Fenestrated Fontan: Physiology, Technique, and Management

1. Introduction

The Fontan procedure establishes a circulation in which systemic venous blood flows directly into the pulmonary arteries without a subpulmonary ventricle. Pulmonary flow consequently depends on low pulmonary vascular resistance (PVR), unobstructed cavopulmonary pathways, and adequate systemic ventricular filling.

Fontan fenestration is a deliberately created communication between the Fontan pathway and the pulmonary venous atrium. It permits controlled right-to-left shunting to reduce systemic venous pressure and preserve ventricular preload and cardiac output. The trade-offs are systemic arterial desaturation and potential paradoxical thromboembolism. Routine fenestration in otherwise low-risk patients remains controversial.[1,2]

2. Concept and Physiology

2.1 Hemodynamics of a Nonfenestrated Fontan

Pulmonary blood flow is driven by the pressure difference between the systemic venous pathway and pulmonary venous atrium, and is impeded by pulmonary vascular resistance:

Here, Qp is pulmonary blood flow; PFontan is cavopulmonary pressure; PLA is pulmonary venous atrial pressure; and Rpulmonary is the effective resistance of the pulmonary circuit. This is a simplified pressure–flow relationship, not a complete representation of pulsatile flow or vascular compliance.

Without significant collateral flow or residual shunting:

Increased PVR restricts pulmonary flow and ventricular filling even if systemic ventricular systolic function is preserved. Systemic venous pressure can rise to sustain the transpulmonary pressure gradient, but prolonged venous hypertension promotes pleural effusions, lymphatic congestion, hepatic congestion, and impaired organ perfusion.[1]

2.2 Hemodynamic Effects of Fenestration

When Fontan pressure exceeds atrial pressure, a fenestration directs venous blood into the pulmonary venous atrium. The major effects are:

• Venous decompression: reduces Fontan pressure and may decrease congestion.
• Maintenance of preload: allows systemic venous blood to reach the ventricle despite limited pulmonary flow.
• Arterial desaturation: bypasses pulmonary gas exchange.

In the simplified absence of major collateral flow:

where Qfen represents right-to-left fenestration flow. Systemic blood flow may thus exceed pulmonary blood flow. Importantly, oxygen delivery depends on cardiac output and oxygen content:

Mild desaturation may be an acceptable cost if systemic flow improves sufficiently; marked desaturation may instead impair oxygen delivery. An isolated SpO₂ value is therefore an insufficient measure of Fontan performance.[1,2]

2.3 Fenestration as a Safety Valve

A fenestration is a pressure-relieving pop-off in patients with increased pulmonary resistance or impaired ventricular filling. Potentially relevant conditions include elevated PVR, small or stenotic pulmonary arteries, ventricular diastolic dysfunction, important atrioventricular valve regurgitation, or borderline output at separation from cardiopulmonary bypass (CPB).

However, severe PVR elevation, poor ventricular function, or anatomical obstruction may indicate an unsuitable Fontan circulation rather than a problem that fenestration alone can remedy. Fenestration is not a substitute for treating the underlying lesion.

3. Surgical Procedure

3.1 Extracardiac Fontan Completion

The illustrated operation uses an extracardiac conduit with a direct conduit-to-atrium fenestration. Following exposure and institution of CPB, the pulmonary arteries and superior cavopulmonary connection are inspected. Important branch pulmonary artery narrowing should be repaired.

1. Pulmonary artery preparation: mobilize the confluence, and perform pulmonary arterioplasty if required.
2. Superior conduit anastomosis: connect the extracardiac conduit to the pulmonary artery with a wide, tension-free anastomosis that does not distort the branch pulmonary arteries.
3. IVC separation: divide the right atrium from the IVC cuff, preserve adequate tissue for the inferior connection, and securely close the atrial opening.
4. Inferior conduit anastomosis: connect the conduit to the IVC cuff without kinking, rotation, redundancy, or narrowing.

Expanded polytetrafluoroethylene (ePTFE) is commonly used. Conduit diameter and orientation depend on anatomy, intrathoracic space, anticipated growth, and operative strategy. Placement near the atrial wall facilitates a direct fenestration.

3.2 Creation of the Fenestration

The illustrated technique uses a side-biting atrial clamp to construct a direct communication between the atrium and extracardiac conduit.

A 2.7-mm punch creates a conduit opening, with patency checked using an approximately 3-mm Hegar dilator. These measurements reflect the illustrated technique, not a universal recommended fenestration diameter.

