Background Cardiac output (CO) measurement guides management of various medical conditions, including but not limited to various adult congenital heart diseases (ACHD), and pulmonary hypertension. It is mandatory to calculate patients’ oxygen consumption (VO₂), to measure CO. Ideally VO₂ consumption can be measured by using a facemask apparatus; however, due to complexity in their routine use, various formulae derives assumed VO₂ are incorporated to obtain CO values. The most commonly used formula in catheter laboratories treating adult patients was reported by LaFarge and Miettinen (1970). However, it was based on data from paediatric population, and their use in adult population is not validated. Moreover, these individual formulae were compared with true VO₂ consumption; however, limited information exploring agreement between these formulae is available. Such a comparison is very important, as individual catheter laboratories use these formulae at their discretion to derive cardiac output, influencing patients’ management.

Materials and methods We sought to compare cardiac output measurement based upon four commonly used formulas, (1) LaFarge and Miettenen, (2) Dehmer, Firth and Hills, (3) Bergstra, Van Dijk, Jillege, and (4) Seckeler, Hirsch, Beekman Methodology, in 112 ACHD patients who underwent diagnostic catheterization at the Manchester Royal Infirmary, UK between 1st January 2015 to 31st March 2017. Their CO derived by using 4 different formulae were compared using a one way repeated measures ANOVA test.

Results CO measured by various formulae is reported here with: LaFarge and Miettenen 4.31±1.43 L/min; Dehmer, Firth and Hills – 4.91±1.50 L/min; Bergstra, Van Dijk, Jillege, – 6.1±2.22 L/min; and Seckeler, Hirsch, Beekman Methodology – 2.96±0.88 L/min. LaFarge and Miettenen formula derived CO was lowest in comparison to all other formulae and was significantly lower than Dehmer as well as Bergstra formulae (p<0.0001 for each), whereas non-significantly lower than the Seckeler et al formula.

Conclusion There is no agreement between the assumed VO₂ derived cardiac output measurements, including the most commonly used LaFarge formula, when compared in a cohort of ACHD patients. Using such assumed formulae derived CO may be misleading and such values should be interpreted carefully. Every cardiologist should be cognizant of these limitations. Facemask apparatus should be routinely used in catheter laboratories to obtain true VO₂, especially, when such a value is likely to influence major management decisions.

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Abstract 61 Figure 1