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


(a) Sketch a graph of the ECG trace for a healthy heart. Label each axis with appropriate units and scales.

time/seconds on x-axis and potential/ mV on y-axis

correct value on x axis (between 0.9 and 1.0 s to end of trace)

correct values on y axis (start at 0, highest point between 0.8 and 1.0 mV)

shape of curve - you were not asked for the letters - but they are useful to add!

4 marks

(b) When obtaining such a trace, electrodes are attached to the patient. State and explain two precautions which should be taken when attaching the electrodes to ensure reception of the best signal.

attach firmly
stop noise
remove dead skin/hair
reduce contact resistance
use conducting gel
remove air for better electrical contact
positioning of electrodes
to get largest pd

2 marks maximum

Total 6 marks