Page 169 - Small Animal Internal Medicine, 6th Edition

CHAPTER 7
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Myocardial Diseases

of the Dog

Heart muscle disease that leads to contractile dysfunction mutation is only approximately 67%, and some Dobermans
and cardiac chamber enlargement is an important cause of with DCM are homozygous-negative for this mutation. Mul-
heart failure in dogs. Idiopathic or primary dilated cardio- tiple other mutations associated with DCM likely exist in
myopathy (DCM) is most common and mainly affects the Dobermans and other breeds. In at least some Great Danes,
larger breeds. Arrhythmogenic right ventricular cardiomy- DCM appears to be an X-linked recessive trait. DCM in Irish
opathy (ARVC), previously known as Boxer cardiomyopa- Wolfhounds appears to be familial, with an autosomal reces-
thy, is an important myocardial disease in Boxers but sive inheritance with sex-specific alleles. The familial DCM
uncommon in other breeds. Secondary and infective myo- affecting young Portuguese Water Dogs has an autosomal
cardial diseases (see p. 150) occur less often. Hypertrophic recessive inheritance pattern and is rapidly fatal in puppies
cardiomyopathy (HCM) is recognized infrequently in dogs that are homozygous for the mutation.
(see p. 152). Various biochemical defects, nutritional deficiencies,
toxins, immunologic mechanisms, and infectious agents
may be involved in the pathogenesis of DCM in different
DILATED CARDIOMYOPATHY cases. Impaired intracellular energy homeostasis and
decreased myocardial adenosine triphosphate (ATP) con-
Etiology and Pathophysiology centrations have been found in myocardial biochemical
DCM is a disease characterized by poor myocardial con- studies of affected Doberman Pinschers. Abnormal gene
tractility, with or without arrhythmias. Although considered expression related to cardiac ryanodine receptor regulation
++
idiopathic, DCM as an entity probably represents the end and intracardiac Ca release has been reported in Great
stage of different pathologic processes or metabolic defects Danes with DCM. Idiopathic DCM has also been associated
involving myocardial cells or the intercellular matrix rather with prior viral infections in people. However, on the basis
than a single disease. A genetic basis is thought to exist for of polymerase chain reaction (PCR) analysis of myocardial
many cases of idiopathic DCM, especially in breeds with samples from a small number of dogs with DCM, viral
a high prevalence or a familial occurrence of the disease. agents do not seem to be commonly associated with DCM
Large and giant breeds are most commonly affected, includ- in this species.
ing Doberman Pinschers, Great Danes, Saint Bernards, Decreased ventricular contractility (systolic dysfunction)
Scottish Deerhounds, Irish Wolfhounds, Labrador Retriev- is the major functional defect in dogs with DCM. Progressive
ers, Newfoundlands, Afghan Hounds, and Dalmatians. cardiac chamber dilation (eccentric hypertrophy and remod-
Some smaller breeds such as Cocker Spaniels can also be eling) develops as systolic pump function and cardiac output
affected. The disease is rarely seen in dogs that weigh less worsen, and compensatory mechanisms become activated.
than 12 kg. Doberman Pinschers appear to have the highest Poor cardiac output can cause weakness, syncope, and ulti-
prevalence of DCM with an autosomal dominant pattern of mately cardiogenic shock. Increased diastolic stiffness also
inheritance. A causative genetic mutation on chromosome contributes to the development of high end-diastolic pres-
14 has been associated with DCM in Doberman Pinschers; sures, venous congestion, and congestive heart failure (CHF).
the affected protein codes for a mitochondrial protein asso- Cardiac enlargement and papillary muscle dysfunction often
ciated with regulation of cardiac glucose metabolism, and cause poor systolic apposition of mitral and tricuspid leaf-
mutation is associated with poor systolic function. Testing lets, leading to mild to moderate valve insufficiency.
for the mutation is commercially available (North Carolina As cardiac output decreases, sympathetic, hormonal,
State University Veterinary Cardiac Genetics Laboratory; and renal compensatory mechanisms become activated.
https://cvm.ncsu.edu/genetics/); however, penetrance of this These mechanisms increase heart rate, peripheral vascular

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