Dilated Cardiomyopathy in Dogs
Veterinary & Aquatic Services Department, Drs. Foster & Smith

What is dilated cardiomyopathy in dogs?

Dilated cardiomyopathy (DCM) is a condition in which the heart's ventricular walls are stretched, causing the walls to become thinner. As the walls become thinner, the whole heart enlarges. Think of the heart as a balloon: in dilated cardiomyopathy, the walls become very thin as the balloon expands.

DCM is defined by its name, literally: dilated=stretched or expanded, cardio=heart, myo=muscle, pathy=disease. The ventricles are the primary pumping chambers of the dog's heart. In most cases of dilated cardiomyopathy in dogs, the left ventricle is the primary chamber affected but both ventricles can be involved. The left ventricle is the chamber of the heart that receives freshly oxygenated blood from the lungs via the upper chamber of the heart; the left atrium. It is then the left ventricle's job to pump this blood out of the heart and on to the rest of the body. The left ventricle is normally very muscular and an efficient pumping mechanism. When the ventricular wall is dilated as a result of DCM, it loses its ability to efficiently pump the required amount of blood. DCM can also affect the valves that separate the ventricle from the atrium. When this happens, blood begins to back up in the circulatory system. This has a negative effect on the dog's heath. DCM is one of the most common heart diseases in dogs.

Normal Heart Dilated Cardiomyopathy       
illustration of heart illustration of heart
Left atrium
Left ventricle
Pulmonary artery
Pulmonary vein
Right atrium
Right ventricle
Vena cava
NOTE: Ventricles enlarged, with thin walls

Which dogs get dilated cardiomopathy?

There appear to be several dog breeds that are genetically predisposed to DCM. These breeds include Great Danes, Doberman Pinschers, Irish Wolfhounds, Boxers, Newfoundlands, St. Bernards, Boxers, Dalmatians, Portuguese Water Dogs and Cocker Spaniels. While these breeds tend to experience DCM more than others, DCM is not limited to these breeds. Any of the giant or larger breed dogs can be affected by DCM, but it is less common in smaller breed dogs. DCM typically affects dogs between the ages of 6-8 years although this condition has been diagnosed in dogs as young as three. Male dogs tend to be affected by DCM at a higher rate than females.

What causes dilated cardiomyopathy in dogs?

BoxerBecause there is such a strong breed association with DCM, this condition is most likely inherited although the situation is unique in each breed. In other words, there is no common gene across dog breeds or a universal genetic test for DCM in canines. A genetic test may need to be developed for each breed.

There are also a variety of other causes of DCM:

Nutritional deficiencies such as an inadequate amount of the amino acid Taurine can lead to DCM in some breeds of dogs, especially Newfoundlands and Cocker Spaniels. Taurine, an amino acid that is only derived from animal tissues, is required for the proper development of the heart muscle. Dog owners that have elected to feed their dogs a vegetarian diet need to be sure Taurine is supplemented in their dog's diet.

Certain medications, especially the anti-cancer drug doxorubicin, can cause DCM.

Certain infections can also result in dilated cardiomyopathy in dogs. Puppies, infected with canine parvovirus at two to four weeks of age, may develop dilated cardiomyopathy, but this is very rare. Dogs of any age infected with an organism called Trypanosoma (the disease is called trypanosomiasis or Chagas disease) can develop DCM.

What are the effects of dilated cardomyopathy in dogs?

As stated above, DCM most commonly affects the left ventricle of the dog's heart (although both ventricles may become involved). When the left ventricle is not able to pump its required amount of blood, because of DCM, this creates a pressure imbalance within the blood vessels and fluids will escape the blood vessels and enter the surrounding tissues. In the case of the left ventricle, these fluids will enter the lung tissue causing pulmonary edema. In addition, the much needed oxygenated blood is not pumped out to the body affectively lowering the oxygen that is available to the body's tissues. If the right ventricle is affected, the fluids exit the blood vessels of the body and enter the tissues of the body; particularly in the abdomen. As dilated cardiomyopathy progresses, congestive heart failure develops.

