Patel ND, Friedman C, Herrington C, Wood JC, Cheng AL. J Thorac Cardiovasc Surg. 2021 Aug;162(2):372-380.e2. doi: 10.1016/j.jtcvs.2020.09.140. PMID: 33220959
Take Home Points:
- The minimum Fontan CSA/BSA was not associated with cardiac index or pulmonary artery size but did correlate with % predicted peak oxygen consumption. Smaller minimum CSA/BSA was associated with decreased exercise capacity.
Commentary from Dr. Manoj Gupta (New York City, NY, USA), chief section editor of Pediatric & Fetal Cardiology Journal Watch.
While most children receive an 18- or 20-mm conduit, the optimal size is not known. The authors sought to characterize changes in Fontan conduit size over time in single-ventricle population and determine if a decrease in conduit CSA affects cardiac output, pulmonary artery growth, and exercise capacity.
The authors observed a significant reduction in both minimum and average Fontan conduit CSA in the majority of patients. The median percentage decrease in minimum conduit CSA was 33% and in average conduit CSA was 24%.
Pulmonary Artery Size
Nakata index was not associated with minimum Fontan conduit CSA/BSA (p = 0.09, P = .29) when combining the cardiac catherization and MRI data. Nakata index based on initial Fontan conduit size, the difference in median Nakata index did not differ (175.4 mm2 /m2 [153.3, 191.2] for 16 mm vs 185.0 mm2 /m2 [150.7, 212.3] for 18 mm, 149.3 mm2 /m2 [112.6, 176] for 20 mm, P = .10). Interestingly, the patients with the 18-mm conduit on average had a greater Nakata index than patients with both smaller and larger conduits.
Cardiac index was not associated with minimum Fontan conduit CSA/BSA whether the cardiac MRI and cardiac catheterization data were considered together (p = – 0.003, P = .97) or separately. Pulmonary blood flow distribution measured by cardiac MRI, quantified as percentage of flow to the RPA, was not associated with minimum Fontan conduit CSA/BSA (p = 0.10, P = .44), average Fontan conduit CSA/BSA (p = 0.09, P = .50), or time from Fontan (p –0.11, P = .39).
The minimum Fontan CSA indexed to BSA at CPET had a weakly positive correlation with % predicted peak VO2 (r – 0.31, P = .013). By multiple regression analysis, % predicted peak VO2 was greater in patients with a larger Fontan conduit minimum CSA/BSA. Among patients with a 20-mm conduit, % predicted peak VO2 was lower when compared with those with a 16-mm conduit. % predicted VO2 was not influenced by time from Fontan, cardiac index, or sex. % predicted VO2 at anaerobic threshold was also greater in patients with a larger Fontan conduit minimum CSA/BSA.
The authors observed a significant decrease in Fontan conduit CSA over a mean follow-up period of 10 years. By both cardiac MRI and cardiac catheterization, Fontan conduit size did not appear to affect cardiac index at rest or pulmonary artery growth; however, it did correlate with exercise capacity.
Lee and colleagues determined that a Fontan CSA of 12.5 mm/m2 (18- or 20-mm diameter conduit in an adult sized patient) was associated with the greatest exercise capacity, with both smaller and larger conduits being associated with lower exercise capacity.
The authors observed a significant decrease in Fontan conduit CSA over a mean follow-up period of 10 years. These changes in CSA were observed as early as 6 months after surgery. Percentage CSA loss was also independent of initial conduit size. Conduit CSA indexed to BSA was not associated with cardiac index or pulmonary artery size but did correlate with exercise capacity.