Clinical Utility of Superior Vena Cava Flow Velocity Waveform Measured from the Subcostal Window for Estimating Right Atrial Pressure

Background: The superior vena cava (SVC) flow velocity waveform from the supraclavicular window reflects right atrial pressure (RAP) status. Recent guidelines have stated that the subcostal window is an alternative view for recording SVC flow, but the validity of this approach remains unclear. The aim of this study was to determine the usefulness of SVC flow evaluation from the subcostal window for estimating RAP. Methods: Differences in SVC flow characteristics between opposite approaches were examined in 38 healthy adults. In 115 patients with cardiovascular diseases who underwent cardiac catheterization and echocardiography within 48 hours, the ratio of peak systolic to diastolic forward SVC flow (SVC-S/D) was measured, and the diagnostic ability of SVC-S/D for elevated RAP was tested. A validation cohort was used to confirm the diagnostic ability of SVC-S/D in 48 patients who underwent both cardiac catheterization and echocardiography within 24 hours. In 59 patients in the derivation and validation cohorts, the relationship between SVC flow and RAP was compared between the opposite windows. Results: Both systolic and diastolic SVC flow velocities were higher in the subcostal than in the supraclavicular approach, and effect of position change on subcostal SVC-S/D was smaller than that on supraclavicular SVCS/D in healthy adults. Measurement of SVC-S/D from the subcostal window was feasible in 98 patients (85%). RAP was inversely correlated with SVC-S/D (r = -0.50, P