Five days after an anterior STEMI, a 58-year-old man develops sudden severe dyspnoea. Examination reveals a new pansystolic murmur loudest at the lower left sternal border with a thrill. BP is 88/60 mmHg. Which complication has occurred and what is the distinguishing feature from papillary muscle rupture?
- A Papillary muscle rupture — step-up in oxygen saturation in the right ventricle
- B Ventricular septal defect — step-up in oxygen saturation from right atrium to pulmonary artery on Swan-Ganz catheterization ✓
- C Free wall rupture with cardiac tamponade — elevated JVP and muffled heart sounds
- D Acute pericarditis — friction rub and pleuritic chest pain
Correct answer: B. Ventricular septal defect — step-up in oxygen saturation from right atrium to pulmonary artery on Swan-Ganz catheterization
Explanation
Post-infarction ventricular septal defect (VSD) causes acute left-to-right shunting and presents with a harsh pansystolic murmur at the lower left sternal border. The definitive haemodynamic finding on right heart catheterisation is an oxygen saturation step-up between right atrium and pulmonary artery (indicating left-to-right shunt through the VSD). Papillary muscle rupture causes severe mitral regurgitation; murmur radiates to the axilla and no oxygen step-up occurs in the right heart (no shunt). Free wall rupture presents with tamponade and no murmur.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.