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First diagonal branch (D1) of LAD

The first diagonal branch (D1) is the largest and most proximal diagonal branch of the left anterior descending artery (LAD). It arises from the anterolateral aspect of the proximal or mid-LAD, typically within the anterior interventricular sulcus, and courses obliquely across the anterior wall of the left ventricle toward the lateral wall.

The D1 branch primarily supplies the anterolateral wall of the left ventricle, often perfusing myocardial segments corresponding to segments 6 and 7 (mid-anterolateral and apical lateral walls) in the AHA 17-segment model. Its size and dominance vary considerably — in some individuals, D1 is large and supplies a broad myocardial territory, while in others, it is small or absent, with supply shared by subsequent diagonal branches or obtuse marginal branches.

Clinically, disease of D1 is important because significant stenosis can cause anterolateral wall ischemia and contribute to angina or myocardial infarction. Its anatomical course makes it a common target for percutaneous coronary intervention (PCI) and an important consideration in coronary artery bypass grafting (CABG), where it may be grafted using the left internal mammary artery or a saphenous vein graft.

Synonyms

  • D1 artery

  • First diagonal branch of LAD

  • Ramus diagonalis primus

Function

  • Supplies the anterolateral wall of the left ventricle

  • Contributes to perfusion of apical and mid-lateral myocardial segments

  • Plays a role in maintaining LV systolic function and wall motion

  • Provides collateral flow with obtuse marginal branches of the left circumflex artery

Branches

  • Usually a single trunk, may bifurcate into smaller diagonal twigs

  • Anastomoses with obtuse marginal branches from the LCx and other diagonal branches of LAD

MRI Appearance

T1-weighted images (non-contrast):

  • D1 lumen appears as a signal void (black) due to flowing blood

  • Epicardial fat helps distinguish its oblique course across the LV wall

T2-weighted images:

  • Flow void persists

  • Myocardial edema from ischemia in D1 territory appears hyperintense in the anterolateral LV wall

STIR (Short Tau Inversion Recovery):

  • Suppresses fat, highlighting myocardial edema in the D1 perfusion zone

  • Useful in acute coronary syndrome evaluation

T1 Post-Contrast (Gadolinium-enhanced):

  • Vessel lumen enhances brightly

  • Myocardial late gadolinium enhancement (LGE) highlights infarcts or fibrosis in the anterolateral wall supplied by D1

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

  • D1 visualized as a bright, oblique branch from LAD in 3D whole-heart acquisition

  • Useful for identifying origin, course, and caliber without contrast

  • Helps evaluate congenital anomalies or proximal stenosis

CT Appearance

Non-contrast CT (Calcium Scoring):

  • D1 not well delineated unless calcified plaques are present at its origin

CT Coronary Angiography (CCTA):

  • Excellent for mapping origin, course, caliber, and dominance of D1

  • Detects atherosclerotic plaques, stenosis, occlusion, or anomalous branching

  • Multiplanar reformats and 3D reconstructions provide clear visualization for PCI and CABG planning

  • Particularly useful in defining bifurcation lesions at LAD-D1 junction

MRI image

First diagonal branch (D1) of LAD mri axial image

CT image

First diagonal branch (D1) of LAD anantomy CT axial image -img-00000-00000