Heart Disease

HEART DISEASE

1. DILATED CARDIOMYOPATHY

Cardiomyopathy is degeneration of the heart muscle so that the heart, which is basically a pumping machine, progressively fails.

As a result of this degeneration the muscle becomes thinner, particularly the thick muscle wall of the left ventricle whose contraction pumps blood around the body. The pressure of the blood inside the heart then allows this thin wall to stretch resulting in a much larger left ventricle and this is then described as dilated cardiomopathy.
How common is the condition?

Dilated cardiomyopathy is the most common cause of heart failure in the large breeds of dogs. These include Boxers, Dobermanns, and Great Danes. Occasionally medium sized breeds such as Cocker Spaniels, English Springer Spaniels and German Shepherd Dogs are also affected. Small breeds are only affected occasionally.

My dog suddenly seemed to get very slow and the vet says he’s got Dilated Cardiomyopathy( DCM). Can this happen so quickly?

Dilated cardiomyopathy may have a very sudden onset. Some dogs may go into severe heart failure in only a few hours. Rapid heavy breathing, a blue tongue, excessive drooling or collapse may be the first signs.

How is the condition diagnosed?

Before a diagnosis of dilated cardiomyopathy is made, several tests are used that assess different aspects of heart function.

1. Ausculation which is listening with a stethoscope. This allows us to identify murmurs due to the improper closure of heart valves, their location and their intensity. In addition we can pick up abnormal heart rhythms, (arrhythmias and dysrythmias) and the stethoscope also allows us to pick up lung sounds. This aids our understanding of what is happening within the chest since with many heart conditions the lungs are also affected.

2. Laboratory tests involve both blood and urine. These do not give direct information about heart function but they allow us to appreciate other disorders in the body that may affect heart function and influence our treatment of the heart problem.

3. X-rays. Chest radiographs allow us to examine the lungs and also the size and shape of the heart. Dilated cardiomyopathy usually causes very obvious enlargement of the heart, particularly the left side which is very apparent on x-ray.

4. Electrocardiogram (ECG). This is an assessment based on the electrical activity of the heart. It allows us to accurately determine heart rate and to pin point any abnormalities of rhythm that we may have picked up on auscultation.

5. Ultrasound examination (echocardiogram or ultrasonography). This gives the most accurate determination of the size of each heart chamber and actually permits measurement of the thickness of the heart walls. This can be seen on the monitor and the contractions of the heart can be watched and evaluated. Certain measurements can be taken which allow the actual strength of the heart’s contraction to be measured which we can compare with the normal animal. Ultrasound equipment is now widely available in veterinary practice.

It is the combination of all these tests that give us our best evaluation of the dog and its heart function. However to carry out a full cardiac evaluation may prove to be quite expensive.

What is the treatment?

A collection of drugs can be used to treat dilated cardiomyopathy. Initially stabilisation depends upon the use of:

1. Diuretics. These are drugs that stimulate the kidneys to remove excess fluid from the body. Frusemide is most commonly used although there are others that are selected in certain circumstances.

2. Digitalis glycosides. These drugs improve heart function in several ways. Mainly they are used to slow the heart rate and strengthen each contraction of the heart so the blood is pumped more effectively.

3. In addition various other drugs are used, particularly enzyme blockers or so-called ACE. (Angiotensin Converting Enzyme) inhibitors. They work by treating raised blood pressure and imminent heart failure by preventing the conversion of certain enzymes which have an adverse effect on the heart. Today they are one of the most powerful and commonly used groups of drugs for certain forms of heart disease, including DCM, which involve the need to decrease blood pressure.

4. Vasodilators. These drugs dilate the arteries and/or veins of the body so that the heart does not have to generate so much pressure and work so hard in order to pump the blood around the body. They are used as effective long term treatment to stabilise the patient with DCM.

5. Bronchodilators. These drugs help a lung that has been affected by a fluid build up due to the failing heart and help breathing.

As a result of all these tests and treatment, is there any guarantee that my dog will live much longer?

This question cannot be answered with certainty. Dogs are not people and as soon as your pet feels better he will want to continue his normal life style. Therefore if he was normally a very active or excitable dog it is important that you exercise much greater control. The results of the tests at least lead us to a positive diagnosis. The response that occurs to the drugs within the first few days gives a good indication of how much success we are likely to have.

If response does not occur within a few hours to days the prognosis is not good. Dogs that stabilise quickly often live for a period of months but long term prognosis always has to be guarded.

