Survival is better for patients presenting with VT or VF than for those with bradyarrhythmic or asystolic mechanisms.S6-32 Rapid arrival of paramedical personnel is the major determinant of survival. A number of strat- egies for responding to unexpected cardiac arrest, including rapid defibrillation and initiation of CPR for a witnessed cardiac arrest, have improved sur- vival probabilities for cardiac arrest victims.S6-2,S6-3 Nonetheless, the absolute number and propor- tion of survivors remain low, except in unique circumstances where there is an extraordinarily rapid response time to victims in VF or VT such as in monitored intensive care units, where sur- vival is >90%.S6-33 S6-36 Survival decreases rapidly after the initial 2 minutes from the onset of car- diac arrest, so that by 4 to 5 minutes, survival may be 25%, and by 10 minutes it is 0%.S6-33,S6-35,S6-36 Advanced life support activities, other than those directly related to cardioversion and defibrillation for control of tachyarrhythmias, have led to the generation of comprehensive protocols to guide responders. These AHA documents cover the broad expanse of clinical circumstances and con- siderations of mechanisms.S6-1,S6-37 2. 