Cardiopulmonary exercise testing in adult congenital heart disease: can we predict exercise capacity from a submaximal test?

<bold>Introduction</bold> Assessment of exercise capacity by cardiopulmonary exercise testing (CPET) in adults with congenital heart disease (CHD) is important for prognostication and preoperative assessment. Peak oxygen uptake (PVO2) is used commonly, but can be challenging. <bold>Aims:</bold> We explored whether oxygen uptake efficiency slope (OUES) at anaerobic threshold (AT), the point during CPET at which OUES becomes strongly correlated with PVO₂, and is more reliably available from submaximal CPET, can predict PVO₂ in adults with CHD. <bold>Methods:</bold> We assessed consecutive individuals undergoing CPET and spirometry at our cardiorespiratory centre. Parametric data are presented using Pearson’s correlation coefficient and non-parametric data using Spearman’s rho. We employed linear regression modelling to analyse the association between PVO₂ and OUES at AT. <bold>Results:</bold> We analysed 391 individuals (177 female, age 32±11 years). Mean±SD PVO2 was 1724±540ml/min, peak VE 86.7±25.4l/min. The point of AT as a percentage of PVO₂ achieved was 66.5±9.4%, and AT as a percentage of predicted PVO₂ 46.9±11.4%. PVO₂ was correlated with OUES at 100% (R=0.91, p<.001), 90% (R=0.91, P<.001), 75% (R=0.89, P<.001) of maximum, and AT (R=0.83, P<.001). PVO₂ (ml/min/kg) could be predicted by: (OUES at AT)*685.245 + (BMI [kg/m²])*5.045 + (FEV₁ [l])*223.620 – 153.205. <bold>Conclusions:</bold> OUES at AT can calculate PVO₂ accurately. To our knowledge, this is the first equation using OUES at AT to predict PVO₂ in adults with CHD. In a population who may find maximal CPET difficult, this may be a useful submaximal measurement of cardiovascular fitness.