Paradoxical S2 is most commonly associated with which conduction abnormality?

Paradoxical S2 is most commonly associated with which conduction abnormality?

• A. Left bundle branch block
• B. Right bundle branch block
• C. Atrial septal defect
• D. Pulmonary stenosis

Answer: (A)

Paradoxical S2 happens when the timing of the two components of the second heart sound is reversed because the left ventricle’s contraction is slowed. Normally the aortic valve closes before the pulmonic valve (A2 before P2). When left ventricular conduction is delayed, as in left bundle branch block, LV systole is prolonged and the aortic valve closes later than usual. The pulmonic valve closes earlier in the sequence, so P2 occurs before A2. This reversal creates a paradoxical split, most classically seen with left bundle branch block. Right bundle branch block delays the pulmonic component (P2) more than the aortic component, so it tends to produce a wide split that is not paradoxical. Atrial septal defect causes fixed wide splitting due to increased flow across the pulmonary valve, not a reversal of the S2 sequence. Pulmonary stenosis delays P2 as well, which changes the split pattern but again does not produce the paradoxical reversal seen with LV conduction delay.

Paradoxical S2 happens when the timing of the two components of the second heart sound is reversed because the left ventricle’s contraction is slowed. Normally the aortic valve closes before the pulmonic valve (A2 before P2). When left ventricular conduction is delayed, as in left bundle branch block, LV systole is prolonged and the aortic valve closes later than usual. The pulmonic valve closes earlier in the sequence, so P2 occurs before A2. This reversal creates a paradoxical split, most classically seen with left bundle branch block.

Right bundle branch block delays the pulmonic component (P2) more than the aortic component, so it tends to produce a wide split that is not paradoxical. Atrial septal defect causes fixed wide splitting due to increased flow across the pulmonary valve, not a reversal of the S2 sequence. Pulmonary stenosis delays P2 as well, which changes the split pattern but again does not produce the paradoxical reversal seen with LV conduction delay.