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Heart Sounds
A LearnTheHeart.com
Slideshow Presentation
What are heart sounds?
A heart sound is a distinct audible event that occurs at a
specific point in the cardiac cycle. There are two normal
heart sounds (S1 and S2) and many abnormal heart
sounds including S3, S4, clicks, and snaps.
How to listen to the heart
A = aortic listening post
P = pulmonic listening post
E
T = tricuspid listening post
M = mitral listening post
E = “Erb’s point”
The stethoscope basics
The stethoscope
• Every stethoscope has a “bell” and a “diaphragm”.
• The bell is used to hear low pitched sounds and the
diaphragm is used to hear high pitched sounds.
The First Heart Sound (S1)
What is the first heart sound (S1)
• The first heart sound results from the closing of the mitral
and tricuspid valves.
• S1 is a high pitched sound heard best with the diaphragm
of the stethoscope.
• S1 can be divided into two components, M1 and T1.
The Second Heart Sound (S2)
What is the second heart sound (S2)
• The second heart sound results from the closure of the
aortic and and pulmonic valves.
• S2 is a high pitched sound heard best with the diaphragm
of the stethoscope.
• S2 can be divided into two components, A2 and P2.
Normal 1st and 2nd heart sounds
Normal heart sounds
• Normal heart sounds are described mainly by intensity and
“splitting” (S1 and S2 sounds) or by their presence or
absence (S3 and S4 sounds).
• Any changes from normal can be a very important clinical
indicator of certain cardiac diseases, thus learning heart
sounds is critical to diagnosis in patients with cardiac
diseases.
The 1st heart sound
The first heart sound
• There are two components of the first heart sound
designated T1 (tricuspid valve sound) and M1 (mitral valve
sound).
• The T1 sound is softer than M1 due to the lower pressures
on the right side of the heart.
• In up to 40% of normal people, the T1 sound can be
distinguished from the M1 sound! Where would you listen
to hear a split S1?
The 1st heart sound
The first heart sound – splitting
• Normal splitting is very brief, however certain situations
can increase or decrease the splitting of S1.
The 1st heart sound
The 1st heart sound
The 1st heart sound - intensity
The first heart sound
• Certain cardiac conditions/abnormalities can alter the
intensity of the S1 heart sound. Since M1 is much louder
than T1, only things that effect M1 alter the S1 intensity.
• Three things affect the intensity of the 1st heart sound:
1) The mobility of the mitral valve leaflets
2) The distance that separate the leaflets at the onset of
ventricular contraction
3) The rate/intensity of ventricular contraction
The 1st heart sound - intensity
The mobility of the valve leaflets
• If the valve leaflets are unable to open fully due to severe
calcification/stenosis, then when they close they will not
produce as loud of a sound.
• A good example is mitral stenosis (MS).
• In severe MS, the valves simply can’t open hardly at all, so
the intensity of the S1 is decreased.
• When MS is mild, the high pressure in the left atrial (LA)
forces the mobile parts of the valve farther apart, so when
they close the S1 is louder. (see next slide)
The 1st heart sound - intensity
The distance of the valve leaflets
• Valves close very quickly, so the further apart the valve
leaflets are at the onset of valve closure, the greater the
force of valve closure.
• A good example is mild MS. In mild MS, the pressures in
the LA are elevated to the point that the mobile part of the
mitral valve leaflets are forced far apart, so when they
close quickly, a greater force is produced causing a louder
1st heart sound.
The 1st heart sound - intensity
The distance of the valve leaflets – PR interval
• The PR interval on the EKG is another determinant of the
intensity of the 1st heart sound.
• What part of the cardiac cycle does the PR interval represent?
The 1st heart sound - intensity
The PR interval starts as the
sinus node generates an action
potential that spreads through
the atrium. The P wave
represents atrial depolarization
and occurs at the onset of atrial
contraction. The QRS complex
represents ventricular
depolarization. Therefore, the PR
interval is the time it takes for
the action potential to travel from
the SA node, through the atrium,
then through the AV node to the
ventricles.
The 1st heart sound - intensity
The distance of the valve leaflets
• In a person with a long PR interval (1st degree AV block), the
time between atrial contraction and ventricular contraction is
short.
• This results in greater filling of the ventricles. When the ventricles are
full at the onset of contraction, the valve leaflets are closer, thus the
S1 heart sound is very soft.
The 1st heart sound - intensity
The distance of the valve leaflets
• In a person with a short PR interval, the time between
atrial contraction and ventricular contraction is short.
• This results in less filling of the ventricles. When the ventricles
are less full at the onset of contraction, the valve leaflets are
further apart, thus the S1 heart sound is very soft.
