Left Main Coronary Artery Territory
The left main coronary artery (LMCA) supplies approximately 75% of the left ventricular myocardium 1.
Anatomical Distribution
The LMCA arises from the left aortic sinus just below the sinotubular junction and bifurcates (or trifurcates) to supply blood through its major branches 1:
Primary Branching Pattern
Two-thirds of patients: The LMCA bifurcates into:
- Left anterior descending artery (LAD)
- Left circumflex artery (LCx)
One-third of patients: The LMCA trifurcates into:
- Left anterior descending artery (LAD)
- Left circumflex artery (LCx)
- Ramus intermedius
Specific Myocardial Territories Supplied
Left Anterior Descending (LAD) territory 2:
- Anterior wall of the left ventricle
- Anterolateral wall (via diagonal branches)
- Interventricular septum (via septal perforators)
- Apex of the heart
Left Circumflex (LCx) territory 2:
- Lateral wall of the left ventricle (via obtuse marginal branches)
- In left-dominant systems: posterior and inferior walls via the posterior descending artery
Clinical Significance
The massive territory supplied by the LMCA explains why LMCA disease carries the highest mortality among coronary artery disease manifestations 3, 4. In right-dominant coronary systems, the LMCA can supply up to 80% of total blood flow to the left ventricle 3.
Important Hemodynamic Considerations
Recent evidence demonstrates that microvascular resistance differs between LAD and LCx territories, with the LAD having lower microvascular resistance than the LCx 5. This physiological difference means that pressure-derived indices (FFR, iFR) measured in the LAD are systematically lower than those in the LCx, even when the LMCA lesion is identical. This has critical implications for functional assessment of LMCA disease—measuring only in the LCx can result in 21% misclassification rate for FFR and 28% for iFR 5.
Anatomical Dimensions
The LMCA has an average length of 10.8 ± 5.2 mm (range 2-23 mm) and an average diameter of 4.9 ± 0.8 mm 1. The vessel is divided into three segments: ostium, body (midshaft), and distal bifurcation 1.