A 62-year-old woman from Mumbai with a history of diabetes and dyslipidemia presents with recurrent episodes of chest tightness lasting 15–20 minutes, occurring at rest and with minimal exertion over the past 3 days. She denies chest pain at this moment. Vital signs are stable. Physical examination is unremarkable. ECG performed during a pain-free interval shows normal sinus rhythm with no ST changes, but T waves appear flattened in leads II, III, and aVF. Troponin I is 0.02 ng/mL (normal <0.04). What is the most likely diagnosis?

Explanation

## Clinical Diagnosis **Key Point:** This patient has **Unstable Angina (UA)**, characterized by: 1. **Anginal symptoms** — chest tightness, 15–20 minutes duration 2. **New or worsening pattern** — recurrent episodes over 3 days 3. **Negative troponin** — 0.02 ng/mL (normal, <0.04) 4. **ECG changes without ST elevation** — T wave flattening (non-specific ischemic change) ## Acute Coronary Syndrome Classification ```mermaid flowchart TD A[Acute Coronary Syndrome]:::outcome --> B{ST Elevation on ECG?}:::decision B -->|Yes| C[STEMI]:::outcome B -->|No| D{Troponin Elevated?}:::decision D -->|Yes| E[NSTEMI]:::outcome D -->|No| F{Anginal Symptoms + Ischemic ECG Changes?}:::decision F -->|Yes| G[Unstable Angina]:::outcome F -->|No| H[Not ACS]:::outcome ``` ## Differential Diagnosis: UA vs. NSTEMI vs. Stable Angina | Feature | Unstable Angina | NSTEMI | Stable Angina | |---------|-----------------|--------|---------------| | **Troponin** | Negative | **Elevated** | Negative | | **Symptom Pattern** | New onset or worsening | New onset or worsening | Predictable, reproducible | | **Timing** | At rest or minimal exertion | At rest or minimal exertion | With exertion, relieved by rest | | **ECG** | ST depression, T inversion, or normal | ST depression, T inversion | Normal or old changes | | **Prognosis** | High risk of progression to MI | Acute myocardial injury | Lower risk | **High-Yield:** The **key distinguishing feature** between UA and NSTEMI is **troponin elevation**. Both present with acute coronary symptoms and ECG changes, but only NSTEMI has elevated cardiac biomarkers. ## Why This Patient Has Unstable Angina ### Negative Troponin **Clinical Pearl:** Troponin 0.02 ng/mL is **below the upper reference limit** (normal <0.04). This excludes myocardial infarction (NSTEMI) and indicates **myocardial ischemia without necrosis**. ### Acute Presentation with Ischemic ECG Changes The **flattened T waves in inferior leads (II, III, aVF)** suggest ischemia in the territory of the right coronary artery. Combined with acute anginal symptoms, this is diagnostic of unstable angina. ### Not Stable Angina Stable angina is **predictable and reproducible** with exertion and relieved by rest or nitroglycerin. This patient has **new-onset, recurrent symptoms at rest**, which is unstable. ## Management of Unstable Angina **Key Point:** UA requires the same aggressive dual antiplatelet therapy and anticoagulation as NSTEMI, despite negative troponin: 1. **Aspirin** — 300–325 mg loading, then 75–100 mg daily 2. **P2Y12 inhibitor** — Clopidogrel, ticagrelor, or prasugrel 3. **Anticoagulation** — UFH or LMWH 4. **Risk stratification** — High-risk UA (recurrent symptoms, ECG changes, hemodynamic instability) requires **early invasive strategy** 5. **Beta-blockers, ACE inhibitors, statins** — For symptom relief and secondary prevention **Warning:** Do not dismiss UA as "just chest pain." UA carries a **30% risk of progression to MI within 48 hours** if not treated aggressively [cite:Harrison 21e Ch 297].