An in-vitro evaluation of the flow haemodynamic performance of Gore-Tex extracardiac conduits for univentricular circulation.

OBJECTIVE(S): The Fontan procedure is a common palliative intervention for sufferers of single ventricle congenital heart defects that results in an anastomosis of the venous return to the pulmonary arteries called the total cavopulmonary connection (TCPC). In patients with palliated single ventricular heart defects, the Fontan circulation passively directs systemic venous return to the pulmonary circulation in the absence of a functional sub-pulmonary ventricle. Therefore, the Fontan circulation is highly dependent on favourable flow and energetics, and minimal energy loss is of great importance. The majority of in vitro studies, to date, employ a rigid TCPC model. Recently, few studies have incorporated flexible TCPC models, without the inclusion of commercially available conduits used in these surgical scenarios. METHOD: The methodology set out in this study successfully utilizes patient-specific phantoms along with the corresponding flowrate waveforms to characterise the flow haemodynamic performance of extracardiac Gore-Tex conduits. This was achieved by comparing a rigid and flexible TCPC models against a flexible model with an integrated Gore-Tex conduit. RESULTS: The flexible model with the integrated Gore-Tex graft exhibited greater levels of energy losses when compared to the rigid walled model. With this, the flow fields showed greater levels of turbulence in the complaint and Gore-Tex models compared to the rigid model under ultrasound analysis. CONCLUSION: This study shows that vessel compliance along with the incorporation of Gore-Tex extracardiac conduits have significant impact on the flow haemodynamics in a patient-specific surgical scenario.

Fluid-structure interaction analysis of a collapsible axial flow blood pump impeller and protective cage for Fontan patients.

Limited donor organs and alternative therapies have led to a growing interest in the use of blood pumps as a treatment strategy for patients with single functional ventricle. The present study examines the use of collapsible and flexible impeller, cage, and diffuser designs of an axial blood pump for Fontan patients. Using one-way fluid-structure interaction (FSI) studies, the impact of blade deformation on blood damage and pump performance was investigated for flexible impellers. We evaluated biocompatible materials, including Nitinol, Bionate 80A polyurethane, and silicone for flow rates between 2.0-4.0 L/min and rotational speeds of 3000-9000 rpm. The level of deformation experienced by a cage and diffuser made of surgical stainless steel (control), Nitinol, and Bionate 80A polyurethane was also predicted using one-way FSI. The fluid pressure on the surface of the impeller, cage, and diffuser was determined using computational fluid dynamics (CFD), and then, the surface pressure was exported and used to investigate the impeller, cage, and diffuser deformation using finite element analysis. Finally, deformed impeller geometries were imported into the CFD software to determine the implication of deformation on pressure generation, blood damage index, and fluid streamlines. It was found that rotational speed, and not flow rate, is the largest determinant of impeller deformation, occurring at the blade trailing edges. The models predicted the maximum impeller deformation for Nitinol to be 40 nm, Bionate 80A polyurethane to be 106 µm, and silicone to be 2.8 mm, all occurring at 9000 rpm. The effects of silicone deformation on performance were significant, particularly at speeds above 5000 rpm where a decrease in pressure generation of more than 10% was observed. Despite this loss, the pressure generation at 5000 rpm exceeded the level required to alleviate Fontan complications. A blood damage estimation was performed and levels remained low. The effect of significant impeller deformation on blood damage was inconsistent and requires additional investigation. Cage and diffuser geometries made of steel and Nitinol deformed minimally but Bionate 80A experienced unacceptable levels of deformation, particularly in the free-flow case without a spinning impeller. These results support the continued evaluation of a flexible, pitch-adjusting, axial-flow, mechanical assist device as a clinical therapeutic option for patients with dysfunctional Fontan physiology.

Transcatheter creation of bidirectional cavopulmonary connections by needle punctures in two patients.

We report on two patients who received a transcatheter cavopulmonary connection by a needle puncture under deep conscious sedation. In both patients, the vessel-to-vessel connection was achieved by a venous access into the superior caval vein and direct needle puncture of the pulmonary artery. The two cavopulmonary anastomoses were held open by a covered stent and a bare-metal stent, respectively.

Role of surgeon intuition and computer-aided design in Fontan optimization: A computational fluid dynamics simulation study.

