FELINE
HEART DISEASE
Heart
disease in domestic cats is actually quite common, which
may come as a surprise to feline owners. It can strike any
age or any breed of cat. One of the most challenging aspects
of feline heart disease is that cats may not show any warning
signs (such as exercise intolerance, coughing, weakness)until
the process is very advanced. This means that a cat can
literally be playing vigorously one day, and suddenly have
trouble breathing. Untreated heart disease often progresses
to heart failure, blood clot formation, and death.
The
detection of a new heart murmur by your veterinarian (often
on routine examination) can be the first sign that changes
in the heart have taken place. While not every murmur signals
the onset of heart disease, a further investigation is warranted
since those murmurs which are a result of heart disease
cannot be distinguished from "innocent" murmurs by
routine tests alone.
Fortunately,
advances in companion animal medicine enable veterinarians
to efficiently diagnose cardiovascular disease in cats,
even in its early stages. In many instances, if heart disease
is detected prior to the stage of actual heart failure,
it can be successfully controlled with medication(s). A
feline with carefully controlled heart disease may live
symptom-free for years!
--
TESTING FOR HEART DISEASE --
The
first test for heart disease begins with a thorough physical
examination. During the exam, the veterinarian will determine
your cat's heart rate and rhythm. A persistently elevated
rate, or a rhythm that is irregular can be associated with
heart disease in cats. The presence of a murmur (especially
one not previously detected) may be further evidence of
heart disease. In advanced cases of heart disease, abnormal
sounds in the lungs may be heard. A weak or irregular pulse
can also occur. The results of the physical exam may lead
to further testing, all of which we perform regularly at
Bath-Brunswick Veterinary Associates, Inc.
Chest
Radiographs (x-rays)
Chest radiographs are important components in the diagnosis
of feline heart disease. A diseased heart will most often
enlarge over time. In advanced stages, fluid may be detectable
in the chest cavity (pleural effusion) or in the lungs themselves
(pulmonary edema).
Electrocardiogram
(EKG or ECG)
An electrocardiogram (EKG or ECG) is a tracing of the electrical
activity of the heart. It documents heart rate and rhythm.
In addition, subtle changes can occur in the shape of the
ECG spikes that can reveal certain types of pathological
changes in the heart. It is a rapid and painless test that
can be performed right in the veterinary office.
Echocardiogram
An echocardiogram, also known as a cardiac ultrasound
exam, is one of the most advanced and sensitive tests for
determining the presence of heart disease in animals. It
is painless and generally does not require sedation. The
technique uses sound waves to actually visualize the heart
in action. From this exam, the dimensions of each heart
chamber can be determined.
Ultrasound
can also detect the presence or absence of fluid in the
sac around the heart (pericardial effusion), fluid in the
chest, congenital heart defects, abnormalities of the heart
valves, blood clots within the heart itself, or heart tumors
(rare in cats). Most importantly, the echocardiogram can
actually determine the type and degree of heart dysfunction.
An accurate assessment of heart disease is paramount to
effective treatment.
--TYPES OF FELINE HEART
DISEASE--
Dilative
cardiomyopathy
Dilative cardiomyopathy denotes heart disease that results
in an enlarged heart with thinning and weakening of its
muscular walls. The weakened heart cannot pump efficiently
which subsequently can lead to fluid accumulation in the
lungs and/or chest cavity (analogous to congestive heart
failure in humans). Enlargement of the heart can lead to
leakage at the heart valves, creating a murmur.
This
form, although more difficult to successfully control, has
become less common in recent years. A few years ago, research
showed that deficiency of the amino acid taurine in the
feline diet was one of the main causes of dilative cardiomyopathy.
Since that time, most commercially made feline diets are
supplemented with taurine.
Hypertrophic
cardiomyopathy
Hypertrophic cardiomyopathy is the most commonly diagnosed
heart disease in cats. The walls of the heart become much
thicker and stiffer than normal. This results in a smaller
chamber to hold the blood, and diminishes the amount of
blood pumped out with each beat. Consequently, the heart
has to accelerate and use more energy to accomplish its
original task. The geometric changes in the heart can lead
to leakage at the valves, and development of a murmur. As
the disease progresses, the heart can become so thickened
that it cannot pump the blood forward at an adequate rate.
