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S2 Heart Sound

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S2 Heart Sound, Second Heart Sound

  • See Also
  1. Heart Auscultation
  2. S1 Heart Sound
  3. S3 Heart Sound
  4. S4 Heart Sound
  5. Heart Murmur
  6. Pediatric Murmur
  • Physiology
  1. S2 Heart Sound represents closure of the aortic valve and pulmonic valve
  2. The aortic valve typically closes slightly before the pulmonic valve
    1. Higher pressures in the systemic circulation force the aortic valve closed sooner
  3. During expiration, the S2 Heart Sound is typically heard as one sound (not split)
  4. During inspiration, the S2 Heart Sound is physiologically split
    1. Represents a more significant timing difference between the closure of aortic (A2) and pulmonic valves (P2)
    2. Greater right sided than left sided filling with inspiration results in a greater duration between A2 and P2
      1. Inspiration creates negative intrathoracic pressure
      2. Negative chest pressure increases right ventricular filling and volume (Preload)
      3. Negative chest pressure decreases left sided filling from lungs
  • Causes
  • S2 Wide Split
  1. Right Bundle Branch Block
    1. Slower right ventricular contraction delays pulmonic valve closure
  2. Pulmonic Stenosis
    1. Prolonged right ventricular emptying due to obstructed flow, results in delayed pulmonic valve closure
  3. Mitral Regurgitation
  • Causes
  • S2 Fixed Split
  1. Atrial Septal Defect
  2. Right Heart Failure
  3. Pulmonary Hypertension
    1. P2 is also louder due to forced closure of the pulmonic valve
  • Causes
  • S2 Paradoxical Split (S2 splits during expiration)
  1. Left Bundle Branch Block
    1. Slower left ventricular contraction delays aortic valve closure
    2. Pulmonic valve (P2) closes before aortic valve (A2), most prominent during expiration
    3. During inspiration, P2 is delayed, and therefore coincides with A2, resulting in paradoxical split
  2. Aortic Stenosis
    1. Prolonged left ventricular emptying due to obstructed flow, results in delayed aortic valve closure
  • Causes
  • Loud S2
  1. Pulmonic Stenosis
    1. P2 is louder due to forced closure of the pulmonic valve
  2. Arterial Hypertension
    1. A2 is louder due to forced closure of the aortic valve
  • Resources
  1. University of Michigan Heart Sound and Murmur Library
    1. http://www.med.umich.edu/lrc/psb/heartsounds/
  • References
  1. Goldberg (2014) Clinical Physiology, MedMaster, p. 48-9