ABSTRACT
Chronic degenerative (myxomatous) atrioventricular (AV) valve disease is the most common heart disease and cause of congestive heart failure (CHF) in dogs. The mitral valve, especially the anterior leaflet, usually is the most affected. Degenerative mitral valve disease (DMVD) is characterized by a prolonged preclinical phase, where valve lesions might only be apparent on postmortem exam. Early lesions appear grossly as small nodules on the free margins of the valve. Progressive accumulation of glycosaminoglycans and other substances within the leaflets, along with collagen and elastin degeneration, cause nodular thickening, deformity, and weakening of the valve and its chordae tendineae. The pathogenesis of myxomatous valvular degeneration involves multiple factors. Dysregulation of micro-ribonucleic acids (miRNAs) also could play an important role in DMVD pathogenesis. Chronic mechanical stress on the valve leaflets from repeated impact is thought to play a role in initiating the process of myxomatous degeneration and contributing to its progression.
