The impact of dominant ventricle morphology and additional ventricular chamber size on clinical outcomes in patients with Fontan circulation

Objectives: The functional roles of ventricular dominance and additional ventricular chamber after Fontan operation are still uncertain. We aim to assess and correlate such anatomical features to late clinical outcomes. Methods: Fontan patients undergoing cardiac MRI and cardiopulmonary exercise test between January 2020 and December 2022 were retrospectively reviewed. Clinical, cardiac MRI, and cardiopulmonary exercise test data from the last follow-up were analysed. Results: Fifty patients were analysed: left dominance was present in 29 patients (58%, median age 20 years, interquartile range:16-26). At a median follow-up after the Fontan operation was 16 years (interquartile range: 4-42), NYHA classes III and IV was present in 3 patients (6%), 4 (8%) underwent Fontan conversion, 2 (4%) were listed for heart transplantation, and 2 (4%) died. Statistical analysis showed that the additional ventricular chamber was larger (>20 mL/m2) in patients with a right dominant ventricle (p = 0.01), and right dominance was associated with a higher incidence of post-operative low-cardiac output syndrome (p = 0.043). Left ventricular dominance was associated with a better ejection fraction (p = 0.04), less extent of late gadolinium enhancement (p = 0.022), higher metabolic equivalents (p = 0.01), and higher peak oxygen consumption (p = 0.033). A larger additional ventricular chamber was associated with a higher need for post-operative extracorporeal membrane oxygenation support (p = 0.007), but it did not influence functional parameters on cardiac MRI or cardiopulmonary exercise test. Conclusions: In Fontan patients, left ventricular dominance correlated to better functional outcomes. Conversely, a larger additional ventricular chamber is more frequent in right ventricular dominance and can negatively affect the early post-Fontan course.