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Fontan procedure

The Fontan procedure is a palliative surgical intervention designed for patients with congenital heart defects featuring a functional single ventricle, in which systemic venous blood is rerouted directly to the pulmonary arteries to facilitate passive blood flow to the lungs, thereby separating the systemic and pulmonary circulations without reliance on a subpulmonary ventricle.^[1] First described and performed in 1968 by French surgeons Francis Fontan and Eugene Baudet for the treatment of tricuspid atresia, the procedure marked a significant advancement in managing univentricular heart physiology, evolving from earlier experimental approaches to address cyanotic congenital heart disease.^[2] Over the subsequent decades, it has become the standard final stage in a multistage palliation strategy, typically following initial procedures like the Norwood operation in infancy and the bidirectional Glenn shunt around 4–6 months of age, with completion occurring between 2 and 5 years old.^[1]^[3] Indications for the Fontan procedure include complex congenital anomalies such as hypoplastic left heart syndrome, tricuspid atresia, double inlet left ventricle, and other forms of functional univentricular heart, which collectively account for approximately 7.7% of all congenital heart defects and result in inadequate separation of oxygenated and deoxygenated blood.^[2] Candidates must exhibit favorable preoperative criteria, including normal or near-normal ventricular function, low pulmonary vascular resistance, adequate pulmonary artery size, and minimal atrioventricular valve regurgitation, to optimize postoperative hemodynamics.^[1] Surgical techniques have progressed through several variations to minimize long-term complications: the original atriopulmonary connection (1971), the intra-atrial lateral tunnel (1980s), and the modern extracardiac conduit method, which often incorporates fenestration—a small shunt allowing temporary right-to-left shunting to reduce early pressure overload.^[2] These operations are performed under cardiopulmonary bypass, connecting the inferior vena cava to the pulmonary arteries while preserving the single ventricle's role in systemic circulation.^[1] Short-term outcomes are favorable, with operative mortality rates as low as 1.2% in contemporary series, reflecting refinements in perioperative care and patient selection.^[1] Long-term survival reaches approximately 83% at 25 years, though only about 29% of patients remain free from severe morbidity, with reduced exercise capacity and neurodevelopmental challenges common due to chronic low cardiac output.^[2] Complications, which often manifest in adulthood, encompass supraventricular arrhythmias (affecting up to 50% by age 30), protein-losing enteropathy (in 5–15% of cases, carrying a 50% five-year mortality), thromboembolic events, hepatic fibrosis, and ventricular dysfunction, necessitating lifelong multidisciplinary surveillance.^[1]^[2]

Background and Indications

Relevant Congenital Heart Defects

Single ventricle defects encompass a spectrum of complex congenital heart malformations in which only one ventricle is capable of supporting systemic circulation, often due to the hypoplasia or absence of the second ventricle. These conditions arise from abnormal embryonic cardiac development and include tricuspid atresia, hypoplastic left heart syndrome (HLHS), and double inlet left ventricle (DILV). In tricuspid atresia, the tricuspid valve fails to develop, resulting in blood flow from the right atrium to the left ventricle via an atrial septal defect and an underdeveloped right ventricle. HLHS is characterized by underdevelopment of the left ventricle, mitral valve, aortic valve, and ascending aorta, with systemic output dependent on a patent ductus arteriosus. DILV involves both atrioventricular valves draining into a single, morphologically left ventricle, accompanied by a rudimentary right ventricle and often associated great vessel anomalies.^[4]^[5]^[6] In these defects, the systemic and pulmonary circulations function in parallel rather than the normal series arrangement, leading to obligatory mixing of oxygenated pulmonary venous blood and deoxygenated systemic venous blood, typically at the atrial or ventricular level through septal defects or shunts. This admixture results in reduced systemic oxygen saturation (typically 75–85%), manifesting as cyanosis that worsens with closure of fetal shunts like the ductus arteriosus. Excessive pulmonary blood flow, driven by low pulmonary vascular resistance postnatally, imposes a volume overload on the single ventricle, predisposing to congestive heart failure with symptoms such as tachypnea, poor feeding, and hepatomegaly. The Fontan procedure ultimately seeks to separate these circulations by routing systemic venous return passively to the pulmonary arteries.^[6]^[4] Anatomically, single ventricle defects feature a dominant ventricle responsible for systemic output, a rudimentary or hypoplastic contralateral ventricle unable to contribute meaningfully to circulation, and atrioventricular valve abnormalities such as atresia, straddling, or dysplasia that impair unidirectional flow. Great vessel arrangements are often discordant, including transposition of the great arteries—where the aorta arises from the pulmonary ventricle and the pulmonary artery from the systemic ventricle—or double outlet right ventricle with subaortic stenosis, further complicating hemodynamics by increasing the risk of obstruction or regurgitation.^[4]^[5]^[6] Diagnosis relies on multimodal imaging to delineate anatomy and physiology. Echocardiography serves as the cornerstone, providing real-time visualization of ventricular morphology, valve competence, septal defects, and flow patterns via Doppler, often confirming the defect prenatally or shortly after birth. Cardiac magnetic resonance imaging (MRI) offers superior tissue characterization and quantification of ventricular mass, volumes, and ejection fraction, particularly in cases with poor echocardiographic windows or for serial assessment. Cardiac catheterization provides invasive hemodynamic data, including oxygen saturations to quantify shunting, pressure gradients across outflows, and pulmonary vascular resistance, essential for risk stratification.^[4]^[7]

