Tricuspid Atresia #7: Second- and Third-Stage Palliation with the Glenn and Fontan Procedures

1. Overview

After neonatal stabilization and any required first-stage intervention, patients with tricuspid atresia generally proceed through staged single-ventricle palliation:

1. Bidirectional Glenn procedure
2. Fontan completion

The Glenn directs superior vena caval blood to the pulmonary arteries and reduces systemic ventricular volume load. The Fontan then directs the remaining systemic venous return to the pulmonary circulation, producing near-complete separation of pulmonary and systemic blood flow.

This pathway transforms the circulation from one in which the single ventricle supports both systemic and pulmonary output into one in which pulmonary blood flow is driven passively by systemic venous pressure.

The completed Fontan circulation is intrinsically characterized by:

• Elevated systemic venous pressure.
• Reduced ventricular preload.
• Relatively low cardiac output.
• Dependence on low pulmonary vascular resistance.
• Dependence on low ventricular filling pressure.
• Absence of a subpulmonary ventricle.

Systemic venous hypertension and reduced cardiac output are not merely late complications; they are fundamental features of Fontan physiology [1,2].

2. Hemodynamic Transition During Staged Palliation

Before cavopulmonary palliation, systemic and pulmonary blood flow operate largely in parallel, and the single ventricle generates the combined output:

Ventricular output ≈ Qs + Qp

Excessive pulmonary blood flow causes ventricular volume overload, atrioventricular valve dilation, and heart failure. Restricted pulmonary blood flow produces cyanosis and may require ductal patency, a systemic-to-pulmonary shunt, or another source of pulmonary blood flow.

After the Glenn:

• Superior vena caval blood bypasses the heart.
• Inferior vena caval blood continues to enter the atrium and ventricle.
• Ventricular volume load is reduced but not eliminated.
• Systemic arterial desaturation persists.

After the Fontan:

• Both superior and inferior vena caval blood are directed to the lungs.
• The ventricle primarily supports systemic output.
• Pulmonary and systemic blood flow become approximately equal.
• Ventricular preload depends on passive transpulmonary flow.

3. The Bidirectional Glenn Procedure

3.1 Surgical construction

The superior vena cava is divided near its junction with the right atrium. Its cephalad end is anastomosed end-to-side to the right pulmonary artery, permitting flow to both branch pulmonary arteries. The cardiac end is closed.

The operation:

• Removes superior vena caval return from the ventricle.
• Routes upper-body venous blood directly to the pulmonary arteries.
• Preserves inferior vena caval return to the heart.
• Partially unloads the systemic ventricle.

Any important branch pulmonary artery stenosis should be repaired because passive cavopulmonary flow is highly sensitive to pathway obstruction.

3.2 Glenn physiology

After the Glenn:

Qp ≈ SVC flow + additional antegrade pulmonary flow + collateral flow

Inferior vena caval blood continues to mix with pulmonary venous blood, so systemic arterial saturation remains below normal. Saturation depends on:

• Pulmonary vascular resistance.
• Branch pulmonary artery anatomy.
• Pulmonary venous pressure.
• Hemoglobin concentration.
• Venovenous and aortopulmonary collaterals.
• Antegrade pulmonary blood flow.
• Pulmonary arteriovenous malformations.

As the child grows, lower-body venous return becomes a larger proportion of total venous return, and cyanosis may gradually increase before Fontan completion.

3.3 Ventricular unloading

The Glenn reduces ventricular end-diastolic volume, wall stress, and atrioventricular valve annular dilation by removing superior vena caval return from the ventricular workload.

However, pulmonary venous return and ventricular preload also decrease. A ventricle with impaired compliance or elevated filling pressure may therefore remain unable to generate adequate cardiac output despite successful volume unloading.

3.4 Driving pressure

Pulmonary blood flow is driven by:

SVC pressure − pulmonary venous atrial pressure

Glenn flow is favored by:

• Low pulmonary vascular resistance.
• Low ventricular end-diastolic pressure.
• Low pulmonary venous pressure.
• Unobstructed pulmonary arteries and veins.
• An unobstructed cavopulmonary anastomosis.
• Spontaneous ventilation.

