Anotomy of the heart

The right and left coronary arteries most often arise independently from individual ostia in association with the right and left aortic valve cusps.

The left anterior descending (LAD) and left circumflex (LCX) coronary arteries arise at the left main coronary artery bifurcation; they supply the anterior LV, the bulk of the interventricular septum (anterior two thirds), the apex, and the lateral and posterior LV walls. The right coronary artery (RCA) generally supplies the right ventricle (RV), the posterior third of the interventricular septum, the inferior wall (diaphragmatic surface) of the left ventricle (LV), and a portion of the posterior wall of the LV (by means of the posterior descending branch).

When the posterior descending coronary artery (PDA), which supplies the posterior interventricular septum, arises from the LCX artery, the circulation is called left dominant. Most often, the PDA arises from the RCA; this anatomy is called right-dominant circulation.

In two thirds of patients, the first branch of the RCA is the conus artery, which supplies the conus arteriosus (RV outflow tract); occasionally the conus arteriosus arises from a separate orifice.

In 60% of patients, the sinus node artery arises from the proximal RCA, and in 40% of patients, it arises from the LCX artery. The anterior branches supply the free wall of the RV, and the acute marginal branches supply the RV. When the RCA extends to the crux (the origin of the PDA), it supplies the atrioventricular (AV) node (90%); otherwise, the AV node is supplied by the LCX.

Therefore, obstruction of the RCA commonly affects the sinus node and the AV node, resulting in bradycardia, with or without heart block. Not surprisingly, RCA occlusion frequently manifests with sinus bradycardia, AV block, RV myocardial infarction, and/or inferoposterior myocardial infarction (of the LV). (See Eti