A 52-year-old man with a history of smoking and dyslipidaemia presents with acute inferior STEMI. ECG shows ST elevation in leads II, III, aVF with reciprocal ST depression in I, aVL. Regarding the diagnostic and risk stratification features of STEMI, all of the following statements are correct EXCEPT:

Question

Accepted Answer

D. T-wave inversion in the acute phase of STEMI indicates reperfusion and is associated with improved myocardial salvage. ## STEMI Diagnosis and Risk Stratification

**Key Point:** T-wave inversion in acute STEMI is a sign of **ischaemia**, not reperfusion. Reperfusion is indicated by resolution of ST elevation, not development of T-wave inversion.

### ECG Diagnostic Criteria for STEMI

| Feature | Criterion | Significance |
|---------|-----------|---------------|
| ST elevation | ≥1 mm in ≥2 contiguous limb leads OR ≥2 mm in ≥2 contiguous precordial leads | Diagnostic of STEMI |
| New LBBB | In acute chest pain + biomarker elevation | Equivalent to STEMI; requires urgent reperfusion |
| T-wave inversion | Develops during evolution of ischaemia | Sign of ongoing ischaemia, NOT reperfusion |
| ST resolution | Decrease in ST elevation during reperfusion | Marker of successful reperfusion |

**High-Yield:** T-wave inversion develops as part of the **natural evolution of myocardial ischaemia** and represents the progression from hyperacute phase (peaked T waves) → acute phase (ST elevation) → evolution phase (T-wave inversion). It is **NOT** a sign of reperfusion; in fact, persistent T-wave inversion without ST resolution suggests ongoing ischaemia or incomplete reperfusion.

### Cardiac Biomarkers in STEMI

**High-Sensitivity Troponin (hs-cTn):**
- Detectable: 2–4 hours after symptom onset
- Peak: 48–72 hours
- Sensitivity: >95% at 3 hours with serial measurement
- Specificity: Lower than conventional troponin (rises in any myocardial injury, not just ACS)

**Clinical Pearl:** Serial troponin measurement (0 and 3 hours, or 0 and 1 hour with hs-cTn) improves diagnostic accuracy and allows early rule-out of MI in low-risk patients.

**Warning:** Do not confuse T-wave inversion with reperfusion. T-wave inversion is a marker of **ischaemic evolution**, not successful reperfusion. Successful reperfusion is indicated by:
- Resolution of ST elevation (≥50% reduction within 60–90 minutes)
- Restoration of coronary blood flow (TIMI grade 3)
- Absence of new arrhythmias

### New LBBB in Acute Chest Pain

**Key Point:** New LBBB in the setting of acute chest pain + elevated cardiac biomarkers is considered **equivalent to STEMI** and mandates urgent reperfusion therapy (primary PCI or thrombolysis) [cite:Harrison 21e Ch 297].

[cite:Harrison 21e Ch 297]

Answer

A. Elevated cardiac troponin (high-sensitivity troponin) becomes detectable within 2–4 hours of symptom onset and peaks at 48–72 hours

Answer

B. New left bundle branch block (LBBB) in the setting of acute chest pain is considered equivalent to STEMI for the purpose of urgent reperfusion therapy

Answer

C. ST elevation ≥1 mm in two contiguous limb leads or ≥2 mm in two contiguous precordial leads is diagnostic of STEMI

Explanation

STEMI Diagnosis and Risk Stratification

ECG Diagnostic Criteria for STEMI

Cardiac Biomarkers in STEMI

New LBBB in Acute Chest Pain

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Feature	Criterion	Significance
ST elevation	≥1 mm in ≥2 contiguous limb leads OR ≥2 mm in ≥2 contiguous precordial leads	Diagnostic of STEMI
New LBBB	In acute chest pain + biomarker elevation	Equivalent to STEMI; requires urgent reperfusion
T-wave inversion	Develops during evolution of ischaemia	Sign of ongoing ischaemia, NOT reperfusion
ST resolution	Decrease in ST elevation during reperfusion	Marker of successful reperfusion