Left coronary artery

Origin and course

The left coronary artery emerges from the left side of the base of the ascending aorta. Its opening lies on the dilated wall of the ascending aorta, just superior to the left semilunar cusp of the aortic valve. The space between the dilated wall at the origin of the ascending aorta and the left semilunar aortic cusp forms the aortic sinus.

From its origin, the left coronary artery travels between the left aspect of the pulmonary trunk and the left auricle within the subepicardial fat tissue. It typically does not give branches in this area but can rarely have the sinuatrial nodal artery. The left coronary artery continues into the superior aspect of the anterior interventricular groove where it bifurcates into its two terminal branches; the left anterior descending artery (anterior interventricular artery) and the circumflex artery.

Branches and supply

The left coronary artery has two branches;

• The left anterior descending artery travels obliquely down the anterior interventricular groove to reach the apex of the heart. It usually loops around the inferior border of the heart into the inferior (posterior) interventricular groove and forms anastomoses with the inferior (posterior) interventricular (descending) branch of the right coronary artery. By means of its septal branches, the left anterior descending artery supplies both ventricles of the heart. Along its course, the left anterior descending artery usually gives rise to a diagonal branch, that runs across the anterior surface of the left ventricle.
• The circumflex branch which is the smaller branch of the left coronary artery courses along the left part of the atrioventricular groove (coronary sulcus) (coronary sulcus), looping around the left heart border onto the inferior surface of the heart. It usually terminates within the coronary sulcus prior to reaching the inferior interventricular groove. The circumflex artery typically gives rise to a large branch, the left marginal artery, which runs along the border of the left heart to supply the left ventricle. Additionally, there are smaller anterior and inferior branches that arise from the circumflex artery to supply the left ventricle.

The structures that are usually supplied by the left coronary artery include: the left atrium, left ventricle, part of the right ventricle, anterior two thirds of the interventricular septum including the atrioventricular bundle and its branches, and the sinuatrial node in about 40% of individuals.

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Anatomical variations

The anatomical variations of the cardiac arteries are common. Variations of the LCA may include length differences, variations in origination and course, branches, the angle of bifurcation or in some cases, a complete absence of the LCA, in which case its branches arise directly from the ascending aorta. Some of the common variations noted in the literature include:

• Differences in length from a few millimeters up to 25 mm
• Trifurcation, resulting in an intermediate branch
• Origination from the posterior aortic sinus, higher on the ascending aorta or from the brachiocephalic trunk