Fenestrated Fontan #3: Postoperative Management, Thromboembolic Risk, and Fenestration Closure

1. Management Goals

A Fontan fenestration is a controlled communication between the systemic venous pathway and the pulmonary venous atrium. It permits right-to-left shunting when pressure within the Fontan pathway exceeds atrial pressure, thereby decompressing the systemic venous circulation and augmenting ventricular preload. This mechanism can preserve cardiac output during the vulnerable early period after Fontan completion, particularly when pulmonary vascular resistance, ventricular filling pressure, or intrathoracic pressure temporarily limits passive pulmonary blood flow [1,2].

The physiologic benefit is inseparable from its principal cost: systemic venous blood bypasses the pulmonary circulation and lowers arterial oxygen saturation. Management must therefore balance:

• Adequate systemic cardiac output and oxygen delivery
• Acceptably low systemic venous and Fontan pressures
• Tolerable arterial desaturation
• Prevention of paradoxical systemic embolization
• Identification of patients who can safely undergo later closure

The fenestration should not be assessed as an isolated defect. Its function reflects the interaction among pulmonary vascular resistance, Fontan pathway resistance, ventricular compliance, atrioventricular valve competence, circulating volume, respiratory mechanics, and metabolic demand.

2. Prioritize Oxygen Delivery Rather Than Normal Saturation

The immediate postoperative objective is preservation of systemic perfusion and oxygen delivery rather than normalization of arterial oxygen saturation.

Systemic oxygen delivery can be conceptualized as:

DO₂ = systemic cardiac output × arterial oxygen content

Arterial oxygen content is determined primarily by hemoglobin concentration and arterial oxygen saturation. A patent fenestration lowers saturation but may increase ventricular preload and systemic output sufficiently to improve net oxygen delivery. Early hemodynamic studies demonstrated that an open fenestration could maintain a higher cardiac index and greater calculated oxygen delivery than temporary closure, particularly during volume loading [2].

The clinical interpretation of cyanosis must therefore include:

• Arterial pressure and pulse quality
• Peripheral temperature and capillary refill
• Urine output
• Lactate trend
• Cerebral and somatic near-infrared spectroscopy
• Systemic or mixed venous oxygen saturation
• Ventricular systolic and diastolic function
• Atrioventricular valve regurgitation
• Rhythm and heart rate
• Hemoglobin concentration
• Work of breathing and metabolic demand

A mildly desaturated patient with preserved blood pressure, warm extremities, adequate urine output, low lactate, and stable regional oxygenation may have satisfactory systemic oxygen delivery. Conversely, a patient with a relatively acceptable arterial saturation may remain in a low-output state if pulmonary blood flow and ventricular preload are inadequate.

Attempts to improve saturation by increasing airway pressure, reducing preload, or prematurely closing the fenestration may worsen systemic perfusion. Temporary occlusion studies have shown that closure can increase arterial saturation while simultaneously reducing systemic blood flow and total systemic oxygen transport [3]. Saturation must therefore be interpreted as one component of oxygen delivery rather than as the sole therapeutic target.

3. Maintain a Low-Resistance Fontan Pathway

Fontan flow is passive. The systemic venous pressure must provide the energy required to drive blood through the pulmonary arteries, pulmonary microcirculation, pulmonary veins, and atrium. Even a modest increase in resistance can substantially reduce pulmonary blood flow or require a higher systemic venous pressure.

Persistent elevation of Fontan pressure contributes to:

• Pleural and pericardial effusions
• Ascites and peripheral edema
• Hepatic and renal venous congestion
• Impaired lymphatic drainage
• Pulmonary interstitial edema
• Reduced ventricular preload
• Prolonged hospitalization

A high Fontan pressure should trigger systematic evaluation rather than automatic volume administration or diuresis. Potential mechanical causes include conduit obstruction, distortion of the cavopulmonary connections, branch pulmonary artery stenosis, pulmonary venous obstruction, residual arch obstruction, or external compression.

The fenestration may partially mask these lesions by allowing systemic venous blood to bypass the pulmonary circuit. Persistent dependence on a large right-to-left shunt should therefore prompt examination of the entire Fontan pathway.

4. Optimize Pulmonary Vascular Resistance

Pulmonary vascular resistance is a major modifiable determinant of Fontan flow. Management should minimize factors that constrict the pulmonary vascular bed or increase intrathoracic pressure.

