Endothelin inhibitors lower pulmonary vascular resistance and improve functional capacity in patients with Fontan circulation

Pulmonary vascular disease and optical coherence tomography imaging in patients with Fontan palliation

INTRODUCTION

The Fontan procedure is the palliative procedure of choice for patients with single ventricle physiology. Pulmonary vascular disease (PVD) is an important contributor to Fontan circulatory failure.

AREAS COVERED

We review the pathophysiology of PVD in patients with Fontan palliation and share our initial experience with optical coherence tomography (OCT) in supplementing standard hemodynamics in characterizing Fontan-associated PVD. In the absence of a sub-pulmonary ventricle, low pulmonary vascular resistance (PVR; ≤2 WU/m2) is required to sustain optimal pulmonary blood flow. PVD is associated with adverse pulmonary artery (PA) remodeling resulting from the non-pulsatile low-shear low-flow circulation. Predisposing factors to PVD include impaired PA growth, endothelial dysfunction, hypercoagulable state, and increased ventricular end-diastolic pressure. OCT parameters that show promise in characterizing Fontan-associated PVD include the PA intima-to-media ratio and wall area ratio (i.e. difference between the whole-vessel area and the luminal area divided by the whole-vessel area).

EXPERT OPINION

OCT carries potential in characterizing PVD in patients with Fontan palliation. PA remodeling is marked by intimal hyperplasia, with medial regression. Further studies are required to determine the role of OCT in informing management decisions and assessing therapeutic responses.

Decreased erythrocyte aggregation in Glenn and Fontan: univentricular circulation as a rheologic disease model

BACKGROUND

In the Fontan palliation for single ventricle heart disease (SVHD), pulmonary blood flow is non-pulsatile/passive, low velocity, and low shear, making viscous power loss a critical determinant of cardiac output. The rheologic properties of blood in SVHD patients are essential for understanding and modulating their limited cardiac output and they have not been systematically studied. We hypothesize that viscosity is decreased in single ventricle circulation.

METHODS

We evaluated whole blood viscosity, red blood cell (RBC) aggregation, and RBC deformability to evaluate changes in healthy children and SVHD patients. We altered suspending media to understand cellular and plasma differences contributing to rheologic differences.

RESULTS

Whole blood viscosity was similar between SVHD and healthy at their native hematocrits, while viscosity was lower at equivalent hematocrits for SVHD patients. RBC deformability is increased, and RBC aggregation is decreased in SVHD patients. Suspending SVHD RBCs in healthy plasma resulted in increased RBC aggregation and suspending healthy RBCs in SVHD plasma resulted in lower RBC aggregation.

CONCLUSIONS

Hematocrit corrected blood viscosity is lower in SVHD vs. healthy due to decreased RBC aggregation and higher RBC deformability, a viscous adaptation of blood in patients whose cardiac output is dependent on minimizing viscous power loss.

IMPACT

Patients with single ventricle circulation have decreased red blood cell aggregation and increased red blood cell deformability, both of which result in a decrease in blood viscosity across a large shear rate range. Since the unique Fontan circulation has very low-shear and low velocity flow in the pulmonary arteries, blood viscosity plays an increased role in vascular resistance, therefore this work is the first to describe a novel mechanism to target pulmonary vascular resistance as a modifiable risk factor. This is a novel, modifiable risk factor in this patient population.

Pulmonary vasodilators and exercise in Fontan circulation: a systematic review and meta-analysis

OBJECTIVE

In Fontan circulation, pulmonary arterial hypertension (PAH)-targeted therapies could improve the patients' exercise capacity. This study aimed to investigate the effects of PAH agents on different exercise parameters in stable Fontan patients by synthesising evidence of randomised controlled trials (RCTs).

METHODS

A systematic search of PubMed, Cochrane Central Register of Controlled Trials and Web of Science databases, as well as of ClinicalTrials.gov, was performed. Primary outcomes were specific cardiopulmonary exercise test parameters: peak oxygen uptake (peak VO2), peak heart rate (peak HR), the minute ventilation/produced carbon dioxide (VE/VCO2) slope and the oxygen uptake, both measured at the anaerobic threshold (VO2@AT).

RESULTS

Five RCTs were included in the analysis including 573 Fontan patients (mean age 21.2 years, 60% male). PAH-targeted therapies did not affect peak VO2 (mean difference (MD) 0.72, 95% CI -0.25 to 1.70) or peak HR (MD -0.67, 95% CI -3.81 to 2.47), but resulted in a small, significant improvement in VO2@AT (standardised MD 0.24, 95% CI 0.02 to 0.47). VE/VCO2 slope at the anaerobic threshold was also reduced (MD -1.13, 95% CI -2.25 to -0.01).

CONCLUSIONS

Although PAH-targeted therapies did not affect exercise parameters at maximal effort, they induced slight improvements in indices of submaximal effort, measured at the anaerobic threshold. Pharmacological improvement of submaximal exercise seems to be a more suitable indicator of Fontan individuals' exercise capacity. Larger RCTs, recruiting specific subpopulations and focusing also on the anaerobic threshold, are warranted to draw more robust conclusions.

PROSPERO REGISTRATION NUMBER

CRD42022306674.

EASL-ERN position paper on liver involvement in patients with Fontan-type circulation

Fontan-type surgery is the final step in the sequential palliative surgical treatment of infants born with a univentricular heart. The resulting long-term haemodynamic changes promote liver damage, leading to Fontan-associated liver disease (FALD), in virtually all patients with Fontan circulation. Owing to the lack of a uniform definition of FALD and the competitive risk of other complications developed by Fontan patients, the impact of FALD on the prognosis of these patients is currently debatable. However, based on the increasing number of adult Fontan patients and recent research interest, the European Association for The Study of the Liver and the European Reference Network on Rare Liver Diseases thought a position paper timely. The aims of the current paper are: (1) to provide a clear definition and description of FALD, including clinical, analytical, radiological, haemodynamic, and histological features; (2) to facilitate guidance for staging the liver disease; and (3) to provide evidence- and experience-based recommendations for the management of different clinical scenarios.

