Electrocardiograms
7.8 iii) Understand how the use of electrocardiograms (ECGs) can aid the diagnosis of cardiovascular
disease (CVD) and other heart conditions.
Electrocardiographs
• Electrocardiograph: A machine that record the electrical activity of the heart.
• Heart muscle depolarises when it contracts and repolarises when it relaxes.
• An electrocardiograph records changes in electrical charge using electrodes placed on the chest.
• A trace produced by an electrocardiograph is called an electrocardiogram (ECG).
Electrocardiograms (ECGs)
• P Wave: Depolarisation/contraction of the atria (atrial systole); initiated by the SAN.
• PR Interval: Time for impulses to be conducted from the SAN across the atria to the ventricles,
through the AVN.
• QRS Complex: Depolarisation/contraction of the ventricles (ventricular systole).
• T Wave: Repolarisation/relaxation of the ventricles (diastole).
Heart Conditions
• Tachycardia: Increased heart rate (>100bpm).
• Bradycardia: Reduced heart rate (<60pbm).
• Fibrillation: Irregular heart beat – atria and ventricles have lost their rhythm.
• Ischaemia: Heart muscle does not receive blood due to atherosclerosis blocking coronary arteries.
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