Page 130 - Feline Cardiology

Chapter 11: Hypertrophic Cardiomyopathy 129

not devoid of risk of adverse cardiac sequelae. Additional
information in cats with focal basilar septal hypertrophy
is needed, including genetic analysis, detailed assessment
RV of other concurrent cardiac abnormalities such as dia-
stolic dysfunction, SAM of the mitral valve, clinical
course, and pathologic evaluation, which may better
Ao characterize this subset of feline patients.
P LV
Left ventricular wall thickness obtained by
2-dimensional echocardiography is useful for obtaining
LA the diagnosis, but measurements vary according to
region of the left ventricle measured and the time within
the cardiac cycle that the image frame was obtained for
measurements. There is high inter- and intraobserver Cardiomyopathies
Figure 11.11. Right parasternal long-axis view of concentric variability for measurements of septal and left ventricu-
hypertrophy of the basilar interventricular septum in a cat with lar free wall end- diastolic thicknesses in awake cats
hypertrophic cardiomyopathy. Sometimes there is asymmetrical (18% and 20%, respectively) (Chetboul et al. 2004).
or segmental hypertrophy of the left ventricle in cats with HCM. Therefore, serial quantification of left ventricular hyper-
This cat has severe basilar interventricular septal hypertrophy (ar- trophy and assessment of changes in left ventricular
row; 9 mm thickness), papillary (P) hypertrophy, and equivocal to hypertrophy following pharmacologic therapy can be
mild left ventricular free wall concentric hypertrophy. Sometimes challenging and highly dependent on the sites chosen for
the basilar interventricular septum is best imaged by the right wall measurement.
parasternal long-axis left ventricular outflow tract view as shown Although left ventricular concentric hypertrophy is
here, and measurement of this region can be done using this view.
typically defined as a maximal end-diastolic wall thick-
ness of 6 mm or greater, there are alternative criteria
septum compared to the short-axis view (see Figure used by some cardiologists. One proposed method is to
11.11). divide the interventricular septum into two regions
Focal basilar concentric hypertrophy of the interven- (basilar to middle; middle to apical) measured in both
tricular septum (i.e., “basal or septal bulge”) may be seen long-axis and short-axis views, and the left ventricular
in some cats with HCM, although there is debate in both (posterior) free wall measured in both long- and short-
human medicine and veterinary medicine over whether axis views on 2D echocardiography (Paige et al. 2009).
normal individuals may also develop this as a benign, Presence of concentric hypertrophy is defined as an end-
age-related variant of normal versus a forme fruste of diastolic wall thickness of 6 mm or greater in more than
HCM (i.e., an atypical or attenuated manifestation of 50% of a wall segment, not just the maximal thickness
the disease) (Belenkie et al. 1988; Spirito et al. 1986; in one part of the wall (Paige et al. 2009). This method
Krasnow 1997; Hecht et al. 1992). Unfortunately, the yields fewer positive diagnoses of HCM. Another pro-
debate is largely based on conjecture and opinion and posed criterion is to define increased end-diastolic left
lacks substantial data regarding clinical, pathologic, and ventricular wall or septal thickness as 5.5 mm or greater,
genetic characterization. Some leading human cardiolo- because most normal cats do not have wall thickness of
gists specializing in familial HCM favor the hypothesis 5.5 mm or greater, which yields greater positive diagno-
that focal septal hypertrophy is a less severe form of ses and higher prevalence rates of LV hypertrophy in the
HCM caused by less malignant cardiac genetic muta- general feline population (Wagner et al. 2010). For
tions, and result in a more benign course associated with example, when using the criteria of 6 mm or greater wall
lack of symptoms and long survival times (Spirito et al. thickness measured by 2D, 34% of 92 clinically healthy
1989; Shapiro and Zezulka 1883). However, the course cats were diagnosed with left ventricular hypertrophy,
of disease may not be as benign in people as initially compared to a lower prevalence rate of 23% of cats using
thought, and this hypothesis was evaluated in a prospec- a more stringent criteria of >50% of a wall segment
tive study following a subset of 29 human patients with having 6 mm or greater thickness (Wagner et al. 2010).
no symptoms and mild focal left ventricular hypertro- Likewise, the lowest prevalence rate (12%) was obtained
phy attributed to HCM. Although 76% (22/29) of these using the criteria of 6 mm or greater wall thickness mea-
patients never developed symptoms over an average of sured by M-mode, likely because M-mode missed many
8 years of follow-up, 4 (14%) people died suddenly and cats with segmental ventricular hypertrophy (Wagner
3 (10%) had progression of symptoms, indicating that et al. 2010). Using a lower value of 5.5 mm or greater
despite a later onset of mild hypertrophy, patients are for diagnosing left ventricular hypertrophy led to the