Correlation analysis of cardiac indexes using echocardiography and indirect Fick method in patients with pulmonary arterial hypertension

  AIM  To compare the correlation between echocardiography (Echo) and cardiac index (CI) results measured by right heart catheterization (RHC) in pulmonary arterial hypertension (PAH).

  METHODS  Sixty-eight patients with PAH were retrospectively selected from the Department of Congenital Heart Disease of the General Hospital of Northern Theater Command the Chinese People’s Liberation Army, including 22 patients with idiopathic PAH, 42 patients with postoperative PAH of congenital heart disease, and 4 patients with chronic thromboembolic pulmonary hypertension. All patients were measured cardiac output and calculated CI by biplane Simpson method and indirect Fick method within 24 hours. According to the CI results measured by indirect Fick method, the patients were divided into low cardiac output group n=35,<2.5 L/(min×m²) and normal cardiac output group n=33, ≥ 2.5 L/(min×m²), and the correlation analysis and Bland-Altman consistency analysis of the whole group and each group were carried out respectively. Then the risk stratification of PAH was carried out according to the CI values measured by the two methods.

  RESULTS   CI-Echo and CI-RHC were (2.52 ± 0.56) L/(min) respectively×m²) and (2.49 ± 0.79) L/(min×m²), there were no statistical difference between the two groups. CI-Echo was significantly positively correlated with CI-RHC. Overall: r=0.67, P<0.01; normal cardiac output: r=0.57, P<0.01; low cardiac output: r=0.48, P<0.01. Normal cardiac output group: CI-Echo is (2.82 ± 0.46) L/(min×m²), CI-RHC is (3.09 ± 0.54) L/(min×m²), the difference (Echo-RHC) was (−0.27) ± 0.51) L/(min×m²), 95% confidence interval (−0.45)～(−0.09), there were no statistical difference in the overall mean of the two groups of data. Low cardiac output group: CI-Echo was (2.24 ± 0.51) L/(min×m²), CI-RHC was (1.92 ± 0.37) L/(min×m²), the difference (Echo-RHC) was (0.33 ± 0.43) L/(min×m²), 95% confidence interval (0.18～0.48) , there were no statistical difference in the overall mean of the two groups of data. Overall R² linearity=0.452, normal cardiac displacement R² linearity=0.267, low cardiac displacement R² linearity=0.365. The Bland-Altman diagram showed that the two measurement methods and their good consistency in different CI groups. The proportion of consistency between Echo and indirect Fick method in determining CI for PAH risk stratification is 68%. If the CI measured by RHC is used as the reference standard for risk stratification, the consistency proportion of low risk, medium risk and high risk groups were 84.8%, 52.9% and 50% respectively.

  CONCLUSION  Echo biplane Simpson method and RHC indirect Fick method show a significant positive correlation and the results of risk stratification for PAH determined by both methods are fairly consistent.