Individualized computer-based surgical planning to address pulmonary arteriovenous malformations in patients with a single ventricle with an interrupted inferior vena cava and azygous continuation

Impact of Age-Related Change in Caval Flow Ratio on Hepatic Flow Distribution in the Fontan Circulation

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 conduit or a lateral tunnel 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. The effect of age-related changes in caval inflows on HFD was evaluated using cardiac magnetic resonance data and patient-specific computational fluid dynamics modeling.

METHODS

SVC and IVC flow from 414 patients with Fontan were collected to establish a relationship between SVC:IVC flow ratio and age. Computational fluid dynamics modeling was performed in 60 (30 extracardiac and 30 lateral tunnel) 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 extracardiac but statistically significant for lateral tunnel cohorts. For all 3 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 to 0.5 (age, 3-15+) years, the correlation's strength decreased from 0.87 to 0.64, due to potential flow perturbation as IVC flow momentum increased.

CONCLUSIONS

Our analysis provided quantitative insights into the impact of the changing caval inflows on Fontan's long-term HFD, highlighting the importance of SVC:IVC variations over time on Fontan's long-term hemodynamics. These findings broaden our understanding of Fontan hemodynamics and patient outcomes.

Impact of Age-related change in Caval Flow Ratio on Hepatic Flow Distribution in Fontan

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.

The prediction and verification of outcome of extracardiac conduits fontan based on computational fluid dynamics simulation

Objective: This study applied preoperative computed tomography angiography (CTA) and computational fluid dynamics (CFD) simulation to predicte and verify the outcome of Y-shaped extracardiac conduits Fontan for functional single ventricle. Methods: Based on the preoperative CTA data of functional single ventricle (FSV), 4 types of spatial structures of extracardiac conduits were designed for 4 experimental groups: Group A, a traditional TCPC group (20 mm); Group B, a diameter-preserving Y-shaped TCPC (YCPC) group (branch 10 mm); Group C, YCPC group (branch 12 mm); and Group D, an area-preserving YCPC group (branch14 mm). Four indicators including flow velocity, pressure gradient (PG), energy efficiency and inferior vena cava (IVC) blood flow distribution were compared. The optimal procedure was applied. The radionuclide lung perfusion, CTA, echocardiography, cardiovascular angiography and catheterization were performed postoperatively. Results: There were the lowest PG, the lowest flow velocity of branches, the highest energy efficiency, and a relatively balanced and stable distribution of IVC flow for group D. Subsequently, the group D, a handcrafted Y-shaped conduit (14 mm) was used for the YCPC procedure. There was no postoperative PG between the conduit and pulmonary artery with normal pressure and resistance. IVC flow was distributed uniformly. Conclusion: CTA-based CFD provided more guidance for the clinical application of TCPC. A comprehensive surgical design could bring good postoperative outcome. Area-preserving YCPC has more advantages than TCPC and the diameter-preserving YCPC. The study effectively improved the feasibility of clinical applications of YCPC.

Virtual treatment planning in three patients with univentricular physiology using computational fluid dynamics—Pitfalls and strategies

Background

Uneven hepatic venous blood flow distribution (HFD) to the pulmonary arteries is hypothesized to be responsible for the development of intrapulmonary arteriovenous malformations (PAVM) in patients with univentricular physiology. Thus, achieving uniform distribution of hepatic blood flow is considered favorable. However, no established method for the prediction of the post-interventional hemodynamics currently exists. Computational fluid dynamics (CFD) offers the possibility to quantify HFD in patient-specific anatomies before and after virtual treatment. In this study, we evaluated the potential benefit of CFD-assisted treatment planning.

Materials and methods

Three patients with total cavopulmonary connection (TCPC) and PAVM underwent cardiovascular magnetic resonance imaging (CMR) and computed tomography imaging (CT). Based on this imaging data, the patient-specific anatomy was reconstructed. These patients were considered for surgery or catheter-based intervention aiming at hepatic blood flow re-routing. CFD simulations were then performed for the untreated state as well as for different surgical and interventional treatment options. These treatment options were applied as suggested by treating cardiologists and congenital heart surgeons with longstanding experience in interventional and surgical treatment of patients with univentricular physiology. HFD was quantified for all simulations to identify the most viable treatment decision regarding redistribution of hepatic blood flow.

Results

For all three patients, the complex TCPC anatomy could be reconstructed. However, due to the presence of metallic stent implants, hybrid models generated from CT as well as CMR data were required. Numerical simulation of pre-interventional HFD agreed well with angiographic assessment and physiologic considerations. One treatment option resulting in improvement of HFD was identified for each patient. In one patient follow-up data after treatment was available. Here, the virtual treatment simulation and the CMR flow measurements differed by 15%.

Conclusion

The combination of modern computational methods as well as imaging methods for assessment of patient-specific anatomy and flow might allow to optimize patient-specific therapy planning in patients with pronounced hepatic flow mismatch and PAVM. In this study, we demonstrate that these methods can also be applied in patients with complex univentricular physiology and extensive prior interventions. However, in those cases, hybrid approaches utilizing information of different image modalities may be required.