Recent Advances in Pediatric Pulmonary Hypertension: Implications for Diagnosis and Treatment

PURPOSE

Pediatric pulmonary hypertension (PH) is a condition characterized by elevated pulmonary arterial pressure, which has the potential to be life-limiting. The etiology of pediatric PH varies. When compared with adult cohorts, the etiology is often multifactorial, with contributions from prenatal, genetic, and developmental factors. This review aims to provide an up-to-date overview of the causes and classification of pediatric PH, describe current therapeutics in pediatric PH, and discuss upcoming and necessary research in pediatric PH.

METHODS

PubMed was searched for articles relating to pediatric pulmonary hypertension, with a particular focus on articles published within the past 10 years. Literature was reviewed for pertinent areas related to this topic.

FINDINGS

The evaluation and approach to pediatric PH are unique when compared with that of adults, in large part because of the different, often multifactorial, causes of the disease in children. Collaborative registry studies have found that the most common disease causes include developmental lung disease and subsets of pulmonary arterial hypertension, which includes genetic variants and PH associated with congenital heart disease. Treatment with PH-targeted therapies in pediatrics is often guided by extrapolation of adult data, small clinical studies in pediatrics, and/or expert consensus opinion. We review diagnostic considerations and treatment in some of the more common pediatric subpopulations of patients with PH, including developmental lung diseases, congenital heart disease, and trisomy 21.

IMPLICATIONS

The care of pediatric patients with PH requires consideration of unique pediatric-specific factors. With significant variability in disease etiology, ongoing efforts are needed to optimize treatment strategies based on disease phenotype and guide evidence-based practices.

Efficacy of a phosphodiesterase type 5 inhibitor on the pulmonary artery index and postoperative hemodynamics after a Fontan operation

There have been no reports regarding the influence of a change in the pulmonary artery index before or after a Fontan operation. Moreover, the factors that might affect the change in the pulmonary artery index are unclear. This was a retrospective study, which included 94 patients who underwent a Fontan operation. We divided the patients into two groups according to the change in the pulmonary artery index before and after the Fontan operation: the increased pulmonary artery index group (n = 51) and decreased pulmonary artery index group (n = 43). The pulmonary artery index after the Fontan operation was significantly higher in the increased pulmonary artery index group than decreased pulmonary artery index group (p < 0.0001). The central venous pressure (p < 0.0001) and pulmonary vascular resistance (p = 0.007) were significantly lower in the increased pulmonary artery index group. The mixed venous oxygen saturation was significantly higher in the increased pulmonary artery index group (p < 0.0001). The pulmonary artery index was more increased in the patients who were administered a phosphodiesterase type 5 inhibitor than in those who were not (p = 0.03). The change in the pulmonary artery index reflected the hemodynamics after a Fontan operation during the short term. In that respect, phosphodiesterase type 5 inhibitors might be involved in the process.

Induction of aggressive arterial and venous dilation therapy in addition to pulmonary dilation therapy (super-Fontan strategy) improves Fontan circulation both at rest and during treadmill exercise

Objective

Methods

Results

Conclusions

Optimal Fenestration of the Fontan Circulation

In this paper, we develop a pulsatile compartmental model of the Fontan circulation and use it to explore the effects of a fenestration added to this physiology. A fenestration is a shunt between the systemic and pulmonary veins that is added either at the time of Fontan conversion or at a later time for the treatment of complications. This shunt increases cardiac output and decreases systemic venous pressure. However, these hemodynamic benefits are achieved at the expense of a decrease in the arterial oxygen saturation. The model developed in this paper incorporates fenestration size as a parameter and describes both blood flow and oxygen transport. It is calibrated to clinical data from Fontan patients, and we use it to study the impact of a fenestration on several hemodynamic variables, including systemic oxygen availability, effective oxygen availability, and systemic venous pressure. In certain scenarios corresponding to high-risk Fontan physiology, we demonstrate the existence of a range of fenestration sizes in which the systemic oxygen availability remains relatively constant while the systemic venous pressure decreases.

Exercising with a Single Ventricle: Limitations and Therapies

Treatment for Hypoplastic Left Heart Syndrome (HLHS) and other single ventricle conditions requires a series of surgical interventions for long-term survival, typically culminating in the Fontan procedure. The result is an abnormal circulatory physiology with an absence of a sub-pulmonary ventricle. Exercise capacity in the Fontan circulation is often limited and is due to multiple factors, both central and peripheral. Multiple interventions, both pharmacologic and nonpharmacologic, have been studied to attempt to overcome these inherent limitations. This review will focus on the physiology of the exercising Fontan patient and on the interventions aimed at the enhancement of exercise capacity studied thus far.

Pharmacology Management in Improving Exercise Capacity of Patients with Fontan Circulation: A Systematic Review and Meta-analysis

BACKGROUND

The Fontan procedure is currently the mainstay therapy for single functional ventricles. However, with prolonged follow-up duration, various complications have been observed that seriously influence the quality of life of patients.

OBJECTIVES

The aim of this meta-analysis is to compare the effectiveness of pharmacologic agents in improving exercise capacity in patients with Fontan circulation.

METHODS

This meta-analysis was conducted according to the Preferred Reporting Items for Systematic Review and Meta-analysis (PRISMA) statement and has been registered in the International Prospective Register for Systematic Reviews database with registration no. 282352. Quality assessments of the included studies were assessed using the Strengthening Reporting of Observational Studies in Epidemiology (STROBE) statement.

