We have reviewed the findings of a normal patient at the upper right and upper left sternal edges. At the upper right sternal edge, we heard only the first and second heart sounds. At the upper left sternal edge, we heard normal inspiratory splitting of the second heart sound. We shall now listen at the lower left sternal edge in the normal patient, where we shall hear splitting of the first heart sound. While this finding is not one of "The Big 12," it must be differentiated from other acoustic events. Let us listen together.
First Heart Sound
The normal first heart sound may be single or split. Splitting is due to asynchronous mitral then tricuspid valve closure. The evaluation of first heart sound splitting is of limited diagnostic value, although it may reflect pathology. For example, wide splitting due to delayed tricuspid closure is seen in patients with right bundle branch block. Most important, split first sounds must be differentiated from other acoustic events, for example, a fourth sound and a first sound.
No Respiratory Variation
Let us listen together. Note that both components of the first sound are high frequency.