Background:The Fontan operation is a palliative technique for patients born with single ventricle heart disease. The superior vena cava (SVC), inferior vena cava (IVC), and hepatic veins are connected to the pulmonary arteries in a total cavopulmonary connection by an extracardiac (EC) conduit or a lateral tunnel (LT) connection. A balanced hepatic flow distribution (HFD) to both lungs is essential to prevent pulmonary arteriovenous malformations and cyanosis. HFD is highly dependent on the local hemodynamics. Objective:The effect of age-related changes in caval inflows on HFD was evaluated using cardiac MRI (CMR) data and patient-specific computational fluid dynamics (CFD) modeling. Methods:SVC and IVC flow from 414 Fontan patients were collected to establish a relationship between SVC:IVC flow ratio and age. CFD modeling was performed in 60 (30 EC and 30 LT) patient models to quantify the HFD that corresponded to patient ages of 3, 8, and 15 years, respectively. Results:SVC:IVC flow ratio inverted at ∼8 years of age, indicating a clear shift to lower body flow predominance. Our data showed that variation of HFD in response to age-related changes in caval inflows (SVC:IVC = 2,1, and 0.5 corresponded to ages 3, 8, and 15+ respectively) was not significant for EC but statistically significant for LT cohorts. For all three caval inflow ratios, a positive correlation existed between the IVC flow distribution to both the lungs and the HFD. However, as the SVC:IVC ratio changed from 2→0.5 (age 3→15+), the correlation's strength decreased from 0.87→0.64, due to potential flow perturbation as IVC flow momentum increased. Conclusion:Our analysis provided quantitative insights into the impact of the changing caval inflows on Fontan's long-term HFD, highlighting the importance of including SVC:IVC variations over time to understand Fontan's long-term hemodynamics. These findings broaden our understanding of Fontan hemodynamics and patient outcomes. Clinical Perspective:With improvement in standard of care and management of single ventricle patients with Fontan physiology, the population of adults with Fontan circulation is increasing. Consequently, there is a clinical need to comprehend the impact of patient growth on Fontan hemodynamics. Using CMR data, we were able to quantify the relationship between changing caval inflows and somatic growth. We then used patient-specific computational flow modeling to quantify how this relationship affected the distribution of long-term hepatic flow in extracardiac and lateral tunnel Fontan types. Our findings demonstrated the significance of including SVC:IVC changes over time in CFD modeling to learn more about the long-term hemodynamics of Fontan. Fontan surgical approaches are increasingly planned and optimized using computational flow modeling. For a patient undergoing a Fontan procedure, the workflow presented in this study that takes into account the variations in Caval inflows over time can aid in predicting the long-term hemodynamics in a planned Fontan pathway.

BackgroundSingle ventricle (SV) patients with interrupted inferior vena cava (iIVC) and azygos continuation are at high risk for unbalanced hepatic venous flow (HVF) distribution to the lungs after Fontan completion and subsequent pulmonary arteriovenous malformations (AVMs) formation.ObjectivesThe aim of the study was to utilize computational fluid dynamics (CFD) analysis to avoid maldistribution of HVF to the lungs after Fontan surgery.MethodsFour SV subjects with iIVC were prospectively studied with a 3-dimensional (3D) modeling workflow with digital 3D models created from segmented magnetic resonance images or computer tomography scans, virtual surgery, and CFD analysis over multiple physiologic states for the evaluation of operative plans to achieve balanced HVF to both lungs. Three of the patients were Fontan revision candidates with existing AVMs. All patients underwent Fontan completion or revision surgery.ResultsCFD predicted that existing or proposed Fontan completion in all patients would result in 100% of HVF to one lung. Improved HVF balance was achieved with CFD analysis of alternative surgical approaches resulting in the average distribution of HVF to the right/left pulmonary arteries of 37%/63% ± 10.4%. A hepatoazygos shunt was required in all patients and additional creation of an innominate vein in one. CFD analysis was validated by the comparison of pre-operative predicted and postoperative MRI-measured total right/left pulmonary flow (51%/49% ± 5.4% vs 49%/51% ± 8.5%).ConclusionsA 3D modeling workflow with CFD simulation for SV patients with iIVC may avoid HVF maldistribution and development of AVMs after Fontan completion.

