Pediatric Ventricular Assist Device Research Articles

The influence of operational protocol on the fluid dynamics in the 12 cc Penn state pulsatile pediatric ventricular assist device: the effect of end-diastolic delay.

The success of adult ventricular assist devices (VADs), coupled with the high transplant waiting list mortality of infants (40%) has prompted Penn State to develop a pediatric version of the clinically successful adult device. Although the primary use of this device will be bridge-to-transplant, there has been sufficient clinical data to demonstrate the efficacy of VADs in a bridge-to-recovery setting. However, removing the patient from the device, a process known as weaning, demands operation of the device at a lower beat rate and concomitant increased risk for thromboembolism. Previous studies have shown that the interrelated flow characteristics necessary for the prevention of thrombosis in a pulsatile VAD are a strong inlet jet, a late diastolic recirculating flow, and a wall shear rate greater than 500/s. In an effort to develop a strong inlet jet and rotational flow pattern at a lower beat and flow rate, we have compressed diastole by altering the end-diastolic delay time (EDD). Particle image velocimetry was used to compare the flow fields and wall shear rates in the chamber of the 12 cc Penn State pulsatile pediatric VAD operated at 50 beats per minute using EDDs of 10, 50, and 100 ms. Although we expected the 100 ms EDD to have the best wall shear profiles, we found that the 50 ms EDD condition was superior to both the 10 and 100 EDD conditions, due to a longer sustained inlet jet.

Hemodynamics of an End-to-Side Anastomotic Graft for a Pulsatile Pediatric Ventricular Assist Device

Numerical simulations are performed to investigate the flow within the end-to-side proximal anastomosis of a pulsatile pediatric ventricular assist device (PVAD) to an aorta. The anastomotic model is constructed from a patient-specific pediatric aorta. The three great vessels originating from the aortic arch--brachiocephalic (innominate), left common carotid, and left subclavian arteries--are included. An implicit large eddy simulation method based on a finite volume approach is used to study the resulting turbulent flow. A resistance boundary condition is applied at each branch outlet to study flow splitting. The PVAD anastomosis is found to alter the aortic flow dramatically. More flow is diverted into the great vessels with the PVAD support. Turbulence is found in the jet impingement area at peak systole for 100% bypass, and a maximum principal normal Reynolds stress of 7081 dyn/cm(2) is estimated based on ten flow cycles. This may be high enough to cause hemolysis and platelet activation. Regions prone to intimal hyperplasia are identified by combining the time-averaged wall shear stress and oscillatory shear index. These regions are found to vary, depending on the percentage of the flow bypass.

360: In Vivo Assessment of Thrombogenicity of the Penn State Pediatric Ventricular Assist Device

Penn State has recently completed the design and feasibility testing of a pulsatile pediatric Ventricular Assist Device (VAD) under the 5 year NHLBI contract program “Pediatric Circulatory Support”. The Infant VAD is a pneumatically-actuated pulsatile pump with a 14 ml stroke volume, based on the adult Thoratec (Pierce-Donachy) VAD. The Pediatric VAD may provide left, right, or biventricular support for long term bridge-to-transplant or weaning applications. The primary design objective has been to minimize thromboembolic risk; thrombogenicity has been assessed in 30 day chronic animal studies.

Flow visualization of three-dimensionality inside the 12 cc Penn State pulsatile pediatric ventricular assist device.

In order to aid the ongoing concern of limited organ availability for pediatric heart transplants, Penn State has continued development of a pulsatile Pediatric Ventricular Assist Device (PVAD). Initial studies of the PVAD observed an increase in thrombus formation due to differences in flow field physics when compared to adult sized devices, which included a higher degree of three-dimensionality. This unique flow field brings into question the use of 2D planar particle image velocimetry (PIV) as a flow visualization technique, however the small size and high curvature of the PVAD make other tools such as stereoscopic PIV impractical. In order to test the reliability of the 2D results, we perform a pseudo-3D PIV study using planes both parallel and normal to the diaphragm employing a mock circulatory loop containing a viscoelastic fluid that mimics 40% hematocrit blood. We find that while the third component of velocity is extremely helpful to a physical understanding of the flow, particularly of the diastolic jet and the development of a desired rotational pattern, the flow data taken parallel to the diaphragm is sufficient to describe the wall shear rates, a critical aspect to the study of thrombosis and design of such pumps.

