Early identification of SOX17 deficiency in infants to guide management of heritable pulmonary arterial hypertension using PDA stent to create reverse Potts shunt physiology.

Heritable pulmonary arterial hypertension (HPAH) is a rare progressive condition that includes patients with an identified genetic cause of pulmonary arterial hypertension (PAH). HPAH and idiopathic PAH (IPAH) have an estimated combined incidence of 0.5-0.9 cases per million children-years. Several pathogenic variants have been associated with HPAH in children and adults, including genes BMPR2, TBX4, and ACVRL1, and more rarely with variants in genes such as SOX17. HPAH is often difficult to manage and has poor prognosis despite advances in medical therapy with many patients progressing to lung transplantation, right heart failure and death. Surgical and transcatheter Potts shunt creation can reduce systolic burden and has shown reduction in morbidity and mortality in children. Early genetic testing can provide both diagnostic and prognostic value in managing and counseling children with severe PAH and it can guide transcatheter or surgical management in refractory cases despite maximal medical therapies. We describe a patient with HPAH (SOX17 mutation) who underwent percutaneous patent ductus arteriosus stent for right ventricle decompression at 2 months of age with clinical management guidance by genetic testing results.

Stage 1 and 2 Palliation: Comparing Ductal Stenting and Aorto-Pulmonary Shunts in Single Ventricles with Duct-Dependent Pulmonary Blood Flow.

Patent ductus arteriosus stenting (PDAS) for ductal-dependent pulmonary blood flow (DDPBF) provides a new paradigm for managing neonates with single ventricles (SV). Currently, sparse data exist regarding outcomes for subsequent palliation. We describe our experience with inter-stage care and stage 2 (S2P) conversion with PDAS in comparison to a prior era of patients who received surgical aorto-pulmonary shunts (APS). Retrospective review of 18 consecutive DDPBF SV patients treated with PDAS between 2016 and 2021 was done and compared with 9 who underwent APS from 2010 to 2016. Patient outcomes and pulmonary artery (PA) growth were analyzed. S2P was completed in all 18 with PDAS with no cardiac arrests and one post-S2P mortality. In the 9 APS patients, there was one cardiac arrest requiring ECMO and one mortality inter-stage. Off cardiopulmonary bypass strategy was utilized in 10/18 in the PDAS and 1/9 in the APS group (p = 0.005) at S2P. Shorter ventilation time, earlier PO feeding, and shorter hospital stay were noted in the PDAS group (p = 0.01, p = 0.006, p = 0.03) (S2P). Median Nakata index increase inter-stage was not significant between the PDAS and APS at 94.1 mm2/m2 versus 71.7 mm2/m2 (p = 0.94). Median change in pulmonary artery symmetry (PAS) was - 0.02 and - 0.24, respectively, which was statistically significant (p = 0.008). Neurodevelopmental outcomes were better in the PDAS group compared to the APS group (p = 0.02). PDAS provides excellent PA growth, inter-stage survival, progression along multistage single-ventricle palliation, and potentially improved neurodevelopmental outcomes. Most patients can be transitioned through 2 stages of palliation without CPB.

Chronic active Epstein-Barr virus and hydroa vacciniforme-like lymphoproliferative disorder in a pediatric patient complicated by fatal ruptured cerebral artery aneurysm.

Hydroa vacciniforme-like lymphoproliferative disorder (HV-LPD) is a rare cutaneous form of chronic active Epstein-Barr virus (CAEBV) that presents with vesicular lesions induced by sun-exposure. Arterial aneurysm is a rare but potentially fatal complication of CAEBV and HV-LPD.

Surgical Mitral Valve Replacement Using a Catheter-Based MelodyTM Valve in a Landing Zone Constructed With a PTFE-Covered Expandable Cheatham-PlatinumTM Stent.

Mitral valve replacement using a Melody valve is a promising solution to the challenge of surgical mitral valve replacement in infants with a hypoplastic annulus. We report the creation of a landing zone in the mitral valve annulus using a Cheatham-Platinum (CP)-covered stent that facilitates Melody valve placement, helps prevent paravalvular leak, minimizes left ventricular outflow tract obstruction, and allows for potential future dilation of the valve.

Safety and Short-Term Outcomes for Infants < 2.5 kg Undergoing PDA Device Closure: A C3PO Registry Study.