BACKGROUND:The Fontan operation, a palliative procedure for single ventricle patients, has evolved to improve outcomes and reduce complications. While extracardiac conduit (ECC) is favored for its simplicity and potential hemodynamic benefits, concerns arise about conduit size adequacy over time. Undersized ECC conduits may cause hemodynamic inefficiencies and long-term complications, while oversizing can lead to flow disturbances, stagnation, and thrombosis, necessitating surgical revision or upsizing to optimize hemodynamics. OBJECTIVES:The study aimed to predict the impact of upsizing by developing a patient-specific workflow using cardiac magnetic resonance-based imaging and computational fluid dynamics to assess Fontan hemodynamic changes and determine the most optimal conduit size. METHODS:We simulated upsizing in patient-specific models, computing reduction in power loss (PL), and analyzed pressure gradients, wall shear stress (WSS), and other local flow dynamic parameters such as vorticity and viscous dissipation that influence PL in a Fontan. Additionally, we quantified the impact of upsizing on hepatic flow distribution (HFD). RESULTS:Across the patient cohort, upsizing resulted in a PL reduction of 16 %-63 %, with the greatest reduction observed in patients with the smallest pre-existing conduit sizes (14 mm). The optimal conduit size for minimizing PL was highly patient-specific. For instance, a 20 mm conduit reduced PL by 63 % in one patient, while another patient showed 16 % reduction with upsizing. Pressure gradients decreased by 15 %-35 %, correlating with the reduction in PL, while WSS decreased consistently with upsizing. Vorticity and viscous dissipation exhibited more variability but followed the overall trend of reduced PL. HFD changes were modest with a maximum variation of 30 %. CONCLUSIONS:Our findings underscore the importance of individualized approaches in Fontan conduit upsizing. CFD-based quantitative evaluations of PL, pressure gradients, HFD, and WSS can guide optimal conduit sizing, improving long-term outcomes for patients.

Commentary: Calcific aortic stenosis in progeria: A personalized approach to a difficult problemThe Journal of Thoracic and Cardiovascular SurgeryVol. 166Issue 5PreviewAlthough the mechanism of atherosclerosis was described more than 100 years ago,1 the molecular mechanisms of dramatic progression of atherosclerosis in rare patients with Hutchinson–Gilford progeria syndrome (HGPS) became somewhat clearer only recently. HGPS is extremely rare condition (1 in 18-20 million new births).2,3 Because of its rarity, limited information is available regarding the natural history of cardiac and vascular abnormalities in this syndrome. HGPS is characterized by accelerated cardiovascular disease, which leads to significant morbidity and mortality from myocardial infarction or stroke at an average age of 13 years. Full-Text PDF

Introduction: The Fontan procedure is performed between 2-4 years of age and is a palliative technique for patients born with single ventricle defects. The Fontan physiology is the result of a total cavopulmonary connection between superior and inferior vena cava (SVC and IVC) and the hepatic veins to the pulmonary arteries (PA). Maldistribution of hepatic blood flow to the lungs can result in the formation of pulmonary arteriovenous malformations (PAVM) and resulting cyanosis. Hepatic blood flow distribution (HFD) to right and left lungs is highly dependent on the local flow dynamics. We sought to investigate the impact of SVC-to-IVC flow ratio and age on HFD. Methods: SVC and IVC flow data measured by cardiac MRI (CMR) from 81 Fontan patients were collected to establish the relationship between SVC: IVC flow ratio vs. age. 3D Patient-specific computational fluid dynamics (CFD) modeling was performed for 5 patients who underwent Fontan procedure with an extracardiac conduit to quantify the HFD to the right and left PAs. We evaluated the dependency of HFD on SVC: IVC flow ratio by quantifying HFD to different SVC: IVC flow ratios (2, 1.0, and 0.5) for a given Fontan anatomy. Results: SVC: IVC flow ratio inverted at ~10 years of age (n=81, Figure A) indicating a clear shift to lower body predominance in overall caval flow. CFD analysis (n=5) showed that the shift in SVC-IVC flow had a significant effect on the HFD (Fig. B-F). Change in HFD was more substantial as SVC: IVC flow ratio shifted from 2 to 1 [~5-10 years] with an average % change of 21±6 compared to the HFD change that occurred for a shift of 1 to 0.5 [9±11 for ~10-20 years] (Fig. B-F). Conclusion: Well-balanced distribution of HFD is essential to prevent PAVMs and to ensure long-term efficacy of a Fontan. This study highlights how SVC: IVC flow ratios change over time and can impact HFD to PAs. Interventions to address HFD maldistribution should not be considered in isolation and should incorporate predictions of SVC: IVC changes over time.

Heterotaxy (HTX) syndrome is associated with complex congenital heart disease (CCHD) and AV node (AVN) anomalies. Superior or inferior AVN displacement has been believed to be dictated by ventricular looping. Biventricular (BiV) repair of CCHD in HTX requires extensive AV valve and outflow tract surgery, jeopardizing the AVN, and has been associated with rates of AV block (AVB) of 15-25%.