RESULTS

Twelve studies met the predetermined inclusion criteria and were included in this metaanalysis. This meta-analysis found that treatment with bosentan significantly improved New York Heart Association Functional Class (NYHA FC) in Fontan patients (standard mean difference - 0.59, 95% CI -0.94 - -0.25; P=0.0008; I2 = 1%). However, the use of bosentan (P=0.66) and sildenafil (P=0.13) did not show a significant improvement in the maximum rate of oxygen consumption (VO2 max).

CONCLUSION

This meta-analysis shows that people with Fontan circulation may benefit from using bosentan as it decreases postexercise heart rate and improves NYHA FC and 6-minute walking test results. Therefore, indirectly improving exercise capacity. Nonetheless, considerable work is required to strengthen our knowledge in improving the exercise capacity of Fontan patients.

Late Fontan failure in adult patients is predominantly associated with deteriorating ventricular function

BACKGROUND

The Fontan operation is a palliative procedure and a substantial number of patients eventually experiences late Fontan circulation failure. Previous concepts of Fontan failure implicate increasing pulmonary vascular resistance (PVR) as a key contributor to late circulatory failure. However, data to support this assumption are sparse. We sought to characterize longitudinal hemodynamic and echocardiographic findings in adult failing Fontan patients.

METHODS

We performed a retrospective cohort study in adult Fontan patients, identifying patients with Fontan failure. Hemodynamic, echocardiographic and clinical data were recorded.

RESULTS

Of 173 adult patients (median follow-up after Fontan 20.2 years [IQR 15.7-24.3]), 48 (28%) showed signs of clinical Fontan failure. Thirty-seven patients (77.1%) exhibited ventricular dysfunction (systolic dysfunction defined by ejection fraction ≤45%, n = 22, or diastolic dysfunction defined by systemic ventricular end-diastolic pressure (SVEDP) ≥12 mmHg, n = 15). Elevated indexed PVR (≥2.5 WU*m²) was only observed in 9 (18.8%) patients. Ejection fraction declined from 60% [IQR 55-65] to 47% [IQR 35-55] during follow-up (p < 0.001). Mean pulmonary artery pressure and SVEDP increased from 11 mmHg [IQR 9-15] to 15 mmHg [IQR 12-18] and from 7 mmHg [IQR 4-10] to 11 mmHg [IQR 8-15] (both p < 0.001), respectively, while indexed PVR did not change significantly (2.1 [IQR 1.1-2.4] vs. 1.7 [IQR 1.1-2.5] WU*m², p = 0.949). Fontan failure-associated mortality during follow-up was substantial (23/48; 48%).

CONCLUSIONS

Systolic and diastolic ventricular dysfunction are frequent features in late Fontan failure in adults, while increases in PVR were rarely observed. The intricate interplay between hemodynamic compromises in Fontan failure deserves further research to optimize treatment strategies and outcome.

Clinical application of pulmonary vascular resistance in patients with pulmonary arterial hypertension

Pulmonary arterial hypertension is a type of malignant pulmonary vascular disease, which is mainly caused by the increase of pulmonary vascular resistance due to the pathological changes of the pulmonary arteriole itself, which eventually leads to right heart failure and death. As one of the diagnostic indicators of hemodynamics, pulmonary vascular resistance plays an irreplaceable role in the pathophysiology, diagnosis and treatment of pulmonary arterial hypertension. It provides more references for the evaluation of pulmonary arterial hypertension patients. This article summarizes the clinical application of pulmonary vascular resistance in patients with pulmonary arterial hypertension.

Pulmonary vascular disease in Fontan circulation-is there a rationale for pulmonary vasodilator therapies?

The Fontan circulation is a palliative concept for patients with univentricular hearts. The central veins are connected directly to the pulmonary arteries (cavo-pulmonary connection) to separate the pulmonary and the systemic circulation. There is no sub-pulmonary ventricle that generates pressure to drive blood through the pulmonary arteries. Pulmonary blood flow is determined by central venous pressure (CVP) and pulmonary vascular resistance (PVR). The capability of the Fontan circulation to compensate for alterations in PVR is limited, as CVP can only be increased within narrow ranges without adverse clinical consequences. Consequently, systemic ventricular preload and cardiac output are dependent on a healthy lung with low PVR. Failure of the Fontan circulation is relatively common. In addition to ventricular dysfunction, maladaptive pulmonary vascular remodeling resulting in increased pulmonary resistance may play a key role. The pathophysiology of the maladaptive vascular processes remains largely unclear and diagnosis of an increased PVR is challenging in Fontan circulation as accurate measurement of pulmonary arterial blood flow is difficult. In the absence of a sub-pulmonary ventricle, pulmonary artery pressure will almost never reach the threshold conventionally used to define pulmonary arterial hypertension. There is a need for markers of pulmonary vascular disease complementary to invasive hemodynamic data in Fontan patients. In order to treat or prevent failure of the Fontan circulation, pathophysiological considerations support the use of pulmonary vasodilators to augment pulmonary blood flow and systemic ventricular preload and lower CVP. However, to date the available trial data have neither yielded enough evidence to support routine use of pulmonary vasodilators in every Fontan patient nor have they been helpful in defining subgroups of patients that might benefit from such therapies. This review discusses potential pathomechanisms of pulmonary vascular disease; it summarizes the current knowledge of the effects and efficacy of pulmonary vasodilator therapy in Fontan patients and tries to outline areas of potential future research on the diagnosis and treatment of pulmonary vascular disease and Fontan failure.

