Tricuspid Atresia #2: Normally Related Great Arteries vs Transposed Great Arteries

1. Core Concept

Tricuspid atresia is defined by congenital absence of a direct atrioventricular connection between the right atrium and right ventricle. Systemic venous return must cross an interatrial communication into the left atrium, pass through the mitral valve into the dominant left ventricle, and then be distributed to the systemic and pulmonary circulations according to the ventriculoarterial connection and the size of the ventricular septal communication.

The relationship of the great arteries is a fundamental determinant of physiology in tricuspid atresia. It defines which circulation is supplied directly by the dominant left ventricle and which circulation depends on the ventricular septal defect or bulboventricular foramen and the rudimentary right ventricle [1].

A historical clinical comparison of tricuspid atresia with increased pulmonary blood flow showed that patients with transposed great arteries often presented with more severe heart failure and early mortality than those with normally related great arteries, emphasizing the physiologic importance of great artery relationship rather than the diagnosis of tricuspid atresia alone [2].

2. Normally Related Great Arteries: Type I Tricuspid Atresia

In tricuspid atresia with normally related great arteries, the dominant left ventricle ejects directly into the aorta. Therefore, systemic output is supplied directly by the left ventricle.

Pulmonary blood flow reaches the pulmonary artery through the ventricular septal defect, rudimentary right ventricle, and right ventricular outflow tract.

Physiologic pathway

Systemic circulation:

LV → Ao

Pulmonary circulation:

LV → VSD/BVF → RV → PA

In this anatomy, the VSD or bulboventricular foramen functions primarily as the gateway to pulmonary blood flow. Therefore, VSD/BVF size, rudimentary right ventricular cavity size, pulmonary valve morphology, right ventricular outflow tract obstruction, ductal contribution, and pulmonary artery development determine whether pulmonary blood flow is restricted, balanced, or excessive.

3. Clinical Physiology in Type I Anatomy

Because the left ventricle supplies the aorta directly, systemic output is usually preserved unless ventricular dysfunction, atrial-level restriction, systemic illness, or associated left-sided obstruction is present.

The major physiologic issue is pulmonary blood flow.

A small or restrictive VSD/BVF limits antegrade pulmonary blood flow and produces cyanosis. Severe restriction may lead to ductal dependency if pulmonary blood flow cannot be maintained through the ventricular septal communication and right ventricular outflow tract.

A large VSD/BVF with little pulmonary stenosis may produce excessive pulmonary blood flow, pulmonary overcirculation, congestive heart failure, and risk of pulmonary vascular disease. Older clinical series demonstrated that the clinical course of tricuspid atresia varies substantially according to pulmonary blood flow pattern and associated anatomy [3].

Modern surgical series reinforce the principle that the initial operation should be matched to morphology. In neonates with tricuspid atresia, morphology-directed palliation has been associated with improved outcomes, with systemic-to-pulmonary shunts commonly used when pulmonary blood flow is inadequate and pulmonary artery banding considered when pulmonary blood flow is excessive [4,5].

Some selected patients with normally related great arteries and severe pulmonary outflow obstruction have historically undergone palliative reconstruction of the right ventricular outflow tract, although contemporary management is usually individualized according to age, pulmonary artery anatomy, ventricular morphology, and the intended single-ventricle pathway [6].

The size of the BVF is clinically relevant even in normally related great arteries. In infants with tricuspid atresia or double-inlet left ventricle and normally related great arteries, an indexed BVF area of ≤1.8 cm²/m² on the initial postnatal echocardiogram was associated with need for early intervention, supporting careful quantitative assessment rather than qualitative description alone [7].

Normally related great arteries do not completely exclude systemic outflow concerns. A subgroup of patients may have associated left-sided obstruction, and these patients require separate evaluation of the aortic valve, subaortic region, and aortic arch in addition to pulmonary blood flow assessment [8].

4. Transposed Great Arteries: Type II Tricuspid Atresia

In tricuspid atresia with transposed great arteries, the dominant left ventricle ejects directly into the pulmonary artery. Therefore, pulmonary blood flow is supplied directly by the left ventricle.

Systemic output cannot exit directly from the dominant left ventricle into the aorta. Instead, systemic blood flow must pass through the VSD or bulboventricular foramen into the rudimentary right ventricle and then into the aorta.

Physiologic pathway

Pulmonary circulation:

LV → PA

Systemic circulation:

LV → VSD/BVF → RV → Ao

This arrangement reverses the physiologic importance of the VSD/BVF. In Type I anatomy, the VSD/BVF is mainly the pulmonary outflow pathway. In Type II anatomy, the VSD/BVF is the systemic outflow pathway.