Animal model development for the Penn State pediatric ventricular assist device.

In March 2004, the National Heart, Lung, and Blood Institute awarded five contracts to develop devices providing circulatory support for infants and small children with congenital and acquired cardiac disease. Since 2004, the team at Penn State College of Medicine has developed a pneumatically actuated ventricular assist device (VAD) with mechanical tilting disk valves. To date, hemodynamic performance, thrombogenesis, and hemolysis have been chronically evaluated in 16 animals, including 4 pygmy goats and 12 sheep. Major complications, mainly respiratory failure, have been encountered and resolved by a multi-disciplinary team. Multi-modal analgesia, appropriate antibiotic therapy, and attentive animal care have contributed to successful outcomes. Time after implant has ranged from 0 to 40 days. Most recently, a sheep implanted with Version 3 Infant VAD was electively terminated at 35 days postimplant, with no major adverse events. This report describes a successful in vivo model for evaluating a pediatric VAD.

Ventricular Assist Device Implantation in the Pediatric Population: Does Pump Size Selection and Associated Hemodynamics Impact Outcomes?

The use of pediatric ventricular assist devices (VADs) continues to evolve with the availability of smaller blood pumps. We examine the correlation of implanting appropriate sized blood pumps with a lower incidence of VAD related complications (VADRC). A 7-year retrospective review was undertaken for all pediatric VAD patients. Optimal VAD hemodynamics were defined as cardiac index of 2.7 L/m2 and rate of 80 beats per minute (bpm) with complete fill/empty of the blood pump. Patient/blood pump size match, VAD rate and fill/empty ratios were calculated (optimum = 1.0) and then correlated with incidence of VADRC. The study included 22 patients, mean age 9.77 years (6 mo-18 yrs) and mean body surface area (BSA) of 1.14 m2 (0.14 m2-2.32 m2), who underwent VAD implantation. VADRC included death while on support (n = 5), bleeding requiring reoperation (n = 8), hemolysis (n = 2), neurologic events (n = 2), thrombus formation (n = 3), and infection (n = 3). Six patients were bridged to transplant without any VADRC. This subset of patients had a mean blood pump size match ratio of 0.98, VAD rate ratio of 0.92 and fill/empty ratio of 1.00. Patients with VADRC (n = 16) were found to have a mean blood pump size match ratio of 0.72, VAD rate ratio of 0.72 and fill/empty ratio of 0.78. We report a series of pediatric patients with wide ranging BSA receiving VAD implantation. Selection of appropriate sized blood pumps can be correlated with decreased VADRC.

Development of an Interprofessional Pediatric Ventricular Assist Device Support Team

Caring for pediatric patients with a ventricular assist device (VAD) requires a collaborative approach from an interprofessional team to ensure maximum patient safety and optimal outcomes. Initiating a VAD program is challenging, due to the complex medical and technical nature of this device and associated learning needs. At our institution, the development of the interprofessional VAD support team was established in four phases. Initial Education, Core Team Formation, Expansion, and Evaluation. A "core VAD team" was created after the initial education at an established VAD center. In a third step, all efforts were directed toward increasing the number of health care professionals caring for the VAD patients in the Cardiac Critical Care setting and on the Cardiac ward. The last phase consists of ongoing evaluation. Several key areas imperative to the care of a patient on a VAD were identified and further elaborated. The complex care of a patient on a VAD needs a specialized team approach to cover all patient care needs. Ongoing interprofessional education continues to improve competency of care. Continuity of care was assured on all levels of service to ensure the best possible outcomes.

