innocent murmurs

Last reviewed 01/2018

Many babies and children have heart murmurs in the absence of any structural abnormality.

The diagnosis of an innocent murmur is usually on the basis of clinical symptoms and signs but if investigations are necessary they are always normal.

Types of innocent murmurs include:

• venous hum - a continuous blowing noise heard just below the clavicles. It varies with respiration and disappears if the child lies down. It is due to turbulent flow in the systemic great veins

• pulmonary flow murmur (right ventricular outflow tract murmur) - is a soft ejection murmur heard in the second left intercostal space. It is a flow murmur of a normal pulmonary valve. The increased flow of anaemia, pyrexia and exercise makes this murmur louder

• vibratory murmur - this is a buzzing noise heard around the apex. It varies with posture
  • "..The commonest innocent murmur in children of any age (most often heard at age three to six years) is the parasternal vibratory ejection systolic murmur which has a very characteristic low-frequency ‘twanging’ or musical quality. It is localised to the left mid-sternal border or midway between the apex and left lower sternal border, is of short duration, low intensity and is loudest when the child is supine often varying markedly with posture... " (1)

If a murmur has any of the following characteristics then it probably is NOT innocent:

• pansystolic
• diastolic
• loud or long
• associated with a thrill or cardiac symptoms

In addition to listening for murmurs careful attention should be paid to the presence of other evidence of cardiac pathology. The features listed below indicate that a murmur is likely to be pathological and that prompt expert evaluation is needed (1). Central cyanosis or heart failure should prompt urgent specialist referral even if there are no murmurs.

• cyanosis or clubbing
• abnormal breathing (tachypnoea, intercostal recession)
• failure to thrive
• abnormal pulses - diminished or absent femorals
• abnormal cardiac impulse
• hepatomegaly
• thrill over precordium or suprasternal notch
• presence of an ejection click
• radiation of murmur to the back
• a murmur which is purely diastolic
• abnormal heart sounds

Asymptomatic murmurs found incidentally during febrile illness, if innocent, may well disappear when the child has recovered.

Investigations

• chest X-ray and electrocardiography are very rarely useful in deciding if a murmur is innocent and are no longer indicated as routine investigations for children with asymptomatic murmurs. If genuine pathology is suspected echocardiography, in expert hands, will almost always enable a complete diagnosis to be achieved

Notes:

• continuous murmurs are heard throughout systole and diastole and are a feature of persistent ductus arteriosus or vascular malformation. With the exception of the venous hum they are always pathological

Reference:

• (1) British Heart Foundation Factfile (February 2011). Cardiac murmurs in children