Patient Selection and Contraindications

The Fontan procedure is primarily indicated for patients with functional single ventricle physiology who have completed prior stages of palliation, such as the Norwood or bidirectional Glenn procedures, to achieve separation of systemic and pulmonary circulations. Ideal candidates are typically children aged 2 to 5 years with preserved systemic ventricular function, evidenced by an ejection fraction greater than 55%, low pulmonary vascular resistance (PVR less than 4 Wood units per square meter, ideally under 2.5 indexed Wood units), mean pulmonary artery pressure below 15 mm Hg, and adequate pulmonary artery dimensions without significant distortion or hypoplasia.^[1]^[8] These criteria ensure the passive pulmonary blood flow inherent to Fontan physiology can be tolerated without excessive venous congestion or inadequate cardiac output. Patient evaluation for Fontan candidacy requires multidisciplinary assessment, including echocardiography, cardiac magnetic resonance imaging, and invasive cardiac catheterization to quantify hemodynamics. Key catheterization metrics include a mean pulmonary artery pressure of 15 mm Hg or less, indexed pulmonary vascular resistance (PVRi) under 3 Wood units per square meter (or approximately 250 to 300 dynes·s·cm⁻⁵·m²), and systemic ventricular end-diastolic pressure below 12 mm Hg, alongside assessment of atrioventricular valve competence and pulmonary artery patency.^[1]^[9] Oxygen saturation levels above 75% post-Glenn procedure and normal sinus rhythm further support suitability, with any modifiable risk factors, such as branch pulmonary artery stenosis, addressed preoperatively to optimize outcomes.^[10] Absolute contraindications to the Fontan procedure encompass conditions that preclude safe establishment of passive pulmonary flow, including irreversible pulmonary hypertension with PVR exceeding 4 Wood units per square meter, severe systemic ventricular dysfunction (ejection fraction below 50%), hypoplastic or absent pulmonary arteries in one lung, and major extracardiac morbidities such as end-stage renal or hepatic disease.^[1]^[8] These factors predict high perioperative mortality or early failure due to inability to maintain adequate pulmonary perfusion or ventricular filling. Relative contraindications involve scenarios where the procedure may be feasible but carries elevated risk, warranting careful consideration and potential interventions. These include moderate to severe atrioventricular valve regurgitation, complex heterotaxy syndrome with interrupted inferior vena cava or bilateral superior vena cava, persistent arrhythmias, or an elevated transpulmonary gradient greater than 6 to 10 mm Hg.^[1]^[8] In such cases, preoperative optimization, such as valve repair or pulmonary vasodilator therapy, may mitigate risks, though outcomes remain guarded compared to ideal candidates.

Surgical Techniques

Types of Fontan Procedures

The Fontan procedure encompasses several variations designed to redirect inferior vena cava flow to the pulmonary arteries while minimizing long-term hemodynamic inefficiencies in single-ventricle physiology. These types differ primarily in the method of connection and involvement of the right atrium, with evolution driven by efforts to reduce complications like atrial arrhythmias and dilation. The classical atriopulmonary connection, first described in 1971, establishes a direct anastomosis between the right atrium and main pulmonary artery. This historical technique bypasses the right ventricle but promotes turbulent flow and right atrial enlargement over time, leading to its obsolescence in favor of more physiologically efficient designs. Long-term outcomes show higher rates of arrhythmia and heart failure compared to modern variants, with only 45% of patients free from death, transplantation, or heart failure at 28 years. The lateral tunnel, or intracardiac total cavopulmonary connection, constructs a baffle within the right atrium using atrial tissue and synthetic material to channel inferior vena cava blood directly to the pulmonary arteries. This approach reduces energy loss from atrial contraction against a non-compliant pathway and preserves low-pressure conditions in the coronary sinus atrium. It offers improved survival rates, with approximately 85% transplantation-free survival at 30 years, though it still involves intra-atrial suture lines that can contribute to arrhythmias. The extracardiac conduit type uses an external prosthetic tube, typically polytetrafluoroethylene, to connect the inferior vena cava to the pulmonary arteries, circumventing the right atrium entirely. This method minimizes atrial dilation, stasis, and arrhythmogenic substrates, resulting in lower long-term arrhythmia incidence and comparable 85% 30-year survival to the lateral tunnel. It can often be performed without cardiopulmonary bypass, shortening operative times, and is the predominant choice in current practice for its hemodynamic advantages. Fenestration is an adjunct feature in both lateral tunnel and extracardiac procedures, creating a small atrial-level communication—typically 3 to 6 mm in diameter—to permit controlled right-to-left shunting of deoxygenated blood. This decompresses the Fontan circuit, lowering early postoperative pleural effusions, hospital stay, and mortality risk in high-risk patients, though it introduces mild cyanosis and potential thromboembolism that often necessitates transcatheter closure once hemodynamics stabilize. Fenestration is used selectively or routinely depending on center protocols and patient risk profiles. Type selection is influenced by patient-specific factors, including age, anatomy, and institutional expertise. Extracardiac conduits are frequently preferred for older children or adolescents to leverage shorter bypass requirements and for complex cases like heterotaxy syndrome, where anomalous venous drainage complicates intra-atrial baffling. Surgeon and center preference also plays a role, as no definitive superiority exists between lateral tunnel and extracardiac approaches in low-risk patients. The procedure typically completes a staged palliation sequence.

