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Acute Coronary Syndrome: UA / NSTEMI / STEMI

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ACS recognition, ECG/troponin workflow, risk stratification, antiplatelet/anticoagulation basics, cath timing, and red flags.

Combines unstable angina, NSTEMI, and STEMI.

Last reviewed

June 12, 2026

Sources / guidelines to verify

2025 ACC/AHA/ACEP/NAEMSP/SCAI Acute Coronary Syndromes Guideline (unified ACS guideline)
2021 AHA/ACC Chest Pain Guideline (hs-troponin 0/1h–0/2h pathways)
Sgarbossa EB, et al. NEJM 1996; Smith SW, et al. (modified Sgarbossa) Ann Emerg Med 2012, validated Meyers HP, et al. 2015 — STEMI within LBBB/paced rhythm
Local STEMI activation & door-to-balloon protocol

Disclaimer: Educational reference only. Not a substitute for clinician judgment, local protocols, or current guideline review.

One-page reference

Clinically reviewed by the site owner. Still verify against the sources above and local protocol before clinical use.

What it is / why it matters

Spectrum from unstable angina / NSTEMI to STEMI, driven by plaque rupture and thrombosis.
Time-critical — "time is muscle."

Key diagnostic clues

Chest pain/pressure ± radiation, dyspnea, diaphoresis, nausea; often atypical in women, elderly, and patients with diabetes.
STEMI: ST-segment elevation meeting criteria. New LBBB with ischemic symptoms → apply Sgarbossa/modified-Sgarbossa, not automatic activation.
NSTEMI: ST depression, T-wave inversions, or a nondiagnostic ECG.
Serial high-sensitivity troponin using a 0/1-h or 0/2-h algorithm.

Initial workup

12-lead ECG within 10 minutes of arrival; repeat if symptoms persist.
Serial hs-troponin, IV access, continuous monitoring, aspirin.
Risk-stratify (HEART/GRACE/TIMI); echo; CCTA for low–intermediate risk without ischemia.

Management framework

STEMI

Emergent reperfusion — primary PCI (door-to-balloon <90 min)
Fibrinolysis if timely PCI is unavailable

NSTEMI

Risk-stratify; early invasive strategy (≤24 h) for high-risk features
Antithrombotic therapy

Antithrombotics & adjuncts

Aspirin + a P2Y12 inhibitor (ticagrelor or prasugrel preferred)
Anticoagulation (e.g., heparin)
High-intensity statin; beta-blocker if no shock; nitrates for symptoms; treat hypoxia/pain

Secondary prevention

DAPT, statin to LDL <55, BP control, GDMT if reduced EF, cardiac rehab, risk-factor modification

Red flags / escalate now

STEMI → activate the cath lab immediately.
Ongoing/refractory chest pain, hemodynamic instability, or cardiogenic shock.
Sustained VT/VF; mechanical complications (new murmur, tamponade).

Follow-up / monitoring

Trend troponin; echo for EF.
Reinforce secondary prevention, medication adherence, and cardiac rehab.

Clinic pearls

Get the ECG fast and repeat it with ongoing pain.
A single normal troponin is not enough early — use serial/0-1h sampling.
Posterior MI: V1–V3 ST depression with a tall R wave — obtain posterior leads.

Related quick references

📄 Stable Angina / Chronic Coronary Disease 📄 Coronary Vasospasm / Prinzmetal Angina 📄 Cardiogenic Shock

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