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Sheikh Zayed Institute of Pediatric Surgical Innovation, Children's National Hospital, Washington, DCDivision of Cardiology, Children's National Hospital, Washington, DC
Address for reprints: Laura Olivieri, MD, Division of Pediatric Cardiology, University of Pittsburg Medical Center, Children's Hospital Dr, 4401 Penn Ave, Pittsburgh, PA 15224.
Sheikh Zayed Institute of Pediatric Surgical Innovation, Children's National Hospital, Washington, DCDivision of Pediatric Cardiology, University of Pittsburgh Medical Center, Pittsburgh, Pa
The current total cavopulmonary connection Fontan has competing inflows and outflows, creating hemodynamic inefficiencies that contribute to Fontan failure and complicate placement and efficiency of mechanical circulatory support. We propose a novel convergent cavopulmonary connection (CCPC) Fontan design to create a single, converged venous outflow to the pulmonary arteries, thus increasing efficiency and mechanical circulatory support access. We then evaluate the feasibility and hemodynamic performance of the CCPC in various patient sizes using computational fluid dynamic assessments of computer-aided designs.
Methods
Cardiac magnetic resonance imaging data from 12 patients with single ventricle (10 total cavopulmonary connection, 2 Glenn) physiology (body surface area, 0.5-2.0 m2) were segmented to create 3-dimensional replicas of all thoracic structures. Surgically feasible CCPC shapes within constraints of anatomy were created using iterative computational fluid dynamic and clinician input. Designs varied based on superior and inferior vena cava conduit sizes, coronal attachment height, coronal entry angle, and axial entry angle of the superior vena cava to the inferior vena cava. CCPC designs were optimized based on efficiency (indexed power loss), risk of arteriovenous malformations (hepatic flow distribution), and risk of flow stasis (% nonphysiologic wall shear stress).
Results
All CCPC designs met hemodynamic performance thresholds for indexed power loss and hepatic flow distribution. CCPC designs showed improvements in reducing % nonphysiologic wall shear stress and balancing HFD.
Conclusions
CCPC is physiologically and surgically feasible in various patient sizes using validated computational fluid dynamic models. CCPC configuration has analogous indexed power loss, hepatic flow distribution, and % nonphysiologic wall shear stress compared with total cavopulmonary connection, and the single inflow and outflow may ease mechanical circulatory support therapies. Further studies are required for design optimization and mechanical circulatory support institution.
The convergent cavopulmonary connection eliminates competing inflows and creates a single inflow and outflow, suggesting improved Fontan performance and easier institution of mechanical support.
The so-called failing Fontan population is exponentially growing, and mechanical support options are limited due to the traditional Fontan shape that creates 2 competing venous inflows and separate outflows. The convergent cavopulmonary connection provides streamlined flows and creates a single inflow and outflow, likely improving hemodynamic efficiency and simplifying mechanical support incorporation.
Despite improving outcomes of single ventricle palliation, a significant proportion of patients often develop Fontan failure with elevated venous pressures and low cardiac output.
The current preferred Fontan configuration, known as total cavopulmonary connection (TCPC), relies on passively routing systemic venous return into the pulmonary arteries. This Fontan operation has suboptimal long-term outcomes, including heart failure,
Reference values for exercise limitations among adults with congenital heart disease. Relation to activities of daily life—single centre experience and review of published data.
A multicenter, randomized trial comparing heparin/warfarin and acetylsalicylic acid as primary thromboprophylaxis for 2 years after the Fontan procedure in children.
When Fontan circulation fails, there are limited options for treatment. Cardiac transplant is high-risk, anatomically complicated, may not reverse previous functional deterioration,
Adding mechanical circulatory support (MCS), such as a ventricular assist device, can improve hemodynamics, reduce postsurgical complications, and lengthen the life span of selected Fontan patients.
However, the TCPC's perpendicular competing inflows of the superior vena cava (SVC) and inferior vena cava (IVC), as well as its perpendicular outflows to the branch pulmonary arteries, make MCS institution in a TCPC challenging.
Thus, there is an urgent need for more patient-specific therapies to mitigate the significant challenges present in the current TCPC geometry.
