Download 1. HEART FAILURE

1. HEART FAILURE
What is heart failure?
Heart failure is the inability of the heart to maintain a circulation sufficient to meet
the body’s needs. Heart failure usually describes failure of the heart muscle
(myocardial failure). This can affect the right or the left side of the heart ventricle. Dilated cardiac myopathy (DCM) which is most common 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 (cardiomyopathy)
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 usually the result of myocardial infarction (MI). This is the death of cells of part of the
heart muscle (myocardium) and usually is due to lack of oxygen caused by obstruction to the coronary vessels.
This is not a common disease in dogs but it can occur. Canine heart failure is more commonly due to either DCM
or to congestive heart failure (CHF) which are 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 veins
to the vena cava then the right atrium. Here it is stored briefly and then pumped into the right ventricle which, when
it contracts, pumps the blood to the lungs where it is re-oxygenated. It flows from the lungs into the left atrium and
then passes to the left ventricle which has the largest and strongest of the heart muscles. This muscle mass is
necessary 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 mitral valve lies between the left atrium and the left ventricle.
Due to the pressure this valve has to withstand throughout the dog’s life it often starts to leak with age, resulting in
a ‘backflow’ of blood which can be detected with a stethoscope. This 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, (DCM), 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 about 6
years of age. Often this is asymptomatic (it causes no obvious signs). With time
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.
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 without showing any signs. Usually the first signs are exercise
intolerance and/or a cough and often treatment is not commenced until these become apparent. However, if the
dog is very energetic it is wise to reduce exercise and also to reduce weight if there is any obesity.
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 is also reduced.
Does this mean that he will have a heart attack and die?
Not necessarily. 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, which is listening with a stethoscope. This is the usual way the valve
defect is first picked up. Chest x-rays (radiographs) 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.
Using ultrasound the contractions of the heart can be evaluated in the conscious patient
without any risk.
A combination of these tests will provide evaluation of heart function, but a full work-up
of this nature is expensive. If your dog is not insured please feel free to discuss cost
prior to any tests since these only lead to diagnosis. Additionally there is the cost of
treatment which is often lifelong and depends on the medication required.
What does treatment usually involve?
There is a wide collection of drugs available which are effective to control 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 any 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. Please
feel free to discuss any concerns.