Tutorial | Part 1: Definitions

APPENDIX I: Segment definitions

1 RCA proximal  From ostium to one half the distance to the acute margin of the heart.
2 RCA mid  From end of first segment to acute margin of heart.
3 RCA distal From the acute margin of the heart to the origin of the posterior descending artery.
4 Posterior descending Running in the posterior interventricular groove.
16 Posterolateral from RCA Posterolateral branch originating from the distal coronary artery distal to the crux.
16a Posterolateral from RCA  First posterolateral branch from segment 16.
16b Posterolateral from RCA  Second posterolateral branch from segment 16.
16c Posterolateral from RCA  Third posterolateral branch from segment 16.
5 Left main  From the ostium of the LCA through bifurcation into left anterior descending and left circumflex branches.
6 LAD proximal  Proximal to and including first major septal branch.
7 LAD mid  LAD immediately distal to origin of first septal branch and extending to the point where LAD forms an angle (RAO view). If this angle is not identifiable this segment ends at one half the distance from the first septal to the apex of the heart.
8 LAD apical Terminal portion of LAD, beginning at the end of previous segment and extending to or beyond the apex.
9 First diagonal  The first diagonal originating from segment 6 or 7.
9a First diagonal a Additional first diagonal originating from segment 6 or 7, before segment 8.
10 Second diagonal  Second diagonal originating from segment 8 or the transition between segment 7 and 8.
10a Second diagonal a  Additional second diagonal originating from segment 8.
11 Proximal circumflex  Main stem of circumflex from its origin of left main to and including origin of first obtuse marginal branch.
12 Intermediate/anterolateral  Branch from trifurcating left main other than proximal LAD or LCX. Belongs to the circumflex territory.
12a Obtuse marginal a  First side branch of circumflex running in general to the area of obtuse margin of the heart.
12b Obtuse marginal b  Second additional branch of circumflex running in the same direction as 12.
13 Distal circumflex  The stem of the circumflex distal to the origin of the most distal obtuse marginal branch and running along the posterior left atrioventricular grooves. Caliber may be small or artery absent.
14  Left posterolateral  Running to the posterolateral surface of the left ventricle. May be absent or a division of obtuse marginal branch.
14a Left posterolateral a  Distal from 14 and running in the same direction.
14b Left posterolateral b   Distal from 14 and 14 a and running in the same direction.
15 Posterior descending Most distal part of dominant left circumflex when present. Gives origin to septal branches. When this artery is present, segment 4 is usually absent.