Heart sounds (first, soft)
Possible causes of a soft first heart sound include:
- early atrioventricular closure (in this situation the leaflets are semi-closed at the end of diastole)
- a low flow at the end of diastole
- a P-R interval that is greater than 0.2 s
- a rigid calcified valve will cause a soft first heart sound
- if the left ventricle is not contracting efficiently then there may be a soft first heart sound produced
- a delayed onset of left ventricular systole
Hence, causes include:
- mitral regurgitation
- low blood pressure, for example with M.I.
- rheumatic carditis
- severe heart failure
- left bundle branch block
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