Coronary Vessel Involvement in Posterior Medial Papillary Muscle Infarction with Mitral Regurgitation
The right coronary artery (RCA) or left circumflex artery (LCx) is the culprit vessel in posteromedial papillary muscle involvement with mitral regurgitation. 1, 2, 3
Blood Supply Anatomy
The posteromedial papillary muscle has a singular blood supply, making it significantly more vulnerable to ischemic injury than the anterolateral papillary muscle, which receives dual blood supply. 2, 4 This anatomic difference explains why posteromedial papillary muscle rupture is far more common than anterolateral rupture. 1, 5, 3
Specific Vascular Distribution
- Right coronary artery (RCA) supplies the posteromedial papillary muscle in most patients 1, 2, 3
- Left circumflex artery (LCx) supplies this muscle in a significant minority of cases 1, 3
- 80% of patients with severe ischemic mitral regurgitation have >70% stenosis of both RCA and LCx, with or without LAD involvement 3
- The posteromedial papillary muscle receives single-vessel perfusion in 63% of patients, compared to only 29% for the anterolateral papillary muscle 4
Clinical Context and Infarct Pattern
Inferior wall myocardial infarction is the typical presentation when posteromedial papillary muscle is involved. 2, 3 In the study by Nishimura et al., 86% of patients with severe ischemic mitral regurgitation had inferior wall asynergy. 3
Important Caveat
While RCA or LCx are the typical culprits, rare anatomic variants exist. One case report documented posteromedial papillary muscle rupture from an isolated LAD lesion, attributed to an apex-forming LAD coupled with an apically located posteromedial papillary muscle. 5 However, this represents an exceptional anatomic variant rather than the standard pattern.
Diagnostic Implications
When you encounter posteromedial papillary muscle dysfunction or rupture with mitral regurgitation:
- Expect RCA or LCx disease as the primary culprit 1, 2, 3
- Look for inferior wall motion abnormalities on echocardiography 3
- Coronary angiography will typically reveal significant stenosis in the RCA, LCx, or both 3
- The presence of single-vessel supply to the posteromedial papillary muscle increases risk of dysfunction after infarction compared to dual supply 4
Critical Management Point
Regardless of which vessel is involved, urgent surgical consultation is mandatory when papillary muscle rupture is suspected, as this mechanical complication carries near-certain mortality without operation despite 20% surgical mortality. 1, 2 Concomitant CABG to the culprit vessel must accompany mitral valve replacement. 2