Treatment of pulmonary arterial hypertension in children

Pulmonary arterial hypertension (PAH) is a devastating illness causing already significant morbidity in childhood. Currently approved treatment options for children comprise the endothelin receptor antagonist bosentan, as well as the phosphodiesterase-5 inhibitor sildenafil. But PAH treatment has advanced significantly over the past decade, and new classes of targeted drug therapies, such as stimulators of the soluble guanylate cyclase (riociguat) or prostacyclin receptor agonists (selexipag), are currently evaluated regarding their efficacy and safety in children, in order to limit off-label use. Due to the different etiologies in children, such as PAH-CHD, there is no evidence that initial combination therapy in children is superior to a mono-therapy with respect to survival. Special attention should also be paid to the pharmacology of PAH drugs in children, which might be impacted by ontogeny or drug-drug-interactions. Therapeutic drug monitoring may be useful in pediatric patients. There is a clear need for more controlled studies of PAH medications, alone or in combination therapy in the pediatric age group. Data from clinical trials as well as from patient registries should be pooled to optimize drug development and evaluation, trial design, and evidence-based pharmacotherapy in pediatric patients with PAH. In this review, the current treatment options of pediatric PAH are summarized, and an overview of new treatment concepts, which are already evaluated in adults, is presented.

Evidence base for specific pulmonary vasodilators in adults with congenital heart disease

After reviewing the current definitions and classification of pulmonary hypertension (PH) associated with congenital heart disease (CHD), based on an analysis of 59 clinical trials (of which 14 are randomized controlled trials) drugs registered in the Russian Federation, the evidence base for PH therapy in adults with CHD is provided. The presence of a randomized controlled trial of bosentan BREATHE-5 and uncontrolled trials of other drugs became the basis for a higher class and level of evidence of bosentan (IB) compared to other drugs (IIaC) for Eisenmenger syndrome in the current European (ERS/ESC 2015) and updated Russian (2020) guidelines. According to the updated European (ESC 2020) guidelines for congenital heart disease in adults, in Eisenmenger patients with reduced exercise capacity (6MWT distance 450 m), a treatment strategy with initial endothelin receptor antagonist monotherapy should be considered followed by combination therapy if patients fail to improve (IIaB), in low- and intermediate-risk patients with repaired simple lesions and pre-capillary PH, initial oral combination therapy or sequential combination therapy is recommended and high-risk patients should be treated with initial combination therapy including parenteral prostanoids (IA) and endothelin receptor antagonists and phosphodiesterase 5 inhibitors may be considered in selected patients with elevated pulmonary pressure/resistance in the absence of elevated ventricular end diastolic pressure (IIbC). Only three (bosentan, macitentan and selexipag) out of seven specific pulmonary vasodilators registered in the Russian Federation have indications for pulmonary arterial hypertension associated with congenital heart disease and Eisenmenger syndrome or pulmonary arterial hypertension associated with corrected simple congenital heart disease in the instructions for use.

The pulmonary vascular bed in patients with functionally univentricular physiology and a Fontan circulation

Fontan palliation represents one of the most remarkable surgical advances in the management of individuals born with functionally univentricular physiology. The operation secures adult survival for all but a few with unfavourable anatomy and/or physiology. Inherent to the physiology is passive transpulmonary blood flow, which produces a vulnerability to adequate filling of the systemic ventricle at rest and during exertion. Similarly, the upstream effects of passive flow in the lungs are venous congestion and venous hypertension, especially marked during physical activity. The pulmonary vascular bed has emerged as a defining character on the stage of Fontan circulatory behaviour and clinical outcomes. Its pharmacologic regulation and anatomic rehabilitation therefore seem important strategic therapeutic targets. This review seeks to delineate the important aspects of pulmonary artery development and maturation in functionally univentricular physiology patients, pulmonary artery biology, pulmonary vascular reserve with exercise, and pulmonary artery morphologic and pharmacologic rehabilitation.

Total vascular resistance increases during volume-unloading in asymptomatic single ventricle patients

OBJECTIVE

While the surgical stages of single ventricle (SV) palliation serve to separate pulmonary venous and systemic venous return, and to volume-unload the SV, staged palliation also results in transition from parallel to series circulation, increasing total vascular resistance. How this transition affects pressure loading of the SV is as yet unreported.

METHODS

We performed a retrospective chart review of Stage I, II, and III cardiac catheterization (CC) and echocardiographic data from 2001-2017 in all SV pts, with focus on systemic, pulmonary, and total vascular resistance (SVR, PVR, TVR respectively). Longitudinal analyses were performed with log-transformed variables. Effects of SVR-lowering medications were analyzed using Wilcoxon rank-sum testing.

RESULTS

There were 372 total patients who underwent CC at a Stage I (median age of 4.4 months, n=310), Stage II (median age 2.7 years, n = 244), and Stage III (median age 7.3 years, n = 113). Total volume loading decreases with progression to Stage III (P< 0.001). While PVR gradually increases from Stage II to Stage III, and SVR increases from Stage I to Stage III, TVR dramatically increases with progress towards series circulation. TVR was not affected by use of systemic vasodilator therapy. TVR, PVR, SVR, and CI did not correlate with indices of SV function at Stage III.

CONCLUSIONS

TVR steadily increases with an increasing contribution from SVR over progressive stages. TVR was not affected by systemic vasodilator agents. TVR did not correlate with echo-based indices of SV function. Further studies are needed to see if modulating TVR can improve exercise tolerance and outcomes.

