“In simple terms, each beat of the heart is triggered by an electrical signal that spreads through some special fibres (conduction bundles, similar to electrical wires in everyday life) in the heart, causing the various parts of the heart to contract in a rational and regular manner, in a certain order and frequency.
There is usually only one pathway (wire) for normal heart conduction, but there are also some abnormal ‘wires’ in the heart, which are mostly congenital and are not normally involved in the conduction of electrical signals in the heart.
In certain circumstances (e.g. when sympathetic excitement is caused by emotional stress, exertion, alcohol consumption, etc.), an occasional pre-term contraction energizes the abnormal “wires”, causing the current to keep turning in a local loop, forming a foldback, with each turn conducting an electrical signal, causing the heart to beat once, and the continuous turning eventually leads to Tachycardia occurs.”