Page 274 - Feline Cardiology

Chapter 19: Congestive Heart Failure 281

Doppler echocardiography, color-tissue Doppler echo- Although there is a lack of data in cats with heart disease,
cardiography, and quantification of left ventricular wall an echocardiographic index of left ventricular filling
stress and strain. Measurement of mitral inflow veloci- pressure has been evaluated in people and dogs with
ties is relatively simple and fast and may readily identify heart disease. The index of transmitral early mitral
delayed relaxation or restrictive filling patterns. Delayed inflow velocity (E) to early diastolic mitral annular
left ventricular relaxation commonly occurs in cats velocity (E′) is a useful, noninvasive method to estimate
with HCM, most often in the initial stage of diastolic LV filling pressure in normal people (r = 0.87) and
dysfunction. Identification of a restrictive filling pattern people with HCM (r = 0.8) (Nagueh et al. 1997, 1999).
(early to late diastolic filling wave ratio [E : A] >2, E/E′ >10 predicted LV filling pressure (just before atrial
decreased deceleration time, and decreased isovolumic systole) of >15 mm Hg, and yielded the best sensitivity
relaxation period) indicates severe diastolic dysfunction (92%) and specificity (85%) compared to TDI measure-
and severely elevated left atrial pressure. Fusion of early ments (E′) or mitral velocity profiles alone in people
diastolic filling wave (E) and late diastolic filling wave (Nagueh 1999). In dogs with acute experimentally
(A) during tachycardia (HR > 180 bpm) disables the induced mitral regurgitation, E/E′ was highly correlated
ability to assess diastolic dysfunction by this technique. (r = 0.83) with mean left atrial pressure (Oyama et al.
Likewise, a pseudonormal pattern may be identified in 2004). An LA pressure >20 mm Hg was highly probable
cats with moderate diastolic dysfunction, which is chal- when mean E/E′ was >9.1 (Oyama et al. 2004). Mitral
lenging to differentiate from normal mitral inflow inflow E/velocity of propagation by TDI was moderately
velocity profile (see Chapters 7 and 11). Tissue Doppler correlated to LV end-diastolic pressure in anesthetized
imaging (TDI) echocardiography is a sensitive test for normal cats (r = 0.64) (Chapter 11) (Schober et al. 2003).
diagnosis of diastolic dysfunction in cats with a variety No studies have evaluated the ability of E/E′ to predict Congestive Heart Failure
of cardiac diseases. It is not plagued by a “pseudonor- pulmonary capillary pressure in cats with cardiac disease.
mal” filling pattern, and there are varying opinions
about its validity when E′ and A′ waves are summated Arterial blood pressure
during tachycardias whereby an individual E′ wave is Measurement of arterial blood pressure is an important
not measurable. Pulsed-wave TDI is a fast and relatively diagnostic test to evaluate for systemic hypertension or
simple technique that does not require postprocess hypotension. Systemic hypertension may contribute to
analysis and is readily available on many moderate- concentric hypertrophy and diastolic dysfunction, but in
level echocardiographs. Diastolic dysfunction is identi- the absence of other heart disease does not lead to heart
fied as a reduced early diastolic wave velocity. Diastolic failure (see Chapter 21). Systemic hypertension must be
function of the longitudinal muscle fibers is assessed distinguished from high sympathetic tone and “white
by measurement of the mitral annular and septal myo- coat” hypertension, which may be present in a stressed
cardial velocities using the 4-chamber left apical view. cat. Dyspneic cats with high sympathetic tone may have
Diastolic function of the circumferential myocardial a physiologically elevated blood pressure that improves
fibers of the interventricular septum and left ventricu- once they are clinically stabilized with resolution of
lar free wall is assessed from the right parasternal cross- dyspnea and normalized sympathetic tone. If there is
sectional view at the level of the papillary muscles. The persistently elevated blood pressure (>160 mm Hg) on
longitudinal fibers are often the first to develop dia- serial measurements in the stable heart failure patient,
stolic dysfunction in HCM, so measurement of the antihypertensive treatment of the systemic hypertension
lateral mitral annular velocity and septal velocity using is recommended (see Chapter 21). Cats with severe
the left apical view may be most useful (Koffas et al. mitral valvular disease and heart failure may benefit
2002). Color TDI echocardiography is another tech- from antihypertensive medications as an afterload
nique to assess diastolic dysfunction and is much less reducer, and systolic blood pressure should be main-
impacted by translational movement of the heart. tained at or below 140 mm Hg, unless a cat shows intol- -
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Color TDI allows for simultaneous assessment of myo- erance to the medication’s effect (i.e., becomes clinically
cardial function in limitless regions of the ventricle and hypotensive). Avoidance of hypotension and reflex
quantifies endocardial to epicardial velocity gradients. tachycardia is important in cats with HCM who have
Limitations include the need for postprocessing impaired diastolic filling, and hypotension also worsens
imaging and a higher level of expertise to appropriately the severity of left ventricular outflow tract obstruction
analyze the data. in these cats. In cardiac patients, systemic hypotension
A noninvasive method to assess left atrial pressure is often an end-stage abnormality in cats with markedly
would be useful to confirm the diagnosis of left-sided reduced cardiac output and low output heart failure.
congestive heart failure and track response to therapy. Identification of systemic hypotension is important, as