Computational modeling of a quadricuspid truncal valve in neonatal hemodynamic conditions

Truncus arteriosus is a rare congenital heart disease in which blood from both ventricles enters the truncal valve through a ventricular septal defect. Downstream of the valve, the pulmonary and systemic circulation share a common truncus. Around a quarter of the affected patients have a quadricuspid truncal valve featuring four, often thickened, leaflets. Quadricuspid valve morphology is related to valve regurgitation and increased risk for reoperation. When truncal patients undergo surgery, the septal defect is closed and the pulmonary arteries are reconnected to the right ventricle separating the pulmonary and systemic circulation. This repair subjects the truncal valve to a sudden change in pressure and flow environment. How these altered conditions affect the hemodynamics downstream of the valve remains unclear. In this study, we simulate the interaction of the blood flow with a quadricuspid truncal valve in a patient-specific neonatal geometry after truncal repair. The valve is constructed using a design-based approach. Assuming that the valve supports a prescribed pressure, we derive partial differential equations describing its mechanical equilibrium. Their solution predicts a loaded leaflet configuration including leaflet geometry and fiber orientations. From this configuration, we derive a constitutive law for the valve with scaled membrane stiffnesses to achieve the predicted tensions. Fluid-structure interaction (FSI) simulations are performed with an Immersed Boundary Method. Boundary conditions are derived from patient data to reflect the hemodynamic environment in a neonate after truncal repair. During valve opening, an accelerating aortic jet emerges which is deflected toward the outer curvature of the aortic arch while a recirculation zone develops along the inner curvature. During systolic deceleration, the adverse pressure gradient across the valve leads to transient backward flow in the ascending aorta and consequently valve closure. As the four leaflets do not coapt in the center of the valve, we observe a retrograde central jet through the remaining orifice consistent with regurgitation documented in the patient's clinical reports. Our study provides the first FSI simulation of a quadricuspid truncal valve in neonatal hemodynamic conditions.