Electrocardiogram (ECG)

Question 1

Cardiac Cycle

Answer 1

Phases of cardiac cycle:

1. Atrial depolarisation
2. Ventricular depolarisation (alongside ‘invisible’/obscured atrial repolarisation)
3. Ventricular repolarisation

Question 2

Placement of Positive electrode in Classical ECG reading

Answer 2

Positive electrode at apex of heart

Question 3

1st wave in Classical ECG Recording

Answer 3

Wave of depolarisation of atrial cells causes upwards deflection, then back to ‘isoelectrical cells’ as there is no movement of charge

Question 4

What happens after the 1st wave in a classical ECG recording

Answer 4

Straight line as a result of delay from AV node

Question 5

What happens during the beginning of ventricular depolarisation

Answer 5

Septum first depolarises away from the positive electrode causing a small dip in the ECG trace

Question 6

What happens during the main wave of an ECG

Answer 6

The charge goes from the septum through to the ventricular wall; mainly towards the electrode, causing a huge upwards deflection in the trace; magnitude indicates the number of cells

Question 7

Describe the ECG trace after the main spike

Answer 7

Once all the cells have depolarised, there stops being a change in charge and the spike returns back to the isoelectric point;
there may be some overshoot as a result of depolarisation coming around the heart away from the positive electrode;

After this, the impulse ends and a return to the isoelectric point occurs

Question 8

What occurs during the repolarisation of the heart on an ECG

Answer 8

Cardiomyocytes repolarise beginning at the apex and move in the opposite direction of the depolarisation wave