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This is the fourth and last
article in a series addressing canine cardiac diseases, with an
emphasis on diseases that more commonly afflict Bichons Frises.
Refer to the first article in the series
www.bichonhealth.org/HealthInfo/CanineCardiac.asp
while you read this article, for descriptions of basic cardiac
anatomy and blood flow through the heart.
Significance
Cardiac disease in dogs
is prevalent, accounting for about 11% of dogs seen by
veterinarians, of which 75-80% have chronic valve diseases. At
least 3 million dogs examined by veterinarians via ultrasounds in
the US have acquired heart diseases and may be in heart failure.
Cardiac disease is the third most common cause of death in dogs less
than 10 years of age. Mitral valve disease, which can be acquired
and/or hereditary, is the most common cardiac disease in dogs.
Acquired heart diseases strike after puppyhood, during or after the
breeding years. Acquired heart diseases, both inherited and
obtained from influences outside the body such as infections, is the
focus of this article.
The incidence of cardiac
disease in Bichons has risen significantly in the last few years,
moving from the #11 position to #7. Hopefully this article will
encourage Bichon breeders to obtain the OFA cardiac certifications
prior to breeding, reduce the incidence of heart disease in Bichons,
and help improve the health of our beloved Bichons.
There are basically 3
categories of heart disease in dogs that all progress to heart
failure if left untreated or interventions are ineffective:
1.
Hereditary diseases that may appear later than birth, such as
valve diseases, dilated cardiomyopathy (disease of the cardiac
muscle), and sub aortic stenosis (a narrowing of the ventricle below
the aortic valve)
2.
Congenital heart diseases that are present at birth and
genetically transmitted, such as patent ductus arteriosis (PDA)
3.
Acquired diseases such as coronary artery disease and chronic
valve diseases, which also may have an inherited component
The focus of this
article will be chronic degenerative valve disease, the most common
canine cardiac disease. Of the 4 cardiac valves, the mitral valve is
most often affected. Chronic valve disease most commonly afflicts
small to medium dogs that are middle age or older, with estimates
that 25-30% of older small breed dogs are affected. There are
several reported cases of valve disease in Bichons, and many reports
of clinical signs that may indicate valve disease, but no definitive
diagnosis was obtained.
Coronary artery disease
that leads to heart attacks, another acquired heart disease that
also has a genetic component, is very rare in dogs most likely due
to their short lifespan (this disease requires many years to
develop) and how they synthesize lipids (fats in the blood).
Hyperlipidemia (elevated cholesterol and other lipids in the blood),
one of the major risk factors for coronary artery disease, is
extremely rare in dogs but is hereditary in a few breeds and some
mixed breeds. Hyperlipidemia may also occur as a consequence of
other diseases such as diabetes, pancreatitis, or hypothyroidism.
Currently, there are 2 reports of Bichons with coronary artery
disease, and one with hyperlipidemia. Autoimmune disorders than can
cause coronary artery disease are atherosclerosis and vasculitis
(inflammation of the blood vessels). See this article on the Bichon
health web site for more information:
http://www.bichonhealth.org/HealthInfo/DefAutoimmune.asp.
Causes of
Degenerative Valve Diseases
In most cases,
development of chronic valve disease is suspected to be genetic and
discovered later in the dog’s life. If the disease occurs early in
a dog’s life, it is assumed to be genetic. There are rare cases
reported of mitral valve dysplasia (abnormal development) present in
embryos, which would define the disease as congenital.
Infections can cause
damage to heart valves, which is not considered hereditary.
Normally, microorganisms (bacteria, viruses, fungi) are present on
your skin and in your mouth, intestines, and urinary tract. The
blood is normally free of microorganisms, but they can gain access
to the bloodstream during dental or surgical procedures. In
addition, the mouth is a very vascular area, so infections present
in the teeth and gums can gain access to the bloodstream. These
microorganisms can travel quickly to the heart due to its proximity
to the mouth, causing damage to the heart valves and/or endocarditis,
infection of the lining of the inside of the heart chambers. The
leaflets of the valves become malformed and thickened. As the heart
valves and endocardium heal, clumps of tissue form called
vegetations. If large enough pieces of the vegetations break off,
they can travel to blood vessels and block blood flow, causing
dangerous circumstances such as a stroke or a pulmonary embolism. In
addition, diseased gums can release high levels of bacterial
pro-inflammatory components that travel through the bloodstream and
damage the heart and other organs.
