolkit provides recommendations for a range of acceptable approaches to follow-up care for the patient with Fontan circulation. Gaps in knowledge and areas for future focus of investigation are highlighted, with the objective of laying the groundwork for creating a normal quality and duration of life for these unique individuals.

Preclinical performance of a pediatric mechanical circulatory support device: The PediaFlow ventricular assist device

OBJECTIVES

The PediaFlow (HeartWare International, Inc, Framingham, Mass) is a miniature, implantable, rotodynamic, fully magnetically levitated, continuous-flow pediatric ventricular assist device. The fourth-generation PediaFlow was evaluated in vitro and in vivo to characterize performance and biocompatibility.

METHODS

Supported by 2 National Heart, Lung, and Blood Institute contract initiatives to address the limited options available for pediatric patients with congenital or acquired cardiac disease, the PediaFlow was developed with the intent to provide chronic cardiac support for infants as small as 3 kg. The University of Pittsburgh-led Consortium evaluated fourth-generation PediaFlow prototypes both in vitro and within a preclinical ovine model (n = 11). The latter experiments led to multiple redesigns of the inflow cannula and outflow graft, resulting in the implantable design represented in the most recent implants (n = 2).

RESULTS

With more than a decade of extensive computational and experimental efforts spanning 4 device iterations, the AA battery-sized fourth-generation PediaFlow has an operating range of 0.5 to 1.5 L/min with minimal hemolysis in vitro and excellent hemocompatibility (eg, minimal hemolysis and platelet activation) in vivo. The pump and finalized accompanying implantable components demonstrated preclinical hemodynamics suitable for the intended pediatric application for up to 60 days.

CONCLUSIONS

Designated a Humanitarian Use Device for "mechanical circulatory support in neonates, infants, and toddlers weighing up to 20 kg as a bridge to transplant, a bridge to other therapeutic intervention such as surgery, or as a bridge to recovery" by the Food and Drug Administration, these initial results document the biocompatibility and potential of the fourth-generation PediaFlow design to provide chronic pediatric cardiac support.

The Evolution of a Pediatric Ventricular Assist Device Program: The Boston Children's Hospital Experience

Mechanical circulatory support in the form of ventricular assist devices (VADs) in children has undergone rapid growth in the last decade. With expansion of device options available for larger children and adolescents, the field of outpatient VAD support has flourished, with many programs unprepared for the clinical, programmatic, and administrative responsibilities. From preimplantation VAD evaluation and patient education to postimplant VAD management, the VAD program, staffed with an interdisciplinary team, is essential to providing safe, effective, and sustainable care for a new technology in an exceedingly complex patient population. Herein, this paper describes the Boston Children's Hospital VAD experience over a decade and important lessons learned from developing a pediatric program focusing on a high-risk but low-volume population. We highlight the paramount role of the VAD coordinator, clinical infrastructure requirements, as well as innovation in care spanning inpatient and outpatient VAD supports at Boston Children's Hospital.

Association Between Hematologic and Inflammatory Markers and 31 Thrombotic and Hemorrhagic Events in Berlin Heart Excor Patients

Bleeding and thrombotic events remain a significant cause of morbidity in pediatric patients supported with ventricular assist devices (VADs). The objective of this study is to identify the association between markers of anticoagulation and bleeding and thrombosis events during Berlin Heart ExCor support. A retrospective, single-center analysis of 9 patients supported with the Berlin Heart ExCor was performed. Inflammatory and anticoagulation parameters including C-reactive protein, fibrinogen, partial thromboplastin time (PTT), and platelet count were measured at 48 and 24 h before and after bleeding or thrombosis events. Patients served as their own controls, and the same parameters were measured during a control period where subjects did not experience either event. All patients received the anticoagulation regimen proposed by Berlin Heart. A total of 31 bleeding or thrombotic events were identified and matched to 18 control events. Patient with predominantly thrombotic events tended to weigh less than those with bleeding events (Δ7.7 kg, p < 0.001). PTT levels were higher before and after bleeding (Δ17.36, p = 0.002) and thrombosis (Δ8.75, p < 0.001) events relative to control. Heparin dose decreased after a thrombosis event (Δ-5.67, p = 0.097), and this decrease was significantly different from control (p = 0.032). Non-collinearity between heparin dose and PTT should prompt further inflammatory and hematological investigation. In addition, heavier patients were more prone to bleeding complications. The role of inflammation in the development of thrombus or hemorrhages in the pediatric VAD population needs to be studied further.

