## Diagnostic Criteria and ECG Interpretation in STEMI ### Correct Statement Evaluation **Key Point:** Elevated troponin within 3 hours of symptom onset does NOT rule out acute myocardial infarction. In fact, troponin may be negative in the first 3 hours despite ongoing infarction because troponin release takes time. ### Troponin Kinetics in Acute MI **High-Yield:** Troponin elevation timeline: - **First appearance:** 2–4 hours after symptom onset - **Peak:** 24–72 hours - **Normalization:** 7–14 days (troponin I) or up to 2–3 weeks (troponin T) **Clinical Pearl:** A negative troponin in the first 3 hours does NOT exclude MI. Serial troponin measurement (at 0, 3, and 6 hours) or high-sensitivity troponin assays are needed for early rule-out. ### Verified True Statements | Diagnostic Feature | Status | Details | |---|---|---| | ST elevation ≥2 mm in 2 contiguous precordial leads | **TRUE** | Diagnostic criterion for anterior STEMI [cite:Harrison 21e Ch 297] | | Reciprocal ST depression in inferior STEMI | **TRUE** | Common finding; increases specificity for inferior MI | | Elevated troponin within 3 hrs rules out MI | **FALSE** | Troponin may still be negative; cannot rule out early MI | | RV involvement detected by V4R | **TRUE** | Right-sided ECG essential for RV infarction diagnosis | ### ECG Diagnostic Criteria for STEMI **Mnemonic:** **STEMI criteria = ST elevation in 2 contiguous leads + clinical context** - Anterior: V1–V4 (≥2 mm in men, ≥1.5 mm in women) - Inferior: II, III, aVF (≥1 mm) - Lateral: I, aVL, V5–V6 (≥1 mm) ### Right Ventricular Infarction **Warning:** RV infarction occurs in ~40% of inferior STEMIs. Key features: - ST elevation in V4R (most sensitive) - Hypotension with clear lungs (elevated JVP) - Avoid nitrates and diuretics—maintain preload ### Why Troponin Timing Matters 1. **Early presentation (<3 hrs):** Troponin may be negative despite active MI 2. **Serial measurement:** Repeat at 3 and 6 hours improves sensitivity 3. **High-sensitivity troponin:** Can detect MI within 1–2 hours but requires clinical correlation
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