Page 273 - Feline Cardiology

280 Section G: Congestive Heart Failure

left ventricle do not necessarily have congestive heart failure from restrictive cardiomyopathy include marked,
failure, but combined with left atrial dilation or an diffusely thickened and hyperechoic endocardium and
acute triggering event, this finding suggests a diagnosis hyperechoic subendocardium possibly obliterating the
of congestive heart failure. In cats with severe dilated papillary muscles; fibromuscular bridging band tether-
cardiomyopathy, the myocardial failure is often ing the left ventricle and the septum; restrictive filling
obvious by subjective assessment. Left ventricular mea- pattern on pulsed-wave Doppler interrogation of the
surements obtained by two-dimensional measurements mitral inflow; and moderate to severe left atrial dilation.
or M-mode measurements of the left ventricle at the Typical abnormalities seen cats with congestive heart
level of the papillary muscles at end-diastole and end- failure secondary to unclassified cardiomyopathy include
systole (see Chapter 7). Increased end-systolic diameter moderate to severe left atrial dilation and/or right atrial
over 11 mm and decreased fractional shortening <28% dilation in the absence of significant myocardial failure
together indicate myocardial failure. Cats with dilated or concentric hypertrophy. Color-flow Doppler may
cardiomyopathy do not develop congestive heart failure identify mild centrally arising atrioventricular valvular
until there is moderate to severe myocardial failure, with insufficiency.
a fractional shortening <20% (usually <15%) (K. Evaluation of congenital heart disease also requires a
MacDonald, personal observation). Right ventricular detailed comprehensive echocardiogram. A thorough
assessment of the hemodynamic effects of the congenital
eccentric hypertrophy (i.e., increased right ventricular
Congestive Heart Failure is subjectively evaluated. Cats with severe mitral regur- treatment plan and to identify patients that may be suit-
heart malformation is essential to form an appropriate
diastolic diameter) is also present in cats with DCM and
gitation may develop secondary myocardial failure,
able for surgical correction. Difficulties in assessment of
congenital heart disease may arise when there are multi-
especially of the left ventricular free wall, but fractional
shortening is usually >28%. Marked or extreme enlarge-
ple congenital abnormalities present, requiring a high
ment of one or both atria, with echocardiographically
normal-appearing ventricles, suggests restrictive or
of two dimensional echocardiography, color-flow
Doppler, pulsed-wave Doppler, and continuous-wave
unclassified cardiomyopathy as the cause of congestive level of expertise for accurate diagnosis. A combination
heart failure. Doppler is needed for adequate evaluation of congenital
heart diseases. A positive contrast echocardiogram (using
Comprehensive echocardiogram agitated saline) is often necessary to identify the presence
A comprehensive echocardiogram is warranted in all and location of right to left shunting defects. Two-
cats with suspected or confirmed congestive heart failure dimensional echocardiography is used to assess for
since accurate determination of the underlying heart chamber enlargement, concentric hypertrophy, morpho-
disease leads to optimal treatment and prognostication. logic defects of the cardiac valves, myocardial failure (in
End-diastolic interventricular septal thickness and left addition to M-mode echocardiography), and pulmonary
ventricular free wall thickness are measured using two- artery dilation. Color-flow Doppler is used to assess val-
dimensional or M-mode echocardiography. Concentric vular insufficiency, blood flow turbulence associated with
hypertrophy is defined as interventricular septal and/or stenotic lesions, and left to right shunting congenital
left ventricular wall thickness of 6 mm or greater, and defects. Continuous-wave Doppler is used to measure the
may be present in cats with hypertrophic cardiomyopa- peak velocity between two chambers, and the modified
thy or secondary causes of concentric hypertrophy (i.e., Bernouilli equation (i.e., pressure gradient = 4× velocity)
systemic hypertension and hyperthyroidism) (see (Rush 2002) is used to calculate intracardiac and extra-
Chapter 11). Cats with secondary causes of concentric cardiac (aortic and pulmonary arteries) pressure gradi-
hypertrophy (i.e., hyperthyroidism or systemic hyper- ents (see Chapter 7). This technique is necessary to
tension) do not usually develop heart failure without determine the severity of the congenital heart disease and
additional underlying heart disease (i.e., concurrent to assess for presence of pulmonary hypertension. Please
hypertrophic cardiomyopathy or unclassified cardiomy- refer to Chapter 10 for detailed information regarding
opathy). Systolic anterior motion (SAM) of the mitral principles and application of echocardiography for diag-
valve is visualized by two-dimensional Doppler and nosis of specific congenital heart diseases.
color-flow Doppler, and the severity is quantified by Assessment of diastolic function is not essential to
continuous-wave Doppler measurement of aortic blood diagnose or treat heart failure, but it may provide
flow velocity. SAM of the mitral valve adds weight to the information that supports the diagnosis of diastolic
suspicion of primary myocardial disease (hypertrophic heart failure (Zile and Brutsaert 2002). Techniques used
cardiomyopathy) but is not absolutely specific for HCM. to assess diastolic function include pulsed-wave Doppler
Abnormalities that may be identified in cats with heart interrogation of the mitral inflow, pulsed-wave tissue