Circumflex artery

Course

The left coronary artery typically divides into two major branches: the left anterior descending artery and the circumflex artery. The smaller branch, circumflex artery, continues the course of the left coronary running between the left atrium and left ventricle, along the coronary sulcus. The coronary sulcus is also referred to as the atrioventricular sulcus or groove.

The proximal segment of the artery is usually covered by the left atrial appendage. When the circumflex artery reaches the left cardiac margin, it wraps around the left side of the heart, emerging on its diaphragmatic surface. In most people, the circumflex artery terminates before reaching the crux of the heart. This is the point on the diaphragmatic surface where the interatrial and interventricular septa converge. In the left-dominant coronary circulation, the circumflex artery reaches the crux of the heart and gives rise to the inferior interventricular artery.

The "dominance" of either side of the coronary circulation is determined by which artery provides the inferior interventricular artery to supply the diaphragmatic surface. For example, dominance of the left side indicates that the left coronary artery supplies the diaphragmatic surface of the heart. This occurs in about 15% of the population. Research describes a "codominance" in about 18% of people. This means that the branches of both coronary arteries reach the crux of the heart and give rise to posterior branches that course in or near the posterior interventricular groove.

Branches and supply

The circumflex artery typically supplies the anterolateral and posterolateral aspects of the left ventricle. It's important to keep in mind that all coronary vessels often vary in their origin, course, distribution and number, so the supply territory should always be determined individually.

• The atrial and anterior ventricular branches arise at the proximal segment of the circumflex artery and supply the sternocostal (anterior) surface of the left atrium and ventricle.
• The left marginal branch originates perpendicularly from the left coronary, around the left cardiac margin. It descends down the rounded left cardiac margin towards the apex of the heart. When the marginal branch is larger in diameter, it supplies the lateral aspect of the left ventricle, all the way to the apex.
• The posterior left ventricular branch arises from the posterior segment to supply the diaphragmatic surface of the left ventricle. Typically, this branch is smaller than its anterior counterparts, since the diaphragmatic aspect of the left ventricle is usually supplied by the right coronary artery.
• The sinuatrial nodal branch originates from the circumflex artery in 40% of cases. This branch arises at the proximal anterior segment of the artery, supplying the left atrium and the SA node.
• The atrioventricular nodal branch arises from the circumflex artery in about 20% of the cases. It typically arises on the diaphragmatic aspect of the left-dominant heart to supply the AV node.

Learn more about the coronary vessels with our articles, videos, labeled diagrams and quizzes.

Anatomical variations

Out of all coronary arteries, the circumflex artery manifests the greatest variability in terms of length and distribution. In most cases, the circumflex artery terminates between the left margin and the crux of the heart. However, in about 20-30% of cases, it terminates before reaching the left margin. As previously mentioned, in left-dominant circulation, it reaches the crux of the heart or even goes beyond it.

In terms of the origin of the circumflex artery, it can arise separately from the left aortic sinus or from the anterior descending artery.