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ObjectiveSeveral authors have detailed their experiences with small cohorts of patients in light of expanding interest in using minimally invasive surgery (MIS) to treat Tetralogy of Fallot (ToF). The goal of this study was to review an innovative MIS technique that results in a small tube-free surgical field. The technique’s clinical outcomes were examined in the largest cohort to date of patients with ToF treated with an MIS technique.MethodsWe reviewed all patients who underwent MIS at a single center between 2013 and 2017. The MIS procedure (including establishment of cavopulmonary bypass) is described. The inter-, peri- and postoperative data are reported and compared with those in the contemporary literature on ToF MIS.ResultsA total of 105 patients with ToF were identified. All patients, including 2 under 6 months of age, had good postoperative oxygen saturation (99% [98-100]). The incision size was 3 mm for patients younger than 3 years and 3-5 mm for older patients. No conversions to sternotomy or reinterventions were needed. Postoperative complications occurred in 14 patients (13.3%), including 1 death in the intensive care unit, which was not felt to be cardiac in origin. The primary hospital course metrics were comparable to previously published data.ConclusionsThe MIS technique with a tube-free surgical field has been successfully performed in 105 patients. The overall outcomes are favorable, including those for 2 patients younger than 6 months. This innovative MIS could be a promising approach for facilitating ToF repair in patients of all ages.Central PictureArtist depiction of operative incisions for the proposed minimally invasive surgery.Central MessageThis study shows the favorable outcomes of an innovative MIS technique with a tube-free surgical field by reviewing its use in 105 ToF patients, to date the largest cohort undergoing MIS for ToF.Perspective StatementThe proposed MIS technique with a tube-free surgical field presents a promising method for ToF repair; smaller incisions reduce patient pain, facilitate recovery, and enhance cosmesis. This technique achieved overall favorable outcomes for patients with ToF. Also, it can be a good option for early primary ToF repairs.

Background Cardiovascular simulations for patients with single ventricles undergoing the Fontan procedure can assess patient-specific hemodynamics, explore surgical advances, and develop personalized strategies for surgery and patient care. These simulations have not yet been broadly accepted as a routine clinical tool owing to a number of limitations. Numerous approaches have been explored to seek innovative solutions for improving methodologies and eliminating these limitations. Purpose This article first reviews the current state of cardiovascular simulations of Fontan hemodynamics. Then, it will discuss the technical progress of Fontan simulations with the emphasis of its clinical impact, noting that substantial improvements have been made in the considerations of patient-specific anatomy, flow, and blood rheology. The article concludes with insights into potential future directions involving clinical validation, uncertainty quantification, and computational efficiency. The advancements in these aspects could promote the clinical usage of Fontan simulations, facilitating its integration into routine clinical practice.

Surgical planning has shown great potential for optimizing outcomes for patients affected by single ventricle (SV) malformations. Phase-contrast magnetic resonance imaging (PC-MRI) is the routine technique used for flow acquisition in the surgical planning paradigm. However, PC-MRI may suffer from possible artifacts in certain cases; furthermore, this technology may not be readily available for patients in low and lower-middle-income countries. Therefore, this study aims to investigate the effectiveness of using Doppler echocardiography (echo-Doppler) for flow acquisitions of SV surgical planning. This study included eight patients whose blood flow data was acquired by both PC-MRI and echo-Doppler. A virtual surgery platform was used to generate two surgical options for each patient: (1) a traditional Fontan conduit and (2) a Y-graft. Computational fluid dynamics (CFD) simulations were conducted using the two flow acquisitions to assess clinically relevant hemodynamic metrics: indexed power loss (iPL) and hepatic flow distribution (HFD). Differences exist in flow data acquired by PC-MRI and echo-Doppler, but no statistical significance was obtained. Flow fields, therefore, exhibit discrepancies between simulations using flow acquisitions by PC-MRI and echo-Doppler. In virtual surgery, the two surgical options were ranked based on these metrics. No difference was observed in the ranking of surgical options between using different flow acquisitions. Doppler echocardiography is an adequate alternative approach to acquire flow data for SV surgical planning. This finding encourages broader usage of SV surgical planning with echo-Doppler when MRI may present artifacts or is not available, especially in low and lower-middle-income countries.

In silico modeling has been proposed as a tool to simulate left ventricular (LV) outflow tract (LVOT) obstruction in patients undergoing transcatheter mitral valve replacement (TMVR). This study validated a simplified approach to simulate LV outflow hemodynamics in the setting of TMVR with anterior leaflet laceration, a clinical technique used to mitigate the risk of LVOT obstruction. Personalized, 3-dimensional computational fluid dynamics models were developed from computed tomography images of six patients who underwent TMVR with anterior leaflet laceration. LV outflow hemodynamics were simulated using the patient-specific anatomy and the peak systolic flow rate as boundary conditions. The peak outflow velocity, a clinically relevant hemodynamic metric, was extracted from each simulation (vsim-peak) and compared with the clinical measurement from Doppler echocardiography (vclin-peak) for validation. In silico models were successfully developed and implemented for all patients. The pre-processing time was 2 h per model and the simulation could be completed within 3 h. In three patients, the lacerated anterior leaflet exposed open cells of the transcatheter valve to flow. Good agreement was obtained between vsim-peak and vclin-peak (r = 0.97, p

