Fontan Procedure #3: Lateral Tunnel Fontan

1. Concept

The lateral tunnel Fontan is an intracardiac form of total cavopulmonary connection in which the inferior vena caval blood flow is directed through a surgically created tunnel inside the right atrium and then into the pulmonary artery. The pathway is constructed using the native atrial wall and patch material, creating an intra-atrial baffle that separates systemic venous return from the functional atrial chamber.

In contrast to the extracardiac conduit Fontan, which uses an external prosthetic tube graft between the IVC and pulmonary artery, the lateral tunnel Fontan uses the right atrium itself as part of the Fontan pathway. This design provides a more intracardiac and anatomically integrated route, with potential advantages in smaller children, including some capacity for growth and easy creation of a fenestration [1, 2].

However, because the lateral tunnel requires a right atriotomy and a long intra-atrial suture line, it may create a substrate for atrial arrhythmia, sinus node dysfunction, atrial dilation, baffle leak, thrombus formation, and late pathway-related complications [2–4].

2. Surgical Construction

The lateral tunnel Fontan can be understood as the construction of a controlled venous channel within the right atrium.

2.1 Right Atriotomy

The operation begins with opening the right atrium. This provides exposure of the IVC orifice, atrial septal region, pulmonary venous atrium, and the superior atrial pathway toward the pulmonary artery.

The surgical goal is to design a route that allows IVC blood to pass smoothly toward the pulmonary artery without disturbing pulmonary venous return, atrioventricular valve function, or atrial geometry.

2.2 Tunnel Patch Suturing

A patch is sutured inside the right atrium to construct the lateral tunnel. The tunnel is therefore composed of:

• Native atrial wall
• Patch material
• A long intra-atrial suture line

The geometry of this tunnel is critical. It must be wide enough to avoid systemic venous obstruction, smooth enough to minimize energy loss, and positioned carefully to prevent pulmonary venous pathway compromise.

A narrow, angulated, or irregular tunnel can increase resistance within the Fontan pathway. In Fontan physiology, even mild obstruction can become clinically important because pulmonary blood flow is passive and depends on low-resistance venous return.

2.3 Pulmonary Arteriotomy

A pulmonary arteriotomy is created at the planned superior connection site. This opening becomes the outflow of the lateral tunnel into the pulmonary artery.

The arteriotomy must be large and well-positioned. A small or distorted connection may increase transpulmonary gradient and systemic venous pressure, impairing Fontan efficiency.

2.4 Superior Tunnel–Pulmonary Artery Anastomosis

The superior end of the intra-atrial tunnel is connected to the pulmonary artery. After this step, the systemic venous circulation is separated into two passive pulmonary inflow pathways:

• SVC flow enters the pulmonary arteries through the bidirectional Glenn pathway.
• IVC flow enters the pulmonary arteries through the lateral tunnel.

Together, these complete the total cavopulmonary connection.

2.5 Atrial Closure

The right atrium is then closed. After completion, the surgeon must confirm that the Fontan pathway is unobstructed and that there is no important residual shunt or pulmonary venous obstruction.

Key intraoperative assessment points include:

• Patency of the IVC-to-PA pathway
• Absence of significant baffle leak
• Pulmonary venous drainage without obstruction
• Adequate branch pulmonary artery flow
• Ventricular function
• Atrioventricular valve competence
• Fenestration flow, if created

3. Hemodynamic Principle

The lateral tunnel Fontan converts the circulation into a passive cavopulmonary system, in which systemic venous blood reaches the pulmonary arteries without a subpulmonary ventricle.

This circulation depends on several essential conditions:

1. Low pulmonary vascular resistance

Elevated pulmonary vascular resistance directly increases systemic venous pressure and reduces pulmonary blood flow.

2. Unobstructed pulmonary arteries

Branch PA stenosis or distortion increases energy loss and may compromise the entire Fontan circuit.

3. Good ventricular function

The single ventricle must support systemic output with preload limited by passive pulmonary venous return.

4. Competent atrioventricular valve

AV valve regurgitation increases atrial pressure and worsens systemic venous congestion.

5. No significant baffle obstruction or leak

Obstruction raises venous pressure; leak may cause systemic desaturation or inefficient Fontan flow.

In early postoperative comparisons, extracardiac conduit Fontan has been associated with lower central venous pressure and lower transpulmonary gradient than lateral tunnel Fontan in some series, suggesting a possible hemodynamic advantage of the extracardiac pathway in selected patients [5].

