L-TGA Refresher Course

L-TGA is known by many names, the most common being L-TGA, or levo-transposition of the great arteries, CC-TGA, or congenitally corrected transposition of the great arteries, Double Discordance, and Ventricular Inversion. L-TGA is thought to be the rarest of congenital heart defects. L-TGA is unique in that the ventricles form on the wrong side of the heart, and the great arteries rise up from the wrong ventricle. 

Approximately one out of every 100 babies will be born with some form of heart defect. L-TGA accounts for approximately 0.5% of all congenital heart defects. It is thought that L-TGA affects 1 out of every 33,000 live births. So approximately 120-200 babies are born with this heart defect in the U.S. each year. It is estimated that approximately 5,000-10,000 people are living in the U.S with L-TGA. Keep in mind that the population of the U.S. in 2014 was 318.9 million people. 

L-TGA need not be confused with D-TGA, which is the more common form of transposition. D-TGA only involves the great arteries, the pulmonary artery and aorta, and typically there will be a hole in the heart where the red and blue blood mixes. The left and right ventricles are positioned on the correct side of the heart. Babies born with D-TGA will be born blue, or cyanotic, and require heart surgery in the first days or weeks of birth, or else they will die. In this surgery the great arteries are switched back to the opposite ventricle. 

In L-TGA, the lower chambers of the heart, the ventricles, form on the opposite side of the heart, and the great arteries rise from the wrong ventricle. In other words, two wrongs made it right. If two wrongs made it right, what's the big deal? Each ventricle is designed to do a specific job. The typical left ventricle is round and thick. It pumps under high pressure and pumps oxygenated blood out through the aorta to the entire body. The typical right ventricle is crescent shaped and much thinner than the left ventricle. It pumps under lower pressure and sends de-oxygenated blood from the heart through the pulmonary artery to the lungs to pick up oxygen. The right and left ventricles have certain characteristics that are unique to them. 

L-TGA often presents with other defects. Up to 70% of people with L-TGA have a ventricular septal defect (VSD), or hole between the lower chambers of the heart. Approximately 50% of those with L-TGA will have pulmonary stenosis in which there is an obstruction on or near the pulmonary valve, in turn making it more difficult for blood to pass through the pulmonary valve. 20% of L-TGA people will have dextrocardia, where the heart sits to the right of the chest. 
Other common problems include tricuspid valve leakage and complete heart block. The tricuspid valve is the most delicate valve in the heart and since it is the valve connected to the right ventricle, the L-TGA systemic ventricle, it has a high likelihood of failing in the lifetime. This will contribute to right ventricular heart failure and can lead to the need for a heart transplant. If the L-TGA person has  complete heart block, the person will need a pacemaker.