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Dr. Alessandro Giardini
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Completing the Fontan operation is a profound moment for families who have navigated the surgical pathway of hypoplastic left heart syndrome. It is the endpoint of the staged palliation, and for many children it opens a period of relative stability and functional improvement that can feel, at last, like a kind of normal.
The Fontan circulation is not normal. It sustains life remarkably well in childhood and adolescence, but it does so by imposing a sustained physiological burden on the body that accumulates over decades. Understanding what that means in practice, what complications to watch for, and why lifelong specialist follow-up is not optional but structural is what this post addresses.
After the Fontan operation, all systemic venous blood flows passively to the lungs, driven by the pressure difference between the systemic veins and the pulmonary circulation, without passing through a pumping chamber. The single right ventricle pumps only oxygenated blood to the body.
This arrangement works, but it creates two persistent abnormalities that have consequences for every organ system over time. First, systemic venous pressure is chronically elevated because venous blood must flow uphill against pulmonary vascular resistance without a pump to drive it. Second, cardiac output is chronically limited because the passive pulmonary flow cannot increase as effectively as normal in response to exertion, so the ventricle cannot receive and pump more blood when the body demands it during exercise or illness.
These two abnormalities, elevated systemic venous pressure and limited cardiac output reserve, are the roots from which most long-term Fontan complications grow.
The most pervasive long-term complication of the Fontan circulation is liver disease. Chronically elevated hepatic venous pressure, transmitted from the high-pressure Fontan circuit to the hepatic sinusoids, causes progressive congestive hepatopathy. Over years and decades, this leads to hepatic fibrosis, and in a proportion of patients to cirrhosis and hepatocellular carcinoma.
Fontan-associated liver disease develops in virtually every patient with a Fontan circulation given sufficient time. The rate of progression varies considerably between individuals and is associated with the degree of Fontan circuit pressure, the duration of the Fontan, and individual biological factors. It is detectable long before it becomes symptomatic.
Liver surveillance is now a standard component of HLHS follow-up from childhood onwards. This includes regular liver function blood tests and abdominal imaging at defined intervals. The purpose of surveillance is to detect progressive fibrosis before it reaches the stage at which hepatic complications become symptomatic or irreversible. Families should ensure this component of follow-up is occurring and understand what the results mean.
Arrhythmias are among the most common long-term complications of the Fontan circulation and one of the most clinically significant in terms of the acute risk they carry. The altered atrial haemodynamics, the surgical scars from the Fontan construction, and the chronically elevated atrial pressures all create a substrate for abnormal atrial rhythm disturbances.
Atrial flutter and atrial fibrillation are the most common sustained arrhythmias in adult Fontan patients. They are important not only because they cause symptoms and reduce cardiac output, but because they can precipitate acute haemodynamic deterioration in a circulation that has little reserve. An atrial arrhythmia that would be haemodynamically tolerated in a normal heart can rapidly lead to clinical collapse in a Fontan patient.
Ventricular arrhythmias, including ventricular tachycardia, also occur with increasing frequency as the right ventricle ages and develops fibrosis. The management of arrhythmias in Fontan patients requires specialist expertise and typically involves a combination of catheter ablation, antiarrhythmic medication, and implantable devices where appropriate.
Every child with a Fontan circulation should have ECG reviews as part of their follow-up, and any new palpitations, pre-syncope, or symptoms of reduced exercise tolerance should prompt prompt cardiological assessment.
Protein-losing enteropathy (PLE) is a serious complication of the Fontan circulation in which protein leaks from the gut into the intestinal lumen at a rate that exceeds the liver's ability to replace it. The result is chronically low protein levels in the blood, leading to oedema, ascites, and significant immunological vulnerability.
PLE occurs in approximately 5 to 10% of Fontan patients and is associated with a substantially reduced life expectancy if it does not respond to treatment. Its development reflects elevated intestinal lymphatic pressure from the high Fontan circuit pressures, combined in some cases with a reduced cardiac output that compromises gut perfusion. Management involves a combination of dietary modifications, diuretics, anticoagulation adjustments, and in some cases catheter-based interventions to improve Fontan haemodynamics. Cardiac transplantation may be considered in cases that do not respond.
PLE should be actively looked for past the first decade of life at annual review through measurement of serum albumin and total protein levels. Early detection allows more treatment options.
Plastic bronchitis is an uncommon but potentially life-threatening complication in which thick, rubbery casts of lymphatic material form within the bronchial tree, causing airway obstruction. It is related to the same lymphatic hypertension that drives PLE, but manifests in the lungs rather than the gut.
