Cyanotic congenital heart defects: Pathology review

At the pediatric cardiology clinic, two mothers were chatting about their kids. One mom spoke about a 5 year old boy named Blake, who was a bluish color at birth and had a continuous machine-like heart murmur between the scapulas.

Another mom spoke about her 12 year old son, Paul, who was healthy at birth, but when he was breastfeeding or crying, his skin turned pale, and then blue. As a child, Paul got out of breath easily and needed to squat down to recover. And during his school physical, he was found to have a heart murmur.

Both Blake and Paul have cyanotic congenital heart defects, or CHDs, which usually start causing problems within the first 3-8 weeks of life. They can be broadly grouped into life-threatening cyanotic heart defects, or the less dangerous acyanotic heart defects.

Let’s go over 5 of the life-threatening cyanotic congenital heart defects: persistent truncus arteriosus, transposition of the great vessels, tetralogy of fallot, total anomalous pulmonary venous return, and tricuspid atresia.

Now the first 3 are caused by outflow tract defects that develop during the formation of the aorta and pulmonary artery. In fetal development the heart looks like a long tube; the top part is the truncus arteriosus and the part inferior to that is the bulbus cordis. Neural crest cells migrate into the bulbus cordis and trigger the formation of the aorticopulmonary septum. This structure is formed when two endocardial cushions appear on the right-superior and left-inferior walls. These grow like a spiral - imagine a corkscrew - and they wrap around each other forming a single septum that divides the truncus into the roots of the aorta. One root connects to the primitive left ventricle, and the other connects to the pulmonary artery and primitive right ventricle. That’s how blood gets routed to the right place!