Cardiovascular · Topic 2 of 48

STEMI

Cardiovascular · acute coronary syndrome

STEMI

An occluded coronary artery. Read the ECG within 10 minutes and open the artery — primary PCI within 90 minutes of first contact.

Key numbers

New ST elevation in 2 contiguous leads≥ 1 mm

Obtain a 12-lead ECG within 10 minutes≤ 10 min

Primary PCI within 90 minutesFMC → device ≤ 90 min

Fibrinolysis if PCI over 120 mindoor → needle ≤ 30 min

Oxygen only if SpO₂ is below 90%SpO₂ < 90%

01 · Defined byNew ST elevation in 2 contiguous leads

STEMI = new J-point ST elevation in 2 or more contiguous leads: ≥ 1 mm in all leads except V2–V3, where it is ≥ 2 mm (men 40+), ≥ 2.5 mm (men under 40) or ≥ 1.5 mm (women).

02 · DoPrimary PCI within 90 minutes

Primary PCI is the preferred reperfusion: first medical contact to device within 90 minutes when the patient reaches a PCI-capable hospital, or within 120 minutes when a hospital-to-hospital transfer is needed.

03 · DoFibrinolysis if PCI over 120 min

If PCI cannot happen within 120 minutes of first contact and symptoms began within 12 hours, give a fibrinolytic (usually tenecteplase or reteplase) — door-to-needle goal 30 minutes; benefit peaks in the first 3 hours.

Presentation

What you'll see

Inferior STEMI: check right-sided leadsInferior STEMI with hypotension, clear lungs and raised JVP suggests right ventricular infarction: record right-sided leads (ST elevation in V4R), give IV fluid, and avoid nitrates and diuretics.

Posterior MI: ST depression in V1–V3ST depression in V1–V3 with tall R waves may be a posterior STEMI (left circumflex): record posterior leads V7–V9, where ST elevation of 0.5 mm or more confirms it.

Do right now

In this order

First moves

Obtain a 12-lead ECG within 10 minutes≤ 10 min

→

Aspirin 162–325 mg, chewed

→

Load a P2Y12 inhibitor before PCI

→

Primary PCI within 90 minutesFMC → device ≤ 90 min

Why each step

Obtain a 12-lead ECG within 10 minutesEvery patient with suspected ACS gets a 12-lead ECG within 10 minutes of first medical contact, in or out of the hospital — the ECG, not the troponin, triggers reperfusion in STEMI.

Aspirin 162–325 mg, chewedGive non-enteric-coated aspirin 162–325 mg chewed as soon as ACS is suspected, then 81 mg daily indefinitely; chewing speeds absorption and aspirin lowers mortality.

Load a P2Y12 inhibitor before PCIAdd a P2Y12 loading dose for PCI: ticagrelor 180 mg or prasugrel 60 mg (faster onset, preferred) or clopidogrel 600 mg; continue dual antiplatelet therapy for 12 months by default.

Primary PCI within 90 minutesPrimary PCI is the preferred reperfusion: first medical contact to device within 90 minutes when the patient reaches a PCI-capable hospital, or within 120 minutes when a hospital-to-hospital transfer is needed.

Management

Orders

Anticoagulate with heparin during PCIGive a parenteral anticoagulant with reperfusion — unfractionated heparin during primary PCI (bivalirudin is the alternative, including with prior HIT); enoxaparin dosing is reduced in patients over 75 receiving a fibrinolytic.

Oxygen only if SpO₂ is below 90%Give supplemental oxygen only for hypoxemia (SpO₂ below 90%) or respiratory distress; routine oxygen in normoxic MI has no benefit.

Use opioids sparingly for refractory painReserve morphine or fentanyl for pain despite nitrates: opioids delay and weaken oral P2Y12 inhibitor absorption and morphine has been associated with worse outcomes.

Start a high-intensity statin in the hospitalStart a high-intensity statin (atorvastatin 40–80 mg or rosuvastatin 20–40 mg) before discharge in every ACS patient, adding nonstatin therapy when LDL-C stays above goal.