This hemodynamic feasibility study examined total cavopulmonary connection (TCPC) designs connecting the extracardiac conduit to the anterior surface of pulmonary arteries (PAs) or superior vena cava (SVC) rather than to the inferior PA surface (traditional TCPC). The study involved twenty-five consecutive Fontan patients meeting inclusion criteria from a single institution. A virtual surgical platform mimicked the completed traditional TCPC and generated three anterior anastomosis designs: Anterior-PA, Middle-SVC, and SVC-Inn (Inn: innominate vein). Hemodynamic performance of anterior anastomosis designs was compared with the traditional TCPC regarding indexed power loss (iPL) and hepatic flow distribution (HFD). Compared to the traditional TCPC, the Anterior-PA design produces a similar iPL. The Middle-SVC design is also similar, though the iPL difference is positively correlated with the anastomosing height. The SVC-Inn design had significantly more iPL. The three anterior anastomosis designs did not have a significant difference in HFD (from traditional TCPC). Pulmonary flow distribution (PFD) has a stronger correlation with HFD from the anterior anastomosis designs than the traditional TCPC. This hemodynamic feasibility study examined anterior anastomosis, extracardiac TCPC designs that may offer surgeons clinical dexterity. The Anterior-PA design may be equivalent to the traditional TCPC. Fontan extracardiac conduit anastomosis just superior to the PAs (Middle-SVC) also preserves hemodynamic performance and avoids direct PA anastomosis. These designs could simplify surgical Fontan completion, and may particularly benefit patients requiring surgical dissection, having atypical PA orientation, or after PA stent angioplasty.

Transcatheter mitral valve replacement (TMVR) is an emerging therapy for patients with severe mitral valve disease considered unsuitable for conventional surgery. Pre-procedural planning is paramou...

Introduction: The purpose of this study was to investigate the hemodynamic impact of LAMPOON (Laceration of the Anterior Mitral leaflet to Prevent Outflow ObstructioN) in transcatheter mitral valve replacement (TMVR) using patient-specific in silico modeling. Methods: Eight subjects from the LAMPOON investigational device exemption trial were included. All subjects were at prohibitive risk of outflow tract obstruction from TMVR based on computed tomography (CT), and underwent successful LAMPOON immediately followed by TMVR. A validated computational fluid dynamics (CFD) model was used to compare simulated hemodynamics and 3D flow patterns between two modeled conditions: 1) TMVR with LAMPOON and 2) TMVR without LAMPOON. Using the post-procedure CT scans, anatomical models of TMVR with LAMPOON were created for each subject. The open transcatheter valve cells were then virtually closed to model TMVR without LAMPOON for each subject. Finally, CFD was performed for each condition to simulate the systolic flow fields. Results: As compared to TMVR without LAMPOON, TMVR with LAMPOON resulted in lower peak velocity, lower peak LVOT gradient, and higher peak LVOT effective orifice area by 13 ± 6% (p=0.004), 28 ± 14% (p=0.008), and 15 ± 8% (p=0.002), respectively. LAMPOON provided flow communication through exposed cells of the transcatheter valve, thereby decreasing the flow constriction and reducing flow stasis in the vicinity of the neo-LVOT (Figure). The hemodynamic benefit of LAMPOON was observed to be greater in subjects with a smaller neo-LVOT area measured post-implant (p Conclusions: In silico modeling allowed for a quantitative patient-specific comparison of TMVR with and without LAMPOON, which is impossible to study clinically. The LAMPOON procedure improved simulated hemodynamics in all subjects, with a greater hemodynamic impact observed in subjects with a smaller post-implant neo-LVOT area.

Aims To characterize the dynamic nature of the left ventricular outflow tract (LVOT) geometry and flow rate in patients following transcatheter mitral valve replacement (TMVR) with anterior leaflet laceration (LAMPOON) and derive insights to help guide future patient selection. Methods and results Time-resolved LVOT geometry and haemodynamics were analysed with post-procedure computed tomography and echocardiography in subjects (N = 19) from the LAMPOON investigational device exemption trial. A novel post hoc definition for LVOT obstruction was employed to account for systolic flow rate and quality of life improvement [obstruction was defined as LVOT gradient >30 mmHg or LVOT effective orifice area (EOA) ≤1.15 cm2]. The neo-LVOT and skirt neo-LVOT were observed to vary substantially in area throughout systole (64 ± 27% and 25 ± 14% change in area, respectively). The peak systolic flow rate occurred most commonly just prior to mid-systole, while minimum neo-LVOT (and skirt neo-LVOT) area occurred most commonly in early-diastole. Subjects with LVOT obstruction (n = 5) had smaller skirt neo-LVOT values across systole. Optimal thresholds for skirt neo-LVOT area were phase-specific (260, 210, 200, and 180 mm2 for early-systole, peak flow, mid-systole, and end-systole, respectively). Conclusion The LVOT geometry and flow rate exhibit dynamic characteristics following TMVR with LAMPOON. Subjects with LVOT obstruction had smaller skirt neo-LVOT areas across systole. The authors recommend the use of phase-specific threshold values for skirt neo-LVOT area to guide future patient selection for this procedure. LVOT EOA is a ‘flow-independent’ metric which has the potential to aid in characterizing LVOT obstruction severity.