The atrial opening is aligned opposite the conduit opening. A direct anastomosis is constructed without excessive tension or narrowing. Operative priorities include preserving the main conduit lumen, preventing suture-line bleeding, avoiding distortion, and ensuring a patent communication. Alternative surgical techniques include a kissing anastomosis and short interposition grafts for cases in which direct atrial approximation is difficult.[3–5]

3.3 Size and Patency

A larger orifice usually provides more decompression but may cause greater systemic desaturation; a smaller orifice limits shunting but may inadequately decompress the circuit. Flow is also determined by the pressure gradient and effective orifice geometry.

Premature fenestration obstruction can eliminate an important early postoperative decompression route and contribute to venous hypertension or low cardiac output in vulnerable patients.[3,4]

3.4 Separation From CPB

Weaning from CPB requires adequate but not excessive preload, effective ventilation, correction of acidosis and hypothermia, and satisfactory rhythm and ventricular performance. Minimize PVR while avoiding excessive positive intrathoracic pressure.

Transesophageal echocardiography should evaluate ventricular function, atrioventricular valve regurgitation, cavopulmonary pathway patency, and fenestration flow. Assess the integrated hemodynamic profile rather than any single pressure or saturation measurement.

4. Postoperative Management

4.1 Principal Objectives

Early care prioritizes systemic perfusion and oxygen delivery with controlled systemic venous pressure. Serial assessment includes blood pressure, perfusion, lactate, urine output, trends in venous and atrial pressures, and echocardiography.

• Optimize PVR: prevent hypoxemia, marked hypercapnia, acidosis, atelectasis, and excessive airway pressure.
• Balance volume and diuresis: maintain sufficient filling while preventing systemic venous congestion.
• Confirm fenestration function: ensure decompression is present without disproportionate shunting or hypoxemia.
• Identify residual lesions: investigate conduit obstruction, pulmonary artery stenosis, elevated atrial pressure, atrioventricular regurgitation, and ventricular dysfunction.

A lower Fontan pressure is not automatically better if cardiac output and perfusion deteriorate.

4.2 Interpreting Fenestration Physiology

These patterns are not independently diagnostic: pulmonary venous saturation, collateral flows, and cardiac output also influence SpO₂.

4.3 Ventilation and PVR

Positive-pressure ventilation may decrease systemic venous return and the effective driving pressure for cavopulmonary flow. Excessive PEEP can increase PVR through overdistension, whereas inadequate recruitment and atelectasis can also raise PVR. Ventilation should preserve recruitment while avoiding unnecessary mean airway pressure.

Spontaneous breathing can assist pulmonary venous return and Fontan flow through negative intrathoracic pressure. Early extubation may benefit selected patients, but should not be pursued at the expense of respiratory or circulatory stability. Pulmonary vasodilators may be considered when elevated PVR contributes to dysfunction; anatomical obstruction still requires correction.

4.4 Fluid Balance and Venous Congestion

Underfilling limits ventricular preload. Overfilling raises systemic venous pressure and may increase pleural effusions without increasing forward flow. Volume therapy should be guided by perfusion and fluid responsiveness, not CVP alone. Once stable, cautious diuresis may reduce congestion. Persistent pleural drainage warrants assessment for PVR elevation, pathway obstruction, raised ventricular filling pressure, and atrioventricular valve regurgitation.[1,6]

5. Complications and Long-Term Considerations

5.1 Persistent Desaturation

Right-to-left fenestration flow causes predictable systemic desaturation. Clinically important hypoxemia may impair oxygen delivery and exercise performance. Evaluate persistent or progressive desaturation for a large fenestration, additional baffle leaks, veno-venous collaterals, and pulmonary arteriovenous malformations.

5.2 Paradoxical Embolism and Thromboprophylaxis

A fenestration allows venous thrombus or air to bypass the pulmonary capillary filter and reach systemic arteries, potentially causing stroke. Strict intravenous line and air management are important. Thromboprophylaxis is also central to Fontan care because low-flow pathways and prosthetic material predispose to thrombosis. Aspirin and anticoagulant strategies are used according to clinical risk; randomized evidence has not established one universally superior regimen for every Fontan patient.[1,7]

5.3 Catheter-Based Fenestration Closure

Once Fontan physiology is stable, transcatheter closure may be considered for persistent clinically relevant desaturation. Catheterization assesses Fontan pressure, atrial filling pressure, anatomy, and output. Temporary balloon test occlusion evaluates the immediate effects of eliminating the shunt.

A significant pressure increase, reduced cardiac output, or impaired systemic perfusion argues against closure. No single hemodynamic threshold is universally applicable. Some patients should remain fenestrated when pulmonary vascular or ventricular filling reserve is limited.[8,9]

6. Evidence and Outcomes

In a prospective randomized trial of 49 patients, Lemler and colleagues reported improved early postoperative outcomes with fenestration, including less pleural drainage and a shorter recovery in selected patients.[10] Other surgical series have been heterogeneous, particularly in contemporary extracardiac Fontan populations.

