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

Abstract

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. 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 48hours, 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 24hours. In 59 patients in the derivation and validation cohorts, the relationship between SVC flow and RAP was compared between the opposite windows. 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 SVC-S/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<.001) and was an independent determinant of SVC-S/D after adjustment for right ventricular systolic function (β=-0.48, P<.001). A cutoff value of 1.9 for SVC-S/D showed 85% sensitivity and 74% specificity in identifying elevated RAP. Additionally, SVC-S/D showed an incremental diagnostic value combined with inferior vena cava size and collapsibility (P=.006). When a cutoff value of SVC-S/D<1.9 was applied to the validation cohort, it showed acceptable accuracy of 72% and incremental diagnostic value combined with inferior vena cava parameters (P=.033). SVC-S/D from the subcostal window correlated better with RAP than that from the supraclavicular window (P<.001, Meng's test). Measurement of SVC flow velocity from the subcostal window was feasible, and SVC-S/D from the subcostal window could be an additive parameter for estimating RAP.