Impact of Norwood Shunt Type on Cardiac Function and Clinical Outcomes in Survivors to Early Adolescence with Hypoplastic Left Heart Syndrome and Other Single Right Ventricular Anomalies: A Report from the Single Ventricle Reconstruction (SVR) III Study

Introduction: The SVR Trial demonstrated that the right ventricle-to-pulmonary artery shunt (RVPAS) vs. modified Blalock-Taussig-Thomas shunt (MBTTS) at Norwood operation was associated with better early survival for children with hypoplastic left heart syndrome (HLHS). However, it remains unclear if shunt type is associated with cardiac function, morbidities or survival in older children. Methods: SVR Trial survivors were followed annually. Cardiac MRI and cycle ergometry were performed at 10-12 years (y) of age for SVR III participants. Outcomes were compared by shunt type received (presented) and intention to treat, using linear, Poisson and Cox proportional hazards regression. Results: Among 549 children in the SVR Trial, 237 of 313 eligible transplant-free survivors returned for follow-up at median (IQR) 10.9 (10.4-11.5) y. Transplant-free survival at 12 y was 59% for the RVPAS vs 54% for the MBTTS, with no difference in survival conditional on Stage II survival. Ejection fraction (EF) was measured by MRI in 168 participants, with no difference between groups (RVPAS median 53 [IQR 46-58] and MBTTS 52 [IQR 48-56], p=.38). In multivariable modeling, the percent variance in EF explained by pre-Norwood and Norwood variables including shunt type was low (R 2 < .2). Cycle ergometry was performed in 181 participants with no difference by shunt type in peak VO 2 (ml/kg/minute) (RVPAS 30 [IQR 25-36] vs. MBTTS 29 [IQR 24-33], p=.26) or in peak work rate (RVPAS 67±24 watts vs MBTTS 66±20 watts, p=.61). By age 12 y, the RVPAS group had a higher rate of PLE (5% vs. 2%, p =.04) and catheter interventions (14 vs 10 per 100 pt-y; p=0.01). Otherwise the cumulative incidence of events and complications were similar for shunt groups with stroke in 7%, seizure 14%, plastic bronchitis 1%, atrial tachyarrhythmias 7% and ventricular tachyarrhythmias 3%. Conclusion: By 12 y after Norwood, shunt type has minimal effect on post-Stage II transplant-free survival, cardiac function or exercise performance. EF is preserved in most transplant-free survivors. However, low and declining transplant-free survival, poor exercise performance, and accruing morbidities highlight the critical need for innovative strategies to improve long-term outcomes in patients with HLHS.