Right atrial expansion index compared with inferior vena cava assessment for right atrial pressure estimation

Assessing right atrial pressure (RAP) is crucial for evaluating volume status and optimizing the management of cardiac diseases. While right heart catheterization (RHC) or central venous line catheters provide direct RAP measurement, these methods are invasive and reserved for select patients. Non-invasive RAP estimation typically relies on echocardiographic evaluation of the inferior vena cava (IVC), but this approach has inherent limitations. The echocardiographic right atrial expansion index (RAEI) quantifies right atrial compliance by evaluating the relative increase in RA volume during the reservoir phase. This study aims to validate RAEI as a non-invasive parameter for RAP estimation. We retrospectively enrolled 1020 patients (728 in the derivation cohort and 292 in the validation cohort) with different chronic cardiac conditions who underwent clinically indicated RHC and TTE within 24 hours. Elevated RAP was defined as a value greater than 10 mmHg, as measured during RHC. RAEI and other TTE parameters were analyzed offline, with the results blinded to the RHC findings. In the derivation cohort, RAEI demonstrated a strong logarithmic correlation with RAP (lnRAEI-RAP: r=-0.65, p<0.001). lnRAEI emerged as an independent and additive predictor of RAP, surpassing clinical, hemodynamic, and echocardiographic parameters, including IVC assessment. For identifying RAP≥10 mmHg, lnRAEI proved more accurate assessment than IVC (AUC lnRAEI: 0.840, p<0.001; optimal cut-off = lnRAEI<3.53). In the validation cohort, the lnRAEI cut-off of <3.53 outperformed IVC assessment in identifying RAP≥10 mmHg (Accuracy: lnRAEI 78% vs. IVC 74%). Lastly, the equation RAP=19.3-(3.29xlnRAEI), derived from the derivation cohort, estimated RAP more accurately (-0.2±3.1 mmHg) compared to the IVC-based guidelines (1.5±4.2 mmHg) in the validation cohort. In this patient cohort, lnRAEI demonstrated superior accuracy compared to IVC assessment for non-invasive estimation of RAP.