Page 179 - Feline Cardiology

Chapter 12: Restrictive/Unclassified Cardiomyopathy 179

II

Speed: 50 mm/sec Limb: 20 mm/mV

Figure 12.3. Lead II electrocardiogram from a cat with restrictive cardiomyopathy. Atrial fibrillation is noted due to the lack of P waves
and the irregular rhythm. Cardiomyopathies

Additionally, in some cases, end-stage hypertrophic car-
diomyopathy with ventricular wall thinning secondary
to a myocardial infarct may have a similar presentation
to RCM. There may be some cases in which it is not
possible to state with certainty that a specific diagnosis AO
of RCM, unclassified cardiomyopathy, or end-stage
HCM exists. However, at this time, the distinction is
clinically negligible because the disorders are treated LA
identically and have the same prognosis.

DIAGNOSTIC TESTING

Electrocardiography
There are no specific electrocardiographic findings for Figure 12.4. 2D short-axis echocardiographic view from a cat
RCM although a left axis shift may be observed. with restrictive cardiomyopathy. Note the large dilated left atrium
Supraventricular or ventricular premature complexes (LA) in comparison to the aorta (Ao).
may be identified. Atrial fibrillation has been frequently
observed and is likely associated with the very large atria
that are often observed with this disease (Figure 12.3) scarring that may obstruct some of the left ventricular
(Côté et al. 2004). lumen. An irregular hyperechoic endocardial region that
obstructs some of the left ventricular lumen may be
Radiography observed.
Evidence of moderate to severe left atrial or biatrial Doppler echocardiography may identify mitral regur-
enlargement is often seen (Fox 2004). Left or biventricu- gitation, typically mild. Transmitral flow velocities may
lar heart failure may be observed, including pulmonary be used to help assess diastolic function (see Chapter
edema or pleural effusion. 13). Abnormal relaxation patterns including an increased
isovolumetric relaxation time, an E wave with reduced
Echocardiography peak velocity, and an increased A wave velocity (low E:A
Moderate to severe left atrial or biatrial enlargement is ratio) may be observed. More commonly, a restrictive
the most common finding, and when observed in the filling pattern with a shortened relaxation time, increased
face of normal left ventricular wall thickness and normal E wave, and shortened A wave (high E:A ratio) is present
or mildly decreased systolic function, a diagnosis of (Luis Fuentes 2003) (Figure 12.5). However, transmitral
RCM should be considered (Figure 12.4). Pericardial flow velocities may be difficult to identify in the cat with
effusion is sometimes observed in severe cases with con- a rapid heart rate.
gestive heart failure.
Some cats have a form of RCM characterized by Diagnosis
endomyocardial fibrosis. This may be identified by Ultimately the diagnosis of RCM will be dependent
endocardium involvement, with obvious thickening or on echocardiographic findings of severe left atrial