Sudden cardiac arrest claims 350,000–450,000 lives per year in the United States alone, and is responsible for more than half of all deaths due to cardiovascular disease. Unfortunately, it remains difficult to identify patients who are at high risk―in fact, cardiac arrest is the first “symptom” of cardiovascular disease in 50% of patients with the disease. As a result, 90% of cardiac arrests occur without warning and outside the hospital setting; and lacking hospital care, the survival rate averages from 1% to 5%.

Cardiac arrest refers to the moment when electrical impulses in the heart are no longer capable of generating an effective heartbeat. The most common electrical disturbance is called ventricular fibrillation , which, if left untreated, will result in brain death in just 4 to 6 minutes. However, cardiac arrest can be reversed in 80-90% of cases if CPR and defibrillation therapy are administered within the first few minutes. CPR consists of mouth-to-mouth breathing and chest compressions that keep the heart pumping and lungs oxygenating; defibrillation consists of an electric shock to the heart that essentially overrides the chaotic fibrillations allowing the heart to restore its own normal heart rhythm. While CPR is only helpful in stalling for time, it is defibrillation that ultimately saves the life of a cardiac arrest victim. Each minute that defibrillation is delayed reduces chance for recovery by at least 10%.

Considering the urgent circumstances of out-of-hospital cardiac arrest, the American Heart Association set forth a four-point “chain of survival” plan to guide community response to these events. The four priorities include early access to care, early initiation of cardiopulmonary resuscitation (CPR), rapid defibrillation, and early advanced cardiac life support.

Traditionally, emergency medical personnel have delivered “rapid defibrillation.” But new, portable devices known as Automatic External Defibrillators (AEDs) have become more widely available for use by members of the general public who are on the scene. These AEDs are designed specifically for the medically uneducated and they are lightweight, relatively inexpensive, require little maintenance, and facilitate use by automatically diagnosing heart rhythms to confirm cardiac arrest. In tests, sixth graders used them expertly after minimal training.

To determine how much public access to defibrillation can improve cardiac arrest survival rates, researchers compared the outcomes of arrests responded to by community volunteers trained in either CPR alone or CPR and defibrillation. Their results, published in the August 12, 2004 issue of the New England Journal of Medicine, showed that cardiac arrests treated by volunteers trained in both CPR and defibrillation were twice as likely to recover.

About the Study

Volunteers who sign up as cardiac arrest emergency responders are ordinarily trained to contact emergency medical services and administer CPR. Researchers behind this study, the Public Access Defibrillation (PAD) Trial, compared volunteers trained in this method to volunteers trained to use portable defibrillators (AEDs) as well.

More than 19,000 volunteers were trained to respond to public-setting cardiac arrests. Highly populated areas such as shopping malls, hotels, and apartment complexes (n=993) were monitored for cardiac arrest from July 2000 through September 2003. For comparison, each area was assigned to a volunteer team trained in either CPR or CPR plus defibrillation.

The Findings

During an average time span of two years for each area, 526 presumed cardiac arrests occurred, of which 235 cases were treated by volunteer responders. Of these, the 107 cases assigned to CPR-plus-AED units had the twice the chance of survival (29 survivors) than the 128 cases assigned to CPR-alone response units (15 survivors).

How Does This Affect You?

Given the dismal survival rate for cardiac arrests that occur outside the hospital, any increase attributable to public access to defibrillators is extremely encouraging. However, this study found a doubling of survival rate only in the public settings it surveyed (shopping malls, recreation centers, etc.), not in the residential settings. Only two victims of cardiac arrest survived at residential complexes in this study, and the majority of out-of-hospital cardiac arrests (79-84%) do indeed occur within the private home. The missing factor here is often a witness who can call for help.

Nonetheless, based on the results of this and other research, it seems desirable to expand organized public defibrillation response programs, even if they do not successfully intervene with cardiac arrests in the home.

As for the American Heart Association’s “chain of survival,” another study published in the same issue of the New England Journal of Medicine concluded that “early advanced cardiac life support” was actually of no help to victims of cardiac arrest. Patients treated with advanced life support, including endotracheal intubation (to help oxygen flow) and intravenous drugs, were no more likely to survive than patients who received no such services. The same study confirmed the improved survival rates from both CPR and rapid defibrillation. This second study only reinforces the potential benefits and cost-effectiveness of public volunteers minimally trained in the use of AEDs who can rapidly respond to a cardiac arrest victim.