Even though heart murmurs usually are not a sign of heart disease, they are frequently a source of concern to parents. This is because many parents have heard about a child with an abnormal heart who had a murmur. In order to understand heart murmurs, it is important to know how the heart works.
The heart is a pump made of muscle tissue. It is about the size of a person’s fist. The heart has four hollow parts or chambers. The upper two chambers are the atria and the lower two are the ventricles (see diagram). Blood is pumped by the muscular walls of the chambers.
The direction of the flow is controlled by four heart valves. The valves open and close to let the blood flow in one direction. The four heart valves are:
Dark red blood, low in oxygen, flows back to the heart after circulating through the body. It returns to the heart through veins and enters the right atrium. This chamber empties blood through the tricuspid valve into the right ventricle. The right ventricle pumps the blood under low pressure through the pulmonary valve into the pulmonary artery. From there the blood goes to the lungs where it receives oxygen. After the blood is replenished with oxygen, it is bright red. It then returns by pulmonary veins to the left atrium. From there it passes through the mitral valve and enters the left ventricle.
The left ventricle pumps the red, oxygen-rich blood out through the aortic valve into the aorta. The oxygen-rich blood then travels throughout the body by way of arteries. As the body uses up the oxygen, the blood changes from bright to dark red. The dark red blood returns to the heart by way of veins where the blood is again pumped through the lungs back to the heart and away to the body again.
You’ve likely heard the lub-dup, lub-dup of heart sounds on medical TV programs. The first sound, lub, is caused by the contraction of the heart muscle and closure of the mitral and tricuspid valves. The second sound, dup, is caused by the closure of the aortic and pulmonary valves. The flow of blood through the heart produces a soft whooshing sound, normally too faint to hear through the stethoscope on the chest.
If blood flow is more turbulent than usual, it causes a whooshing sound between the lub and dup, like water flowing through pipes in a house. This rushing sound is the heart murmur and it may be heard through the chest with a stethoscope.
The most common innocent murmur is caused by turbulent flow in the left ventricle. It is heard between the first, lub, and the second, dup, heart sounds. The murmur varies as the child moves and breathes. It may be louder than usual when the outflow from the heart is increased. This occurs when the child has a fever or is exercising. Other less common innocent murmurs may sometimes be heard over the upper chest and pulmonary artery, over the carotid artery or over the veins of the neck.
As a child grows, the chest wall becomes thick and there is less turbulent blood flow through the heart, so murmurs become difficult to hear. Hence, innocent murmurs are heard in only about 15 per cent of adults. Some people retain innocent murmurs throughout their lives.
Some heart murmurs are not innocent and may need medical attention. One cause of these may be congenital heart defects. The word congenital means inborn or existing at birth. A defect results when the heart or blood vessels near the heart do not develop normally before birth. The cause of these defects is usually unknown. The result is a leak in a heart valve, between two of the four chambers of the heart, or abnormality in the large blood vessels around the heart. The unusual blood flow patterns cause the murmur.
Certain conditions that affect multiple organs such as Down Syndrome can also involve the heart. Women who drink alcohol while they are pregnant run an increased risk of having a child with heart defects. In the past, Rheumatic fever was a common cause of heart valve damage and heart murmurs but, fortunately, it is now uncommon in Canadian children.
The trained ear of the family doctor is an excellent detective of innocent murmurs. If the doctor has some doubt about the murmur, diagnostic tests such as a chest x-ray or an electrocardiogram (ECG) might be ordered. A special test called an echocardiogram can add valuable information about the structure and function of the heart muscle. It uses ultrasound waves to create images of the heart structures. This test can detect leakage from valves or other defects that cause murmurs that are not innocent. The child may be referred to a heart specialist or pediatrician.
YES. Children with innocent murmurs are normal, healthy people who should not be restricted in their physical activities. Athletic potential lies in a combination of genes, muscle co-ordination, speed and motivation. The innocent heart murmur will have no bearing on their success in sports or their enjoyment of life.
Parents who are told their child has a heart murmur will naturally be concerned. The encouraging fact is, however, that most heart murmurs in children do not indicate heart disease. Children with heart murmurs can live an active life without restriction.