Predicting Hemodynamic Performance of Fontan Operation for Glenn Physiology using Computational Fluid Dynamics: Ten Patient-specific Cases

Single ventricle hearts have only one ventricle that can pump blood effectively and the treatment requires three stages of operations to reconfigure the heart and circulatory system. At the second stage, Glenn procedure is performed to connect superior vena cava (SVC) to the pulmonary arteries (PA). For the third and most complex operation, called Fontan, an extracardiac conduit is used to connect inferior vena cava (IVC) to the PL and thereafter no deoxygenated blood goes to the heart. Predicting Hemodynamic Performance of Fontan Operation using computational fluid dynamics (CFD) is hypothesized to improve outcomes and optimize this treatment planning in children with single-ventricle heart disease. An important reason for this surgical planning is to reduce the development of pulmonary arteriovenous malformations (PAVM) and the need to perform Fontan revisions. The purpose of this study was to develop amodel for Fontan surgical planning and use this model to compare blood circulation in two designed graft types of Fontan operation known as T-shape and Y-graft. The functionality of grafts was compared in terms of power loss (PL) and hepatic flow distribution (HFD), a known factor in PAVM development. To perform this study, ten single-ventricle children with Glenn physiology were included and a CFD model was developed to estimate the blood flow circulation to the left and right pulmonary arteries. The estimated blood flow by CFD was compared with that measured by cardiovascular magnetic resonance. Results showed that there was an excellent agreement between the net blood flow in the right and left pulmonary arteries computed by CFD and CMR (ICC= 0.98, P-value ≥0.21). After validating the accuracy of each CFD model, Fontan operations using T-shape and Y-graft conduits were performed in silico for each patient and the developed CFD model was used to predict the post-surgical PL and HFD. We found that the PL in the Y-graft was significantly lower than in the T-shape (P-value ≤0.001) and HFD was significantly better balanced in Y-graft compared to the T-shape (P-value=0.004).

Interventional Planning for Endovascular Revision of a Lateral Tunnel Fontan: A Patient-Specific Computational Analysis

Introduction

A 2-year-old female with hypoplastic left heart syndrome (HLHS)-variant, a complex congenital heart defect (CHD) characterized by the underdevelopment of the left ventricle, presented with complications following single ventricle palliation. Diagnostic work-up revealed elevated Fontan pathway pressures, as well as significant dilation of the inferior Fontan pathway with inefficient swirling flow and hepatic venous reflux. Due to the frail condition of the patient, the clinical team considered an endovascular revision of the Fontan pathway. In this work, we performed a computational fluid dynamics (CFD) analysis informed by data on anatomy, flow, and pressure to investigate the hemodynamic effect of the endovascular Fontan revision.

Methods

A patient-specific anatomical model of the Fontan pathway was constructed from magnetic resonance imaging (MRI) data using the cardiovascular modeling software CardiovasculaR Integrated Modeling and SimulatiON (CRIMSON). We first created and calibrated a pre-intervention 3D-0D multi-scale model of the patient’s circulation using fluid-structure interaction (FSI) analyses and custom lumped parameter models (LPMs), including the Fontan pathway, the single ventricle, arterial and venous systemic, and pulmonary circulations. Model parameters were iteratively tuned until simulation results matched clinical data on flow and pressure. Following calibration of the pre-intervention model, a custom bifurcated endograft was introduced into the anatomical model to virtually assess post-intervention hemodynamics.

Results

The pre-intervention model successfully reproduced the clinical hemodynamic data on regional flow splits, pressures, and hepatic venous reflux. The proposed endovascular repair model revealed increases of mean and pulse pressure at the inferior vena cava (IVC) of 6 and 29%, respectively. Inflows at the superior vena cava (SVC) and IVC were each reduced by 5%, whereas outflows at the left pulmonary artery (LPA) and right pulmonary artery (RPA) increased by 4%. Hepatic venous reflux increased by 6%.

Conclusion

Our computational analysis indicated that the proposed endovascular revision would lead to unfavorable hemodynamic conditions. For these reasons, the clinical team decided to forgo the proposed endovascular repair and to reassess the management of this patient. This study confirms the relevance of CFD modeling as a beneficial tool in surgical planning for single ventricle CHD patients.

A Tribute to Ajit Yoganathan's Cardiovascular Fluid Mechanics Lab: A Survey of Its Contributions to Our Understanding of the Physiology and Management of Single-Ventricle Patients

INTRODUCTION

Among patients with congenital heart disease, those born with only a single working ventricle represent a particularly complex sub-population, typically requiring multiple surgeries and suffering from high levels of mortality and morbidity. Their cardiac care is complex and has evolved considerably since surgical palliation was first introduced more than 50 years ago. Improvements in treatment have been driven both by growing clinical experience and by knowledge gained through experimental and computational studies of blood flow in these patients. The Cardiovascular Fluid Mechanics Lab at the Georgia Institute of Technology, founded 30 years ago by Dr. Ajit Yoganathan, has pioneered work in this field.