2. HEART FAILURE

Heart failure is the inability of the heart to maintain a circulation sufficient to meet the body’s needs. Heart failure most usually describes a failure of the heart muscle (myocardial failure). This can affect the right or the left ventricle.

Dilated cardiac myopathy which occurs most commonly in large breed dogs often results in sudden heart failure.

My dog ran down the garden and suddenly dropped dead. The vet said it was due to acute heart failure. What does this mean?
Sudden cardiac arrest can occur for a variety of reasons of which degeneration of cardiac muscle (cardio myopathy) is only one. Death quickly follows due to lack of oxygen to the tissues, especially the brain. Sometimes sudden death is preceded by a brief convulsion (fit) or the dog may suddenly develop fluid in the lungs, pulmonary oedema, due to the inability of the heart to circulate blood efficiently.

Is this the same as a heart attack?

In humans a heart attack is more strictly myocardial infarction (MI). This is death of the cells of an area of the heart muscle (myocardium). This is usually due to oxygen deprivation caused by obstruction to the coronary vessels. It is not a common disease in dogs but it can occur. In dogs heart failure is more commonly due to either DCM or to congestive heart failure (CHF) which are both separately described, or mitral valve disease.

What is the mitral valve?

The heart has four chambers. The upper chambers are the atria (or auricles) and the lower the ventricles. The heart is also divided into right and left sides. Blood flows back from the tissues and organs of the body via the vena cava into the right atrium. Here it is stored briefly and then pumped into the right ventricle which, when it contracts, pumps the blood into the lungs where it is re-oxygenated. It flows from the lungs back into the left atrium and then passes to the left ventricle which is surrounded by the largest and strongest of the heart muscles. This muscle mass is necessary in order to generate sufficient pressure to pump the re-oxygenated blood to all parts of the body. The auricle and ventricle on each side of the heart is separated by a valve which prevents the blood from going back into the atrium when the heart contracts. The valve between the left atrium and the left ventricle is the mitral valve. Because of the pressure that this valve has to withstand during the dog’s life it often starts to wear out. This can be detected with a stethoscope and is called a mitral murmur.

How common is mitral valve disease?

Mitral valve disease is the most common cause of heart failure in small dogs. In large dogs dilated cardiomyopathy, i.e. a weakness of the cardiac muscle, is usually the most common cause of heart failure.

How serious is a leaking mitral valve?

Many dogs of the smaller breeds have an audible mitral murmur from 6 years of age onwards. Often this is asymptomatic, in other words it causes no obvious signs. However as time goes on the leak becomes more severe and as more blood leaks back into the atrium this results in reduced pumping efficiency. Eventually congestive heart failure occurs. However this can sometimes be months or years from the time when the murmur was first detected.

When I took my little dog for his annual booster the vet told me he had a mitral murmur but said he was not going to treat it at this stage. Is this correct?

Many dogs have audible left side murmurs and provided there is no exercise intolerance, cough or other signs of a problem. It is not unusual to do nothing initially except perhaps reduce exercise if the dog is normally very energetic and perhaps also ensure that any excess weight is reduced. However, it is wise to reduce exercise if your dog is very energetic and to diet if at all overweight.

How will I know if heart failure is present?

When the heart is not pumping the blood properly and some is leaking back into the left auricle the blood moves more slowly through the lungs. This results in a collection of fluid in the lungs. The usual sign is that a cough develops as the dog attempts to get rid of this fluid. It is as though he is trying to clear the throat. Exercise tolerance will also be reduced.

Does this mean that he will have a heart attack and die?

No, not necessarily, because initially the body tries to compensate and apart from a cough you may not notice much difference except the dog will appear to be slowing down. Ultimately, however, without treatment congestive heart failure will develop. We have a separate information sheet on this condition.

How is the leaky valve assessed?

With any heart problem a similar collection of tests is carried out.

These include auscultation, listening with a stethoscope, which is the usual way the valve defect is first picked up.

Chest x-rays are then used to check the lungs and also the size and shape of the heart.

Blood and urine tests are performed to give an indication of any other disorders in the body, particularly those affecting the liver and kidneys which may have significance on heart function.

An electrocardiogram (ECG) will also be carried out. This assesses the electrical activity of the heart and allows accurate determination of both heart rate and rhythm. Any abnormal rhythms, (arrhythmias or dysrhythmias) can be detected and evaluated.

