Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Two The Thorax 151
Radiographic findings include right atrial dilation, which is radiographically apparent
only if massive, and right ventricular enlargement (see Fig. 2-101). Hepatomegaly and
pleural or abdominal effusion and persistent caudal vena caval dilation may be present if
right heart failure occurs. Combinations of the above findings may be noted if both conditions
coexist (Fig. 2-126).
Echocardiographic findings of mitral insufficiency include marked left atrial dilation,
left ventricular dilation, and mild left ventricular hypertrophy. Malformations may include
displaced papillary muscles, abnormal chordae tendineae, and shortened and thickened
valve leaflets. Prolapse of the valve leaflets (i.e., displacement of one or more valve leaflets
into the atrium) may be seen. Fractional shortening is typically normal or increased but
may be decreased late in the course of disease. 350,351 Carefully performed Doppler studies
will confirm a diagnosis of mitral regurgitation. Because the regurgitant flow may be narrow
or directed angularly into the left atrium, the study may require Doppler mapping (i.e.,
sampling at multiple locations throughout the atrium) unless color-flow studies are used
to define the site of maximal regurgitation. The use of color Doppler readily confirms the
diagnosis and requires a great deal less time to perform. 352 Further, the degree of regurgitation
may be estimated with the color-flow study.
Echocardiographic findings of tricuspid insufficiency include severe right atrial dilation
and right ventricular enlargement. Abnormal papillary muscles, chordae tendineae,
and valvular prolapse may be seen (Figs. 2-127 and 2-128). Positioning of the valves low in
the ventricle away from the annulus may be seen in Ebstein’s anomaly. Doppler findings
will be similar to those seen with mitral regurgitation.
M I T R A L S T E N O S I S A N D T R I C U S P I D S T E N O S I S
Stenosis of atrioventricular valves has been reported in the dog and cat but involvement
of the tricuspid valve is very uncommon. 353-356 Radiographic abnormalities
noted may include left atrial enlargement and possibly pulmonary venous congestion
and pulmonary edema. Two-dimensional echocardiography may reveal incomplete
diastolic leaflet separation, lack of leaflet closure in middiastole, and doming of
the mitral valve. 356 Doppler studies will reveal an increased velocity of flow
across the mitral valve with associated turbulence. Mitral insufficiency may be demonstrated
also.
P R I M A RY E N D O C A R D I A L F I B R O E L A S T O S I S
Endocardial fibroelastosis has been reported in dogs, has also been reported in Siamese
cats, and has been documented as a congenital anomaly in Burmese cats. 357-359
Radiographically, left heart enlargement or generalized cardiomegaly may be seen.
Expected echocardiographic findings would include hyperechoic endocardium, dilation of
the left atrium and ventricle, and decreased fractional shortening and possibly thickening
of the mitral valve leaflets.
C O M B I N E D A N D M I S C E L L A N E O U S C O N G E N I TA L D E F E C T S
There have been several reports of animals with multiple congenital cardiac
anomalies. 360-368 Their radiographic and echocardiographic appearance will reflect both
the anatomical defects as well as their alterations in hemodynamics.
ACQUIRED CARDIAC DISEASE
AC Q U I R E D AT R I O V E N T R I C U L A R VA LV U L A R I N S U F F I C I E N C Y
Insufficiency of the mitral or the tricuspid valve or both is seen frequently in older, mostly
small-breed dogs and is usually the result of endocardiosis. An inherited predisposition to
endocardiosis and mitral valve prolapse is present in Cavalier King Charles Spaniels. 369-372
Endocardiosis, also sometimes termed mucoid valvular degeneration and myxomatous
transformation of the AV valves, is a degenerative process that results in thickened, shortened,
nodular, and distorted valve leaflets. 373 Although it may affect any heart valve, the
mitral and tricuspid valves are involved most commonly. A less common cause of valvular
insufficiency is trauma to the heart resulting in disruption of part or all of the valve. 374,375