Computational study of the hemodynamics in single ventricle physiology: an approach to patient-specific surgical planning

Abstract

Patient-specific surgical planning for single ventricle patients represents a crucial stage within their clinical life. Computational-aided diagnoses and evaluations, by means of the use of imaging techniques, designing tools, mathematical models and computational fluid dynamics (CFD), suppose a significant progress in reducing uncertainty of treatments or surgeries and, so, enhancing patients’ quality of life and enlarging their life expectancy. Based on this context, this study reproduces a surgical planning in a Fontan patient in order to offer a general overview of the different stages, tools, procedures, models and techniques that are used so as to understand and replicate subject’s hemodynamics. Lumped parameter mathematical models are presented in this research as a way to inexpensively estimate the cardiovascular circulation in the whole body. Tuning the parameters on an existing model to achieve the replication of patient-specific flow conditions has been explored as a minimization problem. Different heuristic methods (particle swarm optimization, genetic algorithm, simulated annealing and SHERPA) have been tested in specific optimization software (HEEDS MDO and Matlab). Validation has been performed with patient experimental data and results show a good performance of the described procedure. The threshold of defining the acceptability criteria at 20% of error can be significantly lowered down with similar time resources, in comparison to manual tuning, or just maintained by drastically reducing the time resources. On the other hand, Fontan patient hemodynamics has been thoroughly studied through the reproduction of a complete real surgical planning case, including a follow-up exploration to examine patient’s current state. The patient, diagnosed with severe hypoxemia and pulmonary arteriovenous malformation in the left lung, caused by a heavily unbalanced hepatic flow distribution (HFD), was required to undergo a palliative surgery to prevent Fontan failure. Surgical planning before surgery provided clinicians with an exhaustive assessment of different anatomic configurations. Obtainment of the proposed anatomies using computer-aided design (CAD) tools has allowed the exploration of the hemodynamics by means of CFD analyses. The connection of the hepatic vein to the azygous vein has been shown to improve total cavopulmonary connection (TCPC) performance and to balance the HFD. Clinicians used this option to perform surgery and follow-up visits showed a notorious improvement of the blood oxygen levels. Recent follow-up examination has allowed the replication of the flow by means of CFD. Improved flow distribution has been observed and a more balanced HFD has been achieved. ANSYS Fluent 17.0 has been used as CFD solver and previous validation in a physiological case has been carried out. Power loss in the TCPC and the flow patterns in different slices of the anatomy have been compared to experimental particle image velocimetry data and previous CFD simulations. The shown good agreement allows the validation of the CFD solver and its legitimate use when reproducing physiological situations.