In the embryo there is a tube which undergoes a series of twists and turns to become a heart with four chambers separated by valves and sprouting the great vessels. Although this can be described in words it is so much easier with modern technology and educational methods to take advantage of the available videos online.
A fundamental of fetal circulation is the blood to a great extent is not passed thought he lungs, since it is oxygenated at the placenta, the shunting mechanisms involved are the ductus arteriosus between the pulmonary artery and the aorta, and the foramen ovale between the right and left atria. These two close at birth, failure to close results in a persisting by-pass of the lungs and defective oxygenation of the post-natal blood.
The system of formation of the heart is so complex that it is not surprising to learn that of every 1000 children born, as many as 50 may have a heart defect that is of functional significance, but as many as 30% of adults may have an abnormality of formation that does not interfere with the heart’s function to a significant degree. The failure may be either in formation or in function, and they are not uncommonly associated with other congenital anomalies, on the basis that if one abnormality is found there may be two, if two are found almost certainly there are more.
Failure to develop fully (hypoplasia): one or other side of the heart may not develop to the size necessary to support post-natal circulation and life.
Defects causing obstruction to blood flow: a narrowing of valvular opening or vessel, called stenosis may occur with any of the great vessels leaving the heart, any of the valves within the heart or in the aorta beyond the heart where it is called coarctation of the aorta.
Defects in formation of septa: the tube twists, membranes form and four chambers develop. These may fail to develop completely, which is of less significance between the atria (30% adults have small defects) than it is between the ventricles; a ventricular septal defect is likely to provoke heart failure in the infant.
Cyanotic defects: the so-called blue babies in whom there are various combinations of failure of formation, or defective formation, such as the tetralogy of Fallot; patent ductus arteriosus; transposition of vessels; and tricuspid atresia.
Patent ductus arteriosus: this short vessel runs between the pulmonary artery and the aorta; its function in the fetus is to permit the blood from the right ventricle to by-pass the lungs and travel directly to the body. It closes at birth so the blood then passes to the lungs to be oxygenated. When the duct has not closed there is a distinctive loud murmur. Closure can be effected in 80% of cases of failure by administering Indomethacin. In contrast, there are occasions when it is considered necessary to keep this abnormality open to compensate for another, and closure can be prevented by giving prostaglandin.
Coarctation of the aorta: constriction at the point where the aorta is joined by the ductus arteriosus. This leads to raised cardiac effort, raised blood pressure, heart failure or sometimes aortic rupture.
Tetrallogy of Fallot: as the name implies, there are four abnormalities of formation: the ventricles are inadequately separated, the right ventricle opens into the aorta as well as the pulmonary artery whose valves are stenosed; this is one of the conditions which are benefited by keeping the ductus arteriosus open.
An abnormality may be noticed when the routine ante-natal ultrasound study is performed, or the child at birth may be found to have respiratory difficulties, to be persistently blue, and to have abnormal cardiac sounds when listened to with the stethoscope and abnormal function when examined by ultrasound. Or the diagnosis may not be made until a routine examination finds an abnormal noise at the heart or a specific examination is made because of failure to thrive, defective exercise tolerance or several other less specific complaints. Further examination will then be made by a pediatric cardiologist who will require cardiogram and cardiac ultrasound and echocardiography studies and possibly a catheterization study.
Some structural conditions are life threatening, some interfere with function, some do not. In cases where surgery is indicated this may be directed at correcting the defect, or making a compensating defect to reverse the problem, or in some cases only a heart transplant can save the child. Stenotic conditions may be correctible by dilating them with an inflatable balloon passed by catheter from the groin to the heart, or open heart surgery may be required for a direct visual approach to the region to be corrected.
There are a number of genetically determined conditions in which the heart appears perfectly normal both to structure and function, but there is an abnormality of electrical conduction or transmission through the heart and sudden death may occur with exertion, shock or unknown provocation.
There are several forms, but they are collectively grouped as long QT syndrome, based on the appearance of the ECG.