An atrial septal
defect (ASD) is a hole in the wall between the two upper chambers of your heart
(atria) (Ferri, 2017).
The condition is present from birth (congenital) and Small atrial septal
defects may close on their own during infancy or early childhood (Rochester and
Minn 2017)

The heart has two sides, separated
by an inner wall called the septum and hole in the septum between the heart’s
two upper chambers (or “atria”) is called an atrial septal defect (Ferri, 2017).
This congenital (present at birth) heart defect occurs when normal heart
development is disrupted during the first eight weeks of pregnancy (Ferri,
2017).

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An atrial septal defect allows
blood to pass from the left side of the heart to the right side. Thus,
oxygen-rich (red) blood mixes with oxygen-poor (blue) blood, and some
oxygen-rich blood is pumped to the lungs instead of the body (Kutty , Hazeem ,
Brown 2012).

There are four major types of
atrial septal defects:

Ostium secundum ASD:
This type of ASD results from incomplete adhesion between the flap valve
associated with the foramen ovale and the septum secundum after birth
(Kutty , Hazeem , Brown 2012). The patent foramen ovale usually results
from abnormal resorption of the septum primum during the formation of the
foramen secundum. Resorption in abnormal locations causes a fenestrated or
netlike septum primum and excessive resorption of the septum primum
results in a short septum primum that does not close the foramen ovale
(Kutty , Hazeem , Brown 2012). An abnormally large foramen ovale can occur
as a result of defective development of the septum secundum     (Kutty , Hazeem , Brown 2012). The
normal septum primum does not close this type of abnormal foramen ovale at
birth and combination
of excessive resorption of the septum primum and a large foramen ovale
produces a large ostium secundum ASD (Kutty , Hazeem , Brown 2012).

 

 

Ostium primum ASD:
These defects are caused by incomplete fusion of septum primum with the
endocardial cushion. The defect lies immediately adjacent to the
atrioventricular (AV) valves, either of which may be deformed and incompetent
(Putra, Djer , Idris et al,  2015). In most cases, only the anterior
or septal leaflet of the mitral valve is displaced, and it is commonly
cleft. The tricuspid valve is usually not involved (Kutty , Hazeem , Brown
2012).

 

Sinus venosus ASD:
Abnormal fusion between the embryologic sinus venosus and the atrium
causes these defects (Ostermayer , Srivastava, Doucette 2015). In most
cases, the defect lies superior in the atrial septum near the entry of
superior vena cava and often there is associated anomalous drainage of the
right superior pulmonary vein ( Ostermayer , Srivastava, Doucette 2015).
The relatively uncommon inferior type is associated with partial anomalous
drainage of the right inferior pulmonary vein. Anomalous drainage can be
into the right atrium, the superior vena cava, or the inferior vena cava. (
Ostermayer , Srivastava, Doucette 2015).

 

Coronary sinus ASD:
The coronary sinus defect is characterized by unroofed coronary sinus and
persistent left superior vena cava that drains into the left atrium. A
dilated coronary sinus often suggests this defect (Kutty , Hazeem , Brown
2012). This can result is desaturation due to right-to-left shunt into the
left atrium and the diagnosis can be made by injecting contrast agent into
left upper extremity; coronary sinus opacification precedes right atrial
opacification (Kutty , Hazeem , Brown 2012).

 

 

 

 

 

Epidemiology

The three major types of atrial
septal defect (ASD) account for 10% of all congenital heart disease and as much
as 20-40% of congenital heart disease presenting in adulthood. The most common
types of ASD include the following (Krumsdorf , Ostermayer , Billinger, 2004).

?  Ostium secundum: The most common type of ASD accounting for 75% of all ASD cases,
representing approximately 7% of all congenital cardiac defects and 30-40% of
all congenital heart disease in patients older than 40 years (Krumsdorf ,
Ostermayer , Billinger, 2004).

?  Ostium primum: The second most common type of ASD accounts for 15-20% of all
ASDs. Primum ASD is a form of atrioventricular septal defect and is commonly
associated with mitral valve abnormalities (Krumsdorf , Ostermayer , Billinger,
2004).

?  Sinus venosus: The least common of the three, sinus venosus (SV) ASD is seen in
5-10% of all ASDs. The defect is located along the superior aspect of the
atrial septum. Anomalous connection of the right-sided pulmonary veins is
common and should be expected (Krumsdorf , Ostermayer , Billinger, 2004).

 

Sex- and age-related demographics

ASD occurs with a female-to-male ratio
of approximately 2:1.Patients with ASD can be asymptomatic through infancy and
childhood, though the timing of clinical presentation depends on the degree of
left-to-right shunt (Krumsdorf , Ostermayer , Billinger, 2004). Symptoms become
more common with advancing age 40, 90% of untreated patients have symptoms of
exertional dyspnea, fatigue, palpitation, sustained arrhythmia, or even
evidence of heart failure (Krumsdorf , Ostermayer , Billinger, 2004).