OBJECTIVE: Customized Fontan designs, generated by computer-aided design (CAD) and optimized by computational fluid dynamics simulations, can lead to novel, patient-specific Fontan conduits unconstrained by off-the-shelf grafts. The relative contributions of both surgical expertise and CAD to Fontan optimization have not been addressed. In this study, we assessed hemodynamic performance of Fontans designed by both surgeon's unconstrained modeling (SUM) and by CAD. METHODS: Ten cardiac magnetic resonance imaging datasets were used to create 3-dimensional (3D) models of Fontans. Baseline computational fluid dynamics simulations assessed Fontan indexed power loss (iPL), hepatic flow distribution, and percentage of conduit surface area with abnormally low wall shear stress for venous flow (<1 dyne/cm2). Fontans not meeting thresholds were redesigned using 2 methods: SUM (ie, original venous anatomy without the Fontan was 3D printed and sent to surgeon for Fontan redesign with clay modeling) and CAD (ie, the same 3D geometry was sent to engineers for iterative Fontan redesign guided by computational fluid dynamics). Both groups were blinded to each other's results. RESULTS: Eight Fontans were redesigned by SUM and CAD methods. Both SUM and CAD redesigns met iPL thresholds. SUM had lower iPL, whereas CAD demonstrated balanced hepatic flow distribution and lower wall shear stress percentage. Wall shear stress percentage shared an inverse relationship with iPL, preventing oversized Fontan designs. CONCLUSIONS: Customized Fontan conduits with low iPL can be created by either a surgeon or CAD. CAD can also improve hepatic flow distribution and prevent oversized Fontan designs. Future studies should investigate workflows that combine SUM and CAD to optimize Fontan conduits.

Y-graft modification to the Fontan procedure: Increasingly balanced flow over time.

OBJECTIVE: The use of Y-grafts for Fontan completion is hypothesized to offer more balanced hepatic flow distribution (HFD) and decreased energy losses. The purpose of this study was to evaluate the hemodynamic performance of Y-grafts over time using serial cardiac magnetic resonance data and to compare their performance with extracardiac Fontan connections. METHODS: Ten Fontan patients with commercially available Y-graft connections and serial postoperative cardiac magnetic resonance data were included in this study. Patient-specific computational fluid dynamics simulations were used to estimate HFD and energy losses. Y-graft performance was compared with 3 extracardiac conduit Fontan groups (n = 10 for each) whose follow-up times straddle the Y-graft time points. RESULTS: Y-graft HFD became significantly more balanced over time (deviation from 50% decreased from 18% ± 14% to 8% ± 8%; P = .015). Total cavopulmonary connection resistance did not significantly change. Y-grafts at 3-year follow-up showed more balanced HFD than the extracardiac conduit groups at both the earlier and later follow-up times. Total cavopulmonary connection resistance was not significantly different between any Y-graft or extracardiac conduit group. CONCLUSIONS: Y-grafts showed significantly more balanced HFD over a 3-year follow-up without an increase in total cavopulmonary connection resistance, and therefore may be a valuable option for Fontan completion. Additional follow-up data at longer follow-up times are still needed to thoroughly characterize the potential advantages of Y-graft use.

Energetics of blood flow in Fontan circulation under VAD support.

The need to simulate the normal operating conditions of the human body is the key factor in every study and engineering process of bioelectronic devices designed for implantation. The Fontan procedure is an example of such a process aimed to support the human body function. It is a standard treatment method for patients with a functionally univentricular heart. However, it has significant drawbacks such as overload of the only functional heart ventricle that often leads to the necessity of the heart transplantation. In this study, we analyze the total cavopulmonary connection (TCPC) influence on the blood with and without connected auxiliary blood circulation pump. We investigate four different types of TCPC configurations, analyze blood pressure and different flow rate, study the turbulent kinetic energy distribution, and evaluate hydraulic and power losses for various cases. Finally, we calculate volumetric scalar shear stresses distribution and demonstrate the high potential of TCPC configuration with connected rotary pump as a tool for the load redistribution in the functional heart ventricle. This work is particularly relevant for improving existing TCPCs' quality that can extend the life of Fontan patients. Moreover, it also applies to the reduction of morbidity and mortality of the patients waiting for the heart transplantation.

