Page 140 - Feline Cardiology

Chapter 11: Hypertrophic Cardiomyopathy 139

function that are less influenced by alterations in load. was reduced in aged cats with HCM, but was normal in
At the present time, cardiologists generally do not use cats with hyperthyroidism, who had increased S’ veloci-
spectral Doppler information on diastolic function to ties (Simpson et al. 2009). However, TDI measurements
make specific treatment decisions, but it may contribute of diastolic function were abnormal in both cats with
to the overall clinical picture along with other abnor- HCM and cats with systemic hypertension and occurred
malities identified clinically, radiographically, and echo- independently from presence of concentric hypertrophy,
cardiographically. Abnormal spectral Doppler so they may be less useful in discriminating HCM and
measurements of diastolic function may thus help dif- systemic hypertension in cats (Carlos et al. 2006).
ferentiate normal cats from abnormal cats when the TDI has been shown to be an excellent method for
diagnosis is equivocal. Serial characterization of diastolic noninvasive assessment of diastolic function because it
inflow patterns (normal, delayed relaxation, pseudonor- is less sensitive to preload and therefore to alterations
mal, or restrictive) in an individual patient may also due to hydration status, heart rate, or other variables
clinically parallel the overall impact of HCM and pro- than traditional PW Doppler measurement of mitral Cardiomyopathies
gressive elevation in left atrial pressure that may be inflow (Schober et al. 2003; Sohn et al. 1997; Nagueh
present in cats as HCM worsens. et al. 1997). TDI uses the same principle that assesses the
movement of blood flow, but it amplifies the lower veloc-
Tissue Doppler imaging ity, higher amplitude movement of the myocardium.
Assessment of diastolic function can be an intimidating TDI has both spectral and color-flow modalities, and the
topic to many veterinarians and often involves use of pattern of velocity of the ventricular walls during dias-
specific techniques different from those used for tradi- tole helps to identify the earliest abnormalities of ven-
tional echocardiography (2D, color flow, M-mode, and tricular relaxation. TDI measurements may be obtained
spectral Doppler). However, assessment of diastolic from several sites within the left and right ventricles,
function can be as basic as assessment of the left atrial notably the mitral annulus. There are several techniques
size in cats with HCM, since in this disease left atrial of TDI including PW Doppler, color M-mode of the
dilation occurs when there is clinically relevant diastolic myocardium, and 2-dimensional color TDI. PW TDI is
dysfunction (excluding influence of anemia, fluid the most readily applicable technique that does not
administration, etc.). However, there are more specific require offline analysis, and it allows measurement of
technical methods to evaluate diastolic dysfunction that peak myocardial velocity during systole (S), early dias-
may aid in early diagnosis of HCM, possibly prior to tole (E’ or Em), and atrial systole during late diastole (A’
development of left ventricular hypertrophy, which may or Am). Color TDI allows measurement of myocardial
be important for breeding population screening or velocity gradient (MVG) and calculation of mean myo-
monitoring at risk breeds (MacDonald et al. 2007; cardial velocity. MVG is the transmyocardial velocity
Chetboul et al. 2006; Carlos et al. 2009). gradient from the endocardium to the epicardium
Tissue Doppler imaging (TDI) is the preferred echo- throughout the cardiac cycle. The fastest myocardial
cardiographic method to specifically evaluate diastolic velocities are in the endocardial region, and they decre-
dysfunction in cats with various heart diseases, particu- mentally decrease toward the epicardium (Chetboul et al.
larly HCM (Koffas et al. 2002; Gavaghan et al. 1999). It 2004). Myocardial velocities measured by PW Doppler are
is not essential for making a diagnosis of HCM, but it higher than by color M-mode because PW Doppler TDI
may contribute additional information in patients that measures peak velocities, whereas color Doppler mea-
are equivocal for HCM and breeds at risk for HCM, or sures mean myocardial velocities (Nikitin and Witte
for following progression of disease. TDI accurately 2004). Ideally, TDI measurements of diastolic and sys-
diagnoses diastolic dysfunction in a variety of cardiac tolic function would be load-independent, and not con-
diseases in people (HCM, endomyocardial fibrosis, founded by changes in hydration status, presence of
hypertensive heart disease, restrictive cardiomyopathy, valvular insufficiency, or increased afterload. No tech-
and Duchenne’s muscular dystrophy) as well as in cats nique is totally devoid of these influences. The effect of
with HCM (Chetboul et al. 2004; MacDonald et al. 2007; preload on TDI measurements has been assessed in dogs,
Carlos et al. 2009; Koffas et al. 2002, 2006; Gavaghan people, and healthy cats. In an experimental canine
et al. 1999; Oki et al. 2000; Garcia et al. 1996; Rodriguez model of abnormal LV relaxation, early diastolic mitral
et al. 1996). TDI has been used to distinguish HCM from annular velocity (E’) dependence on preload was more
other secondary causes of left ventricular hypertrophy prominent in the normal physiologic state, but depen-
in people (Vinereanu et al. 2001). This principle was dence was markedly diminished with diastolic dysfunc-
tested in cats with HCM and with hyperthyroidism, and tion (Firstenberg et al. 2001). TDI is a highly reproducible
the early diastolic myocardial velocity (E’, also called Em) and accurate method to assess diastolic and systolic