Acute Coronary Syndrome
Unstable angina, NSTEMI and STEMI (2025 ACC/AHA ACS Guideline)
Unstable angina
Chest pain at rest, new, or worsening. Troponin normal. No ST elevation. Emergency: can progress to MI.
NSTEMI
Troponin elevated. No persistent ST elevation (may show ST depression or T-wave inversion).
STEMI
ST elevation in 2 contiguous leads + rising troponin. Complete blockage: time is muscle.
Recognize it
- Pressure, squeezing or heaviness in the chest; may spread to arm, jaw, neck, back; sweating, nausea, dyspnea.
- Women, older adults and people with diabetes often have atypical symptoms: fatigue, dyspnea, nausea, epigastric discomfort.
- 12-lead EKG within 10 minutes of arrival.
- High-sensitivity troponin at arrival and repeated (rises within hours; stays up 1–2 weeks).
Which leads, which artery
| Inferior | II, III, aVF | Right coronary |
| Anterior/septal | V1–V4 | Left anterior descending |
| Lateral | I, aVL, V5–V6 | Circumflex |
Inferior MI: get right-sided leads. A right ventricular infarct is preload-dependent: avoid nitrates and diuretics; give IV fluids for hypotension.
Immediate treatment
- Aspirin 162–325 mg chewed (non-enteric-coated), unless true allergy or active bleeding.
- Nitroglycerin 0.4 mg SL every 5 min, up to 3 doses, if systolic BP ≥90. Not with sildenafil/vardenafil in the last 24 h or tadalafil in 48 h, or RV infarct.
- Oxygen only if SpO₂ <90%. Updated
- Morphine only for pain not relieved by nitrates. Updated
- Second antiplatelet (P2Y12: ticagrelor, prasugrel, clopidogrel) + anticoagulant (heparin).
- High-intensity statin; beta blocker within 24 h if no HF, shock or bradycardia.
- STEMI → PCI: first medical contact-to-device ≤90 min (≤120 min if transferring). If PCI can't happen in time: fibrinolytic within 30 min of arrival.
After PCI (cardiac cath)
- Check site, distal pulses, color, temperature and sensation as per protocol (e.g., every 15 min at first).
- Radial: compression band, release per protocol; no BP or blood draws on that arm.
- Femoral: keep leg straight and HOB low as ordered. Back or flank pain + hypotension → retroperitoneal bleed: report now.
- Contrast: hydrate; watch urine output and creatinine.
Discharge teaching
- Dual antiplatelet therapy (usually 12 months): never stop without the cardiologist; bleeding precautions.
- Chest pain at home: stop, sit, take 1 SL nitroglycerin. If not better or worse after 5 min, call emergency services; may repeat every 5 min, max 3.
- Keep nitroglycerin in its original dark glass bottle; carry it always.
- Cardiac rehab; stop smoking; heart-healthy diet; sex is usually safe once able to climb 2 flights of stairs, as cleared.
Updated: "MONA" is no longer the rule
Older guides teach Morphine, Oxygen, Nitrates, Aspirin for every MI. Routine oxygen in patients with normal saturation gives no benefit, and morphine can delay the effect of oral antiplatelet drugs. Give aspirin and nitrates; oxygen only if SpO₂ <90%; morphine only for refractory pain.