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The First Heart Sound (S1)
Chapter 7
Ara G. Tilkian, MD, FACC
Instructor
Patricia L. Thomas, MBA, RCIS
Outline
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Components of S1
How to recognize S1 at Rapid Heart Rate
Physiological Splitting of S1
Differential Diagnosis
S1 as a Single Sound
Factors Influencing the Intensity of S1
Components of S1
• Marks the mitral (M1)and tricuspid (T1)
closure
• Loudest heart sound
• High frequency components
• Vibrations set up in the valve cusps,
chordae, papillary muscles and ventricular
walls before aortic ejection
Where to Listen
• Listen with the diaphragm & bell of the
stethoscope at the apex & 4th left intercostal
space
How to Recognize S1 at Rapid Heart Rates
• During Auscultation
• Slow Heart Rates
– Defines the onset of systole which is of shorter
duration than diastole
• Rapid Heart Rates > 130 b/m
– Palpate the Carotid artery: S1 precedes the
palpable arterial upstroke
– S2 immediately follows this pulse
Differential Diagnosis
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Sounds of the Cardiac Cycle In Perspective
Pathological Splitting of S1
The S4-S1 Combination
S1 Followed by an Ejection Sound
The Presystolic Murmur-S1 Combination
Sounds of the Cardiac Cycle in Perspective
Physiological Splitting of S1
Factors Influencing the Intensity of S1
• Any condition that increases the force of
ventricular contraction
• Shortens, the PR interval
• Brings the heart closer to the chest wall makes S1
louder (loud in children and young adults)
• When heart rate is normal, a loud S1 should alert
the examiner of a possible short PR interval.
• Ventricular Contractility
• Pathological alteration of the cardiovascular
system
Ventricular Contractility
• Influence by the contractility of the Left
Ventricle than by the Right Ventricle
– Enhanced Contractility
• S1 is accentuated (anemia, fever, pregnancy, exercise,
anxiety)
– Poor Contractility
• Decrease in the rate of pressure rise in the left ventricle, the
first sound softens. (MI, cardiomypathies, shock)
The PR Interval
• Reflects AV conduction time
• The time between atrial and ventricular
contraction
• The shorter the PR interval, the louder the first
heart sound (mitral valve leaflets are wide open
and deep within the ventricle when contraction
begins causing the leaflets to close forcefully.
• The longer the PR interval, the softer the first
sound
• The PR interval directly influences the position of
valve leaflets at the onset of ventricular systole
Mitral Stenosis
• Mobile mitral cusp, one of the first and
most consistent diagnostic clues is a
typically loud and slapping heart sound.
• The loud S1 of mitral stenosis is caused by
the closure of the mitral valve occurring on
the steep upslope of the LV pressure curve
during isometric contraction.
• Short PR interval
Aortic Insufficiency
• S1 is diminished or absent in patients
• Mitral valve may be prematurely closed
when systole begins because of a long PR
interval or high Lvedp
• Pressures within the aorta a ventricle
approach each other during diastole,
isovolumic systole is either short or absent,
causing a softening of S1
Mitral Regurgitation
• S1 absent or weak
• Valve leaflets may fail to seal the AV
opening during ventricular systole because
of structural defects or widening of the
valve ring.
• Dissipation of LV pressure and the LA
• Decrease in the rate of rise of LV pressure
weakens the intensity of S1
The heart has been sectioned to reveal the mitral valve as seen from
above in the left atrium. The mitral valve demonstrates the typical
"fish mouth" shape with chronic,
Left Atrial Myxoma
• S1 is loud in patients with mobile myxoma
of the LA because of a delay in mitral valve
closure
• Echocardiography can provide a definitive
diagnosis
• Mechanism is similar to a short PR interval
when the mitral leaflets are widely opened
immediately before the onset of ventricular
systole
THE END
OF
CHAPTER 7
Tilkian, Ara MD Understanding Heart Sounds and Murmurs,
Fourth Edition, W.B. Sunders Company. 2002, pp. 58-71.