Anatomy - RCx

The Ramus Circumflexus (RCx), also known as the left circumflex or LCx, is a branch of the left coronary artery. The RCx runs along the left atrioventricular sulcus, a groove in between the left atrium and the left ventricle. As the RCx courses in this groove, it gives rise to several branches to supply the lateral aspect of the left ventricle. These branches are called Obtuse Marginal (OM) branches or Obtuse Marginal arteries. The point of origin of the first obtuse marginal branch (OM1) is used as a reference point to divide the RCx into 2 segments. The segment of the RCx prior to the origin of OM1 is designated as the proximal RCx while the segment distal to this point of origin is called the distal RCx.

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As the RCx courses to the posterior region of the heart, the distal RCx gives rise to one or more branches called posterolateral branches (PL branches). In 85% of cases, the RCx terminates after giving off the PL branches.

In 7% of cases, the RCx continues to the posterior interventricular sulcus (PIVS) and terminates as the Ramus Descendens Posterior (RDP), also known as the Posterior Descending Artery (PDA). The RDP supplies the inferior and posterior aspects of the heart. As the RDP courses through the posterior interventricular sulcus, it gives off several septal perforators to supply blood to the inferoposterior segment of the interventricular septum.

In 8% of cases, the coronary circulation is co-dominant. In this type of coronary circulation, the RCA gives off a right RDP (or right PDA) while the RCx supplies all posterolateral branches to the left ventricle. In some of these cases the RCx may also give rise to a left RDP (or left PDA) which courses in the posterior interventricular sulcus parallel to the right RDP.

In the 85% of cases where the RCx terminates after giving off the PL branches, the RDP branches off from the distal RCA, which also gives off the right posterolateral artery (RPLA). The right posterolateral artery then gives rise to one or more posterolateral branches to the left ventricle. This coronary artery system is described as a right-dominant coronary artery system.

Left Dominant vs. Right Dominant vs. Co-dominant Coronary Circulation

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left-dominant

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co-dominant

In describing the dominance of the coronary circulation the coronary arteries supplying the RDP are used as reference.

  • Right Dominant - In 85% of cases, the RDP is a branch of the right coronary artery and the RCA gives one or more posterolateral branches to the left ventricle. This type of coronary system is described as a right-dominant system.
  • Left Dominant – In 7% of cases, the RDP is a branch of the RCx and the RCx gives off all posterolateral branches to the left ventricle. This type of coronary system is described as a left-dominant system.
  • Co-dominant - In 8% of cases, the coronary circulation is co-dominant. In this type of coronary circulation, the RCA gives off a right RDP (or right PDA) while the RCx supplies all posterolateral branches to the left ventricle. In some of these cases the RCx may also give rise to a left RDP (or left PDA) which courses in the posterior interventricular sulcus parallel to the right RDP.
 

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