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Intro to Heart Sounds
The ability to detect abnormal heart sounds
can give important information about the heart’s ability to function adequately. Normal individuals
have at least two heart sounds – the first heart sound (S1)
and the second heart sound (S2). Some individuals may also have a
third heart sound (S3) and/or a fourth heart sound (S4). Closure
of the mitral (and possibly also of the tricuspid) valve at the beginning
of systole produces the S1. Closure of the aortic and pulmonic valves
at the end of systole is responsible for the S2.
The S3 results from vigorous filling of the ventricle early in diastole.
The S3 is a passive phenomenon in that its production does not require
contraction of the muscle of any of the cardiac chambers. The S3
is present in many normal, asymptomatic individuals below the age
of 40. However, in patients with symptoms consistent with HF, especially
patients above the age of 40, the S3 is highly specific for HF.
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Location of Heart Sounds in the Cardiac Cycle |
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According to an article published in the New England Journal of
Medicine in 2001 by Drazner et al, the third heart sound is 99% specific
for heart failure. Furthermore the study indicates patients with
a third heart sound are at significantly greater risk for hospitalization,
adverse outcomes, and death.
The S4 occurs as blood enters a relatively non-compliant ventricle
late in diastole. Unlike the S3, the S4 is an active sound whose
production requires forceful contraction of the atrial muscle.
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