Overview

The circumflex runs in the left coronary sulcus beneath the left auricle, alongside the great cardiac vein and the coronary sinus. Its obtuse marginal branches (OM1–OM3) descend over the lateral wall of the left ventricle, which forms the obtuse margin of the heart.

In about 40% of hearts it gives off the SA nodal artery. In left-dominant hearts (about 5–10%) it continues to the crux and gives rise to the posterior interventricular artery and the AV nodal artery.

Anatomy

Course: It starts at the bifurcation of the left main stem and runs in the left atrioventricular groove around the left (obtuse) margin onto the diaphragmatic surface, ending short of the crux unless the heart is left-dominant.
Branches: Obtuse marginal branches, left atrial branches, the SA nodal artery (≈40%), posterolateral branches and, in left dominance, the posterior interventricular and AV nodal arteries.

Function

Supplies the lateral and posterolateral left ventricular wall and the left atrium.
Shares the supply of the anterolateral papillary muscle.
In left-dominant hearts, supplies the inferior wall, the posterior septum and the AV node.

Clinical significance

Lateral and posterior MI

Circumflex occlusion causes ST elevation in I, aVL, V5 and V6. It is often "electrically silent" on the standard 12-lead ECG. A posterior infarct shows only as ST depression with tall R waves in V1–V3, and posterior leads V7–V9 confirm it.

Proximity to the mitral annulus and coronary sinus

The circumflex runs close to the mitral annulus and the coronary sinus. It can therefore be injured during mitral valve surgery and during procedures performed through the coronary sinus.

Related structures

Artery · CardiovascularLeft coronary artery Organ part · CardiovascularLeft atrium Organ part · CardiovascularLeft ventricle Vein · CardiovascularCoronary sinus Artery · CardiovascularPosterior interventricular artery Vein · CardiovascularGreat cardiac vein