Important targets include:

• Adequate lung recruitment without overdistension
• Avoidance of unnecessary positive end-expiratory pressure
• Correction of significant hypercarbia
• Correction of metabolic and respiratory acidosis
• Maintenance of normothermia
• Treatment of atelectasis and pulmonary edema
• Adequate analgesia and sedation
• Reduction of excessive work of breathing
• Treatment of pulmonary vasoconstriction when clinically indicated

Positive-pressure ventilation may be necessary early after surgery, but excessive mean airway pressure impedes systemic venous return and increases resistance to passive pulmonary flow. Spontaneous breathing generally supports Fontan circulation by generating negative intrathoracic pressure. However, premature extubation can be counterproductive when agitation, airway obstruction, atelectasis, or increased respiratory effort markedly raises oxygen consumption.

Selective pulmonary vasodilator therapy may be useful when pulmonary vasoconstriction is an important contributor. It does not correct conduit obstruction, pulmonary artery distortion, elevated atrial pressure, ventricular dysfunction, or excessive intrathoracic pressure.

5. Balance Preload and Venous Congestion

The Fontan circulation is simultaneously preload dependent and intolerant of excessive venous pressure.

Underfilling may produce:

• Reduced transpulmonary flow
• Inadequate ventricular preload
• Low stroke volume
• Hypotension
• Increased right-to-left fenestration flow
• Reduced systemic oxygen delivery

Overfilling may produce:

• Elevated Fontan and atrial pressures
• Pleural drainage and tissue edema
• Pulmonary interstitial fluid
• Impaired lung compliance
• Increased pulmonary vascular resistance
• Hepatic, renal, and lymphatic congestion

Volume administration should be guided by the relationship between Fontan pressure, atrial pressure, cardiac output, and tissue perfusion. High Fontan pressure with low atrial pressure suggests an excessive transpulmonary gradient caused by pulmonary vascular resistance or pathway obstruction. Simultaneous elevation of Fontan and atrial pressures suggests ventricular diastolic dysfunction, systolic dysfunction, atrioventricular valve regurgitation, or excessive circulating volume.

Once perfusion is stable and capillary leak is resolving, controlled diuresis can reduce venous congestion and improve respiratory mechanics. Diuresis should be reassessed against blood pressure, urine output, lactate, regional oxygenation, weight, chest drainage, and filling-pressure trends.

6. Determine Whether the Fenestration Is Appropriately Balanced

Elevated Fontan Pressure With Limited Desaturation

This pattern suggests inadequate decompression. Potential explanations include a restrictive fenestration, unfavorable fenestration geometry, partial spontaneous closure, obstruction by tissue, or severe resistance within the pulmonary circuit.

Before enlarging or recreating a fenestration, the team should exclude Fontan pathway obstruction, pulmonary vascular disease, high ventricular filling pressure, and significant atrioventricular valve regurgitation.

Marked Desaturation With Acceptable Fontan Pressure

This pattern may indicate excessive right-to-left flow, but high pulmonary vascular resistance may also divert a disproportionate volume through an otherwise appropriately sized fenestration.

Additional causes of desaturation include:

• Venovenous collateral vessels
• Pulmonary arteriovenous malformations
• Pulmonary venous desaturation
• Severe ventilation-perfusion mismatch
• Low mixed venous saturation
• Inadequate hemoglobin concentration
• Low systemic cardiac output

The distinction is important because closing the fenestration will not correct pulmonary disease or low mixed venous oxygen saturation and may reduce cardiac output.

Elevated Fontan Pressure With Marked Desaturation

This is an unfavorable combination. It indicates that the fenestration is not adequately protecting the venous circulation and that effective pulmonary blood flow remains impaired. Urgent investigation should address pulmonary vascular resistance, pathway obstruction, ventricular dysfunction, atrioventricular valve regurgitation, pulmonary venous obstruction, and respiratory disease.

7. Paradoxical Embolism and Line Management

A patent fenestration permits venous thrombus, air, or particulate material to enter the systemic arterial circulation without passing through the pulmonary vascular filter. Intravenous access must therefore be managed as functionally “arterialized venous” flow.

Practical precautions include:

• Meticulous removal of air from all intravenous tubing
• Secure line and stopcock connections
• Air-eliminating filters when compatible with the infusion
• Minimal unnecessary line disconnection
• Careful central venous catheter placement and removal
• Controlled contrast and rapid-infusion administration
• Immediate assessment of new neurologic or systemic ischemic findings

Post-Fontan thromboprophylaxis should be individualized according to institutional practice, bleeding risk, prior thrombosis, rhythm, ventricular function, prosthetic material, hepatic dysfunction, and other Fontan-associated risk factors. The available closure studies provide limited comparative data regarding paradoxical thromboembolic events; therefore, the presence of a fenestration should heighten preventive vigilance without being interpreted as establishing one universal anticoagulation regimen.

