C19 - Anatomical Distribution of Chordae Tendineae Rupture in Dogs with Myxomatous Mitral Valve Disease

Abstract: Background Myxomatous mitral valve disease (MMVD) is the most common cardiac disease in small-breed dogs, and shares histopathological features with degenerative mitral valve disease in humans. MMVD is characterized by leaflet thickening, chordae tendineae elongation, or chordae tendineae rupture (CTR), with CTR contributing to acute worsening of mitral regurgitation. In humans, CTR commonly occurs in the central posterior leaflet; however, its anatomical distribution in living dogs remains poorly understood. Objectives To clarify the frequency and anatomical distribution of CTR in MMVD dogs using intraoperative macroscopic evaluation. Animals A total of 2743 client-owned MMVD dogs underwent mitral valve repair. Methods This retrospective study assessed CTR intraoperatively across 10 segments based on the mitral leaflet regions (anterior, posterior, and commissural) and papillary muscle connections (anterior and posterior). Results Chordal elongation was observed in all the dogs. CTR was identified in 75.9% of the cases, markedly exceeding previously reported values based on echocardiographic assessment (16.1%). Rupture was most frequently observed in the central anterior leaflet. Severe mitral regurgitation requiring surgical repair was observed in 24.1% of dogs, despite the absence of CTR. Conclusions and Clinical Importance CTR was predominantly observed in the central anterior leaflet, a finding that differs from that reported in humans. Species-specific differences in the cardiac anatomy and mechanical loading may underlie the differences in CTR’s anatomical distribution. Moreover, dogs without CTR exhibiting disease severity warranting surgical repair indicate that factors other than CTR, such as leaflet thickening, chordal elongation, and annular deformation, also play important roles in MMVD progression.