PA-IVS — #1 Pulmonary Blood Flow Patterns

PA-IVS is a rare cyanotic lesion with marked morphologic heterogeneity of the right ventricle (RV), tricuspid valve, and coronary circulation.[1,2] Decisions about initial palliation and long-term strategy hinge on how pulmonary blood flow (PBF) is provided and on the potential for RV growth toward biventricular, 1.5-ventricle, or single-ventricle circulation.[3,4,8]

From a hemodynamic standpoint, three practical PBF patterns are useful to recognize:

1. Ductal-dependent flow only
2. Antegrade RV–pulmonary artery (RV–PA) flow
3. Dual-supply flow in which both the ductus and native RV–PA pathway contribute

Understanding which pattern predominates helps tailor both early stabilization and long-term planning.

1. Ductal-Dependent Pulmonary Blood Flow

In many neonates with PA-IVS, all PBF is supplied by the ductus arteriosus.

• Systemic output from the left ventricle enters the aorta and then runs retrograde through the PDA into the main and branch pulmonary arteries.
• Because the pulmonary valve is atretic, there is no antegrade RV–PA flow, and the RV may be severely hypoplastic or decompressed only via tricuspid regurgitation into the right atrium.[1,2]

In this configuration, pulmonary perfusion is exquisitely dependent on ductal patency:

• Prostaglandin E₁ (PGE₁) is initiated immediately after birth to prevent ductal constriction.
• For more durable palliation, many centers now favor PDA stenting over a surgical systemic-to-pulmonary shunt when anatomy is suitable.[5,6]

Compared with classic Blalock–Taussig–type shunts, PDA stenting in ductal-dependent circulations has been associated with similar survival but shorter ventilation and ICU stay, fewer early complications, and comparable pulmonary artery growth.[5] In PA-IVS specifically, multicenter data suggest that PDA stents permit earlier extubation, lower vasoactive requirements, and shorter mechanical ventilation than surgical shunts, albeit at the cost of more frequent unplanned reinterventions for hypoxemia.[6]

Because systemic and pulmonary circuits are tightly coupled through the ductus, any change in pulmonary vascular resistance (PVR) or ductal caliber can quickly shift the balance between systemic and pulmonary flows, causing either hypoxemia or systemic hypoperfusion. Meticulous control of oxygenation, ventilation, and ductal patency is therefore essential in the early neonatal period.[2]

2. Antegrade RV–PA Flow and “RV Rehabilitation”

When the RV cavity is at least moderately developed and the infundibulum is not severely hypoplastic, antegrade RV–PA flow may be present or can be created. This is usually achieved by catheter-based perforation and balloon dilation or by surgical valvotomy of the atretic pulmonary valve, often combined with a systemic-to-pulmonary shunt or PDA stent.[2–4]

Once antegrade flow is established:

• PBF becomes increasingly dependent on RV pressure and function, rather than solely on the ductus.
• The RV begins to eject against the pulmonary vascular bed, which can promote:
• Growth and remodeling of the RV cavity and outflow tract, especially in patients with “bipartite” or “tripartite” RV morphology and only mild–moderate tricuspid hypoplasia (“RV rehabilitation”).[1,4]
• Progressive improvement in coupling between RV contractility and PVR, potentially allowing later biventricular or 1.5-ventricle repair.[3,4,8]

Staged decompression strategies—such as initial valvotomy plus shunt followed by later RV “re-recruitment”—have shown that proportionate RV volume growth is mainly achieved in patients ultimately reaching biventricular repair, whereas those destined for single-ventricle pathways exhibit limited RV growth despite similar early interventions.[4]

In this physiology, management aims to encourage forward RV output while avoiding excessive RV pressure that could:

• Worsen tricuspid regurgitation and RV dilation
• Compromise coronary perfusion, particularly in patients with RV-dependent coronary circulation, in whom sudden RV decompression may precipitate ischemia or death[2,3,7]

Careful titration of pulmonary blood flow (via shunt size, PDA stent, or supplemental oxygen) and stepwise RV decompression are therefore crucial.

3. Dual-Supply Pulmonary Blood Flow (PDA + Antegrade RV–PA Flow)

A subset of infants exhibit both a patent ductus arteriosus and antegrade RV–PA flow:

• PBF then has two sources:
1. Retrograde flow from the aorta via the PDA, and
2. Antegrade flow from the RV through the newly established RV–PA connection.

This “dual-supply” state often occurs after pulmonary valvotomy or perforation while PGE or a PDA stent is still in place. It can be beneficial by guaranteeing robust PBF during the vulnerable early phase, but it also complicates hemodynamic management:

• Excessive combined flow may lead to pulmonary overcirculation, diastolic runoff from the systemic circulation, and congestive heart failure.
• If ductal flow dominates, the RV may remain relatively unloaded, diminishing the stimulus for RV growth and limiting the effects of RV rehabilitation.

Therefore, clinicians frequently need to fine-tune ductal support—for example, by gradually weaning PGE, allowing spontaneous ductal constriction, or electively closing the PDA (surgical ligation or stent removal) once reliable antegrade RV–PA flow is confirmed and oxygen saturations are acceptable.

