Fontan Procedure #1–#3: Fontan Circulation, Extracardiac Conduit, and Lateral Tunnel Fontan

1. Fontan Circulation: Final-Stage Palliation for Single-Ventricle Physiology

The Fontan procedure is the final stage of surgical palliation for patients with functional single-ventricle physiology. Its purpose is to separate systemic venous return from pulmonary venous return by directing superior and inferior caval blood directly into the pulmonary arteries without an intervening subpulmonary ventricle.

The operation improves systemic arterial oxygen saturation by eliminating obligatory intracardiac mixing of systemic venous and pulmonary venous blood. However, it does not create a normal biventricular circulation. In the absence of a subpulmonary ventricle, pulmonary blood flow becomes dependent on systemic venous pressure, low pulmonary vascular resistance, and an unobstructed pathway through the pulmonary vascular bed [1,2].

In an ideal nonfenestrated Fontan circulation without significant collateral flow or residual shunting:

Systemic ventricular output ≈ systemic blood flow ≈ pulmonary blood flow

COsv ≈ Qs ≈ Qp

This relationship becomes altered when there is fenestration, systemic venous collateral flow, pulmonary arteriovenous malformations, aortopulmonary collateral flow, residual intracardiac shunting, or pathway obstruction.

2. Hemodynamic Principle

Fontan pulmonary blood flow is driven by a pressure gradient rather than by a subpulmonary pump.

The essential pathway is:

Systemic veins / Fontan pathway → pulmonary arteries → pulmonary capillary bed → pulmonary veins → atrium → single ventricle → systemic arteries

The clinically important pressure gradient is the gradient from the Fontan pathway and pulmonary arteries to the pulmonary venous atrium. This requires:

• Low pulmonary vascular resistance
• Adequate pulmonary artery size and architecture
• No pulmonary artery distortion or branch pulmonary artery stenosis
• No obstruction of the superior vena cava, inferior vena cava, conduit, or baffle pathway
• Low pulmonary venous atrial pressure
• Preserved ventricular systolic and diastolic function
• Competent atrioventricular valve function
• No significant pulmonary venous obstruction
• No significant systemic outflow tract obstruction or arch obstruction
• Sinus rhythm and adequate atrioventricular synchrony

A large 500-patient Fontan experience identified several risk factors for early Fontan failure, including mean preoperative pulmonary artery pressure ≥19 mm Hg, younger age at operation, heterotaxy syndrome, a right-sided tricuspid valve as the only systemic atrioventricular valve, pulmonary artery distortion, atriopulmonary connection, absence of fenestration, and longer cardiopulmonary bypass time. Preoperative pacemaker was associated with late failure [3]. Contemporary series similarly emphasize elevated pulmonary artery pressure and common atrioventricular valve anatomy as important risk factors for mortality [4].

3. Physiologic Trade-Off

The Fontan procedure exchanges cyanosis for systemic venous hypertension.

The benefit is improved systemic oxygen saturation. The cost is chronically elevated systemic venous pressure and limited preload reserve. Therefore, Fontan physiology should be understood as a venous-pressure-dependent circulation, not as a completed anatomic repair.

This physiology predisposes patients to:

• Pleural effusion
• Ascites
• Hepatic congestion and Fontan-associated liver disease
• Protein-losing enteropathy
• Plastic bronchitis
• Lymphatic failure
• Exercise intolerance
• Atrial and ventricular arrhythmias
• Thromboembolism
• Ventricular dysfunction
• Atrioventricular valve regurgitation
• Late Fontan failure

Long-term outcomes are strongly influenced by surgical era, patient selection, anatomy, and late complications. A 1,052-patient 40-year follow-up study reported overall 10-, 20-, and 30-year survival of 74%, 61%, and 43%, with clinically significant late atrial or ventricular arrhythmias in 44% and protein-losing enteropathy in 9% [5]. In more contemporary cohorts and reviews, 10-year survival after Fontan completion is substantially higher, but late morbidity from systemic venous hypertension, arrhythmia, ventricular dysfunction, and end-organ disease remains central to lifelong management [6].

