🎓 Prepared by students from Boğaziçi University

What is Coronary Circulation?

Coronary circulation is the network of arteries and veins that supplies oxygenated blood to the heart muscle itself and drains deoxygenated blood back to the right atrium. Because the heart never stops working, knowing which artery supplies which region is essential for interpreting ECGs and predicting infarct territory.

Short answer

The heart is supplied by the right coronary artery (RCA) and left coronary artery (LCA, which splits into the LAD and circumflex), arising from the aortic sinuses just above the aortic valve and distributing blood to specific myocardial territories.

Coronary Blood Flow Pathway

1
Aortic sinuses
Right & left coronary ostia arise just above the aortic valve
↓
2
Right coronary artery (RCA)
Supplies right atrium, right ventricle, SA/AV nodes (in most people)
↓
3
Left main coronary artery
Splits into LAD and circumflex
↓
4
Left anterior descending (LAD)
Supplies the anterior wall and interventricular septum
↓
5
Circumflex artery
Supplies the lateral and posterior left ventricle wall
↓
6
Capillary beds
Gas and nutrient exchange in the myocardium
↓
7
Cardiac veins & coronary sinus
Deoxygenated blood drains into the right atrium

Step-by-step worked examples

A patient has an ST-elevation MI with changes in leads V1–V4. Which artery is most likely occluded?

V1–V4 reflect the anterior/septal wall of the left ventricle
The LAD (left anterior descending) supplies the anterior wall and interventricular septum
Conclusion: LAD occlusion is most likely

In about 85% of people, which artery supplies the SA node and AV node?

This pattern is called 'right dominant' circulation, present in ~85% of people
The right coronary artery (RCA) gives off the SA nodal and AV nodal arteries in right-dominant hearts
Occlusion of the proximal RCA can therefore cause bradyarrhythmias or heart block

Why do coronary arteries fill mainly during diastole rather than systole?

During systole, the contracting myocardium compresses the intramural coronary vessels, especially in the left ventricle
Aortic valve cusps also partly cover the coronary ostia during systole
During diastole the myocardium relaxes and aortic pressure drives blood into the relaxed coronary arteries — so most coronary flow happens in diastole

Flashcards

Quick quiz

Q1.Which artery most commonly supplies the SA node?

Correct answer: C. In ~85% of people (right-dominant), the RCA gives rise to the SA nodal artery.

Q2.ST elevation in leads V1–V4 suggests occlusion of:

Correct answer: B. V1–V4 correspond to the anteroseptal territory supplied by the LAD.

Q3.Coronary arteries fill primarily during:

Correct answer: B. Myocardial compression during systole blocks flow; diastolic relaxation allows coronary filling.

Q4.Coronary venous blood returns to the heart mainly via:

Correct answer: B. Most cardiac veins converge into the coronary sinus, which empties into the right atrium.

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Common mistakes

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Assuming coronary arteries fill mainly during systole, like other arteries. — Correct: They fill mainly during diastole because systolic myocardial contraction compresses them.

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Thinking the LAD and circumflex arise separately from the aorta. — Correct: Both arise from a single left main coronary artery, which then bifurcates.

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Assuming the SA node blood supply is always from the RCA. — Correct: It's from the RCA in ~85% (right-dominant) but from the circumflex in ~15% (left-dominant) hearts.

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Believing all cardiac venous blood follows the same path as systemic veins. — Correct: Most drains via the coronary sinus to the right atrium, but thebesian veins drain directly into cardiac chambers, bypassing the venous system.

FAQ

What is coronary circulation?

It's the blood supply of the heart itself — the right and left coronary arteries deliver oxygenated blood to the myocardium, and cardiac veins drain it back to the right atrium via the coronary sinus.

What is the distribution of the coronary arteries?

The RCA supplies the right atrium, right ventricle, and (usually) the SA/AV nodes; the LAD supplies the anterior wall and septum; the circumflex supplies the lateral/posterior left ventricle.

What are clinical examples of coronary circulation problems?

LAD occlusion causing anterior STEMI, RCA occlusion causing inferior STEMI with possible heart block, and reduced diastolic filling time in tachycardia causing ischemia.

How do you determine which coronary artery is affected in an MI?

Match the ECG lead territory to the artery: V1–V4 → LAD, II/III/aVF → RCA (usually), I/aVL/V5–V6 → circumflex.