More types of arrhythmias
Ventricular fibrillation
In ventricular fibrillation (VF) many random electrical impulses 'fire off' from different parts of the ventricles. The ventricles then 'fibrillate'. This means they only partially contract, which is not enough to push blood out of the heart. This is life-threatening and a common cause of 'cardiac arrest'. It is fatal unless corrected within a few minutes. It is a complication of various heart disorders, most commonly after a large heart attack (myocardial infarction).
Heart block
This is where the electrical impulses are partially or fully blocked between the atria and the ventricles. The SA node in the right atrium 'fires' at the normal rate, but the rate at which the ventricles contract (pulse rate) depends on how many impulses get through to the ventricles.
- First degree heart block means there is a slight delay in each impulse going from the atria to the ventricles. But, each impulse does get through and the heart rate is normal.
- Second degree heart block means that some impulses from the atria are not conducted through to the ventricles. The rate that the ventricles contract can then be slow.
- Third degree or 'complete heart block' means that no impulses are conducted through. The ventricles then contract at their own in-built rate of about 20-40 beats per minute. So, you have a very slow pulse.
Sick sinus syndrome
This condition is where the SA node (the heart's natural pacemaker) becomes damaged. The heart then tends to beat slowly or miss a few beats. But, in some cases the heart alternates between beating slow for a while, and then fast for a while.
There are other rare types of arrhythmias.
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