What is cardiomyopathy?
Cardiomyopathy is the name given to any disease affecting the heart muscle. This is the most common form of heart disease seen in cats; it is the most common cause of heart failure. Unlike dogs and humans, disease of the heart valves is not very common in cats.
Three types of primary cardiomyopathy are seen most commonly in cats:
Most feline cardiomyopathies are primary diseases, meaning they are the result of genetics or unknown causes. Three types of heart disease account for nearly all of the primary cardiomyopathies:
Hypertrophic cardiomyopathy is diagnosed in 85 to 90 percent of primary cardiomyopathy cases. Many times there is no explanation other than the strong likelihood of genetic influence. This cardiomyopathy is characterized by a thickening of the muscle tissue associated with the left ventricle (lower chamber of the heart).
Restrictive cardiomyopathy accounts for approximately 10 percent of the primary heart muscle diseases; it is caused by the excessive buildup of scar tissue on the inner lining and muscle of a ventricle. This prevents the heart muscle from relaxing completely which does not allow blood to flow normally between chambers. Most often affecting older cats, this disorder is also characterized by severely enlarged atria (upper heart chambers) and reduced cardiac filling and pumping efficiency.
Dilated cardiomyopathy is comparatively rare, probably accounting for only one or two percent of primary cardiomyopathy cases. It is characterized by an enlarged left ventricle with a thin muscle wall. The weak muscle does not pump blood forward through the heart very effectively. The heart will appear enlarged on radiographs. This disease has been associated with taurine deficiencies in the diet. Taurine is an amino acid that is found in meat; it must be supplied in the cat's diet.
Causes of secondary cardiomyopathy may include:
- Hyperthyroidism - tumors of the thyroid gland produce excess thyroid hormone which causes metabolism to speed up. The heart beats faster, leading to enlargement of the heart muscle and hypertrophic cardiomyopathy. These cats commonly also have hypertension and kidney disease.
- Hypertension - high blood pressure can be seen with hyperthyroidism or kidney disease which can lead to hypertrophic cardiomyopathy. High blood pressure affects one in eight cats over age nine.
- Anemia - lack of red blood cells carrying oxygen causes the heart to work harder.
- Acromegaly - increased growth hormone production (usually from a pituitary gland tumor) causes heart enlargement and heart failure.
- Toxins - may damage the heart muscle or cause inflammation of the heart muscle. Some chemotherapy drugs and anti-viral drugs can damage the heart muscle.
- Cancers - lymphoma and other cancers can infiltrate the heart muscle.
- Viral infections - FIV (Feline Immunodeficiency Virus) has been associated with viral myocarditis (inflammation of the heart muscle).
Are certain cats more likely to develop heart disease?
- Maine Coon cats, Persians, and Ragdolls have a genetic predisposition to develop hypertrophic cardiomyopathy. Genetic tests may help identify whether your cat has an increased risk of HCM, but this does not guarantee he will get the disease.
- Males are much more likely than females to have heart disease.
- Older cats are more likely to have heart disease than younger cats, although predisposed breeds may show disease at a young age.
What are the symptoms of cardiomyopathy in cats?
Symptoms can vary from none to sudden death. Early warning signs that might be noticed can include:
- Heart murmur heard during veterinary exam - not all cats will have a murmur.
- Abnormally high heart rate.
- Skipped beats or abnormal rhythm noticed on auscultation (listening to the heart).
- Panting or open-mouth breathing.
- Exaggerated respiratory effort.
- Increased respiratory rate.
- Cold legs and feet due to poor circulation.
- Pale mucous membranes due to poor circulation.
- Exercise intolerance.
- Inability to move the hind legs which may be accompanied by severe pain - this means a blood clot has lodged in the arteries supplying the hind legs.
- Loss of appetite.
- Gagging - Coughing is rarely a sign of heart disease in cats - this is more likely to be associated with airway disease.
How is cardiomyopathy diagnosed in cats?
If cardiomyopathy is suspected based on symptoms and physical examination, blood will be drawn to check for kidney disease, hyperthyroidism, and anemia. Blood pressure should be measured to check for hypertension. Radiographs are not generally diagnostic, unless the cat has dilated cardiomyopathy which can be seen on x-rays. An electrocardiogram will show if there are abnormalities in the rate or rhythm of the heart beat. Ultimately, an echocardiogram or ultrasound of the heart will be needed to diagnose the condition.
What treatments are used for cardiomyopathy in cats?
Although there is no known cure, a specialized care plan can help manage clinical signs of the condition in your cat. Treatment goals include controlling the heart rate, eliminating fluid buildup in the lungs from congestive heart failure, and preventing the formation of blood clots.
Any underlying conditions such as hypertension, hyperthyroidism, and kidney disease must also be treated.
Medication can help manage cardiomyopathy, and can be administered orally to stable patients or by injection in more serious situations. The cardiologist will determine which medications are appropriate for each individual pet.
Unfortunately, no therapy has been shown to prevent the progression of cardiomyopathy, even when started before clinical signs are observed.
Supplements to support cardiac function include:
- Omega 3 fatty acids - found in fish oil or fish
- Taurine - this is an essential amino acid and must be included in the diet of cats. Meat, fish, and organs contain taurine.
- Cats should be fed a species-appropriate, high-meat diet.
- CoQ10 - This antioxidant has been shown to be cardioprotective.
What is the prognosis if my cat is diagnosed with cardiomyopathy?
The prognosis for cats with heart disease is extremely variable. Some cats with no symptoms can remain stable and survive for years. Cardiomyopathy is generally a progressive disease with a worse prognosis once the cat develops heart failure. Cats with severe disease can sometimes go months or years without symptoms, while others will deteriorate very quickly.