Wearable defibrillators are not for everyone who experiences life-threatening heart rhythm abnormalities, but for some patients it may represent an attractive middle ground between conventional and implanted devices.

Like an implantable cardiac defibrillator (ICD), the wearable defibrillator — which resembles a fishing vest with defibrillator electrodes — is designed to provide constant monitoring of erratic heart rhythms. Unlike an ICD that is permanently implanted in a patient’s chest, a wearable defibrillator is only temporary and is worn under street clothes.

The wearable defibrillator emits an alarm and vibrates. If the wearer feels normal, he/she presses a button within one minute to indicate that an electric shock is not needed. If the button is not pressed, it will send a shock to the heart through electrodes to return heart rate back to normal.

Until now, there has been scant evidence supporting the systematic use of wearable defibrillators, and randomized clinical trials are still needed to determine if the device can improve outcomes.

“Although a growing number of patients are being prescribed wearable cardiac defibrillators by their doctors, there have been very few well-designed and completed studies of these devices,” said Dr. Jonathan Paul Piccini, lead author of the advisory and a cardiac electrophysiologist at Duke University Medical Center in Durham, North Carolina, in a statement.

“Widespread use of the wearable defibrillator is not advisable because there isn’t enough clinical evidence to support its use, except in a small number of patients with known life-threatening arrhythmias, but for whom surgery to implant an ICD is not advised in the short-term,” he continued.

Currently, biomedical engineers are working on making the devices smaller, more lightweight and less burdensome, since patients complain that the device is uncomfortable.

The first large, randomized study of the wearable defibrillator is underway with the help of Dr. Byron Lee, a research director at the University of California, San Francisco’s Division of Cardiology, according to CBS News.

Lee said that the device should only be taken off in the shower and during sex because wearing the device while having sexual intercourse could trigger an unnecessary shock. However, walking and light exercise are fine.

CBS also reported that current evidence shows the device properly shocks people between 90 to 100 percent of the time with a 1 to 2 percent error.

Abnormal heart rhythm that is not treated could potentially result in sudden cardiac death, according to the study. It is also common in people who have recently had a heart attack, undergone procedures to open blocked blood vessels or have cardiomyopathies, which are diseases of the heart muscle.

Other patients who might benefit from the device are those who have life-threatening arrhythmias and who need an ICD but are unable to undergo surgery for the implant due to infection. Heart failure patients waiting for a heart transplant may also be candidates.

Leroy Gamble, a 79 year old man, suffered cardiac arrest and was consequently diagnosed with a heart condition. He was prescribed a wearable defibrillator by Dr. James Kneller, a Kadlec Clinic electrophysiology cardiologist, while he waited for an implantable defibrillator, reported Washington's Tri-City Herald.

In April, Gamble suffered a second cardiac arrest, and the wearable defibrillator ended up saving his life. “Sudden cardiac death risk is very real. Appropriate patients should be offered defibrillator protection. Part of [that] is the wearable defibrillator,” said Kneller.

If prescribed by a doctor, the device will most likely be covered by insurance.