Split First Heart Sound


The first component of the first heart sound is created by the closing of the mitral valve leaflets and the second by the closing of the tricuspid valve leaflets. There is normal asynchrony in the closure of mitral (M1) and tricuspid (T1) valves, the mitral closure preceding tricuspid closure by 20 to 30 msec (0.02 to 0.03 sec.). This produces two audible components (M1-T1) referred to as normal or physiologic splitting of the first heart sound. Such narrow splitting is usually best heard at the lower left sternal border with the stethoscope diaphragm. The tricuspid component, which may increase with inspiration, is best heard in this location but is poorly transmitted to the apical region. The mitral component, in contrast, is best heard at the apex but is intense enough to be heard throughout the precordium. During auscultation please determine whether the first sound is split into its two components (mitral and tricuspid) and, if so, which component is loudest.
First Heart Sound Unsplit
First Heart Sound Split

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