The rationale for the use of early defibrillation stems from four observations: (1) ventricular tachydysrhythmias are the most common cause of SCD in adults; (2) defibrillation is the most effective treatment for VT and VF; (3) the effectiveness of defibrillation diminishes rapidly over time; and (4) unless treated promptly, VF becomes less coarse and eventually converts to the less treatable rhythm of fine VF or asystole.
The best outcomes from VT and VF in adults occur regularly in the electrophysiology laboratories, where prompt defibrillation (typically within 20 to 30 s of dysrhythmia onset) from pulseless VT or VF results in virtually 100 percent survival. The next best outcomes have been noted in cardiac rehabilitation programs, where defibrillation can be performed within the first minute or two. In such "ideal" settings, as many as 85 to 90 percent of patients are resuscitated and return to their prearrest neurologic status. Survival from out-of-hospital VT and VF treated by police officers equipped with automatic external defibrillators (AEDs) in Rochester, Minnesota, has averaged 50 percent, with a median time from collapse to defibrillation of about 5 min. Outcomes in many locations with EMS systems that cannot provide defibrillation until 10 min or more after a patient's collapse typically yield survival rates of less than 10 percent. 8
The best survival is attained in EMS systems that can provide early defibrillation to a large percentage of patients. In most cases, this is most cost-effectively accomplished by a tiered response system, in which large numbers of rapid first-response firefighters or emergency medical technicians (EMTs) are trained and equipped to provide first aid, CPR, and early defibrillation using an AED. Unfortunately, not all communities in the United States have yet implemented a comprehensive, tiered EMS system. Many systems, particularly in suburban or rural areas, have EMTs who are neither trained nor equipped to defibrillate. For such areas, adding rapid defibrillation capability offers a cost-effective alternative that can significantly improve survival from out-of-hospital VF or pulseless VT.
The American Heart Association advocates the widespread implementation of rapid defibrillation programs throughout the nation in its belief that "all emergency personnel should be trained and permitted to operate an appropriately maintained defibrillator if their professional activities require that they respond to persons experiencing cardiac arrest. This includes all first responding emergency personnel, both hospital and nonhospital (e.g., emergency medical technicians (EMTs), non-EMT first responders, fire fighters, volunteer emergency personnel, physicians, nurses, and paramedics). To further facilitate early defibrillation, it is essential that a defibrillator be immediately available to emergency personnel responding to a cardiac arrest. Therefore, all emergency ambulances and other emergency vehicles that respond to or transport cardiac patients should be equipped with a defibrillator." 33
More novel strategies have also been tried to increase the availability of rapid defibrillation in the community. There are many densely populated public areas in which conventional EMS systems cannot respond within an acceptable response time interval. The most innovative idea is termed public access defibrillation (PAD), so named because the intent is to have citizens from outside the health care fields perform early defibrillation using AEDs.
There are four "levels" of PAD based on the type of potential first responder expected to use the AED ( T.§ble 7.-2.). There has been considerable experience demonstrating benefit with minimal risk for level I (firefighters) and level II (police officers and airline flight attendants) first responders. 3 35 and 36 Other experimental approaches to rapid defibrillation in the workplace include use in British rail stations, oil platforms in the North sea, electricity plants, passenger cruise ships, and merchant marine vessels.8 There has been little experience thus far with level III PAD, and the few studies that have been reported have been somewhat disappointing. For example, Eisenberg et al. trained family members of 59 patients who had survived out-of-hospital cardiac arrest in King County, Washington. 37 Only 6 of the 10 cardiac arrests that occurred in these patients were defibrillated successfully, and only 1 patient survived for a few months and sustained new neurologic impairment. Since AEDs are currently approved for marketing in United States under prescription only, there has been no experience thus far with level IV PAD.
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