**3. Diagnosis**

studies strongly suggested genetic etiology for this disease, although other study found the aging is the major cause for this disease [11]. In these dog breeds, the CMVI is occurred at younger age and progressed more rapidly. List of dog breeds having high prevalence rate for CMVI are Chihuahuas, Malteses, Yorkshire Terriers, Poodles, Papillons, Pekingeses, Miniature Pinschers, Bologneses, Dachshunds, Shih Tzus, Cairn Terriers, Miniature Schnauzers, Bichon Frises, Carvalier King Charles Spaniels, Pugs, West Highland White Terriers, Fox Terriers, Boston Terriers, Welsh Terriers, Whippets, American Cocker Spaniels, Beagles, German Shepherds, and Great Danes [12], although almost one‐quarter of dogs over the age of 10 have degenerative changes on mitral valve in any breeds of dog. Higher prevalence rate in Maltese and Shih Tzu has been found in some Asian countries including Korea, Japan, and

CMVI is an animal model of human mitral valve prolapse (MVP), which is suggested of poly‐ genic inheritance [14]. Several canine studies also suggested polygenic inheritance for CMVI [6, 8, 15]. Male dogs have higher rate of prevalence almost 1.5 times than female dogs [3]. One study found that the mitral valve was affected in ~60% case of CMVI, and tricuspid valve only was affected in ~10% of CMVI, while both atrioventricular valves (mitral valve and tricuspid

Pathological features of canine CMVI are degenerative changes on mitral valve, mitral valve thickening and opacity, several degrees of leaflet retraction, node of valve's end, and length‐ ened chordae tendineae (**Figure 1**) [17, 18] and are similar to human MVP [19, 20]. Disruption of collagen and deposition of glycosaminoglycans in mitral valve are also common micro‐ scopic feature in this disease [11, 19, 21]. Long‐standing mitral valvular insufficiency can

**Figure 1.** Pathological features of canine chronic mitral valvular insufficiency are degenerative changes on mitral valve, mitral valve thickening and opacity, several degrees of leaflet retraction, node of valve's end and lengthened chordae tendineae. (A) Diagram of normal mitral valve (top) and mitral regurgitation (bottom), (B) diagram of mitral valve

insufficiency from chronic degenerative changes on mitral valve leaflets (box).

Taiwan [13].

valve) were affected in ~30% of CMVI [16].

96 Canine Medicine - Recent Topics and Advanced Research

**2. Pathogenesis and clinical signs**
