Dilated cardiomyopathy is a disease of the heart muscle itself. The term
"dilated cardiomyopathy" probably encompasses several different diseases, each
having, however, the same end result: the heart muscle gradually becomes
dysfunctional over time. Dilated cardiomyopathy has been recognized in a number
of species, including dogs, cats and human beings (artificial heart transplant
recipient Dr. Barney Clark had this disease). In cats, dilated cardiomyopathy is
due primarily to a dietary deficiency of the amino acid taurine. In dogs, the
cause of the disease is generally unknown but the disease itself is highly
breed-specific, being observed most commonly in Doberman Pinschers, Boxers,
Great Danes, Irish Wolfhounds, Saint Bernards, Cocker Spaniels, Golden
Retrievers and German Shepherd Dogs. More than 90% of cases of canine dilated
cardiomyopathy are confined to these eight breeds. Dilated cardiomyopathy occurs
only rarely in mixed-breed dogs. The disease is most likely genetic in origin,
although this has not been proved and the mode of inheritance has yet to be
documented.
Dilated cardiomyopathy has been studied most thoroughly in Doberman Pinschers.
In this breed it appears that the disease is of relatively early onset (2 to 5
years of age), after which it progresses slowly and insidiously over the ensuing
several years. Only an echocardiogram or a 24-hour recording of an ECG (Holter
monitor) can identify the illness at this early stage. On an echocardiogram, the
walls of the left ventricle usually exhibit an impaired ability to contract. A
Holter monitor often will reveal an increased number of premature ventricular
contractions (PVCs), which are produced by the diseased heart muscle. As the
illness progresses the affected heart muscle grows weaker and weaker, while the
left ventricle compensates by enlarging. In male dogs, dilated cardiomyopathy
usually becomes severe between 5 and 8 years of age. Females often show no
clinical signs until they are about 9 to 12 years of age. The signs themselves
often appear suddenly, as if the affected animal has become ill only within the
last few days; in reality, the dogs by this time have already progressed through
the early stages of the disease and are now in severe heart failure.
Heart failure often can be controlled by medication (diuretics, ACE inhibitors,
digoxin). If the disease is very severe, however, an affected dog may not
survive the initial hospitalization. Even if the illness is initially
controlled, the long-term prognosis is poor; most affected Dobermans will die
within 1 to 6 months. The prognosis in other breeds can be somewhat better, but
in almost all cases the disease is ultimately fatal. Exceptions to the rule are
some Cocker Spaniels that are taurine-deficient and respond to the
administration of taurine and carnitine (an amino acid required for energy
production), some Boxers (and rarely other breeds) that may respond to
carnitine, and a few dogs that are taurine-deficient and that may respond to
taurine therapy.