F308
Heart Disease
patent ductus arteriosus | aortic
stenosis | pulmonic stenosis | mitral
valve insufficiency | infective
endocarditis | cardiomyopathy
Introduction:
The heart is an extremely complex organ upon which the life of any animal
depends from minute to minute. It is responsible for providing the power to
circulate blood throughout the body. In a large dog, the heart normally pumps
approximately 300 liters of blood per hour! Heart problems are relatively common
in canine patients seen at veterinary hospitals. Most dogs with heart problems
are 7 years and older. Some heart diseases, however, are more common in younger
dogs. Heart disease in dogs can be very complicated and must be treated on an
individual basis. Therefore, this section will give only a brief overview of
some of the more common heart disorders seen in dogs. The intent of this
material is to give the pet owner a better understanding of the clinical signs,
diagnosis, and treatment for many of the problems associated with the canine
heart.
Common Terms:
- Cardiac - Adjective referring to the heart.
- Artery - A blood vessel carrying blood away
from the heart.
- Vein - A blood vessel carrying blood toward
the heart.
- Capillary - Tiny vessel from which oxygen and
nutrients dissolve out of the blood stream and into the surrounding tissue.
Capillaries are present everywhere in the body and are the connection
between arteries and veins.
- Atrium - Upper chambers in the heart. Dogs
have two atria, right and left.
- Ventricle - Lower chambers in the heart. Dogs
have two ventricles, right and left.
- Valve - "Doorways" into and out of
the ventricles. Each ventricle has two valves, one for inflow and one for
outflow. Subsequently, each canine heart has four valves. The valves which
allow blood to flow into the ventricles open during the first phase of a
heartbeat and close during the second phase. The valves which allow blood to
flow out of the ventricles function in the opposite manner, closing during
the first phase of the heartbeat and opening during the second phase. The
four canine heart valves are described as follows:
- Right atrioventricular valve (tricuspid
valve): Valve which separates the right atrium from the right ventricle.
- Pulmonic valve: Valve which controls the
outflow of blood from the right ventricle into the lungs.
- Left atrioventricular valve (mitral valve):
Valve which separates the left atrium from the left ventricle.
- Aortic valve:
Valve which controls the outflow of blood from the left ventricle into the
aorta and the rest of the body.
The "lub-DUB, lub-DUB"
sound heard when listening to the heart with a stethoscope is actually the
noise made when the valves shut and create turbulence in the blood. The
pulmonic and aortic valves close on the "lub" portion of the sound,
while the right and left atrioventricular valves close on the "DUB"
portion of the sound.
- Aorta - The largest artery in the body. The
aorta carries blood from the left ventricle down through the chest and into
the abdomen. Arteries branch off the aorta carrying blood to all parts of
the body.
- Pulmonic artery - The major vessel which
carries blood from the right ventricle into the lungs to receive oxygen. The
pulmonic artery and its branches are the only arteries in the body that
normally carry blood which is low in oxygen content.
- Vena cava - The largest veins in the body. All
veins eventually empty into one of these two veins. One carries blood from
the head and upper body into the heart, and the other carries blood from the
lower body. Both empty into the right atrium.
- Pulmonic veins - Veins which drain blood from
the lungs back into the heart. The pulmonic veins empty into the left atrium
and are the only veins in the body which carry blood high in oxygen content.
- Systole - Contraction or pumping phase of the
heartbeat. During systole, the heart contracts and empties its chambers,
pumping blood into the body.
- Diastole - Resting or filling phase of the
heartbeat that occurs in between heartbeats. During this brief resting
phase, the heart fills with blood.
- Murmur - An abnormal heart sound heard with a
stethoscope. Murmurs may be caused by turbulent blood flowing through a
defect in the heart or through a faulty valve that is not closing when it
should.
- Arrhythmia - An abnormality in the electrical
activity of the heart. Some types of arrhythmias can be life-threatening
emergencies.
