A congenital cardiac anomaly that consists of four
defects: pulmonic stenosis, ventricular septal defect, malposition
of the aorta so that it arises from the septal defect or the right
ventricle, and right ventricular hypertrophy.
The heart is roughly normal size. The curve of the right
heart margin is tall. The cardiac apex is elevated above the
diaphragm. There is a visible aortic knuckle. The curve of the left
ventricular margin begins immediately below this and also looks
longer than usual. The pulmonary vessels are undersized.
Tetralogy of Fallot is actually four defects in combination. First,
the septum that divides the two ventricles is incomplete (so there
is a ventricular septal defect), and oxygen-poor blood is thus
allowed to mix with oxygen-rich blood. Second, the passageway from
the right ventricle to the lungs is markedly narrowed. Third, the
origin of the aorta is shifted toward the right side of the heart
from the left. Fourth, the muscle in the wall of the right ventricle
is thickened and stiffened. Only the first two of these defects
cause significant trouble or require an operation. Tetralogy of
Fallot constitutes about 10 percent of all congenital heart disease.
It is the most common cyanotic heart defect; nearly 3,000 new cases
a year occur in the U.S.. A French physician, Etienne Fallot,
described this defect in 1888.
These defects result in decreased blood flow to the lungs
and circulation of blue (unoxygenated) blood to the body tissues;
both of these effects cause bluish skin (cyanosis), clubbing
(bulging of the nailbeds) of the fingers and toes, shortness of
breath, and extreme fatigue.
Infants may require surgery (for example, the Blalock-Taussig shunt
procedure) to improve blood flow to the lungs and decrease cyanosis.
Once the child is past infancy, corrective open heart surgery is
performed. The results of successful complete repair of Tetralogy of
Fallot are good: cyanosis disappears, exercise tolerance improves,
and people may lead normal lives. Without an operation, only about
30 percent of people with Tetralogy of Fallot would survive to the
age of 40 years. Surgery results in almost 90 percent of patients
surviving for at least 25 years from the time of surgery; generally,
the results are best if the defect is corrected before the patient
is 12 years old