Pulmonary arteriovenous malformations after cavopulmonary anastomosis

Estimation of pulmonary vascular resistance for Glenn physiology

Children with single ventricle heart disease typically require a series of three operations, (1) Norwood, (2) Glenn, and (3) Fontan, which ultimately results in complete separation of the pulmonary and systemic circuits to improve pulmonary/systemic circulation. In the last stage, the Fontan operation, the inferior vena cava (IVC) is connected to the pulmonary arteries (PAs), allowing the remainder of deoxygenated blood to passively flow to the pulmonary circuit. It is hypothesized that optimizing the Fontan anatomy would lead to decreased power loss and more balanced hepatic flow distribution. One approach to optimizing the geometry is to create a patient-specific digital twin to simulate various configurations of the Fontan conduit, which requires a computational model of the proximal PA anatomy and resistance, as well as the distal Pulmonary Vascular Resistance (PVR), at the Glenn stage. To that end, an optimization pipeline was developed using 3D computational fluid dynamics (CFD) and 0D lumped parameter (LP) simulations to iteratively refine the PVR of each lung by minimizing the simulated flow and pressure error relative to patients' cardiac magnetic resonance (CMR) and catheterization (CATH) data. While the PVR can also be estimated directly by computing the ratio of pressure gradients and flow from CATH and CMR data, the computational approach can separately identify the different components of PVR along the Glenn pathway, allowing for a more detailed depiction of the Glenn vasculature. Results indicate good correlation between the optimized PVR of the CFD and LP models (n = 16), with an intraclass correlation coefficient (ICC) of 0.998 (p = 0.976) and 0.991 (p = 0.943) for the left and right lung, respectively. Furthermore, compared to CMR flow and CATH pressure data, the optimized PVR estimates result in mean outlet flow and pressure errors of less than 5%. The optimized PVR estimates also agree well with the computed PVR estimates from CATH pressure and CMR flow for both lungs, yielding a mean difference of less than 4%.

Outcomes of Patients Undergoing the Kawashima Procedure at an Early Age: A Single Center Experience

BACKGROUND

Previous reports have demonstrated the safety and efficacy of performing early Kawashima procedure (KP). Despite this, more recent studies have shown that the average age at the time of operation remains greater than one year of age. We report our experience with performing KP at an earlier age than previously reported.

METHODS

A retrospective review was completed of patients undergoing KP at a single center (January 2000 to June 2020). Clinical outcomes were examined.

RESULTS

Initial palliation was performed in 11 out of 12 patients. Age and weight at time of KP were 8.25 months (6.4-9.7) and 7.7 kg (6.5-8.6). Intensive care unit stay was 3.16 days (1-12), overall length of stay was 9.5 days (3-22). There was one unplanned reoperation, and no mortality in the cohort. Discharge oxygen saturation was 88% (80%-98%). Seven patients developed pulmonary arteriovenous malformations (PAVMs) with six proceeding to hepatic vein incorporation (HVI). Interval time to development of PAVMs was 42.3 months (16-121). Four of the 12 patients were left with antegrade pulmonary blood flow (PBF) and three (75%) remain without PAVMs. Median follow-up was 10 years (1.5-22) with 11 of 12 (91.67%) survival for the cohort.

CONCLUSIONS

The KP can be done at a younger age than previously reported with adequate early and late results. Most patients will go on to develop PAVMs and require HVI but leaving patients with some antegrade PBF is likely protective but will need further investigation to show definitive benefit.

Glenn circulation causes early and progressive shunting in a surgical model of pulmonary arteriovenous malformations

Background

Pulmonary arteriovenous malformations (PAVMs) universally develop in patients with single ventricle congenital heart disease (CHD). Single ventricle PAVMs have been recognized for over 50 years, yet they are poorly understood, and we lack any medical therapies. To improve our understanding of single ventricle PAVM initiation and progression, we developed a surgical rat model of Glenn circulation and characterized PAVM physiology over multiple time points.

Methods

Using adult rats, we performed a left thoracotomy and end-to-end anastomosis of the left superior vena cava to the left pulmonary artery (unilateral Glenn), or sham surgical control. To assess for PAVM physiology in the left lung, we quantified intrapulmonary shunting using two independent methods (bubble echocardiography and fluorescent microsphere injection) at 2 weeks, 2 months, and 6 months. Additionally, we performed arterial blood gas measurements to assess oxygenation and plethysmography to assess ventilation.

Results

We identified pathologic intrapulmonary shunting by bubble echocardiography as early as 2 weeks post-Glenn surgery, and shunting continued chronically at 2- and 6-months post-Glenn. Shunting also progressed over time, demonstrated by increased shunting of 10µm microspheres at 6 months. Shunting was accompanied by mildly decreased arterial oxygenation, but there were no differences in ventilation as quantified by plethysmography.

Conclusions

Our surgical animal model of unilateral Glenn circulation re-creates the clinical condition of single ventricle PAVMs with early and progressive intrapulmonary shunting. This model is poised to characterize single ventricle PAVM pathophysiology and lead to mechanistic and therapeutic discovery.

Graphic Abstract

In vivo hepatic flow distribution by computational fluid dynamics can predict pulmonary flow distribution in patients with Fontan circulation

In Fontan patients, a lung deprived of hepatic blood may develop pulmonary arterio-venous malformations (PAVMs) resulting in shunting, reduced pulmonary vascular resistance (PVR) and decreased oxygenation. To provide guidance for corrective invasive interventions, we aimed to non-invasively determine how the hepatic to pulmonary blood flow balance correlates with pulmonary flow, PVR, and with oxygen saturation. Magnetic resonance imaging (MRI) data from eighteen Fontan patients (eight females, age 3-14 years) was used to construct patient-specific computational fluid dynamics (CFD) models to calculate the hepatic to pulmonary blood flow. This was correlated with pulmonary vein flow, simulated PVR and oxygen saturation. Clinical applicability of the findings was demonstrated with an interventional patient case. The hepatic to pulmonary blood flow balance correlated with right/left pulmonary vein flow (R2 = 0.50), left/right simulated PVR (R2 = 0.47), and oxygen saturation at rest (R2 = 0.56). In the interventional patient, CFD predictions agreed with post-interventional MRI measurements and with regressions in the cohort. The balance of hepatic blood to the lungs has a continuous effect on PVR and oxygen saturation, even without PAVM diagnosis. MRI combined with CFD may help in planning of surgical and interventional designs affecting the hepatic to pulmonary blood flow balance in Fontan patients.

