Page 133 - Feline Cardiology

132 Section D: Cardiomyopathies

Ao
RA
Ao
LA Laur

LA
Cardiomyopathies A B

AO
Ao

LA
LA
PV

C
D
Figure 11.13. Two-dimensional echocardiography of cats with HCM, showing normal, mild, moderate, and severe left atrial dilation.
(A) This right parasternal short-axis view at the level of the aortic cusps of a cat with moderate HCM (same cat as in Figure 11.16A)
shows normal left atrial size, with a left atrial diameter to aortic diameter ratio of < 1.5. Image (B) shows a cat with moderate HCM and
mild left atrial dilation along with a prominent left auricle, and the left atrial to aortic ratio (LA : Ao) = 1.6. Image (C) shows moderate
left atrial dilation (LA : Ao = 1.8) in a cat with severe HCM. This cat has diastolic dysfunction leading to increased left ventricular diastolic
filling pressure and increased left atrial pressure, which causes left atrial dilation. The measurement lines are oriented slightly differ-
ently than the description in the text. Image (D) shows severe left atrial dilation (LA : Ao = 3), left auricular dilation, and a distended
pulmonary vein (PV) in a cat with severe HCM and congestive heart failure. Cats with left atrial enlargement should be evaluated by
radiographs as they may have congestive heart failure. LA = left atrium; Laur = left auricle; RA= right atrium; Ao = aorta.

11.13) (Schober et al. 2007; Abbott and MacLean 2006). than measurements taken by M-mode (Abbott and
The ratio of left atrial diameter to aortic diameter MacLean 2006). Care must be taken to measure the body
(LA:Ao) is used to eliminate the influence of body size of the left atrium and not the left auricle, which would
on left atrial size and provides a dimensionless index of underestimate left atrial size. Other pitfalls that may
atrial size, which is especially important when evaluat- occur include measurement of the far wall of the left
ing patients of markedly different body size (i.e., differ- atrium to include the pulmonary vein, which would
ent breeds of dogs). Since cats have less variability in overexaggerate the left atrial size, or mistaking the pul-
body size and conformation, some cardiologists assess monary artery for the left atrium. Given the aforemen-
left atrial size by the absolute left atrial diameter tioned limitations of M-mode, 2-dimensional
(>16 mm) rather than LA:Ao (see Box 11.2). echocardiography is the recommended technique for
LA:Ao can be measured by 2-dimensional echocar- measurement of left atrial size, since it is not limited by
diography or 2-dimensional guided M-mode echocar- the location and alignment of a cursor when using
diography. These measurements are not interchangeable M-mode. LA:Ao is measured from the right parasternal
because measurements taken by 2D tend to be larger short-axis view at the heart base at the level of the aortic