A multicenter study of the impella device for mechanical support of the systemic circulation in pediatric and adolescent patients

OBJECTIVES

The objective was to review the use of Impella devices (Abiomed Inc, Danvers, MA) for temporary circulatory support in pediatric and adolescent patients (age ≤ 21 yrs).

BACKGROUND

Options for minimally invasive circulatory support in children are limited, and published data are confined to case reports and small case series.

METHODS

This was a retrospective, multicenter review of Impella implants in pediatric and adolescent patients from 2009-15, using standardized data collection and INTERMACS definitions.

RESULTS

A total of 39 implants were performed in 38 patients from 16 centers. Median age and weight were 16 yrs (4-21 yrs) and 62 kg (15-134 kg). The primary indication for implant was cardiogenic shock in 28 patients (72%). Cardiac allograft rejection, myocarditis, or cardiomyopathy were the underlying diagnosis in 23 patients (59%); 11 patients had congenital heart disease. The median duration of support was 45 hr (1-1224 hr). Indications for explant included ventricular recovery in 16 patients, transition to another device in 12, death in 5, and transplant in 1. Survival was 85% at 7 days and 68% at 30 days. Major adverse events occurred in 8 patients: hemolysis in 3, bleeding in 2, stroke in 1 (unclear if related to Impella), sepsis in 1, and critical leg ischemia in 1. An increase in aortic regurgitation was noted in three patients, with no evidence of valve injury.

CONCLUSION

Temporary circulatory support with Impella devices is feasible in pediatric and adolescent patients, with acceptable risk profiles. More experience and follow up is needed to improve technical performance and patient selection. © 2017 Wiley Periodicals, Inc.

Comparison of Blood Viscoelasticity in Pediatric and Adult Cardiac Patients

Evidence is accumulating that blood flow patterns in the cardiovascular system and in cardiovascular devices do, in some instances, depend on blood viscoelasticity. Thus, to better understand the challenges to providing circulatory support and surgical therapies for pediatric and adult patients, viscous and elastic components of complex blood viscoelasticity of 31 pediatric patients were compared to those of 29 adult patients with a Vilastic-3 rheometer. A random effects model with categorical age covariates found statistically significant differences between pediatric and adult patients for log viscosity (p = 0.005). Log strain (p < 0.0001) and hematocrit (p < 0.0001) effects were also significant, as were the hematocrit-by-log-strain (p = 0.0006) and age-by-log strain (p = 0.001) interactions. The hematocrit-by-age interaction was not significant. For log elasticity, age differences were insignificant (p = 0.39). The model for log elasticity had significant log strain (p < 0.0001), log strain squared (p < 0.0001) and hematocrit (p < 0.0001) effects, as well as hematocrit-by-log-strain and hematocrit-by-log-strain-squared interactions (p = 0.014). A model for log viscosity with continuous age was also fit to the data, which can be used to refine cardiovascular device design and operation to the age of the patient. We conclude that there are distinct differences between pediatric and adult blood viscosity, as well as substantial variation within the pediatric population, that may impact the performance of devices and procedures.

Orphan devices: yesterday is history; tomorrow is mystery: towards a European orphan device directive?

BACKGROUND

Regulatory and economic frameworks stimulated the research and development of orphan drugs, but very little has been done for devices necessary for the in-vivo diagnosis, prevention and treatment of life-threatening conditions with a low prevalence/incidence.

DISCUSSION

A general public consultation in Europe has shown a positive attitude towards an "orphan device" directive. The United States of America have a Humanitarian Use Device exemption, but Europe is still waiting for such a stimulating framework. Post-marketing surveillance ("materio-vigilance") will be necessary for follow-up, patient-reported outcome measures (quality of life versus survival) needed and off-label use data available for patient-safety reasons. The marketing period for devices is shorter than for medicinal products. Incentives are necessary to stimulate research and development of such "orphan devices" especially when surgical intervention is the only option.

