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

Q2. Electrodes are attached to the chest of a healthy person and a normal ECG waveform is obtained.

(a) State two ways of ensuring good electrical contact between the electrodes and the person.

  • electrodes must be made from a material which does not become polarised
  • electrodes must be coated with conducting gel
  • hair and dead skin must be removed from the patient

2 marks maximum

(b) State two properties of the amplifier needed to amplify the signal from the electrodes.

The amplifier nust have:

  • high gain
  • high input impedance
  • low noise
  • frequency response should be even across the frequency range

2 marks

(c) Sketch, on the axes below, the waveform that you would expect to obtain. Label the axes with appropriate scales.

- see graphic for suitable shape

- see graphic for suitable values marked on the axes

Mark on the waveform where the following occur:

(i) atrial depolarisation - see graphic

(ii) ventricular depolarisation - see graphic

(iii) ventricular repolarisation. - see graphic

5 marks

Total 9 marks