Evaluation of Regional Differences in Right Ventricular Systolic Function by Acoustic Quantification Echocardiography and Cine Magnetic Resonance Imaging

Abstract

Background —Accurate quantitative evaluation of right ventricular (RV) function has been limited by its complex structural geometry. Although embryological and anatomic observations suggest that the RV is composed of 2 distinct components, the RV sinus and infundibulum, most studies on RV dimensions and function viewed it as a single chamber. This study was designed to determine the volumes, relative contribution to global systolic function, and temporal course of contraction and relaxation of the RV sinus and infundibulum. Methods and Results —Thirty-one individuals without heart disease (aged 1 month to 17 years, 16 boys and 15 girls) participated in this study. Instantaneous area over time, its derivatives, and the temporal course of contraction and relaxation were studied by acoustic quantification echocardiography and phonocardiography in 20 individuals. Global and regional RV volumes and ejection fraction were determined by cine MRI in 11 individuals. The RV sinus made up 81±6% of the combined RV end-diastolic volume and 87±4% of the combined stroke volume. The infundibulum accounted for the remaining 19±6% and 13±4%, respectively ( P <0.0001). Compared with the infundibulum, the extent of RV sinus fiber shortening was significantly greater: for ejection fraction (56±11% versus 38±13%, P <0.001), fractional area change (42±14% versus 28±9%, P <0.0001), and dA/dt (27±17% versus 13±6%, P <0.0001). Analysis of temporal course of contraction and relaxation (expressed as percentage of the cardiac cycle to adjust for differences in heart rate) showed that the infundibulum follows the RV sinus: onset of contraction 53%±14 versus 19±11% of systole, time to peak systole 115±16% versus 97±19% ( P ≤0.01), indicating a peristalsis-like pattern of contraction and relaxation. Conclusions —The results of this study demonstrate significant regional differences between the sinus and infundibulum components of the RV with regard to contribution to stroke volume, extent of fiber shortening, and sequence of mechanical activation. These data from normal individuals can be used in future research on RV function in pathological conditions.