It is quite often that one is detected to have a heart murmur (cardiac murmur) on routine medical check up. Children are often brought to the clinic after having been detected to have a cardiac murmur during an episode of fever or at school health check up. This does cause a lot of anxiety in parents. Before we go on to heart murmur, which is an abnormal sound from the heart, we can have an overview of normal heart sounds.
Normal heart sounds
When the normal heart beats, two sounds are heard – first heart sound and second heart sound. This is heard using the familiar instrument stethoscope, used by medical personnel. First heart sound occurs when the valves between the upper and lower chambers of the heart close as the heart contracts to pump blood. These valves are the tricuspid valve between the right atrium and right ventricle and the mitral valve between the left atrium and left ventricle.
Second heart sound occurs when the heart starts relaxing after the contraction and is due to the closure of the valve between the great blood vessels and the heart. The aortic valve guards against the backflow of blood from aorta to the left ventricle. The pulmonary valve prevents backflow of blood from the pulmonary artery to the right ventricle.
Blood flow within the heart and blood vessels is usually a silent streamlined flow which does not produce any sound. But when the blood velocity increases, it becomes turbulent and produces a sound known as heart murmur or cardiac murmur. When the blood is thinner as in anemia (reduced content of the oxygen carrying pigment hemoglobin), it becomes less viscous and sound can be produced even with normal flow. When any of the valves are partially obstructed, flow across them becomes turbulent and produces a murmur. In diseases which increase the velocity of blood flow as in increased function of thyroid gland (hyperthyroidism), heart murmur can be heard. A leaky valve leads to an abnormal reverse flow, which produces a murmur if the leak is significant. In children, heart murmurs can occur often without any structural heart disease. These are known as innocent murmurs.
Evaluation of heart murmur
During the evaluation of a cardiac murmur, a good medical history is important. Past history of illnesses like rheumatic fever (a disease of childhood which can affect the heart valves) are documented. A good physical examination is needed to find the location and other characteristics of the murmur which help in identifying the cause. After these, investigations like hemoglobin estimation, electrocardiogram (ECG), chest X-ray when needed and often an echocardiogram (ultrasound imaging of the heart) are performed. As many of the cardiac murmurs can occur without significant heart disease, detection of a murmur by itself need not cause much anxiety, though it calls for an evaluation.