S4 vs. split S1
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Hi grayheel, thank you for this question. Yes there are additional strategies. Let’s review all of them. First of all, as you mentioned, split S1 is a higher-pitched sound, and is best heard with the diaphragm of the stethoscope. In contrast, S4 is a lower-pitched sound, best heard with the bell. The next strategy is timing. The split S1 sounds (M1 and T1) are closer together compared to the S4 and S1. In other words, the time between M1 and T1 is shorter than the time between S4 and S1. And finally, we should judge an extra heart sound “by the company it keeps”. Meaning, if you’re hearing an extra sound near S1 in a patient with risk factors for concentric LV hypertrophy, like aortic stenosis or longstanding hypertension, then that increases the likelihood that the sound you’re hearing is an S4. Or, on the other hand, if you’re hearing this sound in a patient with a right bundle branch block, then a split S1 becomes more likely. We always must consider context when interpreting physical findings.
Location on the chest wall over which the sound is heard best can often be helpful in other circumstances. It cannot help you in this situation as both split S1 and S4 are best heard in the region of the apex. However, location can help when it comes to differentiating a split S2 (best heard over base) from an S3 (best heard near the apex), for example.
Hope this helps. Let me know.
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