4. Main Fontan Modifications

The major Fontan configurations include:

1. Atriopulmonary connection
2. Lateral tunnel Fontan
3. Extracardiac conduit Fontan

The atriopulmonary connection is now largely historical. It connects the right atrium directly to the pulmonary artery but exposes the circulation to atrial dilation, turbulence, thrombus formation, inefficient flow, and a high long-term arrhythmia burden.

Modern Fontan completion is usually performed as a total cavopulmonary connection using either:

• Extracardiac conduit Fontan
• Lateral tunnel Fontan

Both aim to create a wide, low-resistance systemic venous pathway to the pulmonary arteries.

5. Extracardiac Conduit Fontan

The extracardiac conduit Fontan routes inferior vena caval blood to the pulmonary arteries through a prosthetic tube graft outside the heart.

Operative Concept

After a prior superior cavopulmonary connection, the superior vena cava already drains directly into the pulmonary arteries. Fontan completion then requires routing inferior vena caval return to the pulmonary artery confluence or branch pulmonary arteries.

The typical operative sequence includes:

1. The inferior vena cava is divided at or near the right atrial junction.
2. The right atrial opening is closed.
3. A PTFE extracardiac conduit is anastomosed to the inferior vena cava.
4. The conduit is trimmed to achieve an appropriate length, lie, and orientation.
5. A pulmonary arteriotomy is created.
6. The superior end of the conduit is anastomosed to the pulmonary artery.
7. Pulmonary artery patch augmentation is performed when necessary to avoid distortion or narrowing.

Common conduit sizes are approximately 16–20 mm, depending on patient size, anatomy, institutional strategy, and anticipated growth. Ring-reinforced conduits may be used when compression or kinking is a concern.

Advantages

The extracardiac conduit Fontan offers several surgical and physiologic advantages:

• Avoids extensive intra-atrial suture lines
• Minimizes atrial manipulation
• Reduces atrial arrhythmia substrate compared with older atriopulmonary connections
• Provides a smooth extracardiac venous pathway
• Avoids placing prosthetic material inside the atrium
• May reduce atrial dilation and intra-atrial flow disturbance
• Can often be performed with limited intracardiac work

Limitations

Important limitations include:

• No intrinsic growth potential of a standard PTFE conduit
• Risk of conduit thrombosis
• Need for long-term antithrombotic strategy
• Potential conduit stenosis, kinking, compression, or size mismatch
• Risk of late conduit inadequacy as the patient grows
• Need for precise conduit length and geometry to prevent pathway obstruction

In a 193-patient extracardiac Fontan series, overall survival including operative deaths was 85% at 15 years, and freedom from late failure among hospital survivors was 92% at 15 years. Late major problems included arrhythmias in 11%, extracardiac conduit obstruction in 3%, left pulmonary artery obstruction in 3.5%, and late reinterventions in 12.7% [7]. Another extracardiac Fontan series reported operative mortality of 3% and conduit thrombosis of 4.6%; supraventricular arrhythmia risk was higher in patients with systemic ventricular dysfunction, heterotaxy syndrome, and systemic venous anomalies [8].

6. Lateral Tunnel Fontan

The lateral tunnel Fontan creates an intra-atrial pathway that directs inferior vena caval blood through the right atrium toward the pulmonary arteries.

Operative Concept

The lateral tunnel is constructed using the atrial wall and patch material. The patch forms an intracardiac baffle that separates systemic venous flow from pulmonary venous return.

The typical operative sequence includes:

1. A right atriotomy is performed.
2. A patch is sutured within the right atrium to construct an intra-atrial tunnel from the inferior vena cava toward the superior cavopulmonary pathway.
3. A superior opening is created for connection to the pulmonary artery pathway.
4. A pulmonary arteriotomy is performed.
5. The superior portion of the tunnel is connected to the pulmonary artery.
6. The right atrium is closed.