CFD Analysis of a Mag-Lev Ventricular Assist Device for Infants and Children: Fourth Generation Design

Thousands of pediatric patients suffering from heart failure would benefit from longer-term mechanical circulatory support. There are, however, few support systems available in the United States as viable mechanical assist alternatives for these patients. Therefore, we have designed and developed an axial flow pediatric ventricular assist device (PVAD) with an impeller that is fully suspended by magnetic bearings. This blood pump is designed to generate 0.5-4 L/min for pressure rises of 50-95 mm Hg over 6,000-9,000 rpm. We have performed four major design iterations. Building upon the third design phase, we made improvements to create the PVAD4 model. Numerical simulations of the PVAD4 under steady flow simulations were performed to compare the predictions of the latest PVAD4 model to the earlier PVAD3 design. The PVAD4 design resulted in lower fluid stress levels and an increase in pressure generation. A blood damage analysis was also completed. As compared with the earlier PVAD3 design, the damage analysis of the PVAD4 indicated a reduction in the mean and maximum damage index for the new design. All of these numerical findings are encouraging and demonstrate progress toward achieving a superior pump design.

The 12cc Penn State Pulsatile Pediatric Ventricular Assist Device: Fluid Dynamics Associated With Valve Selection

The mortality rate for infants awaiting a heart transplant is 40% because of the extremely limited number of donor organs. Ventricular assist devices (VADs), a common bridge-to-transplant solution in adults, are becoming a viable option for pediatric patients. A major obstacle faced by VAD designers is thromboembolism. Previous studies have shown that the interrelated flow characteristics necessary for the prevention of thrombosis in a pulsatile VAD are a strong inlet jet, a late diastolic recirculating flow, and a wall shear rate greater than 500 s(-1). Particle image velocimetry was used to compare the flow fields in the chamber of the 12 cc Penn State pediatric pulsatile VAD using two mechanical heart valves: Bjork-Shiley monostrut (BSM) tilting disk valves and CarboMedics (CM) bileaflet valves. In conjunction with the flow evaluation, wall shear data were calculated and analyzed to help quantify wall washing. The major orifice inlet jet of the device containing BSM valves was more intense, which led to better recirculation and wall washing than the three jets produced by the CM valves. Regurgitation through the CM valve served as a significant hindrance to the development of the rotational flow.

The 12 cc Penn State Pulsatile Pediatric Ventricular Assist Device: Flow Field Observations at a Reduced Beat Rate With Application to Weaning

Ventricular assist devices (VADs) have become a viable option for adult patients with end-stage heart failure during the bridge-to-transplant period and have recently shown promise in aiding in myocardial recovery. Because the number of available organs is insufficient, mechanical circulatory support systems such as VADs are also being developed for use in pediatric patients. During myocardial recovery, the system must be weaned from the patient to prepare for explant; for pulsatile devices, this often includes a reduction in flow rate, which can change the fluid dynamics of the device. These changes in flow need to be monitored because strong diastolic rotational flow, no areas of blood stasis, low blood residence time, and wall shear rates above 500 s, can help prevent thrombus deposition. Particle image velocimetry was used to observe the planar flow patterns and wall shear rates of the 12 cc Penn State Pneumatic Pediatric VAD (PVAD) at a normal operating condition and a reduced beat rate. At the reduced beat rate, the PVAD showed an earlier loss of rotational pattern, increased blood residence time, and an overall reduction in wall shear rate at the outer walls. Because this reduction in flow rate could lead to a possible increase in thrombus deposition, it may be necessary to look into other options for weaning a patient from the PVAD.

The Cleveland Clinic PediPump: Virtual Fitting Studies in Children Using Three-Dimensional Reconstructions of Cardiac Computed Tomography Scans

The fitting of implantable ventricular assist devices (VADs) is a particular challenge for pediatric patients and patients with small body surface area. The purpose of this study was to determine optimal placement of the PediPump, a pediatric VAD currently under development at the Cleveland Clinic, using virtual three-dimensional (3D) on-screen models. Digital models were created from computed tomographic datasets of pediatric hearts using commercially available 3D image processing software. Pixels representing the myocardium, great vessels, sternum, and rib cage were selected and rendered as on-screen models (n = 13) from pediatric patients with or without congenital heart disease (median age 42 months; range 2 days to 13 years 11 months). Using 3D model manipulation software, virtual models of the PediPump (70 x 10 mm) were combined on-screen with the anatomic models. A variety of virtual fitting options were created, which allowed easy detection of device interference with surrounding tissues. Generation of 3D on-screen models of cardiac structures in relation to PediPump placement has provided useful preliminary fitting information, which is being used to guide further development of this device.