A long-term mechanical cavopulmonary support device for patients with Fontan circulation.

In patients with a single ventricle, failure of the cardiovascular system may be prevented by substituting the missing sub-pulmonary ventricle with a pump. The aim of this study was to design and evaluate a device for long-term cavopulmonary support. A radial pump with two inlets and two outlets, a single impeller, mechanical bearings, and dual motor configuration was developed. Motor and fluid dynamic components were designed and simulated using computational methods including thermal effects. Hydraulic properties were determined in-vitro with 3D-printed prototypes. The pump design was virtually implanted in an MRI-derived total cavopulmonary connection (TCPC). Computational fluid dynamics (CFD) showed flow fields without regions of flow stagnation (velocity < 0.1 m/s) and only minor recirculations within the pump between 2-10 L/min against pressure heads of 0-50 mmHg at 2500-5000 rpm. The computed maximum temperature increase of blood due to motor heat was 1.3 K. Virtual implantation studies showed that the pump would introduce an additional volume of approximately 4 mL. Experimentally determined hydraulic performance results agreed well with CFD (deviation of <1.3 mmHg) and indicated pressure-sensitive characteristics (∼-2.6 mmHg/(L/min)) while balancing the two inlet pressures (∆P < 2.5 mmHg) under imbalanced inflow conditions. Through in-silico and in-vitro investigations, we demonstrated a promising pump design, which fulfills the basic requirements for long-term cavopulmonary support.

Dual-Propeller Cavopulmonary Pump for Assisting Patients with Hypoplastic Right Ventricle.

Various congenital heart defects (CHDs) are characterized by the existence of a single functional ventricle, which perfuses both the systemic and pulmonary circulation. A three-stage palliation procedure, including the final Fontan completion, is often adopted by surgeons to treat patients with such CHDs. The completion Fontan involves the creation of a total cavopulmonary connection (TCPC), commonly accomplished with an extracardiac conduit. This TCPC results in nonphysiologic flow conditions that can lead to systemic venous hypertension, reduced cardiac output, and ultimately the need for heart transplantation. A modest pressure rise of 5-6 mm Hg could correct the abnormal flow dynamics in these patients. To achieve this, we propose a novel conceptual design of a dual-propeller pump inside a flared TCPC. The TCPC dual-propeller conjunction was examined for hydraulic performance, blood flow pattern, and potential for hemolysis inside the TCPC using computational fluid dynamics (CFD). The effect of axial distance between the two propellers on the blood flow interference and energy loss was studied to determine the optimal separation distance. Both the inferior vena cava (IVC) and superior vena cava (SVC) propellers provided a pressure rise of 1-20 mm Hg at flow rates ranging from 0.4 to 7 lpm while rotating at speeds of 6,000-12,000 rpm. Larger separation distance provided favorable performance in terms of flow interference, energy loss, and blood damage potential. The ability of a dual-propeller micropump to provide the required pressure rise would help to augment the cavopulmonary flow and mimic flows seen in normal biventricular circulation.

Chronic In Vivo Test of a Right Heart Replacement Blood Pump for Failed Fontan Circulation.

An implantable rotary blood pump was developed to provide long-term mechanical right heart support for patients who have failing Fontan circulation. The objective of this study was to evaluate the pump in vivo in a 30 day sheep study. Pump speed was set at 3,900 rpm for the duration of the study, and pump power was between 4.3 and 4.6 W. The pump inlet pressures for the superior vena cava (SVC) and inferior vena cava (IVC) were 14 ± 15 and 11 ± 15 mm Hg, respectively, over the duration of the study. Hematocrit remained stable at 30% ± 4%. Partial thromboplastin time (PTT) steadily increased from 30 s preoperatively to a high of 59 s on postoperative day 20, while prothrombin time (PT) remained at 20 ± 2 s for the duration of the study. The implantation and postoperative recovery were successful, and the animal demonstrated normal physiologic pulmonary and venous pressures and cardiac output. On pump inspection, the IVC and SVC inlets were completely clear of any deposits, but there were small thrombi (approximately 0.5 mm diameter) between each of the three rotor blades and along 20% of the parting line of the two volute halves. A complete right heart bypass was performed, postoperative recovery was successful, and the pump demonstrated adequate circulatory support and normal physiologic pulmonary and venous pressures. This study was the first successful test of a right heart replacement device in a chronic animal study.

