Contains the full lesson along with a supporting toolkit, including teachers’ notes.
The Normal Heart-Beat Cycle
The cardiac cycle has two distinct phases – the diastole phase and the systole phase. In the diastole phase, the heart ventricles are relaxed and fill with blood. In the systole phase, the ventricles contract and pump blood around the body through a system ofarteries.
These events are triggered by the sinoatrial node – a collection of modified myocytes that acts as the heart's pacemaker.
Normally the pulse rate (heartbeat rate) is appropriate for the body's oxygen demand. Problems can arise if the heart rate is too low or too high. If the speed is very high it can lead to ventricular fibrillation (VF) in which the heart muscle quivers and does not pump efficiently, if at all. This condition is generally fatal if not treated quickly.
Normal heart-beat can be restored by delivery of a controlled electric shock. This process is called defibrillation.
What is a Defibrillator?
Defibrillators have been in use for about sixty years. The earlier machines were comparatively large and not really portable. Emergency portable defibrillators (also called AEDs or automatic external defibrillators) are today available in many public buildings, schools, clubs etc. and small defibrillators can now be implanted surgically in patients with certain chronicheart problems.