S1 Heart Sound

Aka: S1 Heart Sound, First Heart Sound

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II. Physiology

  1. S1 Heart Sound represents closure of the mitral and tricuspid valves

III. Causes: S1 Augmented or Loud

  1. Normal in children
  2. Increased Cardiac Output: Hyperkinetic or Sinus Tachycardia
    1. Severe Anemia
    2. Fever
    3. Hyperthyroidism
    4. Exercise
    5. Pregnancy
    6. Paget's Disease
    7. Chronic Thiamine deficiency (Beriberi)
  3. Intrinsic Heart Disorders
    1. Mitral Stenosis
    2. Tricuspid Stenosis
    3. Short PR Interval (e.g. WPW Syndrome, nodal rhythm)

IV. Causes: S1 Diminished, Soft or Muffled

  1. First degree AV Block
  2. Mitral Regurgitation (or valve calcification)
  3. Tricuspid Regurgitation (or valve calcification)
  4. Congestive Heart Failure (Right or Left Ventricular Dysfunction)
  5. Acute Coronary Syndrome (acute Myocardial Infarction)
  6. Shock
  7. Overall Muffled heart sounds (thick chest wall, Obesity, COPD, Pericardial Effusion)

V. Causes: Split S1

  1. General
    1. M1 (mitral) is normally louder, and occurs slightly before T1 (tricuspid)
    2. Split S1 is best heard at the tricuspid auscultation point (4th left sternal border)
  2. Widely Split S1
    1. Complete Right Bundle Branch Block
    2. Left ventricular pacing
    3. Ebstein's Anomaly
  3. Reversed Split S1 (delayed M1 falls after T1)
    1. Complete Left Bundle Branch Block
    2. Right ventricular pacing
    3. Severe Mitral Stenosis
    4. Left atrial Myxoma

VI. Causes: S1 Variable

  1. Atrial Fibrillation
  2. Ventricular Tachycardia
  3. Frequent Extrasystole
  4. Third degree AV Block
    1. Intermittent Loud S1 (Cannon sound)

VII. Resources

  1. University of Michigan Heart Sound and Murmur Library
    1. http://www.med.umich.edu/lrc/psb/heartsounds/
  2. Felner in Walker (1990) The Fourth Heart Sound, Clinical Methods, 3rd ed
    1. https://www.ncbi.nlm.nih.gov/books/NBK333/

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