Murmurs, Arrythmias, Heart Disease, & Failure

Basic heart function

The heart is divided into four chambers. The right atrium
receives unoxygenated blood which then goes past the tricuspid
valve into the right ventricle. From here, blood is pumped into
the lungs through the pulmonic arteries as it passes by the
pulmonic valve. Blood flows to the lungs where it is oxygenated.
The blood returns via pulmonary veins into the left atrium. From
here, blood flows past the mitral valve into the left ventricle.
>From here, blood is pumped out to the rest of the body via the
aorta as it passes by the aortic valve. This sequence of events
is coordinated by an electric impulse triggered by the SA node
to result in a regular rhythmic lup-dup of the heart as it
consistently relaxes and contracts.

Heart disease results from any abnormality of the heart. While
heart disease can result in heart failure, it can be present and
never lead to heart failure. Murmurs can be associated with
heart disease that may be minor or serious in nature. Arrythmias
are usually associated with serious heart disease. The heart
disease may or may not necessitate treatment.

Heart failure is the end-result of heart disease and occurs when
the heart is decompensating from its heart disease and is
working inefficiently to cope with the body’s needs. It is
associated with signs of congestion/edema, poor perfusion and
low blood pressure. This condition always necessitates
treatment.

Signs

Some pets may have significant heart disease without signs.
However, their condition can change quickly with stress or
exertion as the heart starts to fail.

Most dogs with significant heart failure will show some or all
of the following signs- coughing, especially at night, fatigue,
tiring with exercise, a change in gum color from pink to a
bluish color, difficulty breathing or rapid, shallow breathing
at rest. These signs occur due to accumulation of fluid in or
around the lungs and in the abdomen.

Most cats, however, show no signs before complete failure
occurs. They can go from being apparently normal cats to open
mouth breathing or fast, shallow breathing or having inability
to use their legs when they have a clot (emboli) originating
from the heart that lodges in their aorta. Cats can also
suddenly die at home and pass away before anything can be done
to help them.

Problems with the heart

Arrythmias

These may be primary, that is, associated with the heart
directly and resulting from a heart condition. Arrythmias can
also be secondary to problems with other organs in the body or
occur in reaction to toxins or anesthesia.

Arrythmias may be heard during a routine physical exam where the
animals shows no outward signs of a problem; they may be heard
when an animal presents for fatigue, collapse or “seizure” like
signs.

Arrythmias are categorized according to the chamber with which
they are associated. Arrythmias of the atrium are called
supraventricular, while arrythmias of the ventricles are called
ventricular. Bradyarrythmia is a decreased heart rate, while
tachyarrythmia is an elevated heart rate.

Murmurs

Murmurs result when there are changes within the heart. These
can be from thickening of the valves (endocardiosis), narrowing
near the valves (stenosis), thickening or thinning of the
chambers (cardiomyopathy) or infection of the heart
(endocarditis).

Murmurs may be heard during a routine physical exam where the
animal has no symptoms of a problem (asymptomatic). Murmurs may
be heard when the animal is showing signs of heart failure
(fatigue, difficulty breathing, fainting or coughing).

Sometimes, with soft murmurs in puppies and kittens, they can be
“innocent”, that is, they will eventually disappear and cause no
problems for the animal. A murmur that develops later in life,
after six months of age, is more likely to be from disease.
Murmurs are graded in loudness on a scale from 1 to 6, one being
a soft, barely heard murmur to six being able to be heard
without a stethoscope. While murmur loudness is useful in its
description, it often doesn’t correlate directly with the
severity of the heart problem.

Murmurs can indicate a primary heart problem or can be secondary
to other conditions such as anemia in dogs and cats (when the
blood is thin and more prone to turbulence) or hyperthyroidism
in cats (when having elevated levels of thyroid hormone put an
excessive strain on the heart).

Congenital Heart Conditions

Animals can be born with a heart condition resulting from a
congenital malformation. These are seen in young animals and can
be hereditary. For this reason, these animals should not be
bred. Certain breeds of dogs and cats are more likely to have
certain congenital heart conditions, but even mixed breeds can
be affected. Some common congenital heart defects are:

Patent Ductus Arteriosis (PDA)

A shunt is present in the fetal state that fails to close in the
young animal, resulting in a direct connection between the
pulmonary artery and aorta. The flow of blood is usually
left-to-right; occasionally, though, if pressure builds up in
the lungs, the flow can be right-to-left. These conditions are
treated differently.