METHODS

In this review, key contributions of Dr. Yoganathan's Cardiovascular Fluid Dynamics Lab are surveyed, including experimental flow loop studies as well as computational fluid dynamics analyses that address many of the critical challenges that cardiologists and surgeons face in treating these patients, including how to reconstruct cardiovascular anatomy to minimize power loss, balance blood flow distribution at key bifurcation points, and avoid other unfavorable hemodynamic conditions.

CONCLUSIONS

Among many contributions in this field, work from the Cardiovascular Fluid Mechanics Lab has led to novel medical devices and patient-specific computational modeling workflows and software tools. These key contributions from this group have enhanced our understanding of the physiology and management of single-ventricle patients.

Is Doppler Echocardiography Adequate for Surgical Planning of Single Ventricle Patients?

PURPOSE

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.

METHODS

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).

RESULTS

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.

CONCLUSION

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.

Emerging 3D technologies and applications within congenital heart disease: teach, predict, plan and guide

3D visualization technologies have evolved to become a mainstay in the management of congenital heart disease (CHD) with a growing presence within multiple facets. Printed and virtual 3D models allow for a more comprehensive approach to educating trainees and care team members. Computational fluid dynamics can take 3D modeling to the next level, by predicting post-procedural outcomes and helping to determine surgical approach. 3D printing and extended reality are developing resources for pre-procedural planning and intra-procedural guidance with the potential to revolutionize decision-making and procedural success. Challenges still remain within existing technologies and their applications to the CHD field. Addressing these gaps, both by those within and outside of CHD, will transform education and patient care within our field.

Novel surgical strategy for complicated pulmonary stenosis using haemodynamic analysis based on a virtual operation with numerical flow analysis

OBJECTIVES

A novel surgical strategy using haemodynamic analyses based on virtual operations with computational simulations has been introduced for complicated pulmonary stenosis. We evaluated the efficacy of this strategy.

METHODS

Six patients were enrolled. Before surgery, the optimal pulmonary arteries were constructed based on computational fluid dynamics using 3-dimensional computed tomography. Energy loss (EL, mW) and wall shear stress (WSS, Pa) were calculated. We compared the shapes of preoperative and optimal pulmonary arteries to determine the surgical strategy, including the incision line and the shape of the patch (virtual surgery). EL and WSS were compared between virtual and actual surgeries using flow analysis.

RESULTS

In both the virtual and actual surgeries, postoperative EL tended to be lower than the preoperative EL, although there were no significant differences (P = 0.12 and P = 0.17, respectively). The mean WSS in the virtual surgery was significantly reduced from 112 ± 130 Pa to 25 ± 24 Pa (P = 0.028). After the actual surgery, the mean WSS was also significantly reduced to 30 ± 23 Pa (P = 0.047). There were no significant differences in the values for EL and WSS before and after surgery or between virtual and actual surgery (P = 0.94 and P = 0.85, respectively).

CONCLUSIONS

Pulmonary artery plasty, using computational fluid dynamics based on virtual surgery, is an efficient surgical strategy. This novel strategy can easily and successfully provide an optimal pulmonary artery plasty equivalent to that using the conventional approach, which is based on the surgeon's personal experience and judgement.

Evaluation and Management of the Child and Adult With Fontan Circulation: A Scientific Statement From the American Heart Association

It has been 50 years since Francis Fontan pioneered the operation that today bears his name. Initially designed for patients with tricuspid atresia, this procedure is now offered for a vast array of congenital cardiac lesions when a circulation with 2 ventricles cannot be achieved. As a result of technical advances and improvements in patient selection and perioperative management, survival has steadily increased, and it is estimated that patients operated on today may hope for a 30-year survival of >80%. Up to 70 000 patients may be alive worldwide today with Fontan circulation, and this population is expected to double in the next 20 years. In the absence of a subpulmonary ventricle, Fontan circulation is characterized by chronically elevated systemic venous pressures and decreased cardiac output. The addition of this acquired abnormal circulation to innate abnormalities associated with single-ventricle congenital heart disease exposes these patients to a variety of complications. Circulatory failure, ventricular dysfunction, atrioventricular valve regurgitation, arrhythmia, protein-losing enteropathy, and plastic bronchitis are potential complications of the Fontan circulation. Abnormalities in body composition, bone structure, and growth have been detected. Liver fibrosis and renal dysfunction are common and may progress over time. Cognitive, neuropsychological, and behavioral deficits are highly prevalent. As a testimony to the success of the current strategy of care, the proportion of adults with Fontan circulation is increasing. Healthcare providers are ill-prepared to tackle these challenges, as well as specific needs such as contraception and pregnancy in female patients. The role of therapies such as cardiovascular drugs to prevent and treat complications, heart transplantation, and mechanical circulatory support remains undetermined. There is a clear need for consensus on how best to follow up patients with Fontan circulation and to treat their complications. This American Heart Association statement summarizes the current state of knowledge on the Fontan circulation and its consequences. A proposed surveillance testing toolkit provides recommendations for a range of acceptable approaches to follow-up care for the patient with Fontan circulation. Gaps in knowledge and areas for future focus of investigation are highlighted, with the objective of laying the groundwork for creating a normal quality and duration of life for these unique individuals.