The result is an intracardiac conduit that channels inferior vena caval return to the pulmonary arteries while pulmonary venous blood returns to the functional ventricle.

Advantages

Potential advantages include:

• Partial use of native atrial tissue
• Some growth potential compared with a fixed prosthetic extracardiac conduit
• Established long-term clinical experience
• Technically straightforward fenestration creation
• Useful in selected anatomic configurations where an extracardiac conduit may be less favorable

Limitations

Important drawbacks include:

• Atrial incision and intra-atrial suture lines
• Potential atrial dilation
• Arrhythmia substrate
• Baffle leak
• Residual or recurrent right-to-left shunt
• Intra-atrial pathway obstruction
• Thrombus formation within the atrial pathway

Compared with the historical atriopulmonary connection, the lateral tunnel reduces atrial dilation and arrhythmia burden. In one contemporary-technique series, 15-year freedom from supraventricular tachycardia was 87% after lateral tunnel compared with 61% after atriopulmonary connection, and 15-year survival was 94% after lateral tunnel compared with 81% after atriopulmonary connection [4].

7. Extracardiac Conduit Versus Lateral Tunnel

Direct superiority of extracardiac conduit Fontan versus lateral tunnel Fontan remains unproven.

The extracardiac conduit is often favored because it avoids intra-atrial prosthetic material and reduces atrial suture-line burden. The lateral tunnel may offer hydrodynamic and growth-related advantages in selected patients because it uses part of the native atrial wall and creates a linearized inferior caval pathway.

Comparative interpretation is difficult because outcomes are influenced by era, age, anatomy, ventricular function, pulmonary artery anatomy, institutional preference, fenestration strategy, and selection bias. A comparative review concluded that available evidence is mixed; some studies reported worse early outcomes with extracardiac conduit Fontan, while proposed extracardiac advantages include reduced atrial manipulation and potentially lower arrhythmia risk [9].

Therefore, the choice between extracardiac conduit and lateral tunnel should be individualized rather than treated as a universally superior technique.

8. Fenestration

A Fontan fenestration is a small intentional communication between the Fontan pathway and the atrium.

Its purpose is to provide controlled right-to-left decompression of the Fontan circuit. This can lower systemic venous pressure and improve cardiac output in the early postoperative period, but at the cost of lower systemic oxygen saturation.

Fenestration may be considered when the Fontan circulation is higher risk, including:

• Borderline pulmonary vascular resistance
• Elevated pulmonary artery pressure
• Small or distorted pulmonary arteries
• Ventricular dysfunction
• Significant atrioventricular valve regurgitation
• High anticipated pleural or lymphatic burden
• Complex heterotaxy or systemic venous anatomy
• Borderline Fontan pathway geometry

The interpretation of fenestration outcome data requires caution. In historical cohorts, absence of fenestration was associated with early failure in selected high-risk settings [3]. In modern series, fenestration may appear associated with worse event-free survival because it is often used selectively in higher-risk patients rather than randomly assigned [10].

9. Perioperative Management Principles

Postoperative Fontan management is directed toward preserving the transpulmonary pressure gradient while minimizing systemic venous congestion.

Key principles include:

• Maintain low pulmonary vascular resistance
• Avoid hypoxia, hypercarbia, acidosis, pain, agitation, and atelectasis
• Avoid excessive positive pressure ventilation and excessive mean airway pressure
• Promote lung recruitment without impairing venous return
• Maintain adequate preload without causing fluid overload
• Preserve sinus rhythm and atrioventricular synchrony
• Treat clinically significant atrioventricular valve regurgitation
• Evaluate early for pulmonary artery stenosis, conduit obstruction, baffle obstruction, pulmonary venous obstruction, or arch obstruction when Fontan pressure is elevated
• Monitor pleural drainage, ascites, lymphatic complications, renal function, hepatic congestion, and oxygen saturation trends

Early extubation is often beneficial because spontaneous respiration generates negative intrathoracic pressure, augments systemic venous return, and facilitates pulmonary blood flow. However, extubation must be balanced against lung mechanics, oxygenation, ventricular function, and overall postoperative stability.

