CONGENITAL HEART DEFECTS

The normal heart is divided into four chambers. Bluish blood, low in oxygen, reaches the heart through veins and enters the right collecting chamber, the right atrium. Blood then flows into the right pumping chamber, the right ventricle, through the tricuspid valve. The right ventricle pumps the blood through the pulmonary artery to the lungs where the blood receives oxygen. After the blood is oxygenated, it is bright red. This blood then returns to the heart through the left collecting chamber, the left atrium.

It then flows through the mitral valve into the left pumping chamber, the left ventricle. From there it is pumped into a large blood vessel called the aorta which feeds it into smaller blood vessels that carry it around the body to supply essential oxygen to the tissues. When the oxygen has been removed, the blood becomes blue again and returns to the right side of the heart.

Usually, it is a heart murmur that first alerts a doctor to the possibility of congenital heart defect. However, not all children have a murmur, so various other clues such as colour (pale, grey, blue), respiratory rate and effort, contours of the chest, and swelling of the eyelids, are all examined. On x-ray an enlarged heart and congested lungs might indicate a congenital heart defect.

An electrocardiogram (ECG) or echocardiogram (using high-frequency sound waves) helps provide additional information which may indicate the need for a cardiac catheterisation. This procedure requires a stay in hospital and can define precisely the extent and location of the defect.

It is common for a congenital heart defect to give rise to a delay in growth and weight gain, and in children with Down's syndrome there is often also decreased muscle tone and motor delay (i.e. they are delayed in learning skills such as crawling, standing, walking, etc.). These symptoms usually improve after surgical correction of the heart defect.

The most common heart defects among children with Down's syndrome are described below.

Atrio ventricular (septal) defects (AV(S)D)

These involve a malformation of the walls and the valves between the atria and the ventricles. The condition amounts to a "hole in the centre of the heart", which can gravely affect the direction and pressure of the blood flow, and impose a strain on the heart and lungs. Nowadays this can often be corrected by major heart surgery in infancy, but for a few babies the operation is not medically advisable.

Ventricular septal defects (VSD)

These defects involve an opening in the septum or wall which separates the two ventricles. If a small opening exists, this will not cause strain on the heart and, in some cases, the opening may close by itself. For large defects surgical correction may be necessary - again this is usually carried out in the first years of life.

Tetralogy of fallot

This is a combination of four defects:

• - a large hole between the two ventricles (ventricular septal defect)
• - a narrowing in or near the pulmonary valve
• - an unusually muscular right ventricle
• - the aorta receives blood from both the right and left ventricles

This condition results in cyanosis or blueness of the lips and fingernails. Total correction is difficult in infants, but an operation can be carried out to provide temporary relief.

Persistent ductus arteriosus (PDA)

All children are born with a ductus arteriosus, an opening between the pulmonary artery and the aorta. Normally, the passageway closes up within a few weeks of birth. When this fails to happen, some of the blood that should go through the aorta and on to the body is sent back to the lungs, thus circulating uselessly between the lungs and heart and imposing extra strain on the heart. If this occurs, the duct can be closed by a simple operation which does not involve operating on the heart itself.

Atrial septal defect (ASD)

These are holes in the wall which separates the two atria. They are often quite small. If large enough to allow a significant amount of blood to flow through, then they may need to be closed by a surgical operation. So-called secundum defects (openings in the upper part of the atrial septum) often close on their own. Ostium primum defects (openings in the lower part of the atrial septum) are very near the valves and often need surgery.