Oxygen uptake efficiency slope at anaerobic threshold can predict peak VO in adult congenital heart disease.

Introduction: 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 (PVO) is used commonly, but can be challenging due to the difficulties of undertaking maximal CPET testing in this population. We explored whether oxygen uptake efficiency slope (OUES) at ventilatory anaerobic threshold (VAT), the point during CPET at which OUES becomes strongly correlated with PVO, and is more reliably available from submaximal CPET, can predict PVO in adults with CHD.

Methods: We assessed consecutive individuals who completed maximal CPET at our cardiorespiratory centre, as part of routine service review, between March 2019 and August 2021, recording data such as PVO, VAT and OUES at various proportions of a maximal test (75 %, 90 %, 100 %, and VAT). We employed linear regression modelling to analyse the association between PVO and OUES at VAT, and subsequently create an equation to predict PVO from OUES at VAT. Parametric data are presented using Pearson's correlation coefficient and non-parametric data using Spearman's rho.

Results: We analysed 391 individuals (177 female, age 32 ± 11 years). Mean ± SD PVO was 23.3 ± 6.86 ml/min/kg or 1724 ± 540 ml/min, peak VE 86.7 ± 25.4 l/min. The point of VAT as a percentage of PVO achieved was 66.5 ± 9.4 %, and VAT as a percentage of predicted PVO 46.9 ± 11.4 %. PVO 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 VAT (R = 0.83, P < .001). PVO could be predicted by: .

Conclusions: OUES at VAT can be used to calculate PVO. To our knowledge, this is the first equation using OUES at VAT to predict PVO in adults with CHD. In a population who may find maximal CPET difficult, this may be a useful submaximal measurement of cardiovascular fitness, and to calculate PVO, which is commonly used in guideline-based decision making in CHD.