What does an electrocardiogram (ECG) record?
Changing potential differences at the body surface arising from electrical activity in the heart.
AQA A-level Physics (7408) · 3.10.3.1
Revise AQA A-level Physics (7408) specification point 3.10.3.1, Simple ECG machines and the normal ECG waveform (A-level only), with free active-recall flashcards. Flip through the set or review every question and answer below.
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What does an electrocardiogram (ECG) record?
Changing potential differences at the body surface arising from electrical activity in the heart.
How do skin electrodes enable an ECG machine to measure voltage?
They provide connections for measuring the voltage difference between selected electrode positions.
What do different ECG leads provide?
Different electrode combinations provide different views of the heart’s electrical activity.
Why does an ECG machine amplify its measured signal?
The signal is small, typically of the order of millivolts.
What is the purpose of filtering an ECG signal?
To reduce unwanted interference.
How is an amplified ECG signal used to produce an ECG trace?
It is displayed or recorded against time.
Do ECG electrodes directly measure the heart’s mechanical movement?
No. They detect electrical signals, not mechanical movement directly.
What does a normal ECG waveform represent?
A repeating pattern of voltage changes from the heart’s electrical activity across successive cardiac cycles, not the contractions themselves.
What do the horizontal and vertical axes of an ECG represent?
Horizontal: time; vertical: measured potential difference.
How does the choice of lead affect the appearance of a normal ECG waveform?
The precise waveform appearance depends on the lead used.
What electrical event does the ECG P wave represent?
Depolarisation spreading through the atria.
What electrical event does the ECG QRS complex represent?
Ventricular depolarisation.
Why is atrial repolarisation normally not visible on an ECG?
It occurs around the same time as ventricular depolarisation and is obscured by the larger QRS complex.
What electrical event does the ECG T wave represent?
Ventricular repolarisation.
What is depolarisation in relation to heart contraction?
Electrical activation that precedes contraction.
What is repolarisation in relation to the next heart activation?
Electrical recovery that precedes readiness for another activation.