'A' Level Medical Option Questions - The Heart - ECG

Q5. Electrodes are placed on the surface of a body to record an ECG trace for a healthy person. The trace obtained for one heartbeat is shown below.


(i) Label approximate scales on each axis.

y-scale: +1 to –0.2 V

x-scale: 0 to 1.0 s

(ii) State what electrical event happens at points A and B and the physical change that results.

position A:

event - sino atrial node fires

result - atria contracts

position B:

event - ventricular node fires

result - ventricles contract

6 marks

(b) State, giving a reason, one precaution you would take when attaching the electrodes to the surface of the skin to ensure a good signal is obtained.

precaution: remove dead skin [or use conducting/electrode gel]

reason: to give best possible contact between person and electrode

2 marks

(c) The amplifier used must have a high gain. State two other properties of the amplifier.

low noise

high input impedance

2 marks

Total 10 marks