Children with plastic bronchitis typically present with episodes of acute respiratory distress, coughing, and occasionally expectoration of visible bronchial casts. The condition is managed by a specialist team combining pulmonology and cardiac expertise, and increasingly, interventional lymphatic procedures to relieve the underlying lymphatic obstruction are being used at specialist centres.
Exercise capacity in children and young adults with a Fontan circulation is meaningfully reduced compared to the general population, reflecting the limited ability of the passive pulmonary circulation to increase cardiac output during exertion. This does not prevent participation in most aspects of daily life and moderate physical activity, but it becomes clinically meaningful in the context of work, sport, and social participation as children grow into adults.
Regular exercise testing is part of long-term Fontan follow-up and provides objective data on functional capacity over time. A declining trajectory on serial exercise tests is an important signal that the Fontan circulation is deteriorating and that intervention, including consideration of cardiac transplantation, may need to be planned.
Fontan failure, the eventual inability of the Fontan circulation to sustain adequate systemic output, is the principal reason that cardiac transplantation is required in adult Fontan patients. It is not an inevitable outcome for all, but it is a recognised progression for a proportion. Transplant-free survival at 35 years in a large published cohort is approximately 31%. Within that, there is a group of high-performing survivors who report good health and quality of life, and the characteristics that predict this trajectory are the subject of active research.
The neurodevelopmental risks of HLHS, arising from altered foetal cerebral circulation and the complexity of neonatal surgery, do not disappear with time. Cognitive difficulties, attentional problems, and learning differences identified in early childhood tend to persist and in some cases become more apparent as academic demands increase in later primary and secondary school years.
Regular formal neurodevelopmental assessment is important throughout childhood, not just in the early years. A child who was managing adequately at age seven may face new challenges at age eleven when the curriculum becomes more abstract and demanding. Early identification of specific learning needs and prompt engagement with educational psychology services makes a substantial difference to academic and social outcomes.
Transition from paediatric to adult congenital heart disease care is one of the most important clinical events in the long-term management of HLHS. It typically occurs in the mid-teens and involves a planned, supported transfer to an adult specialist who understands the Fontan physiology and its complications in depth.
Poor transition is a recognised cause of loss to follow-up, which is itself associated with worse outcomes in adult Fontan patients. Young people who stop attending specialist appointments because they feel well are at risk of presenting with advanced complications that could have been detected and managed earlier.
The transition appointment is not the end of the relationship with the paediatric team. It is a handover, and both teams should be involved in the preparation.
Yes. The complications of the Fontan circulation, including liver disease, arrhythmias, and declining ventricular function, develop insidiously and are detectable before they become symptomatic. The purpose of annual follow-up is precisely to identify these changes while there is still time to intervene effectively. A child who feels completely well is not a child who can safely discontinue specialist review.
Current data suggest transplant-free survival of approximately 31% at 35 years from surgery, with improvements noted over successive eras. However, these are population statistics, and individual outcomes vary considerably. Within the surviving cohort, many report good to excellent quality of life. The goal of careful long-term management is to position each individual child as well as possible within that range, detecting and addressing complications early rather than waiting for them to become symptomatic.
Most individuals with a Fontan circulation are maintained on antiplatelet or anticoagulation therapy long-term to reduce the risk of thromboembolism within the low-flow circuit. The specific agent and dose are reviewed at each follow-up appointment and may change as the child grows. This is not a fixed decision made at the time of the Fontan and left unchanged forever. It requires regular clinical review.
Pregnancy in a woman with a Fontan circulation carries significant risks to both mother and foetus and requires specialist preconception counselling from a team experienced in adult congenital heart disease and obstetric cardiology. It is not universally contraindicated, but it requires careful assessment of Fontan haemodynamics, ventricular function, and the presence of complications. For male patients with HLHS, fertility is not typically affected by the cardiac condition itself, though medications may require review.
Fontan failure is managed by optimising medical therapy, addressing reversible contributors such as arrhythmias or Fontan circuit obstruction, and when these measures are insufficient, by considering cardiac transplantation. Transplantation in a Fontan patient is a complex undertaking that requires specialist surgical expertise, but it is performed at several centres in the UK and remains the most effective rescue strategy when the Fontan circulation is no longer sustainable.
Author: Dr. Alessandro Giardini, MD, PhD, Consultant Paediatric Cardiologist
Written: 22/06/2026