Reference — Cardiac

Coronary Artery Anatomy Reference

Understanding coronary artery territories allows nurses to correlate ECG changes with specific infarct locations, anticipate complications, and apply anatomy to ACS care. Each coronary artery supplies a defined myocardial territory identifiable on ECG.

Educational use only. Coronary anatomy varies between individuals. This reference presents typical anatomy. Clinical correlation is required for all ACS management decisions. This material supports nursing education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional policy, or medical direction. Always follow facility protocols and current provider orders.

Overview of Coronary Circulation

The heart is supplied by two coronary arteries originating from the aortic root: the Left Main Coronary Artery (LMCA) and the Right Coronary Artery (RCA). The left main bifurcates into the LAD and Circumflex.

Coronary dominance refers to which artery supplies the posterior descending artery (PDA): right-dominant (~70%), left-dominant (~15%), or codominant (~15%). Dominance affects which artery is responsible for inferior and posterior MI territory.

Coronary Arteries — Territory and Leads

LMCALeft Main Coronary Artery (LMCA)

Areas Supplied:

›Bifurcates into LAD and Circumflex
›Supplies majority of left ventricular myocardium
›Occlusion affects both LAD and Circumflex territories — catastrophic

ECG Leads: No direct ECG localization — diffuse ST changes; widespread ST depression + aVR elevation suggests LMCA or proximal LAD occlusion

Common Complications:

!Cardiogenic shock
!Acute heart failure
!High mortality — 'widow maker' if proximal LAD involved

LADLeft Anterior Descending (LAD)

Areas Supplied:

›Anterior wall of left ventricle
›Anterior interventricular septum
›Bundle of His and bundle branches (proximal LAD)
›Anterior papillary muscle (partial)

ECG Leads: V1–V4 (anterior leads) — ST elevation in anterior MI

Common Complications:

!Anterior STEMI — largest territory, highest mortality
!Bundle branch block (LBBB or RBBB)
!Complete heart block if proximal
!Ventricular aneurysm (late)

LCxLeft Circumflex (LCx)

Areas Supplied:

›Lateral wall of left ventricle
›Posterior wall (if left-dominant)
›Sinoatrial node (40% of cases)
›AV node (10% of cases, usually RCA)

ECG Leads: I, aVL, V5–V6 (lateral leads) — ST elevation in lateral MI

Common Complications:

!Lateral STEMI
!Posterior MI (may present with ST depression in V1–V3, not elevation)
!SA node dysfunction if LCx is dominant

RCARight Coronary Artery (RCA)

Areas Supplied:

›Right ventricle (anterior and posterior)
›Inferior wall of left ventricle (in right-dominant system)
›Sinoatrial (SA) node (~60% of people)
›AV node (~90% of people)
›Posterior descending artery (PDA) in right-dominant systems

ECG Leads: II, III, aVF (inferior leads) — ST elevation in inferior MI

Common Complications:

!Inferior STEMI
!Right ventricular infarction (seen with inferior STEMI)
!Bradycardia (SA/AV node involvement)
!High-degree AV blocks (2nd degree Mobitz I, 3rd degree)
!Hypotension with RV infarct — preload-dependent

PDAPosterior Descending Artery (PDA)

Areas Supplied:

›Posterior wall of left ventricle
›Posterior interventricular septum

ECG Leads: Posterior MI: ST depression in V1–V3 + tall R in V1 (reciprocal of posterior elevation); confirmed with posterior leads V7–V9

Common Complications:

!Posterior MI — often missed on standard 12-lead
!Must use posterior leads or right-sided leads to confirm

Infarct Location Summary

MI Location	ECG Leads	Artery	Key Watch
Anterior	V1–V4	LAD (proximal)	LBBB, complete heart block, large infarct, cardiogenic shock
Anteroseptal	V1–V2	LAD (septal perforators)	Bundle branch blocks, complete heart block
Anterolateral	V4–V6, I, aVL	LAD or LCx	Large territory; papillary muscle — watch for MR
Lateral	I, aVL, V5–V6	LCx	Often silent or atypical; diagonal branch
Inferior	II, III, aVF	RCA (right-dominant)	RV infarct, bradycardia, AV block, avoid NTG
Right Ventricular	V4R–V6R (right-sided leads)	RCA	Preload-dependent — avoid NTG, diuretics; fluid challenge may be needed
Posterior	V1–V3 depression, tall R in V1 (reciprocal); V7–V9 elevation	RCA or LCx (dominant)	Often missed — obtain posterior leads if suspected

NCLEX Pearls

›LAD supplies the anterior wall — anterior STEMI is the largest and most deadly MI territory.
›RCA supplies the SA node (~60%) and AV node (~90%) — inferior MI causes bradycardia and AV blocks.
›Inferior STEMI (II, III, aVF) = RCA → check right-sided ECG for RV infarct; avoid nitroglycerin.
›Posterior MI shows ST depression + tall R wave in V1–V3 — not elevation. Use posterior leads (V7–V9) to confirm.
›Circumflex territory (lateral) is often silent or presents atypically — ST changes in I, aVL, V5–V6.
›New LBBB in ACS context may represent proximal LAD occlusion — evaluate urgently; apply Sgarbossa criteria rather than treating new LBBB alone as a STEMI equivalent.

Related Resources

STEMI Activation Criteria ReferenceECG criteria, contiguous leads, new LBBB, posterior MI clues

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Coronary Artery Territories ChartArtery, supplies, ECG leads, and common complications side-by-side

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STEMI vs NSTEMI GuideECG differences, troponin findings, treatment priorities, nursing implications

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ECG Interpretation Fundamentals GuideSystematic 9-step ECG reading: intervals, BBB, ST analysis, AV blocks

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Standards & sources

Fact-checked Jun 20, 2026

This page is written to align with American Heart Association (AHA) · American College of Cardiology (ACC) · AHA ACLS Guidelines. It is an educational summary, not a citation of any single document — always verify specific doses, values, and protocols against current guidelines and your facility policy. How we source content →