Fourth Heart Sound (S4)
The fourth heart sound is the sound of the vibration of a non-compliant ventricle that is forced to accept blood during atrial systole. It is very closely approximated to the first heart sound, often producing, in combination with the first heart sound, a stuttering quality. Its frequency is low, often as low as 30 Hz; near the limit of human hearing. Such low frequencies carry a great amount of energy but are easily damped by normal tissue. Therefore, it is easiest to hear with the patient in the left lateral decubitus position with the bell of the stethoscope just making a seal with the skin. Listen for the cadence of "Tennessee" with the "nuh" of Tennessee representing the first heart sound. Another, more musical way of stating this is to listen for "BaBaBump" with the accent on the second "Ba".
A fourth heart sound may be generally seen as a sign of ventricular noncompliance. An audible sign of atrial success overcoming the noncompliant ventricle of hypertensive heart disease, hypertrophy from any mechanism, or ischemic heart disease. The man who originated the Texas Heart Institute heart sounds laboratory, Dr. Robert Hall, often emphasized that while the S3 is the sound of ventricular failure, the S4 is the sound of atrial success.
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Updated February 2010