A 58-year-old man with hypertension and dyslipidemia presents to the emergency department with chest pain of 3 hours duration, radiating to the left arm, associated with diaphoresis. His initial 12-lead ECG shows ST depression in leads II, III, aVF with T-wave inversion. Troponin I at presentation is negative. What is the most appropriate next investigation to confirm acute coronary syndrome and guide risk stratification?

Explanation

## Investigation of Choice in NSTEMI/Unstable Angina **Key Point:** Serial high-sensitivity troponin (hs-cTn) is the gold standard for diagnosis and risk stratification in suspected NSTEMI. A single negative troponin does NOT exclude ACS; serial measurement at 3 hours is mandatory. ### Why Serial High-Sensitivity Troponin? 1. **Diagnostic accuracy**: hs-cTn has >99% sensitivity and specificity for myocardial necrosis 2. **Early detection**: Rises within 2–3 hours of symptom onset (vs. conventional troponin at 6–12 hours) 3. **Risk stratification**: Absolute level and delta (change) predict prognosis 4. **Rule-out protocol**: Negative hs-cTn at 0 and 3 hours with low-risk features safely excludes ACS ### Clinical Context in This Case - **Presentation**: Classic ACS symptoms (3 hours duration) - **ECG**: Diagnostic ST depression + T-wave inversion (NSTEMI pattern) - **Initial troponin**: Negative (expected at 3 hours from onset) - **Next step**: Repeat hs-cTn at 3 hours post-presentation to detect rise/fall pattern **High-Yield:** The 2015 ESC and 2014 ACC/AHA guidelines recommend hs-cTn measurement at 0 and 3 hours (or 0–6 hours) as the standard diagnostic pathway for NSTEMI/unstable angina. ### Comparison with Other Investigations | Investigation | Role in NSTEMI | Timing | Limitation | |---|---|---|---| | Serial hs-troponin | Diagnostic gold standard | 0 & 3 hrs | None — first-line | | Repeat ECG (10 min) | Detects dynamic changes | Immediate | Low sensitivity; not diagnostic | | Coronary angiography | Definitive; therapeutic | 24 hrs (non-urgent) | Invasive; reserved after biomarker confirmation | | Stress echo | Risk assessment | 48 hrs | Contraindicated in acute phase; for post-ACS stratification | **Clinical Pearl:** In NSTEMI, the ECG may show only ST depression or T-wave changes; troponin elevation is essential for diagnosis. Conversely, unstable angina has negative troponin despite ECG changes — serial measurement confirms this distinction.