Single Ventricle Palliation #5: Stage III Fontan Circulation

1. Conceptual Overview

The Fontan operation is the final planned stage of single ventricle palliation. Its objective is to complete the separation of systemic and pulmonary venous return by directing the inferior vena caval return to the pulmonary arteries, thereby creating a total cavopulmonary connection. In this configuration, systemic venous blood reaches the pulmonary vascular bed without an interposed subpulmonary ventricle, while the single ventricle supports the systemic circulation [1].

After the bidirectional Glenn, SVC return is already connected to the pulmonary arteries, but IVC return still enters the atrium and mixes with pulmonary venous blood. Fontan completion incorporates the IVC into the cavopulmonary circuit, reduces systemic venous admixture, and improves arterial oxygen saturation. However, this improvement in oxygenation is achieved at the cost of a chronically pressure-loaded systemic venous circulation.

Modern outcomes have improved substantially with better patient selection, staged palliation, refined cavopulmonary geometry, and contemporary perioperative care. Across five decades of experience, early mortality has decreased, and long-term survival has improved, but late morbidity remains a defining limitation of Fontan physiology [2].

2. Hemodynamic Transition From Glenn to Fontan

2.1 Glenn Circulation

In Glenn physiology:

• The SVC is connected directly to the pulmonary arteries.
• The IVC still drains to the atrium.
• The single ventricle receives a mixture of pulmonary venous blood and IVC blood.
• Arterial oxygen saturation remains limited by residual systemic venous admixture.
• Pulmonary blood flow is partially passive, driven by the SVC-to-pulmonary venous atrium pressure gradient.

This stage reduces ventricular volume load compared with Stage I physiology, but it does not fully separate systemic and pulmonary venous return.

2.2 Fontan Circulation

In Fontan physiology:

• Both SVC and IVC return are directed to the pulmonary arteries.
• The pulmonary circulation is placed upstream of the atrium and ventricle.
• The single ventricle receives predominantly oxygenated pulmonary venous blood.
• Systemic arterial oxygenation improves because IVC desaturation is no longer directly mixed into the systemic ventricular inflow.

The key physiological conversion is that central venous pressure becomes the driving force for pulmonary blood flow.

3. Surgical Strategies for Fontan Completion

3.1 Total Cavopulmonary Connection

The modern Fontan operation is usually performed as a total cavopulmonary connection, most commonly using one of two strategies:

1. Extracardiac conduit Fontan
2. Intra-atrial lateral tunnel Fontan

Both techniques can achieve excellent early survival and effective separation of systemic and pulmonary venous return. Their major differences relate to pathway geometry, atrial suture burden, arrhythmia risk, growth potential, and technical applicability in small children or complex anatomy.

3.2 Extracardiac Conduit Fontan

In an extracardiac Fontan, a prosthetic conduit is placed outside the heart to connect the IVC to the pulmonary arteries. The SVC is already connected to the pulmonary arteries through the Glenn circulation.

Potential advantages include:

• Avoidance of extensive atrial suture lines
• Less atrial distortion and dilation
• Lower theoretical risk of atrial arrhythmias
• Favorable cavopulmonary geometry
• Applicability to complex atrial anatomy
• Avoidance of intracardiac baffle material

Several reviews and institutional experiences have favored the extracardiac conduit approach because of low operative mortality, favorable hemodynamics, and reduced atrial arrhythmia burden compared with older intra-atrial Fontan modifications [3, 4].

However, extracardiac conduit Fontan has limitations. The conduit does not grow with the patient, and conduit size must be selected to balance current flow requirements against future adult body size. Thrombosis, pathway obstruction, conduit compression, and difficult transvenous access for future electrophysiology or pacing interventions remain relevant long-term issues.

3.3 Lateral Tunnel Fontan

In the lateral tunnel Fontan, an intra-atrial baffle channels IVC blood through the right atrium toward the pulmonary arteries. This creates a pathway from the IVC to the pulmonary artery while maintaining the cavopulmonary principle.

Potential advantages include:

• Use of native atrial tissue
• Some growth potential
• Feasibility in smaller patients
• Established long-term experience
• Familiarity in many congenital programs

The main concern is the presence of atrial suture lines and atrial remodeling, which may contribute to sinus node dysfunction, atrial tachyarrhythmias, and late atrial dilation. Long-term lateral tunnel series have demonstrated durable survival in selected patients, but arrhythmia and late morbidity remain important concerns [5, 6].

4. Extracardiac Conduit Versus Lateral Tunnel Fontan

The comparison between extracardiac conduit and lateral tunnel Fontan is not a simple “one is always better” question. The literature supports several practical conclusions.