Impact of pulmonary artery flow distribution on Fontan hemodynamics and flow energetics

BACKGROUND

With improved life expectancy following Fontan palliation, there is an increasing population of patients with a total cavopulmonary connection. However, there is a poor understanding of which patients will experience Fontan failure and when. 4D flow MRI has identified several metrics of clinical interest, but longitudinal studies investigating hemodynamics in Fontan patients are lacking.

OBJECTIVE

We aimed to investigate the relationship between flow distribution to the pulmonary arteries and regional hemodynamic metrics in a unique cohort with follow-up 4D flow MRI.

MATERIALS AND METHODS

Patients with > 6 months of 4D flow MRI follow-up were included. Flow distribution from the caval veins to pulmonary arteries was measured in addition to regional measures of peak velocity, viscous energy loss (EL_mean and EL_tot), and kinetic energy.

RESULTS

Ten patients with total cavopulmonary connection (17.7 ± 8.8 years at baseline, follow-up: 4.4 ± 2.6 years) were included. Five subjects had unequal flow distribution from the IVC to the pulmonary arteries at baseline. Over time, these subjects tended to have larger increases in peak velocity (39.2% vs 6.6%), EL_mean (11.6% vs -38.3%), EL_tot (9.5% vs -36.2%), and kinetic energy (96.1% vs 36.3%) in the IVC. However, these differences were statistically insignificant. We found that changes in EL_mean and EL_tot were significantly associated with changes in peak velocity in the caval veins (R² > 0.5, P < 0.001).

CONCLUSION

Unequal flow distribution from the IVC may drive increasing peak velocities and viscous energy losses, which have been associated with worse clinical outcomes. Changes in peak velocity may serve as a surrogate measure for changes in viscous energy loss.

Update on pulmonary arteriovenous malformations

This review aimed to provide an overview of pulmonary arteriovenous malformations, including the major clinical and radiological presentations, investigation, and treatment algorithm of the condition. The primary etiology of pulmonary arteriovenous malformations is hereditary hemorrhagic telangiectasia (HHT), also known as Rendu-Osler-Weber syndrome, with mutations in the ENG gene on chromosome 9 (HHT type 1) or in the ACVRL1/ALK1 complex (HHT type 2). Epistaxis should always be evaluated when repeated, when associated with anemia, and in some cases of hypoxemia. In the investigation, contrast echocardiography and chest CT are essential for evaluating this condition. Embolization is the best treatment choice, especially for correction in cases of hypoxemia or to avoid systemic infections. Finally, disease management was addressed in special conditions such as pregnancy. CT follow-up should be performed every 3-5 years, depending on the size of the afferent and efferent vessels, and antibiotic prophylactic care should always be oriented. Ultimately, knowledge of the disease by health professionals is a crucial point for the early diagnosis of these patients in clinical practice, which can potentially modify the natural course of the disease.

The Secrets of the Frogs Heart

The heart of the African clawed frog has a double-inlet and single-outlet ventricle supporting systemic and pulmonary circulations via a truncus, and a lifespan of 25-30 years. We sought to understand the unique cardiac anatomic and physiologic characteristics, with balanced circulation and low metabolic rate, by comparing the basic anatomy structures with focused echocardiography and cardiac magnetic resonance imaging. Twenty-four adult female African clawed frogs were randomly subjected to anatomic dissection (n = 4), echocardiography (n = 10), and cardiac magnetic resonance (n = 10). All anatomical features were confirmed and compared with echocardiography and cardiac magnetic resonance imaging. The main characteristics of the cardiovascular circulation in frogs are the following: Intact interatrial septum, with two separate atrio-ventricular valves, preventing atrial mixing of oxygenated and desaturated blood. Single spongiform ventricular cavity, non-conducive for homogeneous mixing. Single outlet with a valve-like mobile spiral structure, actively streaming into systemic and pulmonary arteries. Intact interatrial septum, spongiform ventricle, and valve-like spiral in the conus arteriosus are likely responsible for balanced systemic and pulmonary circulation in frogs, in spite of double-inlet and single-outlet ventricle.

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.

Pulmonary Arteriovenous Malformations: What the Interventional Radiologist Should Know

Pulmonary arteriovenous malformations (PAVMs) are abnormal connections between the pulmonary artery and pulmonary vein bypassing the normal capillary bed causing a right-to-left shunt. The majority (80-90%) of PAVMs are associated with hereditary hemorrhagic telangiectasia (HHT). PAVMs may be asymptomatic or present with symptoms of hypoxia, shortness of breath, migraines, sequelae of paradoxical embolization, or rupture. Transcatheter embolization has become the standard of care. This article will review the clinical presentation, workup, genetics, imaging findings, embolization, complications, and follow-up for patients with PAVMs.

Transcatheter implantation of covered stents serving as extravascular conduits-Proof of a CT-based approach in three cases

BACKGROUND

Covered stents perform similar to surgically implanted conduits, although the stents work inside of vessels. We present a computed tomography (CT)-based workflow for the implantation of covered stents as extravascular conduits.