8. Surveillance of Fenestration Patency

Fenestration status may evolve after discharge. In one retrospective cohort, spontaneous closure occurred in approximately 22% of patients. Elevated pre-Fontan pulmonary vascular resistance and a history of systemic venous thromboembolism were associated with persistent patency [9].

Follow-up assessment should include:

• Resting and exertional oxygen saturation
• Growth and exercise tolerance
• Fontan and atrial pressure when catheterization is performed
• Ventricular function and atrioventricular valve competence
• Pleural effusions, ascites, or peripheral edema
• Protein-losing enteropathy or plastic bronchitis
• Arrhythmias
• Thromboembolic events
• Conduit and pulmonary artery patency
• Venovenous or aortopulmonary collateral vessels

Spontaneous closure may improve saturation but can expose limited Fontan reserve. Persistent patency may represent an intentionally preserved pressure-relief pathway, an excessive residual shunt, or a marker of unfavorable underlying physiology.

9. Selection for Transcatheter Closure

Fenestration closure is generally considered after recovery from Fontan completion when persistent cyanosis is clinically important and the patient appears capable of tolerating complete separation of the systemic venous and pulmonary venous circulations.

Pre-closure evaluation should confirm:

• An unobstructed Fontan pathway
• No major decompressing venovenous collateral vessels
• Acceptable Fontan pressure
• Acceptable atrial or ventricular filling pressure
• Adequate cardiac index
• Preserved ventricular function
• Manageable atrioventricular valve regurgitation
• No major pulmonary venous obstruction
• Acceptable pulmonary vascular resistance

Temporary balloon test occlusion is essential because resting baseline measurements alone may not reveal dependence on the fenestration. During occlusion, the team should assess Fontan pressure, atrial pressure, systemic arterial pressure, cardiac index, venous saturation, arterial saturation, and calculated oxygen transport.

Elevated baseline mean left atrial pressure and a substantial increase in mean Fontan pressure during balloon occlusion have been associated with the decision not to close and with greater subsequent adverse-event burden [4]. These findings emphasize the importance of ventricular filling pressure as well as upstream Fontan pressure.

One institutional protocol required an unobstructed pathway without important decompressing collaterals, baseline Fontan pressure of 15 mmHg or less, baseline cardiac index of at least 2 L/min/m², and a reduction in cardiac index of no more than 20% during test occlusion [5]. These criteria were associated with a substantial improvement in oxygen saturation after closure. They should be considered institutional decision thresholds rather than universal standards.

10. Expected Consequences of Closure

Fenestration closure predictably improves arterial oxygen saturation. A systematic review and meta-analysis of 12 observational studies reported a mean increase in arterial saturation of approximately 7.9% after transcatheter closure. Mean cavopulmonary pressure increased by approximately 1.4 mmHg. Exercise oxygen saturation improved, but the average increase in exercise duration was modest [6].

The hemodynamic trade-off is clinically important. In an acute occlusion study, systemic blood flow decreased from approximately 2.4 to 1.8 L/min/m², systemic oxygen transport decreased, and oxygen extraction increased despite a rise in arterial saturation from approximately 84% to 95% [3]. Earlier operative measurements similarly demonstrated greater cardiac index and oxygen delivery with the fenestration open than closed [2].

Closure should therefore not be judged successful solely because saturation rises. A physiologically successful closure should improve cyanosis without causing:

• A clinically important rise in Fontan pressure
• Elevated atrial or ventricular filling pressure
• Significant reduction in cardiac index
• Hypotension
• Reduced venous oxygen saturation
• Worsening organ congestion
• Deterioration in exercise tolerance

11. Long-Term Outcomes and Interpretation of Persistent Patency

Persistent fenestration has been associated with increased late mortality, Fontan failure, and Fontan-related complications. In a cohort of 326 patients, those with an open fenestration during follow-up had significantly more late deaths, Fontan failure, and complications than patients with a closed fenestration [7].

This association should not be interpreted as definitive proof that closure itself improves survival. Patients who remain fenestrated are frequently those with higher filling pressures, ventricular dysfunction, unfavorable Fontan hemodynamics, or intolerance of test occlusion. Persistent patency may therefore be a marker of physiologic intolerance rather than the direct cause of adverse outcomes.