4. Advantages of the Lateral Tunnel Fontan

4.1 Intracardiac and Anatomic Pathway

The lateral tunnel uses the right atrium as part of the pathway. This allows the surgeon to construct an anatomically integrated channel from the IVC to the pulmonary artery.

4.2 Potential for Growth

Because part of the tunnel is formed by native atrial tissue, the lateral tunnel may have some capacity to accommodate growth. This was one of the historical reasons for its use in smaller children [1].

4.3 Fenestration Is Technically Straightforward

A fenestration can be created between the lateral tunnel and the atrial chamber. This provides a controlled right-to-left decompression route.

Fenestration may be useful when there is concern for:

• High Fontan pressure
• Borderline ventricular function
• Elevated pulmonary vascular resistance
• Prolonged pleural drainage risk
• Low cardiac output after Fontan completion

The trade-off is systemic desaturation, but in selected patients, fenestration can improve early postoperative stability.

4.4 Technical Flexibility in Selected Anatomy

The lateral tunnel may be useful when the intracardiac route offers a more favorable pathway than an external conduit, particularly in patients with complex atrial anatomy, limited extracardiac space, or prior surgical reconstruction.

5. Limitations and Late Concerns

5.1 Atrial Arrhythmia and Sinus Node Dysfunction

The major long-term concern of lateral tunnel Fontan is atrial rhythm disturbance. The right atriotomy, intra-atrial suture line, and potential atrial dilation may create a substrate for atrial tachyarrhythmia and sinus node dysfunction.

Several comparative studies showed higher early or late arrhythmia burden after lateral tunnel Fontan than after extracardiac conduit Fontan [2–4]. In one institutional comparison, sinus node dysfunction was more frequent after lateral tunnel Fontan, and extracardiac conduit Fontan was associated with reduced early and midterm atrial arrhythmia risk [2]. Another study focusing on arrhythmias also supported the concept that lateral tunnel pathways may carry greater rhythm-related morbidity [3].

5.2 Atrial Dilation

Because the pathway is partly constructed within the right atrium, progressive atrial dilation may occur over time. Atrial dilation can reduce flow efficiency, promote blood stasis, and further increase the risk of arrhythmia and thrombosis.

5.3 Baffle Leak and Residual Shunt

The long suture line used to construct the intra-atrial tunnel introduces the possibility of baffle leak. Depending on the pressure relationship and leak direction, this may lead to:

• Systemic desaturation
• Right-to-left shunting
• Paradoxical embolic risk
• Inefficient Fontan circulation

Small leaks may be clinically silent, whereas significant leaks may require catheter-based or surgical intervention.

5.4 Thromboembolic Risk

All Fontan pathways carry thromboembolic risk due to slow venous flow, altered coagulation, prosthetic material, and chronic venous hypertension. In meta-analytic data, thromboembolic event rates were not consistently lower with one technique, and some analyses reported numerically higher thromboembolic rates in extracardiac conduit Fontan despite better arrhythmia outcomes [6].

This highlights an important principle: Fontan pathway design influences risk, but thrombosis is multifactorial, depending on flow dynamics, anticoagulation strategy, rhythm status, ventricular function, and patient-specific factors.

5.5 Fontan Pathway Obstruction

Potential obstruction sites include the IVC entrance, tunnel body, superior tunnel-to-PA anastomosis, and branch pulmonary arteries. Because the Fontan circulation lacks a pumping chamber between the systemic veins and pulmonary arteries, even modest obstruction can produce clinically meaningful elevation of venous pressure.

6. Lateral Tunnel Versus Extracardiac Conduit Fontan

The lateral tunnel and extracardiac conduit techniques share the same physiologic endpoint: completion of total cavopulmonary connection. Their major difference is the construction of the IVC-to-PA pathway.

The literature does not provide a single universal answer. Several studies and meta-analyses favor extracardiac conduit Fontan because of lower arrhythmia burden and favorable long-term freedom from tachyarrhythmia [6, 7]. One meta-analysis of 3,330 patients reported better freedom from tachyarrhythmia and improved long-term survival in the extracardiac conduit group [6]. Another meta-analysis similarly supported extracardiac conduit Fontan for several early and long-term outcomes [7].

However, not all data are concordant. A large single-center study reported better freedom from death and Fontan failure after lateral tunnel Fontan compared with extracardiac conduit Fontan, emphasizing that institutional practice, patient selection, era, conduit size, fenestration strategy, and follow-up duration may strongly influence outcomes [10].