Outcomes of Single Ventricle Patients Undergoing the Kawashima Procedure: Can We Do Better?

Objectives:

Current technology advances in virtual surgery modeling and computational flow dynamics allow preoperative individualized computer-based design of Fontan operation. To determine potential role of those innovations in patients undergoing hepatic vein incorporation (HVI) following Kawashima operation, we retrospectively examined historic cohort of patients who underwent HVI following Kawashima with focus on regression of pulmonary arteriovenous malformations (PAVMs).

Methods:

Twenty-two children with single ventricle and interrupted inferior vena cava underwent Kawashima operation (2002-12). Twenty-one (96%) patients had left atrial isomerism and 21 (96%) had undergone prior first-stage palliation. Clinical outcomes were examined.

Results:

Mean O2 saturation (SaO2) increased from 77% ± 8% to 85% ± 6% ( P = .002) after Kawashima. Fifteen (68%) patients developed PAVMs. Eighteen patients underwent HVI (median age and interval from Kawashima: 4.4 and 3.7 years, respectively). Mean SaO2 prior to HVI was 77% ± 8% and increased to 81% ± 10% at the time of hospital discharge ( P = .250), with five patients requiring home oxygen. On follow-up, mean SaO2 increased to 95% ± 4% ( P < .001). Overall ten-year survival following Kawashima was 94%.

Conclusions:

A large number of patients develop PAVMs and subsequent cyanosis after Kawashima operation. Early following HVI, SaO2 is commonly low and insignificantly different from that prior to HVI. Although SaO2 will improve on follow-up in most patients, a number of patients continue to have low saturations, indicating incomplete resolution of PAVMs. Given the heterogeneity of those patients and lack of preoperative predictors for complete PAVM regression, our findings suggest a role for virtual surgery to determine optimal individual procedure design that would provide even distribution of hepatic blood flow to both pulmonary arteries.

Numerical Investigation of the Effect of Additional Pulmonary Blood Flow on Patient-Specific Bilateral Bidirectional Glenn Hemodynamics

The effect of additional pulmonary blood flow (APBF) on the hemodynamics of bilateral bidirectional Glenn (BBDG) connection was marginally discussed in previous studies. This study assessed this effect using patient-specific numerical simulation. A 15-year-old female patient who underwent BBDG was enrolled in this study. Patient-specific anatomy, flow waveforms, and pressure tracings were obtained using computed tomography, Doppler ultrasound technology, and catheterization, respectively. Computational fluid dynamic simulations were performed to assess flow field and derived hemodynamic metrics of the BBDG connection with various APBF. APBF showed noticeable effects on the hemodynamics of the BBDG connection. It suppressed flow mixing in the connection, which resulted in a more antegrade flow structure. Also, as the APBF rate increases, both power loss and reflux in superior venae cavae (SVCs) monotonically increases while the flow ratio of the right to the left pulmonary artery (RPA/LPA) monotonically decreases. However, a non-monotonic relationship was observed between the APBF rate and indexed power loss. A high APBF rate may result in a good flow ratio of RPA/LPA but with the side effect of bad power loss and remarkable reflux in SVCs, and vice versa. A moderate APBF rate could be favourable because it leads to an optimal indexed power loss and achieves the acceptable flow ratio of RPA/LPA without causing severe power loss and reflux in SVCs. These findings suggest that patient-specific numerical simulation should be used to assist clinicians in determining an appropriate APBF rate based on desired outcomes on a patient-specific basis.

Patient-Specific Modeling of Hemodynamics: Supporting Surgical Planning in a Fontan Circulation Correction

Computational fluid dynamics (CFD) is a modeling technique that enables calculation of the behavior of fluid flows in complex geometries. In cardiovascular medicine, CFD methods are being used to calculate patient-specific hemodynamics for a variety of applications, such as disease research, noninvasive diagnostics, medical device evaluation, and surgical planning. This paper provides a concise overview of the methods to perform patient-specific computational analyses using clinical data, followed by a case study where CFD-supported surgical planning is presented in a patient with Fontan circulation complicated by unilateral pulmonary arteriovenous malformations. In closing, the challenges for implementation and adoption of CFD modeling in clinical practice are discussed.

