This rare genetic disorder involves two defects. First, the aortic arch does not form a complete tube and is divided, or “interrupted.” The aortic arch is the part of the aorta (the major vessel that carries oxygen-rich blood from the heart to the body's tissues) that curves directly above the heart and begins the descent to the lower body.
Second, there is almost always a hole, called a ventricular septal defect (VSD), in the muscle wall (septum) that separates the two ventricles, or pumping chambers of the heart.
Because the aorta is interrupted and cannot carry blood from the left ventricle to the lower body as in a normal heart, it might seem that the child with this anomaly could not survive. However, some blood does enter the lower part of the aorta because of a small vessel, known as the patent ductus arteriosus (PDA) that connects the pulmonary artery to the descending aorta. (The patent ductus arteriosus is a feature of the fetal circulatory system that usually closes soon after birth.)
The pulmonary artery normally carries oxygen-poor blood to the lungs, so it might seem that blood entering the lower aorta from this vessel (through the PDA) would not carry enough oxygen to the lower body. However, in this case the ventricular septal defect (VSD) allows mixing of oxygen-rich blood from the left ventricle into the right ventricle, which pumps blood into the pulmonary artery.