Carvedilol Does Not Improve Exercise Performance in Fontan Patients: Results of a Crossover Trial

Increased circulating catecholamines are associated with worse exercise performance in adult heart failure patients. Patients with Fontan physiology have increased circulating catecholamines and theoretically could benefit from beta blockade. We hypothesized that carvedilol would improve exercise performance in Fontan patients. A double-blind, placebo-controlled, crossover trial of carvedilol was performed. Single ventricle patients between the ages of 10 and 35 years with a previous Fontan operation who were able to complete a maximal exercise test (respiratory exchange ratio > 1.0) were included. Two 12-week treatment arms were separated by a 6-week washout period. Exercise testing was performed at beginning and end of each treatment arm. Primary endpoint was improvement in peak oxygen consumption/kg (pVO₂) from baseline. Of the 26 subjects enrolled, 23 completed the study. Four subjects did not reach goal maximum carvedilol dose, vs. 1 for placebo (p = 0.14). The mean change in pVO₂ between treatments was not different (carvedilol = - 2.1 mL/kg/min v. placebo = - 1.42, p = 0.28). Carvedilol therapy decreased peak heart rate by 4.2 ± 20.2 bpm, (p < 0.01) leading to an increase in peak oxygen pulse (p < 0.01). Serum N-terminal-proBNP increased with carvedilol therapy (mean change of + 23.77 pg/mL) compared to placebo (mean change of - 5.37 pg/mL, p = 0.03). There were no serious adverse events related to study drug. Carvedilol was not associated with improved exercise performance and was associated with mildly increased N-terminal-proBNP. This study does not support the routine administration of carvedilol to healthy Fontan patients.Clinical Trials Registration ClinicalTrials.gov Identifier: NCT02946892. Registered October 27, 2016. Retrospectively Registered. https://clinicaltrials.gov/ct2/show/NCT02946892.

Hemodynamic and Clinical Implications of Impaired Pulmonary Vascular Reserve in the Fontan Circulation

BACKGROUND

Pulmonary vascular disease, pulmonary endothelial dysfunction, liver fibrosis, renal disease, and exercise intolerance are common in adults with Fontan physiology. Although the pathophysiologic mechanisms linking these phenomena have been studied, certain aspects are not well understood.

OBJECTIVES

This study hypothesized that impaired pulmonary vascular reserve (VR) plays a central role linking these abnormalities, and that patients with abnormal pulmonary VR with exercise, compared with patients with normal VR, would display poorer pulmonary endothelial function, greater liver stiffness, more renal dysfunction, and poorer exercise capacity.

METHODS

Symptomatic adults with the Fontan palliation (n = 29) underwent invasive cardiopulmonary exercise testing, echocardiography, and assessment of microvascular function. Abnormal pulmonary VR was defined by the slope of increase in pulmonary pressure relative to cardiac output with exercise >3 mm Hg/l/min. Pulmonary endothelial function was assessed using reactive hyperemia index. End-organ function was assessed using magnetic resonance elastography-derived liver stiffness, glomerular filtration rate, N-terminal pro-B-type natriuretic peptide, and peak oxygen consumption (Vo₂).

RESULTS

Compared with individuals with normal VR (n = 8), those with abnormal VR (n = 21) displayed higher central and pulmonary venous pressures, and more severely impaired cardiac output and stroke volume responses to exertion, but similar pulmonary vascular resistance at rest. Patients with abnormal VR displayed more severely impaired reactive hyperemia index, increased liver stiffness, lower glomerular filtration rate, higher N-terminal pro-B-type natriuretic peptide, and lower peak Vo₂. As compared to pulmonary vascular resistance at rest, slope of increase in pulmonary pressure relative to cardiac output displayed stronger correlations with reactive hyperemia index (r = -0.63 vs. r = -0.31; Meng test p = 0.009), magnetic resonance elastography-derived liver stiffness (r = 0.47 vs. r = 0.29; Meng test p = 0.07), glomerular filtration rate (r = -0.52 vs. r = -0.24; Meng test p = 0.03), N-terminal pro-B-type natriuretic peptide (r = 0.56 vs. r = 0.17; Meng test p = 0.02), and peak Vo₂ (r = -0.63 vs. r = -0.26; Meng test p = 0.02).

CONCLUSIONS

Pulmonary vascular limitations in Fontan physiology are related to pulmonary endothelial and end-organ dysfunction, suggesting a mechanistic link between these commonly observed findings, and these abnormalities are more apparent during exercise testing, with little relationship at rest.

Systemic Artery Vasoconstrictor Therapy in Fontan Patients with High Cardiac Output-Heart Failure: A Single-Center Experience

Failed Fontan Patients with high cardiac output (CO) heart failure (HF) might have vasodilatory syndrome and markedly high mortality rates. The aim of this study was to review the clinical effects of vasoconstrictor therapy (VCT) for failed Fontan hemodynamics. We retrospectively reviewed 10 consecutive patients with Fontan failure (median age, 33 years) and high CO-HF who had received VCT. The hemodynamics were characterized by high central venous pressure (CVP: median, 16 mm Hg), low systolic blood pressure (median, 83 mm Hg), low systemic vascular resistance (median, 8.8 U·m²), high cardiac index (median, 4.6 L/min/m²), and low arterial oxygen saturation (median, 89%). VCT included intravenous noradrenaline infusion for five unstable patients, oral midodrine administration for nine stable patients, and both for four patients. After VCT introduction with a median interval of 1.7 months, the median systolic blood pressure (102 mm Hg, p = 0.004), arterial oxygen saturation (90%, p = 0.03), and systemic vascular resistance (12.1 U·m², p = 0.13) increased without significant changes in CVP or cardiac index. After a median follow-up of 21 months, the number of readmissions per year decreased from 4 (1-11) to 1 (0-9) (p = 0.25), and there were no VCT-related complications; however, five patients (50%) developed hepatic encephalopathy, and six patients (60%) eventually died. VCT was safely introduced and could prevent the rapidly deteriorating Fontan hemodynamics. VCT could be an effective therapeutic strategy for failed Fontan patients with high CO-HF.