4.1 Survival

Both techniques can achieve excellent early and midterm survival in contemporary practice. Contemporary series report low operative mortality and strong 5-year survival, often exceeding 94% in appropriately selected patients [1, 2].

The improvement in survival is not attributable to conduit choice alone. It reflects a broader evolution in Fontan care:

• Earlier staged palliation
• Better neonatal and interstage survival
• More careful Fontan candidacy assessment
• Improved pulmonary artery reconstruction
• Lower pulmonary vascular resistance at Fontan completion
• Better ventricular and atrioventricular valve selection
• Improved intensive care, anticoagulation, and surveillance

4.2 Arrhythmia

The strongest technical advantage of the extracardiac conduit is the reduction of atrial manipulation. In a single-institution comparison, extracardiac Fontan was associated with reduced early and midterm atrial arrhythmia compared with lateral tunnel Fontan [5].

This finding is anatomically plausible: the extracardiac conduit avoids a long intra-atrial baffle suture line and reduces atrial distortion. In contrast, the lateral tunnel places the pathway within the atrium and may expose the atrial myocardium and sinus node region to more surgical and hemodynamic stress.

However, arrhythmia risk is not determined by Fontan type alone. It is also influenced by:

• Underlying cardiac anatomy
• Atrial isomerism or heterotaxy
• Prior atrial surgery
• Sinus node dysfunction
• Preoperative arrhythmia
• Atrioventricular valve regurgitation
• Ventricular dysfunction
• Fontan pressure
• Age and duration of follow-up

Therefore, extracardiac Fontan may reduce arrhythmia risk, but it does not eliminate it.

4.3 Early Outcomes

A large multicenter analysis found that early postoperative outcomes may vary according to the type of cavopulmonary connection, with some data suggesting favorable early outcomes for the lateral tunnel approach in selected patients [8]. This is important because it prevents an overly simplistic interpretation that extracardiac Fontan is universally superior in every setting.

The practical interpretation is that surgical strategy should be individualized. Patient size, pulmonary artery anatomy, atrial anatomy, venous anatomy, need for fenestration, anticipated growth, future catheter access, and institutional expertise all influence the optimal choice.

5. Physiological Requirements for a Successful Fontan Circulation

The Fontan circulation functions only when the pressure gradient from systemic veins to the pulmonary venous atrium is sufficient to maintain pulmonary blood flow.

5.1 Low Pulmonary Vascular Resistance

Low PVR is the most important prerequisite. Because there is no subpulmonary ventricle, even modest increases in PVR can reduce pulmonary blood flow, decrease ventricular preload, and lower cardiac output.

Elevated PVR may result from:

• Hypoxia
• Hypercarbia
• Acidosis
• Atelectasis
• Pulmonary infection
• Pulmonary artery stenosis
• Pulmonary venous obstruction
• Elevated left atrial or ventricular end-diastolic pressure

In Fontan physiology, the pulmonary vascular bed is not simply a downstream vascular bed. It is part of the functional pump.

5.2 Low Atrial Pressure

The downstream pressure of the Fontan circuit is the pulmonary venous atrial pressure. If atrial pressure is elevated, the transpulmonary gradient decreases.

Atrial pressure may be elevated by:

• Ventricular diastolic dysfunction
• Atrioventricular valve regurgitation
• Ventricular hypertrophy
• Systemic ventricular dysfunction
• Pulmonary venous obstruction
• Residual arch obstruction
• Excessive volume load

Thus, Fontan candidacy depends not only on pulmonary arteries and PVR, but also on ventricular compliance and atrioventricular valve competence.

5.3 Adequate Central Venous Pressure

Fontan circulation requires enough central venous pressure to drive blood through the pulmonary arteries. However, excessive central venous pressure produces systemic venous congestion.

This creates a narrow hemodynamic window:

• Too little venous pressure: inadequate pulmonary blood flow, reduced preload, low cardiac output.
• Too much venous pressure: venous congestion, hepatic congestion, lymphatic overload, effusions, ascites, and end-organ injury.

Fontan physiology is therefore a balance between preload generation and venous congestion.

6. Fenestration

A Fontan fenestration is a controlled communication between the Fontan pathway and the atrium. It allows right-to-left shunting from the systemic venous pathway into the atrium.

Potential benefits include:

• Decompression of the Fontan circuit
• Lower systemic venous pressure
• Improved ventricular preload
• Higher cardiac output
• Reduced early pleural effusions
• Protection against acute Fontan failure in borderline physiology

The trade-off is persistent arterial desaturation.

