12-Lead ECG Basics for Paramedic Students
STEMI recognition, reciprocal changes, and the paramedic-level ECG patterns that show up on the NREMT and in the back of the ambulance.
February 18, 2026 · 12 min read
12-lead interpretation is the single biggest jump between AEMT and paramedic practice. Get comfortable with the basics and the rest of paramedic cardiology becomes tractable.
The 12 leads, grouped
- Inferior: II, III, aVF
- Lateral: I, aVL, V5, V6
- Septal: V1, V2
- Anterior: V3, V4
STEMI criteria
≥ 1 mm of ST elevation in two contiguous limb leads, or ≥ 2 mm in two contiguous precordial leads (≥ 1.5 mm in women for V2–V3). New LBBB with symptoms is treated as a STEMI equivalent in many systems.
Reciprocal changes
Reciprocal ST depression in the leads opposite the infarct is highly specific for a true STEMI. An inferior MI (II, III, aVF) with reciprocal depression in I and aVL is a classic pattern.
The right-sided ECG
Inferior STEMI? Always get a V4R. If the right ventricle is involved, nitroglycerin can drop the preload and crash the patient. This is a favorite paramedic exam trap.
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