Comparison of shunt types in the Norwood procedure for single-ventricle lesions

Abstract

Background: The Norwood procedure with a modified Blalock-Taussig (MBT) shunt, the first palliative stage for single-ventricle lesions with systemic outflow obstruction, is associated with high mortality. The right ventricle-pulmonary artery (RVPA) shunt may improve coronary flow but requires a ventriculotomy. We compared the two shunts in infants with hypoplastic heart syndrome or related anomalies.

Methods: Infants undergoing the Norwood procedure were randomly assigned to the MBT shunt (275 infants) or the RVPA shunt (274 infants) at 15 North American centers. The primary outcome was death or cardiac transplantation 12 months after randomization. Secondary outcomes included unintended cardiovascular interventions and right ventricular size and function at 14 months and transplantation-free survival until the last subject reached 14 months of age.

Results: Transplantation-free survival 12 months after randomization was higher with the RVPA shunt than with the MBT shunt (74% vs. 64%, P=0.01). However, the RVPA shunt group had more unintended interventions (P=0.003) and complications (P=0.002). Right ventricular size and function at the age of 14 months and the rate of nonfatal serious adverse events at the age of 12 months were similar in the two groups. Data collected over a mean (+/-SD) follow-up period of 32+/-11 months showed a nonsignificant difference in transplantation-free survival between the two groups (P=0.06). On nonproportional-hazards analysis, the size of the treatment effect differed before and after 12 months (P=0.02).

Conclusions: In children undergoing the Norwood procedure, transplantation-free survival at 12 months was better with the RVPA shunt than with the MBT shunt. After 12 months, available data showed no significant difference in transplantation-free survival between the two groups. (ClinicalTrials.gov number, NCT00115934.)

Figure 1. Hypoplastic Left Heart Syndrome

The hypoplastic left heart syndrome and related disorders involving the single right ventricle are characterized by a total admixture lesion. As in the normal heart, deoxygenated blood returns to the right atrium. Oxygenated blood returning from the left atrium crosses an atrial septal defect to join the deoxygenated blood in the right atrium. This mixed blood is then ejected by the right ventricle into the pulmonary artery. A portion of the blood in the pulmonary artery proceeds as normal to the lungs, as well as to the aorta through a patent ductus arteriosus, to supply the systemic circulation.

Figure 2. The Norwood Procedure with a Modified Blalock – Taussig Shunt and a Right Ventricle – Pulmonary Artery Shunt

In the completed Norwood procedure, one can see the reconstructed aorta (neoaorta) and the isolated pulmonary artery. Pulmonary blood flow is supplied by either a modified Blalock–Taussig shunt (top) or a right ventricle–pulmonary artery shunt (bottom).

Figure 3. Enrollment, Randomization, and Follow-up of Infants with Hypoplastic Left Heart Syndrome

Five infants — two assigned to the right ventricle–pulmonary artery (RVPA) shunt group and three to the modified Blalock–Taussig (MBT) shunt group — did not undergo surgery and were therefore excluded from the 1-year analysis; the decision not to perform surgery was determined to be independent of the shunt assignment. Patients in the intraoperative primary category initially received a shunt that was not the one to which they were randomly assigned owing to some anatomical contraindication; those in the intraoperative secondary category initially received the assigned shunt but were switched to the other shunt because the first shunt was unsuccessful. HLHS denotes hypoplastic left heart syndrome, and LV left ventricular.

Figure 4. Primary Outcome and the Hazard of Death or Transplantation at 12 Months, According to Shunt Assignment

Panel A shows the Kaplan–Meier curves for transplantation-free survival among all infants who underwent the Norwood procedure, according to the intention-to-treat analysis. Panel B shows the estimated hazard of death or transplantation among all infants who underwent the Norwood procedure, according to the assigned shunt. The hazard is an instantaneous rate representing the predicted number of deaths or transplantations per month at a defined time point. P = 0.02 for the difference in the treatment effect for the period before and the period after 12 months. MBT denotes modified Blalock–Taussig, and RVPA right ventricle–pulmonary artery.

Figure 5. Difference in Rate of Death or Transplantation at 12 Months in Prespecified Subgroups, According to Shunt Assignment

P values are from a logistic-regression test of the interaction between shunt assignment and treatment subgroup. The strata for surgeon’s experience and site volume were defined according to the annual number of randomly assigned infants. Bars represent 95% confidence intervals. DHCA denotes deep hypothermic circulatory arrest during the Norwood procedure, MBT modified Blalock–Taussig, PV pulmonary venous, RCP regional cerebral perfusion, and RVPA right ventricle–pulmonary artery.