This thesis project examined the interactive fluid dynamics between a blood pump and the univentricular Fontan circulation. 2-D particle image velocimetry (PIV) measurements were conducted on an idealized total cavopulmonary connection (TCPC) with an axial pump prototype in the inferior vena cava (IVC). Fluid velocity profiles were examined under various physiologic conditions for Fontan patients. The velocity profiles for all cases demonstrated the shunting of flow from the IVC toward the right pulmonary artery. A rotational component in the pump outflow was observed forcing flow to the periphery as compared to the flow profile without a pump present in the IVC. The inclusion of the pump provides a pressure rise of 3 to 9 mmHg. These results demonstrate the ability of the intravascular blood pump to support a Fontan circulation and support the continued optimization and development of the pump.

Various congenital heart defects (CHDs) are characterized by the existence of a single functional ventricle, which perfuses both the systemic and pulmonary circulation in parallel. A three-stage palliation procedure, including the final Fontan Completion, is often adopted by surgeons to treat patients with such CHDs. However, the most common outcome of this surgery, an extra-cardiac total cavopulmonary connection (TCPC), formed by suturing the inferior vena cava (IVC) and superior vena cava (SVC) to the pulmonary arteries (PAs), results in non-physiological flow conditions, systemic venous hypertension, reduced cardiac output, and pressure losses, which ultimately calls for a heart transplantation. A modest pressure rise of 5-6 mm Hg would correct the abnormal flow dynamics in these patients. To achieve this, a novel conceptual design of a percutaneous dual propeller pump inserted and mounted inside the TCPC is developed and studied. The designed blood pump is percutaneously inserted via the Femoral vein and deployed at the center of Total Cavopulmonary Connection (TCPC). The two propellers, each placed in the Superior Vena Cava (SVC) and the Inferior Vena Cava (IVC) are connected by a single shaft and motor, and thus rotate at same speed. The device is supported with the help of a self-expanding stent which would be anchored to the walls of the IVC and the SVC. An inverse design methodology implementing Blade Element Momentum theory and Goldstein's radial momentum loss theory was employed to generate the blade profiles for the studied propeller pumps. The propeller blade profiles generated from the inverse design optimization code were examined for hydraulic performance, blood flow pattern and potential for hemolysis inside the TCPC using 3-D computational fluid dynamics (CFD) analysis. The Lagrangian particle tracking approach in conjunction with a non-linear mathematical power law model was used for predicting the blood damage potential of the analysed blood pump designs by calculating the scalar shear stress history sustained by the red blood cells (RBC). The study demonstrated that the IVC and SVC propeller pumps could provide a pressure rise of 1-20 mm Hg at flow rates ranging from 0.5 to 5 lpm while rotating at speeds of 6,000-12,000 rpm. Moreover, the average Blood Damage Index (BDI), quantifying the level of blood trauma sustained by the RBCs for the analyzed propeller pump designs, was found to be around 3e-04% to 4e-04% which is within the acceptable limits for an axial flow heart assist device. Thus, such a dual propeller blood pump configuration could potentially provide assistance to Fontan patients by unloading the single functional ventricle thereby acting as a bridge to transplantation and recovery until a donor heart is available. / Master of Science / A single functional ventricle is a type of congenital heart defect, where either left or right ventricle is underdeveloped, resulting in a single ventricular chamber to pump blood to both the body as well as lungs. A three-stage surgical procedure called the Fontan procedure, is often adopted by the surgeons to treat this defect by disconnecting the inferior(IVC) and superior vena cava(SVC), the two main veins carrying de-oxygenated blood from the body to the heart, and connecting them to the pulmonary arteries(PAs), the vessels carrying de-oxygenated blood from heart to the lungs. This helps to bypass the underdeveloped ventricle and allows blood to flow directly from the body to the lungs. However, the absence of a pumping chamber in the newly developed blood portal system causes an increase in pressure inside the vena cava and pressure losses inside the pulmonary arteries, which results in vena cava hypertension, reduced cardiac output. A modest pressure rise of 5-6 mm Hg across the vena cava or pulmonary artery should correct the abnormal flow dynamics and should bring the cardiac output of such patients back to normal. To achieve this, a conceptual design of a dual propeller mechanical circulatory support device has been designed and developed in this thesis.

