Page 193 - Feline Cardiology

196 Section E: Other Forms of Structural Heart Disease

uncommon in cats, but it occurs sporadically. Mitral
regurgitation leads to an increase in the left atrial pres-
sure, which can lead to left atrial enlargement. This extra
volume of blood then returns to the left ventricle during
diastole resulting in a volume overload of the left ven-
tricle as well as the left atrium. In this scenario, ventricu-
lar dilation and hypertrophy occur, in which the ratio of
wall thickness and chamber size remains essentially
unchanged. This pattern is termed eccentric hypertrophy.
Ultimately, CHF secondary to elevated pulmonary
venous pressure may occur. When the mitral valve is
involved, CHF is expressed as cardiogenic pulmonary A
Misc. Heart Diseases the tricuspid valve is affected, ventricular volume over-
edema and/or pleural effusion (Figure 15.1A,B). When

load occurs on the right side of the heart and it is associ-
ated with systemic venous congestion causing pleural
effusion and ascites. For more in-depth discussion on
CHF, see Chapter 19.

DIAGNOSIS

The presence of a left apical holosystolic murmur is not
specific for mitral valve degeneration, and an echocar-
diogram is needed for definitive diagnosis. Thoracic
radiographs may reveal left-sided cardiomegaly primar-
ily evident as left atrial dilation, and possibly pulmonary
venous distension, pulmonary edema, and/or pleural
effusion if congestive heart failure is present.
Echocardiography is the essential diagnostic tool for
the diagnosis of degenerative valvular disease. The hall-
mark echocardiographic abnormalities of mitral valve
degeneration and insufficiency include identification of
mitral regurgitation on color-flow Doppler (Figure
15.2), which is often eccentric in nature, left atrial dila-
tion (Figure 15.3), and an increased left ventricular dia-
stolic diameter (i.e., eccentric hypertrophy) due to the
volume overload to the ventricle. There may be mild to B
moderate secondary myocardial failure of the left ven-
tricle, which is evident as decreased left ventricular free Figure 15.1. (A) Lateral thoracic radiograph from a cat with
wall motion and an increased end-systolic diameter. degenerative mitral valve disease, mitral regurgitation, and con-
However, fractional shortening is typically normal to gestive heart failure. Note the generalized heart enlargement
and increased pulmonary interstitial pattern. (B) VD thoracic ra-
high, due to the increased ventricular volume and diograph from the same cat as in (A). Note the generalized car-
reduced afterload (because of the mitral valve leak). The diomegaly, the increased pulmonary interstitial pattern, and the
septal systolic wall motion is often hyperdynamic. Unlike dilated pulmonary vasculature (arrow).
small dogs with myxomatous valve degeneration, mitral
valve prolapse is rarely seen in cats with degenerative DIFFERENTIAL DIAGNOSIS
valve disease, and the valves may appear only slightly
thickened (Figure 15.4). It is important to rule out sys- The most common cause of mitral regurgitation in
tolic anterior motion of the mitral valve as a cause of middle-aged to older cats is systolic anterior motion
mitral regurgitation since, in association with hypertro- (SAM) of the mitral valve, which is seen in some cats
phic obstructive cardiomyopathy, it is much more with hypertrophic cardiomyopathy. The key difference
common than degenerative valve disease and therapy in distinguishing degenerative valve disease from SAM
tends to be different. of the mitral valve is the identification of anterior dis-