To evaluate short-term procedural outcomes and safety for infants < 2.5 kg who underwent catheterization with intended patent ductus arteriosus (PDA) device closure in a multi-center registry, as performance of this procedure becomes widespread. A multi-center retrospective review was performed using data from the Congenital Cardiac Catheterization Project on Outcomes (C3PO) registry. Data were collected for all intended cases of PDA closure in infants < 2.5 kg from April 2019 to December 2020 at 13 participating sites. Successful device closure was defined as device placement at the conclusion of the catheterization. Procedural outcomes and adverse events (AE) were described, and associations between patient characteristics, procedural outcomes and AEs were analyzed. During the study period, 300 cases were performed with a median weight of 1.0 kg (range 0.7-2.4). Successful device closure was achieved in 98.7% of cases with a 1.7% incidence of level 4/5 AEs, including one periprocedural mortality. Neither failed device placement nor adverse events were significantly associated with patient age, weight or institutional volume. Higher incidence of adverse events associated with patients who had non-cardiac problems (p = 0.017) and cases with multiple devices attempted (p = 0.064). Transcatheter PDA closure in small infants can be performed with excellent short-term outcomes and safety across institutions with variable case volume.

Transcatheter Hepatic Conduit-Azygous Vein Connection Reduces Pulmonary Arteriovenous Malformations in a Cyanotic Fontan Patient.

The authors report a closed-chest, transcatheter large-vessel connection (hepatic conduit to azygous vein) to reverse pulmonary arteriovenous malformations in a 10-year-old patient after Fontan for heterotaxy/interrupted inferior vena cava, with an increase in oxygen saturation from 78% to 96%. Computational fluid dynamics estimated a 14-fold increase in hepatic blood flow to the left pulmonary artery (from 1.3% to 14%). (Level of Difficulty: Advanced.).

Exercise Stress Echocardiography in Kawasaki Disease Patients with Coronary Aneurysms.

The most significant sequelae of Kawasaki disease (KD) are coronary artery aneurysms, which can lead to risk of future myocardial ischemia. Exercise stress echocardiography allows for non-invasive assessment of myocardial dysfunction. We reviewed our single center experience with exercise stress echocardiography in patients with previous history of KD with coronary aneurysms. We reviewed the records of 53 KD patients who underwent exercise stress echocardiography from 2000 to 2020. Abnormal stress echocardiograms were defined as those showing no increase in biventricular systolic function post-exercise or regional wall motion abnormalities. Computed tomography angiography and cardiac magnetic resonance imaging were reviewed for patients with abnormal stress echocardiograms. Clinical data were reviewed and correlated with stress echocardiogram results. Of the 53 patients, three (5.7%) had an abnormal exercise stress echocardiogram. All three patients were classified as AHA Risk Level 4 or 5 by coronary Z-score (internal dimension normalized for body surface area) and were confirmed to have coronary aneurysms, stenosis, or myocardial tissue perfusion defects on advanced cardiac imaging that could account for the results seen on stress echocardiogram. Exercise stress echocardiography detected signs of myocardial ischemia in a subset of high-risk patients with Kawasaki disease and coronary aneurysms and may be considered as a useful screening tool for this complex patient cohort.

Selective Use of Pulmonary Vasodilators in Patients with Fontan Physiology.

Background: Fontan-associated liver disease is a well-known sequela following the Fontan procedure for patients living with single-ventricle heart disease. Pulmonary vasodilators, such as phosphodiesterase type 5 inhibitors, have emerged as a potential therapeutic option for lowering central venous pressures by reducing pulmonary vascular resistance. Method: We performed a single-center retrospective review of Fontan patients who were placed on pulmonary vasodilator therapy with prehemodynamic and posthemodynamic, MR elastography, and histologic assessments. Results: A total of 125 patients with Fontan circulation underwent surveillance with cardiac catheterization during the review period. Fifty-three (42%) patients who did not have increased end-diastolic pressures at the time of cardiac catheterization were started on phosphodiesterase type 5 inhibitor therapy. Nine patients (17%) underwent posttherapy follow-up catheterization. The mean Fontan pressure decreased from 15.4 ± 3.3 mmHg to 13.3 ± 2.5 mmHg (p=0.026), after initiation of pulmonary vasodilatory therapy. There was no change in end-diastolic pressure, transpulmonary gradient, wedge pressure, pulmonary vascular resistance, cardiac index, or saturation. Eleven patients (21%) underwent pretherapy MR elastography testing with posttherapy follow-up MR elastography. We found no improvement in liver stiffness score following the application of pulmonary vasodilators. Three patients underwent pretherapy and posttherapy liver biopsies, with variable histological changes observed within the hepatic parenchyma. Conclusions: These data demonstrate indeterminate results for the selective use of pulmonary vasodilators but highlight the need for large prospective randomized control trials of pulmonary vasodilator therapies to fully assess the benefit of such therapies in Fontan-associated liver disease.

