A wide splitting of S2 during expiration in a 2-week-old infant may indicate which condition?

A wide splitting of S2 during expiration in a 2-week-old infant may indicate which condition?

• A. Coarctation of the aorta
• B. Atrial septal defect
• C. Patent ductus arteriosus
• D. Ventricular septal defect

Answer: (B)

Wide splitting of S2 that persists during expiration points to delayed pulmonic valve closure from increased right-heart flow, which is classic for an atrial septal defect. In ASD, blood shunts from left to right at the atrial level, boosting right atrial and right ventricular volumes and pulmonary flow. This extra flow slows the closure of the pulmonic valve (P2), widening the S2 split. Because the delay is due to a fixed amount of right-heart preload and flow, the split remains wide and is not diminished by expiration, unlike normal splitting that narrows with expiration. Other lesions don’t produce this pattern: coarctation of the aorta doesn’t typically cause a fixed wide S2 split; a patent ductus arteriosus causes a continuous murmur and other signs but not the characteristic fixed wide S2 split; a ventricular septal defect changes flow across the ventricles rather than the atrial return in a way that doesn’t produce the same persistent wide splitting pattern.

Wide splitting of S2 that persists during expiration points to delayed pulmonic valve closure from increased right-heart flow, which is classic for an atrial septal defect. In ASD, blood shunts from left to right at the atrial level, boosting right atrial and right ventricular volumes and pulmonary flow. This extra flow slows the closure of the pulmonic valve (P2), widening the S2 split. Because the delay is due to a fixed amount of right-heart preload and flow, the split remains wide and is not diminished by expiration, unlike normal splitting that narrows with expiration.

Other lesions don’t produce this pattern: coarctation of the aorta doesn’t typically cause a fixed wide S2 split; a patent ductus arteriosus causes a continuous murmur and other signs but not the characteristic fixed wide S2 split; a ventricular septal defect changes flow across the ventricles rather than the atrial return in a way that doesn’t produce the same persistent wide splitting pattern.