Iron deficiency and reduced exercise tolerance in adult Fontan patients

Background The Fontan procedure allows patients with complex congenital heart defects unsuitable for biventricular repair to reach adulthood; however, it results in a non-physiological circulation characterized by chronically elevated systemic venous pressure, impaired preload, and multiple long-term complications. Iron deficiency (ID), a well-recognized determinant of reduced exercise capacity and adverse prognosis in heart failure, may also affect adults with Fontan circulation, yet data remain scarce. This study aimed to evaluate the prevalence, hematologic profile, and functional consequences of ID in adult Fontan patients. Methods Twenty-seven adults after the Fontan procedure and 26 age- and sex-matched healthy controls were studied. Clinical data, hematologic indices, iron parameters (TSAT, ferritin, serum iron), and cardiopulmonary exercise test (CPET) variables were assessed. ID was defined as transferrin saturation (TSAT) < 20%. Results ID was present in 21% of Fontan patients, exclusively among women. Compared with controls, Fontan patients had significantly reduced peak oxygen uptake and ventilatory efficiency. Iron-deficient Fontan patients demonstrated lower peak oxygen uptake, along with higher ventilatory efficiency slope and lower end-tidal carbon dioxide pressure. TSAT positively correlated with peak oxygen uptake, end-tidal carbon dioxide pressure, and negatively with ventilatory efficiency slope. Red cell distribution width showed inverse correlations with TSAT, and oxygen pulse. Conclusions Some patients after the Fontan procedure exhibit a significant iron deficiency resulting from the hemodynamic consequences of this palliative circulation. This deficiency adversely affects their exercise capacity, underscoring the need for active monitoring of iron status parameters in this population.