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.
** Has not occurred to any TE dogs, but has occurred in the USA.