Connecting the Centrimag Levitronix Pump to Berlin Heart Excor Cannulae; A New Approach to Bridge to Bridge

An increasing number of children are requiring circulatory support. Hospitals offering pediatric Ventricular Assist Device (VAD) should have devices of different sizes available to cover the full range of patient sizes incurring considerable expense. As in adults, post-operative bleeding often complicates VAD implantation. The use of a Levitronix Centrimag centrifugal pump, connected to Berlin Heart Excor cannulae, seems an attractive and logic combination, both in terms of patient safety and of hospital economics. We describe 3 children with therapy resistant cardiac failure who underwent extracorporeal membrane oxygenation (ECMO) as a rescue before proceeding to placement of the Berlin Heart Excor paracorporeal assist device. The Levitronix Centrimag pump was used as an intermediate device to allow the patients to be stabilised. Therefore, only Berlin Heart cannulae of different sizes have to be readily available; if successful stabilization can be achieved, the Berlin Heart Excor ventricles and the drive unit can then be ordered to replace the Levitronix pump. Two patients were successfully stabilised with the Levitronix pump and were switched to the definitive Berlin Heart Excor ventricles after 6 days of support. The third child succumbed due to intractable pulmonary hemorrhage in severely damaged lungs. No device related complications, especially no thrombo-embolic events, occurred during Levitronix support. The Levitronix Centrimag pump was easy to handle and gave effective circulatory support, the patients were only switched to the Berlin Heart Excor system after stabilization. In patients with a high risk of failure, it is a relatively cheap but safe and effective support system.

Anatomic Fit Assessment for the Penn State Pediatric Ventricular Assist Device

This investigation determined the ages and weights of children that could be supported with 12 and 25 ml Penn State pediatric ventricular assist devices (PVADs) using 6, 8, and 10 mm outlet cannulas and grafts. Future patients will be matched to devices based on cardiac output (CO) and ascending aortic diameter (AA). These were calculated for children 0-10 years with regression formulas given as clinical standards [<5 kg, CO = 0.2171(kg) + 0.0703], [>5 kg, CO = 3.06 (m2) + 0.37], [AA = -0.0427 + 14.54 (m2)1/2]. The 12 ml PVAD will be useful for patients from approximately birth to 3-8 months, weighing 2-7 kg, and having 0.5-1.4 L/min CO; the 25 ml PVAD will be for children 2-6 months to 5-9 years old, weighing 6-23 kg, and having 1.3-3.0 L/min of CO. The 6 mm outlet graft will fit children from 0 to 12 months, weighing 2-8 kg; the 8 mm graft from 0 to 47 months, weighing 4-14 kg; and the 10 mm graft for children 4 months to 8 years, weighing 8-21 kg.

The Cleveland Clinic PediPump: Anatomic Modeling and Virtual Fitting Studies in a Lamb Model

Implantation of ventricular assist devices (VADs) is challenging in small patients with limited space in the chest. We created three-dimensional models of lambs to facilitate fitting of the PediPump, a pediatric VAD currently under development. Serial computed tomography (CT) scans were acquired at multiple time points (n = 8) for three lambs. Digital models were created using these CT datasets and three-dimensional image processing software (Mimics, Materialise). Pixels representing the heart and chest wall were rendered as three-dimensional models. Using three-dimensional model manipulation software (Magics RP, Materialise), on-screen models of extravascular and intravascular VADs were placed in right, left and biventricular support configurations to determine optimal placement. A cannulation strategy was established and in some cases three-dimensional models of the inflow and outflow grafts were created. After the final CT study, an open-chest fitting study was performed using rapid prototype models of the pediatric VAD and cannulas. The pump location and orientation predictions from the virtual fitting studies matched those determined at the time of the open-chest fitting studies. Using three-dimensional modeling, we have established a fitting protocol that facilitates animal implantations; the same modeling techniques may be useful for device fitting in humans.

