A 52-year-old woman with no prior cardiac history presents with acute substernal chest pain for 2 hours. Her initial 12-lead ECG shows nonspecific ST-T wave changes. Troponin I measured at presentation is negative. She remains symptomatic with ongoing chest pain. Which investigation is most appropriate to exclude acute coronary syndrome and guide further management?

## Serial Troponin in Suspected ACS with Nondiagnostic ECG **Key Point:** Serial troponin measurement (high-sensitivity troponin at 0 and 3 hours) is the most appropriate investigation when initial ECG is nondiagnostic and troponin is negative in a symptomatic patient with ongoing chest pain. ### Why Serial Troponin? **High-Yield:** High-sensitivity troponin (hs-troponin) has revolutionized ACS diagnosis. A single negative hs-troponin at presentation does NOT exclude MI — serial measurement at 3 hours is mandatory [cite:Harrison 21e Ch 297]. 1. **Sensitivity and kinetics**: - Troponin rises 2–4 hours after myocardial necrosis - Peak at 24–48 hours - Remains elevated for 7–14 days - Initial negative result does NOT exclude early MI 2. **Serial strategy (0-3 hour rule)**: - Hs-troponin at 0 hours (presentation) - Hs-troponin at 3 hours - If both negative → ACS ruled out with >99% NPV - If either elevated → confirms MI 3. **Cost-effective**: Cheaper and faster than coronary angiography or advanced imaging ### Clinical Context This patient has: - Nonspecific ECG (not diagnostic for STEMI or NSTEMI) - Negative initial troponin - **Ongoing symptoms** → requires serial biomarker testing - No indication for immediate angiography (not STEMI) ### Decision Algorithm ```mermaid flowchart TD A[Chest pain + nondiagnostic ECG]:::outcome --> B[Hs-troponin at 0 hrs]:::action B --> C{Troponin elevated?}:::decision C -->|Yes| D[NSTEMI confirmed]:::outcome C -->|No| E[Repeat troponin at 3 hrs]:::action E --> F{Troponin elevated?}:::decision F -->|Yes| G[NSTEMI diagnosed]:::outcome F -->|No| H[ACS ruled out]:::outcome H --> I[Discharge or further workup for non-ACS]:::action ``` **Mnemonic:** **HEART** score (History, ECG, Age, Risk factors, Troponin) — serial troponin is the T in HEART and critical for risk stratification [cite:Harrison 21e Ch 297]. **Clinical Pearl:** A single negative troponin at presentation, even high-sensitivity assay, does NOT exclude MI in the first 2–3 hours. Serial measurement is the standard of care.