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Restrictive/Unclassified Cardiomyopathy

Key Points

• Restrictive cardiomyopathy is a form of cardiomyopathy characterized by normal ventricular wall thickness and myocardial
dysfunction that is primarily diastolic (filling).
• In the cat it is an adult-onset disorder, with an average age of diagnosis of approximately 7 years.
• Echocardiographic diagnosis is based on the presence of a dilated left or left and right atria with a fairly “normal” appearance
to the ventricle in the absence of other structural defects (ventricular septal defect, mitral valve dysplasia, etc.).
• Treatment is palliative and based on the clinical signs of the individual cat.

RESTRICTIVE CARDIOMYOPATHY ETIOLOGY, PATHOPHYSIOLOGY, AND GROSS
PATHOLOGY
Restrictive cardiomyopathy (RCM) is an adult-onset
myocardial disease that appears to be less prevalent than Etiology
hypertrophic cardiomyopathy but more prevalent than It has been suggested that RCM may actually be the end
dilated cardiomyopathy in cats. One report of 106 cats result of other forms of cardiomyopathy including
with cardiomyopathy identified RCM in approximately severe, end-stage hypertrophic cardiomyopathy that has
20% of them, compared to 58% for hypertrophic car- been complicated by a myocardial infarction or myocar-
diomyopathy (Ferasin et al. 2003). Restrictive cardiomy- dial failure (Bonagura and Fox 1995). An alternative
opathy is characterized by a normal or mildly reduced theory might be that RCM is the result of an infectious
myocardial systolic function, normal wall thickness, and organism since histopathologic evidence of myocarditis
diastolic (filling) dysfunction. Because it can have both and viral DNA from panleukopenia virus was observed
systolic and diastolic dysfunction it was sometimes in a small number of cats with RCM (Meurs et al. 2000).
referred to as an “intermediate cardiomyopathy,” but Finally, in human beings, one form of RCM is associated
restrictive cardiomyopathy is the more proper term. In with infiltration of eosinophils into the myocardium
some cases, endomyocardial fibrosis is also observed and (Kushwaha 1997). This is not likely to be a common
has resulted in the division of RCM into two possible cause of RCM in the cat, although it has been observed
forms: myocardial and endomyocardial restrictive car- in a few case reports (Fox 2004; Saxon 1991). In 1 case,
diomyopathy. By definition, RCM is demonstrated to it was observed with a significant peripheral eosino-
exist via the confirmation of a restrictive diastolic ven- philia (Saxon 1991).
tricular filling pattern, typically with Doppler echocar- Some human beings develop RCM as a familial trait,
diography. Due to various circumstances (tachycardia and causative mutations have been identified in cardiac
causing wave fusion, poor technique, lack of availability troponin I, cardiac troponin T, and cardiac actin
of the Doppler modality, postmortem specimens, etc.), genes (Sen-Chowdhry et al. 2010) The importance of
such a filling pattern may not always be demonstrable an inheritable etiology of RCM in the cat is not yet
in a given cat. known.

Feline Cardiology, First Edition. Etienne Côté, Kristin A. MacDonald, Kathryn M. Meurs, Meg M. Sleeper.
© 2011 John Wiley & Sons, Inc. Published 2011 by John Wiley & Sons, Inc.

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