Review Question - QID 109040

This patient has an atrial septal defect (ASD) and will therefore exhibit fixed splitting of S2 on cardiac auscultation.

This patient has an atrial septal defect (ASD) identified on routine cardiac examination. In the normal individual, the second heart sound (S2) can be heard to split into two distinct beats during inspiration due increased negative intrathoracic pressure leading to increased venous return to the heart. This increased venous return to the right side of the heart causes delayed closure of the pulmonic valve relative to the aortic valve. With an ASD, the left-to-right shunting of blood leads to continually higher volumes on the right side of the heart. This causes the pulmonic valve to consistently be delayed relative to the aortic valve independent of respiratory cycle. The result is a split S2 in both inspiration and expiration, which is also known as fixed splitting.

Incorrect answers:
Answer 1-2: S1 is not split with inspiration or expiration as the mitral and tricuspid valves close at the same time and are unaffected by inspiration.

Answer 3: This patient would not have normal splitting of S2 as the right side of the heart sees increased volumes due to the ASD.

Answer 4: Increased splitting of S2 with inspiration refers to exaggerated normal splitting or wide splitting. This would be caused by conditions that delay RV emptying further than normal inspiration, including pulmonic stenosis or right bundle branch block.

Bullet summary:
This patient has an atrial septal defect (ASD) and will therefore exhibit fixed splitting of S2 on cardiac auscultation due to delayed closure of the pulmonic valve relative to the atrial valve independent of the respiratory cycle.