Page 135 - Feline Cardiology

134 Section D: Cardiomyopathies

Identification of Systolic Anterior Motion ble for SAM, and rather that SAM is caused by alterations
(SAM) of the Mitral Valve in hypertrophied papillary muscle geometry (Sherrid
SAM of the mitral valve is a hallmark pathologic feature 2006; Levine et al. 1995). In HCM, papillary muscles are
of HCM. It can be seen on 2-dimensional echocardiog- almost always hypertrophied and cranioventrally (i.e.,
raphy from the right parasternal long-axis left ventricular anteriorly) displaced within the left ventricle, which pull
outflow tract view (Figure 11.16). SAM was previously the chordae tendinae and the anterior mitral leaflet into
thought to be caused by the Venturi effect, wherein the the left ventricular outflow tract and toward the interven-
rapid blood flow through a narrowed left ventricular tricular septum during systole. During late systole, the
outflow tract sucked the anterior mitral leaflet into the anterior mitral leaflet may even contact the basilar inter-
rapid flow, much like a shower curtain is drawn toward ventricular septum. The result is a dual abnormality of
Cardiomyopathies experiments have proven that this effect is not responsi- ejected out the left ventricle, and retrograde flow from
blood flow: there is greater resistance for blood flow to be
the rapid flow of the water stream in a shower. Later
the ventricle to the left atrium (i.e., mitral regurgitation)
occurs due to the gap in coaptation of the mitral valve
during systole. A fibrotic plaque is often seen as a hyper-
echoic region of the endocardium where the mitral leaflet
contacts the interventricular septum (i.e., “kissing
lesion”). An important differential diagnosis for mitral
regurgitation caused by SAM is mitral regurgitation
caused by mitral valve dysplasia, and these two disorders
have different etiology, pathophysiology, clinical course,
treatment, and prognoses. The mitral valve structure is
normal in cats with SAM, as opposed to mitral valve
dysplasia where the mitral valve is typically thickened,
with clubbed leaflets and thickened short chordae tendi-
nae. SAM can also be visualized using 2-dimensional
echocardiography in the left apical 5-chamber (left ven-
tricular outflow tract) view (see Figure 11.16).
Color-flow Doppler is a useful tool to readily identify
Figure 11.15. Two-dimensional echocardiography showing a the characteristic double turbulent jets of mitral regur-
left atrial thrombus and left atrial dilation in a cat with severe hy- gitation and turbulent systolic ejection blood flow
pertrophic cardiomyopathy. This right parasternal short-axis view arising from the same spot in the left ventricular outflow
at the level of the heart base shows severe left atrial dilation as tract (see Figure 11.16). The anterior mitral leaflet can
well as a hyperechoic, round, soft tissue opacity within the auricle
(arrow), which represents a thrombus. There is also spontaneous be seen at the origin of the turbulent jets. The right
contrast, seen as a hyperechoic, speckled, swirling pattern within parasternal long-axis left ventricular outflow tract
the left atrium, due to red blood cell aggregation. RV = right ven- view is the most useful view to identify this color-flow
tricle; Ao = aorta; LA = left atrium. disturbance, but it can also be identified from the left

Figure 11.16. Two-dimensional and color-flow Doppler echocardiographic assessment of systolic anterior motion of the mitral valve
in a cat with hypertrophic obstructive cardiomyopathy and a cat with hypertrophic cardiomyopathy without systolic anterior motion for
comparison. The right parasternal long-axis left ventricular outflow tract view of a cat with hypertrophic cardiomyopathy but no systolic
anterior motion (SAM) shows no valvular obstruction of blood flow out the left ventricular outflow tract (LVOT) on 2D and color-flow
Doppler (A and B), even though there is evidence of severe basilar septal hypertrophy and papillary hypertrophy. This is in contrast to a
cat with HCM and severe systolic anterior motion of the mitral valve (C and D), where the anterior mitral leaflet obstructs the left ven-
tricular outflow tract during systole (arrow). Color-flow Doppler of the left ventricular outflow tract shows a double turbulent jet where
the anterior mitral leaflet obstructs the left ventricular outflow tract and also creates mitral regurgitation.
The left apical 5-chamber view of a cat with HCM and no SAM shows an unimpeded left ventricular outflow tract and normal mitral
valve coaptation, laminar ejection of blood flow out the LVOT and aorta (blue color), and severe basilar septal concentric hypertrophy (E
and F). In contrast, the left apical 5-chamber view of a cat with severe SAM shows an abnormally positioned mitral valve (arrow) that
touches the interventricular septum, thus obstructing blood flow out the left ventricular outflow tract and creating mitral regurgitation
(G and H). The papillary muscles are hypertrophied, and anteriorly (cranioventrally) positioned, pulling the chordae tendinae and the
anterior leaflet toward the severely hypertrophied basilar interventricular septum. Ao = aorta; IVS = interventricular septum; LA = left
atrium; LV = left ventricle; RA = right atrium; RV = right ventricle