What is the ‘first heart sound’ in Mitral Stenosis?
First heart sound (S1) is typically loud in MS.
Mechanism of Loud S1 in MS
- Because of high pressure in the left atrium, the left ventricle [LV] needs to reach a higher pressure before it can close the mitral valve and hence LV pressure has more time to accelerate
- wide closing excursion of the leaflets – The wide closing excursion of the leaflets happens because the transmitral gradient keeps the valve wide open at the end of diastole rather than allowing the valve to go to a semi-closed position as happens normally without mitral stenosis.
- Intensity of the first heart sound is reduced – if the valve is thickened and calcified.
- Presence of a loud S1 suggests – that the patient may be a likely candidate for balloon mitral valvuloplasty.
- Variable intensity of S1 – With the development of atrial fibrillation – intensity of the S1 will vary depending upon the RR intervals with a louder S1 audible in shorter cycles.
