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

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.

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.

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).

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.