What is a normal ECG?
The electrocardiogram (ECG) is a key diagnostic tool in medicine; providing information on cardiac function and structure. But what does a normal one look like. Let’s start with some basics.
Normal ECG impulse
A normal ECG. The longer version of II at the bottom is called the ‘rhythm strip’.
ECG regions of the heart (see below)
Rate
Normal heart rate is 60-100 bpm
Rhythm
The QRS complex is regular with a and presence/absence of P waves. This is called sinus rhythm.
Axis
Normal Axis = QRS axis between -30° and +90°
Run through of components of ECG
1. P waves
A normal P wave is present and upright, and <2.5 mm (2.5 small squares) high and <3 mm (3 small squares) wide
2. PR interval
Normal PR interval = 3-5mm (5 small squares). You are looking for:
3. Q waves
A small Q wave (2 mm (2 small squares or less) is present and downward in most leads (except V1-3, where they are always pathological).
4. QRS complex
- Width = <3mm (3 small squares)
- Height = <5mm (5 small squares) in the standard (limb) leads or <10 mm in the chest leads.
5. ST section
A normal ST section is flat and on the isoelectric line.
6. T waves
A normal T wave is present and most are upright (I, II, aVF, aVL, and V2-6).
7. Q-T interval
Normal QT interval is 9-11 mm (small squares).
Summary
We have demonstrated a normal ECG. We hope it has been helpful.