 

 

Causes of Atrial Septal Defects

The heart forms during the first eight weeks of
pregnancy and the heart begins as a hollow tube, as the heart develops, it
partitions, creating a wall (or “septum”) dividing the two sides of the heart
(Ruiz-Perez , Ide , Strom, 2000). Atrial septal defects occur when this
partitioning process does not complete, thus leaving a hole in the atrial
septum (Ruiz-Perez , Ide , Strom, 2000).

Heredity may play a role in some congenital heart
defects like ASD. Gene defects, chromosome abnormalities and environmental
exposure can cause heart problems to occur more often in certain families ( Li ,
Newbury-Ecob , Terrett, 1997) . Most atrial septal defects occur by chance (or
sporadically) with no clear cause. Scientists continue to search for the causes
of congenital heart defects like ASD ( Li , Newbury-Ecob , Terrett, 1997).

 However
there are some conditions that you can have or that can occur during pregnancy
may increase your risk of having a baby with a heart defect, including: (Benson
, Silberbach , Kavanaugh-McHugh 1999).

Rubella
infection. Becoming infected with rubella (German
measles) during the first few months of your pregnancy can increase the
risk of fetal heart defects.
Drug,
tobacco or alcohol use, or exposure to certain substances. Use
of certain medications, tobacco, alcohol or drugs, such as cocaine, during
pregnancy can harm the developing fetus.
Diabetes
or lupus. If you have diabetes or lupus, you may be
more likely to have a baby with a heart defect.
Obesity.
Being extremely overweight (obese) may play a role in increasing the risk
of having a baby with a birth defect.
Phenylketonuria
(PKU). If you have PKU and aren’t following your PKU
meal plan, you may be more likely to have a baby with a heart defect.

 

 

 

Pathophysiology

The magnitude of the left-to-right
shunt across the atrial septal defect (ASD) depends on the defect size, the
relative compliance of the ventricles, and the relative resistance in both the
pulmonary and systemic circulation and with small ASD, left atrial pressure may
exceed right atrial pressure by several millimeters of mercury, whereas with
large ASD, mean atrial pressures are nearly identical (Warnes, Williams ,
Bashore, 2008). Shunting across the interatrial septum is usually left-to-right
and occurs predominantly in late ventricular systole and early diastole with
some augmentation which may occur during atrial contraction, a transient and
small right-to-left shunt can occur, especially during respiratory periods of
decreasing intrathoracic pressure, even in the absence of pulmonary arterial
hypertension (Warnes, Williams , Bashore, 2008).

The chronic left-to-right shunt
results in increased pulmonary blood flow and diastolic overload of the right
ventricle. Resistance in the pulmonary vascular bed is commonly normal in children
with ASD, and the volume load is usually well tolerated even though pulmonary
blood flow may be more than 2 times systemic blood flow (Wang , Niu , Wang ,
2016). Altered ventricular compliance with age can result in an increased
left-to-right shunt contributing to symptoms. The chronic significant
left-to-right shunt can alter the pulmonary vascular resistance leading to
pulmonary arterial hypertension, even reversal of shunt and Eisenmenger
syndrome and because of an increase in plasma volume during pregnancy, shunt
volume can increase, leading to symptoms (Wang , Niu , Wang , 2016).

 

Symptoms of Atrial Septal Defects

Many babies born with ASDs have no signs or
symptoms. However, as they grow, these children may be small for their age (
Benson, Silberbach , Kavanaugh-McHugh, 1999). If the ASD is large and permits a
lot of extra blood flow to the right side of the heart, the right atrium, right
ventricle and lungs will become overworked, and it may cause symptoms (Benson,
Silberbach , Kavanaugh-McHugh, 1999). While each child may experience symptoms
of ASD differently, common signs include:

 

Tiring
easily when playing
Fatigue
Sweating
Rapid
breathing
Shortness
of breath
Poor
growth
Frequent
respiratory infections

Diagnosis

It can be diagnose when the doctor first suspect an
atrial septal defect or other heart defect during a regular checkup if he or
she hears a heart murmur while listening to your heart using a stethoscope Or
an atrial septal defect may be found when an ultrasound exam of the heart
(echocardiogram) is done for another reason ( Tsai , Hsiung , Wei, 2017).

If a doctor suspects you have a heart defect, he
may request one or more of the following tests: Echocardiogram,
Chest X-ray, Cardiac catheterization, Magnetic resonance imaging (MRI)
Computerized tomography (CT) scan ( Tsai ,
Hsiung , Wei, 2017).