Blue Baby Syndrome - Tetralogy of Fallot

Tetralogy of Fallot

The most common cause of blue baby syndrome, and the one which was the subject of the classic "blue baby operation" developed at Johns Hopkins in the 1940s, is Tetralogy of Fallot. In the normal heart, there are four separate chambers; the two top chambers, or atria, pump blood simultaneously into the two bottom chambers, or ventricles. Blood first enters the heart at the right atrium, which then empties blood into the right ventricle, which pumps the blood into the lungs through the pulmonary artery to get oxygen. From the lungs, the blood enters the left atrium through the pulmonary vein; the left atrium empties into the left ventricle, which pumps the blood into the aorta and from there reaches the rest of the body. Because the left ventricle is responsible for getting blood to the entire body through the aorta, it is usually the biggest and strongest chamber of the heart.

The following is a depiction of normal blood flow through the body. Valves keep the blood from flowing backwards. Capital letters indicate oxygenated blood:

veins → superior or inferior vena cava → right atrium ——tricuspid valve→ right ventricle ——pulmonary valve→ pulmonary artery → LUNGS → PULMONARY VEIN → LEFT ATRIUM ——mitral valve→ LEFT VENTRICLE ——aortic valve→ AORTA → ARTERIES

After the body uses up the oxygen delivered by the blood flowing through the arteries, then arterioles, then capillaries, the unoxygenated blood returns to the heart by the capillaries, then venules, then veins.

The blue baby syndrome known as Tetralogy of Fallot consists of an incomplete wall between the ventricles (known as a ventricular septal defect or VSD); an aorta that sits over this defect so that its blood comes from both ventricles instead of just from the left (overriding aorta); a defective right ventricular outflow tract near the pulmonary valve that prevents full flow of blood to the lungs; and a muscular right ventricle necessary to accomplish the extra work required to overcome that defect (right ventricular hypertrophy).

The following is a depiction of blood flow in Tetralogy of Fallot. Mixed capital letters indicate partially oxygenated blood.

veins → superior or inferior vena cava → right atrium ——tricuspid valve→ rIgHt vEnTrIcLe ——VSD→ LeFt VeNtRiClE or \__ ——pulmonary valve→ pulmonary artery → LUNGS → PULMONARY VEIN → LEFT ATRIUM ——mitral valve→ LeFt VeNtRiClE <—————————————————————————————————————————rIgHt vEnTrIcLe \__ ——aortic valve→ aOrTa → aRtErIeS

Unoxygenated blood from the right ventricle flows into the aorta preferentially because of the obstructed outflow tract into the lungs. This means less blood has the opportunity to be oxygenated in the lungs. Blood mixes abnormally between the left and right ventricles and into the aorta. Oxygen gives blood its reddish color; cyanosis describes the "blueness" in the baby which results from the pumping of mixed oxygenated and unoxygenated blood throughout the body.