Electrocardiograms (ECGs)
- Electrocardiography can be used to monitor and investigate the electrical activity of the heart
- Electrodes that are capable of detecting electric signals are placed on the skin
- These electrodes produce an electrocardiogram (ECG)
- An ECG shows a number of distinctive electrical waves produced by the activity of the heart
- A healthy heart produces a distinctive shape in an ECG
The ECG of a healthy heart
- The P wave
- Caused by the depolarisation of the atria, which results in atrial contraction (systole)
- The QRS complex
- Caused by the depolarisation of the ventricles, which results in ventricular contraction (systole)
- This is the largest wave because the ventricles have the largest muscle mass
- The T wave
- Caused by the repolarisation of the ventricles, which results in ventricular relaxation (diastole)
- The U wave
- Scientists are still uncertain of the cause of the U wave, some think it is caused by the repolarisation of the Purkyne fibres
Using ECGs to diagnose heart problems
- If someone has a suspected heart problem a doctor will often use an ECG as a diagnostic tool
- Some heart problems produce certain shapes or waves in an ECG which allow for a diagnosis
- Tachycardia
- When the heart beats too fast it is tachycardic
- An individual with a resting heart rate of over 100 bpm is said to have tachycardia
- Bradycardia
- When the heart beats too slow it is bradycardic
- An individual with a resting heart rate below 60 bpm is said to have bradycardia
- A lot of fit individuals or athletes tend to have lower heart rates and it is usually not dangerous
- Ectopic heartbeat
- This condition is caused by an early heartbeat followed by a pause
- It is common in the population and usually requires no treatment unless very severe
- Fibrillation
- An irregular heartbeat will disrupt the rhythm of the heart
- Severe cases of fibrillation can be very dangerous, even fatal
Each of these ECGs shows different faulty heartbeats. The speed or rhythm/regularity of the heartbeat is very important.
