PA-IVS — #3 Determinants of Final Circulation (Single Ventricle vs Biventricular Repair)

In PA-IVS the neonatal priority is to secure pulmonary blood flow, usually by catheter or surgical opening of the RV outflow and/or ductal stenting/shunt. The lifelong question, however, is what circulation the child will ultimately have:

• Single-ventricle (SV) / Fontan-type pathway, or
• Biventricular (BiV) or 1.5-ventricle repair, with the RV supporting pulmonary blood flow.

Large series show that with contemporary treatment, most survivors can be directed to either a durable BiV repair or a Fontan-type circulation, but late outcomes remain strongly influenced by the initial right-heart anatomy and coronary pattern.[1,7]

Four anatomic domains largely drive the choice of final circulation:

1. Tricuspid valve (TV) size
2. Right ventricular (RV) size
3. RV morphology (mono-/bi-/tripartite)
4. Coronary anatomy, particularly RV-dependent coronary circulation (RVDCC)

These variables are inter-related—TV Z-score correlates with RV volume, and severe RV hypoplasia frequently coexists with ventriculo-coronary connections[2,3,4,5]—but they are useful conceptual anchors when planning strategy.

1. Tricuspid Valve Size

The TV annulus Z-score is a practical, easily reproducible surrogate for RV inflow size and growth potential. Multiple series have linked TV Z-score to both the ability to achieve BiV repair and the likelihood of needing a SV pathway.[2,3,4]

General patterns

• BiV-favorable
• TV Z-score > −2 → high probability of ultimately achieving BiV repair.[2]
• Decompression and recruitment of the RV are usually justified if coronary anatomy permits.
• Clearly SV-favorable
• TV Z-score < −3 → strongly associated with severe RV hypoplasia and low likelihood of successful BiV repair.[2]
• Most centers favor a SV / Fontan strategy in this group, particularly when other variables (small RV, abnormal morphology, RVDCC) align with a univentricular pathway.
• Borderline (−2 to −3)
• “Gray zone” often managed with staged RV recruitment (catheter valvotomy, RVOT patch/shunt) and deferred decision on BiV vs SV.[1–3,8]
• These patients are frequent candidates for 1.5-ventricle repair (Glenn + small but functioning RV).

Your practical threshold of TV Z > −3 for BiV vs < −3 for SV fits well with this literature, with the added nuance that Z > −2 is especially predictive of successful BiV repair and Z −2 to −3 should be interpreted in the broader anatomic context.[2]

2. Right Ventricular Size

RV size reflects the chamber’s potential to act as an effective subpulmonary pump once the outflow obstruction is relieved.

Several approaches are used:

• Simple qualitative grading (normal, moderately hypoplastic, severely hypoplastic).
• Quantitative indexes such as the index of RV development and RV–TV indexes.[3,4]
• Comparison with normal reference values (e.g., >60% vs <60% of normal RV volume or length for body size).[4]

Clinical interpretation

• BiV-favorable
• RV size ≈ normal or mildly reduced (often >60% of expected by echo or angio indices).[3,4]
• These ventricles generally remodel well after decompression and can support pulmonary circulation long-term.
• SV-favorable
• Severely hypoplastic RV (markedly reduced longitudinal dimension and cavity volume, often concordant with TV Z < −3).[2–4]
• Even aggressive recruitment rarely produces a functionally useful ventricle; morbidity of a “failed BiV attempt” is high, so most teams choose SV palliation.
• Intermediate RV size
• Moderate hypoplasia requires careful integration of TV size, RV morphology, TR severity, and coronary status.
• Data from the Congenital Catheterization Research Collaborative suggest that smaller RV area and ≤ mild TR at baseline are associated with failure to achieve durable BiV circulation after RV decompression, underlining how RV size and function must be considered together.[8]

3. RV Morphology – Mono-, Bi-, or Tripartite

Beyond absolute size, the internal architecture of the RV is a powerful predictor of eventual circulatory strategy.[3,4]

• A tripartite RV contains:
1. Inflow portion (adjacent to the TV)
2. Trabecular (apical) portion
3. Outflow (infundibular) portion
• A bipartite RV lacks one of these components (often the infundibulum or apical segment).
• A monopartite RV is essentially a small inlet pouch without a developed trabecular or outlet portion.

Yoshimura et al. showed that protocols explicitly incorporating RV morphology (via indices of RV development and RV-TV relationships) can guide selection among BiV, 1.5-ventricle, and SV strategies with good long-term survival.[3]

Implications

• Tripartite RV → BiV (or 1.5-ventricle) candidate
• “Near-normal” geometry, reasonable stroke volume potential after decompression.
• Often combined with TV Z-score > −2 to −3 and absence of RVDCC.[1–4]
• Bi- or monopartite RV → SV candidate
• Markedly abnormal architecture with limited cavity; frequently coexists with severe TV hypoplasia and ventriculo-coronary communications.[3,4,7]
• These features push decision-making toward SV/Fontan or, rarely, primary transplantation when coronary ischemia is prominent.

