Heart sounds (opening snaps)

In the healthy heart the mitral and tricuspid valves open silently during diastole, at the end of isovolaemic relaxation. In certain pathological states the AV valves open more rapidly than normal, this results in an audible opening snap.

A mitral opening snap is said by some experts to be pathognomonic of mitral stenosis. The intensity of the snap is directly proportional to the area of the fused cusps. The timing of the opening snap is influenced by the atrial pressure (higher the pressure earlier the snap) and the duration of the isovolumic relaxation phase (the shorter the relaxation phase the earlier the opening snap).

Differentiation of the opening snap from P2 is achieved by listening to the heart sounds during inspiration: the examiner will hear A2, P2 and the opening snap in quick succession. A mitral opening snap may be caused by:

• mitral stenosis with a mobile valve
• rapid mitral flow causes a soft snap e.g. left to right shunts such as a VSD or PDA. Also may occur in severe mitral regurgitation

A tricuspid opening snap is rare and may be caused by:

• tricuspid valve abnormalities e.g. rheumatic stenosis
• increased tricuspid flow e.g. left to right shunt occuring in an atrial septal defect