Oral beta-blocker within 24 hoursStart an oral beta-blocker within the first 24 hours unless there is heart failure, a low-output state or shock risk, bradycardia, heart block or active bronchospasm; avoid IV beta-blockers in patients at risk of shock.

Angiography 2–24 hours after fibrinolysisAfter fibrinolysis, transfer for angiography: immediately (rescue PCI) if reperfusion fails or shock develops, otherwise routinely within 2–24 hours.

Red flags & don'ts

Avoid harm

No prasugrel after a stroke or TIA avoidPrasugrel is contraindicated with any prior stroke or TIA and is generally avoided at age 75 or older; it is used only for patients going to PCI and never with a fibrinolytic.

Hold nitrates: hypotension, RV infarct, PDE-5 inhibitor avoidNitroglycerin relieves ischemic pain but is withheld for SBP under 90 mmHg, suspected right ventricular infarction, or a phosphodiesterase-5 inhibitor taken recently (sildenafil within 24 h, tadalafil within 48 h).

Absolute bars to fibrinolysis avoidAbsolute contraindications to fibrinolysis: any prior intracranial hemorrhage, known cerebral vascular lesion or malignant intracranial tumor, ischemic stroke or significant head/facial trauma within 3 months, suspected aortic dissection, active bleeding.

Papillary muscle rupture: new apical murmur complicationPapillary muscle rupture, usually after an inferoposterior MI (single-supply posteromedial muscle), causes a new loud apical holosystolic murmur, acute severe MR and pulmonary edema — get an echo and urgent surgery.

Septal rupture: new murmur, thrill and shock complicationSeptal rupture causes a new loud systolic murmur with a thrill at the left lower sternal border plus hypotension; free-wall rupture presents as sudden tamponade or PEA. Both need echo and emergency surgery.

STEMI or acute pericarditis?

Commonly confused

ST elevation	Regional — one coronary territory
Reciprocal ST depression	Yes, in the opposite leads
PR segment	Normal
Pain	Pressure, not positional
Treatment	Reperfusion and antithrombotics

More detail

Reference

Show 4 reference facts

Type 1 MI is a spontaneous plaque rupture or erosion with thrombus; type 2 MI is supply–demand mismatch (anemia, tachyarrhythmia, hypotension) without an acute coronary thrombus.

Large anterior infarcts can form an LV aneurysm or mural thrombus; echocardiography screens for thrombus, which is treated with anticoagulation.

Early peri-infarction pericarditis does not bar anticoagulation, but late post-MI (Dressler) syndrome does; high-dose NSAIDs and steroids are avoided early because they may impair infarct healing.

Proton pump inhibitor co-therapy is advised during dual antiplatelet therapy to lower GI bleeding risk.

Pearl

Time is muscle: the shorter the delay to an open artery, the more myocardium — and the more patients — survive.

Sources · Merck Manual Professional — Acute Myocardial Infarction (MI) · Merck Manual Professional — Overview of Acute Coronary Syndromes · Rao SV et al. 2025 ACC/AHA/ACEP/NAEMSP/SCAI Guideline for the Management of Patients With Acute Coronary Syndromes. Circulation 2025;151:e771–e862 · Merck Manual Professional — Medications for Acute Coronary Syndromes · Prasugrel tablets prescribing information — DailyMed · Merck Manual Professional — Complications of Acute Coronary Syndromes · Merck Manual Professional — Pericarditis · EBM Consult — Contraindications to nitroglycerin in ACS (quotes the 2014 AHA/ACC NSTE-ACS guideline: no nitrates within 24 h of sildenafil/vardenafil or 48 h of tadalafil) · Cialis (tadalafil) prescribing information — DailyMed (≥ 48 h before nitrate administration) · Meyers HP et al. Accuracy of OMI ECG findings versus STEMI criteria for diagnosis of acute coronary occlusion MI. J Am Heart Assoc 2021 (cites the Fourth Universal Definition: ≥ 0.5 mm STE in V7–V9) · Merck Manual Professional — Dyslipidemia (statin intensity table) · Merck Manual Professional — Table: Contraindications to Fibrinolytic Therapy for STEMI · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).