Focused Update on Pulmonary Hypertension in Children-Selected Topics of Interest for the Adult Cardiologist

Pulmonary hypertensive vascular disease (PHVD), and pulmonary hypertension (PH), which is a broader term, are severe conditions associated with high morbidity and mortality at all ages. Treatment guidelines in childhood are widely adopted from adult data and experience, though big differences may exist regarding aetiology, concomitant conditions and presentation. Over the past few years, paediatric aspects have been incorporated into the common guidelines, which currently address both children and adults with pulmonary hypertension (PH). There are multiple facets of PH in the context of cardiac conditions in childhood. Apart from Eisenmenger syndrome (ES), the broad spectrum of congenital heart disease (CHD) comprises PH in failing Fontan physiology, as well as segmental PH. In this review we provide current data and novel aspects on the pathophysiological background and individual management concepts of these conditions. Moreover, we focus on paediatric left heart failure with PH and its challenging issues, including end stage treatment options, such as mechanical support and paediatric transplantation. PH in the context of rare congenital disorders, such as Scimitar Syndrome and sickle cell disease is discussed. Based on current data, we provide an overview on multiple underlying mechanisms of PH involved in these conditions, and different management strategies in children and adulthood. In addition, we summarize the paediatric aspects and the pros and cons of the recently updated definitions of PH. This review provides deeper insights into some challenging conditions of paediatric PH in order to improve current knowledge and care for children and young adults.

Comparison of pleural effusion between fenestrated and nonfenestrated extracardiac Fontan: A prospective randomized study

BACKGROUND

Fenestration of the baffle/conduit is believed to reduce pleural effusion following the Fontan operation. However, equivocal results have been observed with or without fenestration. This study aims to evaluate the efficacy of fenestration on the amount and duration of pleural effusion following the Fontan operation.

METHODS

About 40 patients undergoing extracardiac Fontan (ECF) were randomized into two groups: one with fenestration (ECF-F; n = 20) or without fenestration (ECF-NF; n = 20). Primary outcome was the amount and duration of pleural effusions. Secondary outcomes were time to removal of the chest tubes, hospital stay, and readmission to the hospital because of recurrent pleural within 30 days of the operation.

RESULTS

Mean age was 11.5 ± 5.07 (range, 8.7-13.5) years in the ECF-F group and 13.6 ± 0.4 years (range, 10.5-15.5) in the (ECF-NF) group. The total drain output was 7.89 mL/kg/d in ECF-NF compared with 6.9 mL/kg/d in the ECF-group (P = .14). Time for removal of pleural tubes was 14.6 ± 0.95 days in the ECF-NF group compared with 11.6 ± days in the ECF-F group. Total duration of hospital stay was higher but not significant in the ECF-NF group compared with the ECF-F group. Two patients in ECF-NF required readmission to the hospital within 30 days following discharge, while there were no readmissions in the ECF-F group.

CONCLUSION

Contrary to the literature, the creation of a fenestration in the ECF circuit was not clearly associated with a reduction in the amount and duration of pleural effusion compared with a non-fenestrated Fontan. These findings may be debatable in high risks versus low risk candidates. However in the present study, in a low risk canditates undergoing the Fontan operation, the daily amount of pleural drainage was no different. Larger studies are needed to confirm these findings.

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.

Pulmonary Vasodilator Therapy in Children with Single Ventricle Physiology: Effects on Saturation and Pulmonary Arterial Pressure

In children with single ventricle physiology, increased pulmonary vascular resistance may impede surgical progression or result in failing single ventricle physiology. The use of pulmonary vasodilators has been suggested as a potential therapy. However, knowledge on indication, dosage, and effect is limited. A retrospective case notes review of all (n = 36) children with single ventricle physiology, treated with pulmonary vasodilators by the UK Pulmonary Hypertension Service for Children 2004-2017. Therapy was initiated in Stage 1 (n = 12), Glenn (n = 8), or TCPC (n = 16). Treatment indications were high mean pulmonary arterial pressure, cyanosis, reduced exercise tolerance, protein-losing enteropathy, ascites, or plastic bronchitis. Average dose of sildenafil was 2.0 mg/kg/day and bosentan was 3.3 mg/kg/day. 56% had combination therapy. Therapy was associated with a reduction of the mean pulmonary arterial pressure from 19 to 14 mmHg (n = 17, p < 0.01). Initial therapy with one or two vasodilators was associated with an increase in the mean saturation from 80 to 85%, (n = 16, p < 0.01). Adding a second vasodilator did not give significant additional effect. 5 of 12 patients progressed from Stage 1 to Glenn, Kawashima, or TCPC, and 2 of 8 from Glenn to TCPC during a mean follow-up time of 4.7 years (0-12.8). Bosentan was discontinued in 57% and sildenafil in 14% of treated patients and saturations remained stable. Pulmonary vasodilator therapy was well tolerated and associated with improvements in saturation and mean pulmonary arterial pressure in children with single ventricle physiology. It appears safe to discontinue when no clear benefit is observed.

Results of the FUEL Trial

BACKGROUND

The Fontan operation creates a total cavopulmonary connection, a circulation in which the importance of pulmonary vascular resistance is magnified. Over time, this circulation leads to deterioration of cardiovascular efficiency associated with a decline in exercise performance. Rigorous clinical trials aimed at improving physiology and guiding pharmacotherapy are lacking.

METHODS

The FUEL trial (Fontan Udenafil Exercise Longitudinal) was a phase III clinical trial conducted at 30 centers. Participants were randomly assigned udenafil, 87.5 mg twice daily, or placebo in a 1:1 ratio. The primary outcome was the between-group difference in change in oxygen consumption at peak exercise. Secondary outcomes included between-group differences in changes in submaximal exercise at the ventilatory anaerobic threshold, the myocardial performance index, the natural log of the reactive hyperemia index, and serum brain-type natriuretic peptide.