4. Coronary Anatomy and RV-Dependent Coronary Circulation (RVDCC)

Coronary abnormalities are common in PA-IVS. Necropsy and angiographic studies report ventriculo-coronary connections in >60% of cases, with a sizeable subset demonstrating critical stenoses or atresia of the proximal coronaries.[5]

4.1 Spectrum of Coronary Abnormalities

• RV–coronary fistulous connections with otherwise adequate proximal coronaries
• Segmental proximal stenoses
• Complete ostial atresia and total RVDCC[5,6]

These lesions may make coronary perfusion dependent on high RV systolic pressure.

4.2 Clinical Significance of RVDCC

• Patients with RVDCC have substantially worse outcomes than those without.[1,5–7]
• Classic data from Powell et al. showed that even with carefully planned staged SV palliation, deaths were typically due to coronary ischemia in early infancy.[6]
• Contemporary series confirm the adverse impact of RVDCC:
• Sukhavasi et al. reported mortality on the order of ~40% in patients with RVDCC vs <10% in those without, despite modern catheter and surgical strategies.[1]
• Population studies emphasize RVDCC as a major determinant of both early and late survival and of the feasibility of BiV repair.[5,7]

Strategic implications

• RVDCC present (+)
• RV decompression is hazardous: lowering RV pressure can abruptly reduce coronary perfusion and precipitate ischemia, infarction, or sudden death.[1,5,6]
• These patients are usually considered poor candidates for BiV repair.
• Preferred strategies include:
• SV / Fontan pathway with careful management of coronary perfusion, or
• RV exclusion or obliteration procedures in extreme cases, or
• Primary or early listing for transplantation when coronary anatomy is particularly unfavorable.[1,5–7]
• RVDCC absent (−)
• Coronary perfusion is independent of RV pressure, so RV decompression and recruitment are safer.
• Provided TV size and RV volume/morphology are acceptable, these patients are prime candidates for staged BiV or 1.5-ventricle repair.[1–4,8]

5. Integrating the Variables – Practical Framework

A pragmatic way to think about final circulation planning is to combine the four domains into a simple grid, as in your slide:

Typical pathways

1. Clear SV phenotype
• TV Z < −3, tiny bi/monopartite RV, and/or RVDCC.
• Managed along a Norwood / Glenn / Fontan trajectory, with coronary ischemia risk dictating early decisions and surveillance.[1,3,5–7]
2. Clear BiV phenotype
• TV Z > −2 to −3, reasonably sized tripartite RV, no RVDCC, acceptable TR.
• Undergo catheter or surgical RV decompression, with or without ductal stent/shunt; subsequent procedures aim for complete BiV repair.[1–4,8]
3. Borderline / 1.5-ventricle phenotype
• Intermediate TV Z (−2 to −3), moderately hypoplastic but tripartite RV, no RVDCC.
• Many centers pursue staged RV recruitment, accepting that the final outcome may be:
• BiV repair
• 1.5-ventricle repair (bidirectional Glenn + small but functional RV), or
• Conversion to SV if RV growth and performance remain inadequate.[1–4,7,8]

Across series, no single cutoff or algorithm perfectly classifies every patient. Even large contemporary cohorts emphasize that individualized, morphology-driven decision-making remains essential, ideally within a multidisciplinary team that can reassess anatomy and physiology at each stage.[1–3,7,8]

References

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

[2] Awori MN, Mitema FO, Kebba N. Optimal Z-score use in surgical decision-making in pulmonary atresia with intact ventricular septum. World J Pediatr Congenit Heart Surg. 2017;8(3):385-388.

[3] Yoshimura N, Yamaguchi M, Ohashi H, et al. Pulmonary atresia with intact ventricular septum: strategy based on right ventricular morphology. J Thorac Cardiovasc Surg. 2003;126(5):1417-1426.

[4] Giglia TM, Jenkins KJ, Matitiau A, et al. Influence of right heart size on outcome in pulmonary atresia with intact ventricular septum. Circulation. 1993;88(5 Pt 2):2248-2256.

[5] Calder AL, Peebles CR, Occleshaw CJ. The prevalence of coronary arterial abnormalities in pulmonary atresia with intact ventricular septum and their influence on surgical results. Cardiol Young. 2007;17(4):387-396.

[6] Powell AJ, Mayer JE, Lang P, Lock JE. Outcome in infants with pulmonary atresia, intact ventricular septum, and right ventricle-dependent coronary circulation. Am J Cardiol. 2000;86(11):1272-1274.

[7] Schneider AW, Blom NA, Bruggemans EF, Hazekamp MG. More than 25 years of experience in managing pulmonary atresia with intact ventricular septum. Ann Thorac Surg. 2014;98(5):1680-1686.

[8] Petit CJ, Glatz AC, Qureshi AM, et al. Outcomes after decompression of the right ventricle in infants with pulmonary atresia with intact ventricular septum are associated with degree of tricuspid regurgitation: results from the Congenital Catheterization Research Collaborative. Circ Cardiovasc Interv. 2017;10(5):e004428.