How to Read an ECG Step by Step (EMT and Paramedic Guide)

ECG interpretation feels like pattern recognition to experienced medics, but on the NREMT it is a checklist. Run the same six steps every single time and even unfamiliar strips become answerable.

Step 1 — Rate

Count R waves in a 6-second strip and multiply by 10. Under 60 is bradycardia, over 100 is tachycardia. Rate alone eliminates half the answer choices on most questions.

Step 2 — Regularity

March out the R-R intervals. Regularly irregular suggests a repeating pattern (second-degree block, sinus with PVCs). Irregularly irregular with no P waves is atrial fibrillation.

Step 3 — P waves

• One upright P before every QRS: sinus origin
• No P waves, chaotic baseline: atrial fibrillation
• Sawtooth baseline: atrial flutter
• More P waves than QRS complexes: AV block

Step 4 — PR interval

Normal is 0.12–0.20 seconds (3–5 small boxes). Long but constant is first-degree block. Progressively lengthening until a dropped beat is Wenckebach (second-degree Type I). Constant PR with random dropped beats is Type II — the dangerous one.

Step 5 — QRS width

Under 0.12 seconds is narrow and supraventricular. Wide means ventricular origin, a bundle branch block, or a paced beat. Wide plus fast plus no pulse is treated as ventricular tachycardia — do not talk yourself out of it.

Step 6 — ST segments and T waves

ST elevation of 1 mm or more in two anatomically contiguous leads (2 mm in V2–V3 for men under 40) is a STEMI. Depression and inverted T waves suggest ischemia. Always correlate with the patient in front of you.

The traps

• Treating the monitor instead of the patient — always check a pulse
• Calling artifact a rhythm — reposition and repeat
• Ignoring the reciprocal changes that confirm a STEMI
• Missing that a wide-complex tachycardia in an unstable patient needs electricity, not more diagnosis

Pair this method with our 12-lead placement reference and dysrhythmia drills, then run timed practice questions until the six steps happen automatically.