Carl Sammarco
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Cardiomyopathy in dogs encompasses a wide spectrum of diseases, ranging from systolic and diastolic dysfunction to various
arrhythmias.
There are many sources to review the pathophysiology of cardiomyopathy. This article will discuss the various common breed-specific
variations of cardiomyopathies.
Dilated cardiomyopathy can occur in any breed, although it is seen more frequently in large-breed dogs. According to the Veterinary
Medical Data Base at Purdue University, breeds affected (number of cases in the United States from January 1986 to December
1991) included: Doberman Pinscher (603), Boxer (131), Great Dane (122), Labrador Retriever (73), American Cocker Spaniel (53),
Golden Retriever (42), Irish Wolfhound (38), Saint Bernard (29), Springer Spaniel (25), Newfoundland (22), English Sheepdog
(18), Afghan Hound (15), Scottish Deerhound (7) and English Cocker Spaniel (5). Pertinent information about some of the most
commonly affected breeds will be discussed.
DobermanDoberman Pinschers are the most common breed to develop dilated cardio-myopathy and it is suspected to be inherited by an
autosomal dominant pattern. Male Doberman Pinschers generally present with heart failure at a younger age than females, but
the overall prevalence of the disease is evenly distributed between males and females. The primary cause of their cardiomyopathy
is unknown, but many secondary changes in the muscle have been found, including low cardiac muscle L-carnitine, low myoglobin
and abnormal mitochondrial function. L-carnitine levels can be low in the muscle with normal plasma concentrations. Oral supplementation
produces poor to no response. The disease is most commonly diagnosed from 7 to 10 years of age and dogs diagnosed at 2 years
of age and under appear to have an accelerated progression. Progression of disease in dogs diagnosed older than 6 years tends
to be prolonged. Dobermans can be identified in the occult stage with electrocardiogram (ECG), echocardiography and Holter
monitoring.
Figure 1: Echocardiogram of Doberman with dilated cardiomyopathy. This M-mode was taken from the right parasternal, short
axis position. It shows a dilated left ventricle with poor systolic motion. The underlying rhythm is irregularly irregular.
The dog is in atrial fibrillation. The ECG can be seen at the bottom of the M-mode in blue.
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The majority of Dobermans with dilated cardiomyopathy will present with signs of poor systolic function (Figure 1). Many will
have various forms of atrial and ventricular arrhythmias. If atrial or ventricular tachycardias are present, they may add
to symptomatolgy and require primary antiarrhythmic therapy. If just periodic atrial premature or ventricular premature beats
are present, anti-arrhythmic therapy may not be needed. A small subset of Dobermans may present with ventricular arrhythmias,
particularly ventricular tachycardia, as the primary problem. In these dogs, mild left ventricular abnormalities may be present
with a normal left atrium. They present with weakness or syncope due to their arrhythmia and may not be in congestive heart
failure. These dogs will need primary anti-arrhythmic therapy and their myocardial disease may progress over time.
Therapy for dilated cardiomyopathy with congestive failure is the same for all breeds. Dogs in congestive failure typically
are treated with furosemide, an ACE inhibitor and pimobendan. Other therapy such as spironolactone and beta blockers, including
carvedilol, theoretically are warranted, but clinical studies that prove these medications will improve survival are lacking.
Spironlactone may help prevent potassium depletion in cases with low potassium or in cases where hydrocholorthiazide is added
to furosemide to control congestive failure. Beta-blockers may help control rate, especially if atrial fibrillation is present.
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