A 68-year-old male is admitted with acute anterior wall STEMI. On day 3 post-infarction, he suddenly develops severe dyspnea, hypotension, and a new harsh holosystolic murmur heard best at the lower left sternal border accompanied by a palpable systolic thrill. Right-heart catheterization confirms an oxygen saturation 'step-up' from the right atrium to the right ventricle. What complication has occurred?

Answer and explanation

Correct answer: A. Ventricular septal rupture (VSR)

  1. Step 1: Ventricular septal rupture (VSR) is a mechanical complication typically occurring 3 to 5 days following transmural infarction.
  2. Step 2: The creation of a left-to-right shunt across the necrotic ventricular septum produces a harsh holosystolic murmur with thrill at the left sternal border and an oxygen saturation step-up between the right atrium and right ventricle.
Answer
Ventricular septal rupture (VSR).
Why not the others: 'Free wall rupture with cardiac tamponade' produces Beck's triad (hypotension, JVD, muffled heart sounds) and electrical alternans, without an oxygen step-up; 'Acute papillary muscle rupture' produces an apical holosystolic murmur radiating to the axilla with tall v-waves in the pulmonary capillary wedge tracing without an RV oxygen step-up; 'Dressler syndrome' occurs weeks later and presents with pleuritic chest pain and friction rub.

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