Computational fluid dynamics (CFD) has been an important tool in predicting the hemodynamic parameters in surgical modifications. To optimize Fontan geometry, several parameters in CFD have been considered: lower indexed power loss (iPL) to improve exercise capacity,
Because of their profound clinical implications, these parameters are at the forefront of Fontan research and are key targets in CFD optimization.
We propose a novel convergent cavopulmonary connection (CCPC) Fontan design to eliminate competitive venous inflows and create an access point within a single inflow-single outflow system, thus increasing Fontan efficiency and aiding in MCS incorporation (Figure 1). This study aims to explore the feasibility and hemodynamic performance of the novel CCPC Fontan designs using CFD assessments of computer-aided designs (CAD). We hypothesize that our innovative CCPC designs will not only provide space for easier implantation of an MCS but also improve iPL, HFD, and %WSS measurements.
Figure 1Differences in the total cavopulmonary connection (TCPC) and our novel convergent cavopulmonary connection (CCPC), revealing the superior, inferior, and common limbs of the conduit. The CCPC common limb provides a single inflow and a single outflow to allow easy institution of mechanical circulatory support (MCS). SVC, Superior vena cava; IVC, inferior vena cava.
Virtual cardiac surgical planning through hemodynamics simulation and design optimization of fontan grafts Medical Image Computing and Computer Assisted Intervention - MICCAI 2019. Lecture Notes in Computer Science.
Cardiovascular magnetic resonance imaging datasets from 12 patients with single ventricle (10 TCPC, 2 Glenn) physiology with a body surface area (BSA) of 0.5 to 1.75 m2 (Table 1) and no fenestration were anonymized and exported in Digital Imaging and Communications in Medicine format. These images were collected under approval by the Institutional Review Board of Children's National Health System (No. 00008714, approved August 2, 2017). Cardiac magnetic resonance data included contrast-enhanced magnetic resonance angiography acquired in the late phase with spatial resolution 1.4 × 1.4 mm, and phase contrast imaging for the SVC and IVC and the pulmonary arteries (right pulmonary artery [RPA] and left pulmonary artery [LPA]). Using commercially available image segmentation software (Mimics; Materialise), a 3-dimensional (3D) digital model of the original Fontan was reconstructed through segmentation of the blood pool, including the SVC, IVC, RPA, and LPA. The original Fontan was removed from the 3D reconstruction leaving the SVC, Glenn, IVC, and pulmonary artery bifurcations as fixed targets for the creation of the CCPC. The 3D replica of the cardiothoracic structures was then exported in stereolithography file format, smoothed, and hollowed.
Table 1Patients with single ventricle anatomy included in this study
Model
BSA (m2)
Type
Cardiac anatomy
1
0.52
Bidirectional Glenn
Hypoplastic left heart syndrome
2
0.64
Intra-extra Fontan
Hypoplastic left heart syndrome
3
0.72
Extracardiac Fontan
Hypoplastic left heart syndrome
4
0.73
Bidirectional Glenn
Hypoplastic left heart syndrome
5
0.80
Extracardiac Fontan
Unbalanced atrioventricular canal, bilateral SVC
6
0.89
Lateral tunnel Fontan
Hypoplastic left heart syndrome
7
1.44
Lateral tunnel Fontan
Tricuspid atresia
8
1.45
Extracardiac Fontan
Hypoplastic left heart syndrome
9
1.54
Lateral tunnel Fontan
Double-inlet left ventricle, pulmonary atresia
10
1.64
Lateral tunnel Fontan
Double-outlet right ventricle, remote ventricular septal defect
11
1.65
Lateral tunnel Fontan
Tricuspid atresia
12
1.73
Lateral tunnel Fontan
Transposition of the great arteries
Data are arranged according to ascending BSA by rows. Categories include small (BSA < 0.75 m2), medium (BSA 0.75-1.5 m2), and large (BSA>1.5 m2) models. BSA, Body surface area; SVC, superior vena cava.
Virtual cardiac surgical planning through hemodynamics simulation and design optimization of fontan grafts Medical Image Computing and Computer Assisted Intervention - MICCAI 2019. Lecture Notes in Computer Science.