Other medium-term observational data have shown low procedural morbidity after device closure but no significant difference in overall morbidity or mortality among patients with device closure, spontaneous closure, or persistent patency [8]. Differences among studies likely reflect patient selection, institutional closure thresholds, timing of assessment, and the severity of underlying Fontan physiology.

The appropriate conclusion is not that every fenestration should be closed. Rather, persistent patency should prompt reassessment of the reason the patient remains dependent on the pop-off.

12. Practical Decision Framework

1. Confirm adequate systemic oxygen delivery.

Evaluate cardiac output, hemoglobin, perfusion, lactate, urine output, and regional oxygenation rather than targeting saturation alone.

2. Define the pressure relationship.

Compare Fontan pressure with atrial or ventricular filling pressure.

3. Exclude anatomic obstruction.

Evaluate the conduit, cavopulmonary connections, pulmonary arteries, pulmonary veins, and systemic outflow.

4. Optimize pulmonary vascular resistance.

Correct respiratory, metabolic, thermal, and mechanical factors that restrict pulmonary blood flow.

5. Balance preload and diuresis.

Avoid both underfilling and excessive venous congestion.

6. Assess fenestration function.

Determine whether it provides appropriate decompression, insufficient decompression, or excessive right-to-left shunting.

7. Prevent systemic embolization.

Apply strict air and line control and individualized thromboprophylaxis.

8. Perform test occlusion before closure.

Evaluate pressure, cardiac index, oxygen transport, and systemic perfusion—not saturation alone.

9. Retain the fenestration when physiologically necessary.

Patients with elevated filling pressure, significant pressure increase, or major cardiac-output reduction during occlusion may continue to require decompression.

References

[1] Bridges ND, Lock JE, Castaneda AR. Baffle fenestration with subsequent transcatheter closure: modification of the Fontan operation for patients at increased risk. Circulation. 1990;82(5):1681-1689. (PubMed Central (PMC))

[2] Mavroudis C, Zales VR, Backer CL, Muster AJ, Latson LA. Fenestrated Fontan with delayed catheter closure: effects of volume loading and baffle fenestration on cardiac index and oxygen delivery. Circulation. 1992;86(5 Suppl):II85-II92. (Johns Hopkins University)

[3] Hijazi ZM, Fahey JT, Kleinman CS, Kopf GS, Hellenbrand WE. Hemodynamic evaluation before and after closure of fenestrated Fontan: an acute study of changes in oxygen delivery. Circulation. 1992;86(1):196-202. (American Heart Association Journals)

[4] Kawasaki Y, Sasaki T, Forbes TJ, Ross RD, Kobayashi D. Optimal criteria for transcatheter closure of Fontan fenestration: a single-center experience with a review of literature. Heart Vessels. 2021;36(8):1246-1255. (WashU Research Profiles)

[5] Thatte N, Dimas V, Nugent A, Zellers T, Forbess J, Zabala LM, Zhang S, Reddy SRV. Use of institutional criteria for transcatheter device closure of Fontan fenestration: midterm outcomes. Ann Pediatr Cardiol. 2020;13(4):327-333. (PubMed)

[6] Greenleaf CE, Lim ZN, Li W, LaPar DJ, Salazar JD, Corno AF. Impact on clinical outcomes from transcatheter closure of the Fontan fenestration: a systematic review and meta-analysis. Front Pediatr. 2022;10:915045. (Frontiers)

[7] Kotani Y, Chetan D, Saedi A, Zhu J, Grosse-Wortmann L, Coles JG, Caldarone CA, Van Arsdell GS, Honjo O. Persistent fenestration may be a marker for physiologic intolerance after Fontan completion. J Thorac Cardiovasc Surg. 2014;148(6):2532-2538. (PubMed)

[8] Webb MK, Hunter LE, Kremer TR, Huddleston CB, Fiore AC, Danon S. Extracardiac Fontan fenestration device closure with Amplatzer Vascular Plug II and Septal Occluder: procedure results and medium-term follow-up. Pediatr Cardiol. 2020;41(4):703-708. (Frontiers)

[9] Gorla SR, Jhingoeri NK, Chakraborty A, Raja KR, Garg A, Sandhu S, Rosenkranz E, Swaminathan S. Incidence and factors influencing the spontaneous closure of Fontan fenestration. Congenit Heart Dis. 2018;13:776-781. (researchgate.net)