Despite favorable short-term outcomes, Fontan palliation is associated with comorbidities and diminished quality of life (QOL) in the years after completion. We hypothesized that poor Fontan hemodynamics and ventricular function are associated with worse QOL.This was a single-center study of Fontan survivors aged more than 12 years. Subjects completed a cardiac magnetic resonance scan and QOL questionnaire. Cardiac magnetic resonance-derived variables included Fontan geometry, and hemodynamics. Computational fluid dynamics simulations quantified power loss, pressure drop, and total cavopulmonary connection resistance across the Fontan. Quality of life was assessed by completion of the Pediatric Quality of Life Inventory. Longitudinal and cross-sectional comparisons were made between cardiac magnetic resonance and computational fluid dynamics parameters with patient-reported QOL.We studied 77 Fontan patients, median age 19.7 years (interquartile range, 17.1 to 23.6), median time from Fontan completion 16 years (interquartile range, 13 to 20). Longitudinal data were available for 48 patients; median time between cardiac magnetic resonance and QOL was 8.1 years (interquartile range, 7 to 9.4). Median patient-reported Pediatric Quality of Life Inventory total score was 80 (interquartile range, 67.4 to 88). Greater power loss and smaller left pulmonary artery diameter at baseline were associated with worse QOL at follow-up. Greater pressure drop was associated with worse QOL at the same time point.For Fontan survivors, measures of computational fluid dynamics hemodynamics and geometry are associated with worse QOL. Interventional strategies targeted at optimizing the Fontan may improve QOL.

Simple Summary A fluid-structure interaction (FSI) simulation of an intra-atrial Fontan connection was performed. Power loss and pressure drop results fluctuated less during the FSI simulation than during the simulation run with rigid walls, but there were no observable differences in time-averaged pressure drop, connection power loss or hepatic flow distribution. These results suggested that employing a rigid wall is a reasonable assumption when evaluating time-averaged hemodynamic quantities of the Fontan connection under resting breath-held flow conditions. Abstract Total cavopulmonary connection (TCPC) hemodynamics has been hypothesized to be associated with long-term complications in single ventricle heart defect patients. Rigid wall assumption has been commonly used when evaluating TCPC hemodynamics using computational fluid dynamics (CFD) simulation. Previous study has evaluated impact of wall compliance on extra-cardiac TCPC hemodynamics using fluid-structure interaction (FSI) simulation. However, the impact of ignoring wall compliance on the presumably more compliant intra-atrial TCPC hemodynamics is not fully understood. To narrow this knowledge gap, this study aims to investigate impact of wall compliance on an intra-atrial TCPC hemodynamics. A patient-specific model of an intra-atrial TCPC is simulated with an FSI model. Patient-specific 3D TCPC anatomies were reconstructed from transverse cardiovascular magnetic resonance images. Patient-specific vessel flow rate from phase-contrast magnetic resonance imaging (MRI) at the Fontan pathway and the superior vena cava under resting condition were prescribed at the inlets. From the FSI simulation, the degree of wall deformation was compared with in vivo wall deformation from phase-contrast MRI data as validation of the FSI model. Then, TCPC flow structure, power loss and hepatic flow distribution (HFD) were compared between rigid wall and FSI simulation. There were differences in instantaneous pressure drop, power loss and HFD between rigid wall and FSI simulations, but no difference in the time-averaged quantities. The findings of this study support the use of a rigid wall assumption on evaluation of time-averaged intra-atrial TCPC hemodynamic metric under resting breath-held condition.

In silico modeling has been proposed as a tool to simulate left ventricular (LV) outflow tract (LVOT) obstruction in patients undergoing transcatheter mitral valve replacement (TMVR). This study validated a simplified approach to simulate LV outflow hemodynamics in the setting of TMVR with anterior leaflet laceration, a clinical technique used to mitigate the risk of LVOT obstruction. Personalized, 3-dimensional computational fluid dynamics models were developed from computed tomography images of six patients who underwent TMVR with anterior leaflet laceration. LV outflow hemodynamics were simulated using the patient-specific anatomy and the peak systolic flow rate as boundary conditions. The peak outflow velocity, a clinically relevant hemodynamic metric, was extracted from each simulation (v

Cardiovascular simulations for patients with single ventricles undergoing the Fontan procedure can assess patient-specific hemodynamics, explore surgical advances, and develop personalized strategies for surgery and patient care. These simulations have not yet been broadly accepted as a routine clinical tool owing to a number of limitations. Numerous approaches have been explored to seek innovative solutions for improving methodologies and eliminating these limitations.This article first reviews the current state of cardiovascular simulations of Fontan hemodynamics. Then, it will discuss the technical progress of Fontan simulations with the emphasis of its clinical impact, noting that substantial improvements have been made in the considerations of patient-specific anatomy, flow, and blood rheology. The article concludes with insights into potential future directions involving clinical validation, uncertainty quantification, and computational efficiency. The advancements in these aspects could promote the clinical usage of Fontan simulations, facilitating its integration into routine clinical practice.

