1. Arrhythmia literally translated means absence of a normal heart rhythm. Actually the term dysrhythmia is much more  accurate because this means disturbance of a normal heart rhythm

2. The heart is a pump and to beat most effectively it has to beat at a certain rate and with a certain rhythm and therefore any unsolicited disruption of this will lead to inefficiency of the heart as a pump and therefore any arrhythmia by very definition signifies inefficiency for the duration of that arrhythmia

3. Dysrhythmias can come and go in which case they are considered paroxysmal or they can be present all the time in which they are called persistent

4. Virtually all dysrhythmias are more likely to be triggered by intercurrent illness, stimulants, dehydration, lack of sleep, exhaustion, electrolyte disturbances and stress

5. The thing that makes a dysrhythmia dangerous is the level and duration of inefficiency it causes. So sustained dysrhythmias are more dangerous than non sustained dysrhythmias. Very fast or very slowdysrhythmias are more dangerous than dysrhythmias which occur with a normal heart rate.Ventricular dysrhythmias tend to be more inefficient than atrial or upraventricular dysrhythmias. Finally all dysrhythmias are more sinister in a person with an already damaged or compromised heart compared to a person with a structurally normal heart.