A meta-analysis and best-evidence review support potential early postoperative benefits, but do not establish a universal late survival advantage.[11,12] Recent multicenter observational data continue to examine long-term outcomes in fenestrated versus nonfenestrated extracardiac Fontan patients.[13] Interpretation is limited by confounding by indication: patients receiving fenestrations may have greater baseline risk.

Current practice consequently varies between routine, selective, and nonroutine fenestration. The strongest rationale remains physiological: decompression and preload preservation when Fontan reserve is limited.

7. Key Clinical and Surgical Principles

• Controlled right-to-left shunt: lowers venous pressure and can preserve ventricular filling.
• Oxygen delivery over saturation alone: mild desaturation may be acceptable if systemic flow improves.
• No substitute for adequate reconstruction: residual cavopulmonary or pulmonary artery obstruction requires treatment.
• Geometry matters: select an appropriate opening, avoid tension and distortion, and confirm patency.
• Optimize PVR and fluid balance: maintain lung recruitment and systemic perfusion without excessive venous congestion.
• Prevent paradoxical embolism: meticulous air control and individualized antithrombotic therapy are essential.
• Do not close automatically: test-occlusion hemodynamics and the patient's reserve govern closure decisions.
• Investigate persistent elevated Fontan pressure: a fenestration treats consequences, not the underlying cause.

References

1. Rychik J, Atz AM, Celermajer DS, et al. Evaluation and management of the child and adult with Fontan circulation: A scientific statement from the American Heart Association. Circulation. 2019. DOI: 10.1161/CIR.0000000000000696. PMID: 31256636.
2. Corno AF, Koerner TS, Salazar JD. The pendulum of Fontan fenestration. Transl Pediatr. 2023. DOI: 10.21037/tp-22-562. PMID: 36798929.
3. Nemoto S, Ikeda T, Brizard C, et al. Modified technique creating fenestration in the extracardiac Fontan completion; kissing anastomosis. Kyobu Geka. 2005. PMID: 16167812.
4. Kreutzer C, Schlichter AJ, Simon JL, et al. A new method for reliable fenestration in extracardiac conduit Fontan operations. Ann Thorac Surg. 2003. DOI: 10.1016/S0003-4975(02)04569-1. PMID: 12735607.
5. Türköz R, Çelik M, Palaoğlu E, et al. Easy fenestration technique for extracardiac Fontan operation. World J Pediatr Congenit Heart Surg. 2015. DOI: 10.1177/2150135115576928. PMID: 26467868.
6. Mascio CE, Austin EH. Pleural effusions following the Fontan procedure. Curr Opin Pulm Med. 2010. DOI: 10.1097/MCP.0b013e3283396efc. PMID: 20410822.
7. Monagle P, Cochrane A, Roberts R, et al. A multicenter, randomized trial comparing heparin/warfarin and acetylsalicylic acid as primary thromboprophylaxis for 2 years after the Fontan procedure in children. J Am Coll Cardiol. 2011. DOI: 10.1016/j.jacc.2011.01.061. PMID: 21798429.
8. Bridges ND, Lock JE, Mayer JE Jr, et al. Cardiac catheterization and test occlusion of the interatrial communication after the fenestrated Fontan operation. J Am Coll Cardiol. 1995. DOI: 10.1016/0735-1097(95)00055-9. PMID: 7759728.
9. Kawasaki Y, Sasaki T, Forbes TJ, et al. Optimal criteria for transcatheter closure of Fontan fenestration: A single-center experience with a review of literature. Heart Vessels. 2021. DOI: 10.1007/s00380-021-01798-y. PMID: 33590306.
10. Lemler MS, Scott WA, Leonard SR, et al. Fenestration improves clinical outcome of the Fontan procedure: A prospective, randomized study. Circulation. 2002. DOI: 10.1161/HC0202.102237. PMID: 11790702.
11. Bouhout I, Ben-Ali W, Khalaf D, et al. Effect of fenestration on Fontan procedure outcome: A meta-analysis and review. Ann Thorac Surg. 2020. DOI: 10.1016/j.athoracsur.2019.12.020. PMID: 31987825.
12. Toncu A, Rădulescu C, Dorobantu DM, et al. Does routine fenestration improve early and late postoperative outcomes in patients undergoing Fontan palliation? Interact Cardiovasc Thorac Surg. 2020. DOI: 10.1093/icvts/ivaa002. PMID: 32243525.
13. Ko H, Song J, Chi S, et al. The long-term effects of the fenestration in patients with extracardiac Fontan circulation—a multicenter Korean cohort study based on national Fontan registry. Front Cardiovasc Med. 2024. DOI: 10.3389/fcvm.2024.1341882. PMID: 38774663.