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?

Question

Accepted Answer

B. Serial high-sensitivity troponin at 3 hours. ## 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.

Answer

A. Coronary angiography within 24 hours

Answer

C. Stress echocardiography at 48 hours

Answer

D. Repeat 12-lead ECG after 10 minutes

Explanation

Investigation of Choice in NSTEMI/Unstable Angina

Why Serial High-Sensitivity Troponin?

Clinical Context in This Case

Comparison with Other Investigations

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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