In Vitro Examination of the VentriFlo True Pulse Pump for Failing Fontan Support.

The current methodology of Fontan palliation results in a one "pump" circulatory system with passive flow to the lungs. Inherent hemodynamic differences exist between a biventricular circulatory system and this modified physiology, leading to a host of long-term complications. Mechanical circulatory support (MCS) is a potential option to combat these pathophysiological conditions. In this study, we examine the VentriFlo True Pulse Pump as a MCS option to support a failing Fontan patient. An in vitro circulatory loop was used to model a failing Fontan patient, reproducing pathophysiological pressures and flow rates. The VentriFlo True Pulse Pump was positioned as a right sided support, testing multiple cannulation and baffle restriction strategies, as well as various pumping parameters including flow rate, frequency, stroke volume and the ejection to filling time ratio. A 10 mm Hg decrease in IVC pressure and 0.75 L/min increase in cardiac output were achieved using a complete baffle restriction strategy. Additional cannulation and banding strategies were not as successful. Pump flow rate and frequency significantly impacted hemodynamics, while the ejection to filling time ratio did not. Though not ideal, complete baffle restriction was necessary to achieve successful support. The ability to tune individual pumping parameters for a given MCS device will have a substantial impact on the pressures and flow augmentation seen in a Fontan circulation. Both future pump design and off-label VADs for Fontan use should consider the pump configuration and parameter combinations presented here, which offered successful support.

The Right Tool for the Right Job: Bridging a Failing Fontan to Transplant.

Mechanical circulatory support and heart transplantation are both becoming increasingly common among Fontan patients as this growing cohort of patients is reaching young adulthood. Although device placement may present challenges, the new focus is on selecting the correct cannulation sites and devices at the correct time to successfully bridge these challenging patients to heart transplant. Herein, we report the use of a number of mechanical circulatory support strategies tailored to the clinical setting that culminated in 130 days of support before cardiac transplantation of a young adult with a failing Fontan circulation.

Tissue-engineered Vascular Grafts in Children With Congenital Heart Disease: Intermediate Term Follow-up.

Tissue engineering holds great promise for the advancement of cardiovascular surgery as well as other medical fields. Tissue-engineered vascular grafts have the ability to grow and remodel and could therefore make great advances for pediatric cardiovascular surgery. In 2001, we began a human clinical trial evaluating these grafts in patients with a univentricular physiology. Herein, we report the long-term results of patients who underwent implantation of tissue-engineered vascular grafts as extracardiac total cavopulmonary conduits. Tissue-engineered vascular grafts seeded with autologous bone marrow mononuclear cells were implanted in 25 patients with univentricular physiology. The graft is composed of a woven fabric of poly-l-lactide acid or polyglycolic acid and a 50:50 poly (l-lactic-co-ε-caprolactone) copolymer. Patients were followed up with postoperatively in a multidisciplinary clinic. Median patient age at operation was 5.5 years and the mean follow-up period was 11.1 years. There was no graft-related mortality during the follow-up period. There was also no evidence of aneurysmal formation, graft rupture, graft infection, or calcification. Seven (28%) patients had asymptomatic graft stenosis and underwent successful balloon angioplasty. Stenosis is the primary complication of the tissue-engineered vascular graft. Avoidance of anticoagulation therapy would improve patients' quality of life. Tissue-engineered vascular grafts have feasibility in pediatric cardiovascular surgery.

Virtual surgical planning, flow simulation, and 3-dimensional electrospinning of patient-specific grafts to optimize Fontan hemodynamics.

