Heart Disease Health Center
Tetralogy of Fallot
Tetralogy of Fallot Overview
Tetralogy of Fallot is the most common heart defect in children. The
condition causes mixing of oxygen-poor blood with the oxygen-rich blood being
pumped out of the heart and into the circulatory system of blood vessels.
- The blood leaving the heart has less oxygen than is needed by the organs
and tissues of the body, a condition called hypoxemia.
- Chronic (ongoing, long-term) lack of oxygen causes cyanosis, a bluish color of the skin, lips, and membranes inside the mouth and nose.
The normal heart works as follows:
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- The heart is made up of 4 chambers: 2 upper chambers called atria and 2
lower, larger chambers called ventricles. Each atrium is separated from
its paired ventricle by a valve.
- The heart has a left and a right side. The left and right sides of the
heart are separated by a septum (wall). The right side of the heart receives
oxygen-depleted or blue blood returning by veins (superior vena cava and
inferior vena cava) from the body.
- The blood flows from the right atrium through the tricuspid valve into the
right ventricle, which pumps it through the pulmonic valve into the pulmonary
artery, the main artery to the lungs.
- In the lungs, the blood absorbs oxygen and then returns to the left atrium
through the pulmonary veins.
- From the left atrium, the blood is pumped through the mitral valve to the
left ventricle. The left ventricle pumps the blood out of the heart into the
circulatory system via a large artery known as the aorta.
- The blood moves throughout the body, supplying oxygen and nutrients to
organs and cells.
- Organs cannot work properly if they do not receive enough oxygen-rich blood.
The 4 abnormalities (tetralogy) of the heart described by Fallot include the
following:
- Right ventricular hypertrophy: Narrowing or blockage of the
pulmonary valve and/or muscle under the pulmonary valve coming out of
the right ventricle. This restriction to blood outflow causes an increase
in right ventricular work and pressure, leading to right ventricular thickening
or hypertrophy.
- Ventricular
septal defect (VSD): This is a hole in the heart wall (septum) that
separates the 2 ventricles. The hole is usually large and allows oxygen-poor
blood in the right ventricle to pass through, mixing with oxygen-rich blood in
the left ventricle. This poorly oxygenated blood is then pumped out of the left
ventricle to the rest of the body. The body gets some oxygen, but not all that
it needs. This lack of oxygen in the blood causes cyanosis.
- Abnormal position of the aorta: The aorta, the main artery carrying blood
out of the heart and into the circulatory system, exits the heart from a
position overriding the right and left ventricles. (In the normal heart, the
aorta exits from the left ventricle.) This is not of major importance in
infants.
- Pulmonary valve stenosis (PS): The major issue with tetralogy of Fallot is the degree of pulmonary valve stenosis, since VSD is always present. If the stenosis is mild, minimal cyanosis occurs, since blood still mostly travels to the lungs. However, if the PS is moderate to severe, a smaller amount of blood reaches the lungs, since most is shunted right-to-left through the VSD.
Tetralogy of Fallot accounts for 10-15% of all congenital (newborn) heart defects. Infants with this abnormality develop signs of the condition very early in life.
WebMD Medical Reference from eMedicineHealth
