# A 58-year-old client arrives at the emergency department with crushing substernal chest pain that started 30 minutes ago. The 12-lead ECG shows 3 mm ST-segment elevation in leads II, III, and aVF, and the troponin level is elevated. Which intervention should the nurse anticipate as the priority? > source: MyMerci (mymerci.kr) > url: https://mymerci.kr/pages/nclex_q.php?qn_id=362976&lang=en > language: en > subject: Medical Emergencies > category: PA ## Question A 58-year-old client arrives at the emergency department with crushing substernal chest pain that started 30 minutes ago. The 12-lead ECG shows 3 mm ST-segment elevation in leads II, III, and aVF, and the troponin level is elevated. Which intervention should the nurse anticipate as the priority? ## Option 1. Administer IV morphine 4 mg to decrease myocardial oxygen demand 2. Activate the cardiac catheterization laboratory for primary PCI **✔ Correct answer** 3. Administer sublingual nitroglycerin 0.4 mg every 5 minutes as needed 4. Obtain a portable chest X-ray to assess for pulmonary edema **Correct answer: 2** ## Explanation ST-segment elevation in leads II, III, and aVF with an elevated troponin indicates an inferior STEMI. Option 2 is correct because immediate activation of the cardiac catheterization laboratory for primary PCI addresses the time-critical need for reperfusion. Option 1 is incorrect because routine morphine is not first-line treatment and may delay absorption of oral antiplatelet therapy; it is reserved for pain that persists despite appropriate therapy. Option 3 is not the priority and can be unsafe if a right ventricular infarction is present, because nitroglycerin may markedly reduce preload and cause hypotension; right-sided leads such as V4R should be assessed before nitrate use. Option 4 may provide additional information but must not delay reperfusion. ## In-depth explanation Clinical Judgment Inferior STEMI = ST elevation in II, III, aVF. Time is muscle. Door-to-balloon goal: 90 minutes from first medical contact. The single most outcome-determining action is activating the cath lab. MONA-B (morphine, O2, nitro, aspirin, beta-blocker) supports but does not replace reperfusion. Memory Tip STEMI = Time + Reperfusion. Door-to-balloon <90 min KR vs US US AHA standard: PCI within 90 min, transfer-PCI within 120 min if no PCI center on site. Korea uses identical timeframes; major regional cardiac centers operate 24/7 cath labs and adopt the same Code STEMI workflow. ## Clinical scenario Clinical Practice Guide 2022 AHA/ACC STEMI Guidelines: Door-to-balloon ≤90 minutes for PCI-capable hospitals; door-in-door-out ≤30 minutes for transfer to PCI center. Initial therapy: aspirin 162-325 mg chewed, P2Y12 inhibitor, anticoagulation, oxygen if SpO2 <90%. Avoid routine morphine. Caution Inferior STEMI with right-ventricular involvement is preload-dependent. Avoid nitrates and diuretics in this subset; they can cause profound hypotension. Get a right-sided ECG (V4R) to confirm before nitrates. ## Key concepts - **STEMI** — ST-elevation myocardial infarction. Defined by ≥1 mm ST elevation in 2 contiguous leads or new LBBB with positive troponin. Inferior STEMI: II, III, aVF (right coronary artery). Anterior: V1-V4 (LAD). Lateral: I, aVL, V5-V6. - **Door-to-balloon time** — Time interval from arrival at the hospital to balloon inflation in the culprit coronary artery during PCI. AHA goal: 90 minutes or less. Strongly correlated with mortality reduction in STEMI. - **Troponin** — Cardiac-specific protein released from injured myocytes. Elevation begins 3-6 hours after ischemia, peaks 12-24 hours, returns to baseline 7-14 days. 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