Chronic valve disease (CVD), also called mitral valve disease or endocardiosis, is the most common form of acquired cardiac
disease diagnosed in small- and medium-sized dogs. The mitral valve alone is affected in 60 percent of cases of chronic valve
disease, whereas only the tricuspid valve is affected in 10 percent of cases. Thirty percent will have both the tricuspid
and mitral valves affected. Endocardiosis is an age-related thickening of the mitral valve due to fibroblast proliferation
and an increase in collagen and elastic fibers. The thickening of the mitral valve allows a regurgitant volume of blood to
be forced from the high-pressure left ventricle into the low-pressure left atrium during systole. Over time, regurgitation
can lead to progressive atrial and ventricular enlargement due to volume overload. Severe mitral regurgitation can lead to
left-sided congestive heart failure and pulmonary edema formation. Long-term severe mitral regurgitation can lead to generalized
heart failure. Right heart failure is typically seen with end-stage chronic valve disease. Tricuspid valve endocardiosis alone
typically does not develop into significant disease.
Clinical findings
Historical and physical exam findings for canines with chronic valve disease will vary depending on severity of disease. Typical
signalment includes middle age to geriatric small-breed dogs. Those with mild chronic valve disease typically are asymptomatic.
The heart murmur of mild mitral regurgitation is a soft high-pitched pansystolic heart murmur best auscultated over the apex
at the left 5th intercostal space. The murmur may become coarse as the mitral regurgitation volume increases. Progression
can occur over months to years. A palpable thrill may be noted over the left hemithorax in more advanced cases. A systolic
murmur noted over the right apex is typically due to the mitral regurgitation radiating to the right hemithorax. Occasionally,
a right-sided murmur may be due to significant tricuspid regurgitation, especially if pulmonary hypertension is present. Heart
rates are higher in dogs with more severe disease and in dogs with congestive heart failure.
Figure 1A Right lateral thoracic radiograph: Generalized enlargement to cardiac silhouette. Left atrial enlargement as noted
tracheal elevation and main stem bronchus compression. The caudal dorsal lung fields appear clear.
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Clinical disease may manifest as coughing, lethargy, tachypnea and syncope. Differentials for small-breed dogs that present
with a cough include bronchial disease, collapsing trachea, infectious tracheo-bronchitis and neoplasia. Thoracic radiographs
are an important part of the evaluation for dogs that present with a cough.
Figure 1B DV thoracic radiograph: Orthogonal view of patient in top photo. Generalized enlargement to cardiac silhouette.
A bulge is present in the area of the left auricular appendage. Soft tissue patchy alveolar pattern to caudal lung fields
representing cardiogenic pulmonary edema and congestive heart failure.
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Dogs with CVD may present with coughing due to left mainstem bronchus compression by an enlarged left atrium or due to a combination
of bronchus compression and the formation of pulmonary edema (Figure 1a). Prominent pulmonary vasculature and increased opacity
to the lung fields may be seen with left heart failure (Figure 1b). Dogs may develop right heart failure with ascites and
pleural effusion. Typically this occurs in the later stages of disease.
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