METHODS

We selected three different use cases: 1. Connecting a left-sided partially anomalous drainage of a pulmonary vein to the left atrium. 2. Bypassing an outgrown Dacron conduit in aortic recoarctation. 3. Re-directing hepatic venous blood to the left lung in a Fontan patient with heterotaxy, connecting the innominate vein to the right pulmonary artery like a right-sided cavopulmonary connection. By postprocessing and analyzing CT scans for planning and by the use of long needles under biplane fluoroscopy for the realization of the procedure, we projected and performed the exit of a long needle out of a vessel, the re-entering of a target vessel, and the bridging of the extravascular distance by implantation of covered stents.

RESULTS

In all three cases, the covered stents were placed successfully, connecting vessels of 15-50 mm distance from each other with very good hemodynamic results. In one case, two stents were placed consecutively, overlapping each other to accomplish an exact fitting at the connection sites to the native vessels.

Semi-Automatic Planning and Three-Dimensional Electrospinning of Patient-Specific Grafts for Fontan Surgery

This paper proposes a semi-automatic Fontan surgery planning method for designing and manufacturing hemodynamically optimized patient-specific grafts. Fontan surgery is a palliative procedure for patients with a single ventricle heart defect by creating a new path using a vascular graft for the deoxygenated blood to be directed to the lungs, bypassing the heart. However, designing patient-specific grafts with optimized hemodynamic performance is a complex task due to the variety of patient-specific anatomies, confined surgical planning space, and the requirement of simultaneously considering multiple design criteria for vascular graft optimization. To address these challenges, we used parameterized Fontan pathways to explore patient-specific vascular graft design spaces and search for optimal solutions by formulating a nonlinear constrained optimization problem, which minimizes indexed power loss (iPL) of the Fontan model by constraining hepatic flow distribution (HFD), percentage of abnormal wall shear stress (%WSS) and geometric interference between Fontan pathways and the heart models (InDep) within clinically acceptable thresholds. Gaussian process regression was employed to build surrogate models of the hemodynamic parameters as well as InDep and [Formula: see text] (conduit model smoothness indicator) for optimization by pattern search. We tested the proposed method on two patient-specific models (n=2). The results showed the automatically optimized (AutoOpt) Fontan models hemodynamically outperformed or at least are comparable to manually optimized Fontan models with significantly reduced surgical planning time (15 hours versus over 2 weeks). We also demonstrated feasibility of manufacturing the AutoOpt Fontan conduits by using electrospun nanofibers.

Biventricular Repair Conversion After Temporary One and a Half Ventricular Repair for Hypoplastic Right Ventricle

This was an infant with critical pulmonary stenosis at birth. A temporary one and a half ventricular repair (1.5VR) was performed to increase right ventricular end diastolic volume (RVEDV) and the size of the tricuspid valve annuls before biventricular repair conversion. The 1.5VR was performed using a unidirectional bicval Glenn anastomosis. The RVEDV at 3 years was 73.2% of normal value but with a 64/36 right/left lung perfusion ratio. An anatomical biventricular correction included by removal of the bicaval_Glenn shunt and reconstruction of the contimuity between the right and main pulmonary artery. The 1.5VR made the reconstruction feasible.

Reappraisal of lung manifestations in the setting of Fontan circulation

Fontan circulation is a well-established palliation in patients with functional single ventricles. Absence of a sub-pulmonary pumping chamber creates a unique physiology in which blood flow is mainly guided by negative intrathoracic and elevated central venous pressures. Various pulmonary anatomic or pathophysiologic changes can jeopardize optimal Fontan circulation. Long-term survival of patients who have undergone the contemporary total cavopulmonary connection is satisfactory. Thorough literature review in conjunction with accumulated clinical experience can lead clinicians to extract conclusions regarding Fontan and lung interactions indicating the purpose of this review.

Hepatopulmonary Syndrome and Portopulmonary Hypertension: Pulmonary Vascular Complications of Liver Disease

Pulmonary vascular disease is a frequent complication of chronic liver disease and portal hypertension, affecting up to 30% of patients. There are two distinct pulmonary vascular complications of liver disease: hepatopulmonary syndrome (HPS) and portopulmonary hypertension (POPH). HPS affects 25% of patients with chronic liver disease and is characterized by intrapulmonary vasodilatation and abnormal arterial oxygenation. HPS negatively impacts quality of life and is associated with a 2-fold increased risk of death compared to controls with liver disease without HPS. Angiogenesis, endothelin-1 mediated endothelial dysfunction, monocyte influx, and alveolar type 2 cell dysfunction seem to play important roles in disease pathogenesis but there are currently no effective medical therapies. Fortunately, HPS resolves following liver transplant (LT) with improvements in hypoxemia. POPH is a subtype of pulmonary arterial hypertension (PAH) characterized by an elevated mean pulmonary arterial pressure and pulmonary vascular resistance in the setting of normal left-sided filling pressures. POPH affects 5% to 6% of patients with chronic liver disease. Although the pathogenesis has not been fully elucidated, endothelial dysfunction, inflammation, and estrogen signaling have been identified as key pathways involved in disease pathogenesis. POPH is typically treated with PAH targeted therapy and may also improve with liver transplantation in selected patients. This article highlights what is currently known regarding the diagnosis, management, pathobiology, and outcomes of HPS and POPH. Ongoing research is needed to improve understanding of the pathophysiology and outcomes of these distinct and often misunderstood pulmonary vascular complications of liver disease. © 2021 American Physiological Society. Compr Physiol 11:1-22, 2021.

Asking Bubbles for Direction: Assessment of a Classic Glenn Shunt Using Agitated Saline Contrast Echocardiography

•

Glenn shunt is a common palliative surgery for congenital heart disease.

•

PAVMs are a frequent complication.

•

A saline contrast study can show bubbles first appearing in the left atrium.

•

Treatment options include coil embolization and surgery.

Percutaneous salvage interventions in the Glenn circuit: a case series

Background

In majority of children bidirectional Glenn shunt is a safe and efficacious procedure with minimal post-operative issues. Rarely, there may be dysfunction in the Glenn pathway due loss of anatomical integrity or derangements in normal physiological or hemodynamic milieu. We report 4 cases in the last 3 years (2016-2019) where complications in the Glenn circuit led to serious consequences requiring transcatheter interventions.

