To model the growth of pulmonary artery (PA) branches in children with a functionally univentricular heart between the Glenn procedure and total cavopulmonary connection (TCPC) and to assess whether anterograde pulmonary blood flow (APBF) promotes growth and influences morbidity and mortality.

Patients with a functionally univentricular heart who underwent cardiac catheterization prior to Glenn and TCPC between 2004 and 2024 were included. Growth was assessed by comparing pre-Glenn and pre-TCPC cross-sectional areas. PA growth was modeled using linear regression.

A total of 180 children with a median follow-up of 8.8 years were included: 64 (35.6%) had maintained APBF. PA growth was linear over time (fractional polynomials; P=.20), with an estimated β=11.6mm/y; 95%CI, 5.8-17.4 mm2/y. Maintaining APBF was independently associated with increased PA growth (β=50.9mm; 95%CI, 25.3-76.5 mm2; P <.01), independent of TCPC timing. The multivariable model explained 21% of the variance in PA branch growth. Nine-year survival did not differ significantly between the APBF and non-APBF groups: 86.7% (95%CI, 71.9-93.9) vs 73.4% (95%CI, 61.3-82.3), respectively (P=.21). Morbidity outcomes, including length of hospital stay, hemodynamic contraindications to fenestration closure, and Fontan failure rates, were similar between groups.

PA growth between the Glenn procedure and TCPC is substantial and can be considered linear, suggesting that delaying TCPC optimizes growth potential. Maintaining APBF accelerates PA growth without increasing morbidity or mortality. Due to considerable interindividual variability, these findings are most meaningful at a group level and should be interpreted with caution when applied to individual patients.