Transposition of the great arteries (TGA) occurs when the two main arteries are blood vessels leaving the heart or reversed and there is a hole in the wall between the right and left ventricle called a ventricular septal defect (VSD). The pulmonary artery arises from the left ventricle (instead of the right), sending oxygen-rich blood back to the lungs. The aorta arises from the right ventricle (instead of the left), sending oxygen-poor blood back to the body. This misrouting stops oxygen from being delivered to the body’s tissues and organs and can be life-threatening. The VSD can allow the for the deoxygenated and oxygenated blood to mix. Babies can look blue, especially around the lips and nails. They can have a fast heart rate, fast breathing, and poor feeding.

Transposition of the Great Arteries with VSD

Hypoplastic Left Heart Syndrome (HLHS) is a heart condition where the mitral and aortic valves don’t develop properly. The left ventricle and aorta are also underdeveloped and very small (hypoplastic). This prevents oxygenated blood from reaching the body. Instead, blood is forced through a hole (an atrial septal defect) from the left atrium to the right atrium with blood reaching the aorta though the pulmonary artery and ductus arteriosus (a connection between the aorta and pulmonary artery) to reach the body. There can be other differences in the heart that can occur with HLHS. Your medical team will let you know if there are any other differences that your baby’s heart may have.

Model ID: MS AA

Hypoplastic Left Heart Syndrome (HLHS)

In truncus arteriosus the aorta and pulmonary artery did not separate from each other as the heart was being formed. All the blood that leaves the right and left ventricle exit through one common vessel that then branches into the pulmonary arteries and the aorta. The valve (called the “truncal valve”) leading to the one common vessel is supposed to act as a one-way gate for blood, but can be too tight (stenotic) or leaky (regurgitant). There is also a hole in the ventricular septum (ventricular septal defect or VSD) allowing blood to mix between the right and left ventricle.

Truncus Arteriosus

Blood that has travelled through the body enters the right atrium via the superior and inferior caval vein. It then travels to the right ventricle, passing the tricuspid valve. It is then pumped into the pulmonary artery, towards the lungs. In the lungs, oxygen is bound to the blood; it becomes oxygen-rich. Subsequently, the oxygen-rich blood enters the left atrium. Passing the Mitral valve, the blood enters the left ventricle. The left ventricle pumps the blood into the aorta, upon which it travels to all the organs and tissues in the body, providing them from oxygen. Once it has done so, it travels back to the right atrium.

Healthy heart and lungs

Tetralogy of Fallot (TOF) is a set of 4 changes to the heart that include narrowing of the pulmonary artery (pulmonary stenosis), a hole in the ventricular septum (ventricular septal defect or VSD), the aorta moving towards the right side of the heart (“overriding aorta”), and thickening of the right ventricle (right ventricular hypertrophy).

The baby’s symptoms will depend on the severity of the pulmonary stenosis. With severe pulmonary stenosis, less blood will be able to reach the lungs and the baby’s blood oxygen levels will be lower. Sometimes “Tet spells” can occur when there is suddenly less blood going to the lungs, and these can be an emergency.

Some babies may have less severe pulmonary stenosis and can have blood oxygen levels that are closer to typical for a baby. 

Model ID: AB

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