Case presentation

Two of our patients presented with frank features of superior vena cava syndrome. One of them had right Glenn anastomotic site narrowing leading to severe obstruction along with significant left pulmonary artery origin stenosis. The other child had excessive antegrade flow impeding normal Glenn flow leading to superior vena cava syndrome. The next child in our series was initially lost to follow-up after bidirectional Glenn surgery. Later on, this child was noted to have discontinuous left pulmonary artery with perfusion only to the right lung from the Glenn. The remaining child described in this series had developed a large tortuous venous collateral post Glenn shunt leading to severe cyanosis. All the above children needed prompt percutaneous interventions to revert back to their basal state. On follow-up, the benefit was sustained in all.

Conclusions

Percutaneous intervention procedures often provide a successful bailout option in various complicated situations post Glenn surgery with reasonable efficacy and safety.

Pulmonary arteriovenous malformations in children after the Kawashima procedure: Risk factors and midterm outcome

Background:

Pulmonary arteriovenous malformations (PAVMs) are the major cause of progressive cyanosis in patients palliated with bidirectional cavopulmonary connection (BCPC). The aim of our study is to analyze the occurrence of PAVMs in patients after Kawashima procedure, to study the effect of total cavopulmonary connection (TCPC) on PAVMs, to evaluate the effect of axillary arteriovenous fistula (AAVF) creation on PAVMs, and to study the risk factors for PAVMs.

Methods:

In this retrospective cohort study, all patients with left isomerism and azygous continuation of an interrupted inferior vena cava who underwent Kawashima procedure from July 2001 to December 2017 were included.

Results:

Twenty.six patients after Kawashima procedure were included in our study. PAVMs were diagnosed in 12 patients (46%). Five of these 12 patients underwent TCPC with complete resolution of hypoxemia. Three patients underwent AAVF creation, 2 had complete resolution, while 1 had partial resolution of hypoxemia. Fourteen patients (54%) did not develop PAVMs. Nakata index below 267 mm²/m²and McGoon ratio below 1.9 predicted the development of PAVMs with high sensitivity and specificity.

Conclusions:

PAVMs represent a serious complication in patients who undergo Kawashima procedure. Small size of pulmonary arteries is an important risk factor for the development of PAVMs. Resolution of hypoxemia after TCPC completion supports the hepatic factor hypothesis. Early TCPC completion in these patients may help to avoid the development of PAVMs by restoring the hepatic factor. Resolution of hypoxemia after AAVF creation may support the lack of pulsatile flow hypothesis.

Superior Cavopulmonary Connection: Its Physiology, Limitations, and Anesthetic Implications

The superior cavopulmonary connection (SCPC) or "bidirectional Glenn" is an integral, intermediate stage in palliation of single ventricle patients to the Fontan procedure. The procedure, normally performed at 3 to 6 months of life, increases effective pulmonary blood flow and reduces the ventricular volume load in patients with single ventricle (parallel circulation) physiology. While the SCPC, with or without additional sources of pulmonary blood flow, cannot be considered a long-term palliation strategy, there are a subset of patients who require SCPC palliation for a longer interval than the typical patient. In this article, we will review the physiology of SCPC, the consequences of prolonged SCPC palliation, and modes of failure. We will also discuss strategies to augment pulmonary blood flow in the presence of an SCPC. The anesthetic considerations in SCPC patients will also be discussed, as these patients may present for noncardiac surgery from infancy to adulthood.

Conversion of prior univentricular repairs to septated circulation: Case selection, challenges, and outcomes

Objectives

Complex congenital heart defects that present earlier in life are sometimes channelled in the single ventricle pathway, because of anatomical or logistic challenges involved in biventricular correction. Given the long-term functional and survival advantage, and with the surgeons' improved understanding of the cardiac anatomy, we have consciously explored the feasibility of a biventricular repair in these patients when they presented later for Fontan completion. We present a single institution's 10-year experience in achieving biventricular septation of prior univentricular repairs, the technical and physiological challenges and the surgical outcomes.

Methods

Between June 2010 and December 2019, 246 patients were channelized in the single ventricle pathway, of which 32 patients were identified as potential biventricular candidates at the time of evaluation for Fontan palliation, considering their anatomic feasibility. The surgical technique involves routing of the left ventricle to the aorta across the ventricular septal defect, ensuring an adequate sized right ventricular cavity, establishing right ventricle-pulmonary artery continuity and taking down the Glenn shunt with rerouting of the superior vena cava to the right atrium. This is a retrospective study where we reviewed the unique physiological and surgical characteristics of this subset of patients and analysed their surgical outcomes and complications.

Results

Biventricular conversion was achieved in all cases except in 3 patients, who had the Glenn shunt retained leading to a one and a half ventricle repair. The average age of the patients was 4.9 years of whom 18 were male. The average cardiopulmonary bypass time was 371 min with an average cross clamp time of 162 min. There was one mortality in a patient with corrected transposition of great arteries (c-TGA) with extensive arterio-venous malformations (AVMs). At a median follow-up of 60 months, all patients remained symptom free except two with NYHA II symptoms, one being treated for branch pulmonary artery stenosis with balloon dilatation and the other with multiple AVMs who needed coil closure. One patient with branch pulmonary artery (PA) stenosis required balloon dilatation and stent placement.

Conclusion

The possibility of achieving the surgical goal in this unique subset of patients evolves with the progressive experience of the congenital heart surgeon. Case selection is a crucial aspect in achieving the desired outcome, and this 'borderline' substrate is often recognized at the time of evaluation for the Fontan completion. A comprehensive preoperative imaging and planning helps in achieving the surgical septation and reconnection to achieve the desired physiological circulation. Though technically challenging, the surgery has excellent short- and mid-term outcomes as evidenced by our 10-year experience.

