Tricuspid Atresia: Surgical Palliation and Staged Fontan Circulation

1. Overview and Goals of Staged Palliation

Tricuspid atresia (TA) is characterized by absence of a patent right atrioventricular connection, a hypoplastic right ventricle, and obligatory interatrial communication. The dominant morphologic left ventricle (LV) sustains systemic output and, before cavopulmonary palliation, also supports pulmonary blood flow. The degree of pulmonary outflow obstruction and the ventriculoarterial connections determine whether the initial threat is severe cyanosis, pulmonary overcirculation, or compromised systemic outflow. Accordingly, the first operation is selected by physiology and systemic outflow anatomy, not by the diagnosis of TA alone. Observational cohorts demonstrate that both morphology and the selected initial pathway influence outcomes [1,2].

Staged management aims to protect the pulmonary vascular bed, maintain adequate systemic perfusion, avoid progressive ventricular dysfunction, and ultimately establish a total cavopulmonary connection. The typical sequence is initial stabilization or first-stage palliation, bidirectional Glenn (superior cavopulmonary connection), and Fontan completion. Neither Glenn nor Fontan is an anatomical repair of the absent tricuspid valve; both are physiologic reconstructions that progressively remove pulmonary flow from the ventricular workload.

2. First-Stage Assessment: Pulmonary and Systemic Flow

In the initial parallel circulation, the dominant LV must deliver both systemic and pulmonary outputs. In simplified terms, ventricular output is approximately Qs + Qp, although effective forward output is modified by shunts, valve regurgitation, and collateral flow. After the postnatal fall in pulmonary vascular resistance (PVR), excessive pulmonary flow increases pulmonary venous return, LV end-diastolic volume, and myocardial work. Conversely, inadequate pulmonary flow causes cyanosis and may become critical as the arterial duct closes.

Assessment should establish great artery relationship, pulmonary valve and subvalvar anatomy, ventricular septal defect (VSD)/bulboventricular foramen (BVF) morphology, aortic annulus and arch dimensions, branch pulmonary arteries, pulmonary veins, systemic venous anatomy, and atrial communication. Oxygen saturation alone does not measure effective systemic delivery: a patient with relatively high saturation may have excessive Qp, low systemic blood flow, and metabolic acidosis.

2.1 Decreased Pulmonary Blood Flow

Type Ia TA, with normally related great arteries and pulmonary atresia, and Type IIa TA, with transposed great arteries and pulmonary atresia, may require an alternative source of pulmonary blood flow. Intravenous prostaglandin E1 (PGE1) preserves ductal patency during stabilization. Depending on ductal morphology and institutional expertise, a ductal stent or systemic-to-pulmonary arterial shunt may provide longer-term pulmonary perfusion. The anatomy of pulmonary atresia, branch pulmonary arteries, ductal insertion, and the systemic outflow tract must be reviewed before selecting either intervention.

A modified Blalock–Taussig–Thomas shunt supplies pulmonary flow from a systemic artery through a prosthetic graft. Adequate flow must be balanced against shunt thrombosis, excessive diastolic runoff, pulmonary overcirculation, ventricular volume loading, and pulmonary artery distortion. Ductal stenting avoids thoracotomy in some infants but introduces risks of restenosis, thrombosis, branch pulmonary artery jailing, and reintervention. No single strategy is universally preferable across the heterogeneous TA population [1,2].

2.2 Excessive Pulmonary Blood Flow

In TA without substantial pulmonary outflow restriction, declining PVR may produce tachypnea, feeding difficulty, poor growth, ventricular dilation, and heart failure. Pulmonary artery banding (PAB) can limit Qp and pulmonary arterial pressure while improving effective systemic perfusion. The intended result is balanced circulation rather than a fixed oxygen saturation or band diameter.

PAB requires assessment of the systemic outflow pathway before placement. Its reduction of pulmonary blood flow is potentially beneficial, but increased ventricular pressure loading and progressive muscular hypertrophy may expose or worsen an initially borderline BVF. Band gradients alone cannot confirm an acceptable balance of pulmonary and systemic outputs [3,4].

3. Type II Tricuspid Atresia: The Systemic Outflow Problem

In Type II TA with ventriculoarterial discordance, the pulmonary trunk usually arises from the dominant LV, whereas the aorta arises from the rudimentary right ventricular outlet chamber. Systemic blood therefore travels through LV → VSD/BVF → rudimentary RV → aorta. A restrictive BVF becomes a functional subaortic obstruction, although the narrowed segment may be remote from the conventional anatomical LV outflow tract. Aortic annular hypoplasia, a small ascending aorta, or coarctation can compound this obstruction.

The BVF is not simply a hole in the septum; it may be the obligatory systemic outlet. Its area, muscular borders, alignment, and anticipated growth deserve serial assessment. A modest Doppler gradient in a patient with low cardiac output does not exclude severe obstruction. Pressure loading, ventricular hypertrophy, declining compliance, reduced cardiac output, and worsening atrioventricular valve regurgitation may develop as restriction progresses. Retrospective studies support the association between PAB and later systemic outflow obstruction in anatomically susceptible patients, but the observed risk is also influenced by baseline morphology and selection bias [3,4].

3.1 Strategies for an Unobstructed Systemic Outlet

For substantial systemic outflow obstruction or high-risk BVF anatomy, surgical options include a Damus–Kaye–Stansel (DKS) connection, a Norwood-type reconstruction, or a palliative arterial switch operation (ASO) with appropriate pulmonary flow control. Selective arch repair with PAB and later reassessment is another pathway when systemic outflow is considered adequate.

A DKS connects the proximal pulmonary root, arising from the dominant LV, to the systemic aortic pathway, thereby bypassing the restrictive BVF. The distal pulmonary circulation then requires a controlled separate blood supply before Glenn or Fontan completion. A Norwood-type procedure similarly establishes an unobstructed neoaortic pathway while addressing associated arch hypoplasia and providing pulmonary perfusion through an appropriate shunt or conduit. Both approaches demand attention to semilunar valve competence, coronary perfusion, branch pulmonary artery geometry, and reconstructed arch patency [5,6].

Palliative ASO reassigns the great arterial pathways to place the dominant LV in direct communication with the aorta, with coronary transfer and reconstruction dictated by the great artery relationships. It may offer a favorable systemic outlet in selected anatomy but is a major neonatal reconstruction, particularly when combined with arch repair and PAB. Published experience is based on selected retrospective series rather than randomized comparisons [7,8].

The decision is not simply PAB versus no PAB: it is whether the chosen circulation will preserve durable, unobstructed systemic perfusion throughout ventricular unloading and somatic growth.

4. Second Stage: Bidirectional Glenn

The bidirectional Glenn generally follows the first stage after PVR has decreased sufficiently and the infant is clinically suitable. The superior vena cava (SVC) is disconnected from the right atrium and anastomosed to the pulmonary artery, commonly through an end-to-side SVC–right pulmonary artery connection. SVC flow then distributes to both lungs without traversing the ventricle. The IVC continues to enter the atrium, and its desaturated blood mixes with pulmonary venous return.

This operation reduces systemic ventricular volume loading by removing SVC return from the ventricular output. It may lessen chamber dilation and atrioventricular valve regurgitation, but its reduction in pulmonary venous return also decreases ventricular preload. Glenn physiology should therefore not be described as universally improving cardiac output. The actual benefit depends on preoperative overcirculation, ventricular compliance, afterload, and pulmonary vascular resistance. Contemporary surgical series document variability in interstage progression and risk according to ventricular and associated lesion characteristics [9].

4.1 Glenn Hemodynamics

Without a subpulmonary pump, pulmonary flow is sustained by the difference between cavopulmonary venous pressure and downstream pulmonary venous/atrial pressure. A useful simplified relation is:

Qp ≈ (mean SVC/PA pressure − mean pulmonary venous atrial pressure) / total pulmonary circuit resistance.

This resistance includes anastomotic and branch PA obstruction, the pulmonary vascular bed, and downstream pulmonary venous obstruction. A high SVC pressure is not necessarily adequate driving pressure if the downstream pressure is also elevated. Low PVR, unobstructed pulmonary arteries and veins, acceptable LV diastolic pressure, and controlled atrioventricular valve regurgitation are essential.

Because IVC blood bypasses the lungs, systemic cyanosis persists. Residual native antegrade pulmonary flow or collateral sources may increase oxygen saturation but also maintain ventricular volume loading or elevate Glenn pressure. Preservation or elimination of antegrade pulmonary blood flow should be individualized; increased saturation is not, by itself, evidence of improved overall circulation.

4.2 Technical Priorities and Completion Assessment

Before constructing the Glenn, the operative team must define bilateral SVCs, bridging innominate vein anatomy, prior shunt and ductal stent relationships, and the size and continuity of the pulmonary arteries. The cavopulmonary anastomosis should have a generous lumen without SVC torsion, branch PA compromise, or tension. A prior systemic-to-pulmonary shunt is usually taken down; residual antegrade pulmonary blood flow is managed according to its hemodynamic consequences.

After bypass separation, evaluation includes SVC/Glenn pressure, atrial pressure, arterial oxygen saturation, ventricular filling and function, pulmonary artery flow distribution, and echocardiographic evidence of anastomotic or branch PA narrowing. Excessive Glenn pressure requires evaluation for mechanical obstruction, elevated PVR, high pulmonary venous pressure, ventricular dysfunction, and adverse ventilatory conditions before attributing the finding to a globally unfavorable pulmonary vascular bed.