Current Interventional and Surgical Management of Congenital Heart Disease: Specific Focus on Valvular Disease and Cardiac Arrhythmias

Successful outcome in the care of patients with congenital heart disease depends on a comprehensive multidisciplinary team. Surgery is offered for almost every heart defect, despite complexity. Early mortality for cardiac surgery in the neonatal period is ≈10% and beyond infancy is <5%, with 90% to 95% of patients surviving with a good quality of life into the adult years. Advances in imaging have facilitated accurate diagnosis and planning of interventions and surgical procedures. Similarly, advances in the perioperative medical management of patients, particularly with intensive care, has also contributed to improving outcomes. Arrhythmias and heart failure are the most common late complications for the majority of defects, and reoperation for valvar problems is common. Lifelong surveillance for monitoring of recurrent or residual structural heart defects, as well as periodic assessment of cardiac function and arrhythmia monitoring, is essential for all patients. The field of congenital heart surgery is poised to incorporate new innovations such as bioengineered cells and scaffolds that will iteratively move toward bioengineered patches, conduits, valves, and even whole organs.

Percutaneous Transhepatic Fontan-Kreutzer Completion of Hepatic Vein Inclusion

We report the case of an 11-year-old girl with heterotaxy syndrome, dextrocardia, and azygos continuation of an interrupted inferior vena cava who had developed pulmonary arteriovenous fistulas after a Kawashima procedure consisting of bilateral superior cavopulmonary anastomoses. She presented with profound cyanosis, fatigue, and failure to thrive. An operative procedure to direct hepatic vein effluent to the pulmonary circulation was performed with placement of an extracardiac conduit between the hepatic veins and the left pulmonary artery. Persistence of cyanosis led to investigation, which led to the discovery of an unintentionally excluded right hepatic vein. A percutaneous transhepatic catheter intervention was performed in which a vascular plug was implanted to occlude the "missed" right hepatic vein, redirecting the flow through intrahepatic venovenous channels to the conduit. Clinical condition and arterial oxygen saturation were substantially improved one year after the two-step hepatic vein inclusion procedure.

Can time-averaged flow boundary conditions be used to meet the clinical timeline for Fontan surgical planning?

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.

Synchronization of the Flow and Pressure Waves Obtained With Non-Simultaneous Multipoint Measurements

The use of measured data as boundary conditions renders hemodynamic simulations more patient-specific. However, synchronized acquisition of data at multiple locations is often difficult in clinical practice. This study proposes a method for resynchronizing measured data for use as boundary conditions for flow simulations using frequency analyses, and discusses the optimal cut-off frequency for differentiating cardiac and respiratory variation in hemodynamic data during resynchronization. To demonstrate the utility of the method, a Fontan circulation, which is the final palliative result with single-ventricle physiology, was used. The results suggest that it is optimal to set a cut-off frequency that gives a local minimum in the power spectrum that is slightly lower than the peak frequency of the heartbeat. Additionally, the total energy loss depended on the cut-off frequency, although the overall flow patterns appeared to be similar. The method is applicable to cardiovascular systems other than the Fontan circulation, where hemodynamic data with multifactorial fluctuations are required at various locations but simultaneous measurements are not possible.

Hemodynamic Impact of Superior Vena Cava Placement in the Y-Graft Fontan Connection

BACKGROUND

A Fontan Y-shaped graft using a commercially available aortoiliac graft has been used to connect the inferior vena cava (IVC) to the pulmonary arteries. This modification of the Fontan procedure seeks to improve hepatic flow distribution (HFD) to the lungs. However, patient-specific anatomical restrictions might limit the space available for graft placement. Altering the superior vena cava (SVC) positioning is hypothesized to provide more space for an optimal connection, avoiding caval flow collision. Computational modeling tools were used to retrospectively study the effect of SVC placement on Y-graft hemodynamics.

METHODS

Patient-specific anatomies (N = 10 patients) and vessel flows were reconstructed from retrospective cardiac magnetic resonance (CMR) images after Fontan Y-graft completion. Alternative geometries were created using a virtual surgery environment, altering the SVC position and the offset in relation to the Y-graft branches. Geometric characterization and computational fluid dynamics simulations were performed. Hemodynamic factors (power loss and HFD) were computed.

RESULTS

Patients with a higher IVC return showed less sensitivity to SVC positioning. Patients with low IVC flow showed varied HFD results, depending on SVC location. Balanced HFD values (50% to each lung) were obtained when the SVC lay completely between the Y-graft branches. The effect on power loss was patient specific.

CONCLUSIONS

SVC positioning with respect to the Y-graft affects HFD, especially in patients with lower IVC flow. Careful positioning of the SVC at the time of a bidirectional Glenn (BDG) procedure based on patient-specific anatomy can optimize the hemodynamics of the eventual Fontan completion.