5. Clinical Physiology in Type II Anatomy

Because the dominant left ventricle ejects directly into the pulmonary artery, pulmonary blood flow is often excessive unless pulmonary stenosis, pulmonary vascular resistance, or another limiting lesion is present.

The critical concern is systemic outflow.

A restrictive VSD/BVF can obstruct flow from the left ventricle to the rudimentary right ventricle and aorta. This produces subaortic obstruction, impaired systemic output, ventricular hypertrophy, systemic hypoperfusion, and increased operative risk.

This mechanism is particularly important during staged single-ventricle palliation. Pulmonary artery banding may be necessary to control pulmonary overcirculation, but it increases left ventricular pressure and may unmask or accelerate restriction of the BVF. Progressive systemic outflow obstruction after pulmonary artery banding is therefore a major management issue in tricuspid atresia with transposed great arteries.

Earlier echocardiographic studies of infants with double-inlet left ventricle or tricuspid atresia with transposed great arteries showed that BVF size influences the choice of initial palliation and the risk of developing systemic outflow obstruction [9].

More contemporary surgical data also support this concern. In patients with double-inlet left ventricle or tricuspid atresia with transposed great arteries, 10-year survival was reported at 93.3%, but systemic outflow relief operations were required in approximately two-thirds of patients. Arch obstruction and smaller systemic outflow tract area were important risk factors for systemic outflow intervention [10].

6. Why the VSD/BVF Matters Differently in Type I and Type II

The same anatomic structure has different physiologic meaning depending on the ventriculoarterial connection.

In Type I tricuspid atresia with normally related great arteries, the VSD/BVF determines pulmonary blood flow.

Restriction usually causes:

• Reduced pulmonary blood flow
• Cyanosis
• Possible ductal dependency
• Need for systemic-to-pulmonary shunt, ductal stenting, or another pulmonary blood flow source

In Type II tricuspid atresia with transposed great arteries, the VSD/BVF determines systemic blood flow.

Restriction may cause:

• Subaortic obstruction
• Impaired systemic output
• Ventricular hypertrophy
• Low cardiac output physiology
• Need for Damus–Kaye–Stansel connection, Norwood-type reconstruction, arch repair, or other systemic outflow augmentation

This distinction is essential. A restrictive VSD/BVF in Type I physiology primarily causes cyanosis. A restrictive VSD/BVF in Type II physiology may cause systemic outflow obstruction and circulatory failure.

7. Key Echocardiographic and Surgical Assessment

Evaluation should define both anatomy and physiology.

Important anatomic questions include:

• Are the great arteries normally related or transposed?
• What is the size and location of the VSD or BVF?
• Is there obstruction across the VSD/BVF?
• Does the VSD/BVF supply the pulmonary or systemic circulation?
• Is the pulmonary valve stenotic, atretic, or unobstructed?
• Is the aortic outflow tract unobstructed?
• Is there subaortic obstruction?
• Is the aortic arch normal, hypoplastic, interrupted, or coarcted?
• Are the branch pulmonary arteries adequately developed?
• Is the atrial communication nonrestrictive?
• Is the ductus arteriosus contributing to pulmonary or systemic blood flow?

Important physiologic questions include:

• Is pulmonary blood flow excessive, restricted, or balanced?
• Is systemic output preserved?
• Is oxygen saturation appropriate for the anatomy?
• Is there ventricular volume overload?
• Is there pressure overload of the dominant left ventricle?
• Is there evidence of systemic outflow obstruction?
• Is prostaglandin required to maintain pulmonary or systemic perfusion?
• Will pulmonary artery banding increase the risk of BVF-related systemic outflow obstruction?

These questions directly guide initial stabilization, timing of intervention, and selection of the initial palliative operation.

8. Surgical Implications

The surgical strategy in tricuspid atresia is not determined by the diagnosis alone. It is determined by the relationship of the great arteries, pulmonary blood flow, systemic outflow adequacy, pulmonary artery development, atrial-level decompression, and the risk of progressive outflow obstruction.

Type I: Normally Related Great Arteries

In Type I anatomy, management usually focuses on regulating pulmonary blood flow.

If pulmonary blood flow is restricted, treatment may include:

• Prostaglandin to maintain ductal pulmonary blood flow
• Modified Blalock–Taussig–Thomas shunt
• Ductal stenting in selected anatomy
• Early bidirectional cavopulmonary shunt in appropriate older infants
• Subsequent staged single-ventricle palliation

If pulmonary blood flow is excessive, treatment may include:

• Pulmonary artery banding
• Medical management of heart failure as a bridge to surgery
• Protection of the pulmonary vascular bed before cavopulmonary palliation

The surgical objective is to provide adequate but not excessive pulmonary blood flow while preserving ventricular function and pulmonary artery growth.

