Broadly speaking, arrhythmias are split according to two things: site and heart rate.
Put into medical speak:
- Site of abnormality
- Abnormalities of heart rate
Atrial ectopics are extra contractions of the atria, not part of the normal heart rhythm. You can get premature or abnormal P waves. They only matter to recognise them as not that bad. Sometimes, they are conducted through and you get a ventricular ectopic. These are common. The two big ones are atrial flutter and atrial fibrillation. Re-entry supraventricular tachycardia is where a second electrical connection between atria and ventricles exist. The final thing is Wolff-Parkinson-White syndrome which is important because they like to ask questions on it (though it's pretty rare).
Essentially this is split into narrow complex tachycardia, or broad complex tachycardia which consists of:
Essentially, these are due to a blockage of the hearts conduction system. There are lots of different types: