A 2-month-old infant with Down syndrome is found to have a cardiac murmur on examination. Which of the following is the most common congenital heart defect associated with Down syndrome?

Explanation

## Cardiac Manifestations of Down Syndrome ### Frequency of Congenital Heart Defects in Down Syndrome **Key Point:** Congenital heart disease occurs in **40–50% of children with Down syndrome**, compared to ~0.8% in the general population. This is a critical screening point in all newborns with trisomy 21. ### Most Common Cardiac Lesions | Lesion | Frequency in DS | Frequency in General Population | Pathophysiology | |--------|-----------------|--------------------------------|------------------| | **AVSD** | **40–45%** | <1% | Endocardial cushion defect; ostium primum ASD + inlet VSD ± cleft mitral valve | | VSD | 30–35% | 2–3% | Muscular or perimembranous defect | | ASD | 8–10% | 1–2% | Secundum type most common | | PDA | 5–10% | 0.5–1% | Usually closes spontaneously | | Tetralogy of Fallot | 7–10% | 0.3% | Less common than AVSD | **High-Yield:** **AVSD is pathognomonic for Down syndrome** — it is 200–300 times more common in trisomy 21 than in the general population. When you see AVSD on echocardiography, Down syndrome is the first diagnosis to consider. ### Clinical Presentation 1. **Asymptomatic murmur** — detected on routine newborn screening (most common presentation). 2. **Signs of left-to-right shunt** — bounding pulses, wide pulse pressure, hyperactive precordium. 3. **Heart failure** — if AVSD is large; presents with poor feeding, failure to thrive, respiratory symptoms. 4. **Cyanosis** — rare unless Eisenmenger syndrome develops (years later). ### Diagnostic Approach ```mermaid flowchart TD A[Newborn with Down Syndrome]:::outcome --> B[Clinical cardiac examination]:::action B --> C{Murmur or signs of CHD?}:::decision C -->|Yes or High Suspicion| D[Echocardiography]:::action C -->|No| E[Repeat exam at 6-8 weeks]:::action D --> F{AVSD?}:::decision F -->|Yes| G[Cardiology follow-up<br/>Monitor for heart failure<br/>Surgical planning]:::action F -->|No| H{Other lesion?}:::decision H -->|Yes| I[Manage per defect type]:::action H -->|No| J[Reassurance<br/>Routine follow-up]:::outcome ``` **Clinical Pearl:** All infants with Down syndrome should have **echocardiography in the first 2 months of life**, even if asymptomatic. Early detection allows monitoring for heart failure and timely surgical intervention (typically between 3–6 months of age for AVSD). **Mnemonic:** **"AVSD in DS"** — Atrioventricular Septal Defect is the hallmark cardiac lesion in Down Syndrome.