A 70-year-old man with anterior STEMI 3 days ago develops sudden severe chest pain, new systolic murmur, and cardiogenic shock. Echo shows free-wall rupture versus ventricular septal defect. Which bedside finding would MOST reliably differentiate ventricular septal rupture from acute mitral regurgitation?
- A Pansystolic murmur louder at the left sternal edge with an oxygen step-up in the right ventricle on pulmonary artery catheterization ✓
- B Pulsatile jugular venous distension
- C Third heart sound at the apex
- D ST elevation in V1-V4
Correct answer: A. Pansystolic murmur louder at the left sternal edge with an oxygen step-up in the right ventricle on pulmonary artery catheterization
Explanation
Ventricular septal rupture causes a left-to-right shunt, producing a step-up in oxygen saturation from the right atrium to right ventricle on pulmonary artery catheterization (>5-7% increase indicates significant left-to-right shunt). The murmur of VSR is typically harsh, pansystolic, loudest at the lower left sternal border. In acute mitral regurgitation (papillary muscle rupture), there is NO oxygen step-up in the right heart. The distinction is critical because management differs: VSR requires urgent surgical repair or catheter-based closure.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.