Comparison of the Right Atrial Expansion Index with Inferior Vena Cava Assessment for Echocardiographic Estimation of the Right Atrial Pressure

Background: Evaluating right atrial pressure (RAP) is essential for managing cardiac diseases. Right heart catheterization (RHC) measures RAP directly but is invasive. In contrast, transthoracic echocardiography (TTE) provides a non-invasive estimate of RAP through inferior vena cava (IVC) assessment despite some limitations. The right atrial expansion index (RAEI) reflects RA compliance by measuring the relative increase in volume during the reservoir phase. This study aimed to validate RAEI as a non-invasive parameter for estimating RAP. Methods: We retrospectively enrolled 1020 patients (728 in the derivation and 292 in the validation cohort) with various chronic cardiac diseases who underwent clinically indicated RHC and TTE within 24 hours. RAP was measured during the RHC and defined as elevated when above 10 mmHg. RAEI and other TTE parameters were measured offline and blinded to RHC results. Results: In the derivation cohort, RAEI showed a logarithmic correlation with RAP (lnRAEI-RAP: r=-0.65, p<0.001). lnRAEI was an independent and additive predictor of RAP, outperforming clinical, hemodynamic, and echocardiographic parameters, including IVC assessment. lnRAEI was more accurate than IVC assessment for identifying RAP≥10 mmHg (AUC lnRAEI: 0.840, p<0.001; optimal cut-off: lnRAEI<3.53); this finding was replicated in the validation cohort (AUC lnRAEI: 0.826, p<0.001). Furthermore, lnRAEI<3.53 was confirmed as an optimal cut-off for identifying RAP≥10 mmHg also in the validation cohort (Sensitivity: 74%, Specificity: 79%, Accuracy: 78%). Finally, the equation RAP=19.3-(3.29xlnRAEI) derived from the derivation cohort estimated RAP more accurately (-0.2±3.1 mmHg) than IVC assessment (1.5±4.2 mmHg) in the validation cohort. Conclusions: In this patient cohort, lnRAEI was more accurate than IVC assessment for non-invasive RAP estimation.