A 58-year-old man with hypertension and diabetes presents to the emergency department with acute onset chest pain radiating to the left arm, associated with diaphoresis. His initial 12-lead ECG shows ST-segment elevation in leads II, III, and aVF. What is the investigation of choice to confirm acute myocardial infarction and guide immediate reperfusion therapy?

## Investigation of Choice in Acute STEMI **Key Point:** In a patient with clinical symptoms of acute coronary syndrome (ACS) and diagnostic ST-segment elevation on 12-lead ECG, coronary angiography is the gold-standard investigation and the definitive next step for both diagnosis confirmation and immediate therapeutic intervention (primary percutaneous coronary intervention [PCI]). ### Why Coronary Angiography? 1. **Diagnostic accuracy:** Directly visualizes coronary anatomy and identifies the culprit lesion responsible for the infarction (in this case, likely right coronary artery or left circumflex given inferior STEMI pattern). 2. **Therapeutic capability:** Allows immediate revascularization (balloon angioplasty ± stent placement) within the critical time window (door-to-balloon time <90 minutes). 3. **Prognostic information:** Assesses collateral flow, extent of disease, and left ventricular function in real time. **High-Yield:** In STEMI with ST elevation on ECG, do NOT delay for biomarkers or other investigations — proceed directly to coronary angiography (or thrombolysis if PCI-capable facility unavailable within 120 minutes). ### Comparison of Investigations in Acute STEMI | Investigation | Role in STEMI | Timing | Limitation | |---|---|---|---| | **Coronary angiography** | Gold standard; diagnostic + therapeutic | Immediate (door-to-balloon <90 min) | Invasive; not available in all centers | | Cardiac troponin | Confirms myocardial necrosis; risk stratification | Serial (0, 3, 6 hrs); delayed rise | Not diagnostic of ACS type; delays reperfusion decision | | Echocardiography | Assesses wall motion, EF, complications (MR, VSD, FWR) | After stabilization | Does not identify culprit vessel; not diagnostic | | Chest X-ray | Excludes alternative diagnoses (pneumonia, PE, aortic dissection) | Initial screening | Non-specific; does not guide reperfusion | **Clinical Pearl:** The presence of ST-segment elevation on ECG is sufficient to diagnose STEMI and initiate reperfusion therapy — do not wait for troponin confirmation, which may take hours. Troponin is used for risk stratification and prognostication, not for diagnosis in the acute setting. **Mnemonic: "STEMI = Straight To Emergent angiography for Myocardial Infarction"** — emphasizes that ST elevation mandates immediate catheterization, not serial biomarkers.