Which anatomical feature explains why rupture of the posteromedial papillary muscle occurs far more frequently than rupture of the anterolateral papillary muscle after acute myocardial infarction?
- A It has a single blood supply, usually from the posterior descending artery ✓
- B It is subjected to higher systolic wall stress because it supports two leaflets
- C It is thinner and histologically less collagenous than the anterolateral muscle
- D It lies in a region of greater endocardial shear force during ejection
Correct answer: A. It has a single blood supply, usually from the posterior descending artery
Explanation
The anterolateral papillary muscle has a dual blood supply from branches of both the left anterior descending (diagonal) and the circumflex arteries, whereas the posteromedial papillary muscle depends almost entirely on the posterior descending artery alone. A single occluded vessel therefore devascularizes the entire posteromedial muscle, which is why papillary muscle rupture complicates inferior or posterior infarcts disproportionately. Wall stress, thickness and shear forces do not differ enough between the two muscles to explain the clinical disparity.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.