Heart disease – drug treatment

Heart disease is increasingly recognized in cats. This may be because there has been an increase in their average life expectancy as a result of improved veterinary care. Most commonly heart disease is recognized in middle-aged to older cats. Younger cats most commonly present with congenital disease (defects that are present since birth). Heart disease does not necessarily mean heart failure. Most cats with heart disease have no outward signs of illness and are able to lead relatively normal lives without any medication. However, most heart diseases will get worse and once symptoms start, treatment will probably be required for the remainder of your cat’s life.

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In early stages of heart disease there may be no signs and your cat may just need to be checked regularly by your veterinarian. However, in most cases heart disease does get worse and treatment may be necessary to relieve the signs of disease.

Currently there is no evidence that starting treatment before heart failure occurs is beneficial.

Heart muscle disease
The vast majority of cats with heart disease have an abnormal heart muscle. Most commonly the heart muscle becomes thick and tense (hypertrophic cardiomyopathy). A thick and tense heart muscle is not able to relax which makes it difficult for blood to flow normally. This may eventually lead to heart failure. In some cases, a thicker muscle also contributes to an obstruction to the exit of blood from the heart (obstructive hypertrophic cardiomyopathy). The heart muscle may also become stiff (restrictive cardiomyopathy) or rarely thin and weak (dilated cardiomyopathy).

Depending on the underlying disease drugs may be given to help the heart relax or contract more forcefully.

Heart failure
Once the heart has failed for whatever reason, fluid will start to build up. If the right side of the heart is failing, fluid may accumulate in the abdomen or in the chest (outside the lungs). More commonly the left side of the heart fails and then fluid builds up within the lung itself or also in the chest (outside the lungs).

Not all drugs are appropriate in every animal and your veterinarian will decide on the best treatment program for your cat and will discuss treatment options with you. Often a combination of drugs is needed and the doses of drugs may change with time. Usually once treatment has started it will need to be continued for the rest of your cat’s life. All drugs have some side effects and if you are worried about any aspect of your cat’s treatment or any of the signs it is showing you should contact your own veterinarian for further advice.

For most diseases, there is no evidence that it is beneficial to start treatment before signs of heart failure develop.

Clot formation and embolism
Cats with heart disease in which the heart becomes significantly larger than normal may be at risk of clot formation inside the heart. These clots may breakdown and travel inside the arteries until they eventually block them (thrombosis). This usually happens in the arteries that deliver blood to the hind limbs but may happen anywhere in the body. When it occurs at this location the cat becomes suddenly paralyzed and experiences significant pain.

Heart rhythm disturbance
Sometimes the diseased heart develops an abnormal rhythm. If the average heart rate is rapid, specific medications will be required to reduce the heart rate. If the heart rate is too slow then drugs that increase the heart rate may be necessary.

There are many drugs that can be used to help animals with heart failure. Most commonly a combination of a diuretic and an ACE inhibitor is used.

Diuretics (also sometimes known as ‘water tablets’)
These are used to stop fluid retention which can cause breathing difficulty if it builds up in the lungs or chest. Diuretics help to remove water from the body by increasing the production of urine.

The most commonly used diuretic is furosemide. Furosemide is usually given 2 or 3 times daily. Since animals on diuretics will produce more urine they will also need to drink more water. It is important that you do not restrict the water intake of your cat as they may become dehydrated. Animals receiving diuretics will need to urinate more frequently and sometimes can develop urinary incontinence – either making puddles in the house or leaking small amounts of urine when lying down. As the excess water is washed out of the body it also carries with it some salts and animals receiving diuretics for a long time may become a bit deficient in some salts. Your veterinarian will want to test blood samples from your cat to ensure that they are not developing problems as a consequence of the diuretics but you should not give any other supplements without veterinary advice. If you notice any side effects when your cat is given diuretics you should discuss these with your veterinarian.

ACE inhibitors
There are many drugs in this group and they act by dilating blood vessels which results in a lowering of blood pressure.  In people these drugs are used frequently to treat high blood pressure – in cats they are most often used in heart failure to help prevent fluid retention and make it easier for the heart to pump blood. The most commonly used drugs in this group are enalapril, benazepril, lisinopril and ramipril. These are usually given once or twice daily.

When these drugs are first given it may take your cat some time to get used to the medication, Since these drugs lower blood pressure your cat may suffer signs of lethargy or weakness and very rarely even collapse. If these signs develop when you start the medication, contact your veterinarian immediately to get further advice. The most serious side effects usually seen with these drugs are effects on kidney function. For this reason, if your cat is prescribed ACE inhibitors, your vet will probably recommend some routine blood tests to make the kidneys are working normally before, and during treatment. Vomiting and diarrhea may also be seen in some animals.

ACE inhibitors should not be given to pregnant animals as they can cause birth defects.

Drugs to help the heart relax

Beta Blockers slow the heart rate and help the heart to relax. They reduce the amount of oxygen needed by the heart muscle. These drugs are commonly used in obstructive forms of hypertrophic cardiomyopathy. They can also be used to slow the heart in some rhythm disturbances. The most commonly used beta blockers are propranolol and atenolol and these are given once or twice daily. Beta-blockers may cause low blood pressure, low heart rate and worsen heart failure. Diarrhea may also occur. In some cats with asthma, these drugs may worsen respiratory function. To reduce the risk of side effects, beta blockers are usually given at a low dose to start with and the dose is increased slowly until it has the required effect. Signs to look out for that might indicate an overdose of beta blockers are lethargy, weakness or collapse, or a worsening of signs of heart failure. If you are worried about any signs in your cat call your veterinarian for advice.

Diltiazem may be used in some cats with hypertrophic cardiomyopathy, particularly in obstructive forms, to help the heart to relax and decrease the heart rate. It can also be used to slow the heart in rhythm disturbances. Tablets are usually given three times daily. The most common adverse effects in cats are vomiting and lethargy. Your veterinarian will want to make sure your cat’s kidneys and liver are working normally before prescribing this drug.

Drugs that prevent clot formation

Aspirin is an anti-inflammatory drug that is able to block clot formation. It is used in cats at risk of arterial thrombosis (clot formation and blockage of arteries). Tablets are usually given once every 2 days. Common adverse effects include gastrointestinal irritation and ulceration that may lead to bleeding (blood in the vomit or very dark diarrhea). If you notice any of these signs you should contact your veterinarian immediately. Kidney adverse reactions may also occur. Your veterinarian will want to make sure your cat’s kidneys are working normally and that there is no evidence of gastrointestinal ulceration before prescribing this drug. While your cat is on aspirin it is not recommended to administer any other anti-inflammatory drugs including corticosteroids (ie prednisone, prednisolone). Please seek advice from your veterinarian if your cat does need these drugs at some point for any reason.

Clopicatrel is another drug that blocks clot formation to prevent thrombosis. Tablets are given once daily. Overdose may lead to bleeding. Your veterinarian will want to make sure that there is no evidence of gastrointestinal ulceration before prescribing this drug.