Objectives: Patients with cyanotic congenital heart disease are generally thought to be limited by hypoxemia. To correlate exercise tolerance to the severity of the cardiac abnormality and to further characterize dyspnea in affected patients, we examined 25 adults with uncorrected cyanotic congenital heart disease.
Design and setting: Cohort study at a university hospital.
Methods: Symptom-limited cardiopulmonary exercise testing (CPX) was performed on a treadmill. Expiratory gas was analyzed breath by breath for evaluation of maximal exercise performance, ventilation, and ventilatory efficiency in combination with blood gas analysis during rest and exercise. Symptoms were assessed by the ability index and New York Heart Association class, and the results were compared to 101 healthy volunteers.
Results: Pao2 decreased by 26 ± 8% (mean ± SD) with exercise (from 49 ± 12 to 36 ± 10 mm Hg), while Paco2 was only slightly decreased compared to control subjects. Peak oxygen uptake (V̇o2) was significantly reduced when compared to control subjects: 16.7 ± 6.6 mL/kg/min vs 36.1 ± 7.7 mL/kg/min. Ventilatory efficiency was markedly impaired at rest (minute ventilation [V̇e]/carbon dioxide output [V̇co2] ratio of 70 ± 18; control subjects, 53 ± 11; p < 0.005) and during exercise (V̇e vs V̇co2 slope, 58 ± 31; control subjects, 26 ± 4; p < 0.005). At rest, ventilatory efficiency was correlated to resting pH and Pao2, while during exercise it was linked to Pao2. Ventilatory efficiency during exercise had the strongest correlation with observed symptoms, while hypoxemia and peak V̇o2 were not significantly associated with symptomatic state.
Conclusion: CPX in patients with cyanotic congenital heart disease provides helpful parameters that better define the symptomatic state of these patients. The summation of disease-related factors is best reflected by ventilatory efficiency. This parameter offers additional and independent information when compared to peak V̇o2 and the extent of cyanosis alone.