Defibrillators Combat Cardiac Arrest in Public and at Home

When cardiac arrest strikes in public places or homes in the US, only about 5% of the victims survive. That translates into more than 460,000 sudden deaths beyond hospital walls each year, a statistic that has led to expanded availability of defibrillators in community settings.

Along with "traditional" manual CPR (cardio-pulmonary resuscitation) techniques, defibrillators in high-human-traffic areas such as airports and shopping malls are saving lives. In-home portable defibrillators and wearable defibrillators for some high-risk patients are also being employed.

"From the patient's standpoint, ventricular fibrillation is the rhythm that is in most cases the cause for cardiac arrest," said James A. Roth, MD, Medical College of Wisconsin Associate Professor of Cardiovascular Medicine. "In lay language it's usually referred to as a heart attack, although doctors prefer to describe this situation as cardiac arrest.

"In cardiac arrest, somebody who is awake and fine abruptly passes out and has a fainting spell, but doesn't wake up. They are pulse-less, they are not breathing. Of course, the immediate response of bystanders should be CPR in that situation. CPR can improve survival, but it's only of limited use. The main thing that saves people who have cardiac arrest is prompt resuscitation by defibrillation."

CPR has been proved effective in extending by several minutes the "window" in which cardiac arrest victims stay alive, Dr. Roth said, adding "But, if it goes too long and the patient hasn't been defibrillated, then even with CPR people don't survive or they have brain damage if they do survive. So there's been a great deal of interest in ways to get timely defibrillation done."

Cardiac arrest survival is as low as 1% in some areas, including New York City with its renowned traffic jams. As quickly as trained emergency responders can reach cardiac arrest victims in ambulances or fire trucks, it's not always quickly enough to beat the pace of a heart that has gone out of control.

Multiple Applications
Extremely rapid rhythm disorganizes regular heart pumping to the point that blood circulation stops. Defibrillators deliver jolts of electricity to shock the heart back into normal rhythm after cardiac arrest.

Portable defibrillators are now available and are more fully automated, making it possible for volunteers without emergency response or medical backgrounds to be trained in their use. Defibrillators must be utilized almost immediately, though, because the chance of surviving sudden cardiac arrest drops by 10% for each minute that goes by before a defibrillator is applied.

"There are a couple of other categories where the external defibrillator has an important role," said Marilyn Ezri, MD, FACP, Medical College Associate Professor of Cardiovascular Medicine. "Some have made it to patients who have had a recent heart attack. It's prudent for patients who have just had a heart attack to wait a month or so to find out if they are candidates to have an internal defibrillator implanted. In that waiting period, while you're waiting for the heart muscles to recover and the patient to get stronger, the patient and the family members and the doctors may be well served with an external defibrillator."

Portable external defibrillators can also be of value to patients who have implanted defibrillators that must be replaced due to infection or mechanical malfunction, said Dr. Ezri. "Every once in a while an internal system can get infected and you have to have the surgeon take it out. In those cases you have to wait a month or six weeks for antibiotic treatment to take effect before you can put a new defibrillator in. Thankfully, it's a rare occasion for one of these devices to have a malfunction or be recalled."

Public Defibrillators Double Survival Rate
A national study reported in November 2003 that the use of "public" defibrillators by trained volunteers nearly doubled the survival rate of cardiac arrest victims in community settings when measured against the survival of people who only received manual cardio-pulmonary resuscitation (CPR). Froedtert and Medical College participated in the study, primarily funded by the National Institutes of Health Heart, Lung and Blood Institute and the American Heart Association.

Nearly 20,000 volunteers nationwide were trained for the study - including about 1,000 in Milwaukee - and more than 1,600 portable defibrillators were donated by manufacturers for placement in hundreds of locations nationwide.

Medical College Associate Professor of Emergency Medicine Tom P. Aufderheide, MD, who served as one of the investigators for the study, credited the project with saving three lives in Milwaukee. Nationally, out of more than 230 incidents included in the study, 15 patients survived through discharge from hospitals after being revived on the scene by CPR alone while 29 patients made it out of the hospital after revival on the scene included the use of a defibrillator.

"This should change the national practice of medicine and increase the widespread but careful dissemination of public-access defibrillators throughout our communities," Dr. Aufderheide said in a Milwaukee Journal Sentinel article about the effort. He added that Milwaukee already has an above-average cardiac arrest survival rate of 9% because the city has a good overall emergency medical system.

The American Heart Association estimates that four out of five cardiac arrests occur in the home; so another study is in the works to determine the effectiveness of thousands of defibrillators now located in private residences.

Wearable Models Show Promise
The US Food and Drug Administration approved the first wearable defibrillator in 2001. Wearable defibrillators are designed for people at high risk for cardiac arrest, including patients who have just had a heart attack and those who are in line for a heart transplant.

The wearable devices, with sensors that monitor heartbeat, are strapped to the chest and automatically transmit electrical shock when severe irregularities are detected. FDA analysis of clinical trials determined that these defibrillators were successful in treating sudden cardiac arrest 71% of the time compared to the 25% success rate for people without them who called 911 for help.

Dr. Roth cautioned that even a vastly increased application of public and at-home defibrillators should not be expected to take the place of "heart-healthy" practices on the part of individuals and medical interventions to solve heart problems in general. "The AECD (automatic external cardio-defibrillator) is a potentially tremendous advance, but it is complex to implement because an important component in the system is the public," he said, "but there are several problems in implementing a system in the real world.

"First, no matter how many defibrillators you have available, there are still going to be a limited number. There needs to be some way to apprise the people who have the training of the situation and where the defibrillator is, so you need a system that immediately alerts the appropriate people.

"Second, people who perhaps never had to deal with this in reality before will have to respond and do all the steps correctly, and not get flustered, and successfully resuscitate the patient without panicking. The way that this has been used most consistently and effectively, to my knowledge, is to use personnel who are accustomed to responding to emergency situations."

Dan Ullrich
HealthLink Contributing Writer

This article includes information from the American Heart Association and from a report issued by the National Institutes of Health.

MCW Health News presents up-to-date information on patient care and medical research by the physicians of the Medical College of Wisconsin.