Chapter 3- Basic ECG

Question 0

What is depolarisation and repolarisation in the atrium ?

Answer 0

Depolarisation in the atrium occurs when a positive current spreads across the atrial walls after excitation via the SA node, repolarisation occurs when a negative current spreads restoring the electrical potential of the atrium back to normal

Question 1

How many and where are the electrodes positioned on the body to realise a 12-lead ECG ?

Answer 1

10 electrodes are needed for a 12-lead electrocardiogram:

• 2 on the upper chest : shoulders or the harms or the wrists
• 2 on the legs or down on the foot
• 6 precordial leads across the chest, starting above the sternum down around the left side of the heart

Question 2

What is the first wave on an ECG ?

Answer 2

The first wave is the P wave and corresponds to the depolarisation of the atria

Question 3

What is the QRS complex ?

Answer 3

The QRS complex corresponds to the ventricular depolarisation which begins at the apex, while atrial repolarization occurs

Question 4

What wave corresponds to ventricular repolarization ?

Answer 4

The T wave corresponds to the ventricular repolarization which begins at the apex

Question 5

What the isoelectric line between the P wave and the QRS complex corresponds to ?

Answer 5

With atrial depolarisation complete, the impulse is delay at the AV node, this corresponds to the flat line ( isoelectric line) this give time for the atrial contraction to occur before the ventricles are activated.

Question 6

What is the the significance of the second flat line between the QRS complex and the T wave ?

Answer 6

The ventricular depolarisation is complete