# Basic ECG

oelomar's version from 2017-12-23 14:58

## Section

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.

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.

What does the horizontal axis represent on an ECG graph?Time.
What does the vertical axis on an ECG graph represent?Voltage.
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.
How much voltage does a small square represent?0.1mV.
How much voltage do two large squares represent?1mV (at standard gain setting).
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).