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While ICDs have been shown to improve survival from SCD, placement is not always feasible. Ventricular fibrillation and ventricular tachycardia are the most common arrhythmias associated with SCD. The WCD can be used as a bridge to ICD placement or a bridge for short‐term protection against SCD when cardiac recovery is expected [29].

The WCD is a vest‐type garment with an inner layer containing sensing and energy delivering electrodes in direct contact with the patient’s skin. The holster of the vest contains the monitor, battery packs, and other device contents not in contact with the patient’s skin. The convex, resin‐insulated electrodes sense the patient’s electrical activity and the processor is programmed to detect shockable ventricular arrhythmias and initiate defibrillation if appropriate. The vest alerts the patient to the activation of the shock delivery algorithm via audible alarms and through vibration signals. This gives the patient the opportunity to deactivate the process by pressing two buttons simultaneously if they are alert. If not deactivated, gel is ejected between the electrodes and patient’s skin and a shock between 75 and 150 joules is delivered. The vest contains a lithium‐ion battery pack that provides continuous power for 24 hours [29].

Some of the issues related to the success rate of WCDs in preventing SCD is patient compliance. The device should be worn at all times. It should only be removed when bathing and then only if someone is present to initiate lifesaving measures as appropriate. The device has been redesigned to make it more comfortable and lightweight. The sense of security that the WCD provides also contributes to patient compliance [29].

The trials to date have reported a 75% success rate of WCDs providing appropriate shock therapy. Like ICDs, however, the WCDs also produce inappropriate shocks when ventricular arrhythmia is not present. Although WCDs have built‐in patient response buttons to prevent inappropriate shocks, shocks are still delivered because patients forget how to deactivate the device. Patients also do not receive appropriate shocks due to incorrect positioning of the device or its electrodes [29].

When an EMS clinician encounters a WCD patient, a standard evaluation should be conducted. CPR can be performed with the device in place. However, if it is broadcasting an imminent shock, stop CPR. The device should be allowed to complete the defibrillation of the unconscious patient prior to proceeding. If external defibrillation is available, external pads can be placed after disconnecting the monitor from the electrode belt, or the vest can be removed altogether. Prior to removing the vest, the battery should be removed to prevent an inadvertent shock.