Time-averaged IVC and SVC flow rates were derived from phase velocity data and prescribed as inlet boundary conditions to the CFD simulations. For the outlet boundary conditions, time-averaged RPA and LPA flow rates were prescribed by the product of outlet flow split (the ratio of RPA:LPA flow) with total venous flow (summation of SVC and IVC flow rate). CFD assumptions included blood as an incompressible fluid and Fontan graft as a rigid wall because previous studies showed rigid wall models have comparable results to the fluid-structure interaction wall models.
Laminar viscosity model was adopted in this steady state simulation, as well as extensions beyond inlets and outlets to create parabolic flow profiles.
The hemodynamic parameters studied in our simulations include iPL across the Fontan, HFD, and %WSS as a marker for thrombosis risk. Hemodynamic thresholds were guided based on previous literature, which include iPL ≤0.03,
Because this is a first-time design study to develop initial feasibility models, our CCPC models were optimized to 1.25 times the published hemodynamic thresholds. Thus, the thresholds we used were: iPL ≤0.0375, HFDbalanced: 35% < HFDLPA < 65%, and %WSS <12.5%.
iPL
iPL is a dimensionless resistive index and is calculated using previous methodology
that accounts for varying systemic venous flows between Fontan cases. The absolute power loss (Ploss) is measured as the difference between the total hemodynamic energy at the inlets and the total hemodynamic energy at the outlets, as shown in Equation 1:
(1)
where Q is flow, is static pressure, is density, and is the velocity vector.
Then, the absolute power loss was indexed against cardiac output and BSA to account for variability in flow rates and patient size, as shown in Equation 2:
(2)
where Qs is systemic venous flow and BSA is body surface area.
HFD
HFD is defined as a ratio of the blood from the IVC to the LPA and RPA. Our HFD calculation is based on particle tracking, where a specific number of particles Ntot were seeded uniformly at the IVC inlet. Ntot was determined by evenly spacing particles across the IVC with a 1 mm spacing factor and 0.1 mm marker size. At the end of the simulation, the number of particles passing through the RPA (NRPA) and LPA (NLPA) outlets was calculated using the velocity field over the last 1000 time steps and averaged.
we denoted luminal surface areas with wall shear stress <1 dyne/cm2 (ArealowWSS) as nonphysiologic. The novel parameter %WSS was calculated using CFD by quantifying the areas of low wall shear stress as a percentage of the total surface area of the Fontan model (AreaFontan), as shown in Equation 4:
(4)
Because addition of the SVC-to-Fontan conduit in the CCPC increases the total surface area of the region of interest, the absolute surface area of low wall shear stress of the CCPC was calculated instead because this parameter relates most closely to the risk of thrombus formation.
Creation of CPCC Conduits
Surgically feasible CCPC shapes within the constraints of the patients' anatomy were created using iterative CFD as outlined in previous work,
partnered with clinician input. The CCPC was designed with 3 limbs: the superior limb (from SVC to the common limb), the inferior limb (from the IVC to the common limb), and the common limb (from the convergence of the superior and inferior limbs to the pulmonary arteries) (Figure 1). Particular attention was made to anatomical restraints imposed by the chest wall, airways, lungs, and cardiac structures such as the aorta, pulmonary arteries, pulmonary veins, and atria (Figure 2). Designs were discarded during 3D virtual fit testing if there were any impingement on vital anatomical structures. All patients had levocardia and normal systemic and pulmonary venous anatomy.
Figure 2Visualization of the total cavopulmonary connection (TCPC) (top) and convergent cavopulmonary connection (CCPC) (bottom) within the chest from anterior (left) and posterior (right) views. Purple indicates TCPC, yellow indicates CCPC, red indicates the heart, blue indicates the lungs, and green indicates the liver.
Depending on the BSA, patients were categorized into small (<0.75 m2), medium (0.75-1.5 m2), and large (>1.5 m2) sizes to explore the feasibility and performance from the time of implantation in toddlerhood until adulthood. Standard materials (circular conduits identical to polytetrafluoroethylene tubes available off-the-shelf) were used in the CCPC designs. For each patient, multiple designs were created and tested based on the following specifications: SVC and IVC conduit sizes (12-20 mm), coronal attachment height (high, middle, or low), coronal entry angle (acute, perpendicular, or obtuse) (Figure 3, A), and axial entry angle (leftward, central, and rightward) (Figure 3, B) for a total of 9 to 21 designs per patient. Additionally, the angulation of the superior limb was also evaluated at 5 angles along the transverse plane, incrementing every 15° from 0° in the anterior-posterior view to 60° in the right anterior oblique view (Figure 4, A).
