A 55-year-old woman presents 10 days after an anterior MI with a new holosystolic murmur at the apex, loud S3, worsening dyspnea, and pulmonary congestion on X-ray. Echocardiography shows posterior mitral leaflet flap with severe MR. The most likely mechanism of this acute MR is:
- A Ischemic papillary muscle dysfunction without rupture
- B Anterior papillary muscle rupture (anterolateral papillary muscle)
- C Posterior papillary muscle rupture (posteromedial papillary muscle) ✓
- D Mitral annular dilatation due to LV remodeling
Explanation
Posteromedial papillary muscle rupture is the most common cause of acute post-MI MR leading to hemodynamic compromise. It occurs typically 2–7 days post-MI and is more common after inferior MI (RCA territory) because the posteromedial papillary muscle has a single-vessel blood supply (from RCA or LCX), while the anterolateral papillary muscle has dual supply (LAD and LCX). The posterolateral leaflet is supported by the posteromedial papillary muscle; its rupture causes a flail leaflet with severe MR. Surgical repair/replacement is definitive; medical stabilization with vasodilators (nitroprusside) and IABP bridge to surgery.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.