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Acute Coronary Syndrome / Chest Pain

Category: Medical Sources: raw/protocols/nm-sop-guidelines-treatment-2022.pdf Last updated: 2026-04-03

Overview

Acute Coronary Syndrome (ACS) encompasses unstable angina, non-ST-elevation myocardial infarction (NSTEMI), and ST-elevation myocardial infarction (STEMI). The underlying mechanism is disruption of a coronary artery atherosclerotic plaque, causing partial or complete occlusion and myocardial ischemia. STEMI — complete occlusion with ST elevation on 12-lead EKG — is a time-critical emergency requiring rapid transport to a percutaneous coronary intervention (PCI) capable facility.

Prehospital EMT-B priorities: recognize ACS presentation, administer aspirin, provide oxygen as indicated, minimize scene time, notify the receiving hospital early for STEMI activation.

Key Points

  • Presentation is highly variable — classic crushing substernal chest pressure radiating to left arm/jaw is only one presentation
  • Women, elderly, and diabetic patients more commonly have atypical presentations: nausea, fatigue, jaw pain, back pain, shortness of breath without chest pain
  • Atypical presentations can include CHF, syncope, or shock
  • Do not withhold aspirin based on atypical presentation if ACS is plausible
  • STEMI requires immediate advance notification to receiving hospital — activates cath lab team
  • "Time is muscle" — every minute of STEMI = myocardial cell death

Assessment Relevance

History (history-taking): - OPQRST: Onset (sudden vs. gradual), character (pressure, tightness, crushing, squeezing — not usually sharp), radiation to left arm/jaw/shoulder/back, severity, associated diaphoresis, nausea, dyspnea - SAMPLE: Prior cardiac history, hypertension, diabetes, smoking, medications (nitrates, beta-blockers, statins indicate cardiac disease), allergies (aspirin), last intake, events preceding pain

Physical exam (secondary-assessment): - Vital signs: BP bilaterally if STEMI suspected, pulse quality, SpO2, respiratory rate - Skin: pale, cool, diaphoretic = high acuity - Lung sounds: rales/crackles suggest CHF component - JVD and peripheral edema: suggest heart failure

Priority patient indicators: diaphoresis, hypotension (SBP <100), altered LOC, respiratory distress, syncope

Procedures

  1. Scene size-up: scene-size-up — BSI, scene safety; ACS is medical NOI
  2. Primary assessment: primary-assessment — airway, breathing, circulation; shock signs determine priority
  3. Administer aspirin 324 mg chewed if no contraindications — see aspirin
  4. Apply oxygen if SpO2 <94% or respiratory distress — see oxygen-administration
  5. Position patient of comfort — typically semi-Fowler (unless hypotensive)
  6. Obtain 12-lead EKG if available; transmit to hospital for STEMI identification
  7. Minimize scene time; transport to appropriate facility (PCI center for STEMI if available)
  8. Advance notification to receiving hospital with STEMI alert if indicated
  9. IV access en route (EMT-I/P scope)
  10. Nitroglycerin: requires online medical direction; administer patient's own NTG per protocol
  11. Continuous reassessment: reassessment — vital signs every 5 min, watch for deterioration to cardiac arrest

NM Protocol Notes

From NM EMS Treatment Guidelines (2022):

EMT-B scope: - Administer ASPIRIN 324 mg chewed if suspected ACS and no allergy (standing order for EMT-B) - Oxygen: titrate to maintain SpO2 — do not hyperoxidize a stable patient - Obtain 12-lead EKG if equipment available; transmit to hospital for STEMI screening - Advance notification to receiving hospital for identified STEMI patients — activate hospital STEMI system of care - Minimize scene time; transport to appropriate medical facility - Contact online Medical Control for nitroglycerin administration

Nitroglycerin (patient's own medication, or per protocol — requires medical direction): - 0.3–0.4 mg SL, may repeat every 3–5 minutes, maximum 3 doses - Criteria for NTG: SBP >100 systolic AND HR >60 AND HR <140 - Do NOT give NTG if: patient used sexual performance enhancing drug (SPED/PDE5 inhibitor — sildenafil, tadalafil, vardenafil) within last 72 hours, OR concern for inferior MI - IV must be initiated prior to NTG administration, or given with online Medical Control approval if IV unavailable - If transport is prolonged, contact Medical Control for additional NTG doses

ALS-only medications (not EMT-B scope): Morphine 4–10 mg IV/IO, Fentanyl 25–100 mcg IV/IO, anti-emetics. EMT-B does not administer these but should understand they exist for ALS intercept coordination.

STEMI destination: Transport to hospital with cardiac catheterization laboratory offering PCI. Bypass non-PCI hospital if PCI center is accessible within appropriate time window.

NREMT Relevance

High-frequency topic. Common question angles: - Classic vs. atypical ACS presentation; recognition in women/elderly/diabetics - Aspirin dose (324 mg) and administration method (chewed) - Nitroglycerin contraindications — PDE5 inhibitors within 72 hours is a classic NREMT distractor - STEMI vs. NSTEMI differentiation (ST elevation on EKG) - Priority decision: diaphoresis + chest pain + hypotension = priority transport - Advance hospital notification for STEMI

Sources

  • raw/protocols/nm-sop-guidelines-treatment-2022.pdf — Chest Pain/ACS/STEMI protocol (p. 1–2)