Coronary angiography: the standard projections

1. How the C-arm angles are named

A projection is named after where the image intensifier (the detector above the patient) has moved: LAO towards the patient’s left, RAO towards the right; cranial when it is tilted towards the head, caudal towards the feet. The heart lies obliquely in the chest, so no single view shows a coronary artery without foreshortening or overlap: every segment is filmed in at least two roughly perpendicular views.

Surgeon’s corner: Turn the heart yourself: the panel shows live from which projection you are looking. Switch on the angio look to see the arteries dark on grey, as on the monitor. A rule of thumb: caudal views open the left main and the circumflex, cranial views the LAD.

2. RAO caudal: the circumflex

From the right and below, the left main and the proximal LAD and circumflex open up; the circumflex and its obtuse marginal branches run downwards, free of the LAD. It is often the first view of the left system.

Surgeon’s corner: The obtuse marginals are best judged here. The mid and distal LAD are foreshortened and overlapped by diagonals in this view: never grade a mid or distal LAD lesion from it alone.

3. RAO cranial: the LAD from the side

Tilted towards the head, the mid and distal LAD are seen along their length: the diagonal branches are pulled upwards, away from the LAD, and the septal branches hang down from it into the septum.

Surgeon’s corner: The view for the mid LAD and for the origin of the septals — the LAD-septal bifurcation and the length of a lesion before stenting.

4. LAO cranial: LAD and diagonals

From the left and above, the LAD runs down the middle of the image and the diagonals branch off it to one side, the septals to the other: the best view of the LAD–diagonal bifurcations and of the ostia of the diagonals.

Surgeon’s corner: A more cranial tilt opens the bifurcations further but makes the image darker (the beam crosses the liver and diaphragm): breath held in deep inspiration helps.

5. LAO caudal: the spider view

From the left and below, the heart is seen from under the diaphragm: the left main is seen short, heading down towards the bifurcation, and the LAD and circumflex spread out from it like the legs of a spider. The view for the left main and the LAD–circumflex bifurcation.

Surgeon’s corner: Left main and bifurcation stenting are planned in this view and in the RAO caudal. The image is often grainy (much tissue in the beam) — the price of the unique angle.

6. AP cranial and AP caudal

Without rotation: AP cranial shows the mid LAD and the LAD–diagonal bifurcation; AP caudal shows the body of the left main, the proximal circumflex and the obtuse marginals. Tap the chips to compare them.

Surgeon’s corner: Most operators complete the left system with five or six views; the exact angles are adapted to each heart until every segment has been seen free of overlap and foreshortening.

7. Right coronary artery in LAO: the "C"

In LAO about 40° the right coronary artery runs round the right atrioventricular groove as a letter C: the ostium at the top, the proximal and mid segments along the curve, the crux at the bottom where it turns into the posterior descending artery, which is foreshortened in this view.

Surgeon’s corner: The ostium of the right coronary artery is best judged here. Watch the pressure at the catheter tip on engagement: damping or ventricularisation suggests ostial stenosis, spasm or a tip against the wall or in the conus branch. Do not inject forcefully — withdraw and reposition first: injecting against a damped pressure risks dissection and ventricular fibrillation.

8. Right coronary artery in RAO: the "L"

In RAO about 30° the same artery forms an L: the mid segment runs down the front, and the posterior descending artery runs along the bottom towards the apex, seen over its whole length.

Surgeon’s corner: The mid right coronary artery and the posterior descending artery are best measured here; the proximal segment is foreshortened.

9. The crux: AP cranial

Tilted towards the head, the crux opens: the division of the right coronary artery into the posterior descending artery and the posterolateral branches, which overlap in the plain views. This applies to the usual right-dominant circulation; in left dominance the right coronary artery is small and ends before the crux.

Surgeon’s corner: In a right-dominant system an occlusion at the crux causes an inferior STEMI, often with posterior extension. AV block can occur because the AV node artery arises from the dominant artery at the crux; it is usually nodal and transient.