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Published on: June 14, 2024
Optimization of a Y-graft design for improved hepatic flow distribution in the fontan circulation
Weiguang Yang1, Jeffrey A Feinstein, Shawn C Shadden
1Mechanical and Aerospace Engineering, University of California San Diego, La Jolla, CA 92093, USA. w1yang@ucsd.edu
Insights
Optimizing Y-graft designs for single ventricle heart patients significantly improves hepatic flow distribution (HFD). Patient-specific Y-grafts with equal branch diameters are often sufficient, enhancing outcomes after Fontan surgery.
Area of Science:
- Biomedical Engineering
- Cardiovascular Surgery
- Pediatric Cardiology
Background:
- Single ventricle heart defects necessitate complex surgical palliation, including the Fontan procedure.
- The Fontan surgery connects the superior and inferior vena cava to the pulmonary arteries, creating unique hemodynamic challenges.
- Y-shaped grafts are a novel alternative to traditional tube grafts aiming to improve hemodynamic performance and hepatic flow distribution (HFD) in Fontan patients.
Purpose of the Study:
- To optimize Y-graft designs for improved hemodynamic performance and HFD in Fontan patients.
- To investigate the influence of geometric and hemodynamic factors on HFD within Y-graft configurations.
- To determine if unequal branch diameters in Y-grafts enhance HFD under specific flow conditions.
Main Methods:
- Coupling Lagrangian particle tracking with an optimal design framework.
- Investigating the effects of boundary conditions and geometry on HFD.
- Analyzing Y-graft performance with varying branch diameters, including unequal configurations, under patient-specific flow splits.
Main Results:
- Optimal Y-graft geometry is highly dependent on individual patient pulmonary flow splits.
- Equal-sized Y-graft branches generally achieve comparable or superior HFD compared to unequal designs.
- Patient-specific optimized Y-grafts demonstrated significant improvements in HFD over non-optimized designs.
- Constrained optimization indicated a slight increase in energy efficiency with larger branches, but smaller branches were preferred for optimal HFD with proximal anastomosis.
Conclusions:
- Y-graft design optimization can significantly enhance HFD in single ventricle patients.
- Equal branch diameters in Y-grafts are often sufficient and preferable for optimizing HFD.
- Patient-specific geometric modifications, guided by computational analysis, are crucial for improving Fontan circulation outcomes.
Abstract:
Single ventricle heart defects are among the most serious congenital heart diseases, and are uniformly fatal if left untreated. Typically, a three-staged surgical course, consisting of the Norwood, Glenn, and Fontan surgeries is performed, after which the superior vena cava (SVC) and inferior vena cava (IVC) are directly connected to the pulmonary arteries (PA). In an attempt to improve hemodynamic performance and hepatic flow distribution (HFD) of Fontan patients, a novel Y-shaped graft has recently been proposed to replace the traditional tube-shaped extracardiac grafts. Previous studies have demonstrated that the Y-graft is a promising design with the potential to reduce energy loss and improve HFD. However these studies also found suboptimal Y-graft performance in some patient models. The goal of this work is to determine whether performance can be improved in these models through further design optimization. Geometric and hemodynamic factors that influence the HFD have not been sufficiently investigated in previous work, particularly for the Y-graft. In this work, we couple Lagrangian particle tracking to an optimal design framework to study the effects of boundary conditions and geometry on HFD. Specifically, we investigate the potential of using a Y-graft design with unequal branch diameters to improve hepatic distribution under a highly uneven RPA/LPA flow split. As expected, the resulting optimal Y-graft geometry largely depends on the pulmonary flow split for a particular patient. The unequal branch design is demonstrated to be unnecessary under most conditions, as it is possible to achieve the same or better performance with equal-sized branches. Two patient-specific examples show that optimization-derived Y-grafts effectively improve the HFD, compared to initial nonoptimized designs using equal branch diameters. An instance of constrained optimization shows that energy efficiency slightly increases with increasing branch size for the Y-graft, but that a smaller branch size is preferred when a proximal anastomosis is needed to achieve optimal HFD.