Figure 3The convergent cavopulmonary connection (CCPC), tested by coronal level of entry of the superior conduit (high, middle, and low) and coronary angle of entry (acute, perpendicular, and obtuse) (A) and axial angle of entry (leftward, central, and rightward) (B). SVC, Superior vena cava; P, posterior; IVC, inferior vena cava; R, right; L, left; A, anterior.
Figure 4Adjusting hepatic flow distribution by the angulation of superior limb insertion. A, Our novel convergent cavopulmonary connection (CCPC) designs shown in 3 views, demonstrating the 5 angles along the transverse plane that were measured. B, Effects of superior limb angulation on flow into the pulmonary arteries (PAs). SVC, Superior vena cava; AP, anterior-posterior; RAO, right anterior oblique; IVC, inferior vena cava.
Both native and CCPC designs were evaluated by CFD under steady-state conditions, with SVC/IVC/outflow boundary conditions provided by phase contrast measurements. CFD calculated an approximation of the efficiency (in terms of iPL), risk of arteriovenous malformations (in terms of HFD), and risk of flow stasis (in terms of %WSS) using Navier-Stokes equations. This iterative process continued until acceptable thresholds were met for all three variables in the CCPC and compared with native TCPC. These conditions are standard in our lab and have been used in prior published CFD studies.
Virtual cardiac surgical planning through hemodynamics simulation and design optimization of fontan grafts Medical Image Computing and Computer Assisted Intervention - MICCAI 2019. Lecture Notes in Computer Science.
CCPC and TCPC values between each model were compared using unpaired, nonparametric Kolmogorov-Smirnov tests due to the small sample size. Two-tailed P values were calculated using Prism version 9 (GraphPad Software). Then, scatter plots of the results were generated also using Prism.
Results
CCPC Designs
CCPC designs using off-the-shelf digital conduit materials were anatomically feasible in all 12 models. Across the board, the lowest entry of the superior limb into the IVC had the best performance for iPL in all models, irrespective of the conduit size or the angle of entry in the coronal or the axial plane. Similarly, the perpendicular entry of the superior limb was most consistently optimal in our CCPC designs according to CFD, allowing for the colliding of SVC and IVC flow rather than the contradicting flow present in TCPC.
Conduit sizes and axial angle of entry were tailored to the patient's specific anatomy to create the most optimal CCPC designs in all 12 models. The diameters of the superior, inferior, and common limbs were varied during test conditions from 12 to 20 mm, and the most optimal combination of sizes for each limb was selected using iterative testing. A summary of the optimal design parameters, in terms of SVC conduit size, IVC conduit size, coronal attachment height, coronal entry angle, and axial entry angle, found in each of the 12 models using CFD can be found in Table E1.
Hemodynamic Performance of the CCPC
The raw iPL, HFD, and %WSS data for all 12 models, both TCPC and CCPC, are shown in Table 2. All CCPC designs met hemodynamic performance thresholds for iPL and HFD. The iPL noted in the TCPC models was 0.025 0.016, whereas the iPL of the CCPC models was 0.027 0.008. There were no differences observed between the TCPC and CCPC in terms of iPL (P = .248). However, 3 out of 10 CCPC models had improved iPL hemodynamic performance under the 0.0375 threshold.
Table 2Comparison of total cavopulmonary connection (TCPC) and convergent cavopulmonary connection (CCPC) designs with respect to indexed power loss (iPL), hepatic flow distribution (HFD), and percent nonphysiologic wall shear stress (%WSS)
Boldface type indicates values that are not within our chosen thresholds for iPL (≤0.0375), HFD (<35% or >65%), and %WSS (<12.5%).