Type II: Transposed Great Arteries

In Type II anatomy, management must address both pulmonary overcirculation and systemic outflow.

Pulmonary artery banding alone may control pulmonary blood flow but can increase left ventricular pressure and worsen BVF-related systemic outflow obstruction. Therefore, the surgeon must determine whether systemic outflow is adequate before choosing pulmonary artery banding as an isolated initial palliation.

If systemic outflow is restrictive or high-risk, management may require:

• Damus–Kaye–Stansel connection
• Norwood-type reconstruction
• Aortic arch reconstruction when arch obstruction is present
• Combined systemic outflow relief and pulmonary blood flow control
• Staged cavopulmonary palliation after stabilization of systemic output

The central surgical question is whether the VSD/BVF is large enough to support systemic output safely over time.

9. Practical Summary

With normally related great arteries, the left ventricle supplies systemic output directly through the aorta, while pulmonary blood flow reaches the pulmonary artery through the VSD/BVF, rudimentary right ventricle, and right ventricular outflow tract.

With transposed great arteries, the left ventricle ejects directly into the pulmonary artery, and systemic output must pass through the VSD/BVF to the rudimentary right ventricle and aorta.

The key assessment is flow balance and outflow adequacy:

• Is pulmonary blood flow excessive or restricted?
• Is systemic output preserved?
• Is the VSD/BVF serving the pulmonary or systemic circulation?
• Is there current or potential VSD/BVF-related outflow obstruction?
• Will the planned palliation protect both pulmonary vascular development and systemic perfusion?

In tricuspid atresia, great artery relationship changes the meaning of the VSD/BVF. Recognizing this distinction is essential for safe neonatal stabilization, echocardiographic interpretation, and surgical planning.

References

[1] Rao PS. Tricuspid atresia. 2012. doi:10.1002/9781444398786.ch35.

[2] Marcano B, Riemenschneider TA, Ruttenberg HD, Goldberg SJ, Gyepes M. Tricuspid atresia with increased pulmonary blood flow: an analysis of 13 cases. Circulation. 1969;40(3). doi:10.1161/01.CIR.40.3.399.

[3] Dick M, Fyler DC, Nadas AS. Tricuspid atresia: clinical course in 101 patients. Am J Cardiol. 1975;36(3). doi:10.1016/0002-9149(75)90484-1.

[4] Karamlou T, Ashburn DA, Caldarone CA, Blackstone EH, Jonas RA, Jacobs ML, Williams WG, Ungerleider RM, McCrindle BW. Matching procedure to morphology improves outcomes in neonates with tricuspid atresia. J Thorac Cardiovasc Surg. 2005. doi:10.1016/j.jtcvs.2005.07.024.

[5] Tingelstad JB, Lower RR, Howell TR, Eldredge WJ. Pulmonary artery banding in tricuspid atresia without transposed great arteries. Am J Dis Child. 1971. doi:10.1001/archpedi.1971.02100160104017.

[6] Annecchino F, Fontan F, Chauve A, Quaegebeur J. Palliative reconstruction of the right ventricular outflow tract in tricuspid atresia: a report of 5 patients. Ann Thorac Surg. 1980. doi:10.1016/S0003-4975(10)61478-6.

[7] Skaff AM, Parra DA, Soslow JH, Shuplock JM. Association of bulboventricular foramen size and need for early intervention in infants with tricuspid atresia or double inlet left ventricle with normally related great arteries. J Am Soc Echocardiogr. 2022. doi:10.1016/j.echo.2022.11.009.

[8] Palacio AM, Williams WG, Barron DJ, Argo MB, Jegatheeswaran A, Jacobs ML, Bondarenko I, Welke K, Kirklin JK, Karamlou T, Alsoufi B, McCrindle BW. Management of tricuspid atresia with normally related great arteries and left-sided obstruction. World J Pediatr Congenit Heart Surg. 2024. doi:10.1177/21501351241286441.

[9] Matitiau A, Geva T, Colan SD, Sluysmans T, Parness IA, Spevak PJ, Velde ME, Mayer JE, Sanders SP. Bulboventricular foramen size in infants with double-inlet left ventricle or tricuspid atresia with transposed great arteries: influence on initial palliative operation and rate of growth. J Am Coll Cardiol. 1992. doi:10.1016/0735-1097(92)90065-U.

[10] Park WK, Baek JS, Kwon BS, Im YM, Lee JH, Choi EY, Park CS, Yun TJ. Revisitation of double-inlet left ventricle or tricuspid atresia with transposed great arteries. Ann Thorac Surg. 2019. doi:10.1016/j.athoracsur.2018.11.052.