A 6-month-old infant presents with failure to thrive, recurrent lower respiratory tract infections, and a harsh pansystolic murmur at the left sternal border. Echocardiography confirms a large perimembranous VSD with Qp:Qs ratio of 3:1. Which hemodynamic change is MOST responsible for the recurrent respiratory symptoms?

• A Right-to-left shunting causing systemic hypoxemia and increased respiratory drive
• B Decreased cardiac output causing compensatory tachypnea
• C Increased pulmonary blood flow leading to pulmonary congestion and edema ✓
• D Left ventricular outflow obstruction causing pulmonary venous hypertension

Explanation

In a large VSD, left-to-right shunting (not right-to-left) increases pulmonary blood flow (Qp:Qs = 3:1 means 3x normal pulmonary flow). This causes pulmonary vascular congestion, pulmonary edema, and respiratory symptoms mimicking pneumonia. Systemic hypoxemia does not occur in acyanotic CHD with L-to-R shunt. Cardiac output may be relatively preserved early. Left ventricular outflow obstruction is not a feature of VSD per se.

Reference: Ghai Essential Pediatrics, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.