It is impaired by:

• Pulmonary artery or pulmonary venous obstruction.
• Ventricular dysfunction.
• Significant atrioventricular valve regurgitation.
• Elevated pulmonary vascular resistance.
• Excessive positive-pressure ventilation.
• Hypoxia, hypercarbia, or acidosis.

4. Assessment Before the Glenn Procedure

The Glenn is usually performed after neonatal pulmonary vascular resistance has fallen sufficiently to permit passive pulmonary blood flow.

Preoperative assessment should evaluate:

• Branch pulmonary artery size and symmetry.
• Pulmonary venous anatomy.
• Pulmonary artery pressure and vascular resistance.
• Ventricular systolic and diastolic function.
• Ventricular end-diastolic pressure.
• Atrioventricular valve regurgitation.
• Systemic outflow tract and aortic arch patency.
• Previous shunt, ductal stent, or pulmonary artery band anatomy.
• Systemic venous anatomy.
• Aortopulmonary and venovenous collaterals.
• Adequacy of the atrial communication.

No single hemodynamic threshold defines suitability in every patient. The circulation must permit superior vena caval blood to traverse the pulmonary vascular bed without excessive venous pressure or inadequate ventricular filling.

5. Antegrade Pulmonary Blood Flow at Glenn

At the Glenn procedure, a previous systemic-to-pulmonary shunt is usually divided. Native antegrade pulmonary flow may be eliminated, restricted, or preserved.

Potential benefits include:

• Higher systemic oxygen saturation.
• Pulmonary artery growth.
• Pulmonary arterial pulsatility.

Potential disadvantages include:

• Persistent ventricular volume overload.
• Higher Glenn pressure.
• Increased atrioventricular valve regurgitation.
• Prolonged pleural drainage.
• Pulmonary overcirculation.

In a cohort of 202 patients, maintained antegrade pulmonary blood flow improved oxygen saturation but was associated with worse transplant-free survival, with a hazard ratio of 2.37 [3].

Therefore, improved saturation alone does not establish that unrestricted antegrade flow is beneficial. The decision should reflect Glenn pressure, ventricular loading, atrioventricular valve function, and timing of Fontan completion.

6. Complications After the Glenn Procedure

Potential complications include:

• Superior vena caval hypertension.
• Cavopulmonary anastomotic stenosis.
• Branch pulmonary artery distortion.
• Thrombosis.
• Chylothorax or prolonged pleural effusions.
• Phrenic nerve injury.
• Venovenous collateral formation.
• Progressive cyanosis.
• Pulmonary arteriovenous malformations.
• Low cardiac output from inadequate preload.
• Cerebral venous congestion.

Pulmonary arteriovenous malformations may develop when hepatic venous effluent is excluded from or unevenly distributed to part of the pulmonary circulation.

7. The Fontan Procedure

7.1 Surgical construction

The Fontan completes systemic venous rerouting by directing inferior vena caval blood to the pulmonary arteries.

In an extracardiac Fontan, a prosthetic conduit connects the inferior vena cava to the pulmonary artery confluence. The existing Glenn continues to deliver superior vena caval blood.

In a complete nonfenestrated circulation without major collateral flow:

Qp ≈ Qs

7.2 Fontan hemodynamics

Pulmonary blood flow is driven by:

Fontan pathway pressure − pulmonary venous atrial pressure

This gradient must overcome resistance across the Fontan conduit, cavopulmonary connections, pulmonary arteries, pulmonary vascular bed, and pulmonary veins.

The Fontan circulation therefore produces:

1. Systemic venous hypertension
2. Relative ventricular underfilling

This combination is often termed the Fontan paradox. Because there is no subpulmonary pump, even small increases in pulmonary vascular resistance or ventricular filling pressure may markedly reduce pulmonary blood flow, preload, and cardiac output [1,2].