iPL
HFD(%LPA)
%WSS
Model
BSA
TCPC
CCPC
TCPC
CCPC
TCPC
CCPC
1
0.52
0.031
0.036
20
40
60.04
33.3
2
0.64
0.015
0.024
24
59
39.93
1.20
3
0.72
0.007
0.005
22
42
21.45
54.12
4
0.73
0.064
0.030
31
43
1.34
2.75
5
0.8
0.022
0.029
58
53
31.80
18.08
6
0.89
0.030
0.027
43
49
3.56
6.07
7
1.44
0.011
0.025
19
47
12.14
0.51
8
1.45
0.046
0.027
43
53
4.15
2.04
9
1.54
0.022
0.027
35
58
10.81
0.90
10
1.64
0.048
0.030
31
65
21.34
0.94
11
1.65
0.019
0.022
50
50
7.67
1.10
12
1.73
0.012
0.037
92
40
30.45
0.57
Mean SD
0.025 0.016
0.027 0.008
38.9 19.8
49.8 7.6
20.39 17.63
10.13 17.02
P value
.248
.034
.034
Data are arranged according to ascending BSA by rows. Categories include small (BSA < 0.75 m2), medium (BSA 0.75-1.5 m2), and large (BSA>1.5 m2) models. iPL, Indexed power loss; HFD, hepatic flow distribution; LPA, left pulmonary artery; %WSS, percent nonphysiologic wall shear stress; BSA, body surface area; TCPC, total cavopulmonary connection; CCPC, convergent cavopulmonary connection; SD, standard deviation.
∗ Boldface type indicates values that are not within our chosen thresholds for iPL (≤0.0375), HFD (<35% or >65%), and %WSS (<12.5%).
Moreover, the HFD%LPA calculated in the TCPC models was 38.9 19.8, whereas the HFD%LPA of the CCPC models was 49.8 7.6. We also observed a difference between the TCPC and CCPC in terms of HFD (P = .034). Eight out of 12 CCPC models had improved HFD hemodynamic performance to fall within the 35% to 65% LPA range. Notably, there were profound variations in HFD when the axial angle of entry of the superior limb was adjusted. Changing the right anterior oblique angle of the superior limb insertion influenced the streaming of the SVC flow into the RPA, thereby adjusting hepatic flow from the IVC into the LPA (Figure 4, B). Thus, we demonstrate overall flow improvements in all 12 models in terms of iPL and HFD.
Lastly, there was general improvement in reducing %WSS in our CCPC designs (P = .034). The %WSS found in the TCPC models was 20.39 17.63, whereas the %WSS of the CCPC models was 10.13 17.02. Reduction in %WSS was seen in 9 out of 12 CCPC models. Of note, the patients in the 3 CCPC models that did not meet the %WSS threshold (models 1, 3, and 5) had a BSA <0.8 m2. A scatter plot comparison of the TCPC and CCPC data for iPL, HFD, and %WSS is shown in Figure 5.
Figure 5Scatterplots comparing the total cavopulmonary connection (TCPC) and our novel convergent cavopulmonary connection (CCPC) data for indexed power loss (A), hepatic flow distribution (B), and percent nonphysiologic wall shear stress (C). The bold line in the middle denotes the mean and the error bars represent SDs. LPA, Left pulmonary artery.
We propose and successfully evaluate a novel Fontan configuration, known as CCPC, which converges the SVC and IVC flows. This design eliminates the competing and opposing inflows and provides a single inflow and outflow within the Fontan conduit, thus simplifying implantation of MCS. Our exploratory work demonstrates that the CCPC configuration was a feasible option across a range of sizes in 12 selected patients with normal systemic and pulmonary venous drainage. These conduits can be designed without impingement of other thoracic structures and without increasing hemodynamic inefficiency, hepatic flow maldistribution, or %WSS, a marker for flow stasis and thrombosis.
Despite profound improvements in operative survival of patients with single ventricle physiology, long-term outcomes of Fontan patients are complicated by poor exercise tolerance,
CFD assessments of CADs have been successfully used to provide insights and create designs for Fontan conduits that minimize iPL across the Fontan circuit to maximize its efficiency.
Computational fluid dynamics in the evaluation of hemodynamic performance of cavopulmonary connections after the Norwood procedure for hypoplastic left heart syndrome.
However, the fundamental issue with TCPC is its basic configuration, wherein the SVC and IVC inflows oppose each other, potentially leading to vortical flow formation and energy loss.
Segmental assessment of blood flow efficiency in the total cavopulmonary connection using four-dimensional flow magnetic resonance imaging: vortical flow is associated with increased viscous energy loss rate.