- Edema - Fluid buildup in the tissues. Edema
may be due to various causes; heart defects are one of the more serious
causes in which edema may severely affect the health of the animal.
Heart Disease
A large variety of problems can lead to heart
disease. Deaths stemming from a heart disorder are usually due to either the
development of a fatal arrhythmia or to congestive heart failure and its various
complications. All heart problems can be placed into one of two categories:
congenital or acquired. A few of the more common heart diseases will be
addressed as follows:
Congenital -
These are defects present at birth. Congenital cardiac
defects are among the most common birth defects that occur in puppies.
This is probably due to the complicated process
of cardiac development in the unborn fetus.
- Patent Ductus Arteriosus (PDA) - This
is a shunt or duct, normally present in unborn puppies, which allows blood to
pass from the right side of the heart to the left. This shunt (ductus arteriosus)
is located just above the heart and is a connection between the two main
arteries leading away from the heart, the pulmonic artery and the aorta. The
ductus arteriosus allows blood to bypass the undeveloped lungs and enter
directly into the aorta. The ductus arteriosus normally closes within hours to
days after a puppy is born and starts to breathe on its own. If the ductus
arteriosus fails to close, blood is still shunted through, although the
direction usually reverses itself and shunt blood from the aorta into the pulmonary artery. This
is called a Left-to-Right Shunting PDA. This condition results in overload to
the left side of the heart, and more than 50% of affected puppies will succumb
to heart failure within a year without surgical treatment.
Breeds most commonly affected with PDA include
Bichon Frise, Chihuahua, Cocker Spaniel, Collie, English Springer Spaniel,
German Shepherd, Keeshond, Labrador Retriever, Maltese, Poodle, Pomeranian,
Shetland Sheepdog, and Yorkshire Terrier. Females seem to be at greater risk.
- Clinical Signs: Most dogs with a PDA
experience signs that include failure to gain weight and thrive, difficulty
breathing, and coughing. Most commonly, the condition is detected initially
by a veterinarian listening with a stethoscope to an apparently healthy
puppy’s heart.
- Diagnosis: The murmur caused by a PDA
is unique, notorious for having a continuous or "washing machine"
sound. An ultrasound of the heart, or echocardiogram, is necessary to view
the shunt. An electrocardiogram
(ECG or EKG) is also important to
determine if the condition is causing any abnormalities in the heart’s
electrical rhythm.
- Treatment: Surgery is strongly
recommended for all puppies under 2 years of age that have a PDA. In dogs
over 2 years of age, a cardiologist should be consulted. Surgery consists of
passing suture (stitch) material around the open ductus and tying it closed.
While the procedure may sound simple, it does carry serious risks and must
be performed by a skilled surgeon. Prognosis with surgery is generally
excellent.
-
Aortic Stenosis - This defect consists of a ring of
thickened tissue around or near the
aortic valve where blood flows from the left ventricle into the aorta and rest
of the body. This ring of tissue makes it very difficult for the heart to pump
blood out into the aorta. Blood pressure builds up in the left ventricle, and
the heart begins to overwork itself to perform its normal function.
Golden Retrievers seem to be the breed most
commonly affected. Other affected breeds include Boxer, Bull Terrier, German
Shepherd, German Shorthair Pointer, Great Dane, Newfoundland, Rottweiler, and
Samoyed.
- Clinical Signs: Abnormal signs are
usually absent in puppies, but this does not make the disease any less
serious. A dog may die suddenly and without warning before its owner is even
aware anything is wrong. Fainting spells (syncope) may also occur. As with
PDA, these murmurs are often first noticed during a veterinarian’s
examination of a puppy.
- Diagnosis: The diagnosis is made by
echocardiology (ultrasound of the heart), through which the thickened tissue
ring can be seen and blood pressures inside the heart may be calculated.
Chest radiographs and ECG studies may also be helpful.