RESULTS

Between 2017 and 2019, 30 clinical sites in North America and the Republic of Korea randomly assigned 400 participants with Fontan physiology. The mean age at randomization was 15.5±2 years; 60% of participants were male, and 81% were white. All 400 participants were included in the primary analysis with imputation of the 26-week end point for 21 participants with missing data (11 randomly assigned to udenafil and 10 to placebo). Among randomly assigned participants, peak oxygen consumption increased by 44±245 mL/min (2.8%) in the udenafil group and declined by 3.7±228 mL/min (-0.2%) in the placebo group (P=0.071). Analysis at ventilatory anaerobic threshold demonstrated improvements in the udenafil group versus the placebo group in oxygen consumption (+33±185 [3.2%] versus -9±193 [-0.9%] mL/min, P=0.012), ventilatory equivalents of carbon dioxide (-0.8 versus -0.06, P=0.014), and work rate (+3.8 versus +0.34 W, P=0.021). There was no difference in change of myocardial performance index, the natural log of the reactive hyperemia index, or serum brain-type natriuretic peptide level.

CONCLUSIONS

In the FUEL trial, treatment with udenafil (87.5 mg twice daily) was not associated with an improvement in oxygen consumption at peak exercise but was associated with improvements in multiple measures of exercise performance at the ventilatory anaerobic threshold.

CLINICAL TRIAL REGISTRATION

URL: https://www.clinicaltrials.gov. Unique identifier: NCT02741115.

Hepatic pathology in patients after Fontan operation: A computed tomography imaging study

BACKGROUND

Hepatic dysfunction is an important long-term complication in Fontan patients. The purpose of this study was to evaluate the hepatic computed tomography (CT) findings after Fontan surgery and identify their association with clinical parameters.

METHODS

This study recruited 43 patients (23 male and 20 female patients aged 15.3 ± 6.8 years), who underwent Fontan surgery. Medical records were reviewed to collect their age, sex, congenital heart disease type, date of Fontan surgery, laboratory data, and hepatic CT findings. The relationship between hepatic findings and clinical parameters was analyzed.

RESULTS

The follow-up duration was 6.8 ± 4.1 years. Abnormal hepatic parenchymal enhancement was observed in 77% of the patients, with mild degree in 18, moderate degree in 10, and severe degree in 5 patients. According to the univariate analysis, risk factors for hepatic parenchymal enhancement were follow-up duration (odds ratio [OR]: 1.354 [95% confidence interval (CI): 1.024-2.078]; p = 0.042), hypoplastic left heart syndrome (HLHS) (OR: 3.262 [95% CI: 1.145-5.628]; p = 0.002), mean pulmonary artery pressure (OR: 1.598 [95% CI: 1.089-2.132]; p = 0.026), pulmonary vascular resistance index (OR: 1.263 [95% CI: 1.068-1.245]; p = 0.032), and brain natriuretic peptide (OR: 1.956 [95% CI: 1.085-2.673]; p = 0.045). According to the multivariate analysis, only HLHS (OR: 3.856 [95% CI: 1.389-5.863]; p = 0.001), mean pulmonary artery pressure (OR: 1.846 [95% CI: 1.362-2.549]; p = 0.015), and pulmonary vascular resistance index (OR: 1.185 [95% CI: 1.042-1.736]; p = 0.047) were significant risk factors for abnormal parenchymal enhancement.

CONCLUSION

Abnormal hepatic parenchymal enhancement detected through CT is common in Fontan patients. Regular liver function test in conjunction with imaging studies may be considered when following up Fontan patients.

Venous congestion and pulmonary vascular function in Fontan circulation: Implications for prognosis and treatment

BACKGROUND

Elevation in central venous pressure (CVP) plays a fundamental pathophysiologic role in Fontan circulation. Because there is no sub-pulmonary ventricle in this system, CVP also provides the driving force for pulmonary blood flow. We hypothesized that this would make Fontan patients more susceptible to even low-level elevation in pulmonary vascular resistance index (PVRI), resulting in greater systemic venous congestion and adverse outcomes.

METHODS

Adult Fontan patients and controls without congenital heart disease undergoing clinical evaluation that included cardiac catheterization and echocardiography were examined retrospectively. Outcomes including all-cause mortality and the development of Fontan associated diseases (FAD, defined as protein losing enteropathy, cirrhosis, heart failure hospitalization, arrhythmia, or thromboembolism) were assessed from longitudinal assessment.

RESULTS

As compared to controls (n = 82), Fontan patients (n = 164) were younger (36 vs 45 years, p < 0.001), more likely to be on anticoagulation or antiplatelet therapy, and more likely to have atrial arrhythmia or cirrhosis. There was a strong correlation between CVP and PVRI in the Fontan group (r = 0.79, p < 0.001), but there was no such relationship in controls. Elevated PVRI identified patients at increased risk for FAD (HR 1.92, 95% CI 1.39-2.41, p = 0.01), and composite endpoint of FAD and/or death (HR 1.89, 95% CI 1.32-2.53, p = 0.01) per 1 WU∗m² increment.

CONCLUSIONS

Systemic venous congestion, which is the primary factor in the pathogenesis of FAD and death, is related to even low-level abnormalities in pulmonary vascular function. Multicenter studies are needed to determine whether interventions targeting pulmonary vascular structure and function can improve outcomes in the Fontan population.

Design and rationale of the Fontan Udenafil Exercise Longitudinal (FUEL) trial

The Fontan operation creates a circulation characterized by elevated central venous pressure and low cardiac output. Over time, these characteristics result in a predictable and persistent decline in exercise performance that is associated with an increase in morbidity and mortality. A medical therapy that targets the abnormalities of the Fontan circulation might, therefore, be associated with improved outcomes. Udenafil, a phosphodiesterase type 5 inhibitor, has undergone phase I/II testing in adolescents who have had the Fontan operation and has been shown to be safe and well tolerated in the short term. However, there are no data regarding the long-term efficacy of udenafil in this population. The Fontan Udenafil Exercise Longitudinal (FUEL) Trial is a randomized, double-blind, placebo-controlled phase III clinical trial being conducted by the Pediatric Heart Network in collaboration with Mezzion Pharma Co, Ltd. This trial is designed to test the hypothesis that treatment with udenafil will lead to an improvement in exercise capacity in adolescents who have undergone the Fontan operation. A safety extension trial, the FUEL Open-Label Extension Trial (FUEL OLE), offers the opportunity for all FUEL subjects to obtain open-label udenafil for an additional 12 months following completion of FUEL, and evaluates the long-term safety and tolerability of this medication. This manuscript describes the rationale and study design for FUEL and FUEL OLE. Together, these trials provide an opportunity to better understand the role of medical management in the care of those who have undergone the Fontan operation.

