Dilated Cardiomyopathy

Canine cardiomyopathy is well reported in domestic dogs. It is a diverse group of disorders (dilated cardiomyopathy, hypertrophic cardiomyopathy). The term cardiomyopathy was originally used to describe heart muscle disease of unknown cause.

Dilated cardiomyopathy (DCM) is a condition in which the heart becomes weakened and enlarged, and cannot pump blood efficiently. The decreased heart function can affect the lungs, liver, and other body systems. There are two histologically distinct forms of canine DCM: 1) the cardiomyopathy of Boxers and of Doberman Pinschers, corresponding to the "fatty infiltration-degenerative" type of DCM and 2) the form detected in many giant, large-, and medium-sized breeds (including some Boxers and Doberman Pinschers), which can be classified as the "attenuated wavy fiber" type of DCM when the heart muscle fibers lose their contractile ability.

The fatty infiltration-degenerative type of DCM was first described as "boxer cardiomyopathy". In this type of DCM the muscle fibers degenerate and are replaced by fatty infiltrations. The attenuated wavy fiber type of DCM seems to be the most prevalent form of DCM because many more breeds are afflicted with this disease compared with the fatty infiltration-degenerative type of DCM.

Dilated cardiomyopathy is one of the most common acquired heart diseases of dogs. The diseases is typically seen in middle-aged dogs. DCM has been recognized in many breeds85 but seems to be more prevalent in certain breeds such as English Cocker Spaniels, Doberman Pinschers, Boxers, Newfoundlands, and Irish Wolfhounds. Dogs with idiopathic dilated cardiomyopathies are prone to life-threatening arrhythmias and sudden death.

Causes of Dilated Cardiomyopathy

The cause is generally not established in the individual case of DCM in dogs. However, several causes have been proposed, including genetic factors, nutritional deficiencies, metabolic disorders, immunologic abnormalities, infectious diseases, and drug-, toxin-induced. Canine DCM has been suspected to be an inherited disease because of its prevalence in certain breeds and in specific families of dogs. An autosomal dominant mode of transmission has been reported in the Irish Wolfhound,18 Newfoundlands,24 and Doberman Pinschers. In the juvenile Portuguese Water Dog, an autosomal recessive transmission has been documented. Canine X-linked muscular dystrophy may cause severe cardiac disease. Nutritional abnormalities, i.e., carnitine or taurine deficiencies (or both), have been described in humans, dogs, and cats. Metabolic disorders associated with DCM include hypothyroidism, diabetes mellitus, and pheochromocytoma.

Deficiency of the amino acids (carnitine) has been implicated as a major contributing factor to dilated cardiomyopathy and has been described as a breed-specific condition in various breeds.

Signs

Signs may include difficulty breathing, cough, unwillingness to move, depression, exercise intolerance, loss of appetite, fainting, weight loss, increased thirst and pot-belly appearance due to the accumulation of fluid in the abdomen.

Diagnosis of Dilated Cardiomyopathy

The clinical diagnosis is based on findings on echocardiographic and Doppler examinations, with the active exclusion of other acquired or congenital heart diseases. However, the echocardiographic criteria for the diagnosis of DCM are not wholly specific for the disease, and histologic examination may be necessary for final diagnosis. If not diagnosed early , the condition can lead to sudden death or congestive heart failure.

Prognosis for Dilated Cardiomyopathy

Survival times in dogs with DCM vary from days to several years. Medical treatment, especially the use of angiotensin-converting enzyme inhibitors and β-blocking agents are used to control the symptoms. Although canine dilated cardiomyopathy is generally progressive and fatal, there have been a few cases of several Golden Retrievers with reversible taurine-deficient dilated cardiomyopathy. Significant improvements were recorded within 3 to 6 months of starting taurine supplementation. The dogs regained substantial systolic function, and four were weaned off all cardiac medications except taurine.

Prospective screening of dogs from lines with familial prevalence of DCM may identify dogs with pre-clinical ("occult") DCM. Dogs with other echocardiographic abnormalities or arrhythmias may also be identified. It is clear that dogs, like humans, have a prolonged pre-symptomatic phase of the disease extending over years.

Veterinary cardiologist Mark Oyama, left, has developed the first molecular portrait of multiple gene activity in diseased heart tissue taken from dogs near death from a devastating disease. The discovery at Illinois sheds new light on the heart's response to dilated cardiomyopathy (DCM), a disease of large-breed dogs.

References

1. A. Tidholm and L. Jönsson Albano Animal Hospital of Stockholm. Histologic Characterization of Canine Dilated Cardiomyopathy
2. Belanger MC, Ouellet M, Queney G, Moreau M. Taurine-deficient dilated cardiomyopathy in a family of golden retrievers.
3. Technique provides new look on response of diseased canine heart (www.news.uiuc.edu/news/05/0705genes.html)