How to Read an ECG in 7 Steps

How to Read an ECG in 7 Steps (Beginner’s Guide for Paramedics and Students)

Interpreting an ECG can feel overwhelming at first — all those waves, spikes, and measurements. But it doesn’t have to be.

This guide breaks down ECG interpretation into seven simple, repeatable steps. Whether you're a student, newly qualified paramedic, or brushing up on the basics, this method will give you a structured, confident approach to ECGs — especially in the pre-hospital setting.

Why ECG Interpretation Matters

Electrocardiograms are essential in recognising life-threatening conditions like STEMIs, conduction blocks, and dangerous arrhythmias. A clear, step-by-step method ensures you don’t miss important details, and helps you deliver more confident handovers to hospital teams.

Step 1: What’s the Heart Rate?

Start by working out the heart rate. You can use the 300 method (300 divided by the number of large boxes between R waves) or count the number of QRS complexes in a 10-second strip and multiply by 6.

Ask:

• Is the patient bradycardic or tachycardic?

• Is the rate appropriate for the clinical context?

Step 2: Is the Rhythm Regular?

Mark the R–R intervals across the strip. Are they consistent?

• If regular: Consider sinus rhythm, SVT, or flutter.

• If irregular: Could be atrial fibrillation, frequent ectopics, or second-degree AV block.

Step 3: Is the Axis Normal?

Use leads I, II, and III to assess the QRS axis quickly.

• Positive in I and II = normal axis

• Positive in I, negative in II = possible left axis

• Negative in I, positive in III = right axis

Abnormal axis may point to underlying conduction delays, ventricular strain, or prior infarcts.

Step 4: Are P Waves Present and Is the PR Interval Normal?

Look for P waves before every QRS complex.

• Absent P waves may suggest atrial fibrillation or junctional rhythm.

• A prolonged PR interval (>200 ms) suggests first-degree AV block.

• A short PR interval may indicate pre-excitation (e.g. WPW).

Step 5: Is the QRS Complex Narrow or Broad? What About the QT Interval?

• A narrow QRS (<120 ms) suggests a supraventricular origin.

• A broad QRS (>120 ms) suggests a ventricular origin or bundle branch block.

Check the QT interval (QTc) — if prolonged, the patient may be at risk of arrhythmias like Torsades de Pointes.

Step 6: Is There Any ST Elevation or Depression?

Look closely at the ST segments in contiguous leads.

ST elevation at the J point is significant if it meets the following criteria:

• V2–V3:

  • 2.5 mm in men under 40

  • 2 mm in men over 40

  • 1.5 mm in women

• Other leads: ≥1 mm

Also look for ST depression, which may indicate reciprocal changes or ischaemia.

Step 7: Are There Any T Wave Abnormalities?

T wave changes can provide early clues to ischaemia or electrolyte imbalance.

Look for:

• Peaked T waves (e.g. hyperkalaemia)

• Inverted T waves (e.g. ischaemia, strain)

• Biphasic T waves (e.g. Wellens syndrome)

• Flattened or absent T waves

• Hyperacute T waves (early sign of STEMI)

• Camel-hump T waves (often seen in hypothermia or electrolyte imbalance)

Common Mistakes in ECG Interpretation

• Skipping rhythm analysis

• Ignoring the axis or dismissing it as irrelevant

• Confusing ST elevation with pericarditis or early repolarisation

• Forgetting to correlate ECG findings with the patient’s presentation

Final Thoughts

By using this 7-step approach every time, you’ll develop a structured, methodical way to interpret ECGs — one that holds up under pressure, even on scene.

This isn’t about guessing what’s wrong. It’s about having a clear system to spot the signs, rule in or out key conditions, and support clinical decisions confidently.

Free Resource: Download the ECG eBook

Want to reinforce this method with a printable guide?

Download our free ECG interpretation eBook — the same one used in our 3-part ECG email training series. It breaks down each of the 7 steps with annotated rhythm strips and tips.

[Download the ECG eBook here]

Bonus Tool: The ECG 7-Step Ruler

Want a physical tool to guide you through each of these steps?

Check out our transparent ECG ruler, designed specifically to help students, paramedics, and emergency clinicians interpret ECGs quickly and systematically.

[See the ECG Ruler Now]