- Treatment: Treatment includes various
medications to help reduce stress on the heart muscle. Some surgical
techniques are available, but are difficult to perform, costly, and as a
result, are seldom performed. Aortic stenosis is a difficult disease to
treat, and the prognosis, even with treatment, is not generally good. Any
dog of the above listed breeds with any family history of aortic stenosis
should not be bred.
- Pulmonic Stenosis - This is usually a
defective pulmonic valve. This condition, which is present at birth, includes
any defect in the heart which makes it difficult for blood to exit the right
ventricle and enter the pulmonary artery and lungs. Because of the defect, blood
pressure increases in the right side of the heart and in the vessels that empty
blood from the body back to the heart.
Breeds commonly affected include Basset Hound,
Beagle, Boxer, Chihuahua, Chow Chow, Cocker Spaniel, English Bulldog, Labrador
Retriever, Mastiff, Newfoundland, Samoyed, Schnauzer, and terrier breeds.
- Clinical Signs:
Some mild to moderately affected individuals may live normally without
problems. Severely affected dogs may develop signs of heart failure,
arrhythmias, and fainting spells, especially when excited or exercising.
Sudden death, without warning, may occur. A murmur will usually be detected
by a trained professional using a stethoscope.
- Diagnosis: The diagnosis of pulmonic
stenosis is best made through the use of echocardiography. Chest
X-rays and
ECG studies may also be helpful.
- Treatment: For mild-moderate cases,
treatment may not be necessary. For moderate-severe cases, medication to
alleviate congestive heart failure and/or arrhythmias, as well as some
surgical techniques, are available. A cardiologist should be consulted,
especially if considering surgery. Affected dogs should not be bred.
- Other Congenital Heart Defects: These
include atrial and ventricular septal defects, mitral and tricuspid valve
dysplasia, cor triatriatum dexter, and Tetralogy of Fallot. Each of these
conditions usually occur in specific genetic lines and can lead to failure of
the heart muscle in diseased individuals. Professional advice should be sought
when dealing with any congenital defect of the heart.
Acquired Disorders:
These are disorders which are not
present at birth, but rather develop at some point later in life.
- Mitral Valve Insufficiency - This
condition is the most common heart disorder seen in dogs. One study reported
that 75% of 16 year-old dogs have this disorder. Chronic deterioration of the
left atrioventricular valve (mitral valve) may occur as a result of infection of
the valve leaflets or may be idiopathic (no known cause). As the valve
deteriorates, it begins to allow blood to seep through during its closed phase.
Over time, as the valve continues to fail, the seepage becomes more and more
significant. Blood that crosses the leaky valve during the contraction of the
ventricles ends up in the left atrium instead of in the aorta. Extra volumes of
blood, present in the left atrium as a result of the failing valve, cause
enlargement of the chamber and back up of blood into the lung’s blood vessels.
Eventually, fluid begins to leak out of the distended vessels in the lungs. This
fluid, known as pulmonary edema, fills the lung airspaces and results in a
cough.
Small chords known as
chordae tendineae connect the valve leaflets to the heart muscle. These chords
prevent the leaflets of the valve from being forced open backwards during the
powerful contraction of the heart. When the valve leaflets begin to deteriorate,
the attachment of these chords to the leaflets may also deteriorate.
Occasionally, a dog with minor symptoms of mitral valve insufficiency may
experience a sudden decline or even sudden death. This is often due to rupture
of one or more of these chords. This would, in effect, suddenly turn the small
trickle of blood through the leaky valve into a "large river." The
body has a tremendous capacity to compensate for certain problems over time. If
the same "large river" had slowly developed over months to years, the
animal may still be going strong, with minor symptoms. An acute (sudden)
problem, resulting from a ruptured chordae tendineae, usually results in sudden
weakness and heart failure. Development of arrhythmias may
also result in sudden onset of illness and/or
death.
All breeds can be affected by mitral valve
insufficiency, although it seems to be more common in the small and toy breeds.
Males may be more at risk than females. This problem is very common in the
Cavalier King Charles Spaniel, and starts to affect these dogs at a much younger
age. Mitral valve insufficiency is usually first detected after 5 years of age,
and problems associated with the disease are usually not manifested until
several years later.
