Cardiovascular physiology: S2 heart sound
S2 is caused by the closure of the aortic valve (A2) closely followed by that of the pulmonary valve (P2)
Causes of a loud S2
Causes of a soft S2
Causes of fixed split S2
Causes of a widely split S2
Causes of a reversed (paradoxical) split S2 (P2 occurs before A2)
The diagram below demonstrates the cardiac cycle in relation to the heart sounds.
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Causes of a loud S2
- hypertension: systemic (loud A2) or pulmonary (loud P2)
- hyperdynamic states
- atrial septal defect without pulmonary hypertension
Causes of a soft S2
- aortic stenosis
Causes of fixed split S2
- atrial septal defect
Causes of a widely split S2
- deep inspiration
- RBBB
- pulmonary stenosis
- severe mitral regurgitation
Causes of a reversed (paradoxical) split S2 (P2 occurs before A2)
- LBBB
- severe aortic stenosis
- right ventricular pacing
- WPW type B (causes early P2)
- patent ductus arteriosus
The diagram below demonstrates the cardiac cycle in relation to the heart sounds.
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