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Introduction
In the paediatric population, heart murmurs are incredibly common. 50-80% of children are estimated to have a murmur at some point in their lives.1-4 However, less than 1% of these murmurs represent any underlying pathology.1-2, 5 Despite this, there is a lot of anxiety when a murmur is found.1, 5
It is essential to understand what causes paediatric murmurs and how to identify an innocent murmur. This article will cover how to assess a murmur and the most common innocent murmurs.
Aetiology
Normal heart sounds
Heart sounds are created from vibration when blood moves through the heart.5 When listening to the heart, there are two heart sounds, S1 and S2.
S1 occurs during systole when the ventricles contract. The mitral and tricuspid valves will snap shut, creating an audible S1.3
S2 occurs during diastole when the ventricles relax. The aortic and pulmonary valves snap shut, creating an audible S2.3
Murmurs
A murmur is the extra sound in the heart when blood flow is disturbed.2 This creates turbulence and vibration as the blood moves through the heart, which can happen if there is a change in velocity or pressure.2-5
In children, most murmurs are due to normal blood flow, known as innocent murmurs.5 Anything that increases cardiac output will make an innocent murmur more easily heard, such as anaemia or fever.3, 5
If turbulence is caused by a structural change, such as in congenital heart disease, the murmur is described as pathological.3
The main innocent murmurs to be aware of are Still’s murmur, pulmonary flow murmur and a venous hum murmur.
Clinical features
By definition, innocent murmurs are caused by normal blood flow and are not pathological. Therefore, there should be no other symptoms or signs. However, the focus of your assessment should be to identify any other symptoms or signs that could point towards a pathological cause.
The assessment of a murmur requires more than just auscultation. Therefore, a detailed paediatric history and cardiovascular examination are required. Cardiac auscultation is also included in the newborn baby assessment (NIPE) and may detect a murmur.
Grading of heart murmurs
Heart murmurs can be graded on a scale of 1-6, to describe the intensity of the murmur:6
- 1/6: quieter than the heart sounds
- 2/6: same volume as the heart sounds
- 3/6: louder than the heart sounds
- 4/6: louder than heart sounds with a palpable thrill
- 5/6: can be heard with the stethoscope just about on the chest
- 6/6: can be heard without a stethoscope
Still’s murmur
A Still’s murmur is the most common type of innocent murmur.5 Despite this, the exact cause is not known. Some possible explanations include vibrations as blood moves out of the heart and into the aorta or from blood moving across the chordae tendineae.4
It affects children from three years old and usually improves by early teenage years but can remain into adulthood.4-5
A Still’s murmur is a systolic murmur (graded one to two) located from the lower left sternal edge to the cardiac apex, and is heard easiest with the bell.4-5 It is loudest when lying down and quietest when sitting or standing up, as this reduces venous return.5, 6
Pulmonary flow murmur
The second most common innocent murmur is a pulmonary flow murmur.6 It is caused by normal vibrations through the pulmonary blood vessels as blood leaves the right ventricle during systole.4-5
This affects children aged five to 14 years old, and is the most common innocent murmur in teenagers.4
A pulmonary flow murmur is a systolic murmur (graded one to three) located at the left upper sternal edge and is best heard with the diaphragm.5 It is louder when lying down, as this increases venous return, and will often become quieter when sat up or during the Valsalva manoeuvre.5
It can be confused with pulmonary stenosis as they are both systolic murmurs heard over the pulmonary area. The main differentiating features are that pulmonary stenosis is associated with a click, and it will not change intensity if the patient is repositioned.5
Venous hum murmur
This is the only innocent murmur that has a diastolic component. It is a continuous murmur heard across both systole and diastole, caused by blood draining into the superior vena cava.4, 6
A venous hum will affect children between ages two to eight years old.6
It is located next to the sternocleidomastoid muscle in the lower neck, heard easiest with the bell.5 It is only audible when sitting up, should disappear when lying down, and becomes quieter when the jugular vein is pressed or if the neck is extended.4, 5
Describing a murmur
If a murmur is heard, it should be described by:6
- Where it is heard best on the chest
- Whether it is systolic or diastolic
- How loud the murmur is
- If it radiates to the axilla, neck, or back
- If the murmur changes when the patient moves position
Differential diagnoses
It may not be possible to diagnose the exact type of innocent murmur. Therefore, it is important to know the reassuring features to avoid over-investigation.
If the murmur does not satisfy the seven ‘S’ of innocent murmurs, the main differential would be congenital heart disease. Examples could include
- Atrial septal defects
- Ventricular septal defects
- Atrioventricular septal defects
- Persistent ductus arteriosus
- Pulmonary stenosis and tetralogy of Fallot
The seven ‘S’ of innocent murmurs
An innocent murmur should be:1
- Systolic and never purely diastolic
- Small with no radiation
- Soft, graded at one to three
- Short in duration
- Singular, not associated with other sounds such as clicks or gallops
- Sweet not harsh sounding
- Sensitive to positioning
Investigations
As innocent murmurs are part of normal physiology, no specific tests or investigations are required. However, if a murmur is heard, basic observations should be performed:6
- Blood pressure: recorded in both arms and both legs; this should not vary more than 10-20 mmHg between the arms and legs
- Oxygen saturation: recorded in the right hand (preductal) and a lower limb (postductal); there should be a less than 3% difference, and both over 95%
If there are any concerning features on history or examination, a referral should be made to a paediatric cardiologist. Typical investigations may then include:
- Electrocardiogram
- Chest X-ray
- Echocardiogram
Management
As innocent murmurs result from normal blood flow, if a child is asymptomatic, they do not require monitoring or treatment, even if the murmur is still present as an adult.6
Referral to cardiology is typically indicated if: 4, 7
- The murmur is louder than grade 3/6
- It is a diastolic murmur
- There are associated clicks or gallops
- The murmur radiates
- There is any other abnormality on cardiovascular examination
- There is a family history of cardiac disease in children
The exact underlying diagnosis may not be identified, but if a murmur satisfies the features of an innocent murmur, reassurance is all that is needed.
Reviewer
Dr Ishbel MacGregor
Consultant Paediatrician
Editor
Dr Jamie Scriven
References
- G Bronzetti, A Corzani. The Seven “S” Murmurs: An Alliteration About Innocent Murmurs in Cardiac Auscultation. Clinical Paediatrics. 2010. Available from: [LINK].
- A Huq, A Rahman. Cardiac murmurs in children. Australian Journal of General Practice. 2024. Available from: [LINK].
- R Hueckel, C Leyland. Pediatric Murmurs. Nursing Clinics of North America. 2023. Available from: [LINK].
- B Ford, S Lara, J Park. Heart Murmurs in Children: Evaluation and Management. American Family Physician. 2022. Available from: [LINK].
- A Doshi. Innocent Heart Murmur. Cureus. 2018. Available from: [LINK].
- E Mejia, S Dhuper. Innocent Murmur. StatPearls. 2023. Available from: [LINK].
- S Hendry, B Smith, T Kendrew-Jones. Incidental murmur guideline, paediatrics (399). NHS Greater Glasgow and Clyde Paediatrics. 2018. Available from: [LINK].
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