Older Age at Completion of Fontan Procedure Is Associated with Improved Percentage of Predicted Maximum Oxygen Uptake

We tested the hypothesis that later completion of the Fontan procedure is associated with improved exercise capacity in the current period of staged single-ventricle palliation. We performed a retrospective study, in Fontan patients, of exercise stress test data from April 2003 through March 2011. Patients were included if they had received staged palliations in accordance with current surgical strategy, defined as the performance of a superior cavopulmonary connection at ≤1 year of age, followed in subsequent years by Fontan completion. Patients with a pacemaker or respiratory exchange ratio <1 were excluded. Early and late Fontan groups were created on the basis of whether Fontan completion had been performed at <4 or ≥ 4 years of age. The primary predictor variable was age at Fontan completion, and the primary marker of exercise performance was the percentage of predicted maximum oxygen consumption. During the study period, 55 patients were identified (mean age, 11.7 ± 2.8 yr). Older age at Fontan completion correlated positively with higher percentages of predicted maximum oxygen consumption (R=0.286, P=0.034). Patients in whom Fontan completion was performed at ≥4 years of age had higher percentages of predicted maximum oxygen consumption than did those in whom completion was at <4 years of age (84.4 ± 21.5 vs 72.9 ± 18.1; P=0.041). Later Fontan completion might be associated with improved exercise capacity in patients palliated in accordance with contemporary surgical strategy.

Patient-Specific Surgical Planning, Where Do We Stand? The Example of the Fontan Procedure

The Fontan surgery for single ventricle heart defects is a typical example of a clinical intervention in which patient-specific computational modeling can improve patient outcome: with the functional heterogeneity of the presenting patients, which precludes generic solutions, and the clear influence of the surgically-created Fontan connection on hemodynamics, it is acknowledged that individualized computational optimization of the post-operative hemodynamics can be of clinical value. A large body of literature has thus emerged seeking to provide clinically relevant answers and innovative solutions, with an increasing emphasis on patient-specific approaches. In this review we discuss the benefits and challenges of patient-specific simulations for the Fontan surgery, reviewing state of the art solutions and avenues for future development. We first discuss the clinical impact of patient-specific simulations, notably how they have contributed to our understanding of the link between Fontan hemodynamics and patient outcome. This is followed by a survey of methodologies for capturing patient-specific hemodynamics, with an emphasis on the challenges of defining patient-specific boundary conditions and their extension for prediction of post-operative outcome. We conclude with insights into potential future directions, noting that one of the most pressing issues might be the validation of the predictive capabilities of the developed framework.

Using 4D Cardiovascular Magnetic Resonance Imaging to Validate Computational Fluid Dynamics: A Case Study

Computational fluid dynamics (CFD) can have a complementary predictive role alongside the exquisite visualization capabilities of 4D cardiovascular magnetic resonance (CMR) imaging. In order to exploit these capabilities (e.g., for decision-making), it is necessary to validate computational models against real world data. In this study, we sought to acquire 4D CMR flow data in a controllable, experimental setup and use these data to validate a corresponding computational model. We applied this paradigm to a case of congenital heart disease, namely, transposition of the great arteries (TGA) repaired with arterial switch operation. For this purpose, a mock circulatory loop compatible with the CMR environment was constructed and two detailed aortic 3D models (i.e., one TGA case and one normal aortic anatomy) were tested under realistic hemodynamic conditions, acquiring 4D CMR flow. The same 3D domains were used for multi-scale CFD simulations, whereby the remainder of the mock circulatory system was appropriately summarized with a lumped parameter network. Boundary conditions of the simulations mirrored those measured in vitro. Results showed a very good quantitative agreement between experimental and computational models in terms of pressure (overall maximum % error = 4.4% aortic pressure in the control anatomy) and flow distribution data (overall maximum % error = 3.6% at the subclavian artery outlet of the TGA model). Very good qualitative agreement could also be appreciated in terms of streamlines, throughout the cardiac cycle. Additionally, velocity vectors in the ascending aorta revealed less symmetrical flow in the TGA model, which also exhibited higher wall shear stress in the anterior ascending aorta.

Surgical planning of the total cavopulmonary connection: robustness analysis

In surgical planning of the Fontan connection for single ventricle physiologies, there can be differences between the proposed and implemented options. Here, we developed a surgical planning framework that help determine the best performing option and ensures that the results will be comparable if there are slight geometrical variations. Eight patients with different underlying anatomies were evaluated in this study; surgical variations were created for each connection by changing either angle, offset or baffle diameter. Computational fluid dynamics were performed and the energy efficiency (indexed power loss-iPL) and hepatic flow distribution (HFD) computed. Differences with the original connection were evaluated: iPL was not considerably affected by the changes in geometry. For HFD, the single superior vena cava (SVC) connections presented less variability compared to the other anatomies. The Y-graft connection was the most robust overall, while the extra-cardiac connections showed dependency to offset. Bilateral SVC and interrupted inferior vena cava with azygous continuation showed high variability in HFD. We have developed a framework to assess the robustness of a surgical option for the TCPC; this will be useful to assess the most complex cases where pre-surgery planning could be most beneficial to ensure an efficient and robust hemodynamic performance.

Magnetic resonance imaging-guided surgical design: can we optimise the Fontan operation?