Apicocaval juxtaposition (ACJ) is a rare form of viscerocardiac malpositions in association with single-ventricle congenital heart defects. The Fontan surgery is the common palliation, and possible surgical options include ipsilateral, contralateral, and intra-atrial conduits. Concerns include lower hemodynamic performances or risks of conduit compression by the cardiac mass. This study investigates the hemodynamics and clinical outcomes of ACJ patients and potential surgical improvements. Ten consecutive ACJ patients were included, along with a reference cohort of ten non-ACJ patients. Magnetic resonance images were acquired at 6±0.6 year follow-up for anatomical analysis and hemodynamic assessments using computational fluid dynamics. Metrics of interest are deformation index (DI), indexed power loss (iPL), and hepatic flow distribution (HFD(off)). A “virtual” surgery was performed to explore potential hemodynamic improvements using a straightened conduit. DI for ACJ patients fell within the DI range of non-ACJ patients. Contralateral conduits had insignificantly higher iPL (0.070 [0.032,0.137]) than ipsilateral conduits (0.041 [0.013,0.095]) and non-ACJ conduits (0.034 [0.011,0.061]). HFD(off) was similar for the ipsilateral (21 [12,35]), contralateral (26 [7,41]), and non-ACJ Fontan conduits (17 [0,48]). Virtual surgery demonstrated that a straightened conduit reduced HFD(off) and iPL for the contralateral and ipsilateral conduits, potentially leading to improved clinical outcomes. In this limited sample, the hemodynamic performance of ACJ patients was not significantly different from their non-ACJ counterparts. The use of a straightened conduit option could potentially improve patient outcomes. Additionally, the fear of significant compression of conduits for ACJ patients was unsupported.

Thrombosis in post-transcatheter aortic valve replacement (TAVR) patients has been correlated with flow stasis in the neo-sinus. This study investigated the effect of the post-TAVR geometry on flow stasis. Computed tomography angiography of 155 patients who underwent TAVR using a SAPIEN 3 were used to identify patients with and without thrombosis, and quantify thrombus volumes. Six patients with 23-mm SAPIEN 3 valves were then selected from the cohort and used to create patient-specific post-TAVR computational fluid dynamic models. Regions of flow stasis (%Volstasis, velocities below 0.05 m/s) were identified. The results showed that all post-TAVR anatomical measurements were significantly different in patients with and without thrombus, but only sinus diameter had a linear correlation with thrombus volume (r = 0.471, p = 0.008). A linear correlation was observed between %Volstasis and thrombus volume (r = 0.821, p = 0.007). The combination of anatomy and valve deployment created a unique geometry in each patient, which when combined with patient-specific cardiac output, resulted in distinct flow patterns. While parametric studies have shown individual anatomical or deployment metrics may relate to flow stasis, the combined effects of these metrics potentially contributes to the biomechanical environment promoting thrombosis, therefore hemodynamic studies of TAVR should account for these patient-specific factors.

The governing international standard for the development of prosthetic heart valves is International Organization for Standardization (ISO) 5840. This standard requires the assessment of the thrombus potential of transcatheter heart valve substitutes using an integrated thrombus evaluation. Besides experimental flow field assessment and ex vivo flow testing, computational fluid dynamics is a critical component of this integrated approach. This position paper is intended to provide and discuss best practices for the setup of a computational model, numerical solving, post-processing, data evaluation and reporting, as it relates to transcatheter heart valve substitutes. This paper is not intended to be a review of current computational technology; instead, it represents the position of the ISO working group consisting of experts from academia and industry with regards to considerations for computational fluid dynamic assessment of transcatheter heart valve substitutes.

Energy conversion from vortical flows using flapping wings is widely observed in nature flyers and has great potential for improving energy efficiency of micro aerial vehicles. Therefore, it has re...

Several studies exist modeling the Fontan connection to understand its hemodynamic ties to patient outcomes (Chopski in: Experimental and Computational Assessment of Mechanical Circulatory Assistance of a Patient-Specific Fontan Vessel Configuration. Dissertation, 2013; Khiabani et al. in J Biomech 45:2376-2381, 2012; Taylor and Figueroa in Annu Rev Biomed 11:109-134, 2009; Vukicevic et al. in ASAIO J 59:253-260, 2013). The most patient-accurate of these studies include flexible, patient-specific total cavopulmonary connections. This study improves Fontan hemodynamic modeling by validating Fontan model flexibility against a patient-specific bulk compliance value, and employing real-time phase contrast magnetic resonance flow data. The improved model was employed to acquire velocity field information under breath-held, free-breathing, and exercise conditions to investigate the effect of these conditions on clinically important Fontan hemodynamic metrics including power loss and viscous dissipation rate. The velocity data, obtained by stereoscopic particle image velocimetry, was visualized for qualitative three-dimensional flow field comparisons between the conditions. Key hemodynamic metrics were calculated from the velocity data and used to quantitatively compare the flow conditions. The data shows a multi-factorial and extremely patient-specific nature to Fontan hemodynamics.

