Cardiac Output During Exercise: Thermodilution versus Direct Fick

BACKGROUNDAccurate cardiac output (CO) measurement during invasive cardiopulmonary exercise testing (iCEPT) is essential for classification of diseases such as exercise pulmonary hypertension (ex-PH), exercise pre-capillary PH (ex-prePH), and exercise postcapillary PH (ex-pcPH). The purpose of this study is to compare performance of thermodilution CO (tdCO) to gold-standard direct Fick CO (dfCO) during iCPET. METHODSA single-center prospective cohort study of patients undergoing iCPET over a three-year period. For the primary outcome, we predicted CO at each stage of exercise and recovery using generalized additive modeling. In secondary analysis, we assessed mean differences in CO across exercise stages. Finally, we assessed the impact in classification of ex-PH, ex-prePH, and ex-pcPH between the two CO methods. RESULTSA total of 302 patients were included. In the primary analysis, the generalized additive model smooth term was significantly different between tdCO and dfCO (p < 0.001), with tdCO underestimating dfCO at rest and overestimating dfCO at max exercise. Mean differences between tdCO and dfCO were only significantly different across two stages of exercise. Furthermore, classification rate of ex-PH, ex-prePH, and ex-pcPH was not significantly different between cardiac output methods (4, 3, and 1 patient misclassified by tdCO, respectively). CONCLUSIONWhile there are differences in CO estimation between thermodilution and direct Fick during iCPET, the degree of error did not meaningfully affect the hemodynamic classification of patients with ex-PH, ex-prePH, or ex-pcPH.