Stage 3 — Prioritize hypotheses. A 58-year-old client arrived by EMS with substernal pressure unchanged for 45 minutes at rest, spreading down the left arm, with new breathlessness. EMS gave chewable aspirin 324 mg. He smokes (30 pack-years) and has hypertension and hyperlipidemia. BP is 152/94, HR 102 and regular, RR 20, and SpO2 93% on room air (same as his clinic value last month); lungs are clear. His skin is pale, cool, and diaphoretic. The 12-lead ECG obtained 7 minutes after arrival shows ST elevation in II, III, and aVF with reciprocal ST depression in I and aVL, and no PR depression. Troponin is pending. Complete the diagram by selecting the condition the client is most likely experiencing, 2 actions the nurse should take to address that condition, and 2 parameters the nurse should monitor to assess the client's progress.

Quick answer
Acute inferior STEMI. Activate the catheterization team for PCI and obtain a right-sided ECG with V4R. Monitor heart rhythm with AV conduction and ST segments on serial ECGs.

Why this is correct
ST elevation in the inferior leads with reciprocal depression in the high-lateral leads, plus 45 minutes of unrelieved ischemic pain, defines an inferior STEMI, usually from right coronary artery occlusion. Reperfusion by primary PCI is time-critical and does not wait for troponin. The right coronary artery also supplies the right ventricle and the AV node, so right-sided leads and rhythm monitoring are needed.

Easy analogy or mental picture
An inferior STEMI is a blocked water main under the floor of the house: the damage shows in the floor leads (II, III, aVF), with a mirror image on the opposite wall (I, aVL). Calling the plumber (cath lab) cannot wait for the damage report (troponin).

Memory hook
"II, III, aVF up + I, aVL down = inferior STEMI: cath lab now, look right (V4R), watch the rhythm."

NCLEX decision rule
When the ECG shows STEMI, choose immediate reperfusion and complication screening over tests that only confirm what the ECG already shows.

Why the other choices are wrong
Pericarditis causes diffuse concave ST elevation with PR depression and no reciprocal changes, so NSAIDs with colchicine, friction rubs, and ESR target the wrong problem. NSTEMI and unstable angina are defined by the absence of ST elevation, which this ECG has. Nitroglycerin can ease ischemic pain but does not open the artery, and in an inferior STEMI its use depends on the complete ECG assessment and provider direction, so it is not one of the two priority actions now. Oxygen is given for SpO2 below 90%, and this client's 93% matches his baseline. A lipid panel guides secondary prevention later, not the acute response.