7.3 Benefits and limitations

Fontan completion:

• Improves arterial oxygen saturation.
• Reduces systemic venous admixture.
• Eliminates chronic ventricular volume overload.
• Dedicates the dominant left ventricle to systemic output.

However, it does not restore normal biventricular physiology. Major limitations include:

• Chronically elevated venous pressure.
• Reduced preload reserve.
• Limited exercise cardiac output.
• Sensitivity to positive-pressure ventilation.
• Dependence on low pulmonary vascular resistance.
• Dependence on sinus rhythm and atrioventricular synchrony.

8. Requirements for Fontan Completion

Successful Fontan physiology requires:

• Low pulmonary vascular resistance.
• Acceptable pulmonary artery pressure.
• Adequate and unobstructed branch pulmonary arteries.
• Unobstructed pulmonary veins.
• Unobstructed Glenn and Fontan pathways.
• Preserved ventricular systolic function.
• Favorable ventricular compliance.
• Low ventricular end-diastolic pressure.
• Controlled atrioventricular valve regurgitation.
• Unobstructed systemic outflow and aortic arch.
• Stable rhythm.
• Manageable collateral burden.

Abnormalities that increase pulmonary resistance, ventricular filling pressure, or pathway resistance should be corrected before or during Fontan completion whenever feasible.

9. Predictors of Adverse Outcome

Risk assessment should begin before the Glenn procedure.

In 175 patients undergoing single-ventricle palliation, pre-Glenn moderate-to-severe atrioventricular valve regurgitation independently predicted death or transplantation, with a hazard ratio of 2.41. Moderate ventricular dysfunction was an even stronger predictor, with a hazard ratio of 5.29 [4].

Other adverse factors included:

• Right ventricular-dominant morphology.
• Elevated pre-Glenn ventricular end-diastolic pressure.
• Persistent ventricular dysfunction.
• Significant atrioventricular valve regurgitation.

Higher pre-Glenn ventricular end-diastolic pressure was associated with later death, transplantation, transplant listing, or heart failure symptoms [5].

Classic tricuspid atresia usually has a dominant morphologic left ventricle, so the adverse effect of systemic right ventricular morphology is less directly applicable. However, ventricular dysfunction, elevated filling pressure, and atrioventricular valve regurgitation remain critical determinants of outcome.

10. Fontan Fenestration

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

It provides a pressure-relief route when Fontan pressure is excessive.

Potential benefits include:

• Reduced systemic venous pressure.
• Improved ventricular preload.
• Increased cardiac output.
• Reduced postoperative pleural drainage in selected patients.

Disadvantages include:

• Persistent desaturation.
• Right-to-left shunting.
• Risk of systemic thromboembolism.
• Possible need for later transcatheter closure.

Fenestration is most useful when pulmonary vascular resistance, ventricular compliance, or atrioventricular valve function is marginal.

11. Tricuspid Atresia–Specific Considerations

11.1 Systemic outflow obstruction

In tricuspid atresia with transposed great arteries, systemic output may pass from the dominant left ventricle through the ventricular septal defect or bulboventricular foramen into the rudimentary right ventricle and aorta.

Restriction can produce subaortic stenosis. The systemic outflow tract should therefore be reassessed before each palliative stage. A Damus–Kaye–Stansel connection or another outflow procedure may be required.

11.2 Pulmonary artery anatomy

Previous shunts, ductal stents, pulmonary artery bands, and ductal tissue may distort the branch pulmonary arteries. Because Glenn and Fontan flow is passive, even moderate stenosis may become hemodynamically important.

11.3 Atrioventricular valve function

Regurgitation of the patent left-sided atrioventricular valve increases:

• Atrial and pulmonary venous pressure.
• Glenn or Fontan pressure.
• Ventricular volume load.
• Risk of circulatory failure.

Moderate or greater regurgitation should be assessed carefully before each palliative stage.

11.4 Atrial communication

A nonrestrictive atrial communication is essential before Fontan completion because systemic venous return must reach the dominant left ventricle. Restriction should be excluded before Glenn palliation.

