SMLE Clinical Reasoning Walkthrough: Acute Chest Pain and ECG Interpretation
This walkthrough combines clinical presentation with ECG localisation. Work through the case before reading the explanation, then identify which findings change the differential.
Clinical case
A 62-year-old man with hypertension and type 2 diabetes presents with two hours of crushing central chest pain radiating to his left arm and jaw. He is pale and diaphoretic. His blood pressure is 100/60 mmHg and heart rate is 58 beats/min. The ECG shows ST elevation in II, III and aVF, with reciprocal ST depression in I and aVL. What is the most likely diagnosis?
- Anterior wall myocardial infarction
- Inferior wall myocardial infarction
- Acute pericarditis
- Massive pulmonary embolism
Read the case in two passes
First, identify the clinical problem: acute chest pain with autonomic symptoms and cardiovascular risk factors. Second, localise the ECG changes. Leads II, III and aVF view the inferior territory. In this case, ST elevation in that group together with reciprocal depression in I and aVL supports an inferior STEMI.
The pain description alone does not distinguish every cause of chest pain. The regional ECG pattern is the finding that makes option B the best answer here. It identifies the territory involved; it does not prove which artery is occluded or establish right ventricular involvement.
Why each option fits or fails
A — Anterior infarction: anterior and septal changes are usually sought in V1–V4. This stem instead gives inferior limb-lead elevation with reciprocal high-lateral depression. The patient's symptoms could occur with different infarct territories, so use the ECG rather than the pain description to localise this one.
B — Inferior infarction: this is the best answer. The inferior-lead changes, reciprocal findings and acute ischaemic presentation fit together. The right coronary artery is a common culprit, but the circumflex can also supply this territory. The vignette does not include angiography, so do not turn a likely artery into a confirmed finding.
C — Pericarditis: the usual teaching pattern is pleuritic or positional pain with more diffuse ST elevation and possible PR depression. The regional changes and reciprocal depression supplied here favour infarction. Compare the pattern in the whole case rather than treating any single ECG feature as an absolute rule.
D — Pulmonary embolism: consider it when the history and examination suggest it, including acute dyspnoea or evidence of right-heart strain. Presentations vary, but it is less well supported than inferior infarction by this combination of ischaemic symptoms and regional ECG changes. Do not learn the explanation as a claim that pulmonary embolism can never produce unusual ST changes.
Compare the ECG territories
| Territory | Leads to examine | Typical coronary supply |
|---|---|---|
| Inferior | II, III, aVF | RCA or circumflex, depending on the anatomy |
| Anterior/septal | V1–V4 | LAD |
| Lateral | I, aVL, V5–V6 | Circumflex or a diagonal branch of the LAD |
| Posterior | V7–V9; assess suggestive reciprocal changes in V1–V3 | Posterior descending artery, arising from the RCA or circumflex according to coronary dominance |
Use this table to organise your reading, not as a substitute for the full clinical picture. Lead placement, conduction abnormalities and other causes of ST changes can affect interpretation. The educational case asks for a diagnosis; real patients need urgent assessment through the appropriate acute-care pathway.
What does the slower pulse add?
A heart rate of 58 beats/min is an additional finding to interpret, not a shortcut to the answer. Inferior infarction can be associated with increased vagal activity or impaired blood supply to the sinus or atrioventricular node. Bradycardia alone does not identify the culprit artery or prove right ventricular infarction. Read the rhythm, blood pressure and clinical picture together.
Distinguish localisation from the next management step
Knowing that an infarction is inferior does not answer every subsequent question. If the stem adds hypotension, raised jugular venous pressure or other evidence of right ventricular involvement, reassess the haemodynamics. A right-sided ECG, including V4R, may help assess suspected right ventricular involvement. Inferior infarction and right ventricular infarction are related possibilities, not interchangeable diagnoses.
In right ventricular infarction, reduced preload can worsen hypotension; nitrate use therefore needs particular caution in that setting. This is not a reason to assume every inferior infarction has the same management. Review the separate hypotensive inferior STEMI case to practise how additional findings change the next decision. Actual suspected acute coronary syndrome requires urgent assessment through the appropriate care pathway.
Review without memorising the answer letter
- Explain how the ECG changes support the chosen territory.
- Describe which findings would make a different answer more likely.
- Revisit a new case without looking at the answer choices first.
Takeaway: identify the territory from the ECG, then assess the artery, rhythm and haemodynamic questions separately. Do not use a simple “no ST elevation means no occlusion” branch: posterior infarction may require additional leads and interpretation. Explain the findings that support your answer before memorising a letter or mnemonic.
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Dr. M. Salar Raza
MBBS, MSRA (RCGP), IMC Certified
Dr. Muhammad Salar Raza holds an MBBS, is registered with the Irish Medical Council, has passed MSRA in the UK, and is the author of multiple peer-reviewed publications in medical journals. He reviews all clinical content to ensure accuracy for SMLE students.
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