Congenital heart defects

Congenital heart defects can be life-threatening

Congenital heart defects are present in about 1% of live births and are the result of development problems during pregnancy, sometimes as a result of a viral infection such as rubella contracted by the mother.

Alcohol, illegal drugs and over the counter medicines can also cause defects.

Congenital heart defects take the form of holes between the chambers, blockages in the pathways from the heart to the lungs or the body, or abnormal connections between the chambers and vessels of the heart.

Diagnoses

Diagnoses can be made by scans taken during pregnancy but are usually made in the first days or weeks after birth. Diagnosis may not though be made until much later in life.

Professor Robert Anderson, professor of paediatric cardiac morphology at the Institute of Child Health in London, said: "We are making more and more diagnoses before the child is born.

"Scans are now done at 12 weeks and at 20 weeks. Suspicion of problems can be risen and probably now when this is referred to tertiary centres, we can diagnose two-thirds of the overall proportion of lesions within the heart."

This allows parents to consider whether they want the pregnancy to continue and to prepare themselves if they do decide to continue, he said.

Septal defects - holes in the heart

Holes in the heart can occur in the upper chambers - atrial septal defects - or lower chambers - ventricular septal defects. Or they can exist between all four chambers - atrioventricular septal defects.

Where the hole occurs in the great artery, the defect is called a patent arterial duct.

The holes are part of the circulation system in the foetus but should close up after birth.

More complex conditions include Tetralogy of Fallot, which is one cause of the condition cyanosis, commonly known as "blue babies".

In Tetralogy of Fallot, the baby has a large hole in the heart, allowing blood to pass from the right ventricle to the left without going through the lungs. There is a narrowing at or just below the pulmonary valve, the right ventricle is more muscular than normal and the aorta lies directly over the hole - the ventricular septal defect.

Babies may have rapid breathing or fall unconscious. Older children may become short of breath and faint.

Surgery may be needed to increase blood flow to the lungs with a shunt, linking the aorta and the pulmonary artery. The child is able to develop and the defect can be corrected later.

Other causes of "blue babies" include defective pulmonary veins, which do not come back to the heart, or arteries coming out of the heart which are connected to the wrong ventricles - transposition.

With transposition most of the blood returning from the heart to the body is pumped back without first going to the lungs.

An arterial switch operation may be necessary to reconnect the arteries correctly.

With holes in the heart, oygenated, red blood which has come from the lungs passes into the right side of the heart where it mixes with bluish blood and is sent back to the lungs.

The heart is put under extra strain, potentially causing it to enlarge and causing high blood pressure and blood vessel damage. Growth and nourishment are affected.

Holes in the heart are closed with one or two patches and the single valve is divided into two. Blood circulation should be returned to normal but the reconstructed valve may not work normally.

If the defect is too complex to repair in infancy, pulmonary artery banding may be used to reduce blood flow and high pressure in the lungs - pulmonary hypertension. The band is later removed and surgery carried out.

Obstruction defects

The obstruction, called stenosis, can be of the valves between the upper and lower chambers of the heart - atrioventricular valvular stenosis.

More frequently, the obstruction is between the ventricles and trunks coming from them - arterial valvular stenosis.

This can be either the valve to the lungs - pulmonary valvular stenosis, in which case the right ventricle must pump harder than normal - or the valve to the body - aortic valvular stenosis, in which it is hard to pump blood to the body.

Balloon valvuloplasty is usually used to correct pulmonary valvular stenosis but open heart surgery may be necessary.

Only severe aortic stenosis requires surgery and some children may have the condition without showing any symptoms.

The obstruction can also be within the vessels themselves - aortic coarctation. In this case the narrowing is within the artery and effects supplies of blood to different parts of the body.

This defect may not be picked up until the patient is quite old.

Rarely, only one ventricle is present or both the pulmonary artery and aorta come from the same ventricle. The right or left side of the heart may be incompletely formed, known as hypoplastic heart.