Describe how a doctor can use an electrocardiogram (ECG) to assess the condition of a patient's heart. Include in your answer what an ECG measures and what information it provides.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
An ECG records the electrical activity of the heart.
The electrodes placed on the skin detect the voltage changes produced by depolarisation and repolarisation of the cardiac muscle, producing a trace that shows voltage against time.
From the trace the doctor can count the number of QRS complexes per minute to give the heart rate.
If the pattern of the waves is irregular or shows abnormal intervals, this indicates an arrhythmia or other problem with the heart.
A normal ECG shows a regular, repeating pattern; any deviation from this normal pattern signals a fault, disease or damage to the heart.
The electrodes placed on the skin detect the voltage changes produced by depolarisation and repolarisation of the cardiac muscle, producing a trace that shows voltage against time.
From the trace the doctor can count the number of QRS complexes per minute to give the heart rate.
If the pattern of the waves is irregular or shows abnormal intervals, this indicates an arrhythmia or other problem with the heart.
A normal ECG shows a regular, repeating pattern; any deviation from this normal pattern signals a fault, disease or damage to the heart.
Examiner tips
- Use the exact terms "electrical activity", "voltage against time", "heart rate", "arrhythmia" and "normal repeating pattern".
- Show the logical flow: what is recorded → what the trace shows → how heart rate is derived → how abnormalities are recognised.
- Keep the answer concise, matching the 5 marks exactly.
Common mistakes
- Confusing ECG with other tests such as an ECG machine’s output with a heart‑sound auscultation.
- Using vague phrases like "heart beats" instead of "QRS complexes" or "heart rate".
- Omitting the link between abnormal patterns and arrhythmia or disease.
Mark scheme (5 marks)
- An ECG records/detects the electrical activity of the heart
- The ECG produces a trace/pattern showing voltage against time
- The trace can be used to determine heart rate / how many times the heart beats per minute
- An irregular trace / abnormal pattern indicates an irregular heartbeat / arrhythmia / problem with the heart
- A normal ECG trace has a regular repeating pattern, so differences from normal indicate a fault / disease / damage to the heart
Key terms in this question
Related
- All AQA A-Level Physics (7408) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
More Biological Measurement questions
- Describe how body temperature is measured using a clinical thermometer and expla…
- Explain why blood pressure is measured at two different values and describe what…
- Explain how a spirometer is used to measure lung function and describe what the …
- Explain why it is important that a pulse oximeter can measure both heart rate an…