Discordance between measured vs calculated oxygen consumption in adults with congenital heart disease: Limitations and clinical implications

Introduction. Oxygen consumption (VO2) is frequently estimated using derived formulas for ease of use. We performed a prospective study to assess the correlation and limits of agreement between measured and assumed VO2 (mL/min) in adults with congenital heart disease (CHD). Methods. Consecutive adults with CHD who have undergone cardiac catheterization at Mayo Clinic Rochester from January 2018 to December 2019 were retrospectively enrolled in the study. Expired gas analysis was performed to measure VO2. We estimated VO2 using LaFarge (VO2L), Dehmer (VO2D), and Bergstra (VO2B) formulas. Bland-Altman and linear-regression analyses were used to assess the correlation between measured and calculated VO2. Results. We enrolled 84 patients with a mean age of 43 ± 12 years; 66% were men. Linear correlation analysis showed a moderate correlation of VO2L and VO2B with VO2M (r = 0.58; P<.001 and r = 0.44; P<.01, respectively) and good correlation of VO2D with VO2M (r = 0.79; P<.001). The large spread of limits of agreement assessed using Bland-Altman analysis demonstrates poor agreement of VO2L and VO2B with VO2M (bias, -58; 95% confidence interval [CI], -258 to 48) and bias, 38; 95% CI, -91 to 167, respectively). Te limits of agreement for VO2D have a large spread, demonstrating a low degree of agreement with VO2M (bias, 13; 95% CI, -64 to 89). VO2L predominantly misclassified patients as low cardiac index and VO2D and VO2B misclassified patients as normal/high cardiac index. Conclusion. In adults with CHD, assumed VO2 will lead to a significant error while assessing invasive intracardiac hemodynamics.