Limitations of unidimensional index of right ventricular contractile function in conscious dogs

Abstract

Objective: Our goal was to examine the validity of unidimensional indexes of right ventricular contractile performance in vivo. Methods: Unidimensional indexes and global measurements of right ventricular volume and contractile performance were compared in 6 conscious dogs. Vena caval occlusions were performed before (control) and during pulmonary arterial or aortic constriction. Results: Moderately strong relationships were demonstrated between right ventricular septal-free wall indexes and global measurements of right ventricular end-diastolic and end-systolic volumes, stroke volume, stroke work, and the slope of the preload recruitable stroke work relationship, respectively, under control conditions (mean r2 range 0.69-0.94). These relationships were shifted significantly, however, by increased right ventricular afterload. Increased left ventricular afterload significantly shifted the relationships between right ventricular septal-free wall dimensions and end-diastolic and end-systolic volumes. Relationships between the corresponding regional right ventricular free wall segmental indexes and global measurements under control conditions were weaker (mean r2 range 0.12-0.65) and were significantly more sensitive to distortion by both increased right and left ventricular afterload, the effects of which were generally in opposite directions. These observations are consistent with significant ventricular interactive effects on the relationship between single right ventricular dimensions and right ventricular volume. Conclusion: Unidimensional right ventricular measurements are not reliable surrogates for right ventricular volume when assessing right ventricular contractile performance in the intact heart.