ECG Glossary
A comprehensive A-to-Z reference of electrocardiogram terms, waveforms, and diagnoses.
Medical Disclaimer: This glossary is for educational purposes only. ECG interpretation requires formal training. Always consult a qualified healthcare provider for clinical decisions.
About This ECG Glossary
This glossary covers the fundamental terminology used in electrocardiography (ECG/EKG) — from basic waveform components (P wave, QRS complex, T wave) to clinical diagnoses (atrial fibrillation, bundle branch block, ventricular tachycardia) and technical concepts (lead placement, calibration, artifacts).
Who Is This For?
This resource is designed for medical students, nursing students, paramedics, and health-conscious individuals who want to better understand ECG reports. It provides concise, clinically accurate definitions written in accessible language. For in-depth learning, consider pairing this glossary with dedicated ECG textbooks and clinical practice.
ECG Basics
An electrocardiogram records the electrical activity of the heart over time using electrodes placed on the skin. The standard 12-lead ECG provides a comprehensive view of cardiac electrical activity from multiple angles. Wearable devices like Apple Watch use a single-lead (Lead I) configuration, which is effective for detecting common rhythm abnormalities including atrial fibrillation.
Frequently Asked Questions
What is an ECG (electrocardiogram)?
An ECG (or EKG) is a test that records the electrical activity of your heart over time. It shows the heart's rhythm, rate, and electrical conduction patterns through characteristic waves (P, QRS, T). Modern smartwatches like Apple Watch can record a single-lead ECG, while hospitals use 12-lead ECGs for comprehensive analysis.
What do the P wave, QRS complex, and T wave represent?
The P wave represents atrial depolarization (upper chambers contracting). The QRS complex represents ventricular depolarization (lower chambers contracting) — it's the largest wave because the ventricles are the heart's main pumps. The T wave represents ventricular repolarization (ventricles recovering for the next beat).
What is the difference between ECG and EKG?
ECG and EKG mean exactly the same thing — electrocardiogram. 'EKG' comes from the German spelling 'Elektrokardiogramm' and is commonly used in American English to avoid confusion with 'EEG' (electroencephalogram, which measures brain activity). Both abbreviations are correct and interchangeable.
Can a smartwatch ECG replace a hospital ECG?
No. Smartwatch ECGs record a single lead (Lead I equivalent), while hospital ECGs use 12 leads that view the heart from multiple angles. A smartwatch ECG can detect rhythm abnormalities like atrial fibrillation but cannot diagnose heart attacks, ischemia, or structural issues that require multi-lead analysis.
What ECG terms should I know before talking to my doctor?
Key terms include: sinus rhythm (normal heartbeat), arrhythmia (irregular rhythm), tachycardia (fast heart rate >100 bpm), bradycardia (slow heart rate <60 bpm), premature contractions (PAC/PVC — extra beats), atrial fibrillation (AFib — irregular upper chamber rhythm), and QT interval (time for ventricles to reset).
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