What is the normal coronary artery anatomy, and what is the frequency and significance of anatomic variants?
The left main coronary artery originates from the left sinus of Valsalva and then typically bifurcates into the circumflex and left anterior descending (LAD) branches, or trifurcates with an additional intermediate ramus branch in about one third of cases. The LAD coronary artery usually descends in the anterior interventricular groove. Diagonal branches arise from the LAD coronary artery and descend toward the lateral margin of the left ventricular wall. The circumflex branch enters the left atrioventricular groove to supply obtuse marginal branches to the lateral and posterolateral walls of the left ventricle.
The right coronary artery (RCA) originates from the right coronary sinus of Valsalva at a slightly lower level than the origin of the left main coronary artery. The RCA descends in the anterior right atrioventricular groove. It usually gives off the conus branch as its first branch and then two or three large right ventricular wall branches. The acute marginal branch is the first large branch, which occasionally continues to the apex.
In 70% of patients, the RCA is dominant, passing down the atrioventricular groove to the crux of the heart, where it gives off the posterior descending artery and posterior left ventricular branches. Approximately 20% of patients have a co-dominant supply, in which the posterior descending artery originates from the RCA, but branches from the circumflex artery also supply this territory. In left coronary dominant patients (10%), the circumflex branch travels all the way around the ventricle, supplying both the posterior descending coronary artery and the posterior left ventricular branches.