Targeted metabolomic analysis of serum amino acids in the adult Fontan patient with a dominant left ventricle

Growing interest lies in the assessment of the metabolic status of patients with a univentricular circulation after Fontan operation, especially in changes of amino acid metabolism. Using targeted metabolomic examinations, we investigated amino acid metabolism in a homogeneous adult Fontan-patient group with a dominant left ventricle, seeking biomarker patterns that might permit better understanding of Fontan pathophysiology and early detection of subtle ventricular or circulatory dysfunction. We compared serum amino acid levels (42 analytes; AbsoluteIDQ p180 kit, Biocrates Life Sciences, Innsbruck, Austria) in 20 adult Fontan patients with a dominant left ventricle and those in age- and sex-matched biventricular controls. Serum concentrations of asymmetric dimethylarginine, methionine sulfoxide, glutamic acid, and trans-4-hydroxyproline and the methionine sulfoxide/methionine ratio (Met-SO/Met) were significantly higher and serum concentrations of asparagine, histidine, taurine, and threonine were significantly lower in patients than in controls. Met-SO/Met values exhibited a significant negative correlation with oxygen uptake during exercise. The alterations in amino acid metabolome that we found in Fontan patients suggest links between Fontan pathophysiology, altered cell energy metabolism, oxidative stress, and endothelial dysfunction like those found in biventricular patients with congestive heart failure. Studies of extended amino acid metabolism may allow better understanding of Fontan pathophysiology that will permit early detection of subtle ventricular or circulatory dysfunction in Fontan patients.

Pearls and Pitfalls in Pediatric Fontan Operation Imaging

The Fontan operation or the total cavopulmonary connection is a palliative surgery for single ventricle congenital heart disease where the systemic venous return circumvents a pumping chamber and flows directly into the pulmonary circuit. With surgical and medical advances, there has been improvement in life expectancy of these patients, however, it has also resulted in unique complications from the physiology that requires diligent surveillance. A critical component relies on optimal imaging for diagnosis and treatment of these complications. This article describes the normal anatomy of the Fontan circulation, current imaging modalities and techniques, and frequently encountered complications seen when imaging the patients who have undergone Fontan palliation.

Role of surgeon intuition and computer-aided design in Fontan optimization: A computational fluid dynamics simulation study

OBJECTIVE

Customized Fontan designs, generated by computer-aided design (CAD) and optimized by computational fluid dynamics simulations, can lead to novel, patient-specific Fontan conduits unconstrained by off-the-shelf grafts. The relative contributions of both surgical expertise and CAD to Fontan optimization have not been addressed. In this study, we assessed hemodynamic performance of Fontans designed by both surgeon's unconstrained modeling (SUM) and by CAD.

METHODS

Ten cardiac magnetic resonance imaging datasets were used to create 3-dimensional (3D) models of Fontans. Baseline computational fluid dynamics simulations assessed Fontan indexed power loss (iPL), hepatic flow distribution, and percentage of conduit surface area with abnormally low wall shear stress for venous flow (<1 dyne/cm²). Fontans not meeting thresholds were redesigned using 2 methods: SUM (ie, original venous anatomy without the Fontan was 3D printed and sent to surgeon for Fontan redesign with clay modeling) and CAD (ie, the same 3D geometry was sent to engineers for iterative Fontan redesign guided by computational fluid dynamics). Both groups were blinded to each other's results.

RESULTS

Eight Fontans were redesigned by SUM and CAD methods. Both SUM and CAD redesigns met iPL thresholds. SUM had lower iPL, whereas CAD demonstrated balanced hepatic flow distribution and lower wall shear stress percentage. Wall shear stress percentage shared an inverse relationship with iPL, preventing oversized Fontan designs.

CONCLUSIONS

Customized Fontan conduits with low iPL can be created by either a surgeon or CAD. CAD can also improve hepatic flow distribution and prevent oversized Fontan designs. Future studies should investigate workflows that combine SUM and CAD to optimize Fontan conduits.

Angiopoietin-2 predicts morbidity in adults with Fontan physiology

Morbidity in patients with single-ventricle Fontan circulation is common and includes arrhythmias, edema, and pulmonary arteriovenous malformations (PAVM) among others. We sought to identify biomarkers that may predict such complications. Twenty-five patients with Fontan physiology and 12 control patients with atrial septal defects (ASD) that underwent cardiac catheterization were included. Plasma was collected from the hepatic vein and superior vena cava and underwent protein profiling for a panel of 20 analytes involved in angiogenesis and endothelial dysfunction. Ten (40%) of Fontan patients had evidence of PAVM, eighteen (72%) had a history of arrhythmia, and five (20%) were actively in arrhythmia or had a recent arrhythmia. Angiopoietin-2 (Ang-2) was higher in Fontan patients (8,875.4 ± 3,336.9 pg/mL) versus the ASD group (1,663.6 ± 587.3 pg/mL, p < 0.0001). Ang-2 was higher in Fontan patients with active or recent arrhythmia (11,396.0 ± 3,457.7 vs 8,118.2 ± 2,795.1 pg/mL, p < 0.05). A threshold of 8,500 pg/mL gives Ang-2 a negative predictive value of 100% and positive predictive value of 42% in diagnosing recent arrhythmia. Ang-2 is elevated among adults with Fontan physiology. Ang-2 level is associated with active or recent arrhythmia, but was not found to be associated with PAVM.

