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Feline Myocardial Disease

Virginia Luis Fuentes, MA, VetMB, PhD, CertVR, DVC, MRCVS, DACVIM (Cardiology), DECVIM (Cardiology)

Department of Clinical Sciences and Services, Royal Veterinary College, University of London, Hatfield, Herts, UK

Myocardial disease is extremely common in cats and will thickened left ventricular (LV) walls. Other phenotypes
be encountered regularly by any feline clinician, but can include restrictive cardiomyopathy (RCM), defined as
be hard to recognize. Feline myocardial disease is very relatively normal LV walls but with atrial enlargement and
heterogeneous in presentation, clinical findings, and increased atrial pressures; dilated cardiomyopathy (DCM),
prognosis. Without skilled echocardiography, identify- recognized by atrial and ventricular dilation with global
ing the different subclassifications of cardiomyopathy is LV hypocontractility; and arrhythmogenic right ven-
usually difficult. Fortunately, this is not usually neces- tricular cardiomyopathy (ARVC), which is typically mani-
sary, as the main priorities for the clinician are to identify fested by fibrofatty replacement of predominantly the
those cats with a specific treatable cause of myocardial right heart. There is considerable overlap between pheno-
disease, and to identify cats at high risk of congestive types, so an additional category of “unclassified cardio-
heart failure (CHF) or aortic thromboembolism (ATE). myopathy” or “non-specific phenotype” is sometimes
used to describe patients with a phenotype that does not
correspond with any of the above criteria.
Etiology Unless a causative systemic disease or myocardial
insult can be identified, the etiology is unknown for most
The term “myocardial disease” includes a range of condi- cats with myocardial disease, although familial HCM is
tions with varied etiologies. Cardiomyopathies are recognized. A genetic cause has been established for
usually classified according to a phenotype based on HCM in Maine Coon and ragdoll cats, where two differ-
cardiac structure and function (Figure 27.1). ent genetic mutations have been identified in the myo-
The myocardium can be affected by systemic condi- sin‐binding protein C gene. In contrast, an HCM
tions such as hyperthyroidism, systemic hypertension, phenotype has been associated with over 1400 different
and anemia, where disturbances in hemodynamic load- mutations in humans, although a genetic cause is not
ing conditions may alter cardiac structure and function. identified in all human HCM patients.
The myocardium has a limited range of responses to
injury or insult, so that different underlying causes can
result in the same phenotype. For example, dietary Pathophysiology
taurine deficiency, an uncontrolled tachyarrhythmia or
doxorubicin toxicity can all result in an identical “dilated The functional disturbance and consequent pathophysi-
cardiomyopathy phenotype” characterized by systolic ology vary according to type of cardiomyopathy and
dysfunction and ventricular dilation. In other cats, no severity of disease. With mild myocardial abnormalities,
obvious underlying cause is identified, although a genetic affected cats may not experience any obvious adverse
predisposition is suspected in some. consequences. With severe or advanced myocardial
Traditionally, feline cardiomyopathies have been classi- disease, congestive heart failure is the most commonly
fied according to contemporary human classifications, but recognized sign. Sudden death is also a potential sequela,
controversy currently exists over whether human myocar- but the prevalence is unknown and probably underesti-
dial disease should be classified according to etiology or mated. Systemic or arterial thromboembolism is recog-
phenotype. The most commonly recognized phenotype is nized in many advanced cases of cardiomyopathy with
hypertrophic cardiomyopathy (HCM), characterized by left heart involvement.

Clinical Small Animal Internal Medicine Volume I, First Edition. Edited by David S. Bruyette.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/bruyette/clinical