**Abstract**

The wearable cardioverter-defibrillator (WCD) is a rechargeable external device that can be worn under the clothing all day long and protects the wearer from potentially life-threatening ventricular tachyarrhythmias. When a dangerous arrhythmia is detected, the WCD can deliver high-energy shocks. The WCD has been shown to be effective in accurately detecting and appropriately treating ventricular tachycardia (VT) and ventricular fibrillation (VF). It is intended for temporary use as a bridge to an implantable cardioverter-defibrillator (ICD), heart transplantation, or left ventricular assist device; patients with heart failure with reduced ejection fraction may benefit from the WCD while their condition improves. It can be used temporarily after explant of an ICD until reimplantation is deemed possible. In select patients with myocardial infarction, a WCD may be useful during the immediate period after infarction. It is indicated for use when a permanently implanted ICD must be explanted because of infection; the patient can use the WCD until the infection resolves, and a new ICD can be implanted. The role of the WCD is emerging as an important therapeutic option to protect patients at elevated risk of sudden cardiac death (SCD).

**Keywords:** arrhythmia, cardiomyopathy, heart failure, heart transplantation, implantable cardioverter-defibrillator, sudden cardiac death, wearable cardioverter-defibrillator (WCD)

### **1. Introduction**

Sudden cardiac death (SCD) is mainly due to ventricular tachyarrhythmias even though bradycardia may occur. The population at risk for SCD is heterogeneous and includes those whose risk is based on a transient arrhythmia-provoking electrical event, structural heart disease, a channelopathy, heart failure, cardiomyopathy, or other underlying conditions [1]. For patients at elevated risk for potentially lifethreatening ventricular tachyarrhythmias but with a transient contraindication for an implantable cardioverter-defibrillator (ICD) therapy, the wearable cardioverterdefibrillator (WCD) is an important therapeutic option (LifeVest 4000®, Zoll, Pittsburgh, Pennsylvania, USA). The external vest delivers high-energy rescue therapy in the event a ventricular tachyarrhythmia is detected along with electrogram storage and remote monitoring [2]. First introduced to market in 2001, the WCD is intended for short-term use, typically for a few months [3].
