A heart murmur is an abnormal heart sound produced by turbulent blood flow within the heart or through the heart valves, detected by listening with a stethoscope. Normal heart sounds (the familiar ‘lub-dub’) are produced by the closing of the heart valves; murmurs represent additional sounds created when blood flow becomes turbulent rather than smooth.
Murmurs are graded on a scale of 1 to 6 based on their loudness, and are characterised by their timing (systolic, during ventricular contraction; or diastolic, during ventricular filling), their location, their radiation (whether heard elsewhere, such as the neck or axilla), and their quality (harsh, blowing, rumbling). These features help the clinician determine the likely cause and guide further investigation.
Many heart murmurs are innocent (also called functional or physiological): caused by increased turbulence of normal blood flow without any structural heart abnormality. Innocent murmurs are common in children, in pregnancy, and in states of high cardiac output such as anaemia. A pathological murmur caused by a structural problem (such as a diseased valve, a hole in the heart wall, or outflow tract obstruction) requires further investigation, typically by echocardiography.
For cardiac arrest survivors, any murmur detected during or after hospitalisation should be investigated with echocardiography as part of the standard post-arrest cardiac workup. Murmurs may indicate valve disease, ventricular septal defect, or hypertrophic cardiomyopathy, all of which are directly relevant to the cause and management of the arrest.
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