What causes the heart too beat to fast in sudden cardiac arrest and makes the electrical system go crazy?

Ventricular fibrilla: Ventricular fibrillation causing sudden cardiac death can occur in people with normal or abnormal heart. Those with no structural heart disease such as Long QT Syndrome ,Brugada Syndrome ,etc cause by genetic mutation in ionic channels. In people with structural heart disease Coronary artery disease is common in people over 50 and in younger people ,cardiomyopathy specially Hypertrophic Cardiomy