Background: Patients with univentricular hearts have decreased exercise tolerance and may demonstrate exertional dyspnoea. It is not known if chronic hypoxaemia exacerbates exercise intolerance and contributes to symptomatic limitation. The extent to which surgical correction of a right-to-left shunt by a Fontan-type procedure can increase exercise tolerance by reducing arterial deoxygenation is not well documented. The cardiopulmonary exercise responses and the symptomatic status in two groups of univentricular patients, those who are cyanotic and those who are acyanotic with Fontan-type circulation, were compared.
Methods and findings: Cardiopulmonary exercise testing was performed in 10 univentricular patients with rest or stress-induced cyanosis (age 30.5 +/- 2.3 [SE] years; 5 men) who had palliative or no surgery and eight patients (age 29.4 +/- 1.5 years; 4 men) with Fontan-type circulation. Peak oxygen consumption was comparable in both groups of univentricular patients (21.7 +/- 2.5 vs 21.0 +/- 1.9 ml.kg-1.min-1, P = 0.85) but was less than an age-matched group of 10 healthy subjects (34.7 +/- 1.9 ml.kg-1.min-1, P < 0.001 for both). Arterial oxygen saturation was 90.6% at rest in the cyanotic patients compared with 95.1% in the Fontan patients (P < 0.001) and at peak exercise, 66.2% compared with 90.5% (P < 0.001). Using a modified Borg scale (0-10), the symptoms of dyspnoea and fatigue were also assessed during exercise in the patient groups. The Borg scores for dyspnoea in the cyanotic and the corrected univentricular patients were, respectively, as follows: Stage 1: 0.5 vs 1.7; P= 0.04; Stage 2: 1.8 vs 2.3, P = 0.5; Stage 3: 3.0 vs 3.5, P = 0.7; Peak Exercise: 4.9 vs 4.8, P = 0.9. In addition, the Borg scores for fatigue were: Stage 1: 0.4 vs 1.6, P = 0.08; Stage 2: 2.0 vs 2.2, P = 0.9; Stage 3: 3.0 vs 4.3, P = 0.5; Peak Exercise: 4.9 vs 5.4, P = 0.5. The major limiting symptom at peak exercise was dyspnoea in four cyanotic patients compared with one in the Fontan group (Chi-square 0.982, P > 0.10). The arterial oxygen desaturation at peak exercise in the cyanotic patients limited by dyspnoea was not different from those limited by fatigue (67.5 +/- 10.1% vs 66.7 +/- 13.7%, P = 0.92). Exercise tolerance was also not related to the arterial oxygen saturation at peak exercise (r = 0.47, P = 0.17) in these patients.
Conclusions: Despite correction with Fontan-type surgery, the exercise tolerance and symptoms of these univentricular patients remained similar to those who were cyanosed. Cyanotic patients have adjusted to chronic hypoxaemia and it does not appear to determine the exercise tolerance or the genesis of dyspnoea in these patients. Further randomized prospective studies are required to investigate the long-term benefits of Fontan-type procedures in these patients on exercise tolerance, symptoms and prognosis.