Pulmonary Atresia With Intact Ventricular Septum: From Radiofrequency Perforation to Transcatheter Pulmonary Valve.

OBJECTIVES: We intend to describe an entirely transcatheter management pathway for patients with pulmonary atresia with intact ventricular septum (PA/IVS). BACKGROUND: PA/IVS is a rare cyanotic congenital heart lesion traditionally palliated with multiple procedures and surgeries. Entirely non-surgical transcatheter management from infancy to adulthood may be possible; however, the pathway from neonatal radiofrequency (RF) pulmonary valve perforation to later transcatheter pulmonary valve replacement (TPV) is not well described. METHODS: This retrospective study was performed at a pediatric cardiac center between 2007-2018. All patients with PA/IVS who were managed exclusively with catheterization-based interventions as neonates (RF perforation, pulmonary valvuloplasty, or ductal stenting) were analyzed. Demographic, procedural and clinical data were collected. RESULTS: Fifteen patients had exclusively catheterization-based RV decompression as neonates, 7 of whom did not require subsequent surgery. Six patients required a right ventricular outflow tract (RVOT) augmentation later in life; all were born before 2013. All 6 later had a TPV placed. Two of the patients underwent a surgical Glenn shunt alone. Of the 7 patients that never had surgery, 3 have since undergone a TPV, and 4 are awaiting candidacy for TPV placement. No patients with PA/IVS have had an RVOT augmentation at our institution since 2012. CONCLUSIONS: Patients with PA/IVS who undergo catheterization-based neonatal interventions can make it to TPV without requiring surgery. At our institution, there has been a shift in management over the last 8 years favoring entirely non-surgical transcatheter management from infancy to adulthood.

Institutional Trend in Device Selection for Transcatheter PDA Closure in Premature Infants.

We report our experience with transcatheter patent ductus arteriosus (PDA) closure in premature infants and compare patients grouped by the device used for closure: the Microvascular Plug, "MVP" (Medtronic, Minneapolis, MN); Micro Plug Set, "Micro Plug" (KA Medical, Minneapolis, MN); and Amplatzer Piccolo Occluder, "Piccolo" (Abbot, Santa Clara, CA). We also report trends in device selection over time. Studies examining outcomes according to device selection for PDA closure in premature infants are lacking. We performed a retrospective review of all percutaneous PDA closures in premature infants at a single center (June 2018-May 2021). Patients were grouped by initial device selected for PDA closure (intention to treat). Institutional Review Board approval was obtained. 58 premature infants [MVP (n = 25), Micro Plug (n = 25), and Piccolo (n = 8)] underwent successful transcatheter PDA closure (mean gestational age 27 weeks 2 days; mean weight at procedure 1.4 kg; mean age at procedure 28 days). Pre-procedural demographics, procedural data, and follow-up data were similar between groups. There were no significant procedural adverse events. Three devices (2 MVP, 0 Micro Plug, 1 Piccolo p = 0.27) embolized after the procedure. One other device was removed for concern for aortic obstruction. Device selection evolved with a clear trend toward the Micro Plug device over time. Demographic, procedural, and follow-up data were similar between the MVP, Micro Plug, and Piccolo groups. The Micro Plug did not require exchange for suboptimal fitting or embolize and became our preferred device in most cases.

Neonatal Myocardial Infarction: A Proposed Algorithm for Coronary Arterial Thrombus Management.

