Tricuspid Atresia — Type I (Normally Related Great Arteries)

Definition and Anatomic Substrate

Tricuspid atresia (TA) is defined by the absence of a right-atrium–to–right-ventricle (RA–RV) connection; systemic venous blood must traverse an interatrial communication into the left atrium (LA). The right ventricle (RV) is hypoplastic and the left ventricle (LV) functions as the single effective systemic pump. Among anatomic subtypes, Type I TA—with normally related great arteries (aorta from LV, pulmonary artery from RV)—is the most frequent category in classic series (≈54%) and is typically associated with decreased pulmonary vascularity [1]. In Type I, pulmonary outflow is accessed from the LV via a ventricular septal defect (VSD), i.e., the bulboventricular foramen (BVF), into the RV outflow and the pulmonary valve.

Type I subtypes (by pulmonary outflow)

• Ia – Pulmonary atresia: Ductal-dependent pulmonary blood flow (PBF).
• Ib – Pulmonary stenosis: PBF varies with stenosis severity.
• Ic – No pulmonary stenosis: Large BVF with unobstructed outflow → risk of excessive PBF.

Core Pathophysiology

• Obligate interatrial shunt. A nonrestrictive ASD/PFO is essential for systemic venous return; restriction precipitates venous hypertension, low output, and acidosis. Staged palliation is required to balance flows and ultimately separate the venous return from the systemic ventricle [2].
• Single-ventricle mixing. All venous return mixes in the LA/LV; arterial oxygen content depends on the Qp:Qs balance.
• Determinants of PBF. PBF is governed by BVF size and pulmonary outflow resistance (valvar/subvalvar stenosis and distal PA resistance). A small or progressively restrictive BVF is a key driver of cyanosis and ductal dependency, whereas an unobstructed BVF with a competent pulmonary valve leads to pulmonary overcirculation and LV volume overload. Indexed BVF area ≤1.8 cm²/m² on initial postnatal echocardiography predicts the need for early augmentation of pulmonary flow prior to Glenn [3].

Clinical Presentation

• Ia/Ib: Early cyanosis that worsens as the ductus constricts; tachypnea is modest unless heart failure ensues.
• Ic: Signs of pulmonary overcirculation (tachypnea, diaphoresis during feeds, hepatomegaly, poor weight gain).

ECG commonly shows left-axis deviation with LV dominance; chest radiography varies from oligemic to plethoric lung fields according to PBF.

Diagnostic Priorities (Echocardiography First)

1. Confirm the absent RA–RV connection and ensure a nonrestrictive ASD.
2. Define BVF size and surveil for evolving subaortic obstruction.
3. Characterize pulmonary valve/outflow (atresia vs stenosis vs unobstructed).
4. Assess branch PA size, AV-valve competence, and ventricular function.

Cardiac CT/MRI and catheterization are adjuncts for distal PA anatomy or hemodynamic questions.

Initial Management

• Low PBF (Ia/critical Ib): Prostaglandin E₁ to maintain ductal patency, then establish reliable PBF with a ductal stent or modified Blalock–Taussig–Thomas shunt (mBTTS) according to anatomy and institutional strategy. Strategy should be individualized to morphology; cohort data suggest that smaller shunts and innominate-artery origin improve transition to cavopulmonary connection [4]. Moreover, when an initial systemic-to-pulmonary shunt is used, avoiding concomitant main pulmonary artery (MPA) intervention and ensuring ductal closure are associated with better pre-Fontan survival [5].
• High PBF (Ic): Pulmonary artery banding to curb LV dilation and mitigate pulmonary vascular injury—often as part of a tailored pathway to cavopulmonary connection [4,5].
• Restrictive interatrial communication: Balloon atrial septostomy or surgical septectomy.
• Supportive care: balance oxygen delivery (avoid hyperventilation in ductal-dependent lesions), use diuretics judiciously for overcirculation, and provide meticulous nutrition.

Staged Single-Ventricle Pathway

• Neonatal/early-infancy stabilization: Shunt or PA band as dictated by PBF; address arch lesions or collaterals as needed.
• Bidirectional Glenn/hemifontan (~3–6 months): Offloads the LV and conditions the pulmonary circuit.
• Fontan completion (toddler/early childhood): Total cavopulmonary connection if PVR is low, LV function is robust, and AV-valve regurgitation is minimal. In contemporary series, multistage palliation yields ≈84% survival at 8 years, with most attrition occurring in the interstage periods [6].

Special Considerations and Longitudinal Surveillance

• BVF evolution and LV outflow: BVF narrowing over time can create subaortic obstruction; track gradients serially and escalate if systemic output is threatened. In the uncommon subset of Type I TA with left-sided obstruction/LVOTO, neonatal Norwood or later Damus-Kaye-Stansel (DKS) can be incorporated into the pathway with acceptable outcomes to Fontan [7].
• Pulmonary arteries: Prolonged low PBF risks PA hypoplasia; early, balanced physiology supports later Fontan candidacy.
• AV-valve regurgitation & LV function: These are major determinants of Fontan success; address surgically/medically when feasible.
• Operative nuance that matters: In Type I TA, decision-making that matches procedure to morphology—including smaller shunt caliber and innominate-origin mBTTS—is associated with improved survival to cavopulmonary connection [4]; and in shunt-based strategies, avoiding MPA manipulation and closing the ductus improves survival before Fontan [5].

Practical Take-Home Points

• Survival hinges on three controls: a free atrial septum, appropriately regulated PBF, and timely progression from Glenn to Fontan [2,6].
• Too little PBF → cyanosis and ductal dependency; too much PBF → LV volume overload and heart failure.
• The BVF is the throttle for early physiology; iBVFA ≤1.8 cm²/m² flags the need to plan early augmentation of pulmonary flow [3].
• In shunted pathways, close the ductus and avoid MPA intervention to safeguard interstage survival [5].

References

[1] Dick M, Fyler DC, Nadas AS. Tricuspid atresia: clinical course in 101 patients. Am J Cardiol. 1975;36(3):327-337.

[2] Rao PS. Tricuspid Atresia. Curr Treat Options Cardiovasc Med. 2000;2(6):507-520.

[3] 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. 2023;36(3):327-332.

[4] Karamlou T, Ashburn DA, Caldarone CA, et al.; Members of the Congenital Heart Surgeons’ Society. Matching procedure to morphology improves outcomes in neonates with tricuspid atresia. J Thorac Cardiovasc Surg. 2005;130(6):1503-1510.

[5] Wilder TJ, Ziemer G, Hickey EJ, et al. Surgical management of competing pulmonary blood flow affects survival before Fontan/Kreutzer completion in patients with tricuspid atresia type I. J Thorac Cardiovasc Surg. 2015;150(5):1222-1230.e7.

[6] Alsoufi B, Schlosser B, Mori M, et al. Influence of morphology and initial surgical strategy on survival of infants with tricuspid atresia. Ann Thorac Surg. 2015;100(4):1403-1409; discussion 1409-1410.

[7] Palacio AM, Williams WG, Barron DJ, et al.; Congenital Heart Surgeons’ Society. Management of tricuspid atresia with normally related great arteries and left-sided obstruction. World J Pediatr Congenit Heart Surg. 2025;16(2):254-261.