Digital Histopathological Analysis of Myocardial Tissue in Canine Myxomatous Mitral Valve Disease and Dilated Cardiomyopathy

Abstract:

Background: Histopathological changes in cardiac tissues are incompletely evaluated in dogs with myxomatous mitral valve disease (MMVD) and dilated cardiomyopathy (DCM).

Objectives: Compare proportions of cardiomyocytes, fibrosis, fat, and arterial narrowing between cardiac tissue samples from dogs with MMVD, DCM, and healthy cardiac. Animals: 27 dogs with MMVD, 16 with DCM, and 31 cardiac healthy controls, euthanized due to reasons unrelated to the present study, were enrolled.

Methods: Proportions of cardiomyocytes, fibrosis, fat, and arterial narrowing were quantified in tissue samples from multiple specific cardiac regions in each dog using a semi-automatic quantification pipeline.

Results: Clinical MMVD dogs had higher fibrosis proportions in the left ventricular (LV) lateral wall and posterior papillary muscle (PPM), and left atrium (LA) and higher fat proportions in the LV PPM and interventricular septum (IVS) compared to small-breed controls (all P< 0.05). Clinical DCM dogs had higher fibrosis proportions in the right atrium and LA, and preclinical DCM dogs had higher fat proportions in the right ventricular (RV) lateral wall compared to large-breed controls (all P< 0.05). Preclinical DCM dogs had higher fat proportions in the RV lateral wall compared to preclinical MMVD dogs, and clinical DCM dogs had higher fibrosis proportions in the IVS compared to clinical MMVD dogs (all P< 0.01). Arterial narrowing increased with fibrosis proportions in MMVD dogs and DCM dogs. Conclusion and clinical importance: Proportions of fibrosis and fat replacement varied between cardiac locations and with disease and disease severity, which may highlight the role of these sites in disease pathogenesis.