Fenestration is most useful when the patient has borderline Fontan conditions, such as:

• Mildly elevated PVR
• Ventricular dysfunction
• Elevated ventricular end-diastolic pressure
• Significant AV valve regurgitation
• Pulmonary artery distortion
• Heterotaxy or complex venous anatomy
• High-risk perioperative profile

Fenestration should not be interpreted simply as a marker of surgical preference. It is often a marker of higher-risk physiology. This distinction is important when interpreting outcome studies, because fenestrated patients may have worse event-free survival partly because they were higher risk at baseline [9].

7. Long-Term Morbidity After Fontan Completion

Fontan completion improves oxygenation and reduces ventricular volume load, but it does not restore normal physiology. The circulation remains characterized by:

• Chronically elevated systemic venous pressure
• Absence of a subpulmonary pump
• Limited preload reserve
• Reduced ability to augment cardiac output during exercise
• Vulnerability to pulmonary vascular and lymphatic disturbances

In contemporary series, survival is excellent, but event-free survival is substantially lower than overall survival. One modern-era analysis reported excellent survival after Fontan completion but ongoing risk of morbid events, with 10-year event-free survival around 64% [9].

Important late complications include:

1. Systemic venous congestion

Chronic venous hypertension affects the liver, gut, kidneys, lymphatic system, and systemic venous capacitance bed.

2. Fontan-associated liver disease

Long-standing hepatic venous congestion may lead to fibrosis, cirrhosis, portal hypertension, and rarely hepatocellular carcinoma.

3. Lymphatic failure

Elevated venous pressure impairs lymphatic drainage and contributes to pleural effusions, ascites, protein-losing enteropathy, and plastic bronchitis.

4. Protein-losing enteropathy

PLE reflects failure of the intestinal lymphatic and venous system under chronic Fontan pressure. It is uncommon but clinically serious.

5. Plastic bronchitis

Abnormal lymphatic flow into the airway can produce bronchial casts and respiratory compromise.

6. Arrhythmia

Atrial tachyarrhythmias, sinus node dysfunction, and junctional rhythm can reduce cardiac output by impairing atrioventricular synchrony and preload.

7. Thromboembolism

Low-flow venous pathways, prosthetic material, arrhythmia, and altered coagulation increase thrombotic risk.

8. Exercise limitation

During exercise, the absence of a subpulmonary ventricle limits the ability to increase pulmonary blood flow and ventricular preload.

9. Fontan failure

Fontan failure may present as low cardiac output, cyanosis, refractory effusions, PLE, plastic bronchitis, arrhythmia, ventricular dysfunction, AV valve failure, or end-organ dysfunction.

Adult Fontan cohorts demonstrate that adverse outcomes remain common even among survivors of total cavopulmonary palliation, emphasizing that Fontan patients require lifelong surveillance rather than discharge from congenital cardiac care [10].

8. Respiratory Mechanics and Fontan Physiology

Fontan circulation is highly sensitive to respiratory mechanics. Spontaneous inspiration lowers intrathoracic pressure and augments systemic venous return into the pulmonary vascular bed. Positive-pressure ventilation can increase intrathoracic pressure, reduce venous return, and impair Fontan flow.

Important postoperative goals include:

• Avoid hypoxia
• Avoid hypercarbia
• Avoid acidosis
• Prevent atelectasis
• Maintain low PVR
• Avoid excessive mean airway pressure
• Preserve diaphragmatic function
• Promote early extubation when clinically appropriate

In Fontan physiology, the lung is not merely an oxygen exchange organ. It is an essential part of the circulatory pathway.

9. Clinical Interpretation

Fontan completion should be understood as a physiological trade-off.

It improves systemic oxygenation by routing IVC return to the pulmonary arteries and reducing venous admixture. It also reduces the chronic ventricular volume load that exists before Fontan completion. However, it creates a circulation that depends on passive pulmonary blood flow and chronically elevated systemic venous pressure.

A successful Fontan requires more than a technically patent conduit or tunnel. It requires a favorable entire cardiopulmonary system:

• Unobstructed systemic venous pathway
• Well-developed pulmonary arteries
• Low pulmonary vascular resistance
• Unobstructed pulmonary venous return
• Low atrial pressure
• Competent atrioventricular valve
• Preserved ventricular systolic and diastolic function
• Absence of significant arch obstruction
• Tolerable lymphatic reserve
• Durable rhythm stability

The best Fontan is not simply the operation with the cleanest anatomy. It is the operation performed in a patient whose pulmonary vascular bed, ventricle, atrioventricular valve, venous pathway, and lymphatic system can tolerate the physiology.