Pulmonic Stenosis and Aortic Stenosis

There are areas of constriction or narrowing near or at the
pulmonic or aortic valves.

Atrial Septal Defect (ASD) and Ventricular Septal Defect (VSD)

There are openings due to an incomplete wall between the two
atria or two ventricles.

Mitral or Tricuspid Valve Dysplasia

There are malformed mitral or tricuspid valves that result in
abnormal blood flow.

In general, subaortic and pulmonic stenosis and patent ductus
arteriosus are the most common congenital abnormalities in dogs,
and ventricular septal defect and tricuspid valve dyplasia are
the most common congenital abnormalities in cats.

Hernias

Peritoneopericardial diaphragmatic hernias refer to the
condition in which an animal is born with an opening of the
diaphragm and the pericardial sac, allowing herniation of
abdominal contents into the chest cavity and into the sac that
surrounds the heart.

Acquired Heart Conditions

Most heart disease in animals is acquired, that is, associated
with a condition that develops over time. Certain breeds of dogs
and cats are more likely to have certain acquired heart disease.
The most common conditions are:

Mitral valve disease (MVD)

This occurs when there is thickening of the mitral valve on the
left side of the heart; this results in abnormal blood flow. It
is also known as mitral regurgitation.

Cardiomyopathy

These are disease of the heart muscle. This condition is common
in older small breed dogs.

* Dilative, the most common form in dogs, is when the chamber
walls are thin and the chamber size is enlarged. There is a
higher incidence in Boxers, Doberman pinschers, Cocker spaniels
and Great Danes.

* Hypertrophic, the most common form in cats, is when the
chamber walls are thickened, and there is less room for blood
inside the chamber.

* Restrictive and mixed forms of cardiomyopathy are two other
forms that can occur in cats.

Pericardial disease

This refers to accumulation of fluid in the sac that surrounds
the heart (pericardial sac); this can occur from cancer, trauma,
infection or for no known reason (idiopathic).

Heartworm disease

This can occur in dogs and is acquired via mosquitoes; cats
living in areas frequented with mosquitoes carrying the
heartworm larvae can occasionally acquire this disease.
Heartworms, left untreated, will lead to heart failure.

Cardiac tests

Tests are required to differentiate between the different forms
of heart disease and indicate what type of treatment is needed.

Radiographs

These show the overall heart size and arteries and veins of the
lungs. It can show if one side of the heart is larger than the
other and suggest what chambers may be enlarged. It can also
check for the presence of fluid associated with the lungs
(pulmonary edema or effusion) and for the presence of abdominal
fluid (ascites) and other organ enlargement, especially, the
liver.

Echocardiogram

This is an ultrasound of the heart, the most useful test there
is to determine the presence and type of heart disease. It
allows for the measurement of the chambers (the wall thickness)
and for the evaluation of heart valves’ efficiency. It indicates
overall heart performance and helps to dictate what type of
treatment is needed. Follow-up echocardiograms show if the
treatment is working or not.

Electrocardiogram (ECG or EKG)

This shows the heart’s rate and rhythm and helps to determine
what type of arrythmias are present. It can also suggest if
there is chamber enlargement.

Blood and urine tests

A blood panel and urine test showing organ function is valuable
in evaluating the body as a whole. Sometimes, the heart can
affect other organs; sometimes, the animal has concurrent
disease. It is important to have a “baseline” of the body’s
function, before heart medication is started. Some values,
especially kidney function and electrolytes, may need to be
rechecked over time once treatment is started.

Blood pressure

Hypertension can occur with both heart and kidney disease and
can make the animal’s condition worse. High blood pressure is
treatable and it’s control may help the pet’s heart condition.

Monitoring

Home monitoring

Since a pet is more relaxed at home, heart and respiratory rates
taken at home are more accurate than those in the hospital. It
is important to learn to monitor a pet’s breathing pattern since
this can be a clue of fluid accumulation in the chest and even a
pet’s heart rate can indicate if the heart disease is under
control or not.

