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Acute marginal artery (AM)

The acute marginal artery (AM) is one of the main branches of the right coronary artery (RCA). It typically arises from the mid to distal segment of the RCA and courses along the acute margin (right inferolateral border) of the right ventricle. The AM artery runs within the epicardial fat and supplies blood primarily to the right ventricular free wall.

The number and size of AM branches vary: most individuals have one dominant acute marginal artery, but some may have multiple smaller branches. The vessel is of high clinical importance in right ventricular infarction, since occlusion or disease of the RCA or AM branch can compromise right ventricular contractility and systemic venous return.

Synonyms

  • Right marginal artery

  • Acute marginal branch of RCA

  • AM branch

Function

  • Supplies arterial blood to the right ventricular free wall

  • Contributes to perfusion of the inferolateral right ventricle

  • Supports right ventricular contractility, especially under stress or exercise

  • Plays a role in coronary collateral circulation with branches of the LAD and posterior descending artery (PDA)

Branches

  • Usually a single dominant branch from the RCA

  • May give rise to multiple small epicardial branches to the right ventricular myocardium

  • Connects with collateral branches from the LAD septal perforators and PDA in some individuals

MRI Appearance

T1-weighted images:

  • Lumen appears as a signal void (black) due to flowing blood

  • Vessel wall hypointense; adjacent epicardial fat provides contrast

T2-weighted images:

  • Flow void persists

  • Perivascular edema or infarcted right ventricular myocardium appears hyperintense

STIR (Short Tau Inversion Recovery):

  • Highlights edema or inflammation in the right ventricular myocardium supplied by the AM artery

  • Infarcts or myocarditis in AM territory appear bright hyperintense

T1 Post-Contrast (Gadolinium-enhanced):

  • Lumen enhances brightly

  • Myocardial late gadolinium enhancement (LGE) shows infarcts or scarring in right ventricular free wall supplied by the AM

MRI Non-Contrast Cardiac-Gated 3D Coronary MRA:

  • Depicts AM artery as a bright enhancing tubular structure without contrast

  • Shows origin from the RCA and course along the acute margin

  • Useful for congenital anomaly evaluation or RCA/AM stenosis in patients with renal impairment

CT Appearance

Non-contrast CT (Calcium Scoring):

  • AM artery visualized for coronary calcium scoring

  • Calcified plaques appear as hyperdense foci; scored with Agatston method

CT Coronary Angiography (CCTA):

  • Best non-invasive modality for acute marginal artery visualization

  • Shows origin, course along the acute margin, and right ventricular branches

  • Detects stenosis, occlusion, calcified and non-calcified plaques, aneurysm, or anomalous course

  • Multiplanar reformats and 3D reconstructions help in pre-PCI and surgical planning

  • Critical for assessing right ventricular infarction risk in RCA disease

MRI image

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CT images

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