Authored
by:
Dr. Mark Rishniw, ACVIM
My pet has a heart
murmur – what does this mean?
A heart murmur is one of
several types of abnormal sounds
your veterinarian can hear when
listening to your pet’s heart
with a stethoscope. Normally,
two distinct sounds are heard
when listening to the heart of a
normal dog or cat. These are
often described as “lub” and
“dub”. When listening with a
stethoscope one hears: Lub-dub...Lub-dub....Lub-dub.
A murmur is an abnormal extra
sound (which can sometimes drown
out the normal sounds). Murmurs
most commonly occur between the
“lub” and the “dub” and have a
“shooshing” or “whooshing”
quality.
(Audio files courtesy of
Dr. Clarence Kvart from his book
Cardiac Auscultation &
Phonocardiography, Dog, Cat,
Horse)
Hearing a heart murmur during
a routine physical examination
will often be the first hint to
your veterinarian that your pet
has heart disease. Hearing a
murmur is only a hint that
something may be wrong (a
clinical sign), not a final
diagnosis. Hearing a murmur is
reason to consider more
discussion and tests to
determine the cause of the
murmur (the diagnosis).
Knowing the diagnosis and
severity of the cause of the
murmur allows your veterinarian
(or a cardiologist they consult)
to provide you with an educated
guess (prognosis) regarding how
this heart problem may effect
your pet in the future.
Hearing a murmur is not a
reason to panic. Many dogs and
cats with murmurs live normal
lives and never need any
treatment for heart disease.
But the only way to know for
certain is to work with your
veterinarian to determine the
cause and severity of the cause
of the murmur.
What causes a heart
murmur?
The short answer to this
question is “turbulent blood
flow.” Like the water in a calm
river or stream, blood flowing
normally flows through the heart
with laminar flow – that is, it
is smooth and undisturbed. And
like a river or stream,
narrowing or other causes of
more rapid flow will disrupt
this smooth laminar flow. In a
river the turbulent rapids emit
sounds much louder and less
tranquil than the calmer
sections of river. In the heart
we hear this turbulence as a
murmur.
There are lots of things that
can cause turbulent flow. To
understand what can cause
turbulent flow we need a brief
lesson in heart anatomy and
function:
In Figure 1 below, we can see
that a dog or cat’s heart has
four chambers – two atria and
two ventricles (one of each on
each side). Blood initially
enters the heart in the right
atrium. The blood then passes
through the tricuspid valve into
the right ventricle which pumps
the blood through the pulmonic
valve into the lungs to pick up
oxygen (among other things).
The oxygenated blood then enters
the left atrium. Blood in the
left atrium passes through the
mitral valve to reach the left
ventricle, which then pumps the
blood through the aortic valve
out to the rest of the body.
The purpose of each of the
valves (tricuspid, pulmonic,
mitral, aortic) is to keep the
blood flowing forward, not
backward, through the circuit
described above (RA->RV-> lung >
LA>LV>body). If a valve
malfunctions (e.g., it doesn’t
open or close properly), it can
disturb blood flowing through it
enough to create turbulence and
the result is that your
veterinarian will hear a
murmur. The most common murmurs
in dogs are associated with
leaky mitral valves.
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Heart anatomy |
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In other cases, the
turbulence develops because
there is a “hole in the heart”
between two chambers or two
arteries that are not normally
connected.
Another cause is a narrowing
(stenosis) within a chamber or
vessel through which the blood
has to “squeeze” through, like
water through a pinched hose.
Finally, turbulence can be
heard when the blood is too
“thin” (anemia) or even when a
patient is very excited causing
the heart to pump faster and
harder than normal.
What is a benign or
“innocent” murmur?
Some heart murmurs are called
benign (or innocent or
physiological), meaning there is
no apparent heart disease that
explains the murmur. These
murmurs are often seen in
puppies, and can occur in cats
of any age. They are uncommon
in adult dogs. Benign murmurs
are usually soft (rather than
loud), and can be intermittent.
Benign puppy murmurs will
generally disappear by 12 to 15
weeks of age. Murmurs
associated with anemia or
excitement are also considered
benign murmurs.
What is a congenital
murmur vs. an acquired murmur?
A congenital murmur is a
murmur in a pet that is present
from birth (or near birth).
Congenital murmurs are
associated with heart defects
that the pet was born with.
However, some congenital murmurs
may be missed in puppies or
kittens and only detected later
in life.
An acquired murmur is a
murmur that a pet acquires
during their life. These can be
benign, but more often
(especially in dogs) are
associated with developing heart
or valve disease.
My pet’s murmur has a
“grade.” What does this mean?
Murmur grading is simply your
veterinarian’s way of describing
the loudness of a murmur. There
are six murmur grades. The
lower the grade, the quieter the
murmur. However, it is often
easiest to simply describe them
as “soft,” “moderately,” or
“loud.” There are other terms
that a vet will use to describe
the character of a murmur – this
helps communicate to other
veterinarians the
characteristics of the murmur as
certain types of murmurs are
more common associated with
specific heart or valve
diseases.
The grade or loudness of the
murmur is only sometimes related
to the severity of the heart
abnormality causing it.
Bear in mind that grading is
subjective because it is based
on how it sounds to the
listener. Also, it’s hard to
tell if an animal has a heart
murmur if the pet is excited or
anxious because rapid breathing
sounds can mimic a murmur.
Usually, only a trained
cardiologist can identify a
Grade 1 murmur. A Grade 5 or
Grade 6 murmur is so strong that
it can be felt through the chest
wall (like water being sprayed
against a sheet of cloth).
What should I do if
my pet has a murmur?
Dogs
In many cases, a veterinarian
will be able to determine the
likely cause of a murmur in a
dog just by listening. In some
cases, no additional testing
will be deemed necessary.
However, to be certain, it is
often best to work with your
veterinarian to confirm the
cause of the murmur as well as
the severity of the condition
that is causing the murmur.
This will give you the best idea
of what to expect in the future
-- the prognosis for your pet.
In other cases, where a pet may
be used for breeding, a murmur
may indicate the presence of a
hereditary defect that could be
passed on to progeny.
Cats
The cause of a cat’s murmur
cannot usually be determined by
listening alone. In many cats,
benign murmurs can sound exactly
like murmurs in a cat with
serious heart disease.
In both dogs and cats, your
veterinarian may elect to
perform chest radiographs
(x-rays), an echocardiogram
(ultrasound of the heart), or
other imaging studies, or to
refer your pet to a specialist
for these procedures. The tests
that are performed depend on the
individual case.
How is a murmur
treated?
The murmur itself is not
treated. The underlying cause
of the murmur may or may not be
treated – this depends on the
cause, severity, and other
circumstances (age, well-being
of the pet, cost of treatment
etc). Your veterinarian is best
suited to discuss specific
treatment options with you.
Date Published: 1/29/2007
11:28:00 AM
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