ABSTRACT
Hypoplastic Left Heart Syndrome (HLHS) is a congenital condition which can severely impair the subject's health. In subjects affected by HLHS, the left ventricle is underdeveloped or not functional at all, so that the left ventricle cannot support systemic circulation. Starting from the 1980s, the use of the right ventricle to support systemic circulation is being pursued as the best clinical practice treatment, with a staged approach, whose final step is the implementation of the Total Cavopulmonary Connection (TCPC). A multidisciplinary approach is nevertheless required, due to the complexity of the disease. The surgical treatment of HLHS requires careful planning in order to optimize the mechanical power exerted by the functional ventricle, avoiding power dissipations as much as possible, associated to the newly created connections between different circulatory compartments. The objective of this study is to model the central venous and pulmonary compartments, starting from diagnostic MRI data taken during the follow-up of a HLHS subject, previously operated on at the Bambino Gesu Children's Hospital (Rome), and to calculate the flow field associated to the obtained numerical model. Methods: MRI volume sets were analyzed using open-source image processing software. The binarization of the images, required to label the blood domain, was performed by means of two-level thresholding. A manual pruning of the resulting volume was needed to isolate as much as possible the blood compartment from the rest of the anatomy, though, since two constant thresholds are generally insufficient to perfectly segment vessels throughout the image. The blood compartment volume was then discretized, using an unstructured mesh (more than 1 million tetrahedral cells). Suitable boundary conditions (BC) were set, using clinical data obtained in the follow-up. A computational fluid dynamics (CFD) study was then carried out, using the mathematical model of the anatomy and the BCs, in stationary conditions. Results: The morphology of the calculated flow field was highly dependent on the closeness of the IVC and SVC anastomoses to the right pulmonary bifurcation: this entailed a complex flow field, with a marked deviation of the pathlines' direction, especially along the path from the inferior vena cava to the inferior branch of the right pulmonary artery. The analysis of the pathlines demonstrated that the IVC flow (carrying hepatic factors from the liver) contributes to either RPA branch, as well as to the LPA. This has clinical relevance, considering that the hepatic factors carried by the IVC flow are essential for the physiological growth of the vessels. The good hemodynamical performance of the connection is also confirmed by its high hydraulic efficiency (94%). Conclusion: Patient-specific studies of HLHS or other relevant congenital pathologies are useful for assessing the subject's health status during follow-up, verifying the fluid dynamical features of the surgical outcome.
