Dilated Cardiomyopathy (DCM) in Cats

Overview of Dilated Cardiomyopathy in Cats (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.

Below is an overview of Dilated Cardiomyopathy in Cats (DCM) followed by in-depth information on the diagnosis and treatment of this feline heart disease.

DCM in cats is now comparably rare. In the past, feline dilated cardiomyopathy was due to dietary deficiency in the amino acid taurine and commonly affected breeds such as Burmese, Abyssinian, Siamese and domestic mixed breed cats. Today, reputable cat food companies assure their products are well supplemented with taurine, an essential dietary amino acid for cats.

DCM can occur in cats of any age – from 2 to 20 years. The mean age of onset is approximately 10 years. It appears to be more common in male cats.

Occasional cases of idiopathic DCM, which is cardiomyopathy of unknown cause, are observed in cats. Clinical signs include CHF and development of blood clots (thromboembolism) that obstruct blood flow to one or more legs.

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

What to Watch For

• Shortness of breath
• Coughing (uncommon in cats)
• Exercise intolerance
• Collapse
• Sudden onset of pain and paralysis, usually in the back legs
• Abdominal distension
• Lethargy
• Loss of appetite

The advent of these problems should alert you that a serious emergency is at hand.

Diagnosis of Dilated Cardiomyopathy in Cats

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
• Serum thyroxine (thyroid) test for cats greater than 7 years of age
• Whole blood taurine test in cats with DCM

Treatment of Dilated Cardiomyopathy in Cats (DCM)

• 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. Additional drugs may be added such as the diuretic/hormone antagonist, spironolactone.
• The diet is changed to reduce sodium intake.
• Nutriceuticals 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 cats with or at risk for thromboembolism, special treatments (anticoagulants) are needed.

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. Changes in attitude and appetite are often signs of problems in cats.

Schedule regular veterinary visits to monitor the condition.

Dilated cardiomyopathy in cats can be caused by taurine deficiency. This is often associated with exclusive feeding of a single (off brand or “special” brand) canine or human diet. Feed a balanced, high-quality cat food that is supplemented with taurine.

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

Related Symptoms or Diseases

DCM is thought to be the result of diverse processes that affect heart muscle cell function.

Causes may include:

• Deficiency of metabolic substrates (e.g. taurine)
• Idiopathic (occurring without known cause)
• 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 (e.g. doxorubicin, potassium iodide toxicity)
• Hyperthyroidism (chronic excess of thyroid hormone)
• Persistently abnormal heart rhythms such as sustained ventricular or supraventricular tachycardia (reversible after some weeks if rhythm is controlled)
• Chronic hypokalemia (low blood potassium) which may act by causing taurine deficiency in cats

The vast majority of cases of DCM are idiopathic and probably predisposed by genetic factors. Most reported cases of DCM in the cat have developed secondary to taurine deficiency, but current cases are usually unresponsive to taurine supplementation, indicating there is another reason for cases.

A 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 disease (birth defects)
• Feline hypertrophic cardiomyopathy (genetically programmed thickening of the heart muscle)
• Hyperthyroid heart disease in cats from thyroid tumors
• Feline restrictive cardiomyopathy (scarring or fibrosis of the heart muscle in cats)
• Hypertensive heart disease (heart enlargement from high blood pressure)
• Pericardial diseases, which affects the lining around the heart
• Mediastinal masses (tumors in the front part of the chest cavity)
• Myocarditis (inflammation of the heart muscle most difficult to diagnose)
• Moderate to severe anemia, which can cause heart failure, especially in cats
• Heartworm disease
• Fever, which can cause heart murmurs

Diagnosis In-depth

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) to identify heart enlargement and fluid accumulation in the chest
• An electrocardiogram (EKG). While this test is often abnormal with serious heart disease, it can be normal in many other pets with heart disease.
• An echocardiogram (ultrasound examination of the heart). This test is required for establishing the diagnosis of DCM. Important examination issues include the size of the heart and the ejection fraction (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.
• Thyroid test to exclude hyper-function
• Urinalysis to evaluate kidney function
• Heartworm test if prevention has not been given

Therapy In-depth

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 (abnormal heart rhythms), management of renal failure (kidney failure), treatment of hypotension (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 (a stimulant of heart contraction) is often recommended for 24 to 72 hours. Therapeutic thoracocentesis (tapping accumulated fluid from the chest cavity to improve breathing) 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, angiotensin converting enzyme inhibitor (such as enalapril. or benazepril, and digoxin. Pimobendan is another drug that may be used in some cats.
• The diet is changed to reduce sodium intake.
• Nutriceuticals (e.g. taurine pills, L-carnitine) are recommended in very specific 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.
• Cats with DCM are often affected by thromboembolism, and special treatments (anticoagulants) are needed. Blood clots are usually treated with medications to control pain and prevent expansion of the clot. “Clot-busting” drugs (TPA, streptokinase) have been used effectively in cats, but they have so many very serious side effects that they are essentially impractical.

Follow-up Care for Cats with Dilated Cardiomyopathy

Optimal treatment for your pet 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 cat for labored or rapid breathing or for coughing. If possible, learn to take a respiratory (breathing) rate when your cat 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 to 14 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 cats experience improvement though most show progression of heart muscle disease.
• If your cat was low in blood taurine, a repeated test should be done at one and three months to insure adequate supplementation.
• Switch to a taurine supplemented diet in cats with DCM.
• Of course, the precise follow-up depends on the severity of your cat’s disease, response to therapy, your vet’s recommendations, and your own views.