Pathophysiology: Heart Sounds & Murmurs

Splitting of the Second Heart Sound

Normal

• During expiration, A2 and P2 are separated by less than 30 msec and are heard as a single sound
• During inspiration, P2 is delayed and A2 is slightly earlier due to changes in systemic and pulmonary venous return causing prolonged right and shortened left ventricular ejection
• In younger people, maximal splitting during inspiration is 40 to 50 msec and decreases with age. In people 40 years and older, a single S2 during inspiration and expiration may be normal.

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Causes of audible expiratory splitting

1. Wide physiological splitting primarily due to delayed P2
2. Reverse splitting primarily due to delayed A2
3. Narrow physiological splitting

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Wide physiological splitting of the 2nd Heart Sound

• Delayed pulmonic closure
  • RBBB (right bundle Branch block (delayed electrical activation of right ventricle)
  • Pulmonary stenosis (prolonged right ventricular mechanical systole)
  • Atrial septal defect (decreased impedance in pulmonary vascular bed)
• Early aortic closure
  • Ventricular septal defect (shortened left ventricular mechanical systole)
  • Mitral insufficiency (shortened left ventricular mechanical systole)

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Reverse splitting of the Second Heart Sound

• Delayed aortic closure
  • LBBB (left bundle Branch block (delayed electrical activation of left ventricle or prolonged left ventricular mechanical systole)
  • Hypertensive cardiovascular disease (prolonged left ventricular mechanical systole)
  • Atherosclerotic heart disease (prolonged left ventricular mechanical systole)
• Early pulmonic closure
  • Wolff-Parkinson White (early activation of right ventricle)

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Narrow physiological splitting

• Increased intensity and high frequency of P2
  • Severe pulmonary hypertension {can have normal interval (<30 msec) but both components are audible throughout respiratory cycle.

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