BACKGROUND: Neonatal myocardial infarction is rare and is associated with a high mortality of 40% to 50%. We report our experience with neonatal myocardial infarction, including presentation, management, outcomes, and our current patient management algorithm. METHODS: We reviewed all infants admitted with a diagnosis of coronary artery thrombosis, coronary ischemia, or myocardial infarction between January 2015 and May 2021. RESULTS: We identified 21 patients (median age, 1 [interquartile range (IQR), 0.25-9.00] day; weight, 3.2 [IQR, 2.9-3.7] kg). Presentation included respiratory distress (16), shock (3), and murmur (2). Regional wall motion abnormalities by echocardiogram were a key criterion for diagnosis and were present in all 21 with varying degrees of depressed left ventricular function (severe [8], moderate [6], mild [2], and low normal [5]). Ejection fraction ranged from 20% to 54% (median, 43% [IQR, 34%-51%]). Mitral regurgitation was present in 19 (90%), left atrial dilation in 15 (71%), and pulmonary hypertension in 18 (86%). ECG was abnormal in 19 (90%). Median troponin I was 0.18 (IQR, 0.12-0.56) ng/mL. Median BNP (B-type natriuretic peptide) was 2100 (IQR, 924-2325) pg/mL. Seventeen had documented coronary thrombosis by cardiac catheterization. Seventeen (81%) were treated with intracoronary tPA (tissue-type plasminogen activator) followed by systemic heparin, AT (antithrombin), and intravenous nitroglycerin, and 4 (19%) were treated with systemic heparin, AT, and intravenous nitroglycerin alone. Nineteen of 21 recovered. One died (also had infradiaphragmatic total anomalous pulmonary venous return). One patient required a ventricular assist device and later underwent heart transplant; this patient was diagnosed late at 5 weeks of age and did not respond to tPA. Nineteen of 21 (90%) regained normal left ventricular function (ejection fraction, 60%-74%; mean, 65% [IQR, 61%-67%]) at latest follow-up (median, 6.8 [IQR, 3.58-14.72] months). Two of 21 (10%) had residual trivial mitral regurgitation. After analysis of these results, we present our current algorithm, which developed and matured over time, to manage neonatal myocardial infarction. CONCLUSIONS: We experienced a lower mortality rate for infants with neonatal infarction than that reported in the literature. We propose a post hoc algorithm that may lead to improvement in patient outcomes following coronary artery thrombus.

Aortopulmonary collaterals: An etiology for pediatric tracheostomy hemorrhage.

OBJECTIVE: To report a single-institution's experience of symptomatic aortopulmonary collaterals presenting as tracheostomy tube hemorrhage. STUDY DESIGN: Retrospective case series and Contemporary Review. SETTING: Tertiary care children's hospital. METHODS: Retrospective review, from 2015 to 2020, of patients <18 years old who were treated for tracheostomy hemorrhage with endovascular embolization of aortopulmonary collateral (APC) vessels. RESULTS: 4 patients were identified, 2 males and 2 females, ages 15 months-to 14 years-old, with a range of cyanotic congenital heart diseases. Direct laryngoscopy and bronchoscopy were necessary for excluding proximal airway sources. Chest computed tomography angiography did not localize pulmonary hemorrhage, but helped identify aortopulmonary collaterals. Cardiac catheterization was both diagnostic and therapeutic with use of endovascular embolization techniques by pediatric interventional cardiology and interventional radiology. Previously reported APC-related pulmonary hemorrhages occurred in significantly different settings compared to our patients, and evaluation by an otolaryngologist was key to rule out upper airway etiologies. CONCLUSION: Symptomatic aortopulmonary collaterals is an important etiology in pediatric tracheostomy tube hemorrhage in patients with cyanotic congenital heart disease.

Purpose-Built Transcatheter Cavopulmonary Anastomosis Device Requirements: Multi-Modality Imaging Evaluation.

BACKGROUND/PURPOSE: Patients with a functional single ventricle undergo multiple, palliative open-heart surgeries. This includes a superior cavopulmonary anastomosis or bidirectional Glenn shunt. A less-invasive transcatheter approach may reduce morbidity. METHODS/MATERIALS: We analyzed pre-Glenn X-ray contrast angiography (XA), cardiac computed tomography (CT), and cardiac magnetic resonance (CMR) studies. RESULTS: Over an eleven-year period (1/2007 - 6/2017), 139 Glenn surgeries were performed at our institution. The typical age range at surgery was 59 - 371 days (median = 163; IQR = 138 - 203). Eight-nine XA, ten CT, and ten CMR studies obtained from these patients were analyzed. Cephalad SVC measurements (millimeters) were 7.3 ± 1.7 (XA), 7.7 ± 1.6 (CT) and 6.9 ± 1.8 (CMR). RPA measurements were 7.3 ± 1.9 (XA), 7.4 ± 1.6 (CT) and 6.6 ± 1.9 (CMR). Potential device lengths were 10.9 ± 6 - 17.4 ± 6.4 (XA), 10.1 ± 2.1 - 17.7 ± 2.4 (CT) and 17.3 ± 4. - 23.7 ± 5.5 (CMR). SVC-RPA angle (degrees) was 132.9 ± 13.2 (CT) and 140 ± 10.2 (MRI). Image quality of all CT (100%), almost all XA (SVC 100%, RPA 99%), and most MRI (SVC 80%, RPA 90%) were deemed sufficient. Parametric modeling virtual fit device with 10 mm diameter and 20 - 25 mm length was ideal. CONCLUSIONS: Ideal transcatheter cavopulmonary shunt device for the typical patient would be 10 mm in diameter and 20-25 mm in length.

