Heart Disease: Drug Treatment
Heart disease does not necessarily mean heart failure. Many dogs 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 dog’s life.
In early stages of heart disease there may be no signs and your dog may just need to be checked regularly by your vet. However, in most cases heart disease does get worse and treatment may be necessary to relieve the signs of disease and slow down the rate of disease progression.
Management of heart disease requires a combination of:
- Changes to your dog’s lifestyle, ie he may not be able to exercise as much and it is very important that he is always allowed to rest whenever he wishes.
- Drugs to remove excess fluid retention (ACE inhibitors and diuretics).
- Drugs to improve the strength of the heart beat (pimobendan) or change the heart rate (digoxin, other antiarrhythmics).
- Dietary changes may be recommended by your vet depending on the type of heart disease present.
Heart valve disease
Many animals with mitral valve disease show no signs of heart disease and these patients require no specific treatment. However, heart failure may develop and then appropriate treatment can be started.
Heart muscle failure
In some heart disease the heart muscle itself is affected. It may become thin and weak, in which case drugs can be used to improve heart muscle contraction. In some disease the heart muscle becomes thickened and tense and drugs may be used to help the muscle relax so the heart can expand and fill with blood between contractions. In both cases it may be useful to also give drugs that reduce the resistance in the circulation so that it is easier for the heart to pump blood around the body.
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.
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 or an artificial pacemaker may be necessary.
Not all drugs are appropriate in every animal and your vet will decide on the best treatment programme for your pet 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 pet’s life. All drugs have some side effects and if you are worried about any aspect of your pet’s treatment or any of the signs it is showing you should contact your own vet for further advice.
For most diseases, there is no evidence that it is beneficial to start treatment before signs of heart failure develop.
There are many drugs that can be used to help animals with heart failure. Most commonly a combination of a diuretic, an ACE inhibitor and pimobendan 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. 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. In some more advanced cases other weaker diuretics may be used in combination with furosemide to improve the effect (i.e. spironolactone, hydrochlorothyazide).
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 pet 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 vet will want to test blood samples from your pet 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 pet is given diuretics you should discuss these with your vet.
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 pets 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 pet some time to get used to the medication, Since these drugs lower blood pressure your pet may suffer signs of lethargy or weakness and very rarely even collapse. If these signs develop when you start the medication, contact your vet immediately to get further advice.
The most serious side effect usually seen with these drugs are effects on kidney function. For this reason, if your pet is prescribed ACE inhibitors, your vet will probably recommend some routine blood tests to make sure your pet’s 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 improve heart function
Pimobendan is most often used in dogs with heart valve disease or those with dilated cardiomyopathy. It improves the efficiency of heart function by increasing the force of heart contraction (without increasing the use of energy and oxygen by the heart muscle) and causes blood vessel dilation (which makes it easier for the heart to pump blood around the circulation).
It is often used in conjunction with other drugs in the management of heart failure. Side effects are rare but may include vomiting or irregular heart rhythms and if these occur the dose may need to be reduced. It is usually given twice daily, ideally 1 hour before feeding.
Beta blockers slow the heart rate and therefore reduce the amount of oxygen needed by the heart muscle. 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. 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 pet call your vet for advice.
Digoxin has mild effects on the heart muscle making it contract more strongly. In the past this drug was used commonly to treat heart failure for this property. However these effects are so mild that nowadays this drug is used mainly for the treatment of heart rhythm disturbances, particularly one called atrial fibrillation. It causes the heart to slow down. This drug is usually given twice a day and a liquid form is available as well as tablets.
A few days after starting digoxin your vet will want to test the drug levels in the blood. The sample has to be taken 6-8 hours after administration depending on the lab analyzing the sample. Side effects of digoxin commonly include a loss of appetite and vomiting, diarrhoea and depression. If these signs develop you should contact your vet immediately for advice. Drug levels and kidney function must be routinely monitored (i.e. every 3 months) to make sure they are not above the therapeutic range and that your pet is not at risk of side effects.
Diltiazem is used in some pets with an abnormal heart rhythm to slow the heart rate. It is commonly combined with digoxin to treat atrial fibrillation. Your vet may want to check that your pet’s liver and kidneys are working normally before they prescribe this drug. Tablets are usually given 3 times daily.
Sotalol is used in some pets with an abnormal heart rhythm to slow the heart rate. Side effects may include low blood pressure, low heart rate, depression, nausea, vomiting and diarrhea. If these signs develop you should contact your vet immediately for advice. Your vet will want to check kidney function before prescribing this drug. Tablets are given twice daily.
Amiodarone is used in some pets with an abnormal heart rhythm to slow the heart rate. In most cases it is used when other antiarrhythmic drugs have failed. Dogs on this drug may lose appetite and vomit. Other side effects may include low blood pressure, low heart rate, low thyroid hormone levels and liver toxicity. Your vet will want to do some blood tests to check that your pet does not have liver disease before prescribing this drug and will want to repeat these tests periodically while on treatment. Tablets are usually given twice daily.