Staged Palliation and Surgical Approach

The Fontan procedure represents the final stage in a multi-stage surgical palliation strategy for infants and children with single-ventricle congenital heart defects, aiming to establish passive pulmonary blood flow while minimizing the workload on the systemic ventricle. This staged approach begins in the neonatal period to stabilize hemodynamics and progressively redirects systemic venous return to the pulmonary arteries, allowing for growth and optimization of pulmonary vascular resistance before completion. The pathway typically involves three stages, with careful timing to ensure adequate ventricular function and low pulmonary pressures.^[1] Stage I palliation occurs in the neonatal period, usually within the first week of life, to manage excessive pulmonary blood flow and maintain systemic output. For most single-ventricle lesions, this involves pulmonary artery banding to restrict flow through a patent ductus arteriosus or aortopulmonary shunt, though in hypoplastic left heart syndrome (HLHS), the Norwood procedure is preferred, which reconstructs the aorta using the pulmonary artery and places a systemic-to-pulmonary shunt. This initial intervention stabilizes the infant, promotes balanced circulation, and sets the foundation for subsequent stages.^[11]^[1] Stage II, the bidirectional Glenn shunt, is performed between 3 and 6 months of age, connecting the superior vena cava directly to the pulmonary arteries to offload the ventricle of upper body venous return. This superior cavopulmonary anastomosis reduces volume load on the single ventricle and allows evaluation of pulmonary vascular reactivity, with the procedure often done via sternotomy and without cardiopulmonary bypass in select cases. By this stage, the infant's pulmonary vascular resistance should have decreased naturally, facilitating passive flow.^[11]^[12] The Fontan procedure serves as Stage III, typically completed between 2 and 5 years of age, once pulmonary vascular resistance is low (mean pressure <15-18 mmHg) and ventricular function is preserved. Prior to Fontan, patients are weaned from the Glenn shunt, with cardiac catheterization confirming adequate pulmonary flow and no significant obstructions. This completion redirects inferior vena cava flow to the pulmonary arteries, achieving total cavopulmonary connection and eliminating the need for shunts.^[1]^[11] The surgical approach for Fontan completion generally employs a median sternotomy for access, followed by institution of cardiopulmonary bypass and mild hypothermic cardioplegic arrest to protect the myocardium. Key steps include cannulation of the inferior vena cava for venous drainage, creation of an intracardiac tunnel or extracardiac conduit to baffle or route inferior vena cava blood to the pulmonary arteries, and potential augmentation of the pulmonary arteries with patches if stenoses are present. Fenestration between the conduit/tunnel and the atrium may be added in higher-risk cases to decompress the venous system temporarily. Off-pump techniques, avoiding bypass, are feasible and commonly used for extracardiac conduits in select low-risk patients to minimize inflammation.^[11]^[1] For high-risk neonates, particularly those with HLHS and borderline stability, a hybrid Stage I approach may be used, combining surgical pulmonary artery banding with transcatheter placement of a ductal stent to maintain systemic flow, delaying full Norwood until later. This hybrid strategy bridges to Stage II and reduces early surgical morbidity but requires vigilant monitoring for stent patency and arch obstruction.^[13]

Perioperative Management

Preoperative Preparation

The preoperative preparation for the Fontan procedure involves a multidisciplinary team comprising pediatric cardiologists, congenital heart surgeons, anesthesiologists, nutritionists, and other specialists such as intensivists and nurses to ensure comprehensive patient optimization and coordinated care planning.^[1]^[8] This team focuses on addressing nutritional deficiencies, promoting growth in children who may experience failure to thrive due to chronic cyanosis and increased metabolic demands, and correcting hematologic issues like anemia or thrombocytopenia to improve oxygen-carrying capacity and minimize perioperative bleeding risks.^[1]^[14] Nutritional supplementation and iron store maintenance are prioritized, as poor growth and low hematocrit levels are common in single-ventricle patients and can adversely affect surgical outcomes.^[8] Cardiac evaluation is essential and typically includes repeat echocardiography to assess ventricular function, valve competence, and pulmonary artery dimensions, alongside cardiac magnetic resonance imaging (MRI) or computed tomography to delineate vascular anatomy and quantify ventricular volumes. In select low-risk patients, cardiac magnetic resonance imaging may replace routine catheterization for hemodynamic assessment, as supported by comparative studies showing equivalent outcomes (as of 2024).^[15]^[1]^[14] Cardiac catheterization remains a cornerstone for measuring indexed pulmonary vascular resistance (PVRi), which must be low (ideally <2-3 Wood units·m²) for Fontan candidacy, often involving hemodynamic assessments such as volume loading or calculation of PVR with simulated increased venous return to evaluate tolerance to Fontan physiology.^[8]^[10]^[16] These assessments help confirm patient selection criteria, such as adequate pulmonary artery size and absence of prohibitive pulmonary hypertension.^[1] Medical optimization targets comorbidities to reduce procedural risks, including management of arrhythmias through beta-blockers, antiarrhythmic medications, or preemptive ablation, as atrial tachyarrhythmias occur in up to 60% of adult Fontan candidates and can precipitate hemodynamic instability.^[14] Anticoagulation is initiated or adjusted if venous thrombosis or atrial enlargement is present, typically with aspirin for standard prophylaxis and warfarin for higher-risk cases involving protein-losing enteropathy or ventricular dysfunction, balancing thrombotic (8-33% lifetime risk) and bleeding concerns.^[14] Systemic-to-pulmonary collaterals, which increase volume load and cyanosis, are identified during catheterization and treated via coil embolization to optimize pulmonary blood flow prior to surgery.^[1]^[10] Psychological preparation for the patient and family is conducted through counseling sessions led by the multidisciplinary team, discussing procedural risks such as operative mortality (1-5% in contemporary series), potential complications like prolonged pleural effusions, and long-term implications including the need for lifelong surveillance.^[1]^[14] This informed consent process addresses emotional stressors, including anxiety over the transition to passive pulmonary blood flow, and may involve psychosocial support to enhance coping and adherence to postoperative care.^[8] For high-risk patients with borderline PVR or elevated pulmonary pressures, targeted interventions such as volume loading with intravenous fluids to maintain preload or administration of pulmonary vasodilators like sildenafil are employed preoperatively to lower PVR and improve hemodynamic tolerance, often guided by catheterization data.^[1]^[14] These measures, including minimized fasting periods and early hydration protocols, aim to prevent dehydration-related preload reduction in this preload-dependent circulation.^[10]

