Objective. To evaluate the impact of antioxidant therapy on functional health status in Fontan-palliated patients. Design. Prospective, randomized, double-blind, placebo-controlled trial. Patients. Fifty-three generally asymptomatic Fontan patients. Interventions. Patients were randomized to receive either high-dose ascorbic acid (vitamin C) or placebo for 4 weeks. Outcome Measures. Peripheral vascular function, as measured with endothelium-dependent digital pulse amplitude testing (EndoPAT), and exercise capacity were assessed before and after study drug treatment. Primary outcome measures included the EndoPAT index and peripheral arterial tonometry (PAT) ratio, both validated markers of vascular function. Secondary outcome measures included peak oxygen consumption and work. Results. Twenty-three vitamin C- and 21 placebo-assigned subjects completed the protocol (83%). Median age and time from Fontan completion were 15 (interquartile range [IQR] 11.7–18.2) and 11.9 years (IQR 9.0–15.7), respectively. Right ventricular morphology was dominant in 30 (57%). Outcome measures were similar between groups at baseline. Among all subjects, vitamin C therapy was not associated with a statistical improvement in either primary or secondary outcome measures. In subjects with abnormal vascular function at baseline, compared with placebo, vitamin C therapy more frequently resulted in normalization of the EndoPAT index (45% vs. 17%) and PAT ratio (38% vs. 13%). Conclusions. Short-term therapy with vitamin C does not alter endothelial function or exercise capacity in an asymptomatic Fontan population overall. Vitamin C may provide benefit to a subset of Fontan patients with abnormal vascular function.

After the Fontan operation, patients are at a substantial risk of the development of impaired functional health status. Few early markers of suboptimal outcomes have been identified. We sought to assess the association between peripheral vascular function and functional health status in Fontan-palliated patients. Asymptomatic Fontan patients (n = 51) and age- and gender-matched healthy controls (n = 22) underwent endothelial pulse amplitude testing using a noninvasive fingertip peripheral arterial tonometry (PAT) device. Raw data were transformed into the PAT ratio, an established marker of vascular function. Cardiopulmonary exercise testing was performed using the Bruce protocol. In the Fontan cohort, 94% of patients were New York Heart Association functional class I and 88% had a B-type natriuretic peptide level of <50 pg/ml. The baseline pulse amplitude, a measure that reflects the arterial tone at rest, was greater in the Fontan patients than in the controls (median 2.74, interquartile range 1.96 to 4.13 vs median 1.86, interquartile range 1.14 to 2.79, p = 0.03). The PAT ratio, a measure of reactive hyperemia, was lower in Fontan patients (median 0.17, interquartile range -0.04 to 0.44, vs median 0.50, interquartile range 0.27 to 0.74, p = 0.002). The key parameters of exercise performance, including peak oxygen consumption (median 28.8 ml/kg/min, interquartile range 25.6 to 33.2 vs median 45.5 ml/kg/min, interquartile range 41.7 to 49.9, p <0.0001) and peak work (median 192 W, interquartile range 150 to 246 vs median 330, interquartile range 209 to 402 W, p <0.0001), were lower in Fontan patients than in the controls. The PAT ratio correlated with the peak oxygen consumption (r = 0.28, p = 0.02) and peak work (r = 0.26, p = 0.03). In conclusion, in an asymptomatic Fontan population, there is evidence of reduced basal peripheral arterial tone and vasodilator response, suggesting dysfunction of the endothelium-derived nitric oxide pathway. Vasodilator function appears to correlate with exercise performance.