Early detection is helpful; however, treatment is
usually not started until symptoms begin. The disease is usually first suspected
when a veterinarian hears a heart murmur in a middle-aged or older dog. In other
cases, the owners may notice a minor cough during parts of the day, but until
the cough becomes severe, many do not seek medical help. Valuable time will thus
be lost in slowing the progression of the disease. This is one of many reasons
why routine examinations are essential to a pet’s health.
- Clinical Signs: These are usually
related to chronic, left-sided heart failure. A cough is the most common
early symptom. The cough is usually a dry, hacking cough and may occur with
more frequency at night or with exercise. Inability to exercise, fainting
spells during times of excitement or exertion, increased respiratory rate,
difficulty breathing, restlessness at night, and changes in sleeping
positions may also be noted.
- Diagnosis:
The disease is usually first suspected when a veterinarian hears a heart
murmur in a middle-aged or older dog. Crackling noises in the lungs
(pulmonary edema) may also be heard with a stethoscope. Chest radiographs
are very useful and may show enlargement of the left atrium, elevation of
the trachea/bronchi, and edema in the lungs. A presumptive (preliminary)
diagnosis of mitral valve insufficiency can often be made on the basis of
physical examination findings and chest X-rays. Echocardiography is required
for a definitive, or certain diagnosis. ECG monitoring is recommended to
detect any abnormalities in the heart’s electrical activity.
- Treatment: Treatment should be
initiated when symptoms first begin. A wide variety of medications exist which can be used to help dogs with mitral valve insufficiency. Each
medication has a different goal or purpose; some may help reduce the work
load on the heart, while others may help strengthen the heart’s ability to
contract. One goal of high importance is slowing the progression of heart
failure. This is probably the most important factor in extending the
life-span of a patient suffering from mitral valve insufficiency. Owners of
dogs with this condition should consult a veterinarian regarding this
particular ailment and its treatment.
- Infective Endocarditis - Infective
endocarditis is the infection of the heart muscle, valves, or supporting
structures of the heart. Bacteria are usually responsible for the infection,
although fungal infections can also occur. The bacteria must first enter the
bloodstream and be carried to the heart. Because the bloodstream carries
bacteria to all parts of the body, organs other than the heart (particularly the
kidneys and the spleen) may also be affected. The source of bacteria entering
the bloodstream differs from individual to individual; however, the most common
sources include the mouth, digestive tract, skin, and urinary
tract. Dogs with
bad teeth, urinary tract infections, ear/skin infections, or indiscriminate
eating behavior (will eat anything, including garbage) are more at risk.
The heart valves and supporting structures seem
to be the more common sites of infection within the heart, possibly due to their
constant exposure to turbulent blood. Any of the four heart valves may be
affected. Valves on the left side of the heart (aortic and mitral valves) are
affected more than the valves on the right side of the heart.
German Shepherds and Boxers seem to be more at
risk, although any dog may have this disease.
- Clinical Signs: Heart murmurs
(especially a new heart murmur never previously heard), fever, and sometimes
lameness are found in dogs with infective endocarditis. Other clinical signs
will vary and depend upon where in the heart the infection has occurred and
what other organ systems are involved.
- Diagnosis: Blood cultures are an
important part of making the diagnosis of infective endocarditis. This
diagnostic test requires that blood samples be taken and sent to a
diagnostic laboratory for culture. The culture results may take up to 3
weeks to be finalized; therefore, treatment is usually started before a
final test result can be obtained. If bacteria are found circulating in the
bloodstream, and recent heart problems are present, a definitive (positive)
diagnosis of infective endocarditis can be made. If the actual bacterial
colony is large enough, it may be viewed with echocardiography, thus making
cardiac ultrasound a useful diagnostic tool. Radiographs (X-rays) of the
heart, CBC, blood (serum) chemistry panel, and ECG are other recommended
tests to aid in diagnosis. See Section D for additional information on the
above tests.