Intraoperative and Immediate Postoperative Care

Intraoperative monitoring during the Fontan procedure relies on transesophageal echocardiography (TEE) to evaluate ventricular function, valve competence, and conduit alignment in real time, near-infrared spectroscopy (NIRS) to track cerebral and somatic oxygenation, and invasive hemodynamic assessments including arterial pressure, central venous pressure (CVP), and pulmonary artery pressures. Target CVP post-bypass is typically 10-15 mmHg to balance systemic venous return and pulmonary blood flow without excessive elevation that could impair cardiac output.^[17] Anesthetic management employs a balanced technique featuring high-dose opioids (e.g., fentanyl or sufentanil) combined with muscle relaxants like pancuronium to ensure hemodynamic stability and minimize increases in pulmonary vascular resistance (PVR). High inotropes are avoided to prevent arrhythmias, while weaning from cardiopulmonary bypass involves low-dose inotropic support such as milrinone (0.25-0.75 µg/kg/min) and pulmonary vasodilators including inhaled nitric oxide (iNO) at 10-20 ppm to facilitate passive pulmonary flow and achieve stable hemodynamics.^[18]^[19] Immediate postoperative care occurs in a specialized cardiac intensive care unit, with mechanical ventilation maintained for 24-48 hours using low tidal volumes (4-6 mL/kg) and positive end-expiratory pressure (PEEP) of 3-5 cmH₂O to optimize lung compliance and reduce PVR. Fluid administration is restricted to two-thirds of maintenance requirements (or 80% if chest tubes are present) to mitigate venous hypertension and pleural effusions, while pleural drains are monitored for outputs exceeding 2-3 mL/kg/day, prompting intervention. Early extubation is prioritized based on readiness criteria including stable hemodynamics and adequate oxygenation.^[19] In fenestrated Fontan variants, postoperative echocardiography assesses shunt patency and flow, targeting systemic oxygen saturations of 75-85% to balance decompression of the circulation with cyanosis tolerance. Common early interventions include temporary atrial pacing for junctional ectopic tachycardia or bradycardia, occurring in up to 20-30% of cases, and extracorporeal membrane oxygenation (ECMO) for refractory low cardiac output syndrome, required in fewer than 5% of patients with survival to decannulation around 35-50% in supported cohorts.^[1]^[20]

Complications and Outcomes

Short-term Complications

Short-term complications following the Fontan procedure typically arise in the immediate postoperative period and extend into the first few weeks to months, often related to the abrupt transition to passive pulmonary blood flow and elevated central venous pressure. These include pleural effusions, arrhythmias, low cardiac output states, bleeding, thrombosis, chylothorax, and infections, with overall early complication rates ranging from 20% to 50% in contemporary series.^[21] Management focuses on supportive care, hemodynamic optimization, and targeted interventions to mitigate morbidity and support recovery. Prolonged pleural effusions represent the most common short-term complication, occurring in 20% to 50% of patients and often persisting beyond 2 weeks postoperatively.^[22] These effusions contribute to prolonged hospital stays and are associated with higher central venous pressures and lymphatic congestion in the early Fontan circulation.^[23] Initial management involves low-dose diuretics to reduce fluid overload, while refractory cases may require octreotide to decrease lymphatic production or creation of a fenestration to decompress the venous system and allow right-to-left shunting.^[24] Supraventricular tachyarrhythmias, such as atrial flutter or fibrillation, affect 10% to 30% of patients in the early postoperative period, exacerbated by surgical manipulation of atrial tissue and elevated venous pressures.^[25] These arrhythmias can impair hemodynamics and prolong intensive care unit stays. Treatment typically includes antiarrhythmic agents like amiodarone for rate control and rhythm restoration, with catheter ablation reserved for persistent cases unresponsive to medical therapy.^[8] Low cardiac output syndrome occurs in approximately 9% to 21% of patients shortly after Fontan completion, primarily due to elevated central venous pressure impeding ventricular preload and pulmonary blood flow.^[26] This state manifests as poor perfusion, lactic acidosis, and organ dysfunction. Supportive measures include inotropic agents such as milrinone or epinephrine to enhance contractility, careful volume adjustment to optimize preload, and temporary mechanical support if needed, alongside protocols from immediate postoperative care to maintain systemic output.^[27] Bleeding and thrombosis are interrelated short-term risks, with thromboembolic events reported in 5% to 19% of cases in the first year, peaking early due to endothelial disruption, stasis in the passive circulation, and prothrombotic states.^[28] Bleeding complications arise from surgical hemostasis challenges and anticoagulation needs. Prophylaxis with unfractionated heparin or low-molecular-weight heparin is standard in the perioperative period, transitioning to oral anticoagulants like warfarin if thrombosis is detected via imaging such as echocardiography or CT angiography.^[29] Chylothorax, a subset of pleural complications involving lymphatic leakage, complicates 2% to 10% of Fontan procedures and is linked to thoracic duct injury during surgery.^[30] It leads to significant protein and nutritional losses. Management emphasizes nutritional support with a medium-chain triglyceride-based diet to minimize chyle production, total parenteral nutrition if drainage exceeds 1-2 mL/kg/hour, and somatostatin analogs for refractory cases. Postoperative infections, including wound or pleural space infections, occur in up to 5% of patients and are managed with broad-spectrum antibiotics guided by culture results, alongside strict aseptic techniques and prophylactic regimens.^[31]^[32]

