The Coronary Arteries

 

Coronary arteries and arterial territories

The two main coronary arteries emanate from the aortic bulb (Figure 1):

• The right coronary artery (RCA) originates on the right aspect of the aortic bulb.
• The left main coronary artery (LMCA) originates from the left anterior aspect of the aortic bulb. The LMCA is short and branches into the two arteries supplying the anterior and left side of the heart, as follows:
  • The left anterior descending coronary artery (LAD).
  • The left circumflex coronary artery (LCX).

Figure 1 shows the coronary arteries and their relation to the ECG leads. Note that Figure 1 is a right-dominant system (i.e PDA is supplied from RCA).

Figure 1. The coronary arteries and their relation to the ECG leads. Localization of myocardial infarction / ischemia is done by using ECG changes to determine the affected area and subsequently the occluded coronary artery (culprit).

Figure 2 shows the coronary arterial territories in relation to the 17 segments of the left ventricle.

Figure 2. Assignment of the 17 myocardial segments to the territories of the left anterior descending (LAD), right coronary artery (RCA), and the left circumflex coronary artery (LCX).

Coronary artery dominance: left dominance vs. right dominance

The coronary artery that supplies the PDA (posterior descending coronary artery), which supplies the inferior wall of the left ventricle, determines the coronary artery dominance (Figure 1). A right-dominant system implies that the PDA is supplied by the right coronary artery (RCA). A left-dominant system implies that the PDA is supplied by the left circumflex coronary artery (LCX). The right-dominant system is by far the most common anatomy, occurring in 90% of all individuals.

Right coronary artery (RCA)

• The right coronary artery supplies the entire right ventricle via the right marginal artery (r. marginalis dx).
• In 90% of individuals, the right coronary artery gives off the posterior descending artery (PDA) which supplies the inferior wall of the left ventricle. When the RCA gives off PDA, the anatomy is referred to as a right-dominant system (if the LCX gives off PDA, it is referred to as a left-dominant system).
• In patients with right-dominance the RCA supplies the atrioventricular (AV) node.
• In 60% of individuals, the right coronary artery gives off branches to the sinoatrial (SA) node.
• The posterior third of the interventricular septum is supplied by the right coronary artery.
• Arteries to the posterior wall (these arteries branch of after the right marginal artery) may be given off by the RCA (and otherwise the LCx).

Left anterior descending coronary artery (LAD)

• The LAD supplies the anterior two-thirds of the interventricular septum (this area is referred to as anteroseptal area).
• The LAD supplies the large anteriosuperior wall (often referred to as the anterior wall) and the apical part of the lateral wall.
• The LAD may stretch all the way to the inferior wall and supply its most apical area (this area is referred to as the inferoapical area). Occasionally the LAD is very long and supplies a significant portion of the inferior wall; this type of LAD is called wrap-around LAD (because it wraps around the apex).

Left circumflex coronary artery (LCX)

• In 90% of individuals, the coronary circulation is right-dominant, meaning that the PDA is given off by the RCA. In these individuals, the LCx only supplies the basal and mid parts of the posterolateral wall. As discussed previously, this part of the left ventricle is difficult to capture with the conventional leads in the 12-lead ECG.
• In 10% of individuals, the coronary circulation is left-dominant, meaning that the PDA is given off by the LCx. Thus the LCx supplies the inferior wall in 10% of all individuals.
• The LCx supplies the AV-node in 10% of all individuals.