From which coronary artery does the ramus (acute marginal branch) arise?

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Last updated: May 7, 2026 • View editorial policy

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Ramus Intermedius Origin

The ramus intermedius (also called ramus or ramus intermedius artery) arises from the left main coronary artery as a third branch, in addition to the left anterior descending (LAD) and left circumflex (LCX) arteries 1, 2, 3.

Anatomical Details

The ramus intermedius represents a trifurcation variant of the left main coronary artery, where instead of the typical bifurcation into LAD and LCX, there is a third vessel arising between these two arteries 4, 5. This anatomical variant:

  • Occurs in approximately 15-30% of the population based on angiographic and IVUS studies 5
  • Supplies the lateral wall of the left ventricle, similar to diagonal or obtuse marginal branches
  • Is classified as a "primary vessel" in coronary artery nomenclature when it represents a significant branch 2

Clinical Significance

Diagnostic Considerations

Angiographic identification of the ramus can be challenging, with only 54% of angiographically-identified ramus vessels confirmed by intravascular ultrasound (IVUS) 5. The ramus is frequently confused with:

  • High-origin diagonal branches (19% of cases)
  • High-origin obtuse marginal branches (27% of cases)

IVUS should be considered when precise identification is needed, particularly when planning left main interventions, as misidentification can lead to inappropriate revascularization strategies 5.

Hemodynamic Impact

The presence of a ramus creates turbulent flow patterns at the left main trifurcation that can affect CT-derived fractional flow reserve (FFR-CT) measurements even in the absence of coronary disease 6. Specifically:

  • A large ramus (>2.1 mm diameter) is associated with 7-fold increased odds of distal FFR-CT ≤0.80 in vessels without significant stenosis
  • This may lead to false-positive ischemia assessments on non-invasive testing

Revascularization Implications

When performing left main stenting with one-stent crossover technique, the ramus requires special consideration 5:

  • 14.6% of true ramus vessels develop compromise (>75% ostial stenosis or TIMI flow <3) after crossover stenting
  • This is significantly higher than high-origin obtuse marginal branches (0% compromise rate)
  • Two-stent techniques or provisional side-branch protection may be warranted when the ramus is large or supplies significant myocardial territory

Common Pitfalls

  1. Assuming angiographic identification is definitive - Consider IVUS confirmation for left main lesions involving the ramus
  2. Overlooking ramus disease in multivessel CAD - The ramus can be the sole culprit vessel in acute coronary syndromes 7
  3. Ignoring the protective collateral potential - In cases of multivessel occlusion, a patent ramus may provide critical collateral flow and determine survival 4

References

7
Research

Angioplasty of isolated acute marginal coronary artery disease.

Catheterization and cardiovascular diagnosis, 1996

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The ramus (intermediate) artery is a branch of which coronary artery?
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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.