In a randomized trial conducted at 15 North American centers, the 1-year transplant-free survival rate was 74% with RV-PA shunts and 64% with the MBT shunt. RV-PA shunts were associated with significantly more unintended interventions and complications, however.
In their article, Dr. Richard G. Ohye, at the University of Michigan Medical School, Ann Arbor and the Pediatric Heart Network Investigators note that these major defects are repaired in stages. The first surgery – known as the Norwood procedure – is performed soon after birth. Surgeons connect the right ventricle to a reconstructed aorta using the proximal main pulmonary artery for systemic outflow. Pulmonary blood flow is reestablished with a shunt from the pulmonary artery to the systemic circulation.
In the classic Norwood procedure, the MBT shunt connects the subclavian or innominate artery to the pulmonary artery to supply pulmonary blood flow. But because coronary blood flow occurs primarily during diastole with this procedure, “coronary steal” may cause myocardial ischemia, circulatory instability, and death.
The RV-PA shunt reduces the potential for coronary steal and may therefore be safer – but it has its own set of disadvantages, including potential effects of ventriculotomy and additional volume load due to regurgitation from the nonvalved shunt.
The researchers randomized 274 infants to receive RV-PA shunts and 275 to receive MBT shunts. By 12 months, on intention to treat analysis, there were 68 deaths and 4 heart transplants (26.3%) in the RV-PA group and 91 deaths and 9 transplantations (36.4%) in the MBT group (relative risk 0.72, p = 0.01).
Rates of serious adverse events, including death, were also lower with the RV-PA shunt (57 vs 71 events per 100 infants, p = 0.04).
But babies in the RVPA group had a higher rate of unintended cardiovascular interventions (92 vs 70 per 100 infants, p = 0.003) – mainly due to a higher rate of balloon dilation or stent placement in the shunt or a branch of the pulmonary artery.
Complications (respiratory, neurologic, and infectious) were also more frequent in the RV-PA group (5.3 vs 4.7 per infant, p = 0.002).
Beyond 12 months, however, there was no significant difference between groups in transplantation-free survival (mean follow-up for survivors who did not undergo transplantation, 32 months).
By 14 months, there were no significant differences in ejection fraction, incidence of moderate-to-severe tricuspid-valve regurgitation, or median right ventricular end-diastolic and end-systolic volumes adjusted for body-surface area.
Dr. Ohye’s team plans to continue their follow-up of this cohort, “to determine whether either of these shunts turns out to be superior over the long term.”
In an editorial, Dr. Carolyn A. Bondy, from the National Institute of Child Health and Development, Bethesda, Maryland, writes, “The Pediatric Heart Network investigators have made a remarkable contribution with this well-designed and expeditiously implemented clinical trial.”
However, she adds, “Their work is just beginning” with the advent of new and potentially better treatments.
N Engl J Med 2010;362:1980-1992,2026-2028.