Accuracy of oxygen uptake efficiency slope in adults with congenital heart disease.

BACKGROUND: Given its linearity throughout exercise, oxygen uptake efficiency slope (OUES) obtained with a sub-maximal exercise is considered a reliable predictor of exercise capacity. We sought to assess the linearity of OUES across different exercise stages in adults with various forms of congenital heart disease.

METHODS: Using cardiopulmonary exercise testing, we studied 23 patients after a Fontan operation, and 30 patients after atrial repair for complete transposition of the great arteries, at a mean age of 24+/-10 years. Thirty-five healthy volunteers were used as controls. OUES was calculated from 100% (OUES), the first 50% (OUES(50)), and the last 50% (OUES(50-100)) of the entire exercise duration.

RESULTS: Peak oxygen uptake and OUES were reduced in Fontan patients when compared to atrial repair or control subjects (p<0.05). However, whereas in atrial repair and in control subjects OUES(50), OUES(50-100), and OUES appeared to be similar (p>0.05), in Fontan patients OUES(50) appeared to be lower than OUES(50-100) (1.38+/-0.46 vs. 1.78+/-0.51, p=0.01) and OUES (1.38+/-0.46 vs. 1.72+/-0.56, p=0.032). The difference between OUES(50) and OUES(50-100) appeared particularly large in cyanotic Fontan patients (1.40+/-0.42 vs. 1.93+/-0.68, p=0.001), whereas no difference was observed in Fontan patients with normal saturation (1.33+/-0.59 vs. 1.37+/-0.67, p=0.922).

CONCLUSIONS: In cyanotic Fontan patients, OUES(50) differs substantially from OUES(50-100) and OUES. Therefore, OUES(50) is unable to predict maximal exercise capacity in this population.