Objective Exercise intolerance afflicts Fontan patients with total cavopulmonary connections (TCPCs) causing a reduction in quality of life. Optimising TCPC design is hypothesised to have a beneficial effect on exercise capacity. This study investigates relationships between TCPC geometries and exercise haemodynamics and performance. Methods This study included 47 patients who completed metabolic exercise stress test with cardiac magnetic resonance (CMR). Phase-contrast CMR images were acquired immediately following supine lower limb exercise. Both anatomies and exercise vessel flow rates at ventilatory anaerobic threshold (VAT) were extracted. The vascular modelling toolkits were used to analyse TCPC geometries. Computational simulations were performed to quantify TCPC indexed power loss (iPL) at VAT. Results A highly significant inverse correlation was found between the TCPC diameter index, which factors in the narrowing of TCPC vessels, with iPL at VAT (r=−0.723, p 2 ) at VAT (r=0.373, p=0.01), VO 2 at peak exercise (r=0.485, p=0.001) and work at VAT/weight (r=0.368, p=0.01). iPL at VAT was negatively correlated with VO 2 at VAT (r=−0.337, p=0.02), VO 2 at peak exercise (r=−0.394, p=0.007) and work at VAT/weight (r=−0.208, p=0.17). Conclusions Eliminating vessel narrowing in TCPCs and reducing elevated iPL at VAT could enhance exercise tolerance for patients with TCPCs. These findings could help plan surgical or catheter-based strategies to improve patients’ exercise capacity.

Cardiovascular simulations have great potential as a clinical tool for planning and evaluating patient-specific treatment strategies for those suffering from congenital heart diseases, specifically Fontan patients. However, several bottlenecks have delayed wider deployment of the simulations for clinical use; the main obstacle is simulation cost. Currently, time-averaged clinical flow measurements are utilized as numerical boundary conditions (BCs) in order to reduce the computational power and time needed to offer surgical planning within a clinical time frame. Nevertheless, pulsatile blood flow is observed in vivo, and its significant impact on numerical simulations has been demonstrated. Therefore, it is imperative to carry out a comprehensive study analyzing the sensitivity of using time-averaged BCs. In this study, sensitivity is evaluated based on the discrepancies between hemodynamic metrics calculated using time-averaged and pulsatile BCs; smaller discrepancies indicate less sensitivity. The current study incorporates a comparison between 3D patient-specific CFD simulations using both the time-averaged and pulsatile BCs for 101 Fontan patients. The sensitivity analysis involves two clinically important hemodynamic metrics: hepatic flow distribution (HFD) and indexed power loss (iPL). Paired demographic group comparisons revealed that HFD sensitivity is significantly different between single and bilateral superior vena cava cohorts but no other demographic discrepancies were observed for HFD or iPL. Multivariate regression analyses show that the best predictors for sensitivity involve flow pulsatilities, time-averaged flow rates, and geometric characteristics of the Fontan connection. These predictors provide patient-specific guidelines to determine the effectiveness of analyzing patient-specific surgical options with time-averaged BCs within a clinical time frame.

Computational fluid dynamic (CFD) simulations are widely utilized to assess Fontan hemodynamics that are related to long-term complications. No previous studies have systemically investigated the effects of using different inlet velocity profiles in Fontan simulations. This study implements real, patient-specific velocity profiles for numerical assessment of Fontan hemodynamics using CFD simulations. Four additional, artificial velocity profiles were used for comparison: (1) flat, (2) parabolic, (3) Womersley, and (4) parabolic with inlet extensions [to develop flow before entering the total cavopulmonary connection (TCPC)]. The differences arising from the five velocity profiles, as well as discrepancies between the real and each of the artificial velocity profiles, were quantified by examining clinically important metrics in TCPC hemodynamics: power loss (PL), viscous dissipation rate (VDR), hepatic flow distribution, and regions of low wall shear stress. Statistically significant differences were observed in PL and VDR between simulations using real and flat velocity profiles, but differences between those using real velocity profiles and the other three artificial profiles did not reach statistical significance. These conclusions suggest that the artificial velocity profiles (2)-(4) are acceptable surrogates for real velocity profiles in Fontan simulations, but parabolic profiles are recommended because of their low computational demands and prevalent applicability.

Background Liver fibrosis is a serious complication of single ventricle Fontan survivors. Its causes are of great interest, and potential solutions to halt or delay progression are needed. The purpose of this study is to investigate if prior hemodynamics and anatomy can predict liver fibrosis severity in these patients. Methods Twenty-one Fontan patients with cardiac magnetic resonance (CMR) data obtained greater than 1 year before liver biopsy data were included. Computational fluid dynamic simulations were performed to quantify total cavopulmonary connection (TCPC) flow dynamics using patient-specific anatomies and blood flow waveforms reconstructed from CMR data. Collagen deposition (a measure of liver fibrosis) was quantified by digital image analysis of Sirius red–stained slides. Statistical analyses were performed to investigate potential relationships between Fontan hemodynamics and liver fibrosis. Results With an average time of 6.7 ± 2.9 years (range, 2-11 years) between CMR and biopsy, TCPC resistance and left pulmonary artery stenosis showed significant, positive correlations with magnitude of liver fibrosis (r = 0.54, P = .026; and r = 0.55, P = .028, respectively). The change in inferior vena cava flow rate over time also showed a significant positive correlation with magnitude of liver fibrosis (r = 0.91, P = .001). Conclusions TCPC resistance, left pulmonary artery stenosis, and increased inferior vena cava flow are positively associated with liver fibrosis after Fontan operation and hold promise as important predictors of hepatic decline. These findings encourage preprocedural planning and interventional strategies to improve TCPC performance and reduce vessel stenosis. Further investigation is warranted to design the ideal Fontan circulation and optimize flow dynamics to reduce the risk of liver fibrosis.

