Murmurs without any organic heart disease can be found in children. These have been called by various names like innocent murmur, physiological murmur, normal murmur and even functional murmur. But the term innocent murmur is preferred as it strongly conveys that nothing is abnormal . Less than 1% of murmurs in children are due to congenital heart disease.
Classical flow murmurs heard in children are Still’s murmur, pulmonary flow murmurs, systemic flow murmurs like supraclavicular systemic bruits and venous hum . Still’s murmur was described by George Frederic Still in 1909. This is a low pitched murmur heard in the lower left sternal area. It is best heard with the bell of the stethoscope. As it is flow related, it can change with position and decrease or disappear with Valsalva maneuver. McKusick VA et al described it as a musical murmur . Still’s murmur is a mid systolic murmur, loudest in supine position and diminishes in intensity on sitting and standing as venous return decreases .
Pulmonary flow murmurs are high pitched murmurs heard in the upper left sternal border. They are better heard with the diaphragm of the stethoscope. They are also flow dependent and will change with position and may decrease or disappear with Valsalva maneuver. When the blood flow velocity increases as in fever or anemia, it becomes more prominent.
Systemic flow murmurs and supraclavicular bruits are high pitched murmurs due to normal blood flow into the aorta and head and neck vessels. They are heard high up in the chest and above clavicles. Being high pitched, they are better heard with the diaphragm of the stethoscope. The murmur is better heard in supine position and diminishes in intensity when the neck is hyperextended .
Venous hums are low pitched continuous murmurs due to the blood flow in the great veins. They are heard best with the bell of the stethoscope. Cervical venous hum can be completely obliterated by pressure over the major neck veins. It also changes with position and is better in the sitting position than in the supine position, due to the effect of gravity. Looking down or the side may also make cervical venous hum inaudible . These maneuvers are helpful in differentiating it from the continuous murmur of patent ductus arteriosus. Murmur of patent ductus arteriosus may be associated with multiple clicks known as eddy sounds, which gives the murmur the famous train in tunnel character.
An interesting study on computer aided auscultation (CardioscanTM) involving 126 children in the age group 0-17 years has been published . The technique showed 83.0% sensitivity for detection of potentially pathological murmur at a specificity of 30.3%. When the analysis was limited to subjects with a heart rate between 50-120 beats per minute, the sensitivity was 75.0% and specificity 71.4%.