What are the symptoms of dilated cardiomyopathy in dogs?

There are two stages to canine DCM each with unique symptoms.

The occult phase is marked by no obvious symptoms. The heart does, however, undergo several changes that are evident using diagnostic equipment such as electrocardiography (ECG) and an echocardiography (ultrasound). The walls of the left atrium and ventricle will expand. The heart's ability to contract will be reduced. The heart may also produce pre-mature ventricular contractions. The length of the occult phase is variable lasting months to years. The occult phase ends with the appearance of the first clinical sign.

The second phase of dilated cardiomyopathy in dogs is the overt phase. Generally speaking, the clinical signs of DCM are a loss of appetite, increased heart rate, pale gums, exercise intolerance, difficulty breathing and fainting. If the left ventricle is affected, the dog may also develop a dry cough. If the right ventricle is involved, the dog will develop ascites which is an accumulation of fluid in the abdomen, making the abdomen appear swollen. At times, the only symptom of DCM is the death of the dog.

How is dilated cardiomyopathy in dogs diagnosed?

DCM is diagnosed using ECG. An ECG measures the electrical impulses of the heart. A normal heart beat is very obvious and highly predictable on an ECG as are any abnormalities such as ventricular pre-mature contractions which are common with DCM. To help diagnose DCM, dogs may wear what's called a Holter monitor. This device is an ECG that records and tracks the dog's heartbeat and is worn by a dog for a period of 24 hours. At the end of the test, the dog's heartbeat can be evaluated through the entire time period.

Radiographs or x-rays, are used to evaluate the size and shape of the dog's heart. DCM can produce a highly suggestive cardiac shape. As the walls become thinner, they stretch and the outline of the heart actually is larger than normal.

Echocardiography can be helpful to detect physical changes to the heart. This technology can also reveal the thickness of the ventricular wall and the functionality of the heart valves.

The dog's blood chemistry may reveal evidence of dilated cardiomyopathy as the serum electrolyte values may change.

Hypothyroidism may be a concurrent disease, and the level of thyroid hormone (T4) will be decreased.

How is dilated cardiomyopathy in dogs treated?

Treatment of DCM in dogs is largely symptomatic. A heart that has developed DCM is not able to perform its main function which is pumping blood throughout the dog's body. Therefore, medical treatment involves strengthening the heart's contractions, lowering the pressure in the body's blood vessels and lowering the body's overall fluid load. This can be accomplished with medications that target these issues. These medications include diuretics such as furosemide, plus drugs that act on the heart and blood vessels such as pimobendan and ACE inhibitors like enalapril.

If the DCM is the result of a nutritional deficiency, then the dog will need to be supplemented with taurine, and commonly L-carnitine as well.

What is the prognosis for a dog with dilated cardiomyopathy?

The prognosis for dogs that have DCM is guarded. DCM is a progressive, irreversible disease that ultimately leads to the death of the animal. The survival of the patient depends on the stage of the DCM when the diagnosis is made, the breed of the dog, what type of DCM the dog has developed and the owner's willingness to treat the dog. Each case is different so each prognosis will be different. If your dog is diagnosed with DCM, discuss his prognosis and an appropriate treatment plan with your veterinarian.

References and Further Reading

Martin, MWS; Stafford Johnson, MJ; Strehlau, G; King, JN. Canine dilated cardiomyopathy: A retrospective study of prognostic findings in 367 clinical cases. Journal of Small Animal Practice, August 2010;51(8):428-436.

Oyama, MA. Canine Cardiomyopathy. In Tilley, LP; Smith FWK; Oyama, MA; Sleeper, MM. Manual of Canine and Feline Cardiology 4th Edition. Saunders Co. Philadelphia, PA; 2008; PP 139-149.

Palermo, V; Stafford Johnson, MJ; Sala, E; Brambila, PG; Martin, MWS. Cardiomyopathy in Boxer dogs: A retrospective study of the clinical presentation, diagnostic findings and survival. Journal of Veterinary Cardiology. March 2011;13(1):45-55.

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