Laparoscopic Surgery Requiring Abdominal Insufflation in Patients With Congenital Heart Disease.

OBJECTIVE: To determine if patients with congenital heart disease are undergoing laparoscopic surgery requiring abdominal insufflation and to compare the outcomes of these procedures with those who underwent an open surgical approach. DESIGN, SETTING, PARTICIPANTS: This was a retrospective study using the National Inpatient Sample from 2006 to 2014. Individuals with congenital heart disease who underwent at least one of six selected surgical procedures (laparoscopic or open) were included in the study. Subgroup analysis was performed on patients with Fontan palliation. MEASUREMENTS AND MAIN RESULTS: The primary outcome was to determine the frequency with which congenital heart disease patients undergo laparoscopic surgery requiring abdominal insufflation compared with open surgery. Secondary outcomes included all-cause in-hospital mortality and in-hospital length of stay. Of the 5,527 patients included, nearly half underwent laparoscopic surgery (46.3%), and 128 (2.3%) had single-ventricle circulation. All-cause mortality was significantly higher for those who underwent open surgery compared with the laparoscopic approach (3.6% v 0.9%; odds ratio [OR], 4.0 [2.6-6.3]; p < 0.0001). Subgroup analysis of patients with Fontal palliation older than five years showed 30 (42%) underwent laparoscopic surgery and there was no mortality difference between the laparoscopic and open approaches (OR, 1.4 [0.2-21.3], p = 0.8). Length of stay was significantly shorter for patients undergoing laparoscopic compared with open surgery (median three days [interquartile range, two-five] v six days [three-13], p < 0.0001). CONCLUSIONS: Individuals with congenital heart disease are being offered laparoscopic surgery that requires abdominal insufflation. All-cause mortality and length of stay were higher for patients who underwent open surgical operations.

Interpreting Quality Improvement When Introducing New Technology: A Collaborative Experience in ASD Device Closures.

The objective of this study was to evaluate the impact of the regular introduction of new technologies into interventional cardiac catheterization procedures, in this case new atrial septal defect (ASD) closure devices, while conducting a multi-center collaborative initiative to reduce radiation usage during all procedures. Data were collected prospectively by 8 C3PO institutions between January 1, 2014 and December 31, 2017 for ASD device closure procedures in the cardiac catheterization lab during a quality improvement (QI) initiative aimed at reducing patient radiation exposure. Radiation exposure was measured in dose area product per body weight (µGy*m2/kg). Use of proposed practice change strategies at the beginning and end of the QI intervention period was assessed. Radiation exposure was summarized by institution and by initial type of device used for closure. This study included 602 ASD device closures. Without changes in patient characteristics, total fluoroscopy duration, or number of digital acquisitions, median radiation exposure decreased from 37 DAP/kg to 14 DAP/kg from 2014 to 2017. While all individual centers decreased overall median DAP/kg, the use of novel devices for ASD closure correlated with a temporary period of worsening institutional radiation exposure and increased fluoroscopy time. The introduction of new ASD closure devices resulted in increased radiation exposure during a QI project designed to reduce radiation exposure. Therefore, outcome assessment must be contextualized in QI projects, hospital evaluation, and public reporting, to acknowledge the expected variation during innovation and introduction of novel therapies.

Long-term Results Using Glutaraldehyde-treated Homograft Pericardium in Congenital Heart Surgery.

