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Atrial Septal Defect
Emily Otero
December 6, 2016
Everybody hopes for a healthy baby, but the truth of the matter is that not everyone is
fortunate enough to be born free of major adverse health condition at birth. Approximately 3-4%
of almost four million children born in the United States every year are born with some sort of
congenital abnormality. The term congenital refers to a condition existing at or prior to birth, and
so congenital abnormalities are medical conditions present manifesting in a baby at or before
birth that somehow deviate from what is expected from a conventionally healthy child. While
congenital defects account for 20% of infant deaths in the United States, they do not necessarily
indicate an urgent or life-threatening injury. However, they do require immediate treatment or
supervision from doctors in order to ensure timely and appropriate treatment. Many children
born with congenital defects must continue to see doctors into adolescence, and may stand a risk
of developing complications from their congenital defect, or find themselves at higher risk for
certain adverse medical conditions well into adulthood.
Approximately one third of all children born with congenital defects are born with a heart
defect of some kind or another. Heart defects are very diverse, and are associated with a variety
of afflicted areas, symptoms, causes, risk factors, and consequences. Even the same kind of heart
defect is experienced in radically different ways by different individuals, and may have resulted
from different risk factors and may demand different ranges of treatment or maintenance for
varying amounts of time. For this reason, instead of attempting to analyze a wide variety of heart
defects for a limited understanding of a very broad range of issues, this paper will focus on
examining many different aspects of a single heart defect – the atrial septal defect – in depth.
DEFINITION
In order to fully grasp the complications and symptoms that arise from the atrial septal
defect, it is critical to understand the way a healthy human heart functions.
The function of blood in the body is to provide a vessel with which to transport oxygen
from the lungs to every cell in every corner of the body, so that this oxygen can be converted to
energy for the cells to complete their individual functions. The heart serves a dual purpose: its
pumping allows for the physical act of blood flow throughout the body, and the heart itself also
serves as a crossroads to direct oxygen-rich and oxygen-poor blood out to the rest of the body or
back to the lungs, respectively. The latter function can be easily visualized when taking into
account the internal structure of the human heart, as seen in the figure below.
The main body of the heart is divided into four chambers – two atria and two ventricles.
The atria are situated in the top part of the heart, and collect blood flowing into the heart from
other parts of the body, before being sent into the ventricles. The ventricles make up the lower
part of the organ, and are responsible for pumping blood out of the heart (either to the lungs or to
other parts of the body). The left and right halves of the heart are separated by a wall called the
septum, which does not allow for blood to pass between the two halves, as each half is
responsible for the handling of either oxygen rich blood or oxygen poor blood – never both. Thus
blood cycles through the body in the following way: oxygen-rich blood flows into the left atrium
of the heart from the lungs, then is passed into the left ventricle and then the aorta to be
distributed to the rest of the body. Then, oxygen poor blood is returned to the heart, flowing into
the right atrium, then is passed into the right ventricle and into the pulmonary artery to be
oxygenized again by the lungs, and the cycle begins again. This process is outlined more clearly
in the figure below.
A labeled cross section of a healthy human heart including arrows that represent blood flow.
Blue arrows represent the flow of blood with low levels of oxygen towards the lungs, and red
arrows represent the flow of oxygen-rich blood as it moves from the lungs to the rest of the body.
Image credit: National Heart, Lung, and Blood Institute official website (nhlbi.nih.gov)
The important thing to understand in the context of an atrial septal defect is the presence
of a clear separation between the left and right atriums in a healthy heart. It may be difficult to
determine due to the positioning of the aorta and the pulmonary artery as being superimposed
over the division between the two atria in the above diagram, but a healthy heart would have the
septum that clearly divides the two ventricles and the two atria. This is made clearer in the
diagram below, which has removed the representations of the superimposed aorta and pulmonary
artery.
