Automated Echocardiographic Measures of Right Ventricular Area as an Index of Volume and End-Systolic Pressure-Area Relations to Assess Right Ventricular Function

Abstract

Background On-line determination of right ventricular (RV) volume to assess its function is clinically difficult. Echocardiographic automated border detection measures of left ventricular (LV) cavity area have been shown to reflect changes in volume, and pressure-area relations have been used to estimate LV contractility. The potential for RV cavity area to estimate changes in volume and to assess RV function, however, has not been evaluated. Accordingly, the objective of this study was to determine the relation between echocardiographic automated border-detected RV cross-sectional area and true volume and to assess the potential for end-systolic pressure-area relations to estimate RV function in an isovolumically contracting isolated canine heart preparation. Methods and Results Eight excised dog hearts with both right and left intraventricular balloons were perfused in an ex vivo apparatus in which both ventricular volumes were controlled independently. RV area data from the level of the left midventricular short-axis plane and pressure data were recorded on a computer through a customized hardware and software interface with the ultrasound system. RV volumes were varied from 9.4±3.9 to 43.8±6.9 mL at each of three different LV volume ranges (low range, 12.5±3.8 mL; medium range, 23.9±5.6 mL; and high range, 37.5±5.4 mL). The variation of RV area during isovolumic contraction, which we called deformational area change, was considerable (1.49±0.68 cm 2 mean±SD) but did not change significantly with changing RV and LV volumes. Linear regression analysis correlated the maximum, minimum, and mean automated border-detected RV area during isovolumic contraction with absolute volume. A predominantly linear relation was observed, with the group mean r =.98 ( y =0.16 x +0.97; SEE=0.21 cm 2 ). The effect of LV volume on RV area-volume relation was a significant parallel downward shift ( P <.05) by increases in LV volume. End-systolic pressure-area and pressure-volume relations using simultaneously RV pressure were both highly linear and covaried with changing LV volume. Conclusions Echocardiographic automated border-detected RV area reflects changes in RV volume under a constant LV volume, and the derived end-systolic pressure-area relation has potential for on-line assessment of RV function.