Total cavopulmonary hemodynamics and the single ventricle: functional relationships and translational possibilities
Haggerty, Christopher Mark
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Single ventricle heart defects are a rare but serious form of congenital heart disease, which affect approximately 2000 children born in the United States each year. Staged surgical palliation, culminating with the “Fontan Procedure,” is typically required to achieve adequate supply of blood to both the pulmonary and systemic circulations while avoiding chronic ventricular volume overload. This surgery reroutes the systemic veins to the pulmonary arteries, forming a total cavopulmonary connection (TCPC), to completely bypass the right side of the heart and restore a series configuration to the cardiovascular circuits. Despite improved survival through this operative course in first weeks and years of life, Fontan patients are subjected gradual attrition and decreased life expectancy through a multitude of chronic complications. It is suspected that the adverse hemodynamics of this surgically altered physiology, including those specific to the surgical TCPC, play a role in determining patient outcome. However, the small and heterogeneous 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. In recent decades, advances in medical imaging and image-based computational fluid dynamics (CFD) have redefined the realm of possibility for studying complex biomedical phenomena. Combined, these methods provide the means to create and evaluate patient-specific models of a wide range of cardiovascular structures, including the TCPC, with high fidelity. Results from these models can then be used for a wide array of different analyses, such as identifying regions of flow separation or stagnation, calculating hemodynamic power loss, or quantifying local flow distribution patterns. Through significant effort from numerous past investigators, a robust set of validated computational and image processing tools has been assembled, along with the largest library of cardiac magnetic resonance (CMR) data of TCPC anatomy and flow. These tools are leveraged in this thesis to characterize the functional implications of TCPC power loss at an unprecedented scale: we report the largest CFD analysis of patient-specific TCPC hemodynamics to date with particular focus on identifying functional correlates. Combining these data with imaging-based analysis of ventricle function, we directly compare the CFD-derived hemodynamics to the performance of the single ventricle for the first time. Motivated by the physiologic significance of these findings, the same patient-specific CFD framework is used for the translational application of prospective surgery planning for hemodynamic optimization, including the first implementation of a novel TCPC connection design hypothesized to uniquely streamline the energetic performance. We conclude with a first look at the longitudinal evolution of patient functional status to begin understanding how factors such as TCPC hemodynamics contribute to poor long-term performance in these patients.