Babies with single ventricle heart disease often develop aortopulmonary collaterals (APCs) that help combat chronic cyanosis by increasing pulmonary blood flow and, subsequently, systemic saturation.
However, after staged single ventricle palliation, the higher ventricular volume load generated with APCs potentially leads to heart failure. Studies evaluating the burden of these APCs in assisting or thwarting outcomes are small and difficult to compare, leaving a gray zone for clinicians.
At Monroe Carell Jr. Children’s Hospital at Vanderbilt, chief of pediatric cardiac surgery David Bichell, M.D., and congenital cardiac interventionalist George Nicholson, M.D., conducted a single-center retrospective study assessing the degree of APC burden in children undergoing their second-stage surgical palliation (the bidirectional Glenn procedure) and following up at third-stage palliation (the Fontan procedure).
Their aim was to clarify the short- and long-term impact of APC burden, hoping to add to the existing literature and potentially replace the gray zone with evidence-based risk data to guide treatment standardization.
“The main question we wanted to try to answer is whether a higher burden of APC flow is bad for the baby, because the data are pretty mixed,” Nicholson said. “Then we wanted to see if there were individual contributing factors that led to a high burden.”
“APCs are a well-described yet controversial sequelae of single ventricle palliation,” Bichell said. “Some surgeons advocate for aggressive management, while others argue that their impact is minimal. In this cohort, we found that increasing severity of collateral burden, starting with grade 2 of 4 severity grades, is associated with poorer long- term transplant-free survival.”
Heterogeneity Leaves Questions
The researchers noted that prior studies have described associations of APCs with longer duration of ventilation, greater chest tube use and drainage volume, and longer ICU and overall hospital stays.
Some patients appear to tolerate the larger collateral volume, while others do not.
“I think there is probably a sweet spot in terms of developing APC flow. As long as it’s mild, it is relatively benign. But like anything, too much can be harmful.”
“I think there is probably a sweet spot in terms of developing APC flow. As long as it’s mild, it is relatively benign,” Nicholson said. “But like anything, too much seems to be harmful.”
A Longer-Term Focus
The Monroe Carell team identified 60 children who had angiographic evidence of APCs and underwent a bidirectional Glenn procedure between January 2016 and March 2021. The researchers graded APC severity (1-4) and assessed preoperative and postoperative clinical outcomes, along with transplant-free survival.
Right ventricular morphology was more common in patients with severe pre-Glenn APCs, as expected. Seven patients had transplants and nine died over the study period.
“We hypothesized that greater severity of APC burden would be directly associated with poorer in-hospital and long-term outcomes, particularly transplant-free survival,” Nicholson said.
Nicholson explained that previously published studies on APCs have focused on short-term outcomes.
“Oftentimes, with this kind of disease process, you may not see anything short-term because the burden of the disease process – in this case the APCs – takes time to develop clinical significance,” he said.
Early Advantages Dissipate
The researchers did not find a significant association involving the sites of chest tube insertion in prior surgeries.
“There are so many other variables that go into an individual’s outcomes. But usually, if you have a harder first surgery, your recovery may be a little rockier, and then through a variety of factors that may then promote more APC flow,” Nicholson said.
Patients with grade 2 APCs had shorter ICU stays compared to grade 1, supporting the supposition of short-term benefits of APC development.
However, the higher burden took its toll over time. While transplant-free survival did not differ significantly at one year, both grade 2 and grade 3 APCs were associated with poorer transplant-free survival over the entirety of the study period, compared to grade 1.
Children designated as grades 2 and 3 were equally more likely to progress to transplantation compared to grade 1, helping define the “sweet spot” as a low, grade 1 APC volume.
Nationwide Standards
Nicholson and Bichell believe that better identification of high-risk patients, a more standardized quantification of APC burden, and targeted management (including embolization of some APCs) may improve outcomes.
Nicholson says there has never been a better time to do move forward with a larger, multicenter study.
“For infants born with this condition, the national multicenter collaboration has never been as robust as it is in this current era. In addition, collaborations with well-informed, active family groups has exponentially increased within the entire field as well,” he said.