Fontan surgical planning ranks proposed surgical options according to their hemodynamics assessed by computational fluid dynamic (CFD) modeling. CFD commonly utilizes blood flow acquired under breath-holding (BH) conditions. Ignoring the free-breathing (FB) effect on blood flow waveforms may impact the ranking of surgical options. This study investigates such a potential impact by including ten Fontan patients who had blood flow acquisitions under both BH and FB conditions. A virtual surgery platform was used to generate two surgical options for each patient: (1) a traditional Fontan conduit and (2) a Y-graft. These options were ranked based on clinically relevant hemodynamic metrics: power loss (PL) and hepatic flow distribution (HFD). No difference was found in the ranking of options between using FB and BH flow acquisitions. The findings indicated that decision-making is not affected by the types of flow acquisition for Fontan surgical planning.

The use of mechanical circulatory support for failing Fontan patients is an area of growing interest, as the increased life expectancy of these patients continues to be accompanied by numerous end-organ complications. In vitro work has shown positive results using the CentriMag device for right-sided Fontan support, however the generalizability across various patient anatomies and cannulations is unknown. Computational simulations are first validated against in vitro modeling, then used to assess generalizability and further explore hemodynamic metrics including relative pressure changes, hepatic flow distribution, wall shear stress and power added. Computational modeling matched previous in vitro work very well, with vessel flow rates and relative average pressure change each within 1%. Positive results were seen across all patient anatomies and cannulations. On average, pressure from the vena cava to pulmonary arteries increased by 5.4 mmHg corresponding to 32 mW of power added. Hepatic flow distribution and wall shear stress were within acceptable ranges, with an average hepatic flow distribution of 47% and all patients showing ≤ 1% of the total Fontan connection surface area at a wall shear stress above 150 Pa. The positive results previously seen using CentriMag as a right-sided Fontan support device were found to be repeatable across multiple patient anatomies and cannulations. While animal models and eventual patient studies will provide further insight into the efficacy of this support strategy, our findings here suggest this method may reproduce right heart function.

Left ventricular outflow tract (LVOT) obstruction is a major complication of transcatheter mitral valve replacement (TMVR) and anterior mitral leaflet (AML) laceration has been shown to reduce the risk of this obstruction. Understanding neo-LVOT geometry is critical for determining risk of LVOT

Objective: Transcatheter anterior leaflet laceration is thought to mitigate the risk of left ventricular outflow tract (LVOT) obstruction and valve thrombosis (due to flow stasis) following transca...

Transcatheter mitral valve replacement (TMVR) is an emerging alternative for patients with severe mitral valve regurgitation who are considered at high risk for conventional surgical options. The early clinical experience with TMVR has shown that pre-procedural planning with computed tomography (CT) is needed to mitigate the risk of potentially lethal procedural complications such as left ventricular outflow tract (LVOT) obstruction. The goal of this review is to provide an overview of key concepts relating to TMVR pre-procedural planning, with particular emphasis on imaging-based methods for predicting TMVR-related LVOT obstruction. Risk of LVOT obstruction can be assessed with CT-based pre-procedural planning by using virtual device simulations to estimate the residual ‘neo-LVOT’ cross-sectional area which remains after device implantation. A neo-LVOT area of less than 2 cm2 is currently thought to increase the risk of obstruction; however, additional studies are needed to further validate this cutoff value. Three-dimensional printing and personalized computational simulations are also emerging as valuable tools which may offer insights not readily confered by conventional two-dimensional image analysis. The simulated neo-LVOT should be routinely assessed on pre-procedural CT when evaluating anatomical suitability for TMVR.

Computational modeling can be used to improve understanding of tricuspid valve (TV) biomechanics and supplement knowledge gained from benchtop and large animal experiments. The aim of this study was to develop a computational model of the TV using high resolution micro-computed tomography (μCT) imaging and fluid–structure interaction simulations. A three-dimensional TV model, incorporating detailed leaflet and chordal geometries, was reconstructed from μCT images of an excised porcine TV obtained under diastolic conditions. The leaflets were described using non-linear stress–strain relations and chordal properties were iteratively adjusted until valve closure was obtained. The leaflet coaptation zone obtained from simulation of valve closure was validated against μCT images of the TV captured at peak systole. The computational model was then used to simulate a regurgitant TV morphology and investigate changes in closure dynamics. Overall, the mean stresses in the leaflet belly region and the chordae tendinae of the regurgitant TV were 7% and 3% higher than the same regions of the normal TV. The maximum principal strain in the leaflet belly of the regurgitant TV was also 9% higher than the same regions of the normal TV. It is anticipated that this computational model can be used in future studies for further understanding of TV biomechanics and associated percutaneous repairs.

