CHAPTER 1: So What Is Transposition of the Great Arteries?

I thought I would start things off by sharing a little bit of information about what exactly Transposition of the Great Arteries is for those of you who aren't already familiar with the term, so that you can better understand Joshua's diagnosis.


Transposition of the Great Arteries (TGA) is a congenital heart defect (CHD) where the two large arteries of the heart that carry blood to the lungs (pulmonary artery) and to the body (aorta) are switched. In a normal heart oxygen-poor (blue) blood returns to the right atrium from the body, travels to the right ventricle, then is pumped through the pulmonary artery into the lungs where it receives oxygen. Oxygen-rich (red) blood returns to the left atrium from the lungs, passes into the left ventricle, and then is pumped through the aorta out to the body.


With TGA the aorta is connected to the right ventricle and the pulmonary artery is connected to the left ventricle which is the complete opposite of normal anatomy. This results in two separate circulations. On the left side of the heart, oxygen-rich blood returns to the left atrium from the lungs, passes to the left ventricle and is then pumped through the pulmonary artery back to the lungs. On the right side of the heart, oxygen-poor blood returns to the right atrium from the body, passes to the right ventricle and then is pumped through the aorta back to the body. As you can see the blood being circulated to the body never receives oxygen from the lungs which is why TGA is considered a cyanotic heart defect.


Understandably a TGA heart cannot sustain life unless another heart defect is present that allows mixing of oxygenated and deoxygenated blood such as an atrial septal defect, a ventricular septal defect or a patent ductus arteriosus. In Josh's case he had a patent ductus arteriosus (PDA).


The ductus arteriosus is a small vessel that forms a connection between the aorta and the pulmonary artery and is used in utero to allow blood to bypass the lungs. Since the lungs aren't being used in utero they don't require as much blood and so some is diverted away and kept with the main circulation. When the baby is born this little vessel is no longer needed and begins to close shortly after birth and is often completely closed within the first 2-3 days of life. As a result most TGA babies are identified as such shortly after birth, often before being discharged from hospital. Josh's ductus arteriosus remained patent for an amazing 16 days. What's even more amazing is that he was not blue during these 16 days which likely meant that his body was receiving an adequate supply of oxygen.


What Causes TGA?

I'm often asked what caused Josh's heart defect and unfortunately we just don't know, which is often the case with CHDs. There are certain factors that can increase the risk of a CHD defect such as: a family history of CHDs, having other children with a CHD, contracting rubella or some other virus during the first trimester, excessive alcohol consumption during the first trimester, maternal age over 40 and maternal diabetes. However most of the time the cause is unknown. Any baby that's born with no known risk factors for it has a 1% chance of having a CHD. Josh was that 1%.

How Is It Treated?

Usually the infant will be started on an IV medication called prostaglandins which is used to re-open the ductus arteriosus or if it is open, to keep it patent. The next step is often an atrial septostomy which is performed to create a hole in the wall separating the two atria (if one isn't already present) to allow more mixing of oxygenated and deoxygenated blood. Both of these measures are palliative in that they are not a "cure". Surgical repair of the heart is required as soon as possible.


The surgery involves the following:

• The aorta is moved from the right ventricle to its normal position over the left ventricle.

• The pulmonary artery is moved from the left ventricle to its normal position over the right ventricle.

• The coronary arteries are moved so they will originate from the aorta and take oxygen-rich (red) blood to the heart muscle.

• Other defects, such as atrial or ventricular septal defects or a patent ductus arteriosus, are repaired
  

Possible Long-Term Complications Of TGA Repair

Many infants who undergo TGA surgical repair will grow and develop normally. However, there is the possibility of long-term complications such as: fast, slow, or irregular heart rhythms, leaky heart valves, narrowing of one or both of the great arteries at the switch connection site(s),
narrowing of the coronary arteries at their switch connection site. Those with TGA repair will need to be followed by a pediatric cardiologist to assess for any heart-related problems.