Electrocardiography (ECG)
Physics: AQA A Level, topic 10.3.1
ECG Machines
An electrocardiogram (ECG) is a record of the voltages created by the wave of depolarization and repolarization in the heart.
The heart
- The heart is made up of four chambers, the top two being atriums, the bottom two being ventricles.
- The right and left atria receive blood from the body and lungs, respectively, and pump the blood into the ventricles.
- The right and left ventricles, in turn, pump blood through the lungs and the rest of the body, respectively.
Polarization
- Depolarization of the heart muscle causes it to contract. After contraction, it is repolarized to ready it for the next beat.
- The ECG measures components of depolarization and repolarization of the heart muscle.
- An ECG can give us a lot of information about if the heart is functioning well.
ECG Waveform
The heartbeat and polarization waves create a characteristic waveform.
P wave
- The major features of an ECG wave are labelled P, Q, R, S, and T.
- The P wave is from the depolarization and contraction of the atria as they pump blood into the ventricles.
QRS wave
- The QRS part of the wave is created by the depolarization of the ventricles as they pump blood to the lungs and body.
- The QRS complex has this typical shape and time span.
- The QRS signal also masks the repolarization of the atria, which occur at the same time.
T wave
- Finally, the T wave is generated by the repolarization of the ventricles.
- The T wave is followed by the next P wave in the next heartbeat.
Test yourself on Electrocardiography (ECG)
Which of these statements are true about ECG machines?
What does an ECG measure?
What does the p wave of an ECG represent?