What branch pulmonary artery z‑score is considered operable in a patient with tetralogy of Fallot?

Branch Pulmonary Artery Z-Score Operability in Tetralogy of Fallot

Branch pulmonary arteries with z-scores down to approximately -2.5 to -3.0 are generally considered operable for primary complete repair in TOF patients, though palliation may be preferred for more severe hypoplasia (z-scores below -3.0 to -3.5) to allow for growth before definitive repair.

Evidence-Based Thresholds

The 2023 AATS Expert Consensus Document provides the most comprehensive guidance on this question 1. The literature demonstrates considerable variability in reported z-scores across different studies, but several key patterns emerge:

Preoperative Z-Score Data from Multiple Studies:

• Choi and colleagues: Mean z-score of -2.5 (range -0.9 to more severe)
• Zhao and colleagues: Mean z-score of -3.6 (range -2.6 to -5.3)
• Kasturi and colleagues: Mean z-score of -2.9
• Borodinova and colleagues: Mean z-score of -3.9 preoperatively, improving to -3.0 post-repair

Critical Decision Points:

For primary complete repair, the consensus suggests:

• Branch pulmonary arteries with z-scores greater than -2.5 to -3.0 can typically undergo primary complete repair
• Post-repair z-scores should ideally achieve greater than -1.0 for durable results 1
• A post-repair z-score of less than -1.3 predicts that 25% of patients will have unacceptable gradients (>30 mmHg) 1

For staged palliation, consider when:

• Branch pulmonary arteries have z-scores below -3.0 to -3.5
• Severe asymmetric hypoplasia exists
• Mean z-scores in palliated cohorts ranged from -6.6 to -3.2, with successful growth allowing subsequent repair 1

Clinical Algorithm for Decision-Making

Step 1: Assess Branch PA Z-Scores

• Z-score > -2.5: Proceed with primary complete repair
• Z-score -2.5 to -3.5: Consider primary repair at experienced centers; evaluate for additional risk factors
• Z-score < -3.5: Strong consideration for palliation first (shunt, ductal stent, or RVOT stent)

Step 2: Consider Additional Factors

• Symmetry: Asymmetric hypoplasia may favor palliation even with borderline z-scores
• Patient size: Neonates <2.5 kg may benefit from palliation regardless of PA size 1
• Institutional experience: Centers with expertise in valve-sparing techniques may achieve better outcomes with smaller annuli

Step 3: Palliation Strategy if Chosen

• PDA stenting or RVOT stenting can facilitate significant PA growth 1
• Studies show mean z-scores of -6.6 improving to allow successful complete repair after palliation
• Palliation allows more patients to undergo valve-sparing procedures (7.6% vs 0% in one study) 1

Important Caveats and Pitfalls

Measurement Variability

Critical limitation: Different institutions use different z-score models, causing significant variability in reported values 1. This makes absolute cutoffs less reliable than institutional experience with specific measurement techniques.

Distinguishing True vs. Apparent Hypoplasia

Branch pulmonary arteries may appear hypoplastic because they are underfilled rather than truly hypoplastic 1. This distinction is crucial but difficult to make preoperatively.

Research Evidence on Detection

One study found that branch PA z-score < -2.5 was 88% sensitive and 100% specific for the presence of aortopulmonary collaterals in TOF with pulmonary atresia 2, suggesting this threshold represents significant anatomic compromise.

Post-Repair Targets

The guidelines emphasize that achieving a post-repair z-score > -1.0 is critical for durability 1. If this cannot be achieved, consider transannular patch rather than forcing valve-sparing repair, as residual obstruction leads to reintervention.

Practical Considerations

Avoid the pitfall of using z-scores in isolation. The decision must integrate:

• Bilateral vs. unilateral hypoplasia
• Presence of pulmonary coarctation
• Overall patient risk profile
• Institutional surgical expertise

The evidence shows no correlation between median z-score and reoperation rates across studies examining valve-sparing approaches 1, suggesting that surgical technique and patient selection matter as much as absolute measurements.

The 2023 AATS guidelines acknowledge significant limitations in the existing literature, including lack of uniform data points, inconsistent measurement techniques, and limited long-term follow-up 1. Therefore, these thresholds should guide rather than dictate decision-making, with final choices made by experienced multidisciplinary teams.