The First Heart Sound (S1) Chapter 7

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The First Heart Sound (S1)Chapter 7

• Ara G. Tilkian, MD, FACC
• Instructor
• Patricia L. Thomas, MBA, RCIS

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Outline

• 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

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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

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Where to Listen

• Listen with the diaphragm bell of the
  stethoscope at the apex 4th left intercostal
  space

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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 gt 130 b/m
• Palpate the Carotid artery S1 precedes the
  palpable arterial upstroke
• S2 immediately follows this pulse

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Differential Diagnosis

• 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

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Sounds of the Cardiac Cycle in Perspective
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Physiological Splitting of S1
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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

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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)

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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

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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

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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

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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

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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,
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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

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THE ENDOFCHAPTER 7

• Tilkian, Ara MD Understanding Heart Sounds and
  Murmurs,
• Fourth Edition, W.B. Sunders Company. 2002, pp.
  58-71.