The 1st heart sound - intensity
The rate/intensity of ventricular contraction
• If the ventricle contracts faster and harder, the valves will
also close with more force. This will increase the intensity
of the S1 heart sound.
• So when tachycardia exists, the S1 intensity increases.
• Likewise, with bradycardia, the S1 intensity decreases.
• When the inotropy (contractility) is enhanced by ß1 stimulation,
the S1 is increased.
• When the myocardium is weak/damaged, the S1 is softer.
The 1st heart sound - intensity
Summary – Intensity of S1
Accentuated S1 Diminished S1
• Shortened PR interval • Long PR interval
• Mild MS • Moderate to severe MS
• Tachycardia • Bradycardia
• Increased inotropy • Decreased inotropy
The 2nd heart sound
The 2nd heart sound (S2)
• There are two components of the second heart sound
designated A2 (aortic valve sound) and P2 (pulmonic valve
sound).
• The P2 sound is softer than A2 due to the lower pressures on
the right side of the heart.
• In almost 100% of normal people, the A2 sound can be
distinguished from the P2 sound! This results in a “physiologic”
or normal split S2 heart sound.
• Where would you listen to hear a split S2?
The 2nd heart sound
The 2nd heart sound (S2)
• A great deal of clinical information can be obtained by analyzing the
splitting pattern of the S2 heart sound and by determining the
intensity of S2
• The intensity of the A2 heart sound is increased when the systemic
arterial blood pressure is high.
• Likewise, the P2 heart sound intensity is increased when the
pulmonary artery blood pressure is elevated, as in pulmonary
hypertension.
• When the pulmonic or aortic valves are severely stenosed, their
respective sounds will be diminished. This is an important way to
determine the severity of aortic stenosis on physical examination.
The 2nd heart sound
The 2nd heart sound – types of splitting
• Physiologic or normal splitting of S2
- The A2 comes before the P2 during inspiration only.
• Widened split S2
- The A2 always comes before the P2, but is more pronounced during
inspiration.
• Fixed split S2
- The A2 always comes before the P2 and is equally split throughout
inspiration and expiration.
• Paradoxical split S2
- The P2 comes before the S2 during expiration, and the splitting
disappears during inhalation.
The A2 comes before the P2 during
inspiration only since P2 is significantly
delayed and A2 is slightly premature
during inspiration.
Causes: Normal in 90% of people
The P2 comes before the A2 during
expiration, and the splitting disappears
during inhalation since A2 is always
delayed.
Causes: LBBB, AS, or HOCM
The A2 always comes before the P2, but
the splitting is more pronounced during
inspiration. So P2 is always delayed, but
more so during inspiration.
Causes: RBBB, PS, or severe MR
The A2 always comes before the P2 and is
equally split throughout inspiration and
expiration. So P2 is always delayed, but
equally in inspiration and expiration.
Causes: Atrial septal defect (ASD)
The 2nd heart sound
The 2nd heart sound – physiologic splitting
• Normally, the A2 heart sound will slightly precede the P2 heart
sound during inspiration, but they will occur almost
simultaneously during expiration.
The 2nd heart sound
The 2nd heart sound – physiologic splitting
• This is because inspiration increases venous return of blood to
the right side of the heart, thus more blood flows across the
pulmonic valve delaying it’s closure (major effect).
• Also, during inspiration, filling of the left atrium is decreased
resulting in a slightly premature A2 heart sound (minor effect).
• The combination of a significantly delayed P2 and a slightly
early A2 during inspiration leads to a “physiologic” split S2
during inspiration and the absence of a split S2 during
expiration.
The 2nd heart sound
The 2nd heart sound – Paradoxical splitting
• In certain pathological situations, the A2 heart sound is
significantly delayed to the point that the P2 actually precedes
the A2 heart sound.
The 2nd heart sound
The 2nd heart sound – Paradoxical splitting
• This results in a splitting of S2 during expiration, then when
venous return increases with inspiration (delaying P2), the A2
and P2 sounds overlap causing the splitting of S2 to disappear.
• Causes of a paradoxical split S2 include any condition in which
the A2 is significantly delayed.
• The two most important causes are aortic stenosis and in a
person with a left bundle branch block (LBBB).
The 2nd heart sound
The 2nd heart sound – Paradoxical splitting
• Aortic stenosis makes it difficult to eject blood through the
aortic valve from the left ventricle, so the aortic valve must
remain open for a longer time to maintain cardiac output.
The 2nd heart sound
• A LBBB also causes
significant delay of aortic
valve closure since it
takes longer for the
action potentials to
spread to the left
ventricle.
