A Quick Look At: Heart Murmurs
Symptoms:
The heart operates with a pump-like
action and is divided into four chambers -- right atrium, right ventricle, left
atrium, left ventricle, with four valves that work to keep blood flowing in one
direction. The valve between the left atrium and the left ventricle is called
the mitral valve. The valves open and close, letting blood in and then pumping
it out. A normal heartbeat sounds like ‘lup-dup, lup-dup, lup-dup..’. That
“lup-dup” sound is created from the movement of the valves and blood flow.
When valves become diseased or worn,
they often do not close completely with each heartbeat, resulting in a backwash
of blood. The effect is an abnormal sound called a heart murmur.
The sound a murmur makes depends on when
it occurs in the cardiac cycle. A murmur that occurs when the ventricles are
beating is called a systolic murmur. A murmur that occurs when the ventricles
are relaxed is called a diastolic murmur. Instead of sounding like “lup-dup, lup-dup”,
the heart with a systolic murmur sounds like “lup-shh-dup”; and a heart with a
diastolic murmur makes the sound “lup-dup-shh”.
Most heart murmurs are detected as a
veterinarian listens to the dog’s chest with a stethoscope. Once a murmur has
been detected, further tests are often needed to determine the cause and
severity. Murmurs are graded in severity from 1 to 6, with 1 being the softest
murmur that can be heard and 6 being loud enough to be heard with the
stethoscope not yet touching the chest. Murmurs graded at 4 to 6 can often be
felt if the hand is placed at the right spot on the chest.
Cause:
Heart murmurs may be the result of a
birth defect, or congenital malformation. Congenital heart murmurs are typically
seen in young dogs and are hereditary. Some cardiac murmurs, especially in
puppies, are innocent, meaning they eventually disappear and are usually no
cause for alarm. It's often not possible to determine whether a murmur is
innocent until the dog reaches two or three years of age.
One of the most common conditions
associated with heart murmurs is mitral valve disease (MVD), sometimes referred
to as mitral regurgitation. This is the most common cause of heart failure in
smaller dogs such as Manchesters. Because of the pressure created when the left
ventricle contracts, the mitral valve can wear out. The wearing-out process
begins with a small leak that gradually worsens. The earliest sign of a leaking
mitral valve is a heart murmur. Many dogs develop a murmur as early as age 6
and a much greater number will have a murmur by age 10. As time goes by, the
leak becomes more severe and can result in congestive heart failure. Early
signs of congestive heart failure include a reduced tolerance for exercise,
difficulties in breathing, or a cough at night or at rest. All of these occur
because of a build-up of fluid in the lungs.
Treatment:
Dogs diagnosed with heart murmurs due to
mitral valve disease are now often given an ACE inhibitor such as
Fortekor. This medication is taken long-term and helps dilate the arteries and
veins, permitting better blood flow.
Once congestive heart failure has been
diagnosed, the following medications can be prescribed:
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Diuretics, such as lasix, to help the kidneys remove excess fluid from the
body.
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Digitalis, to improve heart function. The therapeutic dose can border on
toxicity so dogs must be closely monitored for optimal dosage levels.
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Enzyme blockers
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· Pimobendan, sold
under the name Vetmedin, is an entirely new class of drug to treat congestive
heart failure and is an alternative to digitalis. Available in Canada as of
December 2003, many vets are not yet aware of the excellent success rate
Pimobendan (Vetmedin) has in maintaining high quality of life and extending
the life span of dogs in CHF. More information is available at
www.vetmedin.co.uk
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· Nutritional
therapy, including supplements. L-Carnitine, taurine, and COQ10 are all
excellent supplements for heart disease. Vitamin E and fish oil capsules are
also recommended by many veterinary nutritional experts.
Your Breeding Program:
Although the pattern of inheritance has
not been identified, it is agreed that there is a genetic basis for the early
development of mitral valve disease.
To avoid passing on genetic defects to
another generation, it is important to refrain from breeding a dog until it has
been cleared of any problems. A dog with a hereditary heart problem, even one
that has been repaired, should not be bred.
