Exploring the impact of through-plane velocity in Fontan hemodynamics using computational fluid dynamics

Fontan is the most common procedure for single ventricle heart disease patients: it is a complex cardiothoracic surgery composed by three steps that must be carried out in the first years of life of children suffering from this congenital malformation. However, it is a palliative surgery which does not ensure a physiological circulation. Its success allows the patient to survive (especially in the first years of life), but its low efficiency can have bad consequences on future life. Because of its unique flow distribution, Fontan-treated patients are interesting cases to study from a haemodynamic point of view. In particular, computational models of Fontan procedure are powerful tools because they can provide an insight into complex flow phenomena, helpful to understand and improve this technique which is still imperfect. This computational study aims to provide an insight into total cavopulmonary connection. A patient-specific model was studied thanks to software like VMTK and SimVascular. Then, 5 different velocity profiles were imposed as boundary conditions at the inlets. The objective is to understand if the presence of secondary flow in orthogonal plane respect to the vessel longitudinal axis could improve Fontan efficiency, without worsen the atherogenic or thrombogenic situation. To study the different behaviours of these velocity profiles, 5 unsteady simulations were performed on SimVascular for two cardiac cycles, hypothesized with the duration of 1 second each. Different metrics were studied to understand if secondary flow at boundaries have an impact on haemodynamics. Wall shear stress-based descriptors allow to understand if the conditions that cause generation and proliferation of atherosclerotic plaques, thrombosis or hyperplasia are present at luminal surface. Bulk-flow descriptors give us information about flow distribution, visualizing helical patterns and quantifying helical flow. At last, the analysis focused on energy dissipation metrics, allowing to study the efficiency of the patient-specific Fontan connection. Interesting results come from these data: the presence of an in-plane velocity component at the inlets seems to decrease energy dissipation, increasing the cavo-pulmonary connection efficiency. Moreover, secondary flows have good effects even from an atherogenic point of view. Univentricular heart is a mortal defect without surgical treatment. Fontan is a helpful but still imperfect procedure. Surely, computational fluid dynamic is a useful tool to improve its efficiency, getting close as much as possible to the physiological circulation. This topic needs to be studied much more than in the past because the improvement is possible, and the technology can do it. This study is an attempt to help this imperfect surgery to improve: maybe, in future, the procedure will be modified imposing at the venae cavae flows some in-plane velocity patterns, with the aim of increasing the non-physiological connection efficiency and reducing the long terms problem associated with energy dissipation in heamodynamics.