The 2nd heart sound
The 2nd heart sound – Widened splitting
• A widened split S2 occurs when pulmonic valve closure (P2) is
always delayed and inspiration causes a further delay of P2.
This occurs with a RBBB or pulmonic valve stenosis.
The 2nd heart sound
The 2nd heart sound – Fixed splitting
• A fixed split S2 only occurs in one clinical situation which is in
the setting of an atrial septal defect (ASD). The P2 is delayed
the same amount during inspiration and expiration.
Distinguishing Heart Sounds
Which one is S1 and which is S2?
• In the setting of tachycardia, it may be difficult to distinguish S1
from S2.
• Remember: S1 always occurs at the same time as the peripheral
pulses. So feel the radial pulse while listening to the heart to
find S1.
The 3rd heart sound
The 3rd heart sound
• The 3rd heart sound (S3) is produced just after the mitral valve opens
when blood passively fills the left ventricle. This passive filling causes a
compliant left ventricle to rapidly expand in size thus tensing the
chordae tendinae that hold the mitral valve in place. This chordae
tendinae tensing produces the S3 sound. S3 occurs in early diastole.
The 3rd heart sound
The 3rd heart sound
• An S3 will only occur if the left ventricle is very compliant and
able to relax/expand rapidly with passive LV filling.
• In most people, the LV does not expand enough to cause
significant tensing of the chordae, so no S3 sound is heart.
• On physical exam, how could you tell an S3 heart sound apart
from a split S2 heart sound?
• Hint: The S3 heart sound is low-pitched.
The 3rd heart sound
The 3rd heart sound
• An S3 sound is often present in children, pregnant females, and
well trained athletes since their LV is able to expand more than a
normal person.
• S3 is best heard with the patient in the left lateral decubitus
position (laying on their left side). S3 may disappear when sitting.
• An S3 sound is also frequently present with systolic heart failure. In
this situation, the LV is dilated and damaged to the point where it
can rapidly expand upon passive filling.
• An S3 heart sound is an important physical exam finding that may
indicate systolic heart failure in many people!
The 3rd heart sound
S3 present
Normal heart Dilated LV – systolic CHF
The 4th heart sound
The 4th heart sound
• The 4th heart sound (S4) is produced when the left atrium
contracts during the active filling phase of the LV and blood
strikes a non-compliant left ventricle. S4 occurs in late diastole.
The 4th heart sound
The 4th heart sound
• The S4 will only be audible when the ventricle is non-compliant,
thus unable to appropriately relax during LV filling.
• In most people, the LV has at least some compliance, thus atrial
contraction does not normally cause an audible S4.
• On physical exam, how could you tell an S4 heart sound apart
from a split S1 heart sound?
• Hint: The S4 heart sound is low-pitched.
The 4th heart sound
The 4th heart sound
• So an S4 heart sound will be present when there is a non-
compliant LV.
• This occurs most commonly when there is left ventricular
hypertrophy (LVH) or active myocardial ischemia.
• Remember muscle physiology: ATP is required to release myosin
from actin, so during ischemia when ATP can’t be produced,
myosin and actin remain bound and the LV can’t relax. This
results in an S4 occurs.
• An S4 heart sound is an important physical exam finding that
may indicate diastolic heart failure in many people!
The 4th heart sound
The 4th heart sound
• In people with severe systemic hypertension, the long-term
strain on the LV results in LVH. So people with uncontrolled HTN
frequently have an S4 present.
• Once the HTN is well controlled, the LVH can regress over time
causing the S4 sound to disappear.
• So in the setting of HTN, an S4 usually indicates poor control of
blood pressure over a long period of time.
• An S4 heart sound is an important physical exam finding that
may indicate diastolic heart failure in many people!
The 4th heart sound
S4
present
Normal heart LVH – diastolic CHF
Comparing the “gallop” heart sounds
S3 – “ventricular gallop” S4 – “atrial gallop”
• Occurs in early diastole • Occurs in late diastole
• Occurs during passive LV filling • Occurs during active LV filling
• May be normal at times • Almost always abnormal
• Requires a very compliant LV • Requires a non-compliant LV
• Can be a sign of systolic CHF • Can be a sign of diastolic CHF
Extra-systolic heart sounds
Extra-systolic heart sounds
• Includes systolic ejection sounds from the aortic and pulmonic
valves.
• The click of mitral valve prolapse occurs in mid-late systole and
will vary in position based on the volume of the LV.
• With larger LV volumes (squatting), there is less prolapse of the
mitral valve, thus the click moves later in systole.
• With smaller LV volumes (standing or Valsalva), there is more
prolapse of the mitral valve, thus the click moves earlier in
systole.
