Page 132 - Feline Cardiology

Chapter 11: Hypertrophic Cardiomyopathy 131

in cats that are severely dehydrated (Campbell and
Kittleson 2007).
Cats with HCM often have evidence of replacement or
interstitial fibrosis on histopathologic evaluation of the
left ventricle. Echocardiographic assessment of replace-
ment fibrosis may include identification of regional
hyperechogenicity of the subendocardium and myocar-
IVS
dium in hypertrophied regions of the left ventricle. A
fibrotic plaque at the basilar interventricular septum
often occurs secondary to SAM of the mitral valve, and
this may be identified on echocardiography as a thick-
ened hyperechoic region of the endocardium and suben-
docardium of the basilar interventricular septum in the Cardiomyopathies
right parasternal long-axis left ventricular outflow tract
view. Sometimes, a hyperechoic oblique band of myocar-
dium may be seen in the interventricular septum of cats
with HCM and may represent myocardial fibrosis.

A Left atrial size
Assessment of left atrial size is critical in cats with HCM,
since left atrial dilation is present in the face of increased
diastolic filling pressures and identifies significant risk
of development of congestive heart failure and possibly
arterial thromboembolism. The left atrium becomes
dilated in cats with HCM in response to left ventricular
IVS
diastolic dysfunction, which increases ventricular dia-
stolic filling pressure. Elevated ventricular diastolic
filling pressure is transmitted back to the left atrium and
increases left atrial pressure, leading to left atrial enlarge-
P
ment. Mitral regurgitation secondary to SAM of the
mitral valve causes a backward leak of blood into the
left atrium (i.e., mitral regurgitation) and further
LVFW increases left atrial volume and pressure. Other factors
such as an atrial myopathy or replacement of atrial myo-
cytes with fibrosis may also lead to left atrial dilation and
poor left atrial function. Other cats with HCM may have
B
pathologic evidence of a thickened left atrial wall, pos-
Figure 11.12. Two-dimensional echocardiography of a cat with sibly due to the hypertrophic process extending to the
mild hypertrophic cardiomyopathy showing moderate papillary left atrial myocardium, or in response to increased left
muscle hypertrophy. Normal left ventricular papillary muscles atrial pressure. Left atrial dilation is a poor prognostic
are slender and upright (see Figure 11.9A). This cat has mod- indicator, and cats are at risk of congestive heart failure
erate papillary hypertrophy (arrow), and papillary muscles have or arterial thromboembolism. In people with HCM, left
a broad base and are hyperechoic. There is mild concentric hy- atrial enlargement is associated with more adverse
pertrophy of the interventricular septum (IVS), measuring 6.5 mm
at end-diastole, and normal left ventricular free wall thickness cardiac events, greater left ventricular hypertrophy, more
(LVFW) of 3.9 mm. Papillary hypertrophy may be an early abnor- severe diastolic dysfunction, and higher filling pressures
mality in cats with HCM and is typically assessed by subjective (Yang et al. 2005). Similarly, left atrial size was an inde-
impression. There is end-systolic cavity obliteration (B) due to the pendent negative prognostic factor in 260 cats with
moderate papillary hypertrophy (P) and mild septal hypertrophy. HCM (Rush and Freeman 2002).
Using an inner edge to inner edge technique (the
inside edge of the atrial wall), the left atrial diameter is
measured, typically using 2D echocardiography from
the right parasternal short-axis view at the level of the
aortic valve, and compared to the aortic diameter (Figure