Heart Sounds
Listen with the bell part of your stethoscope. Hold the bell gently over
the apex area of the heart. Normal S1 and S2 sounds should be the
first identifiable heart sounds. S1 precedes S2 and they
can be described simply as the basic "lub-dub" sounds.
The basic heart sounds result from the vibrations of the left
ventricular muscle, cardiac skeleton, the valves and great vessels, and
the momentum and velocity of the blood as it flows through the elastic
system. For our purposes, or as the result of closure of the A.V. or
mitral and tricuspid valves, and the aortic and pulmonary valves
respectively.
With this in mind, let us review the cardiac cycle. We will begin
with diastole when blood flows into both the right and left atria
through open A.V. valves. At the end of diastole, when the atria
contract, increased blood flow into the ventricles causes a rise in the
ventricular filling pressure, causing the mitral and tricuspid valves to
snap shut, thus producing the S1 or first heart sound.
During systole the ventricles contract, exerting pressure which
eventually rises higher than the pressure of the aorta and the pulmonary
artery, forcing the aortic and pulmonary valves open. Eventually at the
end of systole the pressure within the ventricles starts to fall as the
ventricles start to eject blood. As the pressure drops below the
pressure in the aorta, and pulmonary artery, the aortic and pulmonary
valves snap shut, eliciting the S2 or second heart sound.
S3 - Ventricular gallop
Another valvular sound, the "opening snap" may be auscultated
at the apex as a high-pitched sound. This is the opening snap of the
mitral valve. Not normally audible, this sound may alert you into the
existence of mitral stenosis. It usually closely follows S2. As
the ventricles fill following opening of the A.V. valves, a third heart
sound may be auscultated. This sound is due to the rapid filling of the
ventricles and is referred to as the S3 sound or ventricular
gallop. It follows S2 in the cardiac cycle and may be confused
with an S2 split (dub-dub). However, remember that an S2
split should normally split on inspiration whereas an S3 will
not. It is a lower pitched sound than the S2 and can best be
heard with the bell. S3 sound is considered by most sources to be
normal in children and young adults, but suggests ventricular
dysfunction or left ventricular hypertrophy in adults over 40 years
S4 - Atrial gallop
This precedes S1 and is the result of vigorous atrial
contraction. It occurs in patients with hypertension, aortic stenosis,
or acute myocardial infarction. S4 has also been studied in patient's
with left ventricular hypertrophy.
Other web resources for heart sounds: Auscultation
Assistant / Anatomy
of the Heart
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