- Treatment: Therapy for infective
endocarditis focuses on antibiotics and heart stabilization. Based on their
general success in helping patients with this condition, antibiotics are
chosen in the beginning before blood culture results can be finalized. After
obtaining blood culture results, a veterinarian will select antibiotics
based on the culture and sensitivity data (please see Culture and
Sensitivity page D135). Treatment for damage done to the heart itself is
based on severity, structures affected, and need.
- Prevention: Maintaining a healthy pet
is critical in preventing this disease. While nothing will guarantee 100%
prevention, providing basic pet hygiene is perhaps the most important part
an owner can take in avoiding this ailment. Brushing a dog’s teeth
regularly and providing annual dental cleaning under the care of a
veterinarian are central in pet hygiene. Keeping a close watch for skin and
ear infections, anal gland impactions, urine
abnormalities, and strictly
monitoring diet are also important components of pet hygiene. Each of these
areas is given special attention in other sections of this manual.
- Cardiomyopathy
- This is a disease of unknown origin affecting the heart muscle. There are
several forms of cardiomyopathy in dogs. The most common of these is termed
Dilated Cardiomyopathy (DCM). This discussion will concentrate on this
variation, because others are seen only occasionally. As stated in the name of the
disease, the heart muscle begins to dilate and weaken. Because the heart muscle
weakens, it is unable to generate sufficient pressures during contraction to
properly pump blood out of the heart. The heart failure which develops is known
as systolic failure. Death occurs from congestive heart failure or development
of fatal arrhythmias.
While this disease seems to be increasing in
spaniels, it is primarily seen in large and giant purebred dogs. Deerhounds,
wolf hounds, Doberman Pinschers, Great Danes, Boxers, and St. Bernards top the
list, although any large or giant breed may be affected. Males seem to be more
prone to DCM than females; some reports state that as many as 70% of DCM cases
are male. Most affected animals are diagnosed when they are between 4 and 10
years of age.
- Clinical Signs: Anorexia,
lethargy,
development of a cough, weakness, abdominal distention, fainting episodes,
and weight loss are common clinical signs.
- Diagnosis: Heart murmurs are
present in approximately half of the affected dogs. These heart murmurs and
other abnormal heart sounds may be heard with a stethoscope. Some animals may
also have an increased heart rate. However, it is important to realize that
even a dog with a severe case of DCM may have a "normal-sounding"
heart. In most cases, a definitive (precise) diagnosis is made with
echocardiography. Radiography of the heart provides sufficient evidence in
some cases to make the diagnosis, but will not give sufficient evidence as to
the degree of heart failure. Because dangerous arrhythmias may develop, ECG testing and evaluation are also important in
dogs with DCM.
- Treatment: Medication for heart failure
and the development of arrhythmias is the only way to manage this disease in
dogs. Quality of life may be improved and life-span may be increased, but
the disease is considered incurable and the prognosis is grave. Death
usually occurs within 2 years.
-
Other Diseases - Myocardial infarction (MI), or
"heart attacks," are commonly blamed for sudden death in dogs. True MI
in dogs, however, is relatively rare.
In MI, an object known as an embolus lodges itself into one of the coronary
arteries and deprives the heart muscle, fed by that artery, of its blood supply.
When deprived of its blood supply and oxygen, the heart muscle will die. If only
a small section of muscle is affected, the heart attack is considered minor. A
massive heart attack is usually caused by blockage of a major artery or many
arteries, and results in the death of a large portion of the heart. The embolus
is usually in the form of a blood clot, but can also be a fragment of dislodged
tissue, a foreign object, or an air bubble. Embolus damage in dogs can also
affect other organs such as the lungs or the kidneys.
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This
is an electrocardiogram (ECG or EKG) machine. This machine is used
to determine if a heart condition is causing any abnormalities in
the heart’s electrical rhythm. It is used to help diagnose
specific arrhythmias of the heart. |
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