Long-term Outcomes and Management

Long-term survival after the Fontan procedure has improved significantly with modern techniques, with 30-year survival rates exceeding 80% in contemporary cohorts.^[8] In a Danish national registry analysis, 30-year survival reached 87%, reflecting advancements in patient selection and perioperative care.^[33] Early mortality in recent series is low, at approximately 1.7% during the operative period.^[34] Prognostic factors include low pulmonary vascular resistance (PVR) prior to surgery, which supports sustained passive pulmonary blood flow, and the use of fenestration, which enhances early hemodynamic stability and overall survival.^[1]^[35] Routine follow-up is essential for detecting and managing late complications in Fontan patients. The American Heart Association recommends cardiology evaluations every 6 to 12 months, including annual echocardiography to assess ventricular function, atrioventricular valve regurgitation, and conduit patency.^[8] Recent guidelines, including the 2025 ACC clinical practice algorithm, provide standardized approaches for follow-up frequency and diagnostic testing tailored to age and risk.^[36] Holter monitoring is advised periodically to screen for arrhythmias, which affect over 50% of patients long-term.^[8] Cardiopulmonary exercise testing should occur every 1 to 2 years in adults to evaluate functional capacity, where peak oxygen consumption typically averages 60% of predicted values.^[8] For Fontan-associated liver disease (FALD), which manifests as fibrosis or cirrhosis in nearly all patients by 17 years post-procedure, liver MRI or CT is recommended every 1 to 2 years in adulthood to monitor progression.^[8] Medical management focuses on supporting hemodynamics, preventing thrombosis, and mitigating organ dysfunction. Angiotensin-converting enzyme (ACE) inhibitors may be used to aid ventricular function and manage atrioventricular valve regurgitation, though evidence is limited.^[8] Anticoagulation, such as warfarin, is indicated for fenestrated Fontan circuits or in the presence of atrial arrhythmias to reduce thromboembolic risk, with alternatives like aspirin considered for lower-risk patients.^[8]^[37] Endocarditis prophylaxis with antibiotics may be considered for dental and other high-risk procedures only in patients with specific conditions per current AHA guidelines, such as prosthetic material or residual shunts, despite the elevated infection risk in complex congenital heart disease.^[8]^[38] Catheter-based interventions play a key role in long-term care. Closure of fenestrations can be performed once hemodynamics stabilize to eliminate cyanosis, typically via transcatheter devices.^[8] For arrhythmias, catheter ablation achieves acute success rates of 54% to 94% in treating intra-atrial reentrant tachycardia.^[8] Protein-losing enteropathy (PLE), a serious late complication, is managed with dietary modifications including high-protein intake (≥2 g/kg/day), low-fat composition (≤25% of calories), and medium-chain triglyceride supplementation; pharmacological options like octreotide or budesonide are used for refractory cases.^[39]^[40] Quality of life in Fontan survivors involves ongoing neurodevelopmental monitoring, as chronic cyanosis in infancy contributes to deficits in cognition, executive function, and visual-spatial skills.^[8] Mean IQ scores are approximately 92, within the normal range but lower than the general population, with impacts on school performance reported in up to 23% of children as below average.^[8]^[41] Periodic neuropsychological assessments are recommended to support educational interventions and optimize long-term outcomes.^[8]

Fontan Physiology

Hemodynamics of Fontan Circulation

The Fontan procedure establishes a total cavopulmonary connection, which redirects systemic venous return directly to the pulmonary arteries, thereby eliminating the role of the right ventricle as a subpulmonary pump.^[42] This creates a passive pulmonary circulation where blood flow to the lungs is driven solely by the pressure gradient from the systemic veins, making it highly dependent on low pulmonary vascular resistance (PVR) to maintain adequate perfusion.^[42] In this setup, the absence of a pumping chamber for pulmonary flow necessitates that systemic venous pressure remains sufficiently elevated to propel deoxygenated blood through the lungs without active ventricular assistance.^[43] Key hemodynamic parameters in Fontan circulation include an elevated central venous pressure (CVP), typically ranging from 8 to 12 mmHg, which is essential for driving pulmonary blood flow while being counterbalanced by low pulmonary venous pressure to prevent overload.^[44] The transpulmonary gradient, defined as the difference between CVP and left atrial pressure (LAP), governs the efficiency of this passive flow, with optimal gradients supporting stable perfusion under resting conditions.^[42] These parameters reflect the circulation's reliance on a delicate balance, where deviations—such as elevated LAP—can compromise overall hemodynamics.^[43] Pulmonary blood flow in Fontan circulation equals systemic blood flow, as there is no intervening pump to regulate distribution, resulting in a fixed output that is particularly sensitive to external influences like the respiratory cycle, gravitational effects in different body positions, and increased demands during exercise.^[42] During respiration, intrathoracic pressure variations can transiently alter venous return and pulmonary flow, while upright posture may reduce flow to dependent lung regions due to gravity.^[42] Exercise further challenges this system by elevating metabolic needs, which increases CVP requirements to sustain flow but can lead to limitations if PVR rises.^[43] The fundamental mathematical concept underlying pulmonary flow can be approximated as:

