What causes Heart failure? 
Heart failure
generally falls into 3 categories:
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Muscle failure
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Valvular Failure
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Congenital abnormalities
Muscle failure
is generally divided into dilated or hypertrophic cardiomyopathy.
Dilated cardiomyopathy is a disease seen mostly in dogs and
is common in certain breeds (particularly large and giant breeds).
 Cats
were commonly afflicted with this problem years ago until a dietary
deficiency of taurine was found to be causative in most cases.
A defect in the heart muscle causes the walls to become
stretched out and thin. In this state, it cannot
function adequately as a pump. Usually
this becomes a problem when it affects the left ventricle and leads
to left sided heart failure.
In
hypertrophic cardiomyopathy, the heart muscle becomes too thick to
be an efficient pump. The muscle can become so
big that there is little
room left in the ventricular chamber for the blood. As a
result, blood backs up into the left atrium and back into the lungs.
This disease is more prominent in cats than dogs. Sometimes
it is caused by excess thyroid hormone (hyperthyroidism), which can
be treated with drugs, surgery or radioactive iodine.
Pets with this disease are prone to having thromboembolism
(strokes).
The valves in
the heart can cause problems in two ways, by becoming leaky
(either due to deterioration with age, or due to lesions on
the edges of the valve caused by bacterial infections) or by being
constricted.
Leaky valves are
common in older pets and in certain breeds.
Because some of the blood
pumps back up through the leaky valve, the heart has to work harder
to meet the body’s demands. The ventricular
muscles will thicken to help compensate for the increased work, but
eventually, they may fail and the pet will go into heart failure.
If the mitral valve is leaky (left side of the heart), the
left atrium may become enlarged as the blood squirts up into it
through the valve. The left atrium lives right
below the trachea. When it enlarges, it may cause a chronic cough as
it hits the trachea.
 Constricted
valves are usually the cause of a congenital defect.
The valves affected are usually the outflow valves (Aortic
valve on the left, or Pulmonic valve on the right).
The ventricles have to work much harder to pump blood through
a narrow valve. Initially, they will thicken to
compensate for the added load, but eventually they will fail and the
pet will experience heart failure.
Congenital
abnormalities range from malformed valves to holes in the inner
walls of the ventricles or atria. Congenital
defects are usually diagnosed within the first few months of life as
the pet will be weaker than littermates and have exercise
intolerance. Some congenital abnormalities can be corrected
surgically while others are often fatal.
What are the symptoms of heart
failure?
Many of the
symptoms of heart failure are common to all the different causes we
have discussed. They include:
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Lethargy
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Increased thirst &
urination
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Difficulty sleeping
through the night
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Coughing
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Weight loss
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Shallow breathing
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Exercise intolerance
As heart failure
progresses the symptoms usually worsen. Sometimes,
the pet will have extreme difficulty breathing and the tongue may turn
bluish purple.
How do we diagnose heart failure?
The diagnosis of heart failure starts
with a complete history from the owners and a thorough physical
examination. Frequently, the veterinarian will hear
a loud murmur in the heart indicating a leaky valve or other defect.
In severe conditions, he may hear sounds of moisture in the
lungs. Dogs in right heart failure may have fluid
buildup in the abdomen (ascites), which is visible during the exam.
Next, we turn to radiographs (x-rays) to evaluate the chest and
belly as well as blood and urine tests. Radiographs
show us the size and shape of the heart and the condition of the lungs.
Blood tests tell us what is going on in the other major organ systems.
If the heart is suspect, we perform electrocardiograms and
echocardiography. The ECG tells us about the rhythm
of the heart and the relative size of the chambers.
Echocardiography is the most effective modality for determining cardiac
function. The ultrasound study allows us to visualize the heart as it
beats. We can visualize abnormalities (valve defects, tumors etc),
measure the size of the walls and chambers and determine if the heart is
pumping efficiently.
How do we treat heart failure?
Treatment for heart failure varies with
the cause of the failure. Most often, we will use
drugs to reduce the water content in the body (diuretics like furosemide)
along with drugs that reduce the blood pressure against which the heart
has to pump (ACE inhibitors like Enalapril).
Sometimes we will use drugs to slow the heart rate to allow it to pump
more efficiently (calcium channel blockers and beta-blockers).
For other conditions, we may need to use drugs to help maintain
the proper rhythm of the heart. Along with drug
therapy, we usually use special diets that are restricted in salt to
help reduce the body’s fluid load. Strict rest is
always part of the treatment protocol if the pet is in actual failure.
What is the prognosis for heart failure?
Again, the prognosis for heart failure
varies with the cause of the failure. Early
detection and intervention will help to prolong the life of the pet with
heart disease. This is one reason why we recommend
physical exams yearly for pets under 9 years of age and twice yearly for
our older patients. Many pets with heart failure can
be helped with the therapies mentioned above. The
survival times for these patients are quite variable and have to be
taken on a case-by-case basis. Survival times may
vary from a few days to a few years. In time, most of these hearts will
fail completely in time, however, the pet may have good quality of life
until that occurs if they respond positively to the therapy.
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