HEART MALFORMATION

also called Congenital Heart Disease, any deformity of the heart that develops within the first two months of fetal life. Such deformities have little effect before birth because, in the fetus, cellular respiration (via the mother's bloodstream) is accomplished through the placenta. After birth, some of these deformities impair the supply of oxygen to the tissues and cause disability or death. The most common heart malformations in the infant are those in which oxygenated blood is recirculated through the lungs because of a left-to-right shunt in the heart. For example, the septum between the auricles may be partly missing; if the resulting opening is high (ostium secundum), the situation is usually not serious. If it is low (ostium primum), however, the opening is usually associated with a defect in the semilunar valves, and there is blood mixing in all four chambers. This condition is serious and is common among infants with Down syndrome. Even more serious are anomalies in which oxygenated and deoxygenated blood mix; the poorly oxygenated blood reaches the tissues, resulting in cyanosis (bluish colouring of the skin) and growth retardation. The septum separating the ventricles may be absent. If so, oxygenated and deoxygenated blood mix freely and are pumped equally to the lungs and body. The right ventricle and pulmonary arteries come under severe strain and may fail. The major valves may be absent (atresia) or narrowed (stenosis), producing abnormal pressures on the heart and requiring accessory abnormal shunts. The tetralogy of Fallot (blue baby syndrome) is an uncommon malformation in which there is ventricular septal defect, pulmonary valve stenosis, right ventricular hypertrophy (overgrowth), and a shift of the aorta from the left to the right side so that it receives blood from both sides of the heart. As the constriction becomes more severe, circulation depends increasingly on accessory connections between the aorta and pulmonary vessels. The aorta and pulmonary trunk may be transposed so that the aorta emerges from the right ventricle and the pulmonary trunk from the left ventricle. In such patients, life is impossible unless there are further anomalies, such as a ventricular septum defect that, by allowing some mixing of venous and arterial blood, permits oxygen to reach the tissues. Abnormalities of the large vessels may also cause symptoms of circulatory failure but are in general less serious. If the fetal connection between the pulmonary trunk and aorta persists (persistent, or patent, ductus arteriosus), some mixing of oxygenated and deoxygenated blood occurs. Alone, this defect is often not serious, and in some malformations of the heart it is actually necessary for continued life. The aorta may be narrowed just below the point where the arteries supplying the upper part of the body emerge (coarctation of the aorta), thus reducing the blood volume and pressure in the lower half of the body, which receives blood only through a bypass from the pulmonary trunk or from an accessory circulation that develops around the abnormal spot in the aorta. Both routes are relatively ineffective in remedying the deficiencies. Malformations of the heart are repaired by modern surgical procedures with varying degrees of success.