Prevention of dental
disease with good oral hygiene is paramount to prevent damage to the
heart valves, considering that dental disease is the #4 disease in
Bichons. This involves brushing your Bichon’s teeth at least
weekly, providing bones to chew that aid in cleaning the teeth,
avoiding tartar accumulation, and aggressively treating any broken
or infected teeth or gums.
Myxomatous mitral valve
disease is the most common acquired heart disease in adult dogs.
This develops as a result of mucus replacing connective tissue in
the leaflets of the mitral valve, which thicken causing incompetence
in the valve. The end result is a fibrous tumor, called a myxoma
that in some humans can be removed. The transmission of this
disease is suspected to be hereditary in dogs, evidenced by the
strong association in certain breeds. At this time, this disease
has not been reported to the BFCA health committee.
Rheumatic fever is an
autoimmune disease that can develop after a strep throat infection
in humans, leading to inflammation and damage of the heart valves,
but this does not seem to exist is dogs. However, an autoimmune
inflammation of the heart and valves can develop in dogs.
Pathophysiology of Mitral Valve Insufficiency
The
heart valves function like trap doors to direct blood flow correctly
through the heart. The mitral valve is the most significant valve,
opening to allow oxygen-rich blood to flow from the lungs into the
left ventricle where it is pumped to the body and organs. The
mitral valve closes when the left ventricle is contracting to
prevent blood from leaking up into the left atrium, thereby
promoting forward flow of blood through the aorta and to the body.
Enduring the highest pressures inside the heart chambers, the mitral
valve is most commonly diseased, followed next by the aortic valve
that opens to allow blood flow out of the heart into the aorta, and
to the body (See figure 1). In addition, the chords that attach the
leaflets of the mitral valve to the wall of the left ventricle are
easily weakened and provide optimal surfaces for growth of
vegetation (See figure 2).
Mitral valve insufficiency, also called mitral regurgitation, occurs
when the mitral valve is damaged to the extent that it cannot close
tightly, so it leaks. This allows blood to flow backward up into
the left atrium when the left ventricle is ejecting blood into the
aorta, diminishing the amount of blood that is sent to the body and
causing a murmur due to turbulent blood flow. The left atrium gets
overloaded with blood, causing it to dilate. Because there are no
valves between the left atrium and the lungs, the excess blood and
pressure in the left atrium is transmitted to the lungs causing
congestion with respiratory symptoms. Next, the right ventricle has
to pump blood to the lungs against the resistance of the excess
blood and pressure, leading to failure of the right ventricle as a
pump. The left ventricle, responsible for our blood pressure, also
fails because it must pump the excess blood volume that resides in
the enlarged left atrium when it empties into the ventricle. The
net result is failure of both ventricles, i.e. heart failure (See
figure 3).
One
other cause of mitral insufficiency is dilated cardiomyopathy, in
which the dilated left ventricle dilates the rings that surround the
leaflets of the valve, rendering the valve incompetent due to the
inability of the leaflets to close properly. (See figure 4).
Figure 1
Figure 2
Figure 3
This
diagram is very busy, but is a good example of the effects of an
incompetent mitral valve. The right and left ventricles are
separated to demonstrate the impact on their particular circuits of
the cardiovascular system. Note the increased size of the left
atrium as compared to the right atrium.
Figure 4
Clinical Signs of Heart Failure
Cardiac valve diseases
eventually lead to heart failure, also called congestive heart
failure (CHF), which is defined as failure of the heart as a pump.
The result is that the heart is unable to supply the body and organs
with sufficient flow of oxygen-rich blood. The heart does not stop,
but functions less efficiently. This inefficiency is due to
weakened muscles in the ventricles, the major pumping chambers of
the heart, causing backup of blood into the venous system and the
lungs. To help you understand this process, see my toilet analogy
in this article posted on the Bichon health web site:
http://www.bichonhealth.org/HealthInfo/CanineCardiac.asp,
(and figure 1). The heart attempts to compensate for the reduced
pumping ability by increasing the heart rate, allowing more outflow
of blood from more frequent heartbeats. Despite many compensatory
mechanisms in the heart and body that preserve the balance short
term, in time the stress on the heart takes its toll.
