“Hemodynamic Risk Assessment by Thermodilution and Direct Fick measurement of Cardiac Output in Pulmonary Hypertension”

Introduction Accurate measurement of cardiac output (CO) is critical in the evaluation and monitoring of pulmonary hypertension (PH). We assessed the accuracy of thermodilution (TD)-CO vs. Direct Fick-CO (DF-CO) among patients with PH and evaluated whether the method of CO measurement affected diagnosis or risk assessment. Methods We included patients who had undergone a right heart catheterization with both TD-CO and DF-CO measurements at UCLA between 01/2021 and 01/2023. Based on cardiac index (CI), patients were classified into low, intermediate, or high-risk hemodynamic status according to ESC/ERS guidelines. Results The analysis included 116 patients with PH. 55% were on PH therapy at the time of catheterization. The median (25th, 75th percentile) age was 59 (50-69) years and 63% were female. Median TD-CO and DF-CO were 4.6 L/min (3.6 – 6.0 L/min) and 5.3 L/min (4.2 – 7.0 L/min) (P = 0.007), respectively. Bland-Altman analysis revealed a mean bias of -0.64 L/min. Median DF-PVR and TD-PVR were 4.7 WU (2.7 – 6.6) and 5.6 WU (3.0 – 8.0), respectively. Among patients with a low Thermodilution CI, almost 40% had a preserved Direct Fick CI. There was 78% agreement between DF and TD hemodynamic risk status. Using TD over DF reclassified 8% of patients with pre-capillary PH (N = 101) from low risk into intermediate or high-risk hemodynamic status. TD had a sensitivity of 97% for appropriately risk stratifying patients into intermediate/high risk status but a specificity of 73%. Overall, there was a strong correlation between DF-CO and TD-CO (concordance correlation coefficient of 0.81 (0.74 – 0.86)). Conclusions Hemodynamic risk status was concordant between TD and DF measurements in almost 80% of patients. V̇O2 measurement should be considered if available on index RHC in patients with PH to aid in hemodynamic risk stratification or in whom strict PVR calculations are required.