Rupture of the posteromedial papillary muscle complicating an inferior myocardial infarction occurs far more frequently than rupture of the anterolateral papillary muscle. The anatomical reason is:

• A The anterolateral papillary muscle has a dual coronary blood supply while the posteromedial papillary muscle has a single supply ✓
• B The posteromedial papillary muscle is larger and under greater systolic tension
• C The posteromedial papillary muscle lies in the highest-pressure region of the left ventricle
• D The mitral valve leaflets tethered to the posteromedial papillary muscle are structurally weaker

Explanation

The anterolateral papillary muscle receives blood from both the left anterior descending artery (diagonal branches) and the left circumflex artery (obtuse marginal branches), giving it collateral protection. The posteromedial papillary muscle depends on a single supply, usually the posterior descending artery from the right coronary artery, so an inferior infarct can cause transmural ischaemia of the entire muscle. This explains its vulnerability rather than any difference in size, pressure exposure, or leaflet structure.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.