Dilated Cardiomyopathy (DCM) in Dogs

Overview of Canine Dilated Cardiomyopathy (DCM)

Dilated cardiomyopathy (DCM) is a disease characterized by dilation or enlargement of the heart chambers and markedly reduced contraction. The left ventricle is most always involved. Advanced cases demonstrate dilation of all cardiac chambers.

DCM is very common in dogs, representing the most common reason for congestive heart failure (CHF). This heart disease also can cause heart valve leakage causing heart murmurs or abnormal electrical activity of the heart-producing arrhythmias (irregular or abnormal heartbeats). Large and giant breed dogs, especially males, are predisposed. Doberman pinschers, Irish wolfhounds, Scottish Deerhound, boxer, Afghan hound, Old English Sheepdog, Great Danes, Dalmatians, Newfoundlands, and Saint Bernards are common breeds. English and American cocker spaniel breeds and Portuguese water dogs also develop DCM.

The clinical condition of canine DCM can range from overtly healthy (occult disease) to severe heart failure. Some dogs experience primary electrical disturbances (arrhythmia) such as atrial fibrillation or ventricular tachycardia.

The disease is thought to be genetic in Doberman pinschers, Irish wolfhounds, Newfoundlands, boxers, and Portuguese water dogs. The disease is sometimes seen in Dalmatians fed a low protein diet and in cocker spaniels and gold retrievers with taurine deficiency.

The average age of onset is 4 to 10 years, although Portuguese water dogs can acquire the disease when very young.

DCM is very serious and the mortality rate, even of treated cases, is very high.

What to Watch For

Symptoms of Dilated Cardiomyopathy in dogs may include:

• Shortness of breath
• Coughing
• Exercise intolerance
• Collapse
• Abdominal distension
• Lethargy
• Loss of appetiteThe advent of these problems should alert you that a serious emergency is at hand.

Diagnosis of Dilated Cardiomyopathy (DCM) in Dogs

Diagnostic tests are needed to recognize dilated cardiomyopathy and exclude all other diseases. Tests may include:

• Complete medical history and physical examination including auscultation of the heart and lungs
• Thoracic radiographs (chest X-rays)
• An electrocardiogram (EKG)
• Arterial blood pressure
• Packed cell volume test or a complete blood count (CBC)
• Serum biochemistries, which are blood tests that are especially important if there is heart failure, thromboembolism or complications in other organs
• Echocardiogram (ultrasound of the heart) to establish the diagnosis and may require referral

Treatment of Dilated Cardiomyopathy (DCM) in Dogs

• In advanced cases leading to congestive heart failure, drug therapy with a diuretic, angiotensin converting enzyme inhibitor (such as enalapril or benazepril and/or digoxin is prescribed. The diet is changed to reduce sodium intake. Additional drugs may be added such as the diuretic/hormone antagonist, spironolactone. Nutraceuticals such as taurine pills or L-carnitine are recommended in very specific instances.
• In cases of “arrhythmogenic” dilated cardiomyopathy, drugs that regulate the electrical heart rhythm are indicated.
• In “occult” dilated cardiomyopathy (healthy dog with early DCM diagnosed by echocardiography), an angiotensin converting enzyme inhibitor drug and possibly a beta-blocker drug is recommended to protect the heart muscle from further damage.

Home Care and Prevention

• Administer any veterinary prescribed medications.
• 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 the condition.

In-depth Information on Dilated Cardiomyopathy (DCM) in Dogs

Related Symptoms or Diseases

DCM is thought to be the result of diverse processes that affect heart muscle cell function. The vast majority of cases of DCM are idiopathic, which means they have no known cause and are probably predisposed by genetic factors. Causes may include:

• Deficiency of metabolic substrates (taurine)
• Myocarditis (inflammation of the myocardium)
• Severe 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)
• IdiopathicA number of other diseases can be easily confused with dilated cardiomyopathy unless an appropriate diagnostic evaluation is completed. Diagnostic tests should help exclude the following conditions from consideration:
• Congenital heart diseases (birth defects)
• Chronic valve disease
• Hypertensive heart disease (heart enlargement from high blood pressure)
• Pericardial diseases (the lining around the heart)
• Mediastinal masses (tumors in the front part of the chest cavity)
• Myocarditis (inflammation of the heart muscle – a most difficult condition to diagnose)
• Moderate to severe anemia (anemia can cause heart failure)
• Heartworm disease
• Fever (fever can result in a heart murmur)

Diagnosis In-depth of Canine Dilated Cardiomyopathy

A complete medical history should be obtained and your veterinarian should complete a thorough physical examination. Medical tests are needed to establish the diagnosis, exclude other diseases, and determine the impact of this disorder on your pet. The following diagnostic tests are often recommended:

