The S2 heart sound can exhibit persistent widened splitting, fixed splitting, paradoxical reversed splitting or the absence of splitting. The S2 heart sound intensity decreases with worsening aortic stenosis due to immobile leaflets. In severe aortic stenosis, the A2 component may not be audible at all. Normally, A2 occurs just before P2, and the combination of these sounds make up S2. A physiologic split S2 occurs when the A2 sound precedes P2 by a great enough distance to allow both sounds to be heard separately.
This happens during inspiration when increased venous return to the right side of the heart delays the closure of the pulmonic valve major effect , and decreased return to the left side of the heart hastens the closure of the aortic valve minor effect , thereby further separating A2 and P2.
During expiration, the distance narrows, and the split S2 is no longer audible. A paradoxical split S2 heart sound occurs when the splitting is heard during expiration and disappears during inspiration — opposite of the physiologic split S2.
A paradoxical split S2 occurs in any setting that delays the closure of the aortic valve including severe aortic stenosis and hypertrophic obstructive cardiomyopathy, or in the presence of a left bundle branch block.
Persistent widened splitting occurs when both A2 and P2 are audible during the entire respiratory cycle, and the splitting becomes greater with inspiration due to increased venous return and less prominent with expiration.
Both A2 and P2 close when the pressure above the respective valves are greater than the pressure in the ventricles below. Given the lower vascular resistance of the pulmonary artery, during inspiration, the pulmonary artery is able to tolerate more volume of blood before the pressure above the valve increases.
Additionally, during inspiration, more blood fills the right ventricle leading to a slightly longer ejection time, adding to the delayed pulmonic valve closure. This video was created by Dr. Click this link to see his collection of medicine educational videos.
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Rick Hodes. Happy Halloween! Clinically, this is more remarkable with slow heart rates. In that case, the split is usually wide and fixed with no change difference between inspiration and expiration due to fixed RV volume see ASD section. In both conditions, the aortic valve A2 closes after the pulmonary valve P2. Since the respiration only affects P2, its effect in paradoxical splitting is the opposite of normal, i. The third heart sound S3 represents a transition from rapid to slow ventricular filling in early diastole.
S3 may be heard in normal children. The fourth heart sound S4 is an abnormal late diastolic sound caused by forcible atrial contraction in the presence of decreased ventricular compliance.
A figure showing normal and abnormal splitting of the second heart sound. Some Rights Reserved.
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