Fontan Subtype, Conduit Size, and Cardiac Morphologic Factors and Their Relationship to Exercise Capacity in the Fontan Circulation: A Single Ventricle Outcomes Network (SV-ONE) Study

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ABSTRACT Background Exercise capacity varies among individuals with a Fontan circulation. Percent predicted peak oxygen consumption (%pVO 2 ) may be influenced by ventricular morphology, Fontan subtype, and conduit characteristics, but data explaining variability in exercise capacity are limited. This study examined whether anatomical and surgical factors are associated with %pVO 2 later in life. Methods Participants enrolled in the multicenter Single Ventricle Outcomes Network (SV-ONE) database who had cardiopulmonary exercise testing (CPET) data were included. Published reference equations were used to estimate %pVO 2 . Multivariable regression models evaluated associations between anthropometric, anatomical (diagnosis and dominant ventricle), and surgical (Fontan subtype, conduit size, and surgical era) factors and %pVO 2 . Restricted spline analyses assessed nonlinearity. Results 561 individuals with a Fontan circulation were included in the analysis; age 20 ± 8 years, 54% male, mean %pVO 2 was 63 ± 16%. Sex and exercise modality were the strongest predictors of %pVO 2 , with females being 12% higher than males and treadmill 4.6% higher than a cycle. Age at CPET was a predictor of exercise capacity with %pVO 2 decreasing by 0.8% per year. Ventricular morphology, diagnosis, and Fontan subtype did not have a statistical association with the primary outcome. In models restricted to patients with an extracardiac conduit (n = 330), conduit diameter and area were not associated with %pVO 2 , even after indexing to body surface area. Univariable nonlinear spline analyses suggested an optimal conduit size of 18 mm for %pVO 2 , but this was not significant after body size adjustments. Conclusion In this large multicenter cohort, surgical and anatomical features were not as important as sex, age, and body size as determinants of exercise performance in patients with a Fontan circulation. Reduced exercise capacity in this population appears to reflect progressive pathophysiological changes of the Fontan circulation rather than specific characteristics such as conduit size, ventricular morphology, or anatomy. CLINICAL PERSPECTIVE What is new? In this large multicenter registry study of 561 patients with a Fontan circulation, we evaluated whether early surgical and anatomical factors, including dominant ventricular morphology, underlying diagnosis, Fontan subtype, and extracardiac conduit size, are associated with exercise performance later in life as measured by percent predicted peak VO 2 . These surgical and anatomical variables explained little of the variability in exercise capacity. In contrast, demographic and testing-related factors, particularly sex, along with age and body size, were much more strongly associated with percent predicted peak VO 2 . What are the clinical implications? Despite longstanding interest in whether Fontan configuration or dominant ventricular morphology confers superior long-term exercise capacity, this study demonstrates that these surgical and anatomical factors contribute little to exercise performance later in life. For patients with a Fontan circulation, reduced exercise capacity should not be attributed primarily to Fontan subtype or conduit size. Instead, clinical care should emphasize modifiable contributors, including regular exercise participation, preservation of skeletal muscle mass, and proactive identification and management of hemodynamic abnormalities as they evolve over time.

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