OBJECTIVE: Fontan surgical planning is an image-based, collaborative effort which is hypothesized to result in improved patient outcomes. A common motivation for Fontan surgical planning is the progression (or concern for progression) of pulmonary arteriovenous malformations (PAVMs). The purpose of this study is to evaluate the accuracy of surgical planning predictions, specifically hepatic flow distribution (HFD, a known factor in PAVM progression), and identify methodological improvements needed to increase prediction accuracy. METHODS: Twelve single ventricle patients who were enrolled in a surgical planning protocol for Fontan surgery with pre- and post-operative cardiac imaging are included in this study. Computational fluid dynamics were used to compare HFD in both the surgical planning prediction and actual post-operative conditions. RESULTS: Overall, HFD prediction error was 17±13%. This error was similar between surgery types (15±18% and 18±10% for revisions vs Fontan completions respectively, p=0.73), but was significantly lower (6±7%, p=0.05) for hepatic to azygous shunts. Y-grafts and extracardiac conduits showed a strong correlation between prediction error and discrepancies in graft insertion points (r=0.99, p

Objective Poor total cavopulmonary connection (TCPC) hemodynamics have been hypothesized to be associated with long-term complications in Fontan patients. Image-based Fontan surgical planning has shown great potential as a clinical tool because it can pre-operatively evaluate patient-specific hemodynamics. Current surgical planning paradigms commonly utilize cardiac-gated phase contrast magnetic resonance (MR) imaging to acquire vessel flows. These acquisitions are often taken under breath-held (BH) conditions and ignore the effect of respiration on blood flow waveforms. This study investigates the effect of respiration-driven flow waveforms on patient-specific hemodynamics using real-time MR acquisitions. Methods Patient-specific TCPCs were reconstructed from cardiovascular MR images. Real-time phase contrast MR images were acquired under both free-breathing (FB) and breath-held conditions for 9 patients. Numerical simulations were employed to assess flow structures and hemodynamics used in Fontan surgical planning including hepatic flow distribution (HFD) and indexed power loss (iPL), which were then compared between FB and BH conditions. Results Differences in TCPC flow structures between FB and BH conditions were observed throughout the respiratory cycle. However, the average differences (BH – FB values for each patient, which are then averaged) in iPL and HFD between these conditions were 0.002 ± 0.011 (p = 0.40) and 1 ± 3% (p = 0.28), respectively, indicating no significant difference in clinically important hemodynamic metrics. Conclusions Respiration affects blood flow waveforms and flow structures, but might not significantly influence the values of iPL or HFD. Therefore, breath-held MR acquisition can be adequate for Fontan surgical planning when focusing on iPL and HFD.

In this chapter, we will briefly discuss the acquisition and processing for medical image, introduce image-based computational simulation technique and describe principles of computational fluid dynamics.

The clinical applications of image-based computational simulation for single ventricle hemodynamics are summarized in this chapter. Furtherly, we will offer an example to illustrate the applications.

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.

This study investigates energy harvesting of a two-dimensional foil in the wake downstream of a cylinder. The foil is passively mobile in the transverse direction. An immersed boundary (IB) method with a fluid–structure interaction (FSI) model is validated and employed to carry out the numerical simulation. For improving numerical stability, this study incorporates a modified low-storage first-order Runge–Kutta scheme for time integration and demonstrates the performance of this temporal scheme on reducing spurious pressure oscillations of the IB method. The simulation shows the foil emerged in a vortical wake achieves better energy harvesting performance than that in a uniform flow. The types of the dynamic response of the energy harvester are identified, and the periodic response is desired for optimal energy harvesting performance. Last, the properties of vortical wakes are found to be of pivotal importance in obtaining this desired periodic response.

The Fontan procedure is a common palliative intervention for sufferers of single ventricle congenital heart defects that results in an anastomosis of the venous return to the pulmonary arteries called the total cavopulmonary connection (TCPC). Local TCPC and global Fontan circulation hemodynamics are studied with in vitro circulatory models because of hemodynamic ties to Fontan patient long-term complications. The majority of in vitro studies, to date, employ a rigid TCPC model. Recently, a few studies have incorporated flexible TCPC models, but provide no justification for the model material properties. The method set forth in this study successfully utilizes patient-specific flow and pressure data from phase contrast magnetic resonance images (PCMRI) (n = 1) and retrospective pulse-pressure data from an age-matched patient cohort (n = 10) to verify the compliance of an in vitro TCPC model. These data were analyzed, and the target compliance was determined as 1.36 ± 0.78 mL/mm Hg. A method of in vitro compliance testing and computational simulations was employed to determine the in vitro flexible TCPC model material properties and then use those material properties to estimate the wall thickness necessary to match the patient-specific target compliance. The resulting in vitro TCPC model compliance was 1.37 ± 0.1 mL/mm Hg—a value within 1% of the patient-specific compliance. The presented method is useful to verify in vitro model accuracy of patient-specific TCPC compliance and thus improve patient-specific hemodynamic modeling.

ObjectiveWe previously described lower leg lean mass Z-scores (LLMZ) in Fontan patients associated with worse peak oxygen consumption on metabolic exercise testing. We hypothesised that LLMZ correlates with indexed systemic flow (Qsi) and cardiac index (CI) on exercise cardiac magnetic resonance (eCMR).MethodsThirteen patients had LLM measured by dual-energy X-ray absorptiometry within mean 40 (range 0–258) days of eCMR. LLM was converted to sex and race-specific Z-scores based on healthy reference data. Ventricular volumes and flow measurements of the ascending and descending (DAO) aorta and superior vena cava (SVC) were obtained by CMR at rest and just after supine ergometer exercise to a heart rate associated with anaerobic threshold on prior exercise test. Baseline and peak exercise measures of Qsi (SVC+DAO/BSA) and CI, as well as change in Qsi and CI with exercise, were compared with LLMZ by linear regression.ResultsLLMZ was not correlated with resting flows, stroke volume or CI. There was a strong linear correlation between LLMZ and change in both CI (r=0.77, p=0.002) and Qsi (r=0.73, p=0.005) from rest to exercise. There was also a significant correlation between LLMZ and Qsi at exercise (r=0.70, p=0.008). The correlation between LLMZ and CI at exercise did not reach significance (r=0.3, p=0.07).ConclusionsIn our cohort, there was a strong linear correlation between LLMZ and change in both CI and Qsi from rest to exercise, suggesting that Fontan patients with higher LLMZ may be better able to augment systemic output during exercise, improving performance.

