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Common Conditions - Articles of Interest - Cardiomyopathy in Pets

Cardiomyopathy in Pets

What is Cardiomyopathy?

Cardiomyopathy is a disease of the heart muscle.  It occurs in both dogs and cats and there are a number of different types.

Types and causes of Cardiomyopathy

There are a number of specific types of cardiomyopathy that occur in dogs and cats and therefore there are a number of causes as well.  Below is an outline of the types and their causes.

Cardiomyopathy in Dog

Dilated cardiomyopathy (DCM)

Dilated cardiomyopathy is by far the most common type of cardiomyopathy that occurs in dogs.  It involves a weakening of the heart muscle, an increase in the size of the heart chambers and a decrease in the heart’s ability to pump blood around the body.

The cause of most cases of DCM is not yet fully understood.  In some cases genetics are thought to play a role as some breeds such as Boxers, Doberman’s and Cocker Spaniels have a higher incidence of the disease.  Some drugs (eg. some chemotherapy drugs) and other toxins (eg. some plants) can cause it as well.  Most dogs that develop DCM are large breed dogs, although smaller breeds can also be affected.  Dogs that develop DCM have signs that include all or some of the following; lethargy, difficulty breathing, coughing, off their food, ascites (a belly full of fluid) and collapsing.

Diagnosis of DCM is made using x-rays and by doing an ultrasound of the heart.

Treatment of DCM is varied depending on the severity of the condition but usually involves the use of 1) a drug to make the heart beat stronger 2) a drug to help eliminate excess fluid that pools in the lungs.

Hypertrophic cardiomyopathy (HCM)

This is a rare type of cardiomyopathy that occurs in dogs.  The cause is unknown, however, a genetic basis is suspected.  In HCM the heart muscle wall thickens markedly.  This means that the heart chambers are smaller than normal and therefore, less blood can be pumped around the body.  Symptoms of HCM are similar to that of DCM, and again diagnosis is made using x-rays and a heart ultrasound.  Treatment of DCM involves the use of drugs that slow down the contraction of the heart and therefore allow the chambers to be filled with more blood to be pumped around the body.

Cardiomyopathy in Cats

Hypertrophic cardiomyopathy (HCM)

This type of cardiomyopathy is by far the most common in cats.  In cats with HCM the heart muscle becomes thicker.  There are a number of causes of this type of cardiomyopathy in cats.  The first is called primary cardiomyopathy.  The cause of primary hypertrophic cardiomyopathy is unknown in cats but a genetic basis is thought to be the most likely cause.  The other common cause of HCM in cats is due to a condition called hyperthyroidism.  Hyperthyroidism is a disease where cats develop a tumour on their thyroid gland that causes the release of an excessive amount of thyroid hormone.  This excessive amount of hormone is responsible for the speeding up of the cat’s metabolism, which includes the speeding up of heart rate.  Therefore, as the heart is working more quickly, its muscle starts to thicken up.

HCM in cats can be diagnosed by taking x-rays and doing an ultrasound of the heart.  The symptoms of HCM in cats are varied.  Some cats can have the disease but show no symptoms for years.  Others that have signs of the disease will have difficulty breathing, become lethargic and stop eating.

Treatment of HCM is similar to what is used in dogs.  Drugs are used to slow the heart down, also to decrease the strength of the heart contractions.  If hyperthyroidism is the underlying cause then it can be treated and the heart will usually go back to normal.

Dilated cardiomyopathy (DCM)

This is an uncommon type of cardiomyopathy in cats.  It occurs when there is a thinning and weakening of the heart muscle walls as well as an increase in the size of the heart chambers.  It has a number of causes.  The main cause is due to the lack of the amino acid taurine in the diet.  This amino acid before 1980 was absent in a lot of canned and dry cat foods.  However, these days most good quality foods will have sufficient taurine levels present.  Other causes of DCM in cats include damage to the heart muscle due to toxins and infection.  Symptoms of DCM are similar to that found in other types of heart disease in cats.  They include difficulty breathing, lethargy, not eating, or signs of acute collapsing if severe.  Diagnosis is made again using chest x-rays and an ultrasound of the heart.  Treatment of DCM in cats is similar to what is done in dogs and involves the use of drugs that help the heart beat stronger as well as drugs that eliminate fluid that may accumulate in the chest.

Restrictive cardiomyopathy (RCM)

This is a rare type of cardiomyopathy that occurs in cats.  It cause is unknown but can result from damage to the heart muscle due to infection or blood clots.  In RCM the muscle wall becomes full of scar tissue.  It has some similarities with both Hypertrophic and dilated cardiomyopathy in symptoms seen and treatment.


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