Inflow typology and ventricular geometry determine efficiency of filling in the hypoplastic left heart

Background: Pediatric patients with hypoplastic left heart syndrome rely solely on the right ventricle, resulting in anatomic maladaptations that can significantly compromise diastolic efficiency and lead to heart failure. Clinical indices to evaluate diastole are generally derived from the adult left ventricle, limiting their relevance to patients with hypoplastic left heart syndrome. We investigated the effect of the ventricular cavity shape and tricuspid inflow typology on the filling dynamics to provide new directions of investigation for assessing diastolic function in these patients. Methods: Magnetic resonance imaging data were used to generate personalized mathematic models of 4 patients with different prognoses after stage I of the Norwood procedures. Two of these patients were also modeled after stage II. Numeric simulations were performed to analyze the interaction between blood flow and the myocardium during diastole. Results: The filling dynamics were characterized by the formation of an organized structure of swirling blood (vortex ring). This was strongly influenced by the ventricular shape and the timing of the E and A wave. Biphasic rather than fused inflows and more elliptical than spherical cavities were found to increase the intraventricular pressure gradients and the filling capacity by optimizing the energy transfer between blood flow and the myocardium. This resulted in a better flow propagation and higher tissue velocities and displacements. Conclusions: The variations in the kinetic energy associated with the blood motion reflected the base-to-apex pressure difference and can therefore be used to quantify the efficiency of filling, providing a potential new metric to assess diastolic function in these patients.