Cardiovascular · Topic 2 of 48

STEMI

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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.

01 · Defined byNew ST elevation ≥ 1 mm, 2 contiguous leads

02 · The targetPrimary PCI within 90 min of first contact

03 · PCI over 120 minFibrinolytic: door to needle ≤ 30 min

Diagnosis: the ECG

The ECG, not the troponin, triggers reperfusion

Thrombus on a disrupted plaque: typically transmural necrosis, ST elevation

12-lead ECG within 10 min of first medical contact first 10 min

New J-point ST elevation ≥ 1 mm in 2+ contiguous leads

V2–V3: ≥ 2 mm men 40+ · ≥ 2.5 mm men under 40 · ≥ 1.5 mm women

Inferior STEMI: record right-sided leads (ST elevation in V4R)

ST depression V1–V3 with tall R waves: record V7–V9

Posterior STEMI: ST elevation ≥ 0.5 mm in V7–V9

Posterior STEMI is usually the left circumflex. Type 1 MI is plaque rupture or erosion with thrombus; type 2 MI is supply–demand mismatch (anemia, tachyarrhythmia, hypotension) without an acute coronary thrombus.

Red flags

Hypotension, clear lungs, raised JVP after inferior MI RV infarct: fluids

RV infarct: give IV fluid, avoid nitrates and diuretics

SBP under 90 mmHg or suspected RV infarction no nitrates

Sildenafil within 24 h or tadalafil within 48 h no nitrates

Prior stroke or TIA: never prasugrel no prasugrel

Age 75 or older, or on a fibrinolytic: avoid prasugrel no prasugrel

Treatment

Open the artery — primary PCI is the preferred reperfusion

First moves, in order

12-lead ECG within 10 minutesthe ECG triggers reperfusion

→

Aspirin 162–325 mg, chewednon-enteric-coated, then 81 mg daily

→

Load a P2Y12 inhibitor before PCIticagrelor 180 mg or prasugrel 60 mg

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Primary PCI within 90 minuteswithin 120 min if transfer needed

PCIpreferred reperfusion

First contact to device ≤ 90 min, ≤ 120 min with transfer

Can't make 120 min? Fibrinolysis

Fibrinolysisno PCI within 120 min

Tenecteplase Reteplase

Symptoms under 12 h: door to needle ≤ 30 min

Benefit peaks in the first 3 hours

Antiplateletsaspirin plus P2Y12

Aspirin 162–325 mg chewed Ticagrelor 180 mg load Prasugrel 60 mg load Clopidogrel 600 mg load

Dual antiplatelet therapy for 12 months by default

Ticagrelor or prasugrel preferred: faster onset

Anticoagulantwith reperfusion

Unfractionated heparin Bivalirudin

Unfractionated heparin during primary PCI

Bivalirudin is the alternative, incl. prior HIT

Oxygenonly for hypoxemia

Oxygen only if SpO₂ under 90% or respiratory distress

Routine oxygen in normoxic MI: no benefit

Painnitrates first

Nitroglycerin Morphine or fentanyl

Opioids only for pain despite nitrates

Opioids delay and weaken oral P2Y12 absorption

Statinbefore discharge

Atorvastatin 40–80 mg Rosuvastatin 20–40 mg

High-intensity statin in every ACS patient

Add nonstatin therapy if LDL-C stays above goal

Beta-blockeroral, within 24 h

Oral beta-blocker within 24 h unless HF or shock risk

No IV beta-blocker in patients at risk of shock

Holds, doses and GI protection

Beta-blocker: hold for theseheart failure, low-output state or shock risk, bradycardia, heart block, active bronchospasm

Morphine and outcomesmorphine has been associated with worse outcomes — reserve opioids for refractory pain

Enoxaparin with a fibrinolyticreduce the dose in patients over 75

Aspirin doseUS references use 162 mg (two 81-mg tablets); Merck quotes 160–325 mg

PPI during dual antiplatelet therapylowers GI bleeding risk

ACC/AHA door-to-needle target is 30 min (Merck lists 30–60). Older protocols gave everyone 2 L/min oxygen. Merck (2026): limited beta-blocker benefit with preserved LVEF (REBOOT, REDUCE-AMI 2025); long-term benefit is clearest for LVEF ≤ 40%.

Fibrinolysis: absolute contraindications

Then angiography 2–24 hours later — sooner if it fails

Any prior intracranial hemorrhage no lytics

Known cerebral vascular lesion or malignant intracranial tumor no lytics

Ischemic stroke or major head/facial trauma within 3 months no lytics

Suspected aortic dissection or active bleeding no lytics

Failed reperfusion or shock: immediate rescue PCI rescue PCI

Reperfused: routine angiography within 2–24 h

Mechanical complications

New murmur or collapse after MI: echo, then surgery

Papillary muscle rupture: new apical holosystolic murmur, may be absent echo + surgery

Acute severe MR and pulmonary edema after inferoposterior MI

Septal rupture: murmur + thrill at left lower sternal border, hypotension echo + surgery

Free-wall rupture: sudden tamponade or PEA emergency surgery

The posteromedial papillary muscle has a single blood supply. Large anterior infarcts can form an LV aneurysm or mural thrombus: echo screens for thrombus, treated with anticoagulation. Early peri-infarction pericarditis does not bar anticoagulation; in Dressler syndrome, avoid it unless strongly indicated. Avoid high-dose NSAIDs and steroids early — they may impair infarct healing.

STEMI or acute pericarditis?

	STEMI	Acute pericarditis
ST elevation	Regional — one coronary territory	Diffuse — most leads
Reciprocal ST depression	Yes, in the opposite leads	No (except aVR and V1)
PR segment	Normal	PR depression
Pain	Pressure, not positional	Sharp, pleuritic, better sitting forward
Treatment	Reperfusion and antithrombotics	NSAID plus colchicine; usually no anticoagulation

Pearl

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

Sources · Acute Myocardial Infarction (Merck Manual Professional) · Overview of Acute Coronary Syndromes (Merck Manual Professional) · 2025 ACC/AHA/ACEP/NAEMSP/SCAI Guideline for Acute Coronary Syndromes (Circulation 2025) · Medications for Acute Coronary Syndromes (Merck Manual Professional) · Prasugrel prescribing information (DailyMed) · Complications of Acute Coronary Syndromes (Merck Manual Professional) · Pericarditis (Merck Manual Professional) · Contraindications to nitroglycerin in ACS (EBM Consult) · Tadalafil prescribing information (DailyMed) · OMI ECG findings versus STEMI criteria (J Am Heart Assoc 2021) · Dyslipidemia (Merck Manual Professional) · Contraindications to Fibrinolytic Therapy for STEMI (Merck Manual Professional) · Mechanical Complications of Acute MI: AHA Scientific Statement (Circulation 2021) · Follow your institution's protocols.