Inferior interventricular branch of circumflex artery of heart

The inferior interventricular branch of the circumflex artery (Left posterior descending artery (left PDA)) is a vessel that arises from the distal continuation of the left circumflex coronary artery (LCx) in individuals with left-dominant coronary circulation (It corresponds to the right Inferior interventricular artery in right-dominant coronary circulation).

Anatomical Definition

The left posterior descending artery (left PDA) is the vessel that arises from the distal continuation of the left atrioventricular artery (itself the terminal portion of the left circumflex artery as it courses through the posterior atrioventricular groove). It travels within the posterior (inferior) interventricular groove (sulcus) on the diaphragmatic surface of the heart and gives off septal perforator branches that supply the inferior portion of the interventricular septum. In the ACC/AHA coronary artery nomenclature, it is designated as segment 26 (BARI segment 27, SNOMED-CT: 56322004).

Relationship to Coronary Dominance

The presence of this vessel defines left coronary dominance, which occurs in approximately 8-10% of the population. Coronary dominance is determined by which artery gives rise to the posterior descending artery (PDA) and posterolateral artery (PLA):

• Right dominance (~80-87%): The PDA and PLA arise from the right coronary artery (RCA).

• Left dominance (~810%): Both the PDA and PLA arise from the left circumflex artery.

• Co-dominance (~35%): The RCA supplies the PDA while the circumflex supplies the PLA.

Course and Territory

The left circumflex artery originates from the left main coronary artery, courses posteriorly in the left atrioventricular groove between the left atrium and ventricle. In left-dominant hearts, the LCx extends beyond its usual termination point, continuing around the crux of the heart (the intersection of the atrioventricular groove and the posterior interventricular groove), where it gives rise to the inferior interventricular branch (left PDA). This branch then descends toward the cardiac apex along the inferior interventricular sulcus, supplying the inferior wall of the left ventricle and the inferior interventricular septum via septal perforators.

Clinical Significance

• Coronary angiography and intervention: Accurate identification of dominance determines which vessel is responsible for inferior wall perfusion and guides percutaneous coronary intervention or bypass surgery planning.

• Myocardial infarction localization: In left-dominant systems, occlusion of the circumflex artery can produce inferior myocardial infarction a territory typically attributed to the RCA in right-dominant hearts. Severe circumflex disease is significantly more prevalent in patients with electrocardiographic posterior or inferoposterior infarction compared to isolated inferior infarction.

• Surgical planning: CT coronary angiography has identified up to 25 different vascularization patterns of the posterior interventricular sulcus, underscoring the anatomical variability that surgeons and interventionalists must consider.