Opening Snap

An opening snap is a high-pitched sound that occurs in mitral stenosis at a variable distance after S2. It is due to the sudden opening of the mitral valve and is followed by the diastolic murmur of mitral stenosis. It can be difficult to distinguish from a widely split S2, but normally occurs rather later in diastole than the pulmonary component of the second heart sound. It is pitched higher than a third heart sound and so is not usually confused with this. It is best heard at the lower left sternal edge with the diaphragm of the stethoscope. Use of the term 'opening snap' implies the diagnosis of mitral or rarely of tricuspid stenosis. OS occurs ~80-90 msec after S2 at the beginning of mid diastole. Hear Opening Snap Here

Extra Edge:

Murmur of Mitral stenosis: Mid Diastolic Murmur

Mitral stenosis results in a uniquely shaped, low-pitched diastolic murmur best heard at the cardiac apex. The opening of the mitral valve produces an "opening snap" due to the high left atrial pressures, which is immediately followed by a decrescendo murmur as blood flows passively from the left atrium to the left ventricle through the stenosed mitral valve creating turbulence. Immediately before the S1 sound, active left ventricular filling occurs when the left atrium contracts and forces more blood through the stenosed mitral valve creating a late diastolic crescendo murmur. In the presence of atrial fibrillation, the active left ventricular filling phase does not take place and the latter part of the mitral stenosis murmur disappears.

As mitral stenosis worsens, left atrial pressure increases forcing the mitral valve open earlier in diastole. Thus, in severe mitral stenosis, the opening snap occurs earlier as does the initial decrescendo part of the murmur. The opening snap and murmur of mitral stenosis also respond to dynamic auscultation.

Related MCQ

5. Which one of the following is characteristic of Opening Snap (on cardiac auscultation)? (UPSC CMS 2013)

(a) Low pitched, early diastolic
(b) High pitched. early diastolic
(c) High pitched, late diastolic
(d) Low pitched, late diastolic

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