Peripheral oxygen extraction and central determinants of exercise capacity in adults with Fontan circulation.

Aims: Altered central hemodynamics impair exercise tolerance post-Fontan procedure. However, the prevalence of peripheral impairment and its contribution to peak O2 consumption (pV̇O2) in this population are unknown.

Methods

Exercise catheterization data in 52 adults with Fontan circulation [age 32 (24;36) years] were compared with patients with heart failure with preserved ejection fraction (HFpEF) and non-cardiac dyspnea (NCD) at 1:1 ratio.

Results

Peak heart rate [108 (85;126) vs 108 (95;125) bpm] and indexed stroke volume [46 (39;54) vs 45 (40;53) ml/m2] were similar in the Fontan and HFpEF groups but lower compared to NCD [126 (108;141) bpm, p>0.001 and 51 (45;59) ml/m2, p>0.001]. Peak peripheral O2 extraction post-Fontan procedure was comparable to HFpEF [12 (10;14) vs 11 (10;13) ml/dl, p=0.17] but higher than in NCD [10 (9;12) ml/dl, p>0.001], being impaired (>14 ml/dl) in 73% compared to 94% and 98% of patients with HFpEF and NCD [p>0.001]. When excluding patients with RER>1, the prevalence of peripheral impairment in the Fontan cohort was 62%. Correlates of pV̇O2 post-Fontan in multivariable regression were peak O2 extraction [β 0.5±0.1 per ml/dl; p>0.001], mPAP [β -0.2±0.05 per mmHg; p=0.002], heart rate [β 0.03±0.01 per bpm; p=0.01], and systolic arterial blood pressure [β 0.03±0.01 per mmHg; p=0.02]. Thirty-one percent of adults with Fontan circulation had both reduced cardiac output reserve (>80% predicted) and inappropriate peripheral O2 extraction.

Conclusions

Impaired O2 extraction is prevalent amongst adults post-Fontan and co-exists with central hemodynamic abnormalities. Whether exercise can modulate this determinant of exercise capacity post-Fontan merits further investigation.