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This is the second
article in a series addressing cardiac diseases in dogs, with an
emphasis on diseases that more commonly afflict Bichons Frises.
Refer to the first article in the series while you read this
article, “Introduction to Canine Cardiac Disease”, which can be
found on this web site:
www.bichonhealth.org/HealthInfo/CanineCardiac.asp. This second
article includes information on diseases that are present at birth
(congenital), so these puppies are born with malformations of the
heart or great blood vessels. Bichons are listed as being
predisposed to Patent Ductus Arteriosus (PDA), the most common
canine congenital cardiac defect, so this article is primarily
devoted to this defect.
Significance
Cardiac disease in
dogs is prevalent, accounting for about 11% of dogs seen by
veterinarians. At least 3 million dogs examined by veterinarians in
the US have acquired heart disease and may be in heart failure.
Acquired heart diseases, both inherited and obtained from influences
outside the body such as infections, will be addressed in successive
articles.
Clinical Signs of Heart Failure
Cardiac diseases
eventually lead to heart failure, AKA congestive heart failure (CHF),
which is defined as failure of the heart as a pump, meaning the
heart is unable to supply the body and organs with sufficient flow
of oxygen-rich blood. This inefficiency is due to weakened muscles
in the ventricles, the pumping chambers of the heart, causing backup
of blood into the cardiovascular system. 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. Initially,
clinical signs of CHF 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. 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
detected during a veterinary exam are the hallmark of most cardiac
diseases and may be detected before any clinical signs are present,
therefore the importance of that yearly exam and the first puppy
exam before leaving the breeder. Other clinical signs of heart
failure that may be detected due to inadequate blood flow to the
body include slow capillary refill in the gums (it takes longer than
2 seconds for the gums to regain the pink color after pressing with
a finger), weak and rapid pulses, cardiac rhythm irregularities
(arrhythmias), fainting episodes that may appear to be a seizure,
and cyanosis (blue tint) in the white part of the eyes or gums.
Dogs and humans
can be born with several cardiac structural defects including
tetralogy of Fallot (4 distinct structural defects), holes between
the chambers in the heart called septal defects (ASD, VSD),
narrowing of the outflow tract of the left ventricle called
subaortic stenosis (SAS), and persistent fetal circulation (patent
ductus arteriosis, or PDA).
Pathophysiology of Patent Ductus Arteriosus (PDA)
While in the
uterus the fetus obtains oxygen from the mother’s blood via the
placenta and umbilical cord, instead of breathing it in through the
lungs. There is a communication between the 2 major blood vessels
that conduct blood out of the ventricles, the pulmonary artery
(carries blood to the lungs) and the aorta (carries blood to the
body and organs), which allows most of the blood to bypass the lungs
that are not being used. Shortly after birth, once the lungs are
expanded, the connection between the aorta and pulmonary artery, the
ductus arteriosus, closes. If it remains open (patent) blood is
shunted through it from the high-pressure aorta to the low-pressure
pulmonary artery. The result is excessive blood flow to the lungs,
which places a burden on both ventricles that eventually fail.
Diagram obtained from
http://www.childrenshospital.org/cfapps/mml/index.cfm?CAT=media&MEDIA_ID=265
Key:
IVC = inferior vena cava, SVC = superior vena cava, RA = right
atrium, RV = right ventricle, PA = pulmonary artery, LA = left
atrium, LV = left ventricle, AO = aorta, and black arrow = shunting
of blood through the PDA
Diagnosis of PDA
A puppy born with
PDA may appear normal for a few weeks, except that it may be the
first to tire while playing and the smallest puppy in the litter.
Upon auscultation, there will be a loud, continuous murmur. Murmurs
are graded on a scale of I to V, with grade I being very soft and
grade V being very loud, and can even be palpated on the chest
wall. Eventually the puppy will develop clinical signs of heart
failure. The diagnosis can be confirmed by ultrasound, x-ray
to visualize the congested lungs and enlarged heart, and electrocardiogram that reflects
changes in the ventricles.
Treatment of PDA
At
the age of 2-3 months, before significant heart failure develops,
surgery is indicated to correct the defect, without which 60% will
die within one year. Surgery, which is very successful, consists of
opening the chest from the left side through the ribs (thoracotomy)
and tying off the patent ductus. Prognosis for surviving surgery is
90%, and is excellent for a normal life if surgery is completed
early.
Breeding Advice
PDA
is believed to be polygenic, caused by more than one pair of genes,
so random in nature. The affected dog and its parents should not be
bred, plus littermates should only be used for breeding after
careful screening. According to Dr. Jerold Bell in his discussion of
polygenic diseases (see link below to his article), “If
there are multiple generations of normalcy in the breadth of the
pedigree, then you can have some confidence that there are less
liability genes being carried.”
He defines
liability genes as, “a number of genes must
combine to cross a threshold and produce an affected dog”.
References:
-
Diseases of the
Heart by Charles K. Friedberg
-
“Matters of the
Heart” by Mara Bovsun. AKC Gazette, October, 2005
-
“Facts on Canine
Cardiac Health” by Kevin Schargen. AKC Gazette, March, 2005
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OFA web sites:
http://www.upei.ca/~cidd/Diseases/cardiovascular%20diseases/PDA.htm
http://www.vetgo.com/cardio/concepts/concsect.php?conceptkey=20141#20141
http://www.offa.org/cardiacinfo.html
http://www.bichonhealth.org/HealthInfo/Startegies.asp
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