BACKGROUND: This study reports the long-term outcomes using glutaraldehyde-treated cryopreserved homograft pericardium (CPH) in neonates, infants, children, and young adults undergoing congenital cardiac surgery. METHODS: A retrospective review was performed of all patients at a single institution (Rady Children's Hospital, San Diego, CA) who had undergone surgical implantation with CPH between 2006 and 2016. The study identified 134 consecutive patients who underwent implantation of a total of 276 patches. The baseline demographic characteristics, primary cardiac diagnosis, surgical characteristics, operative reports, and postoperative catheterization and reoperation reports were analyzed. The use of CPH was categorized by specific anatomic insertion site. RESULTS: The median age at patch implantation was 1.47 years (range, 1 day to 31.6 years). The numbers and locations of patch use were 124 for pulmonary arterial repair, 57 for repair of the aorta, 49 for septal repair, and 43 at other sites. At a median follow-up of 5.29 years, 9 patients had died (6.7%), but none of those deaths were related to CPH. Twelve patients (8.96%) underwent reoperations, and 18 patients (13.4%) underwent catheter interventions at sites of CPH implantation. The 10-year freedom from patch-induced reoperation and catheter intervention rates were 88.5% and 86.9%, respectively. Overall patch failure-free survival was 85.8% and 79.0% at 5 and 10 years, respectively. CONCLUSIONS: The use of CPH patch in the surgical correction of congenital heart disease is effective and durable, as evidenced by the low reintervention rates. These results are comparable to the early and midterm outcomes of other similarly used surgical patches.

Selective Valve Removal for Melody Valve Endocarditis: Practice Variations in a Multicenter Experience.

Guidelines for management of Melody transcatheter pulmonary valve (TPV) infective endocarditis (IE) are lacking. We aimed to identify factors associated with surgical valve removal versus antimicrobial therapy in Melody TPV IE. Multicenter retrospective analysis of all patients receiving Melody TPV from 10/2010 to 3/2019 was performed to identify cases of IE. Surgical explants versus non-surgical cases were compared. Of the 663 Melody TPV implants, there were 66 cases of IE in 59 patients (59/663, 8.8%). 39/66 (59%) were treated with IV antimicrobials and 27/66(41%) underwent valve explantation. 26/59 patients (44%) were treated medically without explantation or recurrence with average follow-up time of 3.5 years (range:1-9). 32% of Streptococcus cases, 53% of MSSA, and all MRSA cases were explanted. 2 of the 4 deaths had MSSA. CART analysis demonstrated two important parameters associated with explantation: a peak echo gradient ≥ 47 mmHg at IE diagnosis(OR 10.6, p < 0.001) and a peak echo gradient increase of > 24 mmHg compared to baseline (OR 6.7, p = 0.01). Rates of explantation varied by institution (27 to 64%). In our multicenter experience, 44% of patients with Melody IE were successfully medically treated without valve explantation or recurrence. The degree of valve stenosis at time of IE diagnosis was strongly associated with explantation. Rates of explantation varied significantly among the institutions.

Prevalence of Venovenous Shunting and High-Output State Quantified with 4D Flow MRI in Patients with Fontan Circulation.

PURPOSE: To assess the ability of four-dimensional (4D) flow MRI to quantify flow volume of the Fontan circuit, including the frequency and hemodynamic contribution of systemic-to-pulmonary venovenous collateral vessels. MATERIALS AND METHODS: In this retrospective study, patients with Fontan circulation were included from three institutions (2017-2021). Flow measurements were performed at several locations along the circuit by two readers, and collateral shunt volumes were quantified. The frequency of venovenous collaterals and structural defects were tabulated from concurrent MR angiography, contemporaneous CT, or catheter angiography and related to Fontan clinical status. Statistical analysis included Pearson and Spearman correlation and Bland-Altman analysis. RESULTS: Seventy-five patients (mean age, 20 years; range, 5-58 years; 46 female and 29 male patients) were included. Interobserver agreement was high for aortic output, pulmonary arteries, pulmonary veins, superior vena cava (Glenn shunt), and inferior vena cava (Fontan conduit) (range, ρ = 0.913-0.975). Calculated shunt volume also showed strong agreement, on the basis of the difference between aortic and pulmonary flow (ρ = 0.935). A total of 37 of 75 (49%) of the patients exhibited shunts exceeding 1.00 L/min, 81% (30 of 37) of whom had pulmonary venous or atrial flow volume step-ups and corresponding venovenous collaterals. A total of 12% of patients (nine of 75) exhibited a high-output state (>4 L/min/m2), most of whom had venovenous shunts exceeding 30% of cardiac output. CONCLUSION: Fontan flow and venovenous shunting can be reliably quantified at 4D flow MRI; high-output states were found in a higher proportion of patients than expected, among whom venovenous collaterals were common and constituted a substantial proportion of cardiac output.Keywords: Pediatrics, MR Angiography, Cardiac, Technology Assessment, Hemodynamics/Flow Dynamics, Congenital Supplemental material is available for this article. © RSNA, 2021.