Page 137 - Feline Cardiology

136 Section D: Cardiomyopathies

IVS
Cardiomyopathies A B D S LVFW MV
D
S
EA

Figure 11.17. M-mode echocardiography showing normal mitral valve motion in a normal cat compared to systolic anterior motion
of the mitral valve in a cat with hypertrophic obstructive cardiomyopathy. M-mode echocardiography is done at the level of the mitral
valve using either the right parasternal short-axis view or the right parasternal long-axis 4-chamber view. Normally, both mitral leaflets
are closed during systole (S) (A). The early (E) and late (A) waves of mitral diastolic movement are summated in this normal cat that has
a high heart rate. In contrast, SAM of the mitral valve is seen when the anterior mitral leaflet nearly touches the interventricular septum
during systole (arrow) in a cat with hypertrophic obstructive cardiomyopathy (B). D = diastole.

parasternal apical 5-chamber view. The severity of mitral
regurgitation secondary to SAM usually ranges from
trivial to moderate and is subjectively assessed.
M-mode echocardiography of the mitral leaflet from
the right parasternal short-axis view may show the ante-
rior mitral leaflet being anteriorly (ventrally) displaced
and touching the interventricular septum during systole,
when it should be closed and coapted with the posterior
leaflet (Figure 11.17).
Continuous-wave Doppler is necessary to measure
the severity of left ventricular outflow tract obstruction.
Using the left apical 5-chamber view, the cursor is
aligned parallel with blood flow ejected out the left ven-
tricular outflow tract and aorta (Figure 11.18). Using the
modified Bernouilli equation, the pressure difference
between the left ventricle and the aorta is calculated as Figure 11.18. Continuous-wave Doppler echocardiography in a
2
pressure gradient = 4 × velocity . Mild, moderate, and cat with severe systolic anterior motion of the mitral valve and
severe obstructions are defined as pressure gradients <50 hypertrophic cardiomyopathy. The severity of SAM is assessed by
mm Hg, 50–80 mm Hg, and >80 mm Hg, respectively. continuous-wave Doppler measurement of the aortic blood flow
Normal cats may have a slight step up in velocity from velocity, using the left apical 5-chamber view. This cat has severe
the left ventricular outflow tract to the aorta, with a SAM as evidenced by an aortic blood flow velocity of 4.7 m/s (nor-
slight pressure gradient. Cats with moderate or severe mal <1.8 m/s; 4.7 m/s corresponds to a left ventricular to aortic
SAM may benefit from medical therapy to reduce the pressure gradient of 87 mm). SAM causes a dynamic obstruction,
severity of the obstruction, because it may also signifi- which worsens later in systole and creates this characteristic con-
cave, late-peaking, dagger-shaped appearance (rather than a
cantly reduce the severity of left ventricular concentric symmetrical cone shape) to the Doppler velocity profile.
hypertrophy. SAM is a dynamic obstruction, which
worsens with greater ventricular systolic force and
tachycardia, and is decreased by negative inotropic and
chronotropic agents (i.e., atenolol). Provoking the cat