Tetralogy of Fallot

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Tetralogy of Fallot is a combination of four ("tetra") abnormalities of the heart, which were first described by a French physician, Dr. Etienne Fallot, in 1888.

The Four Abnormalities

Following is information about the four abnormalities: ventricular septal defect or VSD, infundibular stenosis, overriding aorta, and right ventricular hypertrophy.

Ventricular Septal Defect or VSD

This hole permits blood to flow from the high pressure (red, oxygen carrying) left-sided circulation to the lower pressure (blue, oxygen poor) right-sided circulation. This abnormal blood flow is called a left-to-right shunt and follows this path because the left ventricle usually has a much higher pressure than the right ventricle.

Infundibular Stenosis

The infundibulum is in the outflow area (exit) of the right ventricle just beneath the pulmonary artery and valve. It forms a passageway for deoxygenated (blue) blood to flow to the lungs. Infundibular "stenosis" or narrowing means that there is a narrowing in this passageway that obstructs the flow of blood to the lungs. The degree of obstruction can range from mild to severe. This will cause the pressure inside the right ventricle to go up as it tries to push the blood through the area of obstruction.

An added problem is that the pulmonary valve itself and the pulmonary artery may also be narrowed, which further adds to the obstruction.

Overriding Aorta

The aorta is the artery that carries oxygen rich red blood to the rest of the body and is normally open only to the left ventricle. In tetralogy of Fallot the aorta is shifted toward the right ventricle and sits above or "straddles" the VSD.

The aorta is then open to both the right and left ventricle. This allows mixing of deoxygenated (blue) and oxygenated (red) blood as it flows out of the heart to the rest of the body. Thus the amount of oxygen in the circulation is lower than normal causing symptoms of shortness of breath, fatigue and a decreased activity level.

Right Ventricular Hypertrophy

Hypertrophy is a term used to describe a muscle that is unusually thickened. In tetralogy of Fallot, the right ventricular muscle wall is thickened because the right ventricle must work harder to push blood through the narrowed pulmonary artery and infundibulum.

Unfortunately an increase in heart muscle thickness may precipitate irregular heart rhythms or cause patchy areas of scar tissue making the heart very "irritable." This makes the heart prone to irregular heart rhythms and reduced performance.

The VSD and the infundibular stenosis are the major defects of tetralogy of Fallot. These defects cause:

• Oxygen poor (blue) blood to bypass the lungs and circulate to the body resulting in cyanosis (a blue tinge to the skin)
• Increased pressure inside the right side of the heart making the right heart muscle increase in thickness (hypertrophy)
• Decreased blood flow to the lungs