Why is s2 split in asd

The sound produced by the closure of the aortic valve is termed A2 and the sound produced by the closure of the pulmonic valve is termed P2. When these sounds are distinguishable from each other a split S2 can be heard. The patterns of splitting of the S2 heart sound include physiologic splitting, paradoxical splitting, widened splitting and fixed splitting. A fixed split S2 is not common on cardiac exam. The closing pressure the diastolic arterial pressure on the left is 80 mmHg as compared to only 10 mmHg on the right.

This higher closing pressure leads to earlier closure of the aortic valve. In addition, the more muscular and stiff "less compliant" left ventricle LV empties earlier than the right ventricle.

The venous return to the right ventricle RV increases during inspiration due to negative intrathoracic pressure and P2 is even more delayed, so it is normal for the split of the second heart sound to widen during inspiration and to narrow during expiration. 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.

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.

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