Page 286 - Clinical Small Animal Internal Medicine

254 Section 3 Cardiovascular Disease

blood pressure and tissue perfusion activates a number The overt phase follows, characterized by the onset of
VetBooks.ir of neuroendocrine and cytokine systems intended to clinical signs including syncope, SD, or those typical of
CHF (ACVIM stage C). In the Doberman, 25–30% expe-
maintain stroke volume and blood pressure, primarily
through sodium and water retention and vasoconstric-
of CHF or syncope is again breed and etiology depend-
tion. Stretch receptors and remodeling pathways are rience SD before CHF. Survival time following the onset
triggered, leading to lengthening of individual myocytes ent, with Dobermans and Great Danes experiencing the
(eccentric hypertrophy) and chamber dilation, mala- shortest survival times among breeds (see Prognosis).
daptive extracellular matrix remodeling, and cell death. Risk factors for the development of DCM apart from
Consequences of these alterations in cardiac structure breed may include taurine deficiency (in cocker spaniels,
and function eventually include congestive heart failure Labrador and golden retrievers, or nontraditional DCM
(CHF) and arrhythmias (see Chapter 18). breeds), sustained tachyarrhythmias, myocarditis, or
chemotherapy (anthracyclines).

Epidemiology
Signalment
The prevalence of DCM among canine referral popula-
tions has been reported to be 0.3–1% (equivalent to 1–3 Dilated cardiomyopathy occurs predominantly in mid-
cases per 300 patients examined). Underreporting of sud- dle‐aged to older, medium‐ to large‐breed dogs. The
den death (SD) cases might result in underestimation of most commonly reported breeds in North America and
any figure, thus the true prevalence in the general dog Europe include the Doberman pinscher, IW, Great Dane,
population is unknown. Any prevalence data will be Newfoundland, boxer, Labrador and golden retrievers,
heavily influenced by the distribution of breeds and ages cocker spaniel, Scottish deerhound, Afghan hound, St
(prevalence increases with age) of the population under Bernard, German shepherd, Old English sheepdog,
study. The prevalence is high in certain breeds based on Airedale terrier, standard poodle, Rottweiler, and mastiff.
retrospective studies and prospective screening studies. Small‐breed dogs are uncommonly affected but sporadic
One European study of Irish wolfhounds (IW) found a cases can be found.
prevalence of 24%. In the Great Dane, prevalence has Age at diagnosis is typically between 4 and 8 years,
ranged from 12% to 36% in different geographic areas. depending on breed. Much younger and much older
Prevalence in Dobermans has ranged from 45% to 60% in dogs may certainly be affected, regardless of breed.
various studies. Some studies report overrepresentation Specific juvenile forms of DCM are described in the
of males, while in Dobermans there are gender differ- Portuguese water dog, Doberman, and toy Manchester
ences in how the disease manifests and at what age, with terrier, resulting in rapidly progressive CHF or SD at
females having a higher incidence of ventricular arrhyth- weeks to months of age. Sporadic cases in very young
mias as the sole abnormality and males manifesting echo- dogs of other breeds may occur, and should prompt
cardiographic abnormalities and CHF at an earlier age. consideration of viral myocarditis or primary tachyar-
The mode of inheritance is known for specific breed rhythmia as an underlying cause.
groups. In the Doberman and the Newfoundland, DCM Many studies report a gender bias in males. While this
is inherited as an autosomal dominant trait with incom- is not corroborated in all studies of individual breeds, it
plete penetrance. Both X‐linked and autosomal dominant is the case for the majority of studies involving multiple
patterns of inheritance have been suggested in the Great breeds. Male Dobermans and IWs may be affected at an
Dane, whereas inheritance is autosomal recessive with earlier age than females.
sex‐specific alleles in the IW. The juvenile form described
in the Portuguese water dog is autosomal recessive. History and Clinical Signs
The natural history of the disease is such that dogs
experience a preclinical or occult phase during which History may be unremarkable and preclinical cases iden-
echocardiographic or electrocardiographic evidence of tified by an incidental abnormality on physical exam
the disease is present (see Diagnosis) but clinical signs (such as a heart murmur, gallop, or arrhythmia) or by
are absent (ACVIM stage B). The length of this phase is prospective screening in high‐risk breeds. Some of these
variable and likely extends over months to years, depend- dogs in the preclinical stage may have surprisingly pro-
ing on the breed. In the Doberman, previous retrospec- found cardiac dysfunction in the absence of clinical signs.
tive work suggested a median preclinical phase of just More often, dogs are presented because of clinical signs
over a year whereas new prospective clinical trial data of a fairly acute nature. Respiratory signs are the most
suggest a median of two years with the use of pimobendan. common, including coughing and/or increased respira-
The preclinical phase can be quite prolonged in the IW, tory rate or effort due to pulmonary edema from left‐
averaging 48 months in one trial. sided CHF. With severe pulmonary edema, expectoration