Heart failure ranges in
severity from mild with minimal or no symptoms, to severe.
Initially, clinical signs of heart failure are mild, vague, and easy
to overlook. As time passes more blood backs up into the lungs
causing exercise intolerance, loss of appetite, rapid respirations,
and frequent coughing that can easily be mistaken for a respiratory
infection such as kennel cough. Blood also backs up into the venous
system causing engorged neck veins, liver enlargement, and swelling
in the abdomen and legs. Without adequate blood flow, organs in the
body malfunction and eventually fail, thus causing more severe
clinical signs, such as kidney failure.
Heart murmurs, abnormal
heart sounds, or irregularities in the heart beats (arrhythmias)
detected during a veterinary exam are the hallmark of cardiac
diseases and may be detected before any symptoms are present,
highlighting the importance of an annual veterinary exam, OFA
cardiac certification, and the puppy exam before leaving the
breeder.
Symptoms and clinical signs
of heart failure include:
1.
Slow capillary refill in the gums (> 2 seconds is required
for the gums to regain the pink color after pressing with a finger)
2.
Weak and rapid pulses
3.
Cardiac rhythm irregularities (arrhythmias) that may cause
sudden death
4.
Abnormal heart sounds, murmurs heard with a stethoscope
5.
Congestion heard in the lungs with a stethoscope
6.
Enlarged heart and lung congestion seen on xray
7.
Reduced stamina, weakness, lethargy, loss of appetite
8.
Shortness of breath, wheezing, coughing, rapid respirations
9.
Fainting episodes that may appear to be a seizure
10.
Confusion due to diminished blood flow to the brain
11.
Cyanosis (blue tint) in the white part of the eyes or gums
12.
Abdominal distension
13.
Jugular (neck veins) venous distension
14.
Enlarged liver palpated in the abdomen
15.
Elevated atrial natriuretic peptide (ANP or proANP) that
correlates with the severity of heart failure (blood test)
16.
Late stages: abnormal blood tests that indicate failure of
kidneys, liver, and/or other organs
Diagnosis of
Mitral Valve Disease (MVD)
MVD is primarily an
adult-onset disease, so signs may not be apparent until well into
the breeding years. The first clinical sign that precedes symptoms
is a murmur that can be detected by a veterinarian during an annual
exam or during an OFA cardiac exam. A skilled clinician, such as a
canine cardiologist, will suspect MVD by the characteristics of the
murmur and its location on the chest wall. A definitive diagnosis
of MVD can be obtained by echocardiography (ultrasound) that will
demonstrate the regurgitation of blood through the mitral valve. If
echo is not available, a presumptive diagnosis of MVD is based upon
the physical examination, the characteristics and location of the
murmur, and clinical signs of heart failure; a chest xray that
reveals an enlarged heart with congested lungs; and an
electrocardiogram that reflects enlarged ventricles and left atrium
with possible irregularities in the heart rhythm due to enlarged
heart chambers.
An additional blood test
may reveal elevated atrial natriuretic peptide (ANP or proANP) that
correlates with the severity of heart failure. Heart failure causes
increased pressure in the atria (the heart chambers above the
ventricles) as the blood backs up from the weakened ventricles that
cannot empty properly. The increased pressure in the atria
stimulates the release of the hormone ANP. Early detection of heart
failure facilitates more effective treatment, and screens dogs that
may need further evaluation. A new screening tool for proANP can be
obtained from NationWide Laboratories called “Canine Cardiac Screen”
at this web address
http://www.nwlabs.co.uk/canine-cardiac-screen.html.
Treatment of
Mitral Valve Disease
The only cure is to replace
the defective valve with a prosthetic valve or to surgically repair
the valve, as done in humans and rarely in dogs. In humans surgery
is avoided until signs of heart failure begin, allowing the superior
native valve to last as long as possible. These surgeries are
considered pioneering in dogs, not experimental. The major
limitation is the size of the dog, so most surgeons limit this
surgery to dogs that weigh at least 18-22 pounds, ruling out the
majority Bichons.
Earlier medical treatment,
prior to symptoms of heart failure, will produce a better outcome.
The ultimate goal of medical therapy is to make the dog comfortable
and prolong its life, accomplished by drugs than strengthen the
heart, dietary manipulations, and activity level modifications.