BACKGROUND: Despite advances in the Fontan procedure, there is an unmet clinical need for patient-specific graft designs that are optimized for variations in patient anatomy. The objective of this study is to design and produce patient-specific Fontan geometries, with the goal of improving hepatic flow distribution (HFD) and reducing power loss (Ploss), and manufacturing these designs by electrospinning. METHODS: Cardiac magnetic resonance imaging data from patients who previously underwent a Fontan procedure (n = 2) was used to create 3-dimensional models of their native Fontan geometry using standard image segmentation and geometry reconstruction software. For each patient, alternative designs were explored in silico, including tube-shaped and bifurcated conduits, and their performance in terms of Ploss and HFD probed by computational fluid dynamic (CFD) simulations. The best-performing options were then fabricated using electrospinning. RESULTS: CFD simulations showed that the bifurcated conduit improved HFD between the left and right pulmonary arteries, whereas both types of conduits reduced Ploss. In vitro testing with a flow-loop chamber supported the CFD results. The proposed designs were then successfully electrospun into tissue-engineered vascular grafts. CONCLUSIONS: Our unique virtual cardiac surgery approach has the potential to improve the quality of surgery by manufacturing patient-specific designs before surgery, that are also optimized with balanced HFD and minimal Ploss, based on refinement of commercially available options for image segmentation, computer-aided design, and flow simulations.

Cardiovascular anatomy in children with bidirectional Glenn anastomosis, regarding the transcatheter Fontan completion.

BACKGROUND: Transcatheter stent-secured completion of total cavopulmonary connection (TCPC) after surgical preparations during the Glenn anastomosis procedure has been reported, but complications from this approach have precluded its clinical acceptance. AIMS: To analyse cardiovascular morphology and dimensions in children with bidirectional Glenn anastomosis, regarding the optimal device design for transcatheter Fontan completion without special surgical "preconditionings". METHODS: We retrospectively analysed 60 thoracic computed tomography and magnetic resonance angiograms performed in patients with a median age of 4.1 years (range: 1.8-17.1 years). Additionally, we simulated TCPC completion using different intra-atrial stent-grafts in a three-dimensional model of the representative anatomy, and performed calculations to determine the optimal stent-graft dimensions, using measured distances. RESULTS: Two types of cardiovascular arrangement were identified: left atrium interposing between the right pulmonary artery (RPA) and inferior vena cava, with the right upper pulmonary vein (RUPV) orifice close to the intercaval axis (65%); and intercaval axis traversing only the right(-sided) atrial cavity, with the RUPV located posterior to the atrial wall (35%). In the total population, the shortest median RPA-to-atrial wall distance was 1.9mm (range: 0.6-13.8mm), while the mean intra-atrial distance along the intercaval axis was 50.1±11.2mm. Regardless of the arrangement, 83% of all patients required a deviation of at least 5.9±2.4mm (range: 1.2-12.7mm) of the stent-graft centre at the RUPV level anteriorly to the intercaval axis to avoid covering or compressing this vein. Fixing the anterior deviation of the curved stent-graft centre at 10mm significantly decreased the range of bend angle per every given RUPV-RPA distance. CONCLUSIONS: For both types of cardiovascular arrangement, after conventional bidirectional Glenn anastomosis, the intra-atrial curved stent-graft seemed most suitable for achieving uncomplicated TCPC completion percutaneously without previous surgical "preconditionings" in the majority of children. Experimental study is necessary to validate this conclusion.

Outcomes after extracardiac Fontan procedure with a 16-mm polytetrafluoroethylene conduit.

OBJECTIVES: We evaluated the outcomes of patients who underwent extracardiac Fontan circulation procedures (ECFP) and received 16-mm polytetrafluoroethylene conduits. METHODS: From June 1997 to May 2015, among the 408 patients who underwent ECFP, 66 patients (Group S) also received 16-mm polytetrafluoroethylene conduits. To compare this patient cohort with similarly sized patients who received larger conduits, a matched cohort (66 patients, Group L) was selected according to age and body weight. RESULTS: The mean age, body weight and Nakata index at ECFP in Groups S and L were 2.9 ± 1.2 and 3.1 ± 1.2 years (P = 0.243), 13.0 ± 2.4 and 13.0 ± 2.3 kg (P = 0.101), 175.3 ± 59.0 and 236.1 ± 75.1 mm2/m2 (P = 0.005), respectively. The mean follow-up periods for Groups S and L were 7.8 ± 6.0 and 9.1 ± 4.9 years (P = 0.150), respectively. The conduit size of Group L was 19.2 ± 1.4 mm (P < 0.001). There was no significant difference in mortality between the groups (P = 0.109). The freedom from reoperation was 94.0 ± 3.4% in Group S and 79.3 ± 5.7% in Group L after 10 years (P = 0.070). Late-occurring morbidities included protein-losing enteropathy (2 in Group S, 4 in Group L; P = 0.491) and thromboembolism (0 in Group S, 4 in Group L; P = 0.206). There was a significant difference in conduit-related events between the groups (1 in Group S, 5 in Group L; P = 0.031). In a paired cohort from the 2 groups including patients who were followed-up for more than 10 years (15 patients from each group), the body mass index was 51.0 ± 33.2% in Group S and 30.3 ± 34.2% in Group L. The decreases in the conduit cross-sectional areas for the paired patients in Group S (n = 20) and Group L (n = 20) were 14.9 ± 19.7% and 24.5 ± 15.5% (P = 0.076), respectively. Coarse liver parenchyma was detected in 9 of 23 (39.1%) patients from Group S and in 7 of 18 (38.8%) patients from Group L upon ultrasonography. CONCLUSIONS: The 16-mm polytetrafluoroethylene conduit for ECFP showed acceptable outcomes and good haemodynamic status in small-sized patients. According to our results, small patients do not require large conduits to accommodate their growth potential.