A 4D flow MRI evaluation of the impact of shear-dependent fluid viscosity on in vitro Fontan circulation flow

The Fontan procedure for univentricular heart defects creates a nonphysiologic circulation where systemic venous blood drains directly into the pulmonary arteries, leading to multiorgan dysfunction secondary to chronic low-shear nonpulsatile pulmonary blood flow and central venous hypertension. Although blood viscosity increases exponentially in this low-shear environment, the role of shear-dependent ("non-Newtonian") blood viscosity in this pathophysiology is unclear. We studied three-dimensional (3D)-printed Fontan models in an in vitro flow loop with a Philips 3-T magnetic resonance imaging (MRI) scanner. A 4D flow phase-contrast sequence was used to acquire a time-varying 3D velocity field for each experimental condition. On the basis of blood viscosity of a cohort of patients who had undergone the Fontan procedure, it was decided to use 0.04% xanthan gum as a non-Newtonian blood analog; 45% glycerol was used as a Newtonian control fluid. MRI data were analyzed using GTFlow and MATLAB software. The primary outcome, power loss, was significantly higher with the Newtonian fluid [14.8 (13.3, 16.4) vs. 8.1 (6.4, 9.8)%, medians with 95% confidence interval, P < 0.0001]. The Newtonian fluid also demonstrated marginally higher right pulmonary artery flow, marginally lower shear stress, and a trend toward higher caval flow mixing. Outcomes were modulated by Fontan model complexity, cardiac output, and caval flow ratio. Vortexes, helical flow, and stagnant flow were more prevalent with the non-Newtonian fluid. Our data demonstrate that shear-dependent viscosity significantly alters qualitative flow patterns, power loss, pulmonary flow distribution, shear stress, and caval flow mixing in synthetic models of the Fontan circulation. Potential clinical implications include effects on exercise capacity, ventilation-perfusion matching, risk of pulmonary arteriovenous malformations, and risk of thromboembolism.NEW & NOTEWORTHY Although blood viscosity increases exponentially in low-shear environments, the role of shear-dependent ("non-Newtonian") blood viscosity in the pathophysiology of the low-shear Fontan circulation is unclear. We demonstrate that shear-dependent viscosity significantly alters qualitative flow patterns, power loss, pulmonary flow distribution, shear stress, and caval flow mixing in synthetic models of the Fontan circulation. Potential clinical implications include effects on exercise capacity, ventilation-perfusion matching, risk of pulmonary arteriovenous malformations, and risk of thromboembolism.

Physiological Fontan Procedure

Objective: The conventional Fontan circulation deviates the superior vena cava (SVC = 1/3 of the systemic venous return) toward the right lung (3/5 of total lung volume) and the inferior vena cava (IVC = 2/3 of the systemic venous return) toward the left lung (2/5 of total lung volume). A "physiological" Fontan deviating the SVC toward the left lung and the IVC toward the right lung was compared with the conventional setting by computational fluid dynamics, studying whether this setting achieves a more favorable hemodynamics than the conventional Fontan circulation. Materials and Methods: An in-silico 3D parametric model of the Fontan procedure was developed using idealized vascular geometries with invariant sizes of SVC, IVC, right pulmonary artery (RPA), and left pulmonary artery (LPA), steady inflow velocities at IVC and SVC, and constant equal outflow pressures at RPA and LPA. These parameters were set to perform finite-volume incompressible steady flow simulations, assuming a single-phase, Newtonian, isothermal, laminar blood flow. Numerically converged finite-volume mass and momentum flow balances determined the inlet pressures and the outflow rates. Numerical closed-path integration of energy fluxes across domain boundaries determined the flow energy loss rate through the Fontan circulation. The comparison evaluated: (1) mean IVC pressure; (2) energy loss rate; (3) kinetic energy maximum value throughout the domain volume. Results: The comparison of the physiological vs. conventional Fontan provided these results: (1) mean IVC pressure 13.9 vs. 14.1 mmHg (= 0.2 mmHg reduction); (2) energy loss rate 5.55 vs. 6.61 mW (= 16% reduction); (3) maximum kinetic energy 283 vs. 396 J/m3 (= 29% reduction). Conclusions: A more physiological flow distribution is accompanied by a reduction of mean IVC pressure and by substantial reductions of energy loss rate and of peak kinetic energy. The potential clinical impact of these hemodynamic changes in reducing the incidence and severity of the adverse long-term effects of the Fontan circulation, in particular liver failure and protein-losing enteropathy, still remains to be assessed and will be the subject of future work.

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.

The first cohort of prospective Fontan surgical planning patients with follow-up data: How accurate is surgical planning?

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. The purpose of this study was to evaluate the accuracy of surgical planning predictions, specifically hepatic flow distribution (HFD), a known factor in pulmonary arteriovenous malformation 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 postoperative cardiac imaging were included in this study. Computational fluid dynamics were used to compare HFD in the surgical planning prediction and actual postoperative 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 = .73), but was significantly lower (6 ± 7%; P = .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 < .001). Improving postoperative anatomy prediction significantly reduced overall HFD prediction error to 9 ± 6% (P = .03).

CONCLUSIONS

Although Fontan surgical planning can offer accurate HFD predictions for specific graft types, methodological improvements are needed to increase overall accuracy. Specifically, improving postoperative anatomy prediction was shown to be an important target for future work. Future efforts and refinements to the surgical planning process will benefit from an improved understanding of the current state and will rely heavily on increased follow-up data.

Successful use of calcium channel blocker for management of arterio-venous malformations following Fontan procedure

In diffuse forms of arteriovenous malformation following Fontan procedure, "classical" medical therapy, inhaled nitric oxide and sildenafil, may play a role, until re-direction of hepatic flow to pulmonary circulation cures it. However, in refractory cases, as reported in our 2-year-old patient, unusual medications such as calcium channel blockers can be tried and continued if patients respond adequately.