12. Perioperative Management

After the Glenn procedure

Management should:

• Maintain adequate preload without excessive venous congestion.
• Minimize pulmonary vascular resistance.
• Avoid hypoxia, acidosis, and marked hypercarbia.
• Avoid excessive airway pressure.
• Promote spontaneous ventilation when feasible.
• Preserve cerebral perfusion and atrioventricular synchrony.

Unexpected desaturation should prompt evaluation for pathway obstruction, pulmonary artery stenosis, elevated pulmonary vascular resistance, venovenous collaterals, pulmonary arteriovenous malformations, or low cardiac output.

After the Fontan procedure

Management should:

• Optimize preload.
• Maintain low pulmonary vascular resistance.
• Promote early extubation when appropriate.
• Preserve sinus rhythm.
• Avoid excessive positive-pressure ventilation.
• Monitor Fontan pressure, atrial pressure, lactate, urine output, and systemic perfusion.

Persistent high Fontan pressure requires evaluation for pathway obstruction, pulmonary artery or venous stenosis, ventricular dysfunction, atrioventricular valve regurgitation, elevated pulmonary vascular resistance, collateral flow, or arrhythmia.

13. Long-Term Fontan Consequences

The Fontan circulation is durable palliation but not a physiologic cure. Chronic venous hypertension and reduced cardiac output may cause:

• Ventricular systolic or diastolic dysfunction.
• Atrioventricular valve regurgitation.
• Arrhythmias.
• Fontan pathway thrombosis or obstruction.
• Protein-losing enteropathy.
• Plastic bronchitis.
• Fontan-associated liver disease.
• Lymphatic failure.
• Renal dysfunction.
• Collateral vessel formation.
• Reduced exercise capacity.
• Thromboembolic events.
• Progressive Fontan failure.
• Need for transplantation.

Long-term surveillance should assess cardiac function, rhythm, Fontan pathway patency, exercise capacity, liver and renal disease, lymphatic complications, and thrombotic risk.

14. Key Concepts

• The Glenn routes superior vena caval blood directly to the pulmonary arteries and partially unloads the ventricle.
• The Fontan completes systemic venous rerouting and improves oxygenation.
• Pulmonary blood flow after both procedures is passive.
• Successful Fontan physiology requires low pulmonary vascular resistance, low ventricular filling pressure, and unobstructed pathways.
• Systemic venous hypertension and reduced cardiac output are intrinsic to the Fontan circulation.
• Additional antegrade pulmonary flow may improve saturation but worsen long-term outcome.
• Ventricular dysfunction, atrioventricular valve regurgitation, and elevated ventricular end-diastolic pressure before Glenn predict adverse outcomes.
• Long-term management requires lifelong multisystem surveillance.

References

[1] Van de Bruaene A, Claessen G, Salaets T, Gewillig M. Late Fontan circulatory failure: What drives systemic venous congestion and low cardiac output in adult Fontan patients? Front Cardiovasc Med. 2022;9:825472.

[2] Perrin N, Doré A, Van de Bruaene A, Mongeon FP, Mondésert B, Poirier N, Miró J, Khairy P, Ibrahim R, Chaix MA. The Fontan circulation: From ideal to failing hemodynamics and drug therapies for optimization. Can J Cardiol. 2022.

[3] Baek J, Park C, Choi E, Yun T, Kwon B, Yu J, Kim YH. The impact of additional antegrade pulmonary blood flow at bidirectional Glenn shunt on long-term outcomes. J Thorac Cardiovasc Surg. 2021.

[4] Weisert M, Menteer J, Durazo-Arvizu R, Wood J, Su J. Early prediction of failure to progress in single ventricle palliation: A step toward personalizing care for severe congenital heart disease. J Heart Lung Transplant. 2022.

[5] Schwartz MC, Karunanandaa A, Anderson W, Herlong J, Paolillo J, Wallis G, Kirshbom P, Maxey T. Identification of patient variables that are associated with ventricular end-diastolic pressure before the bidirectional Glenn operation. Cardiol Young. 2021.