**Core Concept**
Paradoxical splitting of the second heart sound (S2) occurs when the aortic valve closes after the pulmonary valve, resulting in a delay in the aortic component of S2. This phenomenon is typically associated with left bundle branch block (LBBB), where the left ventricle is delayed in its contraction.

**Why the Correct Answer is Right**
In LBBB, the left ventricle's delayed contraction leads to a prolonged left ventricular ejection time. As a result, the aortic valve closes after the pulmonary valve, causing the aortic component of S2 to occur after the pulmonary component, resulting in paradoxical splitting. This is because the left ventricle's delayed contraction allows for increased time for the right ventricle to empty, thereby delaying the closure of the aortic valve.

**Why Each Wrong Option is Incorrect**
**Option A:** RBBB (right bundle branch block) typically results in normal or widened splitting of S2, not paradoxical splitting, as the right ventricle's contraction is not delayed.

**Option B:** ASD (atrial septal defect) is characterized by increased flow through the pulmonary valve, leading to wide splitting of S2, not paradoxical splitting.

**Option C:** VSD (ventricular septal defect) results in increased flow through both the aortic and pulmonary valves, leading to wide splitting of S2, not paradoxical splitting.

**Clinical Pearl / High-Yield Fact**
Remember that paradoxical splitting of S2 is a classic sign of LBBB, and it can be a valuable clinical clue in diagnosing this condition.

**✓ Correct Answer: D. LBBB**