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Third diagonal branch (D3) of LAD

The third diagonal branch (D3) is one of the oblique branches arising from the left anterior descending artery (LAD). Diagonal branches typically course laterally and superiorly across the surface of the left ventricle, supplying the anterolateral free wall.

The D3 specifically arises more distally from the LAD compared to the first (D1) and second (D2) diagonal branches. Its origin is variable: in some individuals it is small or absent, while in others it can be well developed and significant. When present, it courses over the anterolateral wall of the left ventricle, often anastomosing with branches of the obtuse marginal arteries from the left circumflex artery (LCx).

While smaller than proximal diagonal branches, the D3 can still play an important role in collateral circulation, particularly in coronary artery disease, and is relevant in percutaneous coronary intervention (PCI) or bypass grafting (CABG).

Synonyms

  • D3 coronary artery

  • Third diagonal branch of LAD

  • Lateral branch of LAD (distal)

Function

  • Supplies oxygenated blood to the anterolateral wall of the left ventricle (distal portions)

  • Contributes to collateral circulation with obtuse marginal branches of the LCx

  • Plays a role in maintaining perfusion during LAD or LCx obstruction

  • May be a target in stenting or bypass grafting, especially when large

Branches

  • Typically no named subdivisions; may give off small muscular branches to the LV wall

  • Anastomoses variably with LCx marginal branches

MRI Appearance

T1-weighted images:

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

  • Vessel wall hypointense; delineated by epicardial fat

T2-weighted images:

  • Flow void persists

  • Perivascular edema or myocardial pathology in D3 territory shows hyperintensity

STIR (Short Tau Inversion Recovery):

  • Fat suppression improves visualization of surrounding myocardial edema or ischemia

  • Vessel itself remains a void; infarcted myocardium in D3 territory appears bright hyperintense

T1 Post-Contrast (Gadolinium-enhanced):

  • D3 lumen enhances brightly

  • Late gadolinium enhancement (LGE) of myocardium identifies infarction or fibrosis in its supply territory

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

  • Demonstrates D3 as a small but bright distal LAD branch

  • Best appreciated in high-resolution, ECG-gated, respiratory-navigated 3D datasets

  • Useful for detecting anomalous course, stenosis, or occlusion in patients not suitable for contrast

CT Appearance

Non-contrast CT (Calcium Scoring):

  • D3 is usually too small to evaluate directly; calcified plaques in proximal LAD may be noted

  • Calcium burden may predict involvement of distal branches including D3

CT Coronary Angiography (CCTA):

  • Best non-invasive modality to visualize D3

  • Clearly depicts origin, course over the anterolateral LV wall, and any stenosis or occlusion

  • Identifies atherosclerotic plaques, anomalous branching, or collateral connections

  • Multiplanar and 3D reconstructions allow detailed mapping for PCI and CABG planning

CT images

Third diagonal branch (D3) of LAD anantomy CT axial image -img-00000-00000

MRI image

Third diagonal branch (D3) of LAD mri axial image