The ultimate goal of Fontan surgical planning is to provide additional insights into the clinical decision-making process. In its current state, surgical planning offers an accurate hemodynamic assessment of the pre-operative condition, provides anatomical constraints for potential surgical options, and produces decent post-operative predictions if boundary conditions are similar enough between the pre-operative and post-operative states. Moving forward, validation with post-operative data is a necessary step in order to assess the accuracy of surgical planning and determine which methodological improvements are needed. Future efforts to automate the surgical planning process will reduce the individual expertise needed and encourage use in the clinic by clinicians. As post-operative physiologic predictions improve, Fontan surgical planning will become an more effective tool to accurately model patient-specific hemodynamics.
OBJECTIVE
Optimizing flow and diminishing power loss in the Fontan circuit can improve hemodynamic efficiency potentially improving long-term outcomes. Computerized modeling has predicted improved energetics with a Y-graft Fontan.
METHODS
From August to December, 2010, six consecutive children had a completion Fontan (n=3) or a Fontan revision (n=3) using a bifurcated polytetrafluoroethylene Y-graft (18×9×9 mm in 2, 20×10×10 mm in 4) connecting the inferior vena cava (IVC) to the right and left pulmonary arteries (PAs) with separate graft limbs. Patents were imaged by magnetic resonance imaging (MRI; n-5) or computerized tomography (n=1). Computational fluid dynamics (CFD) assessed Fontan hemodynamics, power loss, and IVC flow splits to the branch PAs. Clinical parameters were compared with 12 patients immediately preceding this series who had a lateral Fontan procedure.
RESULTS
Despite longer crossclamp and bypass times (not statistically significant), the Y-graft Fontan patients had postoperative courses similar to the conventional Fontan patients. Other than two early readmissions for pleural effusions managed with diuretics, on 6–12 months follow-up (mean 8 months), all six patients have done well. Postoperative flow modeling demonstrated balanced distribution of IVC flow to both PAs with minimal flow disturbance. Improvements in hemodynamics and efficiency were noted when the Y-graft branches were anastomosed distally and aligned tangentially with the branch PAs.
CONCLUSIONS
This preliminary surgical experience demonstrates clinical feasibility of the bifurcated Y-graft Fontan. CFD shows acceptable hemodynamics with low calculated power losses and balanced distribution of IVC flow to the PAs as long as the branch grafts are anastomosed distally.
Virtual modeling of cardiothoracic surgery is a new paradigm that allows for systematic exploration of various operative strategies and uses engineering principles to predict the optimal patient-specific plan. This study investigates the predictive accuracy of such methods for the surgical palliation of single ventricle heart defects. Computational fluid dynamics (CFD)-based surgical planning was used to model the Fontan procedure for four patients prior to surgery. The objective for each was to identify the operative strategy that best distributed hepatic blood flow to the pulmonary arteries. Post-operative magnetic resonance data were acquired to compare (via CFD) the post-operative hemodynamics with predictions. Despite variations in physiologic boundary conditions (e.g., cardiac output, venous flows) and the exact geometry of the surgical baffle, sufficient agreement was observed with respect to hepatic flow distribution (90% confidence interval-14 ± 4.3% difference). There was also good agreement of flow-normalized energetic efficiency predictions (19 ± 4.8% error). The hemodynamic outcomes of prospective patient-specific surgical planning of the Fontan procedure are described for the first time with good quantitative comparisons between preoperatively predicted and postoperative simulations. These results demonstrate that surgical planning can be a useful tool for single ventricle cardiothoracic surgery with the ability to deliver significant clinical impact.
Background: Using a bifurcated Y-graft as the Fontan baffle is hypothesized to streamline and improve flow dynamics through the total cavopulmonary connection (TCPC). This study conducted numerical simulations to evaluate this hypothesis using postoperative data from 5 patients. Methods: Patients were imaged with cardiac magnetic resonance or computed tomography after receiving a bifurcated aorto-iliac Y-graft as their Fontan conduit. Numerical simulations were performed using in vivo flow rates, as well as 2 levels of simulated exercise. Two TCPC models were virtually created for each patient to serve as the basis for hemodynamic comparison. Comparative metrics included connection flow resistance and inferior vena caval flow distribution. Results: Results demonstrate good hemodynamic outcomes for the Y-graft options. The consistency of inferior vena caval flow distribution was improved over TCPC controls, whereas the connection resistances were generally no different from the TCPC values, except for 1 case in which there was a marked improvement under both resting and exercise conditions. Examination of the connection hemodynamics as they relate to surgical Y-graft implementation identified critical strategies and modifications that are needed to potentially realize the theoretical efficiency of such bifurcated connection designs. Conclusions: Five consecutive patients received a Y-graft connection to complete their Fontan procedure with positive hemodynamic results. Refining the surgical technique for implementation should result in further energetic improvements that may help improve long-term outcomes.