4. Clinical Assessment and Strategic Decision-Making

Because PA-IVS spans a wide morphologic and physiologic spectrum, optimal management increasingly relies on individualized algorithms that integrate PBF pattern with RV and tricuspid valve size, coronary anatomy, and institutional expertise.[2,3,7,8]

4.1 Imaging and Hemodynamic Assessment

1. Echocardiography
• Defines ductal size, length, and tortuosity, as well as direction and adequacy of ductal flow.
• Assesses tricuspid valve annulus z-score, RV volumes, and segmental morphology (tripartite vs bipartite vs unipartite RV), which correlate with the feasibility of biventricular or 1.5-ventricle repair.[1,3,8]
• Identifies the presence and adequacy of antegrade RV–PA flow and quantifies tricuspid regurgitation.
2. Cardiac catheterization and advanced imaging (CT/MRI)
• Provide detailed delineation of pulmonary artery anatomy and PVR.
• Define coronary artery anatomy, including RV-dependent coronary circulation or major coronary stenoses, which strongly influence both interventional risk and long-term survival.[2,3,7]

4.2 Linking PBF Pattern to Initial Strategy

Based on these data, contemporary series describe four broad “end-states”: biventricular repair, 1.5-ventricle repair, Fontan (single-ventricle) palliation, or cardiac transplantation.[3,4,8]

• Predominantly ductal-dependent PBF, very small tricuspid annulus, and severely hypoplastic RV
• Usually favor a single-ventricle or transplant pathway, often with PDA stent or surgical shunt as initial palliation.[2,3,8]
• PDA stenting appears particularly advantageous in patients with moderate-to-severe RV hypoplasia, being associated with lower odds of major adverse cardiovascular events (MACE) compared with surgical shunts in one multicenter PA-IVS cohort.[6]
• Moderate RV and tricuspid hypoplasia with feasible RV decompression
• Strategy often aims at staged RV rehabilitation: PDA stent or shunt plus pulmonary valvotomy / perforation, followed by reassessment of RV growth and function.[3,4,7,8]
• Long-term data suggest that patients on a biventricular pathway have better survival than those committed to a single-ventricle strategy, particularly in the absence of RV-dependent coronaries.[3]
• Reasonably sized tricuspid valve (mild hypoplasia) and tripartite RV
• Many centers pursue early or primary biventricular repair, with RV decompression and either temporary PBF augmentation (shunt/PDA stent) or direct repair depending on institutional experience.[3,4]

Recent single-center experience in the era of PDA stenting reports overall survival exceeding 90% with a mix of 2-ventricle, 1.5-ventricle, and Fontan outcomes when strategies are individualized using tricuspid annulus z-score, RV morphology, and coronary status as key decision inputs.[8] Large multicenter registries further emphasize that low birth weight and significant coronary stenoses are major predictors of early MACE after the initial intervention.[7]

5. Summary

Conceptualizing PA-IVS in terms of how PBF is provided—ductal-dependent only, RV-dependent, or dual-supply—offers a practical framework for bedside assessment and for teaching. However, definitive management must also account for the underlying structure and growth potential of the RV and tricuspid valve, as well as coronary anatomy and patient size.

Combining detailed imaging with evolving interventional options such as PDA stenting and staged RV decompression has transformed PA-IVS from a uniformly lethal lesion into one in which biventricular or 1.5-ventricle circulations are achievable for many patients, while single-ventricle palliation and transplantation remain essential options for those with the most severely hypoplastic RV or high-risk coronary patterns.[3,4,6–8]

References

[1] Daubeney PEF, Delany DJ, Anderson RH, Sandor GGS, Slavik Z, Keeton BR, et al. Pulmonary atresia with intact ventricular septum: range of morphology in a population-based study. J Am Coll Cardiol. 2002;39(10):1670-1679. (PubMed)

[2] Chikkabyrappa SM, Loomba RS, Tretter JT. Pulmonary atresia with an intact ventricular septum: preoperative physiology, imaging, and management. Semin Cardiothorac Vasc Anesth. 2018;22(3):245-255. (PubMed)

[3] Sukhavasi A, McHugh-Grant S, Glatz AC, Mondal A, Griffis H, Burnham N, et al. Pulmonary atresia with intact ventricular septum: intended strategies. J Thorac Cardiovasc Surg. 2022;164(5):1277-1288. (PubMed)

[4] Kotani Y, Kasahara S, Fujii Y, Eitoku T, Baba K, Otsuki S-I, et al. A staged decompression of right ventricle allows growth of right ventricle and subsequent biventricular repair in patients with pulmonary atresia and intact ventricular septum. Eur J Cardiothorac Surg. 2016;50(2):298-303. (PubMed)

[5] Tseng SY, Truong VT, Peck D, Kandi S, Brayer S, Jason DP 3rd, et al. Patent ductus arteriosus stent versus surgical aortopulmonary shunt for initial palliation of cyanotic congenital heart disease with ductal-dependent pulmonary blood flow: a systematic review and meta-analysis. J Am Heart Assoc. 2022;11(13):e024721. (PubMed)

[6] Puente BN, Mastropietro CW, Flores S, Cheung EW, Amula V, Radman M, et al. Comparison of ductal stent versus surgical shunt as initial intervention for neonates with pulmonary atresia with intact ventricular septum. Pediatr Cardiol. 2024; doi:10.1007/s00246-024-03529-2. Epub 2024 Jun 6. (PubMed)

[7] Cheung EW, Mastropietro CW, Flores S, Amula V, Radman M, Kwiatkowski D, et al. Procedural outcomes of pulmonary atresia with intact ventricular septum in neonates: a multicenter study. Ann Thorac Surg. 2023;115(6):1470-1477. (PubMed)

[8] Shibbani K, Nigro J, Rao R, Gordon BM, Justino H, AlShawabkeh L, et al. Pulmonary atresia with intact ventricular septum, an evolving strategy in the era of PDA stenting: single center experience. Pediatr Cardiol. 2025; doi:10.1007/s00246-025-03769-w. Epub 2025 Jan 22. (PubMed)