Fourth Heart Sound (S4)

Fourth Heart Sound (S4)

Definition

S4 is a low-frequency gallop sound that results from a forceful atrial contraction during presystole that ejects blood into a ventricle which cannot expand further. S4 occurs ~90 msec before S1.

Listening Areas

Listening Areas for S4

Heard with the stethoscope bell over the LV apex (usually 5LICS) or the RV apex (usually over 4LICS or LMPC).

Associated Conditions

With Left Ventricular Hypertrophy (LVH):

With Right Ventricular Hypertrophy (RVH):

See Also:

Extra sounds near S1

Notes

Compared with an S3, the S4 is somewhat shorter in duration, sounding snappier rather than dull and thudding. The bell of your stethoscope is necessary to hear an S4, lightly applied to the patient's skin. As with an S3, you will not hear an S4 with the diaphragm, and you may not hear it at all with a bad stethoscope.

To improve your chances of hearing an S4, roll the patient on his or her left side (the left lateral decubitus position) to swing the cardiac apex against the chest wall, bringing it closer to your stethoscope chest piece. An irreverent mnemonic: to remember the cadence of S4-S1 S2, think of a percussion sting played on the drums after a bad joke: "ba-DUM bump."

An S4 implies a forceful atrial contraction. Patients with LV hypertrophy become dependent upon this atrial kick to fill their stiff and incompliant ventricles, and can experience dyspnea or chest pain when they lose it with the onset of atrial fibrillation.