The left ventricle in dogs with myxomatous mitral valve disease

The concept of left ventricular (LV) remodeling in dogs with myxomatous mitral valve disease (MMVD) includes changes in the LV occurring in response to mitral regurgitation (MR). The general aim of this thesis was to study LV remodeling and function in dogs with different severities of naturally acquired MMVD using 1) digital signal analysis technique for murmur and heart sound assessment, 2) biomarker analyses of circulating cardiac troponin I (cTnI), C-reactive protein (CRP), and matrix metalloproteinases (MMPs), and 3) real-time three-dimensional (RT3D) echocardiography for assessment of changes in LV shape and volume. Digital linear and nonlinear analyses (using seven different sound variables) of cardiac sounds showed that more severe MR produced a murmur of “harsher” quality, longer duration, and with more complexity in the signal. The energy of the first heart sound was not associated with MR severity (assessed by echocardiography), whereas the energy of the second heart sound decreased with increasing MR severity. Biomarker assessments showed circulating (cTnI) concentration to increase with increasing disease severity, whereas circulating C-reactive protein (CRP) concentration was not associated with disease severity. Neither MMP-2 nor -9 were associated with the MMVD severity groups (which was mainly based on volume overload status), however, MMP-9 activity decreased with worsening systolic function. The RT3D echocardiographic examinations showed prominent LV volume expansions only in dogs with more severe MMVD. The mid LV segment contributed the most to the global volume increase. The LV shape changed from elliptical to more globular in response to increasing volume overload, with the basal and apical segments contributing the most to the increase in sphericity. In conclusion, the findings in the present thesis provide data that might contribute to the understanding of the complex pathophysiology of MMVD; thereby potentially impacting both clinical management and prediction of outcome for affected dogs in the future