The Fontan procedure, although an imperfect solution for children born with a single functional ventricle, is the only reconstruction at present short of transplantation. The haemodynamics associated with the total cavopulmonary connection, the modern approach to Fontan, are severely altered from the normal biventricular circulation and may contribute to the long-term complications that are frequently noted. Through recent technological advances, spear-headed by advances in medical imaging, it is now possible to virtually model these surgical procedures and evaluate the patient-specific haemodynamics as part of the pre-operative planning process. This is a novel paradigm with the potential to revolutionise the approach to Fontan surgery, help to optimise the haemodynamic results, and improve patient outcomes. This review provides a brief overview of these methods, presents preliminary results of their clinical usage, and offers insights into its potential future directions.

Fontan conversion templates: patient-specific hemodynamic performance of the lateral tunnel versus the intraatrial conduit with fenestration

Intraatrial-conduit Fontan is considered a modification of both extracardiac and lateral-tunnel Fontan. In this study, the patient-specific hemodynamic performance of intraatrial-conduit and lateral-tunnel Fontan with fenestration, considered as conversion templates, was investigated based on the authors' patient cohort. Pulsatile computational fluid dynamics simulations were performed using patient-specific models of intraatrial-conduit and lateral-tunnel Fontan patients. Real-time "simultaneous" inferior and superior vena cava, pulmonary artery, and fenestration flow waveforms were acquired from ultrasound. Multiple hemodynamic performance indices were investigated, with particular focus on evaluation of the pulsatile flow performance. Power loss inside the lateral-tunnel Fontan appeared to be significantly higher than with the intraatrial-conduit Fontan for patient-specific cardiac output and normalized connection size. Inclusion of the 4-mm fenestration at a 0.24 L/min mean flow resulted in a lower cavopulmonary pressure gradient and less time-averaged power loss for both Fontan connections. Flow structures within the intraatrial conduit were notability more uniform than within the lateral tunnel. Hepatic flow majorly favored the left lung in both surgical connections: conversion from lateral-tunnel to intraatrial-conduit Fontan resulted in better hemodynamics with less power loss, a lower pressure gradient, and fewer stagnant flow zones along the conduit. This patient-specific computational case study demonstrated superior hemodynamics of intraatrial-conduit Fontan over those of lateral-tunnel Fontan with or without fenestration and improved performance after conversion of the lateral tunnel to the intraatrial conduit. The geometry-specific effect of the nonuniform hepatic flow distribution may motivate new rationales for the surgical design.

Simulating hemodynamics of the Fontan Y-graft based on patient-specific in vivo connections

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.

Treatment planning for a TCPC test case: a numerical investigation under rigid and moving wall assumptions

The hemodynamics in patients with total cavopulmonary connections (TCPC) is generally very complex and characterized by patient-to-patient variability. To better understand its effect on patients' outcome, CFD models are widely used, also to test and optimize surgical options before their implementation. These models often assume rigid geometries, despite the motion experienced by thoracic vessels that could influence the hemodynamics predictions. By improving their accuracy and expanding the range of simulated interventions, the benefit of treatment planning for patients is expected to increase. We simulate three types of intervention on a patient-specific 3D model, and compare their predicted outcome with baseline condition: a decrease in pulmonary vascular resistance obtainable with medications; a surgical revision of the connection design; the introduction of a fenestration in the TCPC wall. The simulations are performed both with rigid wall assumption and including patient-specific TCPC wall motion, reconstructed from a 4DMRI dataset. The results show the effect of each option on clinically important metrics and highlight the impact of patient-specific wall motion. The largest differences between rigid and moving wall models are observed in measures of energetic efficiency of TCPC as well as in hepatic flow distribution and transit time of seeded particles through the connection.

An integrated approach to patient-specific predictive modeling for single ventricle heart palliation

In patients with congenital heart disease and a single ventricle (SV), ventricular support of the circulation is inadequate, and staged palliative surgery (usually 3 stages) is needed for treatment. In the various palliative surgical stages individual differences in the circulation are important and patient-specific surgical planning is ideal. In this study, an integrated approach between clinicians and engineers has been developed, based on patient-specific multi-scale models, and is here applied to predict stage 2 surgical outcomes. This approach involves four distinct steps: (1) collection of pre-operative clinical data from a patient presenting for SV palliation, (2) construction of the pre-operative model, (3) creation of feasible virtual surgical options which couple a three-dimensional model of the surgical anatomy with a lumped parameter model (LPM) of the remainder of the circulation and (4) performance of post-operative simulations to aid clinical decision making. The pre-operative model is described, agreeing well with clinical flow tracings and mean pressures. Two surgical options (bi-directional Glenn and hemi-Fontan operations) are virtually performed and coupled to the pre-operative LPM, with the hemodynamics of both options reported. Results are validated against postoperative clinical data. Ultimately, this work represents the first patient-specific predictive modeling of stage 2 palliation using virtual surgery and closed-loop multi-scale modeling.

