top of page
Search

STEMI Territories & Coronary Anatomy — MRCP Part 1

TL;DR

For MRCP Part 1, you must rapidly localise STEMI using ECG lead groups, link them to myocardial territories, and identify the culprit coronary artery while avoiding classic exam traps. Anterior STEMIs usually reflect LAD occlusion, inferior STEMIs most often RCA (but not always), and posterior STEMIs are commonly missed without mirror-image thinking. This article delivers a high-yield framework, a mini-case, and a practical revision checklist.


Why this topic matters for MRCP candidates

STEMI localisation is repeatedly tested because it blends anatomy, physiology, ECG interpretation, and acute cardiology. Questions rarely stop at “which artery?”—they add layers such as coronary dominance, right ventricular involvement, or posterior infarction. Candidates who memorise lead–artery patterns systematically score consistently here.

If you are building your core syllabus, start with the MRCP Part 1 overview:https://crackmedicine.com/mrcp-part-1/


Core framework: ECG leads → territory → artery

Think in blocks, not isolated leads.

1) Anterior / Septal STEMI

  • Leads: V1–V4 (± V5)

  • Territory: Anterior wall and septum

  • Culprit artery: Left anterior descending (LAD)

  • Exam pearl: Proximal LAD occlusion gives extensive anterior changes and higher mortality.

2) Extensive Anterior STEMI

  • Leads: V1–V6, I, aVL

  • Territory: Anterior + lateral walls

  • Culprit artery: Proximal LAD

  • Common association: Acute heart failure, cardiogenic shock.

3) Inferior STEMI

  • Leads: II, III, aVF

  • Territory: Inferior wall

  • Culprit artery: Right coronary artery (RCA) most commonly

  • Exam pearl: ST elevation in lead III > II favours RCA over LCx.

4) Right Ventricular STEMI

  • Leads: V1, V4R (right-sided leads)

  • Territory: Right ventricle

  • Culprit artery: Proximal RCA

  • Clinical clue: Hypotension after nitrates due to preload dependence.

5) Lateral STEMI

  • Leads: I, aVL (high lateral); V5–V6 (low lateral)

  • Territory: Lateral wall

  • Culprit artery: Left circumflex (LCx) or diagonal branch of LAD.

6) Posterior STEMI

  • Leads: ST depression in V1–V3 with tall R waves (mirror image)

  • Territory: Posterior wall

  • Culprit artery: RCA or LCx

  • Confirmation: ST elevation in posterior leads V7–V9.


Coronary dominance (frequently examined)

  • Right-dominant (~70%): PDA from RCA → inferior STEMI usually RCA.

  • Left-dominant (~10–15%): PDA from LCx → inferior STEMI may be LCx.

  • Co-dominant: Shared supply.

Exam trap: Do not assume all inferior STEMIs are RCA—dominance matters.


Structured ECG study checklist for MRCP Part 1 candidates

High-yield summary table

ECG territory

Leads

Likely artery

Key exam point

Septal/Anterior

V1–V4

LAD

New LBBB may obscure

Extensive anterior

V1–V6, I, aVL

Proximal LAD

High mortality

Inferior

II, III, aVF

RCA > LCx

III > II → RCA

Right ventricular

V4R

Proximal RCA

Avoid nitrates

Lateral

I, aVL, V5–V6

LCx/Diagonal

High vs low lateral

Posterior

V1–V3 depression

RCA/LCx

Think mirror image

Mini-case (MCQ style)

A 64-year-old man presents with acute chest pain. ECG shows ST elevation in II, III, and aVF with reciprocal ST depression in aVL. After sublingual GTN, his blood pressure falls to 85/50 mmHg. What is the most likely culprit artery?

Answer: Proximal right coronary artery. Explanation: Inferior STEMI with lead III elevation greater than II and hypotension after nitrates strongly suggests RCA occlusion with right ventricular involvement.

To practise similar questions under exam conditions, use the Crack Medicine Qbank:https://crackmedicine.com/qbank/


The 5 most tested subtopics

  1. Accurate ECG lead grouping.

  2. Culprit artery identification with dominance awareness.

  3. Recognition of right ventricular infarction.

  4. Posterior STEMI diagnosis using mirror-image changes.

  5. Linking infarct territory to complications (e.g., AV block in inferior MI).


Common exam pitfalls (know these)

  • Missing posterior STEMI by ignoring V1–V3 ST depression.

  • Forgetting right-sided leads in inferior STEMI with hypotension.

  • Confusing high lateral (I, aVL) with low lateral (V5–V6).

  • Over-diagnosing STEMI in diffuse ST depression with aVR elevation (think left main disease).

  • Ignoring coronary dominance in inferior infarction questions.


Practical revision checklist

  • Memorise territories as clusters, not single leads.

  • Always ask: territory → artery → dominance → complication.

  • Practise posterior and right-sided lead interpretation weekly.

  • Sit at least one timed paper from the mock tests section:https://crackmedicine.com/mock-tests/

  • Revisit ECG localisation during your final revision week.

For structured teaching, see Crack Medicine video lectures:https://crackmedicine.com/lectures/


FAQs

Which artery is most commonly involved in anterior STEMI?

The LAD. Proximal LAD occlusion causes extensive anterior infarction with worse prognosis.

How can posterior STEMI be recognised on a standard ECG?

By ST depression in V1–V3 with tall R waves; confirm using posterior leads V7–V9.

Is inferior STEMI always due to RCA occlusion?

No. RCA is most common, but LCx involvement occurs in left-dominant circulation.

Why should nitrates be avoided in right ventricular MI?

Because RV infarction is preload-dependent; nitrates can precipitate severe hypotension.


Ready to start?

Consolidate this topic with targeted practice and exam-style repetition. Start by revising the core syllabus in the MRCP Part 1 hub, then test retention with high-yield questions and a timed paper:


Sources

 
 
 

Comments

bottom of page