The aorta, the largest artery in the body, delivers oxygenated blood directly from the heart. Blood passes through the aorta to a wide variety of increasingly smaller arteries that branch off and eventually into capillaries where blood is delivered directly into the body cells. During normal fetal development, several branches develop, but most of these disappear, leaving an aortic arch that travels around the left side of the trachea, or windpipe. In about one out of a thousand births, however, the aorta lies on the right side of the trachea, forming a right aortic arch.
Although an aortic arch on the right side is considered an abnormality, in most cases it produces no symptoms and requires no treatment. Some conditions often found in conjunction with this uncommon placement can require surgical correction, however. One of these is a vascular ring right aortic arch, in which the abnormal placement of the aorta leads to a vascular structure that completely surrounds the trachea and esophagus. With various arteries and branches of the aorta circling it, the trachea and esophagus can become constricted, interfering with normal breathing and swallowing.
Another condition that requires attention is a mirror image right aortic arch, which in 98% of cases is associated with some form of congenital heart defect. Most commonly seen in conjunction with this condition is a heart defect called tetralogy of Fallot. This is a hole in the wall that divides the left and right heart ventricles, allowing oxygenated and deoxygenated blood to mix. Other defects include a partial blockage of the vein that takes blood from the left ventricle to the lungs and thickening of the left ventricular wall. Tetralogy of Fallot can be corrected surgically, but it often is fatal if left untreated.
Persistent right aortic arch, seen in dogs like Irish setters and German shepherds, creates similar problems to those caused by a vascular ring. This occurs when the placement of the aortic arch formed during fetal development persists after birth, usually creating a ring around the esophagus that traps the it against the heart and restricts food from reaching the stomach. Puppies with this condition are malnourished and do not grow at the same rate as others in the litter. It can be corrected surgically, and after treatment, the puppies will grow and develop at a more normal rate.