Predictive modeling of the virtual Hemi-Fontan operation for second stage single ventricle palliation: two patient-specific cases

Single ventricle hearts are congenital cardiovascular defects in which the heart has only one functional pumping chamber. The treatment for these conditions typically requires a three-staged operative process where Stage 1 is typically achieved by a shunt between the systemic and pulmonary arteries, and Stage 2 by connecting the superior venous return to the pulmonary circulation. Surgically, the Stage 2 circulation can be achieved through a procedure called the Hemi-Fontan, which reconstructs the right atrium and pulmonary artery to allow for an enlarged confluence with the superior vena cava. Based on pre-operative data obtained from two patients prior to Stage 2 surgery, we developed two patient-specific multi-scale computational models, each including the 3D geometrical model of the surgical junction constructed from magnetic resonance imaging, and a closed-loop systemic lumped-parameter network derived from clinical measurements. "Virtual" Hemi-Fontan surgery was performed on the 3D model with guidance from clinical surgeons, and a corresponding multi-scale simulation predicts the patient's post-operative hemodynamic and physiologic conditions. For each patient, a post-operative active scenario with an increase in the heart rate (HR) and a decrease in the pulmonary and systemic vascular resistance (PVR and SVR) was also performed. Results between the baseline and this "active" state were compared to evaluate the hemodynamic and physiologic implications of changing conditions. Simulation results revealed a characteristic swirling vortex in the Hemi-Fontan in both patients, with flow hugging the wall along the SVC to Hemi-Fontan confluence. One patient model had higher levels of swirling, recirculation, and flow stagnation. However, in both models, the power loss within the surgical junction was less than 13% of the total power loss in the pulmonary circulation, and less than 2% of the total ventricular power. This implies little impact of the surgical junction geometry on the SVC pressure, cardiac output, and other systemic parameters. In contrast, varying HR, PVR, and SVR led to significant changes in theses clinically relevant global parameters. Adopting a work-flow of customized virtual planning of the Hemi-Fontan procedure with patient-specific data, this study demonstrates the ability of multi-scale modeling to reproduce patient specific flow conditions under differing physiological states. Results demonstrate that the same operation performed in two different patients can lead to different hemodynamic characteristics, and that modeling can be used to uncover physiologic changes associated with different clinical conditions.

Numerical and experimental investigation of pulsatile hemodynamics in the total cavopulmonary connection

Computational fluid dynamics (CFD) tools have been extensively applied to study the hemodynamics in the total cavopulmonary connection (TCPC) in patients with only a single functioning ventricle. Without the contraction of a sub-pulmonary ventricle, pulsatility of flow through this connection is low and variable across patients, which is usually neglected in most numerical modeling studies. Recent studies suggest that such pulsatility can be non-negligible and can be important in hemodynamic predictions. The goal of this work is to compare the results of an in-house numerical methodology for simulating pulsatile TCPC flow with experimental results. Digital particle image velocimetry (DPIV) was acquired on TCPC in vitro models to evaluate the capability of the CFD tool in predicting pulsatile TCPC flow fields. In vitro hemodynamic measurements were used to compare the numerical prediction of power loss across the connection. The results demonstrated the complexity of the pulsatile TCPC flow fields and the validity of the numerical approach in simulating pulsatile TCPC flow dynamics in both idealized and complex patient specific models.

Preliminary clinical experience with a bifurcated Y-graft Fontan procedure--a feasibility study

OBJECTIVE

Optimizing flow and diminishing power loss in the Fontan circuit can improve hemodynamic efficiency, potentially improving the long-term outcomes. Computerized modeling has predicted improved energetics with a Y-graft Fontan.

METHODS

From August to December 2010, 6 consecutive children underwent completion Fontan (n=3) or 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 to the right and left pulmonary arteries with separate graft limbs. The patents underwent magnetic resonance imaging (n=5) or computed tomography (n=1). Computational fluid dynamics assessed Fontan hemodynamics, power loss, and inferior vena cava flow splits to the branch pulmonary arteries. The clinical parameters were compared with those from 12 patients immediately preceding the present series who had undergone a lateral Fontan procedure.

RESULTS

Despite longer crossclamp and bypass times (not statistically significant), the Y-graft Fontan patients had postoperative courses similar to those of the conventional Fontan patients. Other than 2 early readmissions for pleural effusions managed with diuretics, at 6 to 12 months of follow-up (mean, 8 months), all 6 patients had done well. Postoperative flow modeling demonstrated a balanced distribution of inferior vena cava flow to both pulmonary arteries 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 pulmonary arteries.

CONCLUSIONS

The present preliminary surgical experience has demonstrated the clinical feasibility of the bifurcated Y-graft Fontan. Computational fluid dynamics showed acceptable hemodynamics with low calculated power losses and a balanced distribution of inferior vena cava flow to the pulmonary arteries as long as the branch grafts were anastomosed distally.

Comparing pre- and post-operative Fontan hemodynamic simulations: implications for the reliability of surgical planning

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.