Numerical Design and Experimental Hydraulic Testing of an Axial Flow Ventricular Assist Device for Infants and Children

Mechanical circulatory support options for infants and children are very limited in the United States. Existing circulatory support systems have proven successful for short-term pediatric assist, but are not completely successful as a bridge-to-transplant or bridge-to-recovery. To address this substantial need for alternative pediatric mechanical assist, we are developing a novel, magnetically levitated, axial flow pediatric ventricular assist device (PVAD) intended for longer-term ventricular support. Three major numerical design and optimization phases have been completed. A prototype was built based on the latest numerical design (PVAD3) and hydraulically tested in a flow loop. The plastic PVAD prototype delivered 0.5-4 lpm, generating pressure rises of 50-115 mm Hg for operating speeds of 6,000-9,000 rpm. The experimental testing data and the numerical predictions correlated well. The error between these sets of data was found to be generally 7.8% with a maximum deviation of 24% at higher flow rates. The axial fluid forces for the numerical simulations ranged from 0.5 to 1 N and deviated from the experimental results by generally 8.5% with a maximum deviation of 12% at higher flow rates. These hydraulic results demonstrate the excellent performance of the PVAD3 and illustrate the achievement of the design objectives.

The Effect of Left Ventricular Function and Drive Pressures on the Filling and Ejection of a Pulsatile Pediatric Ventricular Assist Device in an Acute Animal Model

Penn State is currently developing a 12-mL, pulsatile, pneumatically driven pediatric ventricular assist device intended to be used in infants. After extensive in vitro testing of the pump in a passive-filling, mock circulatory loop, an acute animal study was performed to obtain data with a contracting ventricle. The objectives were to determine the range of pneumatic pressures and time required to completely fill and empty the pediatric ventricular assist device under various physiologic conditions, simulate reductions in ventricular contractility and blood volume, and provide data for validation of the mock circulatory loop. A 15-kg goat was used. The cannulation was achieved via left thoracotomy from the left ventricle to the descending aorta. The pump rate and systolic duration were controlled manually to maintain complete filling and ejection. The mean ejection time ranged from 280 ms to 382 ms when the systolic pressure ranged from 350 mm Hg to 200 mm Hg. The mean filling time ranged from 352 ms to 490 ms, for the diastolic pressure range of -60 mm Hg to 0 mm Hg. Esmolol produced a decrease in left ventricular pressure, required longer pump filling time, and reduced LVAD flow.

Fluid Force Predictions and Experimental Measurements for a Magnetically Levitated Pediatric Ventricular Assist Device

The latest generation of artificial blood pumps incorporates the use of magnetic bearings to levitate the rotating component of the pump, the impeller. A magnetic suspension prevents the rotating impeller from contacting the internal surfaces of the pump and reduces regions of stagnant and high shear flow that surround fluid or mechanical bearings. Applying this third-generation technology, the Virginia Artificial Heart Institute has developed a ventricular assist device (VAD) to support infants and children. In consideration of the suspension design, the axial and radial fluid forces exerted on the rotor of the pediatric VAD were estimated using computational fluid dynamics (CFD) such that fluid perturbations would be counterbalanced. In addition, a prototype was built for experimental measurements of the axial fluid forces and estimations of the radial fluid forces during operation using a blood analog mixture. The axial fluid forces for a centered impeller position were found to range from 0.5 +/- 0.01 to 1 +/- 0.02 N in magnitude for 0.5 +/- 0.095 to 3.5 +/- 0.164 Lpm over rotational speeds of 6110 +/- 0.39 to 8030 +/- 0.57% rpm. The CFD predictions for the axial forces deviated from the experimental data by approximately 8.5% with a maximum difference of 18% at higher flow rates. Similarly for the off-centered impeller conditions, the maximum radial fluid force along the y-axis was found to be -0.57 +/- 0.17 N. The maximum cross-coupling force in the x direction was found to be larger with a maximum value of 0.74 +/- 0.22 N. This resulted in a 25-35% overestimate of the radial fluid force as compared to the CFD predictions; this overestimation will lead to a far more robust magnetic suspension design. The axial and radial forces estimated from the computational results are well within a range over which a compact magnetic suspension can compensate for flow perturbations. This study also serves as an effective and novel design methodology for blood pump developers employing magnetic suspensions. Following a final design evaluation, a magnetically suspended pediatric VAD will be constructed for extensive hydraulic and animal testing as well as additional validation of this design methodology.

