Heart murmurs in children are very common. A heart murmur just means a sound. Some heart murmurs are sounds produced by actual defects or abnormalities with the heart. For example, a ventricular septal defect (a hole in the wall separating the lower 2 chambers of the heart) makes a very specific noise as blood travels through the hole. Abnormalities with heart valves like aortic valve stenosis can also produce heart murmurs. As blood flows past the defective valve the turbulent flow can produce a distinctive sound. On the other hand, many heart murmurs are what we call innocent heart murmurs. With an innocent heart murmur, the heart is perfectly normal. The murmur in this case is simply the normal sound that blood is making as it flows through the heart.
There are a number of different innocent heart murmurs. Let’s review 3 relatively common innocent heart murmurs found in children.
Named for English pediatrician George Frederic Still, the Still's murmur is by far and away the most common innocent heart murmur. Many textbooks describe it as a vibratory type noise. I'm not sure myself if this is completely accurate, but at least that's the way it is frequently described. Certainly it is a very unique noise. Once you've heard a Still's murmur several times, it becomes very difficult to confuse it with anything else.
I hear Still's murmurs at every age. I've heard it in babies a few hours old all the way up to full grown adults. I really think that this murmur can be present at pretty much any age. Classically it is most common in school aged children. It's a very distinct noise that is best heard along the left sternal border. Some experts feel that it might be more prominent in the flat position as opposed to sitting or standing, but I have not always found this to be the case.
The cause of the Still's murmur is not entirely clear. Some studies have demonstrated that children with a Still's murmur are more likely to have an accessory mitral valve chord attaching to the ventricular septum (termed a “false tendon”). The chordae tendineae anchor the papillary muscles to the mitral valve leaflets. Occasionally there may be a stray chord that extends from a papillary muscle directly to the ventricular septum. Some experts think that vibrations of these anomalous chords are what produce a Still's murmur.
In my opinion the Still's murmur is very unique. When a classic Still's murmur is present, it's hard to confuse it with anything else. Having said this, many children have slight variations in the sound or quality of the murmur which may suggest more worrisome causes. Rarely subaortic stenosis may be confused with a somewhat harsher Still's murmur. Subaortic stenosis can be caused by an isolated subaortic membrane, or can found in association with heart problems like hypertrophic cardiomyopathy.
By far and away the Still's murmur is the most common innocent heart murmur. Determining the next most common innocent heart murmur is a little difficult. It all depends on what age you are talking about.
Pulmonary flow murmur
A pulmonary flow murmur is just like it sounds. In a pulmonary flow murmur, all you are hearing is normal blood flow across a normal pulmonary valve. Blood is a liquid, and it flows through the heart fairly rapidly in some cases. Sometimes this normal flow can produce extra sounds or noises. The pulmonary valve happens to be one of the most anterior structures in the chest. In other words, it is fairly close to the chest wall. Therefore it makes sense that you might be able to hear normal flow across this valve compared to the other valves in the heart, which are farther back in the chest.
Pulmonary flow murmurs can be heard at any age. They tend to be especially common in older children and teenagers. As you might expect, they are more common in kids who have thin chest walls, where the heart may be physically closer to the stethoscope and therefore easier to hear.
Sometimes a pulmonary flow murmur can be confused with potential true heart disease. For example, an atrial septal defect might make a similar noise. Rarely mild pulmonary valve stenosis might also be confused with a pulmonary flow murmur.
Cervical venous hum
A cervical venous hum is an extremely common type of innocent heart murmur. It is caused by the sound of blood flow returning normally through the veins above the heart. Specifically, the jugular veins drain blood from the head and neck and connect to larger veins which return to the heart. Sometimes a slight angle is produced in these connections which can create slightly turbulent blood flow. Usually this is the source of a cervical venous hum.
Cervical venous hums are most commonly found in young school aged children. They're typically heard only in the sitting or upright position, because in this position gravity is exerting a stronger effect pulling blood down towards the heart. It's very uncommon to hear a cervical venous hum in a child who is laying flat. Exerting light pressure over the veins of the neck or having a child turn his head to one side can compress the veins somewhat and often makes the murmur disappear.
Innocent cervical venous hums may not be detected in many children simply because they are not always listened for. In my experience, however, it's possible to hear this murmur in almost any school age child if you listen closely enough.
Cervical venous hums are different from pathologic murmurs in that they disappear in different positions and with different maneuvers. This helps differentiate them from a patent ductus arteriosus, which can produce a similar type noise but won't disappear with these maneuvers.
Penn Laird II, M.D.