How to Read an ECG Electrocardiogram – A Patient-Friendly Guide by Global Health

By Global Health Cardiology Insights

www.myglobalhealth.online

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Understanding your own heart’s electrical activity might feel like medical-mumbo-jumbo, but it doesn’t have to be. At Global Health we aim to demystify this so you feel confident discussing your results. This article will walk you through the basics of an electrocardiogram (ECG, sometimes also called EKG) and help you understand what your doctor might be talking about.

1. What is an ECG - Electrocardiogram?

An ECG is a simple and non-invasive test that records the electrical activity of your heart. (ACLS Medical Training)Here’s how it works in plain language:

• Your heart has a natural “pacemaker” (the SA node) that sends electrical signals to make the atria (upper chambers) contract, then the ventricles (lower chambers) contract. (ACLS Medical Training)

• The ECG machine records those electrical impulses via electrodes placed on your arms, legs and chest. (Oxford Medical Education)

• The result is a tracing – a graph of waves and lines – which tell your cardiologist or doctor how your heart’s electrical system is working.

2. The Basic Waves & What They Mean

When you look at an ECG, you’ll see a pattern of waves that repeat with each heartbeat. Here’s a breakdown:

• P-wave: This is the first small bump. It represents atrial depolarisation – basically the electrical signal causing the atria to contract. (ACLS Medical Training)

• PR interval: The time from the start of the P-wave to the start of the QRS complex. It shows how long the signal takes to travel from the atria to the ventricles. (Life in the Fast Lane • LITFL)

• QRS complex: The large spike and drop. This shows ventricular depolarisation → the ventricles contracting. (Wikipédia)

• ST-segment: The flat line after QRS before the T wave. It’s the pause as the ventricles prepare to repolarise. (YouTube)

• T-wave: The bump after the ST segment: ventricular repolarisation – the ventricles resetting. (ACLS Medical Training)

• QT-interval: From the start of the QRS to the end of the T-wave. Reflects how long the ventricles take to depolarise AND repolarise. (UTMB WWW (ROOT))

Understanding these parts helps your doctor determine if electrical conduction is normal or abnormal.

3. A Simple System to Check an ECG

To interpret an ECG (or to follow what your doctor is explaining), here’s a systematic approach you can understand:

1. Rate – How fast is the heart beating? Normal adult resting heart rate: 60-100 beats per minute. (ghscme.ethosce.com)

   • On standard ECG paper (25 mm/s), each large square = 0.2 s, each small square = 0.04 s. (UTMB WWW (ROOT))

   • One quick method: count the number of large squares between two successive R-waves, then divide 300 by that number to approximate beats per minute. (UTMB WWW (ROOT))

2. Rhythm – Is it regular (same spacing between beats) or irregular? Are P-waves present before each QRS?

   • If P-waves are missing or inconsistent, or if QRS are irregular → may signal arrhythmia. (Geeky Medics)

3. P-wave and PR interval – Are the P-waves present and normal shape? Is the PR interval within the normal range (≈0.12-0.20 s) ? (YouTube)

4. QRS complex – Is the QRS narrow (normal) or wide (which may suggest conduction delay or bundle branch block)? Normal QRS < about 0.12 s. (YouTube)

5. ST-segment & T-wave – Is the ST-segment flat (isoelectric) or elevated/depressed? Are T-waves upright and normal?

   • ST-elevation may suggest acute myocardial infarction. (Wikipédia)

6. QT interval – Is it prolonged? A prolonged QT can increase risk of certain arrhythmias. (Life in the Fast Lane • LITFL)

Using this checklist helps you follow the medical conversation and deepen understanding of your ECG.

4. What the ECG Can Tell Us

Here are a few examples of what your ECG may indicate:

• Normal findings: Rate 60-100, regular rhythm, normal P-waves, narrow QRS, ST-segment flat/at baseline, upright T-waves.

• Tachycardia: Heart rate >100 bpm.

• Bradycardia: Heart rate <60 bpm (unless athletic or fits your baseline).

• Arrhythmias: If rhythm is irregular, P-waves missing or abnormal, QRS pattern odd.

• Ischaemia/infarction: ST-segment elevation or depression, T-wave inversions/sig­nificant changes.

• Bundle branch block or conduction delay: Wide QRS, abnormal morphology.

• Electrolyte/medication effects: e.g., QT prolongation, U-waves, T-wave changes.

Important: An ECG is one piece of the puzzle. Your symptoms, history, physical exam and other tests matter too. (Verywell Health)

5. What You Can Do as a Patient

• When your doctor shows you your ECG, use the checklist above to follow along: rate → rhythm → P-wave → QRS → ST/T → QT.

• Ask: “Is the rhythm regular?” “Is the ST-segment normal?” “Did you see any abnormality that needs follow-up?”

• Keep prior ECGs if you have them — comparing older tracings helps detect changes over time.

• If told “everything looks normal,” ask the meaning for your particular situation (symptoms, risk factors).

• Don’t panic if you see “minor changes” — many findings are benign or require context. But do make sure your doctor explains what they mean.

6. When to Seek Urgent Care

While many ECG findings are non-urgent, there are red-flags:

• New ST-segment elevation, especially with chest pain or shortness of breath → emergency.

• New high-grade arrhythmia (very fast, very slow, irregular) with symptoms (e.g., fainting, dizziness).

• Markedly prolonged QT, very wide QRS with symptoms.If you feel unwell, do not rely solely on the ECG reading — seek prompt medical attention.

7. Final Thoughts

An ECG may look like a squiggly line, but it holds a wealth of information about your heart’s electrical health. By understanding the basic components and asking the right questions, you become an empowered partner in your care.

At Global Health we encourage you to bring your ECG printout (or digital version) to consultations, ask the meaning of each part, and keep copies for future comparison. Medical jargon becomes much less intimidating when you know the fundamentals.

If you’d like a deeper dive into examples (e.g., atrial fibrillation, bundle branch block, myocardial infarction signs) we’d be happy to prepare a follow-up article. Would you like that?