What have we learned from the evaluation of the contour of our patient’s precordial impulse? Well, we used the cotton swab to clearly bring out the fact that there are two apical impulses. It’s so easy to see that, and you then time those two impulses by using another swab on the carotid vessel.

And you find out that there is a small impulse that occurs just prior to systole, and another sustained impulse that occurs during systole.

And what does that mean? Well, to begin with, the sustained systolic impulse is totally consistent with the enlarged size of the apical impulse. It suggests an hypertrophied ventricle, with the impulse being sustained throughout all of systole. And that previous to systole, or presystolic, movement? That is the palpable equivalent of a fourth heart sound, which occurs when the atrium contracts and blood goes rushing into the ventricle, when the compliance is reduced, that sets up vibrations that are appreciated at the bedside as a palpable presystolic or fourth sound.