The left circumflex artery (LCx) is smaller than the left anterior descending artery (LAD). It takes a course in the left portion of the coronary sulcus, looping around the left margin of the heart and reaching the inferior surface and posterior surface.

The initial part of the artery is covered by the left auricle. Usually, the circumflex artery terminates by anastomosing with the right coronary artery (RCA) within the coronary sulcus near the cardiac crux.

In most people, the LCx does not reach the crux of the heart and posterior interventricular sulcus. However, in a left dominant circulation, it reaches the cardiac crux and gives rise to the posterior descending artery (PDA).

Overall, the left circumflex artery supplies the left anterolateral and posterolateral aspects of the heart. Along its course, it gives off several branches.

Branches

The left atrial branches of the LCx can be subdivided into three groups based on their origin site and position:

The sinoatrial nodal branch arises in around 40 - 50% of cases from the atrial branch of the left circumflex artery instead of the right coronary artery (RCA). It originates from the proximal aspect of the LCx and supplies the left atrium and the sinoatrial (SA) node.

The left ventricular branches of the LCx are called the obtuse marginal arteries. When crossing the left border, the LCx gives off one or several obtuse marginal (left marginal) arteries, which pass along the mentioned margin towards the apex and supply the lateral wall of the left ventricle.

Besides these relatively large branches, the circumflex artery may also give rise to smaller posterior left ventricular (posterolateral) arteries. They supply the diaphragmatic surface of the left ventricle. Usually, the LCx gives rise to these arteries if the left dominant circulation is present. However, they can also arise from the LCx in the right dominant circulation.

Besides the sinoatrial (SA) node, the left circumflex artery can also provide supply to the atrioventricular (AV) node. However, it happens rarely and if the left dominant circulation is present. Therefore, the atrioventricular nodal branch originates from the left circumflex artery in about 20% of cases.

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Left circumflex artery (LCx)