Ultrasound examination (echocardiogram) utilises sound waves which are bounced off the various structures of the heart and are processed by computer and can be read as a trace on a monitor. Using ultrasound the contractions of the heart can be evaluated in the conscious patient without risk either to the dog or to personnel.

A combination of these tests will give good evaluation of heart function. However a full work up of this nature can be quite expensive and if your dog is not insured it is worthwhile discussing cost prior to any tests since these only lead to a diagnosis. Additionally there is the cost of treatment which depends on the medication required.

What does treatment usually involve?

Today we have a wide collection of drugs which are effective in control of the condition although cure is not possible. These include diuretics and also sophisticated drugs acting directly on the heart muscle, improving contraction and regulating rhythm. In addition, special drugs are used which dilate the arteries, sometimes also the veins, thus reducing load on the heart and so easing the pressure on the diseased valve.

Is this treatment costly and is it long term?

Unfortunately most dogs have to remain on treatment for the rest of their lives. However treatment is tailored according to each patient’s needs and sometimes relatively inexpensive drugs are effective.

As a result of all the treatment, how much longer will my dog live?

Unfortunately it is difficult to answer this question with certainty. It depends on the severity of the condition and the initial response to treatment. The more rapid the response once treatment is instituted, the better the prognosis. Many dogs, once stabilised, will live for months, or even years with no reduction in quality of life.

3. CONGESTIVE HEART FAILURE

When the heart fails to pump sufficient blood around the body it tries to compensate by changing the rate and sometimes the strength of contractions. This sometimes improves the situation and symptoms virtually disappear. However without treatment the condition will slowly get worse. Pooling of blood in the organs and tissues of the body leads to signs. The animal will be said to have ‘decompensated’ and to have developed congestive heart failure.

Clinical signs vary depending on whether the dog has left or right sided heart failure. This usually involves failure of the valves of the heart although sometimes the muscle can be involved.

What is the difference in the signs?

With right sided heart failure there is a poor venous return to the heart. In other words, when the heart contracts instead of the right ventricle pushing the blood through the lungs for oxygenation some returns to the right auricle and thus blood is unable to be cleared from the systemic circulation which consequently becomes congested. Accumulations of fluid occur in the abdomen and/or the chest cavity, interfering with the function of the organs in these areas. The abdomen may become enlarged due to fluid and this is called ascites, or dropsy. Sometimes fluid also leaks from the thin walled veins and swelling may appear in the limbs in severe cases.

When CHF involves the left ventricle blood is not moved into the systemic circulation and therefore builds up in the lungs which causes fluid to seep out into the lung tissue resulting in pulmonary oedema. This causes coughing and breathing difficulties.

Is congestive failure due mainly to valvular disease of the heart?

No. There are may other causes. Disease of the heart muscle, (cardiomyopathy), irregularities of rhythm and narrowing of some of the major blood vessels can also cause the condition.

What signs should I expect?

CHF usually results in coughing, ascites, exercise intolerance, general lethargy, weakness and often weight loss although the dog may develop a big abdomen due to the ascites or dropsy. The normal pink colour of the mucous membranes (for example inside the lips or under the eyelids) , may become pale or even a bluish colour.

How is the condition diagnosed?

As with any heart problem, diagnosis involves what is known as a ‘full work-up’ which includes blood and urine tests to establish that there is not a problem in other organs, particularly the liver and kidneys; auscultation which is listening to the heart with a stethoscope, which will detect abnormalities of the valves (murmur) and also irregular rhythms, x-rays which will give an indication of changes in the heart size or shape as well as the state of the lungs; and ultrasound examinations which allow us to examine the heart in motion and, if necessary, take measurements which gives a very accurate diagnosis of heart function.

Are these tests likely to be expensive?

Unfortunately a full work up can cost several hundred pounds but, depending on the condition, and its severity, sometimes only selected tests are necessary.

Is it not possible to treat my dog without these tests since surely it is better to spend the money on treatment?

Accurate diagnosis gives us a much better guide to the type and extent of treatment necessary. Today there are a wide selection of drugs that can be used to treat congestive heart failure and treatment regimes have to be tailored for each animal.

With correct treatment, although this is not curative but merely stabilises the dog, many animals are able to live a normal life often for months or years. If you would like to discuss this further, please do not hesitate to contact us.

This client information sheet is based on material written by Trevor Turner, BVetMed, MRCVS, FRSH, MCIArb, MAE.

Used with permission under license.