11.6 Circumflex Coronary Artery

Circumflex Coronary Artery is a major branch of the left coronary artery that courses around the left atrioventricular groove (also known as the left AV groove or coronary sulcus). It primarily supplies oxygenated blood to the lateral and posterior walls of the left ventricle, the left atrium, and, in some cases, portions of the sinoatrial (SA) and atrioventricular (AV) nodes.

Origin and Course

Origin

The circumflex artery originates from the left coronary artery (LCA) shortly after the LCA arises from the left aortic sinus. It is one of the two primary branches of the LCA, the other being the left anterior descending artery (LAD).

Course

After branching from the LCA, the circumflex artery follows a posterior and lateral course within the left AV groove, which separates the left atrium and left ventricle. The artery travels around the left border of the heart, curving to the posterior surface, where it continues along the coronary sulcus until its termination.

Segments of the Circumflex Artery

Proximal Circumflex Segment

The proximal segment extends from the origin at the left coronary artery to the first major branch, usually located at the anterior portion of the left AV groove. This segment lies close to the left atrial appendage and the pulmonary trunk.

Distal Circumflex Segment

The distal segment runs posteriorly along the left AV groove toward the posterior surface of the heart. It courses near the left atrium and ventricle junction, giving rise to several branches before termination.

Branches of the Circumflex Artery

Left Atrial Branches

These small branches arise early from the circumflex artery and supply the lateral and posterior walls of the left atrium. They contribute to the blood supply of the atrial myocardium and nearby conduction tissue.

Obtuse Marginal Artery

The obtuse marginal artery (also called the left marginal artery) is one of the largest and most consistent branches of the circumflex artery. It courses along the obtuse (left) margin of the heart, providing blood to the lateral wall of the left ventricle. There may be one or more obtuse marginal branches, depending on individual anatomical variation.

Additional Obtuse Marginal Branches

In some hearts, multiple obtuse marginal branches arise from the circumflex artery, supplying progressively more distal portions of the lateral left ventricular wall.

Posterolateral Circumflex Branches

These branches extend from the distal circumflex segment around the posterior surface of the heart. They supply the posterior and lateral walls of the left ventricle and may anastomose with branches of the right coronary artery, contributing to collateral circulation.

Termination

The circumflex artery typically terminates near the posterior interventricular groove, but it does not usually reach the apex. In some anatomical variants, the circumflex artery continues beyond the posterior descending artery or forms part of a "left dominant" coronary circulation pattern, where it supplies the posterior interventricular artery.

Functional and Clinical Significance

The circumflex artery is crucial for perfusing the left atrium and the lateral and posterior walls of the left ventricle. Its branches, especially the obtuse marginal arteries, are important in maintaining adequate myocardial oxygenation.

Obstruction or stenosis in the circumflex artery can lead to ischemia or infarction of the supplied territories, often manifesting as lateral or posterior myocardial infarctions. The artery's course around the left AV groove places it in proximity to the mitral valve annulus, so its injury or occlusion can impact mitral valve function.

Circumflex Artery Branching Map

A simplified branching map of the circumflex artery can be represented as follows:

• Origin: Left coronary artery
• Proximal segment
  • Left atrial branches
• Obtuse marginal arteries (one or more)
• Posterolateral branches
• Termination near posterior interventricular groove (variable)

The circumflex coronary artery is essential to the coronary circulation, supplying regions critical for left ventricular contraction and atrial function, with its branches providing collateral pathways and contributing to the overall myocardial blood supply.