Page 178 - Feline Cardiology

178 Section D: Cardiomyopathies

Pathophysiology SIGNALMENT
A stiffened left ventricle leads to elevated left ventricular This is an adult onset disease. The average age at diag-
diastolic pressure, dilation of the left atrium, pulmonary nosis has been reported as 7 ± 3 years (Ferasin et al.
venous congestion, and left heart failure. Some cats 2003). Specific breed predispositions have not been
appear to develop pulmonary hypertension, and severe identified, although it has been reported in Birmans,
right atrial dilation may be noted. Many cats have greatly Siamese, and Persians as well as domestic shorthair and
dilated left and right atria and develop thromboembolic longhair (Meurs et al. 2000; Ferasin et al. 2003).
episodes as well as atrial tachyarrhythmias including
atrial fibrillation (Côté et al. 2004). HISTORY AND CHIEF COMPLAINT
Cardiomyopathies Heart weight and heart weight to body weight are gener- dyspnea, tachypnea, and anorexia. Restrictive cardiomy-
Pathology
The presenting complaints may be vague and include
opathy does have a high incidence of secondary throm-
ally mildly to moderately increased (Fox 2004). The left
boembolic disease, so hindlimb paralysis may be noted.
ventricular wall thickness should be normal, but there
may be some regional areas of thinning or hypertrophy.
The left atrium is typically severely dilated. The left ven-
tricular endocardium may be covered with an opaque, PHYSICAL EXAMINATION
A gallop sound has been suggested as a common auscul-
white-gray fibrous material, particularly in the left ven- tatory abnormality in some reports although a soft heart
tricular outflow or on the papillary muscles. Some cats murmur is often heard over the left apex or at the
will have an irregular endocardial fibrosis in the left sternum as well. In one report, a murmur was recorded
ventricle that bridges to the interventricular septum in 36% of the cases (Ferasin et al. 2003). A tachyarrhyth-
(Figure 12.1). Focal or diffuse fibrous tissue through the mia may be heard. Importantly, many affected cats will
endocardium, subendocardium, and myocardial regions not have any auscultable abnormalities, which may
are characteristic for the disease (Liu 1985) (Figure explain the perceived severity of this disease if it gener-
12.2). Inflammatory cells consistent with myocarditis ally escapes notice until overt clinical signs are present.
may be present. In advanced cases, arteriosclerosis in the
intramural coronary arterioles may be observed in the DIFFERENTIAL DIAGNOSIS
left ventricular free wall and septum (Liu 1985).
Unclassified cardiomyopathy may have a similar presen-
tation. In general, the term unclassified cardiomyopathy
is used when there are structural hallmarks of RCM
without proof of impaired diastolic ventricular filling.

Ao

LA

LV

Figure 12.1. Gross pathology of a heart from a cat with re-
strictive cardiomyopathy. A large fibrotic bridging band (arrow)
tethers the papillary muscles and left ventricular free wall to the
basilar interventricular septum. Diffuse, severe endomyocardial Figure 12.2. Histopathologic sample from the left ventricle of
fibrosis is evident as a thickened, white appearance of the endo- a cat with restrictive cardiomyopathy. The tissue is stained with
myocardium with a dense hyperechoic scar in the left ventricle a trichrome stain which causes the fibrous tissue to appear blue.
(LV). Left atrial (LA) dilation is observed. Ao = aorta. Note the diffuse fibrous tissue throughout the myocardium.