L14 Heart Sounds

Heart Sounds

• Four heart sounds can be recorded via phonocardiography, but normally only two, the first and the second heart sounds, are audible through a stethoscope.
• Heart sounds are produced by:
  • Vibrations caused by the sudden closure of valves
  • Myocardial contraction
  • Vibration caused by rushing of blood into the chambers of the heart

Volume Pressure Loop

• Definition: Relation between left ventricular volume and left ventricular pressure
• Phases:
  • Isometric contraction phase
  • Ejection phase
  • Isometric relaxation phase
  • Filling phase

First Heart Sound (S1)

• Cause: Sudden closure of AV valves (Mitral and tricuspid valve)
• Occurs: At the beginning of ventricular systole (Isovolumetric contraction phase)
• Characters:
  • Low pitched (25 – 45 Hz)
  • Longer duration (0.14 Sec)
  • Gives the sound of "Lub"
• Site: Auscultated in:
  • Mitral area: Apex of heart (5th intercostal space mid clavicular line)
  • Tricuspid area: Between 4th and 5th space close to lower left quadrant of sternum

Second Heart Sound (S2)

• Cause: Closure of Semilunar valves (Aortic and pulmonary valves)
• Occurs: At the end of ventricular systole (Isovolumetric relaxation phase)
• Characters:
  • High pitched (50 Hz)
  • Shorter duration (0.11 sec)
  • Gives the sound of "Dub"
• Site: Auscultated in:
  • Aortic area: Rt 2nd intercostal space
  • Pulmonary area: Lt 2nd intercostal space

Third Heart Sound (S3)

• Causes: Rushing of blood from atria into ventricle during rapid filling phase
• Also known as: Gallop
• Physiological causes:
  • Normally heard in most children
  • Athletes
  • Pregnant female
• Pathological causes:
  • Congestive heart failure
  • Aortic regurge
  • Dilated cardiomyopathy

Fourth Heart Sound (S4)

• Cause: Atrial contraction (atrial systole) → vibration of ventricular wall
• Occurs: During atrial systole
• Timing: Before S1