Page 145 - Feline Cardiology

144 Section D: Cardiomyopathies

the basilar interventricular septum and the maximal software that enables faster quantification of LV mass or
length of the LV (Figure 11.21). Short-axis slices are then ventricular volumes, but this feature comes at a signifi-
acquired perpendicular to the long-axis, from just above cant financial expense.
the mitral annulus to below the apex (see Figure 11.21).
Short-axis views are used for endocardial and epicardial Cardiac MRI for left ventricular mass
tracings to quantify LV intracardiac volume and LV quantification
mass. LV mass is calculated using Simpson’s rule. The Cardiac MRI (cMRI) has been shown to be the most
endocardial and epicardial borders are traced on slices accurate method of noninvasive LV mass quantification
from base to apex at a defined phase of the cardiac cycle in normal people and people with HCM, as well as in
(Figure 11.22). LV myocardial volumes are summated, animals as small as mice (see Figure 11.22) (Soler et al.
Cardiomyopathies obtain LV mass. There is semiautomated edge detection between cMRI calculated LV mass and actual LV mass
3
2003; Franco et al. 1998). There is good agreement
and multiplied by myocardial density (1.05 g/cm ) to
in dogs and people, with a mean difference of 4.4 and
10 grams for mean LV masses of 87 g and 190 g, respec-
tively (Myerson et al. 2002; Katz et al. 1988). cMRI using
Simpson’s rule more accurately quantifies LV mass in
normal people and people with HCM than using
3-dimensional echocardiography (with Simpson’s rule),
biplane MRI, or biplane echocardiography (Devlin et al.
LA 1999). Whether using cMRI or echocardiography,
Simpson’s rule more accurately quantifies LV mass in
RA
LV people than geometric models, especially in people with
RV
HCM. cMRI allows better complete visualization of the
LV and better morphologic assessment of degree and
extension of LV hypertrophy in humans with HCM. For
example, one study found that LV wall thickness could
be measured in only 67% of myocardial segments using
echocardiography, versus 97% of LV segments using
A
cMRI (Pons-Llado et al. 1997). cMRI also has been shown

RV

LV
1
2

B
Figure 11.21. Four-chamber long-axis view and short-axis view Figure 11.22. Endocardial and epicardial tracing to quantify
of the heart of a cat with hypertrophic cardiomyopathy using car- myocardial mass in a cat with hypertrophic cardiomyopathy us-
diac magnetic resonance imaging. A 4-chamber long-axis view ing cardiac magnetic resonance imaging. Endocardial (2) and epi-
(A) of the heart in this cat with severe HCM is acquired by pre- cardial (1) borders are manually traced at end-systole for all slices
scribing an imaging axis from the sagittal and coronal localizer extending from the mitral annulus to the apex. Myocardial area
views. Slices are placed perpendicular to the long-axis to obtain is the difference between epicardial and endocardial area and is
the short-axis view (B). There is massive concentric hypertrophy multiplied by slice thickness to determine myocardial volume. To-
of the anterior free wall of the left ventricle, and papillary hy- tal myocardial volume is the sum of myocardial volumes of each
3
pertrophy. LA = left atrium; LV = left ventricle; RA = right atrium; slice, and is then multiplied by the density of muscle (1.05 g/cm )
RV = right ventricle. to determine LV mass.