Continuous Flow from Inferior Vena Cava into the Right Atrium Predicts Normal Central Venous Pressure

Background: Respiratory variation in Inferior Vena Cava (IVC) diameter is validated for estimation of Right Atrial Pressure (RAP) by echocardiogram. Although IVC flow into the Right Atrium (RA) can be appreciated in parasternal views, it is not routinely evaluated. We have observed an uninterrupted continuous wave (CW) Doppler flow signal from the IVC during sampling of the Tricuspid Regurgitation (TR) jet. Objectives: The present study aimed to show that this uninterrupted signal was a surrogate for normal/low RAP. Methods: This retrospective study was conducted on 500 consecutive echocardiograms and sought continuous flow from IVC into the RA in the subcostal view. RAP was then measured using IVC dynamics like size and respirophasic variation. Analysis was performed by comparison of the percentages. Results: Out of the 500 echocardiograms, 60 (12%) had Doppler evidence of continuous IVC flow into the RA. Among these 60 echocardiograms, RAP was calculated in 57 patients. Accordingly, RAP was 3 mmHg in 54 (95%) and 8 mmHg in 3 (5%) patients. RAP could not be estimated in three patients due to lack of visualization of IVC. Furthermore, RA volume index was normal in 51 patients (85%), but increased in 9 ones (15%). Right Ventricular (RV) function was also normal in 48 (96%) and low in 2 (4%) patients. Conclusion: The study findings supported the hypothesis that continuous flow from IVC into RA on CW Doppler is a surrogate for IVC dynamics in normal/low RAP and is particularly useful when subcostal views are suboptimal or inaccessible due to poor acoustic windows.