Atrial Septal Defect

ATRIAL SEPTAL DEFECT, A HOLE IN THE SEPTUM
dividing the right and left atrium, is the most common
congenital heart defect observed after age 12 and in adults,
because the lesion is usually so small that it causes little
disturbance in infants. Atrial septal defect accounts for
approximately 10% of all congenital cardiac defects. With
this defect oxygenated blood is shunted from the left
atrium into the right atrium and traverses the pulmonary
arteries and lungs and returns to the left side of the heart
(Fig. 1). This circulatory disturbance is called a left to right
shunt. The shunt is usually small but if the hole is large
enough the right ventricle works harder to pump the
extra blood delivered to it, from the left side, into the
pulmonary arteries and through the pulmonary circulation
back to the left side of the heart. The right ventricle over
time is subjected to more strenuous work than normal.
The muscle of the right ventricle becomes weaker and fails
to expel sufficient blood from the chamber, and a
condition referred to as right heart failure occurs. The
atrial septal defect most often involves the fossa ovalis in
the mid septal region; this is called an ostium secundum
type of defect.

With a small hole in the heart, the infant or young child
is relatively asymptomatic. With larger defects tiredness,
shortness of breath on exertion, and frequent infection of
the lungs may occur. These symptoms are more obvious as
heart failure worsens. A soft heart murmur is usually heard
which leads to further investigations. Because oxygenated
blood is pumped from the left atrium into the right side of
the heart, the organs of the body including the skin receive
oxygenated blood. Thus, the individual does not become
blue in the face, a condition described as cyanosis. Because
of this, atrial septal defect is a cause of noncyanotic
congenital heart disease.

The ECG usually shows evidence of an incomplete right
bundle branch block. This is a clue for the treating
physician. A transesophageal echocardiogram (TEE) is
usually diagnostic. Closure of the hole in the heart is
curative and should be done if symptoms are present.

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