Q_p \approx \frac{\text{mean systemic venous pressure} - \text{pulmonary venous pressure}}{PVR}

where Q_p represents pulmonary blood flow.^[43] This relationship underscores the circulation's vulnerability to elevated PVR, which can drastically reduce flow and precipitate hemodynamic instability, emphasizing the need for low-resistance pulmonary vasculature.^[42] One primary advantage of this hemodynamic arrangement is the correction of cyanosis by fully separating systemic and pulmonary circulations, allowing oxygenated blood from the lungs to reach the systemic arteries without mixing.^[42] Consequently, arterial oxygen saturation normalizes to 90-95% in successful cases, markedly improving tissue oxygenation compared to pre-procedure levels.^[8]

Physiological Challenges and Adaptations

In Fontan circulation, the absence of a subpulmonary ventricle imposes significant physiological challenges, primarily stemming from passive pulmonary blood flow driven by central venous pressure rather than active pumping. This leads to chronic low cardiac output and elevated systemic venous pressures, prompting various adaptive responses in the cardiovascular and other systems. Over time, these adaptations can become maladaptive, contributing to progressive dysfunction.^[8]^[45] The systemic ventricle undergoes notable adaptations to handle the altered hemodynamics, including eccentric hypertrophy from early volume overload during staged palliation, followed by concentric hypertrophy and diastolic dysfunction due to chronic preload deprivation and increased afterload. Systolic function often remains preserved initially but declines progressively, with ventricular end-diastolic pressure rising as a result of fibrosis and impaired relaxation, limiting the ventricle's ability to generate sufficient suction for venous return. These changes contribute to a baseline cardiac index that is approximately 70-80% of normal values at rest.^[8]^[45]^[46] Pulmonary circulation faces unique challenges from nonpulsatile, low-flow conditions, leading to endothelial dysfunction characterized by reduced nitric oxide production and elevated endothelin levels, which drive a gradual increase in pulmonary vascular resistance (PVR) over decades. This rising PVR creates a hemodynamic bottleneck, further impairing cardiac output. As an adaptation, venovenous collaterals often develop, providing decompression of the high-pressure venous system but resulting in right-to-left shunting, cyanosis, and worsened oxygenation during activity.^[8]^[46]^[45] Systemically, the Fontan state results in reduced cardiac output and inability to augment pulmonary blood flow with increased demand, manifesting as exercise intolerance with peak oxygen consumption typically at 60-65% of predicted values in adolescents and adults. This limitation arises from blunted heart rate response, fixed stroke volume, and inability to lower PVR effectively during exertion. Multiorgan impacts are profound: hepatic congestion from sustained venous hypertension leads to Fontan-associated liver disease (FALD), with significant fibrosis observed in up to 50% of patients by 10 years post-procedure and nearly universal centrilobular involvement by adolescence; renal function deteriorates in about 50% of adults due to chronic hypoperfusion and neurohormonal activation; and lymphatic complications, such as plastic bronchitis in 1-4% of cases, stem from lymphatic stasis and insufficiency.^[8]^[46]^[47] Compensatory mechanisms help mitigate these challenges initially, including enhanced systemic oxygen extraction efficiency to offset low cardiac output and lymphatic system rerouting to manage chronic venous congestion and reduce interstitial fluid accumulation. However, these adaptations have limits; for instance, excessive collateral formation exacerbates desaturation, and prolonged hepatic congestion overwhelms regenerative capacity, progressing to advanced fibrosis or cirrhosis in a subset of patients.^[8]^[46]

Special Considerations

Pregnancy and Reproductive Health

Women with Fontan circulation face significant challenges during pregnancy due to the altered hemodynamics of their circulation, which imposes increased preload demands on a passive venous return system. Maternal cardiovascular complications are common, with supraventricular arrhythmias occurring in approximately 7% of cases (range 3-37%) and heart failure in about 4% (range 3-11%). Thromboembolic events affect around 2% of pregnancies, while postpartum hemorrhage is reported in 12-14%. These risks appear higher in patients with non-fenestrated Fontan circulations, where case reports highlight increased incidence of arrhythmias, heart failure, and thrombosis due to elevated central venous pressures and reduced cardiac output reserves. No maternal deaths have been reported in large reviews, but the modified World Health Organization (mWHO) classifies Fontan patients as high-risk (class III), emphasizing the need for careful risk stratification.^[48]^[49]^[50] Fetal and neonatal outcomes are also adversely affected, with spontaneous miscarriage rates reaching 41% (95% CI 33-48%) and preterm delivery in 57% (95% CI 40-74%) of ongoing pregnancies. Low birth weight or small for gestational age infants occur in about 21% (95% CI 14-28%), largely attributable to reduced placental perfusion from the Fontan physiology's limited cardiac output augmentation. Neonatal mortality stands at approximately 4% (95% CI 2-7%), often linked to prematurity and growth restriction. These outcomes underscore the physiologic strain of pregnancy on Fontan circulation, where the inability to increase pulmonary blood flow adequately impacts fetal development.^[49]^[48] Pre-pregnancy counseling is essential for all women of childbearing age with Fontan circulation to assess risks and discuss family planning. Evaluation should include echocardiography to confirm adequate systemic ventricular function (ejection fraction ideally >40-50%), assessment of pulmonary vascular resistance (preferably <2-3 Wood units to ensure venous return tolerance), and review of prior complications such as arrhythmias or protein-losing enteropathy. Contraception options like progestin-only pills or intrauterine devices are recommended to avoid estrogen-related thrombotic risks, with combined oral contraceptives generally contraindicated. Genetic counseling may also be advised given the congenital nature of the underlying heart defect.^[51]^[52]^[53] Management during pregnancy requires a multidisciplinary team involving cardiologists, obstetricians, and anesthesiologists, with frequent monitoring of cardiac function, fluid status, and fetal growth via serial echocardiograms and ultrasounds. Beta-blockers should be continued or initiated for arrhythmia control, while low-dose aspirin (81 mg daily) is often used for thromboprophylaxis in the absence of contraindications; low-molecular-weight heparin may be added if thrombosis risk is elevated. Delivery is preferably vaginal to minimize hemodynamic fluctuations, unless high-risk features like severe ventricular dysfunction necessitate cesarean section, with regional anesthesia favored over general. Postpartum care involves close observation in an intensive care setting for 24-48 hours to monitor for pleural effusions, bleeding, or heart failure exacerbations, with gradual resumption of antithrombotic therapy. Breastfeeding is generally considered safe, provided maternal cardiac stability is maintained and compatible medications are used.^[53]^[52]^[54]