A heart rate can be measured by placing a hand on the pet’s
chest and inside the thigh to feel the femoral artery. An
inexpensive stethoscope can serve this purpose also. Count the
heart rate for 15 seconds and multiply the number by four to get
the number of beats per minute. Similarly, the respiration rate
can be counted. A normal resting heart and respiratory rate for
a dog, respectively, is 100-120 beats per minute and 12-20
respirations per minute. A normal resting heart and respiratory
rate for a cat, respectively, is 120-160 beats per minute and
24-32 respirations per minute.

Hospital monitoring

Rechecks for radiographs to evaluate lung changes, ultrasound to
evaluate heart function, rechecks of blood pressure levels, and
blood and urine tests to evaluate organ function while on
medications are all important to assuring the pet a good quality
of life while coping with heart disease or heart failure. The
goal is to make the heart last longer and prevent complications
of heart disease and failure by giving daily medications.

Treatment

Treatment is usually medical and is directed at helping the
heart cope with the results of its inefficient state. There are
many human drugs that are used to manage pets with heart disease
and in heart failure. However, is surgery is rarely of help;
only in patients with left to right patent ductus arteriosis
(PDA) may benefit from surgery.

Diet

Since sodium/ salt can retain water and further increase work on
the heart, feeding a prescription low sodium diet is recommended
for pets in heart failure. However, it does not appear to be
beneficial in preventing heart failure. Diet changes for a pet
with heart problems include not feeding salty snacks and
commercial dog and cat foods since they tend to have a lot of
sodium. However, low sodium diets are less palatable, and some
pets refuse to eat them. Examples of low-sodium prescription
diets are: Hill’s H/D for dogs and Purina’s CV for cats. For
dogs, there is also a home-made diet formulation.

Diuretics

This is a class of drugs that result in increased urine output
as they “draw” fluid out of the lungs. Examples of commonly used
drugs are lasix (Furosemide or Disal), spironolactone
(Aldactone) and hydrochlorothiazide (Chlorothiazide). These
drugs are overall safe, but animals must be monitored for
dehydration, electrolyte imbalances and for the worsening of
kidney failure, if present.

Angiotension converting enzyme (ACE) inhibitors

This is a class of drugs that reduce the work load on the heart
and lower blood pressure. Examples of commonly used drugs are
enalapril (also known as Vasotec or Enacard) or benazapril
(Lotensin). These drugs are overall safe, but animals must be
monitored for negative effects on the kidneys and excessive
lowering of blood pressure.

Digitalis

This is a class of drugs that increase the strength of
contractions of the heart. They also have anti-arrythmic effects
and are used to control supraventricular arrhythmias. Examples
of commonly used drugs are digoxin (Lanoxin) and digitoxin
(Crystodigin). These drugs can be toxic and must be used
carefully. Blood levels can be monitored as a guide to dosing
the drug. Excessively high levels can cause a decreased
appetite, kidney dysfunction or ventricular arrhythmias.

Calcium channel blockers

This is a class of drugs that relax the heart tissue and
decrease the rate of an excessively fast heart rate, such as in
cases of hypertrophy, so the heart can fill more efficiently.
They can also be used to treat hypertension. Examples include
dilitazem (Cardizem) and amlodipine (Norvasc). These drugs are
overall safe but blood pressure must be monitored.

Beta adrenergic blockers

This is a class of drugs that decrease the heart rate and relax
the heart muscle in cases of hypertrophy. Examples include
atenolol (Tenormin) and sotalol (Betapace).

Oxygen therapy

While it is helpful in an emergency situation for a pet in
fulminant heart failure in a hospital, it is not practical for
home application.

Nutritional supplements

Taurine- in the past, taurine deficiency was a common cause of
dilated cardiomyopathy in cats. Due to supplementation in cat
foods, it is a rare condition now. Some forms of dilated
cardiomyopathy in dogs, especially that occurring in Cocker
spaniels, can be responsive to taurine supplementation.

Carnitine- Some dogs, especially Boxers with dilated
cardiomyopathy, may benefit with supplementation of carnitine.

If you have questions regarding this disease, please don’t
hesitate to call your veterinarian.

The above is general veterinary information. Do not begin
any course of treatment without consulting your regular
veterinarian. All animals should be examined at least once every
12 months.