A 58-year-old man with hypertension presents to the emergency department with acute onset substernal chest pain radiating to the left arm for 2 hours. His blood pressure is 145/92 mmHg, heart rate 98/min. On examination, he has an S4 gallop. A 12-lead ECG shows ST elevation in leads II, III, and aVF with reciprocal ST depression in I and aVL. Which investigation is most appropriate to confirm acute myocardial infarction and guide immediate reperfusion therapy?

Explanation

## Diagnosis and Management of STEMI ### Clinical Context This patient presents with classic acute STEMI features: - Acute chest pain with typical radiation - ST elevation in inferior leads (II, III, aVF) → **inferior wall STEMI** - Reciprocal changes in lateral leads - Hemodynamic signs of acute MI (S4 gallop suggests ventricular dysfunction) ### Investigation of Choice: Coronary Angiography **Key Point:** In a patient with ECG-confirmed STEMI (ST elevation ≥1 mm in two contiguous leads), coronary angiography is the **gold standard** and **definitive diagnostic and therapeutic procedure**. It is both diagnostic AND therapeutic. ### Why Coronary Angiography? 1. **Diagnostic confirmation:** Visualizes the culprit coronary artery and identifies the exact site of occlusion 2. **Therapeutic intervention:** Enables immediate primary percutaneous coronary intervention (PCI) — the preferred reperfusion strategy in STEMI 3. **Risk stratification:** Identifies extent of disease, collaterals, and complications (mechanical) 4. **Time-sensitive:** Should be performed within 90 minutes of first medical contact (door-to-balloon time) ### Role of Other Investigations | Investigation | Role in STEMI | Timing | |---|---|---| | **Troponin (cTnI/cTnT)** | Confirms myocardial necrosis; rises after 3–4 hours | Supportive, not for diagnosis | | **Chest X-ray** | Assesses pulmonary edema, cardiomegaly, complications | Adjunctive; does NOT guide therapy | | **Echocardiography** | Evaluates wall motion abnormalities, complications (VSD, papillary muscle rupture) | Post-PCI or if complications suspected | | **Coronary angiography** | **Gold standard:** identifies culprit vessel, enables PCI | **Immediate** (within 90 min) | ### High-Yield: STEMI Diagnosis Algorithm ```mermaid flowchart TD A[Acute chest pain + ECG changes]:::outcome --> B{ST elevation ≥1 mm<br/>in 2 contiguous leads?}:::decision B -->|Yes| C[STEMI diagnosed]:::outcome C --> D{PCI-capable<br/>hospital?}:::decision D -->|Yes| E[Coronary angiography<br/>+ Primary PCI<br/>within 90 min]:::action D -->|No| F[Thrombolysis<br/>+ Transfer for angiography]:::action E --> G[Reperfusion achieved]:::outcome B -->|No| H[NSTEMI or unstable angina<br/>Risk stratify]:::outcome ``` **Clinical Pearl:** Do NOT delay coronary angiography while awaiting troponin results. ECG + clinical presentation are sufficient to diagnose STEMI and proceed to the catheterization laboratory. Troponin is confirmatory but not required for immediate decision-making. **Warning:** Chest X-ray and echocardiography are NOT diagnostic for acute MI and should NOT delay transfer to the catheterization laboratory. They are adjunctive investigations performed after reperfusion therapy. [cite:Harrison 21e Ch 297]