Quantitative and qualitative histopathological analysis of myocardial tissue in canine myxomatous mitral valve disease and dilated cardiomyopathy.

Myocardial fibrosis patterns differ distinctly between MMVD and DCM, aiding disease characterization.

This comparative histopathological study examined myocardial tissue alterations in 27 dogs with myxomatous mitral valve disease (MMVD), 16 with dilated cardiomyopathy (DCM), and 32 healthy controls. Using quantitative digital image analysis and qualitative assessment of multiple region-matched cardiac specimens, researchers evaluated cardiomyocyte proportions, fibrosis, fat infiltration, and arterial lumen-to-area ratios. Key findings demonstrated that MMVD dogs exhibited predominantly left-sided myocardial changes, including increased fibrosis in the left ventricular lateral wall, posterior papillary muscle, and left atrium, with increased endocardial thickening in the left atrium compared to controls. DCM dogs showed bilateral atrial fibrosis and significantly higher interventricular septal fibrosis compared to MMVD dogs. Additionally, DCM dogs with concurrent atrial fibrillation demonstrated greater atrial fibrosis than DCM dogs without arrhythmias. Notably, arterial lumen-to-area ratios and attenuated wavy fibers showed no significant differences between groups. These findings suggest that histopathological alterations are disease-type and severity-dependent, with distinct regional patterns that may inform understanding of disease pathogenesis and progression in canine cardiac diseases.

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