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Acute Coronary Syndrome / Chest Pain

Category: Medical Sources: raw/protocols/nm-sop-guidelines-treatment-2022.pdf; UCLA EMT Ultimate Study Guide (2026) Last updated: 2026-05-06

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

NREMT Differentiators

Cardiovascular Chest Pain Comparison

Condition Onset Pain Quality NTG Response Distinguishing Finding Priority
Stable Angina Exertion Pressure, predictable Relieved <5 min Reproducible with same exertion Low–Moderate
Unstable Angina Rest or minimal exertion Pressure Partial or no relief New, worsening, or unpredictable High
STEMI / AMI Sudden or gradual Crushing pressure, diaphoresis No relief ST elevation on 12-lead; priority transport Highest
CHF / Pulmonary Edema Gradual Heaviness, orthopnea Partial Bilateral rales, JVD, edema, pink frothy sputum High
Cardiac Tamponade Variable Pressure No Beck's Triad: JVD + muffled heart sounds + hypotension Highest
Hypertensive Emergency Variable Pressure or headache No SBP >180 + end-organ signs (HA, AMS, visual changes) High

KEY DIFFERENTIATOR — Tamponade: Beck's Triad = JVD + muffled/distant heart sounds + hypotension. Narrow pulse pressure. Veins are FULL (opposite of hemorrhagic shock). EMT-B treatment: rapid transport only.

KEY DIFFERENTIATOR — Unstable vs. Stable Angina: Stable = predictable, relieved with rest and NTG. Unstable = at rest, lasts >20 min, NTG doesn't fully relieve it. Unstable angina IS an ACS — treat as MI until proven otherwise.

AMI vs. Aortic Dissection

Feature AMI Aortic Dissection
Pain onset Gradual to sudden Maximal at onset ("worst pain of my life")
Pain quality Pressure, crushing Tearing or ripping
Radiation Left arm, jaw, neck Tearing to back, between shoulder blades
BP finding Often low (cardiogenic shock) Unequal BPs in bilateral arms
NTG May help (if SBP >100) DO NOT give — drops BP dangerously
Key test (field) 12-lead EKG Bilateral BP comparison
Transport PCI center Surgical center

KEY DIFFERENTIATOR — Aortic Dissection: Tearing back pain + unequal bilateral arm BPs = dissection until proven otherwise. NTG is contraindicated. Transport to surgical center, not PCI.

NTG Contraindications

Absolute contraindications — do NOT give NTG if ANY of these are present:

Contraindication Reason
SBP < 100 (hypotension) Will worsen hypotension → cardiovascular collapse
HR < 60 (bradycardia) May indicate inferior MI + RV involvement
HR > 140 (tachycardia) May be compensatory; NTG drops preload dangerously
PDE5 inhibitor within 72 hours Sildenafil (Viagra), tadalafil (Cialis), vardenafil (Levitra) → fatal hypotension
Suspected inferior MI / RV infarct RV depends on preload; NTG kills it

KEY DIFFERENTIATOR — PDE5 Inhibitors: The 72-hour window is the classic NREMT distractor. Ask every ACS patient about erectile dysfunction medications. Sildenafil/Cialis/Levitra within 72 hours = absolute contraindication, no exceptions.

KEY DIFFERENTIATOR — Inferior MI: Right-side leads or clinical suspicion of inferior MI (bradycardia, hypotension, JVD without rales) = do NOT give NTG. RV infarcts are preload-dependent; NTG drops preload → crash.

Anginal Equivalents (Atypical ACS Presentations)

The NREMT loves atypical presentations — especially in women, elderly, and diabetics:

Population Common Atypical Presentation
Women Fatigue, jaw pain, nausea, back pain — no chest pain
Elderly Syncope, weakness, confusion, dyspnea
Diabetics Silent MI — no pain (neuropathy blunts sensation), only diaphoresis/weakness
Inferior MI Epigastric pain ("indigestion") — vagal component; associated bradycardia

NREMT RULE: Never withhold aspirin or ACS treatment because the presentation is atypical. If ACS is plausible, treat it as ACS.

Key Numbers — ACS

Parameter Value
Aspirin dose 324 mg chewed (not swallowed)
NTG dose 0.3–0.4 mg SL, q 3–5 min, max 3 doses
NTG SBP floor SBP ≥ 100
O2 target SpO2 ≥ 94% (do not hyperoxidize stable patient)
STEMI goal Minimize scene time; advance notification; PCI center
PDE5 window 72 hours

Sources

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