Epsilon Archive for Student Projects

Abstract

Introduction. Mitral regurgitation (MR) in dogs is characterised on radiographs by increasing size of the heart, called “general heart enlargement.” The appearance
suggests that the right heart chambers may be enlarged, but there is no agreement on this, or if present, its cause. Concurrent enlargement of the right heart chambers
in MR would have to be explained by pathophysiologic mechanisms that might affect prognosis and treatment.

Aim. To determine presence or absence of echocardiographic changes that indicate right sided heart enlargement in relation to severity of MR.

Materials and methods. Two-dimensional (2-D) echocardiograhic frames of 54 dogs with varying degrees of MR were measured to determine ratios of dimensions of left and right sides of the heart: dimensions of right ventricle (RV) and left ventricle ( LV) in transverse short axis view above mitral valve (MV) at end diastole (ED), dimension of right ventricle (RV) and left ventricle (LV) on long axis at the MV at ED, on transverse section, the septal-free wall angle (SFWA) at ED and ES where the endocardium of RV joined LV. An eccentricity index (EI) of the LV at end diastole (ED) and end systole (ES) was measured to detemine the degree of flattening of the interventricular septum as a measure of RV overload. As the indicator of MR severity, left atrium/aorta root (LA/ Ao) was measured at beginning of diastole. Radiographs of 42 dogs were available. Heart size was measured by the vertebral heart scale (VHS) method. Dimensions were compared with LA/Ao and VHS by regression. The effect of severe LA and heart enlargement on EI were compared with none-moderate enlargement. EI at ED and ES were compared.

Results. The longitudinal and transverse dimensions of right and left side and the SFWA were so variable that although the right side and angle did not increase, no conclusions could be made. ED EI showed no increase in eccentricity with increasing size of LA or VHS. ES EI increased with LA /Ao and VHS, due to increases in some severly enlarged hearts. Five hearts had greater eccentricity at ES, indicating pressure overload on the RV. Three hearts had eccentricity only at ED, indicating volume overload.

Conclusions. No evidence for a consistent effect of increasing sevrity of MR on the right ventricle was found. In “general heart enlargement” on radiographs, it is
unlikely that the right side of the heart enlarges in proportion to severity of MR. The convexity on radiographs is probably caused by the right heart chambers being
displaced by enlarged left side of heart. The RV may be volume or pressure overloaded in some cases of MR.