Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Two The Thorax 161
A
Fig. 2-138 A 9-year-old neutered male domestic short-haired cat with dyspnea. A gallop rhythm was auscultated.
Radiographs revealed mild cardiomegaly, pulmonary edema, and a minimal pleural effusion. A, A right
parasternal long-axis aortic outflow view reveals dilation of the left atrium (la). The left ventricular free wall
(lvw) and interventricular septum (vs) are thickened. The left ventricular cavity (lv) is diminished. The aorta
(ao) is normal. These findings were confirmed on an M-mode study, which was used for mensuration. B, A
right parasternal short-axis view of the left ventricle shows the thickened left ventricular free wall (lvw) and
narrowed left ventricular cavity (lv). The papillary muscles (p) are defined clearly. Diagnosis: Hypertrophic
cardiomyopathy.
B
Fig. 2-139 A 12-year-old neutered male domestic
short-haired cat with dyspnea, tachycardia, and a
grade 4/6 heart murmur. A right parasternal shortaxis
view at the level of the aorta (ao) reveals a large
thrombus (arrows) in the left atrium (la). Diagnosis:
Hypertrophic cardiomyopathy and left atrial thrombus.
Unclassified Cardiomyopathy. Unclassified, also termed intermediate or restrictive,
cardiomyopathy has been described. 413-415 The major factor in restrictive cardiomyopathy
is diastolic dysfunction. The lesions usually are related to endocardial, subendocardial,
or myocardial fibrosis. Radiographic changes are indistinguishable from
those seen with hypertrophic cardiomyopathy. Echocardiographic findings are variable.
The most common feature is severe left atrial dilation (Fig. 2-140). The endomyocardial
form of restrictive cardiomyopathy has a cardinal feature of a pronounced endocardial
scar, a solid fibrous connective tissue band oriented along the long axis of the
ventricle but bridging the free wall to the septum at some level. Other features may
include mild left ventricular hypertrophy, possibly eccentric, and right atrial and right
ventricular enlargement. Rounded or “ball” thrombi may be found in the left atrium
and ventricle. The myocardial form of restrictive cardiomyopathy is characterized by