Medications that may be
prescribed by the veterinarian to improve the efficiency of the
ventricles:
1.
Diuretics such as Furosemide (Lasix) that promote loss of excess
fluid
2.
Pimobendan (Vetmedin)
improves contractility of the ventricles and dilates blood vessels
(decreases the workload of the heart)
3. ACE
inhibitors such as Amlodipine, Enalapril, Benazapril improve
contractility of the ventricles
4.
Drugs to treat arrhythmias that may develop
Dietary supplements that
promote a healthy heart include fish oils, multiple vitamins that
contain minerals and the B vitamins, Vitamin E, Taurine, L-carnitine,
and Coenzyme Q10. However, there are no formal studies to prove
that these supplements benefit the heart.
Sodium restriction in
the diet is essential to avoid stressing the heart and lungs with
excess fluid. Beware that high levels of sodium can be hidden in
cheese, lunchmeats, canned dog foods, and most dog biscuits and
treats. Many commercial dry kibbles do not indicate the levels of
sodium. The best diet to avoid sodium is fresh raw foods and
avoiding table scraps. Also, low sodium prescription diets are
available through your veterinarian.
Limit strenuous
activities to allow for adequate rest. Maintain a normal weight
since extra pounds strain the heart. Seek veterinary services for
any signs of respiratory distress, progressive lethargy, or
fainting.
New technology—stem
cells: Any
disease that results from a premature loss of cells has the
potential for benefit from treatment with stem cells that can be
obtained from the dog’s intrinsic cells or a close relative.
Myocardial (heart muscle) cells do not regenerate after injury,
however stem cells may be able to generate new myocardial cells to
replace those that died and to repair some of the damaged cells. The
stem cells are injected intravenously with hopes they will migrate
to the heart, or they are injected into the coronary arterial
system, or directly into the heart muscle.
Breeding
Advice
Specific genes for mitral
valve disease have not yet been identified in dogs, but the mode of
inheritance is suspected to be polygenic, meaning that several
defective genes produce a disease at random, with at least one gene
originating from each parent who may be affected or carriers. If a
cause can be determined other than genetics, then mitral valve
disease can be labeled acquired.
Affected dogs should be
removed from the breeding program not only for genetic reasons, but
also their fertility and ability to tolerate mating, pregnancy, and
whelping may be in jeopardy. Siblings and parents of affected dogs
should only be used after careful cardiac screening. Avoid
repeating a breeding of the same parents or related dogs. See the
link below to Dr. Jerold Bell’s article for more information on
modes of inheritance.
Avoid breeding Bichons with
significant dental disease that is suspected to be genetic, and may
be linked to weak lower jaws. Dental disease can lead to cardiac
valve disease due to bacteria becoming blood borne and traveling to
the heart, damaging the valves. Provide optimal dental hygiene to
your Bichons to prevent dental infections.
Share any knowledge of
Bichons in your breeding program with cardiac diseases so other
breeders can make informed, selective breedings.
The BFCA
Health Committee
feels that this disease deserves vigilance. You are encouraged to
share data with the committee on any Bichons with cardiac valve
diseases, which will remain confidential, so that current trends in
health problems in Bichons are evident. Many reports submitted
indicate Bichons with heart failure and murmurs, but no actual
diagnosis. More data is needed on the prevalence of specific heart
diseases in Bichons. Contact either a committee member, or complete
a health incident form located on
www.bichonhealth.org.
References:
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Diseases of the Heart
by Charles K. Friedberg
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Cardiovascular Nursing
by Kernicki, Bullock, Matthews
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“Matters of the Heart”
by Mara Bovsun. AKC Gazette, October, 2005
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“Facts on Canine
Cardiac Health” by Kevin Schargen. AKC Gazette, March, 2005
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web sites:
http://www.heartsite.com/ (Excellent site for videos of
the heart in action)
http://www.upei.ca/cidd/intro.htm
http://www.vetgo.com/cardio/concepts/concsect.php?conceptkey=78#78
http://vin.com/VINDBPub/SearchPB/Proceedings/PR05000/PR00034.htm
http://www.offa.org/cardiacinfo.html
http://www.bichonhealth.org/HealthInfo/Startegies.asp
(Dr. Bell’s article)
http://www.newmanveterinary.com/Hyperlipidemia.html
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