10. Key Takeaways

1. Fontan completion incorporates the IVC into the cavopulmonary circuit.

This completes the separation of systemic and pulmonary venous return after Glenn palliation.

2. Pulmonary blood flow becomes entirely passive.

There is no subpulmonary ventricle; flow depends on the systemic venous-to-atrial pressure gradient.

3. Low PVR is mandatory.

Even mild increases in PVR can reduce preload, lower cardiac output, and increase venous congestion.

4. Low atrial pressure is equally critical.

Ventricular diastolic dysfunction or AV valve regurgitation can impair Fontan flow by raising downstream pressure.

5. Extracardiac conduit Fontan may reduce atrial arrhythmia risk.

This advantage is related to reduced atrial suture burden and less atrial distortion, but arrhythmia risk is multifactorial.

6. Lateral tunnel Fontan remains a valid option in selected patients.

It has growth potential and strong long-term experience, but atrial arrhythmia and atrial remodeling remain concerns.

7. Fenestration is a physiological safety valve.

It can improve preload and reduce venous pressure at the cost of systemic desaturation.

8. Survival has improved, but event-free survival remains limited.

Late morbidity is driven by venous congestion, lymphatic failure, arrhythmia, thromboembolism, ventricular dysfunction, and end-organ disease.

9. Fontan physiology is not a cure.

It is a durable but fragile palliation that requires lifelong surveillance and careful management of the heart, lungs, liver, lymphatic system, rhythm, and venous pathway.

References

[1] d'Udekem Y, Iyengar AJ, Cochrane AD, Grigg LE, Ramsay JM, Wheaton GR, Penny DJ, Brizard CP. The Fontan procedure: contemporary techniques have improved long-term outcomes. Circulation. 2007;116(11 Suppl):I157-I164.

[2] Kverneland LS, Kramer P, Ovroutski S. Five decades of the Fontan operation: A systematic review of international reports on outcomes after univentricular palliation. Congenit Heart Dis. 2018;13(2):181-193.

[3] Backer CL, Deal BJ, Kaushal S, Russell HM, Tsao S, Mavroudis C. Extracardiac versus intra-atrial lateral tunnel Fontan: extracardiac is better. Semin Thorac Cardiovasc Surg Pediatr Card Surg Annu. 2011;14(1):4-10.

[4] Katogi T. Extracardiac conduit Fontan procedure versus intra-atrial lateral tunnel Fontan procedure. Gen Thorac Cardiovasc Surg. 2012;60(12):792-795.

[5] Azakie A, McCrindle BW, Van Arsdell G, Benson LN, Coles JG, Hamilton RM, Freedom RM, Williams WG. Extracardiac conduit versus lateral tunnel cavopulmonary connections at a single institution: impact on outcomes. J Thorac Cardiovasc Surg. 2001;122(6):1219-1228.

[6] Stamm C, Friehs I, Mayer JE Jr, Zurakowski D, Triedman JK, Moran AM, Walsh EP, Lock JE, Jonas RA, del Nido PJ. Long-term results of the lateral tunnel Fontan operation. J Thorac Cardiovasc Surg. 2001;121(1):28-41.

[7] Brown JW, Ruzmetov M, Deschner BW, Rodefeld MD, Turrentine MW. Lateral tunnel Fontan in the current era: is it still a good option? Ann Thorac Surg. 2010;89(2):556-562; discussion 562-563.

[8] Stewart RD, Pasquali SK, Jacobs JP, Benjamin DK Jr, Jaggers J, Cheng J, Mavroudis C, Jacobs ML. Contemporary Fontan operation: association between early outcome and type of cavopulmonary connection. Ann Thorac Surg. 2012;93(4):1254-1260; discussion 1261.

[9] Tweddell JS, Nersesian M, Mussatto KA, Nugent M, Simpson P, Mitchell ME, Ghanayem NS, Pelech AN, Marla R, Hoffman GM. Fontan palliation in the modern era: factors impacting mortality and morbidity. Ann Thorac Surg. 2009;88(4):1291-1299.

[10] Anigwe C, Yogeswaran V, Moon-Grady A, McAllister S, Aggarwal A, Blissett S, Harris IS, Kouretas PC, Mahadevan VS, Sabanayagam A, Agarwal A. Outcomes among adult survivors of total cavopulmonary Fontan palliation for single ventricle. Heart. 2022;108(15):1209-1215.