State of the art of the Fontan strategy for treatment of univentricular heart disease

In patients with a functionally univentricular heart, the Fontan strategy achieves separation of the systemic and pulmonary circulation and reduction of ventricular volume overload. Contemporary modifications of surgical techniques have significantly improved survival. However, the resulting Fontan physiology is associated with high morbidity. In this review, we discuss the state of the art of the Fontan strategy by assessing survival and risk factors for mortality. Complications of the Fontan circulation, such as cardiac arrhythmia, thromboembolism, and protein-losing enteropathy, are discussed. Common surgical and catheter-based interventions following Fontan completion are outlined. We describe functional status measurements such as quality of life and developmental outcomes in the contemporary Fontan patient. The current role of drug therapy in the Fontan patient is explored. Furthermore, we assess the current use and outcomes of mechanical circulatory support in the Fontan circulation and novel surgical innovations. Despite large improvements in outcomes for contemporary Fontan patients, a large burden of disease exists in this patient population. Continued efforts to improve outcomes are warranted. Several remaining challenges in the Fontan field are outlined.

Pulmonary arterial hypertension in adult congenital heart disease

Pulmonary arterial hypertension (PAH) is commonly associated with congenital heart disease (CHD) and relates to type of the underlying cardiac defects and repair history. Large systemic to pulmonary shunts may develop PAH if untreated or repaired late. PAH, when present, markedly increases morbidity and mortality in patients with CHD. Significant progress has been made for patients with Eisenmenger syndrome in pathophysiology, prognostication and disease-targeting therapy (DTT), which needs to be applied to routine patient care. Patients with PAH–CHD and systemic to pulmonary shunting may benefit from late defect closure if pulmonary vascular resistance (PVR) is still normal or near normal. Patients with PAH and coincidental defects, or previous repair of CHD should be managed as those with idiopathic PAH. Patients with a Fontan circulation, despite not strictly fulfilling criteria for PAH, may have elevated PVR; recent evidence suggests that they may also benefit from DTT, but more data are required before general recommendations can be made. CHD–PAH is a lifelong, progressive disease; patients should receive tertiary care and benefit from a proactive DTT approach. Novel biomarkers and genetic advances may identify patients with CHD who should be referred for late defect closure and/or patients at high risk of developing PAH despite early closure in childhood. Ongoing vigilance for PAH and further controlled studies are clearly warranted in CHD.

Hemodynamics of Fontan Failure: The Role of Pulmonary Vascular Disease

BACKGROUND

Nonpulsatile pulmonary blood flow in Fontan circulation results in pulmonary vascular disease, but the potential relationships between pulmonary vascular resistance index (PVRI) and Fontan failure have not been studied. The objective was to determine whether the absence of subpulmonary ventricle in the Fontan circulation would make patients more vulnerable to even low-level elevations in PVRI, and when coupled with low cardiac index, this would identify patients at increased risk of Fontan failure.

METHODS AND RESULTS

Two hundred sixty-one adult Fontan patients underwent cardiac catheterization; age 26±3 years, men 146 (56%), atriopulmonary Fontan 144 (55%). Patients were divided into 2 groups: those with high PVRI (>2 WU·m2) and low cardiac index <2.5 L min-1 m-2 (group 1, n=70, 30%), and those with normal PVRI and normal cardiac index (group 2, n=182, 70%). Fontan failure was defined by the composite of all-cause mortality, listing for heart transplantation, or initiation of palliative care. There were 68 (26%) cases of Fontan failure during a mean follow-up of 8.6±2.4 years. When compared with group 2, freedom from Fontan failure was significantly lower in group 1: 66% versus 89% at 5 years. The combination of high PVRI and low cardiac index was an independent risk factor for Fontan failure (hazard ratio, 1.84; 95% confidence interval, 1.09-2.85).

CONCLUSIONS

When coupled with low cardiac index, even mild elevations in PVRI identify patients at high risk of Fontan failure. This suggests that pulmonary vascular disease is a key mechanism underlying Fontan failure and supports further studies to understand the pathophysiology and target treatments to pulmonary vascular tone in this population.

Where Is the "Optimal" Fontan Hemodynamics?

Fontan circulation is generally characterized by high central venous pressure, low cardiac output, and slightly low arterial oxygen saturation, and it is quite different from normal biventricular physiology. Therefore, when a patient with congenital heart disease is selected as a candidate for this type of circulation, the ultimate goals of therapy consist of 2 components. One is a smooth adjustment to the new circulation, and the other is long-term circulatory stabilization after adjustment. When either of these goals is not achieved, the patient is categorized as having "failed" Fontan circulation, and the prognosis is dismal. For the first goal of smooth adjustment, a lot of effort has been made to establish criteria for patient selection and intensive management immediately after the Fontan operation. For the second goal of long-term circulatory stabilization, there is limited evidence of successful strategies for long-term hemodynamic stabilization. Furthermore, there have been no data on optimal hemodynamics in Fontan circulation that could be used as a reference for patient management. Although small clinical trials and case reports are available, the results cannot be generalized to the majority of Fontan survivors. We recently reported the clinical and hemodynamic characteristics of early and late failing Fontan survivors and their association with all-cause mortality. This knowledge could provide insight into the complex Fontan pathophysiology and might help establish a management strategy for long-term hemodynamic stabilization.