Innocent cardiac murmurs in children

Recognising the type of murmur is key to successful murmur management.

Telling parents that their child has a heart murmur is often a difficult consultation. It is natural for parents to be anxious that their child may have a serious heart problem. Yet this is rarely the case.

Diagnosing the cause of the murmur: arrow indicates septal defect

Colour flow mapping can be used to assess the size of the lesion

Reassure the parent
It is worth explaining that a heart murmur is just a noise that is heard with the stethoscope. In most cases the heart is normal and the noise originates from the flow of blood in the heart. It is particularly easy to hear normal flow in young children as there is less soft tissue and bone between the stethoscope and the heart.

The shape of the heart in pre-school children may also make it easier for innocent murmurs to be heard over the chest at the sternal edge.

Many, perhaps more than half of all children have a murmur in the pre-school years.

When to refer
There is a temptation to obtain detailed echocardiography in all cases, which of course is definitive and non-invasive, but this would lead to a huge workload for echo departments.

At present it would be impossible to cope with referring all children with innocent murmurs for echocardiography.

It could be argued that it is sensible to refer these children to a paediatric clinic. However, this could mean up to half of all UK children being seen in hospital for a soft heart murmur.

With increasing specialisation in general practice, many larger practices will have a GP with an interest in paediatrics who would be well placed to develop expertise in paediatric heart murmurs.

Still's murmur
Still's murmur is the most common innocent murmur referred to paediatric cardiologists, therefore it is important for GPs to know its characteristics.

Still's murmur is a short soft midsystolic murmur with a characteristic buzzing quality. It is heard best at the lower left sternal edge, although it can also be heard at the apex.

It varies with posture; it is loudest when the child is supine and softens on standing. It may also disappear if the child hyperextends the back and neck.

A Still's murmur usually is inaudible in the second decade, but can persist into adult life. Like all innocent murmurs it is loudest during high cardiac output such as a fever.

Other innocent murmurs are commonly heard in children and they tend to be managed in primary care.

Pulmonary flow murmur
Pulmonary flow murmur is a soft systolic murmur, which unlike Still's murmur, is heard at the upper left sternal edge and is harsher and higher pitched and can be heard over the child's back.

The murmur will disappear with the Valsalva manoeuvre. Also, unlike Still's murmurs, they are more common in children with pectus excavatum and in adolescents. They are common when cardiac output is high and when a child is anaemic or has a high temperature.

If there is an obvious cause, such as fever, there is no need to refer, but it would be advisable to listen again when the possible cause has gone.

Venous hum
Venous hum is a continuous murmur heard beneath the clavicles and in the neck. It is more often heard in the right side where there is more venous return as the innominate vein joins to form the superior vena cava. Unlike the Still's murmur, venous hum can be heard when the child is standing.

Neck murmur
Innocent murmurs/bruits in the neck are common in normal children. Usually they are harsh and best heard in the neck just above the clavicle, unlike aortic stenosis, which is louder below the clavicle.

They are caused by normal blood flow into the aorta and into the head and neck vessels. The term carotid bruit is best used for adult pathology.

Investigations
If the GP understands how a typical Still's murmur sounds and how to make it vary with posture then more serious pathology will rarely be missed. However, I have seen three major lesions - atrial septal defects, coarctation of the aorta and hypertrophic cardiomyopathy - missed by both GPs and paediatricians. These lesions often have only soft murmurs.

In general the combination of ECG and chest X-ray will detect these diagnoses. Taking the BP in the right arm and checking femoral pulses are also important to diagnose coarctation.

A soft murmur from a minor lesion such as a tiny septal defect, patent ductus or mild valve stenosis could be a problem because of endocarditis.

Murmurs in newborns
Murmurs in newborns should disappear by six months of age and are not associated with any symptoms. They are heard at the base of the heart and radiates into the axillae and the back.

Turbulence is a result of the blood flow from the larger main pulmonary artery into the smaller, distal pulmonary arteries. Before birth only a fraction of cardiac output goes to the lungs. There is therefore a size discrepancy between the main pulmonary artery and the distal pulmonary arteries. This will correct by six months of age.

If an infant is asymptomatic it may be reasonable to wait for the murmur to disappear, if ECG and chest X-ray are normal, and this is the approach of many paediatricians. But regular review of feeding and weight gain are needed and the parents should be told to make contact if there is any sign of poor colour, breathlessness or difficulty feeding.

In my view, it is best for GPs to refer these cases.

  • Dr Burch is consultant paediatric cardiologist and director of cardiothoracic transplantation and heart failure services at Great Ormond Street Hospital, London.

When to refer
Murmurs that should be referred are:

  • Loud.
  • Pansystolic.
  • Diastolic.
  • Continuous, unless a venous hum.

Other warning signs include:

  • When there is a family history of congenital heart disease, cardiomyopathy or sudden death.
  • Failure to thrive, poor growth, difficulty feeding.
  • Abnormal symptoms such as breathlessness, frequent chest infections (indicate high blood flow to the lungs), unable to keep up with friends.
  • Cardiac symptoms such as palpitations, syncope or chest pain (these may not be pathological in children, but are complex problems).
  • Other abnormal cardiac signs (clubbing, cyanosis, clicks or added sounds, rapid heart rate or high BP).

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