Local Hemodynamic Differences Between Commercially Available Y-Grafts and Traditional Fontan Baffles Under Simulated Exercise Conditions: Implications for Exercise Tolerance.

Fontan completion, resulting in a total cavopulmonary connection (TCPC), is accomplished using a lateral tunnel (LT), extracardiac conduit (ECC), or recently a bifurcated Y-graft. The local energetic differences between these graft types have not been substantially analyzed under exercise conditions. The present study evaluates the energetic performance of Y-grafts under simulated exercise conditions, compares their performance to the previous LT/ECC Fontan options, and discusses implications for exercise tolerance and hemodynamic predictability. Twenty Y-graft and 20 LT/ECC patients were analyzed. TCPC anatomies and flow waveforms were reconstructed using patient-specific cardiac magnetic resonance (CMR) images and phase-contrast CMR. Computational fluid dynamics simulations were performed to quantify indexed power loss (iPL) under both resting and simulated exercise conditions. Comparisons between graft types were investigated. iPL was significantly higher (p < 0.01) for Y-grafts at all activity levels. No significant interaction effects were observed between graft type and activity level. iPL at rest was strongly correlated (r 2 = 0.97, p < 0.001) with iPL at moderate exercise for Y-grafts, but less so for the LT/ECC cohort (r 2 = 0.66, p < 0.001). Similar results were seen for intense exercise, with a strong correlation for Y-grafts (r 2 = 0.94, p < 0.001) and a moderate correlation for LT/ECC (r 2 = 0.52, p < 0.001). Commercially available Y-grafts were found to have significantly higher iPL at all activity levels, suggesting worse exercise tolerance than the LT/ECC alternatives. Y-grafts offered impressive hemodynamic predictability which was not seen in the LT/ECC cohort. Our results encourage the further evaluation of an area-preserving Y-graft design to offer both improved energetic performance and hemodynamic predictability. Commercial Y-grafts show worse energetics, but more predictable responses than traditional Fontan connections under simulated exercise conditions. During simulated exercise conditions, commercially available Y-grafts show predictable but inferior energetic performance compared to lateral tunnel and extracardiac conduit Fontan connections, suggesting poorer exercise capacity. If Y-graft use is continued, these results encourage further evaluation of a cross sectional area-preserving Y-graft design as a additional alternative for Fontan completion.

Vascular anatomy in children with univentricular hearts regarding transcatheter bidirectional Glenn anastomosis.