Exercise Tolerance and Lifestyle Factors

Patients with Fontan circulation typically exhibit reduced exercise tolerance, with peak oxygen uptake (VO₂) averaging 60-70% of predicted values for age and sex, primarily attributable to the fixed cardiac output inherent in Fontan physiology, which limits the heart's ability to augment preload during physical exertion.^[55] This impairment arises from central factors such as diminished ventricular compliance and pulmonary vascular resistance, alongside peripheral limitations like skeletal muscle inefficiency.^[56] Despite these constraints, clinical guidelines endorse moderate aerobic exercise for stable Fontan patients, such as walking or cycling for approximately 30 minutes most days of the week, to enhance aerobic capacity, muscle strength, and overall quality of life without exceeding safe thresholds.^[57]^[58] Lifestyle modifications play a crucial role in mitigating risks associated with Fontan circulation. Patients are advised to avoid dehydration, as it can exacerbate reduced preload and lead to hemodynamic instability, particularly during exercise or hot weather.^[59] Travel to high altitudes above 1,500 meters is generally discouraged due to hypobaric hypoxia, which further impairs exercise capacity and oxygen delivery in this population.^[60] Isometric sports, such as heavy weightlifting or competitive wrestling, should be avoided because they increase systemic vascular resistance and intrathoracic pressure, potentially straining the passive pulmonary blood flow.^[61] To prevent infections that could complicate circulation, routine vaccinations, including influenza and pneumococcal vaccines, are strongly recommended as part of preventive care.^[8] Psychological well-being is often affected by activity restrictions and the chronic nature of Fontan circulation, with elevated rates of anxiety and depression reported in up to 30-40% of adult patients, stemming from fears of exertion-related symptoms or long-term uncertainties.^[62]^[63] Participation in support groups tailored for congenital heart disease, such as those offered by patient advocacy organizations, can alleviate isolation, provide coping strategies, and foster emotional resilience.^[64] Transitioning to adult care introduces additional stress, necessitating structured programs that address self-management skills and mental health screening to ensure continuity of psychosocial support.^[65] In terms of employment and education, the majority of Fontan patients achieve typical developmental milestones, including completing schooling and entering the workforce, though chronic fatigue may necessitate accommodations like flexible schedules or part-time roles to manage energy levels.^[66] Fatigue, a common symptom linked to suboptimal cardiac output, requires ongoing monitoring to prevent interference with daily activities or professional performance.^[67] Driving privileges are generally unrestricted for asymptomatic patients but may be limited or prohibited in cases of arrhythmias, such as atrial tachyarrhythmias affecting 15-60% of adults, until stability is confirmed through electrophysiological evaluation and treatment.^[68]^[69] For end-of-life planning, patients with failing Fontan circulation—estimated to affect 10-20% by early adulthood due to progressive ventricular dysfunction or protein-losing enteropathy—should be evaluated for heart transplantation candidacy, as it offers the primary therapeutic option for advanced failure, with referral ideally occurring before multiorgan compromise.^[70]^[71] Early discussions with multidisciplinary teams can facilitate informed decisions regarding transplantation listing and palliative alternatives.^[72]

