A 6-year-old boy from Delhi is brought to the pediatric clinic for evaluation of a cardiac murmur detected during a routine school health checkup. Echocardiography confirms a secundum atrial septal defect (ASD). Which of the following is NOT a characteristic feature of secundum ASD?

## Secundum ASD: Characteristic Features **Key Point:** Secundum ASD is an acyanotic lesion with left-to-right shunting. Cyanosis is NOT a feature of uncomplicated ASD unless Eisenmenger syndrome develops (late, after years of shunting). ### Pathophysiology of Secundum ASD Secundum ASD accounts for ~70% of all ASDs and involves deficiency in the region of the fossa ovalis. | Feature | Presence | Explanation | |---------|----------|-------------| | Left-to-right shunt | ✓ Yes | Low-pressure atrial defect; RA→LA flow due to RV compliance | | Fixed S₂ splitting | ✓ Yes | Increased RV stroke volume → prolonged RV ejection; atrial communication equalizes RA and LA pressures | | Pulmonary plethora | ✓ Yes | Increased pulmonary blood flow (Qp:Qs > 1.5:1) | | Cyanosis in infancy | ✗ No | Acyanotic lesion; shunt is left-to-right, not right-to-left | | RV dilation | ✓ Yes | Chronic volume overload | ### Clinical Presentation 1. **Asymptomatic** — often detected incidentally on routine examination 2. **Murmur** — mid-systolic ejection murmur at left upper sternal border (increased pulmonary flow) 3. **Symptoms** (if present) — dyspnea, fatigue, recurrent respiratory infections (older children) 4. **NO cyanosis** — unless Eisenmenger syndrome develops (rare before adolescence) **High-Yield:** Cyanosis appearing in an ASD patient indicates **Eisenmenger syndrome** — irreversible pulmonary hypertension with shunt reversal. This is a late complication, not an early feature. ### Why Other Options Are Correct - **Left-to-right shunt:** Fundamental to ASD pathophysiology; blood flows from RA to LA because RV is more compliant than LV - **Fixed S₂ splitting:** Pathognomonic finding — splitting does not vary with respiration because the ASD equalizes atrial pressures - **Pulmonary plethora:** Increased pulmonary blood flow is visible on CXR as increased vascular markings and cardiomegaly **Clinical Pearl:** A child with a murmur + fixed S₂ split + no cyanosis = think ASD until proven otherwise. [cite:Park 26e Ch 13]