What we heard at the apex with light pressure on the bell was a low-frequency fourth heart sound followed by a first sound, followed by the second sound. When we palpate the chest wall we can integrate the sound with the movement. Let's everybody listen together at the apex with light pressure on the bell and let's watch closely the way the stethoscope will actually move, and it is the second, most sustained movement, that demarks systole for us. Everybody listen and observe together. [Cut-away]
What a beautiful integration of chest wall movement and auscultation. Particularly, we heard an S4 [sounds]. And what did we see on the chest wall and what can we feel? A presystolic movement. The presystolic movement is the palpable equivalent of the fourth sound we heard. And then, of course, the sustained systolic movement denoted systole and it also told us that this is, again, hypertrophied, thickened ventricle.
So, at the apex we learned quite a bit. We learned that this atrium is pushing blood into a ventricle that it is finding noncompliant. Hence, when blood accelerates in, it decelerates more rapidly and this sets up vibrations that are heard as a fourth sound and palpated as a presystolic impulse.
Oscilloscope
By viewing an oscilloscopic image and simultaneously listening, we can further appreciate these auscultatory events.
Fourth sound graphic
This is a graphic example of an S4 preceeding and S1. Let us listen together. Note that the S4 is low frequency.