BACKGROUND: Transcatheter stent-secured Glenn anastomosis, aiming to reduce the invasiveness of palliation in patients with univentricular heart defects, has been reported in large experimental animals. The advent of biodegradable stents and tissue-engineered vascular grafts will make this procedure a reality in human patients. However, the relationship between the superior vena cava (SVC) and the right pulmonary artery (RPA) is different in humans. AIM: To characterise vascular anatomy in children with univentricular hearts, regarding technical aspects and device design for this procedure. METHODS: Retrospective analysis of 35 thoracic computed tomography angiograms at a mean age of 18.1±22.4 months. RESULTS: Two types of arrangement between the SVC and the RPA were identified: anatomy convenient for immediate wire passage and stent deployment between the two vessels (60%); and pattern of early RPA branching, requiring the perforation wire to traverse the intervascular space to avoid entrance into the upper RPA branch (40%). In patients with the convenient vascular arrangement, the vessels were nearly perpendicular, having immediate contact, with the posterior SVC aspect partially "wrapping" the adjacent RPA in most patients. In patients with early RPA branching, the mean shortest SVC-to-central RPA distance was 4.3±2.7mm. For the total population, the mean length of proximal SVC that allowed stent deployment without covering the brachiocephalic vein was 15.6±5.1mm. CONCLUSIONS: A trumpet-shaped covered stent in a craniocaudal orientation reaching from the SVC into the prebranching RPA seems most suitable for achieving bidirectional Glenn anastomosis percutaneously in humans. However, the short length of the proximal SVC and the presence of early RPA branching pose challenges for optimal design of the dedicated device.

In Vitro Examination of the HeartWare CircuLite Ventricular Assist Device in the Fontan Connection.

The failing Fontan physiology may benefit from ventricular assist device (VAD) mechanical circulatory support, although a subpulmonary VAD placed at the Fontan connection has never successfully supported the Fontan circulation long term. The HeartWare CircuLite continuous flow VAD was examined for Fontan circulatory support in an in vitro mock circulation. The VAD was tested in three different scenarios: VAD in parallel, baffle restricted VAD in parallel, and VAD in series. Successful support was defined as simultaneous decrease in inferior vena cava (IVC) pressure of 5 mm Hg or more and an increase in cardiac output (CO) to 4.25 L/min or greater. The VAD in parallel scenario resulted in a CO decrease to 3.46 L/min and 2.22 mm Hg decrease in IVC pressure. The baffle restricted VAD in parallel scenario resulted in a CO increase to 3.9 L/min increase in CO and 20.5 mm Hg decrease in IVC pressure (at 90% restriction). The VAD in series scenario resulted in a CO of 1.75 L/min and 5.9 mm Hg decrease in IVC pressure. We successfully modeled chronic failing Fontan physiology using patient-specific hemodynamic and anatomic data. Although unsuccessful in supporting Fontan patients as defined here, the HeartWare CircuLite VAD demonstrates the possibility to reduce Fontan pressure and increase CO with a VAD in the Fontan connection. This study provides insight into pump performance and design issues when attempting to support Fontan circulation. Refinements in VAD design with specific parameters to help support this patient population is the subject of our future work.

Concurrent use of continuous and pulsatile flow Ventricular Assist Device on a fontan patient: A simulation study.

The aim of this work is to develop and test a lumped parameter model of the cardiovascular system to simulate the concurrent use of pulsatile (PVAD) and continuous flow (CVAD) ventricular assist device (VAD) on Fontan patients. Echocardiographic and hemodynamic data of five Fontan patients were retrospectively collected and used to simulate the patients' baseline hemodynamics. Then, for each patient, the following assistance modality was simulated for the cavopulmonary and the single ventricle (SV): (a) CVAD for cavopulmonary assistance (RCF) and PVAD assisting the SV (LCF) (RPF + LCF), (b) CVAD assisting SV and PVAD for cavopulmonary assistance (LPF + RCF). The numerical model can well reproduce patients' baseline. The cardiac output increases more importantly in the LCF + RPF configuration (35 vs. 8%). Ventricular volume decreases more evidently in the configuration LCF + RPF (28 vs. 6%), atrial pressure decreases in the LCF + RPF modality (10%), while it slightly increases in the RCF + LPF modality. The pulmonary arterial pressure slightly decreases (increases) in the configuration RCF + LPF (LCF + RPF). Ventricular external work increases in both configurations because of the total increment of the cardiac output. However, artero-ventricular coupling improves in both configurations: RCF + LPF-14%, LCF + RPF-41%. The pulsatility index decreases (increases) by 8% (13.8%) in the configuration LCF + RPF (RCF + LPF). A model could permit us to simulate extreme physiological conditions of the implantation of both CF and PF VAD on the Fontan patient and could permit to choose the proper VAD on the base of patients' condition. The configuration LCF + RPF seems to maximize the hemodynamic benefits.