Coronary Arteries: Anatomy, Branches, and Clinical Ischemia

Overview

The coronary arteries are the first branches of the aorta, arising from the aortic sinuses just above the aortic valve. They supply the myocardium with oxygenated blood during diastole. Understanding coronary anatomy is fundamental for ECG interpretation, infarct localization, and interventional cardiology.

Left Coronary Artery (LCA)

Also called the left main, it arises from the left aortic sinus and runs between the pulmonary trunk and the left auricle for a short distance (typically 1-2 cm) before bifurcating.

Left Anterior Descending (LAD)

The LAD travels in the anterior interventricular groove toward the apex. It supplies:

Anterior wall of the left ventricle
Anterior 2/3 of the interventricular septum
Anterolateral papillary muscle
Bundle of His and proximal bundle branches

Branches: Diagonal branches (lateral LV wall) and septal perforators (septal supply).

Left Circumflex (LCx)

Wraps around the left side in the coronary (atrioventricular) groove. In left-dominant circulation, it also gives off the posterior descending artery (PDA). Supplies the lateral and posterolateral LV wall.

Right Coronary Artery (RCA)

Arises from the right aortic sinus, runs in the right AV groove, and supplies:

Right atrium and right ventricle
Sinoatrial (SA) node in 60% of people (right-dominant)
Atrioventricular (AV) node in 80-90% of people
Inferior wall of LV (via PDA in right-dominant)
Posterior 1/3 of the interventricular septum

Dominance

Defined by which artery gives rise to the PDA.

Right-dominant (~70%): RCA → PDA. Most common.
Left-dominant (~10%): LCx → PDA.
Co-dominant (~20%): RCA and LCx both contribute.

Clinical Correlation: ECG Localization

Anterior MI: LAD occlusion → ST elevation V1-V4
Lateral MI: LCx occlusion → ST elevation I, aVL, V5-V6
Inferior MI: RCA occlusion (right-dominant) → ST elevation II, III, aVF
Posterior MI: Often RCA; reciprocal changes V1-V3 (ST depression with tall R waves)

Coronary Dominance & Surgical Significance

Coronary artery bypass grafts (CABG) and percutaneous interventions are planned based on dominance. Right-dominant patients with proximal RCA occlusion are at higher risk for AV node ischemia and bradyarrhythmias.

Key Takeaway

The LAD is often called the "widow-maker" because proximal occlusion causes massive anterior wall infarction. Always identify coronary dominance before reading an ECG — it changes which artery is the culprit.