A child with Tetralogy of Fallot has a loud ejection systolic murmur at the left upper sternal border. Despite having a large ventricular septal defect, no pansystolic murmur is audible at the lower left sternal border. What is the correct explanation for this auscultatory pattern?
- A The VSD is partially sealed by aneurysmal tissue of the septal leaflet of the tricuspid valve
- B The infundibular obstruction prevents any blood from crossing the VSD during systole
- C Right ventricular outflow tract obstruction, not the VSD, generates the murmur, because the large nonrestrictive VSD allows near-equal ventricular pressures with little turbulent flow across it ✓
- D Left ventricular outflow tract turbulence masks the VSD murmur
Correct answer: C. Right ventricular outflow tract obstruction, not the VSD, generates the murmur, because the large nonrestrictive VSD allows near-equal ventricular pressures with little turbulent flow across it
Explanation
In Tetralogy of Fallot the VSD is large and nonrestrictive, so left and right ventricular systolic pressures are nearly identical and little turbulent shunt flow occurs across the defect. The audible murmur therefore originates from the right ventricular outflow tract and pulmonary valve obstruction. A louder murmur means more flow through the obstructed outflow and a better-oxygenated child, whereas disappearance of the murmur signals a worsening spell.
Reference: Nelson Textbook of Pediatrics, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.