Circumflex branch

The circumflex branch (Cx; circumflex artery in humans) is the continuation of the left coronary artery after the origin of the paraconal interventricular branch (In dogs, the Cx may arise directly from aorta, separately from Pc) . It arises at the level of the coronary groove and courses within this groove on the left (auricular) aspect of the heart, passing caudally toward the atrial surface.

As it follows the coronary groove, the circumflex branch curves around the left border of the heart and reaches the atrial (caudal) surface. Depending on the species, it may terminate near the subsinuosal interventricular groove or continue as the subsinuosal interventricular branch in species with left coronary dominance*.

Along its course, the circumflex branch gives off several collateral branches. These include atrial branches supplying the left atrium, and ventricular branches supplying the left ventricular free wall (with the main termed as intermediate branch [Left ventricular marginal artery]). It may also give rise to branches that vascularize part of the right ventricle near the caudal aspect of the heart. In some species, it provides the sinoatrial nodal branch.

*The coronary dominance of a heart refers to the coronary artery (LCA or RCA) that perfuses the majority of the myocardial tissue and variable methods to determine this have been reported including which coronary artery supplies the subsinuosal interventricular branch, which coronary artery extends beyond the crux of the heart, the relative lengths and number of branches of the LCA or RCA, and the origination and layout of the arteries at the apex of the heart. The dog normally displays a left dominant coronary circulation , the cat is less studied but appears variable with a majority of cases indicating right coronary dominance, the rabbit is variable with predominately left coronary dominance, and the goat, swine, horse and donkey, cow, camelids, and 90% of humans are right dominant. In the mouse and rabbit, the subsinuosal interventricular branch is reported to be absent [1].