Jennifer Fergusson had no history of heart problems and was only 39 when she collapsed at her desk at work from sudden cardiac arrest (search).

And if her company, the Greater New York Hospital Association, hadn’t had a portable defibrillator at the office that some of her co-workers knew how to use, she wouldn't have lived when her heart stopped without warning last year.

“Without the defibrillator, my doctor said I would be dead. He says I’m a miracle,” Fergusson, an event planner, said at a recent conference held by Philips Medical Systems, which makes the HeartStart defibrillator that helped save her.

An automatic external defibrillator (search), or AED, is hooked up to a patient using chest pads and has voice prompts to guide the person controlling it, eventually delivering a shock to revive the patient and get the heart started again if the machine deems it necessary.

It works best when used in conjunction with cardiopulmonary resuscitation (CPR), which the machine advises administering at various points along the way. It also issues reminders to call 911.

The devices have been popping up on airplanes and in airports, schools, offices, houses of worship, police cars, fitness centers and other public places for the past decade, but just last year, the Philips model was approved for over-the-counter home use without a prescription. The current price is $1,495. Other companies, including Zoll Medical Corp., Samaritan and Defibtech LifeLine, make AEDs that are available with a doctor's prescription.

“Nearly 80 percent of cardiac arrests happen in the home,” said Brian Packard, business director of the Philips HeartStart line. “The key to survival is early access to a defibrillator. If you don’t get a defibrillator shock in the first five minutes, your chance of survival is virtually nil.”

Doctors and the American Heart Association (search) agree, though the latter is reluctant to take a firm position on at-home defibrillators until they’ve been around for longer and there is more science to back up their effectiveness.

“The American Heart Association clearly endorses high-quality CPR and training and early effective defibrillation, but has not gone to the extent of endorsing the public in buying AEDs over the counter for home use — only because there isn’t evidence that that actually saves lives,” said Vinay Nadkarni, past chairman of the AHA’s emergency cardiovascular care committee.

Nadkarni said that one of the unknowns with the home defibrillator is how the person using it will react in such a medical emergency.

“We don’t know if the layperson who is not specifically trained to use the AED will appropriately employ it, panic during the incident, etc., more so than just calling 911,” he said.

Other than the possibility of the layperson panicking during an actual emergency, another concern is that the device would be used on someone who hasn't suffered cardiac arrest — either due to human error or mechanical failure.

"If you shock someone who doesn't need it, it could cause an arrhythmia," said Dr. Scott Wright, a cardiologist at the Mayo Clinic in Rochester, Minn., referring to a dangerous irregular heartbeat that is often what makes the heart stop in the first place. "It's rare, but it could happen. There's always the remote chance that if things malfunction, this machine could worsen [the condition]."

But that chance is extremely small, he added. He recommends that his patients practice using AEDs.

"I'm a big proponent of them — I've encouraged my patients to buy them and I've considered buying one myself," said Wright, "It's a great breakthrough."

Nadkarni said he thinks it would take a minimal amount of work for the average person to become adept at handling the device, which comes with a plastic training mat to practice on.

"They're really so simple to use, as simple as 1-2-3," he said. "It takes only a little bit of training to learn how to use them effectively."

Fergusson's rescuer, David Rosenfeld, said he didn't have trouble with the defibrillator once another co-worker, a registered nurse, had determined sudden cardiac arrest was the culprit — even though he was stunned about what was going on at first.

"I was a little shocked — I thought, 'My God, I can't believe this is happening' — but then I got down and did what had to be done," said Rosenfeld. "It was very simple to use."

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The technology of the at-home defibrillators is similar to that of those used by medical professionals in emergency rooms and ambulances. The only difference is the ease of use with the computerized home models, which have more intelligence built into them and do most of the work for the person at the controls.

Those handled by the pros allow doctors and paramedics to do more of their own assessments of the patient's condition. They're also much larger than the at-home models — about the size of a small suitcase.

"Everyone who has a television has an idea of what a defibrillator looks like from the hospital dramas. They're very scary," said David Snyder, a senior research scientist for Philips Medical Systems. "We've taken all that scary stuff out of the home model."

The battery-operated, portable, home defibrillator is about the size of a textbook. With the Philips model, the person controlling it installs the battery in the back and then pushes the green power button, after which the device begins its voice prompts of what to do.

It first instructs the user to pull back the plastic shield in the center of the gadget and take out the two chest pads, which are attached to the machine with wiring.

The person must then remove all clothing from the victim's upper body (the AED kit comes with scissors in case garments need to be cut off), take the pads off their adhesive backing and place one on the upper right corner of the chest below the shoulder and the other on the lower left side under the armpit. Diagrams are included so the pads are put in the right places.

The AED voice then says it is "analyzing" and orders the user not to touch the patient while the machine measures whether or not the victim has suffered cardiac arrest and needs an electric shock delivered to get the heart beating again.

If a shock is required, it tells the person at the controls to press the orange button on the console with more warnings not to touch the patient.

If the patient's heart does not start with one shock, the device will prompt the user to press the orange button again for another shock. It will continue advising the person to administer another shock until the heart restarts or until it's deemed futile to do so because the patient has flatlined.

It also walks the person controlling it through CPR and gives reminders about calling 911.

But not everyone is thrilled at the idea of a co-worker, stranger or other non-medical professional delivering a defibrillator shock to the heart, even if sudden cardiac arrest has occurred.

"If you're not a doctor, God, I think that's scary," said Cristina Barden, a 30-something retail planning manager who lives in Queens, N.Y. "If it's Joe Blow or Jane Doe, that makes me leery. I have a problem with that. I wouldn't want someone treating me for something that serious unless they've had some sort of training for it."

Instead, she'd rather her co-workers just call 911 and leave her in the hands of the pros.

"I would hope they would be able to get me in an ambulance to get proper medical attention," Barden said. "Unless you've got a little bit of training, I'm going to tell you to keep your hands off me."

Still, many are happy the portable defibrillators are becoming more accessible to the general public. Dr. Wright hopes the devices will soon become less expensive so more people can afford to buy them. The current $1495 price of the Philips model is prohibitive, especially since there are other hidden costs — like $75 for replacement chest pads (which can only be used once) and $125 for the battery, which lasts four years.

"I'd like to see them drop to $400 or $500," Wright said.

Though many people struck down by sudden cardiac arrest have a history of heart problems or other factors like heredity that make them more susceptible, others are afflicted without prior indication that anything is wrong.

That was the case with Fergusson, who hadn't had any signs of heart problems before she experienced sudden cardiac arrest because of an arrhythmia (search).

“I had no symptoms, no chest pains,” said Fergusson, who like any high-risk patient now has an implanted defibrillator. “But stress was definitely a factor. My mom had just been placed in a nursing home and I had three events to plan. When I got to my desk, I was feeling overwhelmed.”

And in those situations, an on-site safety device like an AED might be just what the doctor ordered.

"Not only is it giving patients and families rapid access to early defibrillation, it also provides peace of mind," said Wright. "I believe defibrillators at home for certain populations of patients will become as common as fire extinguishers."