Coronary arteries labeled in red text and other landmarks in blue text
Coronary arteries supply blood to the myocardium and other components of the heart. Two coronary arteries originate from the left side of the heart at the beginning (root)
left ventricle. There are three
aortic sinuses (dilations) in the wall of the aorta just superior to the aortic semilunar valve. Two of these, the
left posterior aortic sinus and
anterior aortic sinus, give rise to the
left and
right coronary arteries, respectively. The third sinus, the
right posterior aortic sinus, typically does not give rise to a vessel. Coronary vessel branches that remain on the surface of the heart and follow the sulci of the heart are called
epicardial coronary arteries. The left coronary artery distributes blood to the left side of the heart, the left atrium and ventricle, and the interventricular septum. The
circumflex artery arises from the left coronary artery and follows the
coronary sulcus to the left. Eventually, it will fuse with the small branches of the right coronary artery. The larger
left anterior descending artery (LAD), is the second major branch arising from the left coronary artery. It follows the anterior interventricular sulcus around the pulmonary trunk. Along the way it gives rise to numerous smaller branches that interconnect with the branches of the
posterior interventricular artery, forming
anastomoses. An anastomosis is an area where vessels unite to form interconnections that normally allow blood to circulate to a region even if there may be partial blockage in another branch. The anastomoses in the heart are very small. Therefore, this ability is somewhat restricted in the heart so a
coronary artery blockage often results in
myocardial infarction causing
death of the cells supplied by the particular vessel.
Anastomoses There are some anastomoses between branches of the two coronary arteries. However the coronary arteries are functionally end arteries and so these meetings are referred to as potential
anastomoses, which lack function, as opposed to true anastomoses like that in the palm of the hand. This is because blockage of one coronary artery generally results in death of the heart tissue due to lack of sufficient blood supply from the other branch. When two arteries or their branches join, the area of the myocardium receives dual blood supply. These junctions are called anastomoses. If one coronary artery is obstructed by an
atheroma, the second artery is still able to supply oxygenated blood to the myocardium. However, this can only occur if the atheroma progresses slowly, giving the anastomoses a chance to proliferate. Under the most common configuration of coronary arteries, there are three areas of anastomoses. Small branches of the LAD (left anterior descending/anterior interventricular) branch of the left coronary join with branches of the posterior interventricular branch of the right coronary in the interventricular sulcus (groove). More superiorly, there is an anastomosis between the circumflex artery (a branch of the left coronary artery) and the right coronary artery in the atrioventricular groove. There is also an anastomosis between the septal branches of the two coronary arteries in the interventricular septum. The photograph shows area of heart supplied by the right and the left coronary arteries.
Variation The left and right coronary arteries occasionally arise by a common trunk, or their number may be increased to three; the additional branch being the posterior coronary artery (which is smaller in size). In rare cases, a person will have the third coronary artery run around the root of the aorta. Occasionally, a coronary artery will exist as a double structure (i.e. there are two arteries, parallel to each other, where ordinarily there would be one).
Coronary artery dominance The artery that supplies the posterior third of the
interventricular septum – the
posterior descending artery (PDA) determines the coronary dominance. • If the posterior descending artery is supplied by the
right coronary artery (RCA), then the coronary circulation can be classified as "right-dominant." • If the posterior descending artery is supplied by the
circumflex artery (CX), a branch of the left artery, then the coronary circulation can be classified as "left-dominant." • If the posterior descending artery is supplied by both the right coronary artery and the circumflex artery, then the coronary circulation can be classified as "co-dominant." Approximately 70% of the general population are right-dominant, 20% are co-dominant, and 10% are left-dominant. A precise anatomic definition of dominance would be the artery which gives off supply to the AV node i.e. the AV nodal artery. Most of the time this is the right coronary artery. ==Function==