541: Pneumatic paracorporeal ventricular assist device in infants and children: Initial stanford experience

Purpose: Mechanical circulatory support with the Berlin Heart EXCOR Pediatric VAD has been used successfully in Europe to bridge children with end-stage heart failure to transplantation. Sixty-five devices have been placed in North America through August 2006. We describe our single-center experience with this device in 7 children.

Pediatric Ventricular Assist Devices

Ventricular assist device therapy is continuing to evolve in the practice of pediatric cardiac surgery. Although ECMO is still the most often applied mechanical support for infants and young children, a broader range of pulsatile, paracorporeal, as well as implantable ventricular assist devices are now available for pediatric application. A number of these innovative devices have been developed specifically for pediatric use with miniaturized pumps and optimized cannulas suitable for the entire age range of pediatric patients including neonates. Unlike ECMO, these devices can offer medium- to long-term support and have been successfully utilized as a bridge to transplant as well as a bridge to recovery. This review examines the different types of devices currently available, their clinical indications for use, future devices, and the current results of pediatric ventricular assist device therapy in the treatment of heart failure in the pediatric population.

Improvement in Survival After Mechanical Circulatory Support With Pneumatic Pulsatile Ventricular Assist Devices in Pediatric Patients

Pediatric size pneumatically driven extracorporeal ventricular assist devices (VAD) for infants and small children were introduced into clinical routine in 1992. In the initial period, the results in infants were poor. Since then, several improvements have been introduced with regard to the cannulas, connectors, heparin coating of the blood pump inner surface, anticoagulant treatment and coagulation monitoring, and earlier decision-making in favor of pump implantation before irreversible shock has set in. Since 1990 and as of January 1, 2005, 62 Berlin Heart Excor systems have been implanted in patients below 18 years of age at our institution. The patients were divided into two groups according to the period of treatment: period 1, devices implanted between 1990 and 1998 (n = 34), and period 2, devices implanted between 1999 and 2004 (n = 28). We compared our experience during the earlier and later periods. There were no significant differences in the preoperative patient data between the two periods except for time of support (17.9 +/- 27.7 days versus 53.2 +/- 83.9 days, p = 0.001). In period 1, more patients needed a biventricular VAD whereas in period 2, more patients were effectively treated with a left VAD (p = 0.05). In the later period, the chest could be primarily closed in a significantly higher percentage of infants (0% versus 89%, p = 0.012), and more infants could be extubated on the VAD (0% versus 55%, p = 0.16). Discharge from the hospital after either weaning from the system or heart transplantation was achieved for 35% in period 1 and for 68% in period 2 (p = 0.029). Whereas in period 1 there were no survivors in the group of children younger than 1 year old, during period 2, survival in this age group was similar to that of the two groups of older children (p = 0.024). There was a significant improvement in the discharge rate in period 2 in patients with cardiomyopathy (43% versus 76%, p = 0.045) and postcardiotomy heart failure (0% versus 57%, p = 0.01). Earlier implantation of VADs, heparin coating of the blood pumps, and substantial modifications in cannula design, anticoagulation, and the coagulation monitoring regimen have led to a significant increase in the survival and discharge rate, especially among children under 1 year of age. The pediatric size Berlin Heart Excor VAD is a valuable option as a bridge to heart transplantation or recovery for children suffering from cardiogenic shock.