# ECG Made Easy - Chapter 1 - What the ECG is about

hixatumu's version from 2016-03-06 14:32

## Section 1

Where does electrical discharge of each cardiac cycle start?In the Sino-Atrial Node in the Right Atrium
Where does the wave of depolarisation spread to after the SA node and the atrium?The Atrio-ventricular node
Where does the wave of depolarisation spread down after the AV node?The bundle of His
What does the bundle of His divide into?2 Left Bundle Branches and 1 Right Bundle Branch
Which fibres allow spread of depolarisation through the ventricular muscle?Purkinje fibres
What is meant by sinus rhythm?When the cardiac cycle starts in the SA node

## Section 2

Which wave(s) represents depolarisation of the atria?P wave
Which wave(s) represents depolarisation of the ventricles?QRS complex
Which wave(s) represents repolarisation of the ventricles?T wave
What is a Q wave?A Q wave is a downward deflection that only occurs at the start of the QRS complex (not always present)
What is an R wave?Any upward deflection in a QRS complex
What is an S wave?Any downward deflection below the baseline following an R wave

## Section 3

How much time does a large square represent?0.2 seconds (200 milliseconds)
How much time does a small square represent?0.04 seconds (40 milliseconds)
How many large squares represent a minute?300
If a QRS complex occurs every 1 large square, what is the rhythm?300 bpm
If a QRS complex occurs every 2 large squares, what is the rhythm?150 bpm
If a QRS complex occurs every 3 large squares, what is the rhythm?100 bpm
If a QRS complex occurs every 4 large squares, what is the rhythm?75 bpm
If a QRS complex occurs every 5 large squares, what is the rhythm?60 bpm
If a QRS complex occurs every 6 large squares, what is the rhythm?50 bpm
What is the PR interval?The time between the beginning of the P wave to the beginning of the QRS complex (excitation to spread from SA node to ventricular muscle)
How long is the normal PR interval?0.12 - 0.2 seconds (3-5 small squares, 120-200 milliseconds)
How long is the normal QRS complex?0.12 seconds (120 milliseconds) or less (3 small squares or less)