Overview Of Congenital Heart Defects
The incidence of congenital heart defects is found to be about one in 120 live births, but many of them are not serious conditions. The wall of the heart, valves in the heart or the blood vessels that arise from or lead to the heart may be having defects.
- Abnormalities in the formation of the valves or the wall of the heart may be responsible for the heart defects.
- Bluish discoloration of the skin known as cyanosis, breathing difficulty, growth retardation, inability to exercise, and heat failure are the apparent symptoms of congenital heart defects.
- Ultrasound scanning can detect most of the heart defects in infants.
- Severe heart defects require surgical intervention and correction, but minimally invasive procedures with a balloon-tipped catheter to open up or enlarge valves and vessels, as well as drug therapy with prostaglandins, may help in minor cases.
The blood circulation in fetus is different from that of young children and that of adults. In the normal circulatory pattern of children as well as adults, the blood in the veins is drained into the right atrium of the heart from which it enters the right ventricle. The contraction of the right ventricle pumps this venous blood into the pulmonary artery which takes it to the lungs for oxygenation. Exchange of gases take place in the alveoli or air sacs in the lungs, where the carbon dioxide in the venous blood is released and the oxygen from the fresh air is absorbed by the blood. The oxygenated blood is returned to the left atrium of the heart and then into the left ventricle. When the ventricle contracts, it gets pumped into the aorta from where various major arteries carry it to the different parts of the body. The fetus receives oxygenated blood from the placenta; hence most of the fetal blood takes a different circulatory route, with only some blood passing through the lungs.
In fetal circulation, the blood which drains into the right chambers of the heart is already oxygenated, and it mixes with the blood which drains into the left chambers of the heart after returning from the lungs. There is a septal opening connecting the left and right atria called foramen ovale through which this mixing of venous and arterial blood takes place. In the fetus, a blood vessel called ductus arteriosus connects the pulmonary artery containing venous blood to the major artery aorta arising from the heart, resulting in further mixing up of the blood. Since the placenta is carrying out the oxygenation of the venous blood, this mixing up of venous and arterial blood does not cause any problem in the fetus. However, after birth, the connection to the placenta is severed, and the oxygenation of the blood takes place in the lungs. If the deoxygenated venous blood reaching the heart continues to mix with the oxygenated blood returning to the heart from the lungs, it can significantly reduce the amount of oxygen reaching the various tissues through the arteries. The ductus arteriosus and the foramen ovale normally close up soon after birth to prevent this condition. If they remain open, it is regarded as a heart defect.
Congenital heart defects result in abnormal circulatory patterns. Either rerouting of the blood flow known as shunting, or blockage to the blood flow may occur due to defects in the blood vessels or the heart valves.
Deoxygenated blood which has returned to the right chambers of the heart gets mixed with oxygenated blood pumped out to the body from the left side of the heart due to right-to-left shunting. This causes the deoxygenated blood to circulate in the body causing a bluish discoloration known as cyanosis. The severity of cyanosis depends on the amount of oxygen-poor blood mixing with oxygenated blood being pumped out to the body.
The oxygenated blood from the lungs and the deoxygenated venous blood returning to the heart get mixed up when shunting occurs. It affects the efficiency of blood circulation which provides oxygen to all the tissues in the body. Heart failure may eventually develop as the heart becomes unable to pump adequate amount of oxygenated blood to meet the body’s requirements. When the oxygen-rich blood which is pumped at a higher pressure mixes with the blood going to the lungs, the pulmonary artery as well as the lungs gets damaged by the high pressure.
When heart failure develops, blood may accumulate in other parts of the body, especially in the lungs. Heart failure may also result when blood flow into the heart is blocked and from poor pumping of the heart due to the weakness of the heart muscle in some infants.
Sometimes, blockages occur in the heart valves or in any of the blood vessels carrying blood from the heart. Pulmonary artery stenosis where the blood vessel leading from the heart to the lungs is narrowed, and pulmonary valve stenosis in which the valve allowing the blood flow into the pulmonary artery is narrowed, may restrict blood flow from the heart into the lungs for oxygenation. Aortic valve stenosis or a blockage in the aorta known as coarctation may impede the flow of oxygenated blood to the other parts of the body.
Symptoms and Diagnosis
Many congenital heart defects remain asymptomatic and are not detected in infants in spite of the physical examination conducted after birth. The symptoms of certain mild defects may not appear till the person reaches middle age. Reduced weight gain and growth retardation may be caused by heart defects which result in poor blood supply to the body, as oxygen-rich blood is essential for normal development. Activity demands extra oxygen supply, and children with heart defects may not be able to indulge in vigorous play or exercise. Symptoms like cyanosis and breathing difficulty may appear on exertion. If heart failure results from defects in the heart, fluid collection in the lungs and rapid heartbeat are the usual symptoms. Certain heart defects like patent foramen ovale in the atrial septum increase the risk of clot formation in the heart. If a clot travel to an artery supplying the brain and blocks it, stroke may result. Abnormal circulatory patterns in the heart due to heart defects cause abnormal sounds known as murmurs which can be detected by a stethoscope. However, all heart murmurs occurring in childhood are not due to heart defects.
Ultrasonography test of the fetus may reveal many of the congenital heart defects present even before the infant is born. Typical heart murmurs and symptoms in a newborn alert the doctors to possible heart defects, which are investigated further to diagnose the exact abnormality.
The same diagnostic techniques used for detecting heart problems in adults are used to diagnose congenital heart defects in infants and children. A physical examination and feedback from parents and caregivers of the infant may indicate the nature of the defect to the doctor. An x-ray of the chest, ECG and echocardiography can diagnose most of the heart defects. A minimally invasive procedure called cardiac catheterization may be necessary to detect certain abnormalities which are not easily detected by the other tests. This test is sometimes conducted to determine more accurately the exact nature and extent of a defect detected by echocardiography.
Treatment
Open-heart surgery may be required to correct most of the serious congenital heart defects. The surgery is scheduled depending on the severity of the symptoms and the infant’s condition. Some severe cases may need immediate surgical intervention, but whenever possible, surgery is delayed till the infant grows older.
Constrictions in the blood vessels and narrowed heart valves can be enlarged by minimally invasive procedures in which a thin tube called catheter is threaded through a suitable blood vessel to reach the location of the defect. A tiny balloon at the tip of catheter can be inflated to enlarge the narrowed area. This procedure is termed balloon angioplasty when it is used to widen a narrowed blood vessel, and balloon valvuloplasty when used to open up narrowed heart valves. Minor defects are repaired using these procedures to avoid the risks involved in a major surgery and in giving general anesthesia to the infant, in spite of the fact that open-heart surgery is more effective in correcting most defects.
A severe block in the pulmonary artery or the aorta can be temporarily relieved by creating a shunt to maintain blood circulation. An opening in the atrial septum may be created by a procedure called balloon septostomy. Administering prostaglandins may help the fetal blood vessel ductus arteriosus to remain open, allowing the flow of blood between the pulmonary artery and the aorta. Heart transplant is an option when attempts at surgical correction fail, but it is often limited by the unavailability of suitable donor hearts.
Endocarditis or infections affecting the heart and heart valves are more common in children with serious congenital heart defects. They should take antibiotic therapy before undergoing surgical procedures and treatments.
Most common congenital heart defects are:
- Patent ductus arteriosus
- Atrial septal defect
- Ventricular septal defect
- Fallot tetralogy
- Transposition of the great arteries.
- Aortic valve stenosis
- Pulmonary Valve stenosis
- Coarctation of the aorta
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Yasser Elnahas
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