A 3-year-old boy from Delhi presents with recurrent respiratory tract infections and failure to thrive. His mother reports he tires easily during play and has a persistent cough. On examination, there is a continuous 'machinery' murmur best heard at the left infraclavicular region. Chest X-ray shows cardiomegaly with pulmonary congestion. Echocardiography confirms a left-to-right shunt with increased pulmonary blood flow. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Patent Ductus Arteriosus (PDA) ### Key Clinical Features **Key Point:** The continuous 'machinery' (or 'Gibson') murmur is pathognomonic for PDA. This murmur is heard throughout systole and diastole because the pressure gradient between the aorta and pulmonary artery persists across the entire cardiac cycle. ### Pathophysiology In PDA, the ductus arteriosus (a normal fetal vessel connecting the descending aorta to the left pulmonary artery) fails to close after birth. This creates a persistent left-to-right shunt, leading to: 1. Increased pulmonary blood flow (Qp:Qs > 1.5:1) 2. Left atrial and ventricular volume overload 3. Pulmonary edema and recurrent infections 4. Failure to thrive due to increased metabolic demand ### Characteristic Findings in PDA | Feature | Finding | |---------|----------| | **Murmur** | Continuous 'machinery' murmur (systolic + diastolic) | | **Location** | Left infraclavicular or left subclavian area | | **Pulse pressure** | Widened (bounding pulses, wide pulse pressure) | | **CXR** | Cardiomegaly, pulmonary congestion, ductus bump | | **Echo** | Left-to-right shunt, dilated LA and LV | | **Associated risk** | Prematurity, maternal rubella infection, high altitude birth | ### Why This Is High-Yield **High-Yield:** PDA is one of the most commonly tested acyanotic lesions in NEET PG. The continuous murmur is the single most discriminating clinical sign. **Clinical Pearl:** In premature infants, PDA may present with signs of heart failure (tachypnea, hepatomegaly) without an audible murmur if pulmonary vascular resistance is still elevated. The classic murmur emerges as PVR falls. ### Management Approach ```mermaid flowchart TD A[PDA diagnosed]:::outcome --> B{Symptomatic?}:::decision B -->|No, small shunt| C[Observe, restrict fluids/sodium]:::action B -->|Yes, large shunt| D[Medical vs Surgical closure]:::action D --> E[Indomethacin or Ibuprofen]:::action E --> F{Closure achieved?}:::decision F -->|Yes| G[Discharge]:::outcome F -->|No, or contraindicated| H[Surgical/catheter-based closure]:::action H --> I[Successful closure]:::outcome ``` **Key Point:** NSAIDs (indomethacin, ibuprofen) inhibit prostaglandin synthesis and promote ductal closure in ~70% of premature infants. Surgical or transcatheter closure is reserved for NSAID failure or contraindications.