Defibrillators deliver a shock to restore a normal heart rhythm and they come in several flavors. There’s the implanted variety, which includes an electrical wire threaded into the heart. Newer subcutaneous defibrillators don’t require wires to the heart. And there are today’s ubiquitous AEDs, or automated external defibrillators, stored in wall-mounted boxes at airports and other public places, which bystanders can use in cardiac emergencies.

Finally, defibrillators can also be worn on the body, electrical pads held tight against the chest by a strappy “vest” worn under clothing.

The American Heart Association on Monday released a carefully worded scientific statement on the use of these wearable cardioverter defibrillators, or WCDs, for preventing sudden cardiac death – its first such statement on the device.

The new report indicates potential benefits for these groups of patients: Those with implanted defibrillators needing replacement but who must wait for surgery for some reason, such as infection; those awaiting other, more definitive treatment, such as a heart transplant; and those with an increased risk of sudden cardiac death that may resolve over time or with short-term treatment.

“This is not a guidance document,” cautioned lead author Jonathan P. Piccini, M.D., a heart rhythm specialist at Duke University School of Medicine. “A guideline wouldn’t be appropriate here, because there is not a lot of evidence.”

Rather, Piccini said, the document published in Circulation is meant to educate and inform and “provide a framework for the rational use” of WCDs. The statement emphasizes communication between doctors and patients about the risks, benefits and uncertainty surrounding the device.

In recent years, use of WCDs has proliferated in clinical practice, Piccini and his co-authors noted. Strapped on to adults and sometimes children who are at risk for sudden cardiac arrest, WCDs use sensors to detect an abnormal heart rhythm. If a life-threatening arrhythmia is detected, the device sends a vibration, audio or visual alert. The wearer can then depress a response button to abort. Otherwise, defibrillation begins, delivering a shock often within seconds of detecting the arrhythmia.

To be effective, the device should be worn at all times, except quick breaks for showers or baths. But the devices are not terribly comfortable and discontinuation rates in some studies were as high as 22 percent.

“I’ve seen patients get kind of frustrated by wearing them. It’s like wearing a big bra that has to be configured in a certain way,” said Bradley Knight, M.D., director of the Bluhm Cardiovascular Institute at Northwestern Medicine. “But I’ve had patients wear them for months, even up to nine months, and I’ve had patients who have gotten lifesaving shocks from them.”

The only device currently on the market is LifeVest, manufactured by Pittsburgh-based Zoll.

“These kinds of statements provide very important guidance to physicians making decisions,” said Knight, who was not involved in writing the advisory. But on first read, he said, the new guidance appears conservative.

Take a patient who had an implanted defibrillator, had a cardiac arrest and got a lifesaving shock, but then had to have a lead, or wire, removed because of an infection.

“It would almost be against standard of care to send this patient home without a wearable cardioverter defibrillator,” Knight said. Yet, for those patients, the statement classifies the treatment as “reasonable” rather than something that “should” be done.

“Risks are low, even exceedingly low,” Knight said. “Sometimes we’re too compulsive asking for randomized clinical trial data when there is little downside and it works.”

He and Piccini noted it would be valuable to have more clinical trial results with WCDs, and it would be helpful to have other defibrillation options. But most of all, Piccini said, he hopes the statement triggers conversations. “If this topic makes it into the next grand rounds,” he said, “that’s a win.”