Dyspnoea and exercise intolerance during cardiopulmonary exercise testing in patients with univentricular heart: The effects of chronic hypoxaemia and Fontan procedure

BACKGROUND: Patients with univentricular hearts have decreased exercisetolerance and may demonstrate exertional dyspnoea. It is notknown if chronic hypoxaemia exacerbates exercise intoleranceand contributes to symptomatic limitation. The extent to whichsurgical correction of a right-to-left shunt by a Fontan-typeprocedure can increase exercise tolerance by reducing arterialdeoxygenation is not well documented. The cardiopulmonary exerciseresponses and the symptomatic status in two groups of univentricularpatients, those who are cyanotic and those who are acyanoticwith Fontan-type circulation, were compared. METHODS AND FINDINGS: Cardiopulmonary exercise testing was performed in 10 univentricularpatients with rest or stress-induced cyanosis (age 30·5±2·3[SE] years; 5 men) who had palliative or no surgery and eightpatients (age 29·4±1·5 years; 4 men) withFontan-type circulation. Peak oxygen consumption was comparablein both groups of univentricular patients (21·7±2·5vs 21·0±1·9 ml. kg^–1 . min^–1,P=0·85) but was less than an age-matched group of 10healthy subjects (34·7±1·9 ml. kg^–1. min^–1, P<0·001 for both). Arterial oxygensaturation was 90·6% at rest in the cyanotic patientscompared 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 duringexercise in the patient groups. The Borg scores for dyspnoeain 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 Borgscores 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 symptomat peak exercise was dyspnoea in four cyanotic patients comparedwith one in the Fontan group (Chi-square 0·982, P>0·10).The arterial oxygen desaturation at peak exercise in the cyanoticpatients limited by dyspnoea was not different from those limitedby fatigue (67·5±10·1% vs 66·7±13·7%,P=0·92). Exercise tolerance was also not related to thearterial oxygen saturation at peak exercise (r=0·47,P=0·17) in these patients. CONCLUSION: Despite correction with Fontan-type surgery, the exercise toleranceand symptoms of these univentricular patients remained similarto those who were cyanosed. Cyanotic patients have adjustedto chronic hypoxaemia and it does not appear to determine theexercise tolerance or the genesis of dyspnoea in these patients.Further randomized prospective studies are required to investigatethe long-term benefits of Fontan-type procedures in these patientson exercise tolerance, symptoms and prognosis.