History and Evolution

Development of the Procedure

The conceptual origins of the Fontan procedure stem from experimental studies in the 1940s and 1950s that explored the possibility of directing systemic venous return to the lungs without a subpulmonary ventricle to propel blood flow. In 1949, Rodbard and colleagues demonstrated the feasibility of right ventricular bypass in canine models by anastomosing the right atrium directly to the main pulmonary artery, achieving adequate pulmonary perfusion driven by central venous pressure gradients.^[73] Building on this, further animal experiments in the 1950s, including those involving partial cavopulmonary connections, confirmed that such passive flow could sustain oxygenation without significant hemodynamic compromise in select conditions.^[74] These foundational works challenged the traditional view of the right ventricle as indispensable and laid the groundwork for clinical translation in patients with univentricular hearts. The first human application of the procedure occurred on April 25, 1968, when Francis Fontan and Eugène Baudet operated on a 12-year-old girl with tricuspid atresia in Bordeaux, France, redirecting both venae cavae to the pulmonary arteries via valved conduits and closing an atrial septal defect.^[75] In their seminal 1971 publication, they detailed outcomes for three patients treated between 1968 and 1970, reporting two early survivals (66.7%) but noting one perioperative death due to mitral insufficiency; long-term follow-up on survivors showed stable hemodynamics at 30 and 10 months post-operation. Initial survival rates across early cases remained modest, around 50-70%, reflecting technical limitations such as conduit thrombosis and the need for precise patient selection based on low pulmonary vascular resistance. Early iterations of the atriopulmonary Fontan connection, which directly joined the right atrium to the pulmonary arteries, encountered substantial challenges, including elevated risks of thrombosis from sluggish flow in the enlarged atrium and atrial arrhythmias arising from distension, suture-line scars, and chronic pressure overload.^[76] These complications contributed to reoperation rates exceeding 20% in initial cohorts and underscored the need for refinements to mitigate venous stasis.^[8] In the 1970s, expanding patient series in France (Bordeaux group) and the United States (e.g., Mayo Clinic's first nonfenestrated case in 1973) solidified the procedure's role as a palliative strategy for single-ventricle defects beyond tricuspid atresia, with cumulative experiences reporting 70-80% early survival and functional improvements in oxygenation. By the 1980s, milestones included a shift toward staged palliation, integrating the pre-existing Glenn shunt (introduced in 1958) as an intermediate superior cavopulmonary anastomosis to offload ventricular volume before Fontan completion, thereby reducing early mortality to under 10% in select centers.^[2] This evolution marked a transition from direct total cavopulmonary connection to more physiologically adaptive approaches.

Key Contributors and Recent Advances

The Fontan procedure's development owes much to pioneering surgeons who refined its techniques for single-ventricle congenital heart defects. Francis Fontan, a French cardiothoracic surgeon, first described the procedure in 1968 for tricuspid atresia, establishing the foundational concept of redirecting systemic venous return directly to the pulmonary arteries without a subpulmonary ventricle.^[77] Aldo Castañeda, director of cardiac surgery at Boston Children's Hospital, advanced staged palliation strategies in the 1970s and 1980s, emphasizing progressive volume unloading of the single ventricle to optimize outcomes before the final Fontan completion.^[78] These contributions shifted the approach from high-risk single-stage repairs to multi-stage protocols, improving early survival rates. In the 1980s, Marc R. de Leval introduced the lateral tunnel technique, creating an intra-atrial pathway to connect the inferior vena cava to the pulmonary arteries while preserving the sinus node and reducing arrhythmia risks compared to earlier atriopulmonary anastomoses.^[79] This modification, independently developed around 1988 by de Leval and Castañeda, addressed limitations in flow dynamics and atrial enlargement seen in prior methods.^[79] By the 1990s, surgeons Richard A. Jonas and Pedro J. del Nido further evolved the procedure with the extracardiac conduit approach, using a synthetic tube to bypass the atrium entirely, which minimized atrial dilation, preserved sinus rhythm, and lowered long-term thrombotic complications.^[80] These innovations collectively reduced perioperative mortality from over 20% in the 1970s to under 5% by the early 2000s. Post-2010 advancements have focused on mitigating Fontan circulation's inherent limitations, such as elevated central venous pressure and reduced cardiac output. Fenestration optimization, involving adjustable or device-occluded shunts between the systemic venous pathway and the left atrium, has improved early postoperative hemodynamics by allowing controlled right-to-left shunting to offload pulmonary pressures while minimizing hypoxemia; computational models demonstrate that fenestration sizes of 4-5 mm optimally balance oxygen saturation and ventricular preload.^[81] For hypoplastic left heart syndrome (HLHS), the hybrid Norwood-Fontan strategy—combining initial bilateral pulmonary artery banding and ductal stenting with later Glenn and Fontan stages—has emerged as an alternative to traditional Norwood palliation, reducing early interstage mortality in high-risk neonates to 10-15% in select centers.^[82] Investigational ventricular assist devices (VADs), such as right-sided or cavopulmonary support systems, have shown promise in bridging failing Fontan patients to transplantation, with case reports documenting hemodynamic stabilization and survival extensions of months to years.^[83] Ongoing research frontiers target late complications like pulmonary vascular resistance (PVR) elevation and Fontan-associated liver disease (FALD). While pharmacological PVR reduction remains standard, emerging therapies explore targeted interventions to enhance pulmonary endothelial function, though gene therapy applications are still preclinical.^[84] For FALD, characterized by hepatic congestion and fibrosis in 20-30% of long-term survivors, combined heart-liver transplantation has yielded superior outcomes over isolated heart transplant in patients with moderate-to-severe disease, achieving 5-year survival rates above 70%.^[85]^[86] International registries, such as the Australia and New Zealand Fontan Registry, provide critical longitudinal data; analysis of over 1,400 patients indicates 20-year survival exceeding 85%, with reinterventions required in nearly 50% but overall improved longevity due to refined protocols.^[87]^[88] As of 2025, computational modeling integrates artificial intelligence for preoperative Fontan planning, using patient-specific simulations to predict conduit geometry and flow patterns, potentially reducing postoperative revisions by 20-30% in complex anatomies like heterotaxy.^[89] Biodegradable or bioprinted conduits are in early clinical trials, aiming to promote somatic growth and avoid lifelong anticoagulation; multiphysics studies of pulsatile bioprinted grafts demonstrate enhanced power delivery to the passive pulmonary circulation, with initial implants showing good short-term patency.

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