ECG Basics Flashcards
What is the purpose of an ECG?
It is a graphical representation of the electrical activity of the heart.
What is depolarisation?
Depolarisation occurs when the membrane potential gets smaller and the overall charge on the inside of the becomes more positive than the overall charge outside of the cell.
Which ion is involved in propagating the wave of depolarisation in phase 4?
Ca2+ ions via gap junctions.
Which is the major channel/ion is involved in rapid depolarisation of the cell membrane in phase 0?
Na2+
Voltage-gated sodium channels
Which ion/channel is responsible for stimulating the initial repolarisation of the cell membrane in phase 1?
K+
voltage-gated potassium channels
Which phase is referred to as the “plateau phase?
Phase 2
Which ion is responsible for maintaining the plateau aspect of depolarisation in phase 2?
Ca2+
How many electrodes are placed on the body during a 12-lead ECG?
10 electrodes
How many chest electrodes are there?
6
Where, anatomically, should you place each of the chest electrodes (V1-V6)?
V1: Right 4th intercostal space, sternal border
V2: Left 4th intercostal space, sternal border
V3: midway between V2 and V4
V4: 5th intercostal space, in the mid-clavicular line
V5: 5th intercostal space, in the left anterior axillary line (on the same horizontal plane as V4)
V6: left mid axillary line (same horizontal plane as V4 and V5)
What does the P wave represent?
Atrial depolarisation/contraction
Records the wave of depolarisation travelling from the SA node towards the AV node.
What is represented by the PR segment?
Ventricular filling
Slow spread of depolarisation/conduction at the AV node
What does the Q wave represent?
Depolarisation of the inter-ventricular septum
What does the R wave represent?
Ventricular depolarisation
What does the PR interval represent?
The time taken for the depolarisation to spread from the SA node across the atrium and down to the ventricular muscle via the bundle of His
What does the S wave represent?
Depolarisation at the base of the ventricles
What does the QRS complex represent?
Represents the whole ventricular depolarisation
What does the T wave represent?
Ventricular repolarisation
What does the ST segment represent?
The interval between ventricular depolarisation and repolarisation: the interval in which the entire ventricular myocardium is now depolarised.
Name the views of the heart provided by the chest leads
V1: Septum view V2: Septum view V3: Anterior wall of ventricles V4: Anterior wall of ventricles V5: Lateral/left view V6: Lateral/left view
Names the views of the heart provided by the limb leads
I: Lateral view
II: Inferior view
III: Inferior view
aVF: inferior view
aVL: Lateral view
aVR: lateral view
Which leads have an inferior view of the heart?
I, III and avF
Which leads have a lateral view of the heart?
I, aVL, aVR, V5, V6
Which leads have an anterior view of the heart?
V3, V4