This usually results in fluid accumulation in the lungs.
The
cause in most cases is unknown, but genetics are thought
to play a role in at least some cat breeds. While it is
most common in middle-aged male cats, it can be seen in
either sex as early as 6 months of age. Hypertrophic cardiomyopathy
remains the most treatable form of feline heart disease.
Restrictive
cardiomyopathy
Restrictive cardiomyopathy is a less common, less defined
type of heart disease in cats. It is more difficult to detect,
as many cats will have near normal echocardiograms, but
their heart walls seems "stiffer" and less efficient
at pumping blood forward. It is thought that in such cats
the heart wall muscle cells become slowly replaced with
less functional scar tissue. Cats with this type of disease
may shows signs consistent with either dilative cardiomyopathy,
hypertrophic cardiomyopathy, or both.
--THERAPY
FOR FELINE HEART DISEASE--
Therapy
for feline heart disease depends on which type is diagnosed
and how advanced the disease is. As previously mentioned,
cats with hypertrophic cardiomyopathy have the best long
term outlook The most serious consequences of progressive
heart disease are weight loss, anorexia, difficulty breathing,
weakness, and blood clot formation (with possible limb paralysis).
Cats with advanced heart disease are at risk for sudden
death.
Early
detection and intervention, however, can be very rewarding
for many cats and their owners.
Furosemide
Furosemide (Lasix‰) is a diuretic ("water pill") used
in all types of feline heart disease. It reduces the volume
of fluid that the heart has to pump, and removes fluid from
the lungs. This makes the heart's work easier.
Enalapril
Enalapril
(Vasotec¨ or Enacard‰) is a drug known as a vasodilator.
It is very useful in many types of heart disease. It lowers
blood pressure and reduces the workload of the heart. In
dilating the vessels downstream from the heart, it lowers
the resistance to blood being pumped forward.
Diltiazem
Diltiazem
(Cardizem‰) is a drug used in humans and animals. It is
a "calcium channel blocker." Most commonly used for hypertrophic
cardiomyopathy, it reduces the stiffness and work of heart
walls. It has been documented to prevent or reverse wall
thickening in many cats, and is very well tolerated.
Digitalis
Digitalis
(Digoxin® or Lanoxin®) is a very old but useful
drug utilized in people and animals mainly for treatment
of dilative cardiomyopathy. It strengthens the contraction
of the heart muscle with the goal of improving pumping function.
It also can correct certain types of irregular heart rhythms.
Because it has a narrow safety range, the drug concentrations
in the patient's bloodstream must be monitored periodically.
Betablockers
Betablockers
such as propranolol (Inderal®) or atenolol (Tenormin®)
are prescribed mainly for hypertrophic cardiomyopathy. These
drugs slow the rhythm of the heart, allowing the attenuated
chambers to fully fill with blood between heartbeats. This
increases cardiac output and thus reduces the actual work
of the heart. Betablockers also lower blood pressure and
regulate heart rhythms.
Aspirin
One
of the health risks for feline heart disease patients is
the formation f a blood clot in the heart. The clots can
form in the enlarged heart chambers where the blood undergoes
increased turbulence. If a piece of the clot leaves the
left side of the heart and travels downstream, it often
lodges in the large blood vessel known as the aorta. Since
the aorta is the trunk artery carrying blood to the back
half of the body, loss of this blood flow can cause temporary
or permanent paralysis. The best prevention of this complication
is to 1) adequately control the heart disease and reduce
heart chamber size and 2) low dose aspirin therapy. While
cats can have toxic or lethal reactions to high dose aspirin
or any dose of acetaminophen (Tylenol®), low dose aspirin
can often be used safely. The usual dose is adult regular
aspirin or 1 baby aspirin (81 mg.) per cat TWICE WEEKLY.
