There are any number of underlying conditions that cause it. Some of them are relatively benign, while some can be life-threatening. My family's version can trip from Afib to V-tac; which is usually fatal, unless a defibrillator is handy. Pacing, a pacemaker/IDC, drugs, and ablation, either alcohol or radio (the wire), are all used. Dehydration (think alcohol), salt, or physical strain can all be triggers. A lot of those conditions you have to pay attention to your doctor.