5. Third Stage: Total Cavopulmonary Connection (Fontan)

Fontan completion connects the remaining IVC/hepatic venous return to the pulmonary arteries, while the Glenn continues to carry SVC blood. Contemporary techniques include the extracardiac conduit and intracardiac lateral tunnel. In the extracardiac operation, a prosthetic conduit is anastomosed between the divided IVC and the pulmonary arterial confluence. The conduit must avoid kinking, tension, compression, and obstruction to either pulmonary artery; its relationship to the atrium, pulmonary veins, and adjacent structures must be considered.

The completed circulation substantially reduces systemic venous admixture and restores near-equality of pulmonary and systemic flow when there are no significant fenestration or collateral shunts. The dominant LV supports primarily systemic output, rather than the combined Qs + Qp burden of the initial circulation. Fontan completion improves oxygenation but does not restore a subpulmonary ventricle.

5.1 Fontan Pressure–Flow Relationship

A simplified relationship is:

Qp ≈ (Fontan venous pressure − pulmonary venous atrial pressure) / total Fontan–pulmonary circuit resistance.

The Fontan pressure is upstream of the lungs; left atrial pressure is the downstream pressure. Their difference represents the transpulmonary driving pressure, not ventricular preload itself. With no subpulmonary pump, sustained pulmonary blood flow requires modest pulmonary circuit resistance and sufficiently low atrial filling pressure. The resultant physiology combines systemic venous hypertension with relative ventricular preload deprivation, often called the Fontan paradox [10].

Excessive Fontan pressure can arise from elevated PVR, PA or conduit obstruction, pulmonary venous obstruction, high atrial pressure due to ventricular diastolic dysfunction, or significant AV valve regurgitation. Conversely, low atrial pressure in the setting of high Fontan pressure suggests a substantial upstream pressure drop. Both pressures, and ideally direct flow and imaging, are needed to interpret the cause of low output.

5.2 Fenestration and Perioperative Management

A deliberate Fontan fenestration may provide a pressure-relief pathway from the systemic venous circuit to the atrium. It can augment ventricular preload and cardiac output at the cost of desaturation and a potential paradoxical embolic route. The decision is influenced by measured hemodynamics, ventricular compliance, pulmonary vascular bed, and institutional strategy rather than one universal pressure threshold.

Early management prioritizes low PVR, unobstructed cavopulmonary pathways, preserved venous return, rhythm control, and protection of ventricular filling. Hypoxia, hypercarbia, acidosis, atelectasis, excessive mean airway pressure, and significant pleural effusions may impair pulmonary flow. Spontaneous breathing and carefully adjusted positive-pressure support may help venous return, but extubation timing must also account for pulmonary mechanics, agitation, and overall clinical stability. Persistent low output or severe venous hypertension should prompt early investigation of treatable residual lesions [10].

6. Fontan Candidacy, Complications, and Follow-Up

Pre-Fontan workup characterizes PA anatomy, pulmonary vascular resistance, pulmonary venous drainage, ventricular systolic and diastolic function, AV valve regurgitation, residual arch or systemic outflow obstruction, venovenous and aortopulmonary collaterals, and prior Glenn patency. Echocardiography is foundational; cardiac MRI, CT, and catheterization provide complementary anatomical and invasive hemodynamic information when clinically indicated. Patient selection must be individualized because no isolated numerical threshold captures all relevant pressure–flow relationships.

Early complications may include low cardiac output, prolonged pleural effusions or chylothorax, thrombosis, arrhythmia, pulmonary artery obstruction, and Fontan pathway obstruction. Long-term manifestations encompass exercise intolerance, atrial and ventricular arrhythmias, thromboembolism, protein-losing enteropathy, plastic bronchitis, Fontan-associated liver disease, and progressive ventricular or circulatory failure. The liver is particularly vulnerable to chronic hepatic venous congestion coupled with limited effective forward flow; systematic longitudinal assessment is recommended [10,11].

Contemporary series show improved outcomes compared with historical Fontan eras, although findings are influenced by anatomy, era, selection, surgical configuration, and duration of follow-up [12,13]. TA often provides a morphologic LV as the systemic pump, but this favorable feature does not eliminate the limitations imposed by the passive pulmonary circulation. Ongoing surveillance must consider both cardiovascular and extracardiac manifestations.

7. Key Surgical and Hemodynamic Principles

• First-stage palliation is physiology-specific: augment pulmonary flow when inadequate and restrict it when excessive, while protecting systemic output.
• Type II TA requires systemic outflow surveillance: a restrictive BVF is a functional subaortic lesion, and isolated PAB can be inadequate in susceptible anatomy.
• Glenn is ventricular unloading, not a complete separation: SVC return bypasses the ventricle, whereas IVC admixture and residual cyanosis persist.
• The Fontan circuit is pressure-driven and preload-limited: low PVR, low atrial pressure, and unobstructed pathways are essential.
• Oxygen saturation is not a surrogate for cardiac output: interpretation must incorporate flow, filling pressures, venous congestion, and perfusion.
• Residual obstruction should be actively sought: systemic outflow, branch PAs, Glenn/Fontan connections, and pulmonary veins all matter.

References

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