Pulmonary arteriovenous malformations: diagnosis

Pulmonary arteriovenous malformations (PAVMs) are rare, abnormal low resistance vascular structures that connect a pulmonary artery to a pulmonary vein, thereby bypassing the normal pulmonary capillary bed and resulting in an intrapulmonary right-to-left shunt. The spectrum of PAVMs extends from microscopic lesions causing profound hypoxemia and ground glass appearance on computed tomography (CT) but with normal catheter angiographic findings to classic pulmonary aneurysmal connections that abnormally connect pulmonary veins and arteries. These malformations most commonly are seen in hereditary hemorrhagic telangiectasia (HHT). They are rarely due to secondary conditions such as post congenital heart disease surgery or hepatopulmonary syndrome (HPS). The main complications of PAVM result from intrapulmonary shunt and include stroke, brain abscess, and hypoxemia. Local pulmonary complications include PAVM rupture leading to life-threatening hemoptysis or hemothorax. The preferred screening test for PAVM is transthoracic contrast echocardiography (TTCE). CT has become the gold standard imaging test to establish the presence of PAVM. Endovascular occlusion of the feeding artery is the treatment of choice. Collateralization and recanalization of PAVM following treatment may occur, and hence long term clinical and imaging follow-up is required to assess PAVM enlargement and PAVM reperfusion.

Hepatopulmonary Disorders: Gas Exchange and Vascular Manifestations in Chronic Liver Disease

This review concentrates on the determinants of gas exchange abnormalities in liver-induced pulmonary vascular disorders, more specifically in the hepatopulmonary syndrome. Increased alveolar-arterial O₂ difference, with or without different levels of arterial hypoxemia, and reduced diffusing capacity represent the most characteristic gas exchange disturbances in the absence of cardiac and pulmonary comorbidities. Pulmonary gas exchange abnormalities in the hepatopulmonary syndrome are unique encompassing all three pulmonary factors determining arterial PO₂ , that is, ventilation-perfusion imbalance, increased intrapulmonary shunt and oxygen diffusion limitation that, combined, interplay with two relevant nonpulmonary determinants, that is, increased total ventilation and high cardiac output. Behind the complexity of this lung-liver association there is an abnormal pulmonary vascular tone that combines inhibition of hypoxic pulmonary vasoconstriction with a reduced (or blunted) hypoxic vascular response. The pathology and pathobiology include the presence of intrapulmonary vascular dilatations with or without pulmonary vascular remodeling, i.e. angiogenesis. Liver transplantation, the only effective therapeutic approach to successfully improve and resolve the vast majority of complications induced by the hepatopulmonary syndrome, along with a large list of frustrating pharmacologic interventions, are also reviewed. Another liver-induced pulmonary vascular disorder with less gas exchange involvement, such as portopulmonary hypertension, is also considered. © 2018 American Physiological Society. Compr Physiol 8:711-729, 2018.

Experimental Investigation of the Effect of Non-Newtonian Behavior of Blood Flow in the Fontan Circulation

The Fontan procedure for univentricular heart defects creates a unique circulation where all pulmonary blood flow is passively supplied directly from systemic veins. Computational simulations, aimed at optimizing the surgery, have assumed blood to be a Newtonian fluid without evaluating the potential error introduced by this assumption. We compared flow behavior between a non-Newtonian blood analog (0.04% xanthan gum) and a control Newtonian fluid (45% glycerol) in a simplified model of the Fontan circulation. Particle image velocimetry was used to examine flow behavior at two different cardiac outputs and two caval blood flow distributions. Pressure and flow rates were measured at each inlet and outlet. Velocity, shear strain, and shear stress maps were derived from velocity data. Power loss was calculated from pressure, flow, and velocity data. Power loss was increased in all test conditions with xanthan gum vs. glycerol (mean 10±2.9% vs. 5.6±1.3%, p=0.032). Pulmonary blood flow distribution differed in all conditions, more so at low cardiac output. Caval blood flow mixing patterns and shear stress were also qualitatively different between the solutions in all conditions. We conclude that assuming blood to be a Newtonian fluid introduces considerable error into simulations of the Fontan circulation, where low-shear flow predominates.

Neovasculature can be induced by patching an arterial graft into a vein: A novel in vivo model of spontaneous arteriovenous fistula formation

Arteriovenous malformations consist of tangles of arteries and veins that are often connected by a fistula. The causes and mechanisms of these clinical entities are not fully understood. We discovered that suturing an arterial patch into the common jugular vein of rabbits led to spontaneous neovascularization, the formation of an arteriovenous fistula and the development of an arteriovenous shunt. An arterial patch excised from the common carotid artery was sutured into the common jugular vein. Within a month, a dense nidus-like neovasculature formed around the patch. Angiography and pulse-oximeter analyses showed that the blood flowing into the neovasculature was arterial blood. This indicated that an arteriovenous shunt had formed. Fluorescence in situ hybridization with a Y chromosome probe in female rabbits that received an arterial patch from male rabbits showed that the vessels close to the graft bore the Y chromosome, whereas the vessels further away did not. Enzyme-linked immunosorbent assays and cDNA microarray analysis showed that multiple angiogenic factors were upregulated after patch transplantation. This is the first in vivo model of spontaneous arteriovenous fistula formation. Further research on these differences may help to improve understanding of human vascular anomaly diseases and the basic principles underlying vasculogenesis and/or angiogenesis.

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.

A tale of two cases of pulmonary arteriovenous malformation: How they fared after cardiac transplantation

BACKGROUND

In single ventricle patients, aortopulmonary collaterals (APCs) and pulmonary arteriovenous malformations (PAVMs) following superior cavopulmonary shunt (CPS) can complicate orthotopic heart transplant (OHT) by cyanosis and hemoptysis. Although PAVMs can regress with the restoration of hepatic venous flow to the pulmonary circulation, the effects of hypoxemia on the "unconditioned" allograft are not known.

CASES

Two patients with significant PAVMs after CPS were cyanotic following OHT. One patient with predominantly unilateral left PAVMs had arterial saturation levels less than 70% despite pulmonary vasodilators and ventilation. A custom flow restrictor-covered stent was deployed in the pulmonary artery of the affected side, redirecting the blood flow to the contralateral lung, immediately improving cyanosis. When the PAVMs regressed, the flow restrictor stent was dilated to eliminate the constriction. The second patient with PAVMs had cyanosis and severe hemoptysis from APCs post-OHT. The APCs required an extensive coil embolization, while the cyanosis responded to oxygen and pulmonary vasodilators. Both recipients did well with gradual resolution of PAVMs within 8 months.