• A thorough physical examination. Special attention is paid to auscultation (stethoscope examination) of the heart. Heart murmurs, abnormal heart sounds, and irregular heart rhythms may indicate a problem with the heart.
• Thoracic radiographs. X-rays of the chest identify heart enlargement and fluid accumulation in the chest.
• An electrocardiogram (EKG). While this test is often abnormal in cases of serious heart disease, it can be normal in many other pets with heart disease.
• An echocardiogram. An ultrasound examination of the heart is required for establishing the diagnosis of DCM. Important examination issues include the size of the heart and the ability of the ventricle to contract. This examination may require referral to a specialist.Your veterinarian may recommend additional diagnostic tests to exclude or diagnose other conditions, or to understand the impact of dilated cardiomyopathy on your pet. These tests insure optimal medical care and should be selected on a case-by-case basis. Examples include:
• Complete blood count (CBC). This blood test may be needed to identify anemia or other problems such as infections or inflammations.
• Serum biochemistry tests. This blood test is especially important if there is heart failure or complications in other organs.
• Taurine concentrations may be determined from a blood sample.
• Urinalysis to evaluate kidney function
• Heartworm test if prevention has not been given

Therapy In-depth of Caine Dilated Cardiomyopathy

The principles of therapy depend on the presentation or current condition of the pet. If symptoms are severe, hospital therapy is necessary. Precise treatments depend on the problems caused but may include: treatment of congestive heart failure, control of an arrhythmia or abnormal heart rhythms, management of kidney failure, treatment of low blood pressure or shock caused by severe heart failure, or treatment of complications of thrombosis (blood clots).

• Hospital treatment of severe congestive heart failure includes oxygen, the diuretic furosemide (Lasix®), and often nitroglycerin or nitroprusside. If blood pressure is low or heart function very bad, the drug dobutamine, which is a stimulant of heart contraction, is often recommended for 24 to 72 hours. Therapeutic thoracocentesis taps accumulated fluid from the chest cavity to improve breathing, and is the best treatment for a large pleural effusion (fluid around the lungs).
• When present, chronic congestive heart failure (CHF) is managed with drug therapy, including a diuretic, pimobendan angiotensin converting enzyme inhibitor, such as enalapril or benazepril ,and digoxin. Beta-blocker drugs such as carvedilol , metoprolol or atenolol is also used to help minimize “cardiotoxic” effects.
• The diet is changed to reduce sodium intake.
• Nutriceuticals like taurine pills, L-carnitine , and/or Omega-3 fatty acids are recommended in some instances.
• In cases of arrhythmogenic dilated cardiomyopathy, drugs that regulate the electrical heart rhythm are indicated. If atrial fibrillation is present, digoxin often combined with either a beta blocker or a calcium channel blocker drug is prescribed.
• The dog with “occult” dilated cardiomyopathy is healthy, but has been diagnosed with early DCM by echocardiography. There is evidence that an angiotensin-converting enzyme inhibitor drug can protect the heart muscle from further damage and enlargement. The drugs enalapril (Enacard) and benazepril are the most often used for this purpose. A beta-blocker drug is also effective in preventing further heart muscle damage, but must be chosen and dosed very carefully. See your veterinarian about that.

Follow-up Care for Dogs with Dilated Cardiomyopathy (DCM)

Optimal treatment for your dog with dilated cardiomyopathy requires a combination of home care and professional veterinary care. Follow-up can be critical. Administer prescribed medication and alert your veterinarian if you are experiencing problems treating your pet. Optimal follow-up care often involves the following:

• Administering prescribed medications. Remember – erratic administration of medication is a common reason for treatment failure.
• Observe your pet’s general activity level, appetite, and interest. These are quality-of-life issues of importance to you and your pet.
• Watch your dog for labored or rapid breathing or for coughing. If possible, learn to take a breathing rate when your pet is resting. Ask your veterinarian about this.
• Follow-up chest X-rays may be required to monitor the response to therapy.
• A blood digoxin test is done approximately 7 to14 days after initiation of therapy to identify therapeutic vs. toxic drug levels.
• Blood chemistry is checked periodically to monitor the effects of drugs on the kidneys and electrolytes like potassium. If kidney values or electrolytes are abnormal, the dose of diuretic must often be lowered.
• Arterial blood pressure measurements should be checked periodically.
• An echocardiogram should be done initially and repeated periodically (3 to 6 months after diagnosis and again in 9 to 12 months). Some dogs experience improvement though most show progression of heart muscle disease.
• Of course, the precise follow-up depends on the severity of your dog’s disease, response to therapy, your veterinarian’s recommendations, and your own views.

Prognosis

The prognosis for dogs with DCM is guarded. From diagnosis, the average survival time is 3 months to 2 years.