Any MCS to help promote forward flow would therefore require 2 inflows (SVC and IVC) and 2 outflows (both branch pulmonary arteries), which is not currently incorporated into device designs. The requirement for multiple inflows and outflows make insertion of MCS in this circuit very challenging, fraught with recirculation
The CCPC conduit achieves iPL comparable to TCPC configurations. Although our design completely reverses the SVC flow direction by 180°, any additional power loss is compensated for by eliminating IVC and SVC flow competition at the cavopulmonary connection in the TCPC. HFD was also effectively improved by the angulation of the superior limb insertion, suggesting CCPC as a potential solution to controlling the balance of HFD in Fontan flow. All CCPC conduits were constructed with standard 12 to 20 mm grafts, which leaves room for further optimization by the creation of patient-specific CCPC conduits.
The attempt to minimize potential for thrombus formation in the CCPC was incorporated into the design through use of the %WSS variable based on prior studies.
Virtual cardiac surgical planning through hemodynamics simulation and design optimization of fontan grafts Medical Image Computing and Computer Assisted Intervention - MICCAI 2019. Lecture Notes in Computer Science.
This study revealed that our CCPC conduits were able to achieve considerably lower %WSS compared with TCPC. Although the clinical implications of %WSS are yet to be validated
this would theoretically imply lower thromboembolic complications with CCPC relative to the current TCPC models. We also noticed that smaller patients (BSA <0.8 m2) demonstrated higher %WSS, which may require a different anticoagulation approach in future work. This study does not reflect a comprehensive thrombosis assessment, but rather an initial exploration of this new CCPC geometry that will be further investigated to minimize thrombosis risks.
Theoretically, the optimal strategy for providing circulatory support in Fontan patients would depend on the etiology of circulatory failure. For example, insertion of mechanical circulatory support devices into Fontan patients in the setting of ventricular dysfunction has been successful in selected groups of patients.
The ideal situation would be to create a future where failing Fontan patients had multiple options for stable, safe circulatory support.
Whereas others have been focusing on improving Fontan efficiency or designing TCPC specific devices separately, we have adopted the unique approach of combining both objectives with our novel design. Not only does the CCPC configuration provide potential benefits in its native (unassisted) state compared with TCPC, but also the single inflow and single outflow offered by the CCPC modification would greatly simplify the institution of MCS in Fontan patients by providing an ideal target for addition of a subpulmonary propulsion device. Speculatively, the device could be intraluminal (ie, an Impella [Abiomed] type pump placed transvenously) or it could be a surgically implanted device replacing the common limb of the CCPC. Because our proposed CCPC is advantageous for the placement of a future assist device, patients requiring Fontan revision and insertion of MCS would be ideal early candidates. However, additional data are needed before we can determine whether or not the CCPC should be considered as a primary Fontan design in selected, high-risk patients or as a reoperative procedure after Fontan failure.
Although this surgical operation requires the SVC be divided off the pulmonary arteries, it will not be prohibitive for congenital cardiac surgeons to incorporate this disconnection. The SVC will have to be mobilized circumferentially, rather than mobilized with a snare or clamp around it in a typical Fontan operation. Additionally, the cranial part of the SVC to RPA connection may require patch closure. Although these incremental steps would add to surgical time, it may avert the risk of a failing Fontan.
This study is limited because it is only an early feasibility study using clinical imaging datasets from a selected group of patients. Wider feasibility and application of this configuration needs to be investigated using datasets from a heterogeneous group of patients with wider anatomical variations. The CCPC may not be a solution for every anatomic type because it requires a single superior limb and therefore a single SVC. In the case of bilateral SVCs, the technique may require converging bilateral SVC flows before converging SVC and IVC flows. Evaluating feasibility of CCPC in patients with anatomical variations will be our focus in future studies.
We also recognize that our novel design requires additional polytetrafluoroethylene due to the longer SVC limb (approximately 3 cm), which could be a risk of thrombosis, particularly at the junction of the SVC and IVC grafts previously seen in the Y-split Fontan configuration.
However, similarly sized conduits carrying only hepatic blood flow have historically been used for Fontan completion after a Kawashima operation, with no prominence of higher thrombosis risk. Notably, the choice of conduit is limited by materials currently available for clinical use. In future studies, we intend to create more efficient CCPC conduits using tissue-engineered hemocompatible biomaterials aimed to reduce thrombosis risk.
