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Cardiomyopathy: An Overview

Cardiomyopathy is a serious disease in which the heart muscle becomes inflamed and doesn't work as it should. The term "cardiomyopathy" literally means "sick heart muscle." There are two types of cardiomyopathy in dogs: Hypertrophic Cardiomypathy, and Dilated Cardiomyopthy.

In Hypertrophic Cardiomyopathy the walls of the chambers of the heart thicken, leading to a decrease in pumping efficiency. This form of cardiac failure is quite rare in dogs.

In Dilated Cardiomyopathy (DCM) the chambers of the heart increase in size and the muscles that form the walls of the heart stretch thinner. Canine DCM is one of the causes of Congestive Heart Failure (CHF) and is the more common type of cardiomyopathy in dogs. DCM usually affects the left side of the heart. DCM in the right side of the heart can occur, but is much rarer. In some dogs DCM affect both sides of the heart.

Large and giant breeds are at greater rick of developing DCM, including Doberman Pinschers, Irish Wolfhounds, Scottish Deerhounds, Boxers, Afghan Hounds, Old English Sheepdogs, Great Danes, Dalmatians, Newfoundlands, and Saint Bernards. English and American Cocker Spaniels and Portuguese Water Dogs also develop DCM.

The average age of onset is 4 to 10 years, although Portuguese Water Dogs can acquire the disease at a very young age. DCM is very serious and the mortality rate, even of treated cases, is very high.

Causes of Dilated Cardiomyopathy

The vast majority of cases of DCM are idiopathic (having no known cause,) but certain breeds appear to have an inherited predisposition. Other possible causes may include:

  • Deficiency of metabolic substrates (particularly taurine)
  • Myocarditis (inflammation of the myocardium)
  • Global myocardial ischemia (lack of blood supply to the heart)
  • Toxic injury to the heart muscle cells that can be caused by some drugs like doxorubicin or potassium iodide toxicity
  • Persistently abnormal heart rhythms such as sustained ventricular or supraventricular tachycardia
  • Chronic hypokalemia (low blood potassium)

Prevention of Dilated Cardiomyopathy

There is no way to prevent DCM; however, early screening of dogs of breeds that have a high incidence of DCM may help identify important changes prior to the onset of signs. Affected dogs should not be bred.

Symptoms of Dilated Cardiomyopathy

Early in the disease process there may be no clinical signs. However, there are signs you can look for:

  • Shortness of breath
  • Coughing, excess panting
  • Exercise intolerance
  • Collapse
  • Abdominal distension
  • Lethargy
  • Reluctance to lie down or inability to rest comfortably
  • Loss of appetite

Any of these symptoms may mean your dog needs emergency care.

Diagnosing Dilated Cardiomyopathy

A cardiac exam by a veterinarian can detect abnormal heart sounds (when present) and many signs of heart failure. Diagnostic tests are needed to recognize Dilated Cardiomyopathy and exclude all other diseases.

Other tests to exclude other diseases include:

  • Thorough physical examination: Veterinarian would listen for heart murmurs, abnormal heart sounds, and irregular heart beat.
  • Complete blood count (CBC): This is used to identify anemia, infections or inflammations.
  • Serum biochemistry tests: This blood test is especially important if there is heart failure or complications in other organs.
  • Taurine concentration test (blood test): Deficiency may be a cause of heart failure.
  • Urinalysis: Used to evaluate kidney function.
  • Heartworm test: This test is given if prevention is not used
  • Radiographs: X-rays of the chest to see if there is an enlarged heart and/or fluid accumulation in the chest.
  • Electrocardiogram (EKG): Results may be abnormal in cases of serious heart disease, but can be normal in other dogs with heart disease.
  • Echocardiogram: An ultrasound examination of the heart, which can establish the diagnosis of DCM.

Your veterinarian may recommend additional diagnostic tests to exclude or diagnose other conditions, including:

  • Congenital (at birth) heart disease
  • Chronic valve disease
  • Hypertensive heart disease (heart enlargement from high blood pressure)
  • Pericardial (lining of the heart) diseases
  • Mediastinal masses (tumors in the front part of the chest cavity)
  • Myocarditis (inflammation of the heart muscle, which is very difficult to diagnose)
  • Moderate to severe anemia
  • Heartworm disease
  • Fever (fever can result in a heart murmur)

In some cases, a heart murmur (usually soft), other abnormal heart sounds, and/or irregular heart rhythm may be heard on examination. This is more likely as the disease progresses.

Treating Dilated Cardiomyopathy

There is no cure for DCM. Treatment is aimed at controlling symptoms and delaying the onset of heart failure. Dogs may be treated at home with a combination of the following medications:

  • Furosemide (Lasix): Maintenance dose of Lasix given orally promotes diuresis (urinating excess fluid). Excess fluid in the blood vessels may lead to pulmonary edema (fluid in the lungs). Kidney values should be monitored while on this medication.
  • ACE inhibitors (Enalapril): Helps delay the onset of heart failure by a number of mechanisms. Kidney values should also be monitored while on this medication.
  • Digoxin: May be used to help improve contractility of the heart, or to help control arrhythmias.
  • Calcium channel blockers and Beta blockers: These medications are used to help control cardiac arrhythmias.
  • Nutritional supplementation: Taurine, L-carnitine, and coenzyme Q-10 may be beneficial; however, the effects of these supplements on canine DCM have not been proven.

Dogs that present to the veterinarian in heart failure are treated with oxygen therapy in addition to Furosemide. Therapy is always tailored to the needs of the dog. Since this disease is not reversible and heart failure tends to be progressive, the intensity of therapy (for example, the number of medicines and the dosages used) usually must be increased over time.

Caring for Dogs with Dilated Cardiomyopathy

Administer prescribed medications as directed by your veterinarian. Watch for difficulty in breathing, increase in coughing, lethargy or sudden inability to use one or more limbs. Observe the breathing rate when your pet is relaxing. Schedule regular veterinary visits to monitor your dog?s condition.

The AKC Canine Health Foundation and Dilated Cardiomyopathy

The AKC Canine Health Foundation has funded 13 grants to study dilated cardiomyopathy. These grants are meant to increase the current knowledge about the inheritance and genetic causes of dilated cardiomyopathy, as well as novel treatment methods.

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