CONCLUSIONS

Despite cyanosis from right-to-left intrapulmonary shunting, allograft function recovered. Novel transcatheter interventions can play a role in patients with significant APCs or PAVM following cardiac transplantation.

Virtual surgical planning, flow simulation, and 3-dimensional electrospinning of patient-specific grafts to optimize Fontan hemodynamics

BACKGROUND

Despite advances in the Fontan procedure, there is an unmet clinical need for patient-specific graft designs that are optimized for variations in patient anatomy. The objective of this study is to design and produce patient-specific Fontan geometries, with the goal of improving hepatic flow distribution (HFD) and reducing power loss (P_loss), and manufacturing these designs by electrospinning.

METHODS

Cardiac magnetic resonance imaging data from patients who previously underwent a Fontan procedure (n = 2) was used to create 3-dimensional models of their native Fontan geometry using standard image segmentation and geometry reconstruction software. For each patient, alternative designs were explored in silico, including tube-shaped and bifurcated conduits, and their performance in terms of P_loss and HFD probed by computational fluid dynamic (CFD) simulations. The best-performing options were then fabricated using electrospinning.

RESULTS

CFD simulations showed that the bifurcated conduit improved HFD between the left and right pulmonary arteries, whereas both types of conduits reduced P_loss. In vitro testing with a flow-loop chamber supported the CFD results. The proposed designs were then successfully electrospun into tissue-engineered vascular grafts.

CONCLUSIONS

Our unique virtual cardiac surgery approach has the potential to improve the quality of surgery by manufacturing patient-specific designs before surgery, that are also optimized with balanced HFD and minimal P_loss, based on refinement of commercially available options for image segmentation, computer-aided design, and flow simulations.

Simulation of aortopulmonary collateral flow in Fontan patients for use in prediction of interventional outcomes

PURPOSE

Patients with complex congenital heart disease may need to be converted to a Fontan circulation with systemic venous return surgically connected to the pulmonary circulation. These patients frequently form aortopulmonary collaterals (APC), that is arterial inflows to the pulmonary artery vascular tree. The aim of this study was to develop a method to calculate the effect of APC on the pulmonary flow distribution based on magnetic resonance imaging (MRI) measurements and computational fluid dynamics simulations in order to enable prediction of interventional outcomes in Fontan patients.

METHODS

Patient-specific models of 11 patients were constructed in a 3D-design software based on MRI segmentations. APC flow was quantified as the difference between pulmonary venous flow and pulmonary artery flow, measured by MRI. A method was developed to include the modulating effect of the APC flow by calculating the patient-specific relative pulmonary vascular resistance. Simulations, including interventions with a Y-graft replacement and a stent dilatation, were validated against MRI results.

RESULTS

The bias between simulated and MRI-measured fraction of blood to the left lung was 2·9 ± 5·3%. Including the effects of the APC flow in the simulation (n = 6) reduced simulation error from 9·8 ± 7·0% to 5·2 ± 6·3%. Preliminary findings in two patients show that the effect of surgical and catheter interventions could be predicted using the demonstrated methods.

CONCLUSIONS

The work demonstrates a novel method to include APC flow in predictive simulations of Fontan hemodynamics. APC flow was found to have a significant contribution to the pulmonary flow distribution in Fontan patients.

Arterial desaturation due to pulmonary arteriovenous malformations after the Kawashima Operation

Arterial desaturation may occur after the Kawashima procedure and, in the absence of venovenous collaterals is usually due to pulmonary arteriovenous malformations. Stenting of the pulmonary arteries, oxygen therapy, and pulmonary vasodilators such as sildenafil have not been able to resolve the arterial desaturation and the only way to do this has been Fontan completion. The time course of the formation of these malformations after the Kawashima and the progression of cyanosis and its resolution after the Fontan has only been demonstrated in case reports and small case series. We pool the available data to model arterial saturations in patients with pulmonary arteriovenous malformations after the Kawashima procedure.

Pulmonary Arteriovenous Malformations and Risk of Stroke

Pulmonary arteriovenous malformations (PAVMs) are rare, with an estimated incidence of 2 to 3 cases per 100,000, with most PAVMs (50%-80%) occurring in patients with hereditary hemorrhagic telangiectasia. Hypoxemia and orthodeoxia are some of the more common clinical presentations. The estimated risk of stroke secondary to PAVMs is as high as 2.6% to 25.0%. A combination of chest radiograph and contrast echocardiography is a good screening evaluation in patients with suspected PAVMs. Transcatheter therapy is the most suitable therapeutic option in most patients with PAVMs, and a variety of devices can be used to occlude the PAVMs.

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.

Transarterial embolization for pediatric hepatocellular carcinoma with cardiac cirrhosis

We describe the case of a 15-year-old boy with a history of Fontan operation and multiple intrahepatic tumors. Computed tomography showed multiple hepatic nodules with arterial enhancement. Because hepatocellular carcinoma (HCC) was not detected on biopsies and tumor markers were normal, progress was monitored on imaging. One hepatic tumor increased greatly in size during follow up. At 15 years of age, tumor markers rose rapidly, and he had upper abdominal swelling. Therefore, transarterial embolization (TAE) was performed for the largest tumor, suspected to be a HCC due to cardiac cirrhosis. This tumor had not increased at follow up 4 months later. The patient died from hepatic failure at the age of 17 years, and HCC was diagnosed at autopsy. Although pediatric HCC is rare, its incidence is likely to increase. TAE, with or without anticancer agents, is a therapeutic option for unresectable pediatric HCC, as it is for adult HCC.