Moreover, this study uses solely CFD assessments of CAD models, which requires further validation and fitting using 3D-printed models in a mock circulatory benchtop flow loop and polytetrafluoroethylene conduits in large animal models. Our CAD models also represent the blood pool, which does not take into account neo-intimal hyperplasia; however, limitations in imaging technology prevent the ability to reliably image and segment wall thickness. This would also require repeat cross-sectional imaging data, likely using longitudinal computed tomography images over several years, which we do not perform due to frequent imaging with radiation. Therefore, the blood pool extracted from magnetic resonance imaging data with a standard thickness applied is an acceptable method of using 3D shapes to model and validate hemodynamics because the outer wall does not play a significant role.
Our hemodynamic thresholds for iPL, HFD, and %WSS were also relaxed to create our initial feasibility models. The direct comparison of these fluid dynamic parameters between the TCPC and CCPC is also limited due to the CFD assumption that resistance within the cardiovascular system, and thus the distribution of inflow from the IVC and SVC and outflow to the LPA and RPA, remains constant. In real physiological situations, the total flow rates would change as the resistance of the graft changes. Other assumptions such as steady state flow and laminar viscosity model would also affect the accuracy of result compared with that under physiological conditions. Future work will aim to optimize our CFD simulation so that our models accurately fit within published literature thresholds for these parameters. Lastly, the feasibility and ease of incorporating MCS therapies in the CCPC needs to be further evaluated. Because the SVC conduit covers the posterior side of the graft, axial or intraluminal MCS will be the main target device for CCPC.
Overall, the CCPC is both physiologically and surgically feasible within a variety of patient sizes using validated CFD models. The CCPC configuration has comparable iPL to its native TCPC model. Lower %WSS and more balanced HFD compared with TCPC may imply an improvement in thromboembolic or pulmonary AVM complications within the CCPC design. The single inflow and outflow may also ease MCS therapies, but further studies are required for CCPC design optimization and MCS institution.
Conflict of Interest Statement
The authors reported no conflicts of interest.
The Journal policy requires editors and reviewers to disclose conflicts of interest and to decline handling or reviewing manuscripts for which they may have a conflict of interest. The editors and reviewers of this article have no conflicts of interest.
Appendix E1
Table E1Optimal convergent cavopulmonary connection design parameters for each model predicted by computation fluid dynamics
Model
BSA (m2)
SVC conduit size (mm)
IVC conduit size (mm)
Coronal attachment height
Coronal entry angle
Axial entry angle
1
0.52
12
16
Low
Perpendicular
Central
2
0.64
12
20
Low
Perpendicular
Leftward
3
0.72
12
18
Low
Perpendicular
Rightward
4
0.73
12
16
Low
Perpendicular
Central
5
0.80
12
18
Low
Perpendicular
Central
6
0.89
12
22
Low
Perpendicular
Leftward
7
1.44
12
18
Low
Perpendicular
Rightward
8
1.45
14
22
Low
Perpendicular
Leftward
9
1.54
12
22
Low
Perpendicular
Leftward
10
1.64
14
22
Low
Perpendicular
Leftward
11
1.65
12
22
Low
Perpendicular
Central
12
1.73
14
22
Low
Perpendicular
Leftward
Data are arranged according to ascending BSA by rows. Categories include small (BSA < 0.75 m2), medium (BSA 0.75-1.5 m2), and large (BSA>1.5 m2) models. BSA, Body surface area; SVC, superior vena cava; IVC, inferior vena cava.
Reference values for exercise limitations among adults with congenital heart disease. Relation to activities of daily life—single centre experience and review of published data.
A multicenter, randomized trial comparing heparin/warfarin and acetylsalicylic acid as primary thromboprophylaxis for 2 years after the Fontan procedure in children.
Virtual cardiac surgical planning through hemodynamics simulation and design optimization of fontan grafts Medical Image Computing and Computer Assisted Intervention - MICCAI 2019. Lecture Notes in Computer Science.
Computational fluid dynamics in the evaluation of hemodynamic performance of cavopulmonary connections after the Norwood procedure for hypoplastic left heart syndrome.
Segmental assessment of blood flow efficiency in the total cavopulmonary connection using four-dimensional flow magnetic resonance imaging: vortical flow is associated with increased viscous energy loss rate.
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