Review of the International Society for Heart and Lung Transplantation Practice guidelines for management of heart failure in children

In 2004, practice guidelines for the management of heart failure in children by Rosenthal and colleagues were published in conjunction with the International Society for Heart and Lung Transplantation. These guidelines have not been updated or reviewed since that time. In general, there has been considerable controversy as to the utility and purpose of clinical practice guidelines, but there is general recognition that the relentless progress of medicine leads to the progressive irrelevance of clinical practice guidelines that do not undergo periodic review and updating. Paediatrics and paediatric cardiology, in particular, have had comparatively minimal participation in the clinical practice guidelines realm. As a result, most clinical practice guidelines either specifically exclude paediatrics from consideration, as has been the case for the guidelines related to cardiac failure in adults, or else involve clinical practice guidelines committees that include one or two paediatric cardiologists and produce guidelines that cannot reasonably be considered a consensus paediatric opinion. These circumstances raise a legitimate question as to whether the International Society for Heart and Lung Transplantation paediatric heart failure guidelines should be re-reviewed. The time, effort, and expense involved in producing clinical practice guidelines should be considered before recommending an update to the International Society for Heart and Lung Transplantation Paediatric Heart Failure guidelines. There are specific areas of rapid change in the evaluation and management of heart failure in children that are undoubtedly worthy of updating. These domains include areas such as use of serum and imaging biomarkers, wearable and implantable monitoring devices, and acute heart failure management and mechanical circulatory support. At the time the International Society for Heart and Lung Transplantation guidelines were published, echocardiographic tissue Doppler, 3 dimensional imaging, and strain and strain rate were either novel or non-existent and have now moved into the main stream. Cardiac magnetic resonance imaging (MRI) had very limited availability, and since that time imaging and assessment of myocardial iron content, delayed gadolinium enhancement, and extracellular volume have moved into the mainstream. The only devices discussed in the International Society for Heart and Lung Transplantation guidelines were extracorporeal membrane oxygenators, pacemakers, and defibrillators. Since that time, ventricular assist devices have become mainstream. Despite the relative lack of randomised controlled trials in paediatric heart failure, advances continue to occur. These advances warrant implementation of an update and review process, something that is best done under the auspices of the national and international cardiology societies. A joint activity that includes the International Society for Heart and Lung Transplantation, American College of Cardiology/American Heart Association, the Association for European Paediatric and Congenital Cardiology (AEPC), European Society of Cardiology, Canadian Cardiovascular Society, and others will have more credibility than independent efforts by any of these organisations.

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

The use of ventricular assist devices (VADs) in children is increasing. Stroke and device-related thromboembolism remain the most feared complications associated with VAD therapy in children. The presence of a VAD causes dysregulation of hemostasis due to the presence of foreign materials and sheer forces intrinsic to the device resulting in hypercoagulability and potentially life-threatening thrombosis. The use of antithrombotic therapy in adults with VADs modulates this disruption in hemostasis, decreasing the risk of thrombosis. Yet, differences in hemostasis in children (developmental hemostasis) may result in variances in dysregulation by these devices and preclude the use of adult guidelines. Consequently, pediatric device studies must include safety and efficacy estimates of device-specific antithrombotic therapy guidelines. This review will discuss mechanisms of hemostatic dysregulation as it pertains to VADs, goals of VAD antithrombotic therapy for children and adults, and emerging antithrombotic strategies for VAD use in children.

Mechanical circulatory support in univentricular hearts: current management

Failing single-ventricle patients have now come into focus as the next cohort where improvement in outcomes for mechanical circulatory support can be realized. There is a paucity of published patient reports or management protocols in this patient population. Increased interest exists in finding answers of how to bridge these patients to transplant. We review the current literature and describe our approach to the patient with univentricular heart needing mechanical circulatory support.

Mechanical circulatory support: balancing bleeding and clotting in high-risk patients

Mechanical circulatory support (MCS) provides a bridge to heart transplant in children and adults with life-threatening heart failure and sustains patients ineligible for transplant. Extracorporeal membrane oxygenation (ECMO) provides temporary support for patients in cardiac or pulmonary failure through external gas exchange and continuous flow of blood. Because the median time to heart transplant exceeds event-free time on ECMO, pulsatile left ventricular assist devices (LVADs) are used to support infants and children. Continuous flow LVADs are preferred in adolescents and adults due to increased pump durability and improved overall survival. The shear stress created by the mechanical pumps cause changes in the hematologic system; acquired von Willebrand syndrome occurs in almost all patients treated with MCS. Despite the improvements in survival, major bleeding occurs in one-third of patients with a LVAD and ischemic stroke and LVAD thrombosis can affect 12% of adults and 29% of children. An antithrombotic strategy to mitigate LVAD bleeding and thrombotic complications has been tested in a randomized trial in children, but intensity of antithrombotic therapy in adults varies widely. Consensus guidelines for antithrombotic therapy during ECMO were created due to significant differences in management across centers. Because of the high risk for both bleeding and thrombotic complications, experts in hemostasis can significantly impact care of patients requiring mechanical circulatory support and are a necessary part of the management team.