An immersed-boundary numerical method is applied to simulate the wake downstream of a two-dimensional heaving airfoil. A switch of vortex pattern is found to be the major reason that a deflected asymmetric wake reverses its deflection angle. Parameters of the heaving airfoil and flow that influence the onset and location of the vortex switching are discussed. While the previous literature deliberately discussed the wake deflection in the near wake region, this study shows that the deflection angle can change from the near wake to far wake regions. A cross-flow effective phase velocity is introduced to analyze the already-formed asymmetric wake behind the airfoil. A vortex dipole model and the related vortex dynamics analysis are developed to show that the change of the distance between the vortices is the primary factor that leads to the vortex pattern switching in the far wake.

Left ventricular outflow tract (LVOT) obstruction (LVOTO) is a potentially lethal complication that may arise in transcatheter mitral valve replacement (TMVR). Currently, a 2-dimensional (2-D) Neo-LVOT cross-sectional area of

Liver fibrosis is a serious complication in Fontan survivors and potential solutions to stop or delay progression are needed. The purpose of this study is to investigate if prior hemodynamics are predictive of future liver fibrosis in Fontan patients. 21 Fontan patients who underwent cardiac

This paper studies energy harvesting of a two-dimensional foil in the wake downstream of a cylinder. The airfoil is passively mobile in the transverse direction. An immersed-boundary method with a fluid-structure interaction model is validated and employed to carry out the numerical simulation. For improving the numerical stability, a modified low-storage 3rd-order Runge-Kutta scheme is implemented for time integration. The performance of this temporal scheme on reducing spurious pressure oscillations of the immersed-boundary method is demonstrated. The simulation shows a foil emerged in a vortical wake achieves better energy harvesting performance than that in a uniform flow. The types of dynamic response for the energy harvester are identified and the properties of vortical wakes are found to be of pivotal importance in obtaining the desired periodic response of the foil.Copyright © 2016 by ASME

A parallel implementation of an immersed-boundary (IB) method is presented for low Reynolds number flow simulations in a representative elementary volume (REV) of porous media that are composed of a periodic array of regularly arranged structures. The material of the structure in the REV can be solid (impermeable) or microporous (permeable). Flows both outside and inside the microporous media are computed simultaneously by using an IB method to solve a combination of the Navier–Stokes equation (outside the microporous medium) and the Zwikker–Kosten equation (inside the microporous medium). The numerical simulation is firstly validated using flow through the REVs of impermeable structures, including square rods, circular rods, cubes, and spheres. The resultant pressure gradient over the REVs is compared with analytical solutions of the Ergun equation or Darcy–Forchheimer law. The good agreements demonstrate the validity of the numerical method to simulate the macroscopic flow behavior in porous media. In addition, with the assistance of a scientific parallel computational library, PETSc, good parallel performances are achieved. Finally, the IB method is extended to simulate species transport by coupling with the REV flow simulation. The species sorption behaviors in an REV with impermeable/solid and permeable/microporous materials are then studied.

In simulating fluid/solid-particle multiphase -flows, various methods are available. One approach is the combined Euler-Lagrange method, which simulates the fluid phase flow in the Eulerian framework and the discrete phase (particle) motion in the Lagrangian framework simultaneously. The Lagrangian approach, where particle motion is determined by the current state of the fluid phase flow, is also called the discrete phase model (DPM), in the context of numerical flow simulation. In this method, the influence of the particle motions on the fluid flow can be included (two-way interactions) but are more commonly excluded (one-way interactions, when the discrete phase concentration is dilute. The other approach is to treat the particle number concentration as a continuous species, a necessarily passive quantity determined by the fluid flow, with no influences from the particles on the fluid flow (one-way interactions only), except to the extent the discrete phase “continuum” alters the overall fluid properties, such as density. In this paper, we compare these two methods with experimental data for an indoor environmental chamber. The effects of injection particle numbers and the related boundary conditions are investigated. In the Euler-Lagrange interaction or DPM model for incompressible flow, the Eulerian continuous phase is governed by the Reynolds-averaged N-S (RANS) equations. The motions of particles are governed by Newton’s second law. The effects of particle motions are communicated to the continuous phase through a force term in the RANS equations. The second formulation is a pure Eulerian type, where only the particle-number concentration is addressed, rather than the motion of each individual particle. The fluid flow is governed by the same RANS equations without the particle force term. The particle-number concentration is simulated by a species transport equation. Comparisons among the models and with experimental and literature data are presented. Particularly, results with different numbers of released particles in the DPM will be investigated.Copyright © 2012 by ASME