Image credit: Fairview Ebenezer Health Library
(http://www.fairviewebenezer.org/HealthLibrary/Article/89100)
In prenatal development, it is perfectly normal for fetuses to have many openings along
the septal wall prior to birth. These openings are a perfectly normal aspect of child development,
and are not necessarily cause for concern. However, if these openings have not resolved
themselves by the time the baby is born, they are classified as congenital heart defects and must
be dealt with by a medical professional before the child can be released into the care of the
parents, as they can cause serious health risks. Depending on where the hole is situated on the
septal wall, three different defects, all posing different risks and demanding different treatments,
can occur: if the hole exists in the division between the two ventricles, then it is a ventricular
septal defect; if the hole exists in the division between the two atria, then it is an atrial septal
defect (the focus of this paper); if the hole exists in the middle, affecting both the divisions
between the ventricles and the atria, then it is an atrioventricular septal defect, and requires
immediate surgical correction upon threat of death.
Hearts with the atrial septal defect allow for the comingling of blood between both
atriums. Specifically, oxygenized blood from the left atrium flows into the right atrium, mixing
with the oxygen poor blood. The oxygenized blood in the right atrium is then passed into the
right ventricle and sent straight back to the lungs through the pulmonary artery without having
passed on any oxygen to other parts of the body, elevating the amount of oxygen present in the
lungs and weakening them over time, as they are not used to the higher concentration of oxygen
being presented to them. Additionally, there is now a higher amount of blood in the right atrium,
resulting in a higher volume of blood being passed through the blood vessels around the lungs
than is normal or expected, wearing down the strength of these blood vessels over time, leading
to complications if the problem is left unresolved for long periods of time.
Every instance of atrial septal defect is different, as the sizes of the holes present in the
atrial septum may vary from case to case, and thus require different treatments and pose different
threats to varying degrees of urgency. In general, there are four major types:
The ostium primum atrial septal defect is, in actuality, associated with atrioventricular
canal defects, and is characterized by a cleft in the mitral valve of the heart in the left atrium. The
mitral valve operates as a “gate” that separates blood from the left atrium from the left ventricle,
so as to not allow blood to flow from the ventricle into the aorta while still letting blood flow
into the left ventricle. A cleft in this valve renders this capability null.
The sinus venosus atrial septal defect is a defect that occurs in the right atrium, at the
junction with the pulmonary veins that allow deoxygenated blood to flow into the heart. This
results in abnormal drainage, and the flow of blood into the heart leaks into the left atrium.
The coronary sinus atrial septal defect is when there is an opening in the coronary sinus
in the right atrium, where the veins in the right atrium drain into the chamber proper.
The ostium secundum atrial septal defect is the most common type. Approximately 70%
of all children born with atrial septal defects are affected by this variety. It is characterized by the
presence of a hole in the center of the atrial septal wall, an opening that never closed while the
heart was still in neonatal development.
A diagram of a heart with an atrial septal defect, with an arrow demonstrating the flow of
oxygenized blood (represented by the red arrow and chambers) to deoxygenized areas
(represented by the blue chambers). Image source: Centers for Disease Control and Prevention
official website (cdc.gov)
PREVALENCE
Out of all the children born with congenital heart defects, approximately from 5 to 10%
of children are diagnosed with the atrial septal defect. For every one thousand five hundred live
births, one is detected with an atrial septal defect. Female babies are twice as likely to develop an
atrial septal defect than male babies. The reasons for this are not yet understood.
Likely due to the fact that atrial septal defects are often minor and sometimes
asymptomatic, and can sometimes go undiagnosed until adverse health effects manifest
themselves later in life, approximately 30 to 40 percent of congenital heart diseases present in
surviving adults are atrial septal defects.
DIAGNOSIS
Identification of abnormal heart development is usually a focus in prenatal and very early
childhood development. Medical professionals use ultrasounds to get a general picture of the
health of the heart. This will usually portray the presence of a serious or obvious atrial septal
defect. After birth, pediatricians will begin the regular process of auscultation, or the close
listening of internal bodily functions through a stethoscope, at check-ups. They may notice
palpitations or a heart murmur in the fetus, which will warrant further testing by a pediatric
cardiologist.
Further tests can include x-rays, which can tip doctors off to the presence of an atrial
septal defect because of possible swelling in or enlargement of the heart as a result of the
increased blood flow in the right half of the heart. Electrocardiograms measure electrical activity
of the heart through the placement of plastic patches called electrodes on the surface of the skin
of a child. Abnormal electrical readings may be symptomatic of muscle stress or arrhythmia, a
type of abnormal heart rhythm. The presence of arrhythmia may be indicative of a congenital
heart defect. Once the presence of such an anomaly is suspected, echocardiograms use
ultrasound to capture a real-time, moving image of the heart and its internal structures, and can
reveal more details about the specifics of the defect. It can visually depict information about the
pattern of blood flow within the heart, and this information can be used to determine the size of
the opening and the amount of blood passing through it.
