CONGENITAL
HEART DISEASE
Your
pet was born with a congenital heart defect. Congenital
defects are abnormalities that occur in the developing fetus
and are usually recognized soon after birth. If the defect
is too sever, the embryo dies before birth. Other situations,
not as sever, allow embryo development to birth, and the
pet can live until the defect interferes with normal functioning
(here, the cardiovascular system). Most congenital defects
are first recognized at or near the time of weaning when
the pet is taken to the veterinarian for a first examination.
Sometimes these problems may not be identified until later
in life. Congenital defects are most often the result of
abnormalities in the genetic makeup of the pet. The abnormal
genes may or may not be present in other members of the
litter but are carried by the mother and/or father, sometimes
without compromising their health. Other causes of congenital
defects include exposure to radiation, toxins, or physical
events that occurred during the animal's embryonic stage.
There
are numerous ways to classify congenital heart defects,
but for simplicity we will consider them in four major categories:
(1) obstruction of blood flow within the heart: (2) abnormal
communication between the two sides of the heart, increasing
the blood flow from the left (systemic) to the right (lung)
side of the heart: (3) abnormal communications sending blood
in the opposite direction of flow, from the right (lung)
to the left (systemic) side of the heart: and (4) vessel
(vascular) abnormalities that obstruct a body part and interfere
with normal function.
Obstruction
of blood flow within the heart includes conditions such
as pulmonic, mitral, or aortic valvular stenosis. Valvular
obstruction is caused by a narrowing of an area of blood
flow, decreasing circulation from the heart to some part
of the body. These conditions vary from mild to severe.
They may be minimal and require no care. However, in other
cases, medication only, opening the obstruction with a special
catheter, or surgical correction may be needed. Surgery,
although commonly performed in humans, is both difficult
and infrequent in veterinary medicine.
Blood
may flow abnormally from the left to the right side of the
heart because of a hole between the two sides of the heart
that did not close during embryonic formation. One such
condition, patent ductus arteriosus (PDA), is a remnant
of normal embryonic heart function. If PDA is diagnosed
early, it may be corrected surgically and the pet may be
able to lead a normal life. Other conditions such as ventricular
or atrial septal defects involve a hole between two chambers
of the heart. Closure of septal defects requires open heart
cardiopulmonary bypass surgery, which is infrequently performed
in veterinary medicine. Blood flow from the right to the
left side of the heart without passing through the lungs
is very abnormal and quite uncommon. Thus, a serious communication
problem exists that results in unoxygenated blood being
transported to the body. Such a situation usually does not
allow the pet to live beyond early adulthood. Because of
the complicated nature of these problems, open heart surgery
is rarely an available option. Surgical procedures may be
available at teaching and specialty clinics to treat such
problems.
Persistent
aortic arch, peripheral arteriovenous shunts, and cor triatriatum
are heart problems that are the result of abnormal vessels
interfering with normal blood flow. These conditions can
usually be corrected surgically if identified early, before
complicating problems develop to preclude normal life.
Because
many congenital heart defects are thought to be due to genetic
problems that can be passed from one generation to the next,
veterinarians recommend that animals with such conditions
be neutered at an early age to prevent breeding and the
dissemination of defective genes to a new generation. Some
congenital heart defects may be surgically corrected; others
are effectively dealt with for variable periods using medications.
Regrettably, most congenital heart defects have a poor long-term
prognosis. It is sad for the owner and for the pet to suffer
needlessly. In selected circumstances, euthanasia may be
recommended if the pet is unable to maintain a good quality
of life.
A
congenital heart defect is suspected after a thorough physical
examination has been performed. The electrocardiogram helps
to identify the presence of abnormal heart chamber size
as well as irregularities of the heart's rate and/or rhythm.
Radiographs (x-rays) are needed to visualize abnormalities
in the size and appearance of the heart, vessels, and lung
structures. The ultrasound (echocardiogram) examination
is a direct, noninvasive means of looking inside the heart's
walls to measure the size of the heart's four chambers and
to identify abnormalities (qualitatively and quantitatively)
in blood flow. Occasionally, more invasive procedures such
as cardiac catherization (passing small tubes into the heart
and blood vessels and injecting dye) or surgical evaluation
may be recommended.
SOURCE:
Textbook of Veterinary Internal Medicine, Client Information
Series, by Stephen J. Ettinger.
