A 70-year-old woman 3 days after anterior STEMI develops a new pansystolic murmur loudest at the lower left sternal border with a systolic thrill. Echocardiography shows a defect in the interventricular septum. Which of the following best describes the pathophysiology of this complication?

• A Papillary muscle infarction causing acute mitral regurgitation
• B Acute pericarditis causing fibrinous exudate over the anterior wall
• C Ventricular septal rupture from coagulative necrosis of the septal myocardium ✓
• D Left ventricular free wall rupture with subsequent haemopericardium

Explanation

Ventricular septal rupture (VSR) is a mechanical complication of STEMI typically occurring 3–5 days post-infarction, when coagulative necrosis weakens the septal myocardium. Anterior STEMIs cause apical VSR while inferior STEMIs cause basal VSR. It presents with a harsh pansystolic murmur with thrill at the lower left sternal border and a left-to-right shunt on echocardiography. Acute mitral regurgitation from papillary muscle rupture also causes a pansystolic murmur but the murmur is loudest at the apex and radiates to the axilla; free wall rupture presents with tamponade rather than a murmur.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.