The Unique Clinical Phenotype and Exercise Adaptation of Fontan Patients With Normal Exercise Capacity

Abstract

Background: Exercise limitation is almost universal among Fontan patients. Identifying unique clinical features in the small fraction of Fontan patients with normal exercise capacity (high-capacity Fontan [HCF]) provides potential to inform clinical strategies for those with low exercise capacity (usual Fontan).

Methods: We performed a retrospective chart review of all patients with single-ventricle physiology palliated with a Fontan operation who underwent incremental cardiopulmonary exercise testing at Cincinnati Children's Hospital Medical Center from 2013 to 2018. Comparison was between patients with peak oxygen uptake < vs ≥ 80% predicted.

Results: A total of 22 of 112 patients were classified as HCF (68% were female; aged 18 ± 7 years). During incremental exercise, peak oxygen uptake (86.1% ± 6.1% vs 62% ± 12.2% predicted; P < 0.001) was greater in HCF vs usual Fontan despite similar chronotropic impairment, resulting in a greater oxygen pulse in HCF. Pulmonary function, breathing reserve, and ventilatory equivalent for CO₂ output slope were not different between groups. Those in the HCF group were more likely to self-report exercise ≥ 4 days/week for at least 30 minutes (77% vs 10%, P < 0.001), have normal systolic function (95% vs 74%, P = 0.003), have fewer postoperative complications (8% vs 36%, P = 0.04), and have shorter post-Fontan length of stay (8 ± 2.8 vs 12.4 ± 0.9 days, P = 0.04).

Conclusions: Approximately 1 in 5 Fontan patients who undergo cardiopulmonary exercise testing have normal exercise capacity despite chronotropic impairment. This implies a better preserved stroke volume, perhaps due to greater muscle pump-mediated preload. Additionally, a complicated perioperative Fontan course is associated with eventual impaired functional capacity.