Therefore, the choice between lateral tunnel and extracardiac conduit Fontan should not be framed as a simple “old versus new” comparison. It is better understood as an individualized surgical decision based on anatomy, patient size, pulmonary artery geometry, rhythm history, prior palliation, and institutional experience.

7. Practical Surgical Message

The lateral tunnel Fontan is not merely an older version of the extracardiac conduit Fontan. It is a distinct surgical strategy that creates a cavopulmonary pathway using the right atrium as part of the conduit.

The essential technical principles are:

1. Create a wide and smooth IVC-to-PA pathway.

The tunnel must avoid narrowing, twisting, and unnecessary flow collision.

2. Protect pulmonary venous return.

The baffle must not encroach on pulmonary venous drainage.

3. Minimize atrial distortion.

Excessive atrial tension or geometric deformation may contribute to late dilation and arrhythmia.

4. Construct a generous superior anastomosis.

The tunnel-to-PA connection should be large enough to avoid postoperative obstruction.

5. Consider fenestration selectively.

Fenestration can stabilize early postoperative physiology but leaves a residual right-to-left shunt.

6. Anticipate late surveillance needs.

Patients require lifelong follow-up for arrhythmia, pathway obstruction, thromboembolism, ventricular dysfunction, protein-losing enteropathy, plastic bronchitis, and Fontan-associated liver disease.

8. Summary

The lateral tunnel Fontan directs IVC blood through an intra-atrial tunnel to the pulmonary arteries, completing the total cavopulmonary connection. The tunnel is constructed from the atrial wall and patch material and is connected superiorly to the pulmonary artery.

Its advantages include an anatomic intracardiac pathway, some growth potential, technical flexibility, and straightforward fenestration. Its limitations include atrial incision, intra-atrial suture lines, atrial dilation, arrhythmia substrate, baffle leak, and thromboembolic risk.

Modern evidence generally favors extracardiac conduit Fontan for lower atrial arrhythmia burden, but survival and Fontan failure data are not completely uniform across studies. The optimal Fontan pathway remains patient-specific and depends on anatomy, physiology, age, prior operations, and surgical judgment [6, 10].

References

[1] Fiore AC, Turrentine M, Rodefeld M, Vijay P, Schwartz TL, Virgo KS, Fischer LK, Brown JW. Fontan operation: a comparison of lateral tunnel with extracardiac conduit. Ann Thorac Surg. 2007;83(2):622-630.

[2] Azakie A, McCrindle BW, Van Arsdell G, Benson LN, Coles J, 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.

[3] Hakacova N, Lakomy M, Kovacikova L. Arrhythmias after Fontan operation: comparison of lateral tunnel and extracardiac conduit. J Electrocardiol. 2008;41(2):173-177.

[4] Kumar SP, Rubinstein CS, Simsic JM, Taylor AB, Saul JP, Bradley SM. Lateral tunnel versus extracardiac conduit Fontan procedure: a concurrent comparison. Ann Thorac Surg. 2003;76(5):1389-1396.

[5] Lee JR, Kwak J, Kim KC, Min SK, Kim WH, Kim YJ, Rho JR. Comparison of lateral tunnel and extracardiac conduit Fontan procedure. Interact Cardiovasc Thorac Surg. 2007;6(3):328-330.

[6] Ben Ali W, Bouhout I, Khairy P, Bouchard D, Poirier N. Extracardiac versus lateral tunnel Fontan: a meta-analysis of long-term results. Ann Thorac Surg. 2019;107(3):837-843.

[7] Lin Z, Ge H, Xue J, Wu G, Du J, Hu X, Zhao Q. Comparison of extracardiac conduit and lateral tunnel for functional single-ventricle patients: a meta-analysis. Congenit Heart Dis. 2017;12(6):711-720.

[8] 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.

[9] Katogi T. Extracardiac conduit Fontan procedure versus intra-atrial lateral tunnel Fontan procedure. Gen Thorac Cardiovasc Surg. 2012;60(12):834-838.

[10] Weixler VHM, Zurakowski D, Kheir J, Guariento A, Kaza AK, Baird CW, Del Nido PJ, Emani SM. Fontan with lateral tunnel is associated with improved survival compared with extracardiac conduit. J Thorac Cardiovasc Surg. 2020;159(4):1480-1491.