Single ventricle heart defects, where systemic and pulmonary venous returns mix in the single functional ventricle, represent the most complex form of congenital heart defect, affecting 2 babies per 1000 live births. Surgical repairs, termed "Fontan Repairs," reroute the systemic venous return directly to the pulmonary arteries, thus preventing venous return mixing and restoring normal oxygenation saturation levels. Unfortunately, these repairs are only palliative and Fontan patients are subjected to a multitude of chronic complications. It has long been suspected that hemodynamics play a role in determining patient outcome. However, the number of anatomical and functional variables that come into play and the inability to conduct large scale clinical evaluations, due to too small a patient population, has hindered decisive progress and there is still not a good understanding of the optimal care strategies on a patient-by-patient basis. Over the past decades, image-guided computational fluid dynamics (CFD) has arisen as an attractive option to accurately model such complex biomedical phenomena, providing a high degree of freedom regarding the geometry and flow conditions to be simulated, and carrying the potential to be automated for large sample size studies. Despite these theoretical advantages, few CFD studies have been able to account for the complexity of patient-specific anatomies and in vivo pulsatile flows. In this thesis, we develop an unstructured Cartesian immersed-boundary flow solver allowing for high resolution, time-accurate simulations in arbitrarily complex geometries, at low computational costs. Combining the proposed and validated CFD solver with an interactive virtual-surgery environment, we present an image-based surgical planning framework that: a) allows for in depth analysis of the pre-operative in vivo hemodynamics; b) enables surgeons to determine the optimum surgical scenario prior to the operation. This framework is first applied to retrospectively investigate the in vivo pulsatile hemodynamics of different Fontan repair techniques, and quantitatively compare their efficiency. We then report the prospective surgical planning investigations conducted for six failing Fontan patients with an interrupted inferior vena cava and azygous continuation. In addition to a direct benefit to the patients under consideration, the knowledge derived from these surgical planning studies will also have a larger impact for the clinical management of Fontan patients as they shed light onto the impact of caval offset, vessel flaring and other design parameters upon the Fontan hemodynamics depending on the underlying patient anatomy. These results provide useful surgical guidelines for each anatomical template, which could benefit the global surgical community, including centers that do not have access to patient-specific surgical planning interfaces.

L’intervention de Fontan est une chirurgie palliative pour les cardiopathies congénitales univentriculaire. A long terme, la défaillance cardiaque, l’hypertension artérielle pulmonaire(HTAP) et l’entéropathie exsudative peuvent mener à l’échec tardif du Fontan.Une mise au point clinique a été realisée en se focalisant secondairement sur les patients adultes.L’intérêt de la cavo bipulmonaire (CBP), étape intermédiaire au Fontan, dans certains cas de retours veineux pulmonaires anormaux totaux a été décrite. Afin d’affiner de futures études cliniques, nous avons discuté de l’intérêt du Brain NatriureticPeptide en post opératoire de Fontan. Nous avons démontré la fiabilité d’une nouvelle technologiede l’oxyme´trie de pouls chez des enfants cyanosés et la non fiabilité d’un nouveau dispositifd’impédancemétrie pour le monitorage non invasif du de´bit cardiaque en comparaison avecun cathéter artériel pulmonaire.Un modèle animal viable et chronique de la CBP a été développé. Il a montré que le flux pulsatileantérograde empêche la formation de fistules artério-veineuses pulmonaires (FAVP), améliorel’hématose et atténue le développement de l’HTAP soutenant cliniquement le maintien de ce fluxlors de la création d’une CBP. Par ailleurs, la perte de pulsatilité, en diminuant le contrainte de cisaillement, entraîne unediminution de l’eNOS synthase et une réponse altérée vaso-relaxante dépendante de l'endothélium artérielle pulmonaire. La micropulsatilité limite ces effets délétères. Ces résultats impliquent desthérapies potentielles contre l’HTAP du Fontan, en maintenant un débit pulmonaire accessoire et la modulation pharmaceutique vaso-relaxante non endothélium-dépendante / The Fontan surgery is a palliative surgery for univentricular congenital heart disease. On the longterm, heart failure, pulmonary arterial hypertension (PAH) and exudative enteropathy may lead tothe Fontan failure.A clinical adjustment has been realized by focusing secondarily on adult patients. The advantage, insome cases of total anomalous pulmonary venous return, of the bidirectional cavopulmonary (BCP),which is an intermediate stage of Fontan, has been described.In order to prepare future clinical studies, we have discussed about Brain Natriuretic Peptide inpostoperative Fontan surgery. We have demonstrated the reliability of a new technology of pulseoxymetry in cyanotic children and the unreliability of a new device of impedance for non-invasivemonitoring of cardiac outpout in comparison with pulmonary arterial catheter.A viable chronic animal model of bidirectional cavo-pulmonary (BCP) has been developed. Itshowed that the antegrade pulsatile flow prevents the formation of pulmonary arteriovenous fistulas(PAVMs) ,improves hematosis and attenuates the development of PAH clinically supporting themaintenance of this flow when creating a BCP.Moreover, the loss of pulsatility while reducing the shear stress causes a decrease in e-NOSsynthase and a dependent vaso-relaxing altered response of the pulmonary arterial endothelium. Themicropulsatility limits these deleterious effects. These results imply potential therapies against thePAH of Fontan surgery, maintaining an accessory pulmonary blood flow and the pharmaceuticalvaso-relaxing non-endothelium dependent modulation.