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

version from 2015-09-14 07:06

## 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)

## Section 4

Do the leads I, II and III move from left to right, or right to left?left to right
Do the leads V1 - V6 move from left to right, or right to left?right to left
If the QRS complex in a lead is predominantly upwards, what does that mean?Depolarisation is moving towards that lead/electrode
If the QRS complex in a lead is predominantly downwards, what does that mean?Depolarisation is moving away from that lead/electrode
If the QRS complex in a lead is even, what does that mean?Depolarisation is moving at a right angle from that lead
In a normal heart, what should the QRS complex in leads I, II and III be?Predominantly upwards, especially II
If the RV becomes hypertrophied, what will happen to the QRS complexes in leads I, II and III?I becomes negative, III will become more positive (this is called right axis deviation)
If the LV becomes hypertrophied, what will happen to the QRS complexes in leads I, II and IIIIII and possible II will become negative - not significant unless II is negative