Shunt resistance is associated with clinically important outcomes after the Norwood operation

BACKGROUND: In single-ventricle physiology, focus on pulmonary vascular resistance neglects the resistance in the conduit supplying the pulmonary inflow. METHODS: Conduit length and diameter, which can approximate conduit resistance, are available in the public dataset of Single Ventricle Reconstruction (SVR) trial. Conduit resistance was then calculated for SVR trial participants and the relationship with clinically important variables (death or transplant at 1 year, pulmonary artery size at second-stage palliation, pulmonary-to-systemic blood flow ratio, and supplemental oxygen requirement) was explored. To validate this calculated resistance, calculated resistance was compared with catheterization measurements at a single institution (not included in the SVR trial). RESULTS: In the institutional dataset, calculated and measured resistances had an intraclass correlation of 0.78 for modified Blalock–Taussig shunts (MBTS). Within the SVR trial, transplant-free survivors had a lower MBTS resistance (median, 8.3 Woods Units [WU]. interquartile range [IQR], 6.5-11.1 WU) than patients who died or required transplantation (median, 13.0 WU; IQR, 9.4-16.6 WU, P = .0001). When we controlled for left pulmonary artery diameter after the Norwood procedure in the SVR trial, for each unit increase in MBTS resistance, the left pulmonary artery diameter at stage II decreased (–0.006 ± 0.002 cm, P = .005). When we controlled for pulmonary vascular resistance, greater MBTS resistance was associated with a decrease in log pulmonary-to-systemic blood flow ratio (–0.04 ± 0.015, P = .0048) in the SVR trial. Patients in the SVR trial requiring supplemental oxygen on admission for stage II palliation had greater MBTS resistance (median. 11.1 WU; IQR, 6.6-16.6 WU) than patients not requiring oxygen (median 8.3, WU; IQR, 6.5-11.1 WU, P = .015). CONCLUSIONS: Conduit resistance is associated with important clinical outcomes after Norwood; however, further studies are required to guide conduit resistance optimization.