Defibrillation or cardioversion may be accomplished by an implantable cardioverter-defibrillator (ICD). For ventricular fibrillation or ventricular tachycardia, a single defibrillation should be attempted. Treatment is with cardiopulmonary resuscitation (CPR) and defibrillation. This allows early intervention with medication, cardioversion or defibrillation, improving the prognosis. Often, more electricity is required for defibrillation than for cardioversion. This scheme works well for defibrillation and cardioversion, as well as for monitoring an ECG. Defibrillation and resuscitation is indicated in these cases. Biphasic defibrillation was originally developed and used for implantable cardioverter-defibrillators. This refers to whether a particular class of cardiac dysrhythmia is treatable using defibrillation. Biphasic defibrillation may be better than monophasic. However, people with severe hypothermia may not respond to pacing or defibrillation. The precordial thump is a manoeuver promoted as a mechanical alternative to defibrillation. It is described in detail in Gurvich's 1957 book, "Heart Fibrillation and Defibrillation". Lidocaine should be given for this indication after defibrillation, CPR, and vasopressors have been initiated. CPR oxygenates the body and brain for defibrillation and advanced life support.