A much more invasive procedure called cardiac catheterization used only when the
presence of the defect is practically confirmed and when more information about the specifics of
how the heart is affected by the defect are needed in order to proceed with treatment. Cardiac
catheterization requires the patient to be sedated as a flexible tube, the catheter, is guided by the
cardiologist through the body into the heart, starting from a blood vessel in the groin. Not only
does the tube make measurements of blood pressure and oxygen levels in each of the four
chambers of the heart, but it also injects a dye to stain the inside walls of the heart, so that
relevant structures are easier to discern from future less invasive techniques to see the heart.
If the defect is not diagnosed early in development (a frequent occurrence, as the swelling
of the heart and the presence of the heart murmur are usually only detected in very serious
cases), the afflicted child may not realize there is a problem until they grow up and develop
medical complications from the defect. Most instances of atrial septal defect are not urgent
causes for medical concern and are often asymptomatic. The symptoms that do exist in some
children are often mistaken for isolated incidents, or may resemble other heart or even mental
conditions. Fatigue, shortness of breath after activities such as playing or feeding, arrhythmia,
heart murmurs, poor physical growth, a susceptibility to respiratory infections are all exhibited
symptoms of children who have atrial septal defects. Most people who discover the defect in
adulthood realize it due to the presence of a heart murmur.
CAUSES
Causes of atrial septal defect are not largely understood, though there is reason to believe
that some children may have a genetic predisposition to being born with a congenital heart
defect. Atrial septal defects in particular are typically associated with Down syndrome (caused
by an abnormality with the number of chromosomes passed down to a child). Women who
consumed alcohol, drugs, or certain medications while pregnant, or women who suffered from a
viral infection in the first trimester of pregnancy were also found to be more likely to have
children with a congenital heart defect.
COMPLICATIONS AND TREATMENT
As mentioned above, when left untreated for long periods of time, the atrial septal defect
can irreparably damage the heart and lungs by the time the individual is well into adulthood.
Though such effects typically don’t manifest until after years of having the defect, swift and
timely correction is preferred so as to minimize the risk of developing adverse effects through
neglect. Some of these consequences include lung disease, exercise intolerance, shortened
lifespan, and an increased risk of stroke.
When detected prenatally or in young childhood, doctors often recommend leaving it
alone to give it the chance to close on its own. In this case, the defect was simply a matter of
belated cardiac development, and should be monitored throughout childhood and minded
throughout life as part of a patient’s resolved medical history. If the defect does not seal itself on
its own, cardiologists will resort to invasive surgeries to manually correct the defect. In some less
serious cases of secundum atrial septal defects, the hole can be sealed through cardiac
catheterization, in which the doctor uses the catheter to guide a device called the septal occluder
into the opening and prevents the flow of blood through it. However, in more severe or complex
cases, the patient may need to undergo open-heart surgery to close the opening with stitches or a
patch, and to manage any damage that may have occurred in the heart as a result of the opening.
Leading up to the procedures to close the heart, young children may be prescribed certain
medications to help manage some of the side effects that result from atrial septal defect. Digoxin
is prescribed in cases in which the heart has already been weakened from the stress, and is not
pumping blood as efficiently as it should be as a result of the septal opening, and its purpose is to
help the heart pump more blood per beat. Diuretics are prescribed when the kidneys are affected
by the lower amounts of oxygen they are receiving from the blood, and help to maintain the
proper water balance in the body by facilitating the removal of excess fluid through the
weakened kidneys.
Children born with atrial septal defects are more susceptible to bacterial infections in the
inner surfaces of the heart, a condition known as bacterial endocarditis. The use of antibiotics
may be prescribed if the patient will undergo an invasive procedure, such as surgery or cardiac
catheterization to reduce the risk of infection.
All in all, the concept of the atrial septal defect as an unpreventable hole in the heart of a
child sounds much scarier than it is in most cases. The truth is that it is a manageable condition
that can be easily corrected, provided that it is detected and diagnosed early in life.
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