10. Surgical Decision-Making

Successful Fontan completion depends more on the global physiologic substrate than on the conduit configuration alone.

Before Fontan completion, the surgeon and heart team must evaluate:

• Pulmonary artery size, continuity, and distortion
• Pulmonary vascular resistance
• Pulmonary venous pathway
• Systemic venous anatomy
• Ventricular systolic and diastolic function
• Atrioventricular valve competence
• Aortic arch and systemic outflow tract patency
• Rhythm status
• Prior operations and adhesions
• Need for pulmonary artery plasty
• Need for atrioventricular valve repair
• Need for fenestration
• Patient size and expected future growth

The technical goal is straightforward but unforgiving:

Create a wide, unobstructed, low-resistance systemic venous pathway to the pulmonary arteries while preserving efficient pulmonary venous return, ventricular filling, and systemic output.

11. Key Takeaways

The Fontan procedure completes single-ventricle palliation by directing systemic venous blood to the pulmonary arteries without a subpulmonary ventricle.

Fontan pulmonary blood flow depends on low pulmonary vascular resistance, unobstructed systemic venous pathways, low pulmonary venous atrial pressure, preserved ventricular function, and competent atrioventricular valves.

The extracardiac conduit Fontan provides a smooth extra-atrial pathway and minimizes atrial manipulation, but it has no intrinsic growth potential and carries conduit-related thrombosis, obstruction, and size-mismatch concerns.

The lateral tunnel Fontan uses an intra-atrial baffle with some growth potential, but atrial involvement creates risk of atrial dilation, arrhythmia substrate, baffle leak, and intra-atrial pathway complications.

Long-term Fontan care is lifelong management of a fragile venous-pressure-dependent circulation, with ongoing risk of arrhythmia, venous congestion, lymphatic failure, thromboembolism, ventricular dysfunction, end-organ disease, and late Fontan failure.

References

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[2] Mazza GA, Gribaudo E, Agnoletti G. The pathophysiology and complications of Fontan circulation. Acta Biomed. 2021;92(5):e2021260.

[3] Gentles TL, Mayer JE Jr, Gauvreau K, Newburger JW, Lock JE, Kupferschmid JP, Burnett J, Jonas RA, Castañeda AR, Wernovsky G. Fontan operation in five hundred consecutive patients: factors influencing early and late outcome. J Thorac Cardiovasc Surg. 1997;114(3):376-391.

[4] 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.

[5] Pundi KN, Johnson JN, Dearani JA, Pundi KN, Li Z, Hinck CA, Dahl SH, Cannon BC, O’Leary PW, Driscoll DJ, Cetta F. 40-Year follow-up after the Fontan operation: long-term outcomes of 1,052 patients. J Am Coll Cardiol. 2015;66(15):1700-1710.

[6] Hsu DT. The Fontan operation: the long-term outlook. Curr Opin Pediatr. 2015;27(5):569-575.

[7] Giannico S, Hammad F, Amodeo A, Michielon G, Drago F, Turchetta A, Di Donato RM, Sanders SP. Clinical outcome of 193 extracardiac Fontan patients: the first 15 years. J Am Coll Cardiol. 2006;47(10):2065-2073.

[8] Chowdhury UK, Airan B, Kothari SS, Talwar S, Saxena A, Singh R, Subramaniam GK, Pradeep KK, Patel CD, Venugopal P. Specific issues after extracardiac Fontan operation: ventricular function, growth potential, arrhythmia, and thromboembolism. Ann Thorac Surg. 2005;80(2):665-672.

[9] Daley M, d’Udekem Y. The optimal Fontan operation: lateral tunnel or extracardiac conduit? J Thorac Cardiovasc Surg. 2021;162(6):1825-1834.

[10] 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.