**2. The WCD and its function**

Currently, there is only one WCD, the LifeVest 4000®, and no other similar products are on the market. The WCD weighs 800 g and is available in a range of sizes with adjustable straps and an elasticized belt to fit snugly next to the skin under clothing (**Figure 1**). The WCD has three pad-style electrodes for defibrillation and four more electrodes for arrhythmia detection (sensing). It is equipped with a battery-powered defibrillation unit capable of generating several highenergy shocks. When the WCD prepares to deliver a shock, it delivers a small amount of gel to the skin at each electrode, and a biphasic waveform of 75 or 150 J is delivered [4].

The WCD detects arrhythmias using an algorithm of heart rate (including rate stability and onset of arrhythmia) and waveform morphology. In the presence of noise or when a waveform template is not available, the detection function can work using rate alone. Once an arrhythmia is detected, the device signals the patient for about 30 s, allowing the wearer to abort the shock by manually depressing two response buttons. If the rate drops below the detection threshold during this 30-s waiting period, the detection is delayed or the shock prevented, depending on whether the slower rate was brief and temporary or persisted [5]. The WCD offers programmable parameters in that the ventricular fibrillation (VF) zone can be set between 120 and 250 beats per minute (bpm) and the ventricular tachycardia (VT) zone can be programmed from 120 bpm to the lower bound of the VF zone [6]. The clinician may also program the time from arrhythmia detection to therapy delivery from 60 to 180 s for the VT zone and 25 to 40 s for the VF zone [5].

The WCD is rechargeable and comes with two lithium-ion batteries. One battery is used at all times in the device, while the other may be charged in about 3.5 h using a proprietary charging station. Battery life is approximately 2 days, but even if the battery signals the patient that it is getting low, there is usually sufficient charge retained for 10 shocks of 150 J each. During an arrhythmic episode, the WCD will deliver up to five shocks. If the arrhythmia persists, the device detects again and repeats the cycle until the rhythm is converted or the battery is exhausted [5]. Once the WCD delivers therapy, it should be replaced.

Patients are given a transmitter which can transmit data from the WCD directly to the clinic via a secure server. Remote transmissions do not require any patient intervention. Like cardiac implantable electronic devices, the WCD can be programmed to send out alerts when specific triggering events occur. The remote monitoring system records the number of hours per day that the patient wears the WCD, and the patient can activate the device to record an electrogram in the event of symptoms. While the WCD will attempt to make a daily remote transmission, if this is not possible, data transmission should occur at least once a week, and monthly in-clinic visits are recommended for WCD patients [5]. Reports from the

The American College of Cardiology, American Heart Association, and European Society of Cardiology (ACC/AHA/ESC) 2006 guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death was the first society-based recommendation for the use of WCD in patients at transient high risk for VF, such as patients waiting for heart transplant; patients at high risk following an acute myocardial infarction or invasive cardiac procedure; and patients whose ICD had to be temporarily explanted, for example, because of an infection [7]. The International Society for Heart and Lung Transplantation

WCD are shown in **Figures 2** and **3**.

**3. Guidelines for the WCD**

**Figure 2.**

**65**

*The wear time: report on the WCD.*

*The Wearable Cardioverter-Defibrillator DOI: http://dx.doi.org/10.5772/intechopen.90663*

#### **Figure 1.**

*The WCD (LifeVest 4000® from Zoll) is worn like a vest and is powered by a rechargeable battery, capable of delivering high-energy shocks to convert a potentially life-threatening ventricular tachyarrhythmia. Art by Todd Cooper.*

**2. The WCD and its function**

*Sudden Cardiac Death*

is delivered [4].

**Figure 1.**

*Cooper.*

**64**

Currently, there is only one WCD, the LifeVest 4000®, and no other similar products are on the market. The WCD weighs 800 g and is available in a range of sizes with adjustable straps and an elasticized belt to fit snugly next to the skin under clothing (**Figure 1**). The WCD has three pad-style electrodes for defibrillation and four more electrodes for arrhythmia detection (sensing). It is equipped with a battery-powered defibrillation unit capable of generating several highenergy shocks. When the WCD prepares to deliver a shock, it delivers a small amount of gel to the skin at each electrode, and a biphasic waveform of 75 or 150 J

The WCD detects arrhythmias using an algorithm of heart rate (including rate stability and onset of arrhythmia) and waveform morphology. In the presence of noise or when a waveform template is not available, the detection function can work using rate alone. Once an arrhythmia is detected, the device signals the patient for about 30 s, allowing the wearer to abort the shock by manually depressing two response buttons. If the rate drops below the detection threshold during this 30-s waiting period, the detection is delayed or the shock prevented, depending on whether the slower rate was brief and temporary or persisted [5]. The WCD offers programmable parameters in that the ventricular fibrillation (VF) zone can be set between 120 and 250 beats per minute (bpm) and the ventricular tachycardia (VT) zone can be programmed from 120 bpm to the lower bound of the VF zone [6]. The clinician may also program the time from arrhythmia detection to therapy delivery from 60 to 180 s for the VT zone and 25 to 40 s for the VF zone [5].

The WCD is rechargeable and comes with two lithium-ion batteries. One battery is used at all times in the device, while the other may be charged in about 3.5 h using a proprietary charging station. Battery life is approximately 2 days, but even if the battery signals the patient that it is getting low, there is usually sufficient charge retained for 10 shocks of 150 J each. During an arrhythmic episode, the WCD will deliver up to five shocks. If the arrhythmia persists, the device detects again and repeats the cycle until the rhythm is converted or the battery is exhausted [5]. Once

*The WCD (LifeVest 4000® from Zoll) is worn like a vest and is powered by a rechargeable battery, capable of delivering high-energy shocks to convert a potentially life-threatening ventricular tachyarrhythmia. Art by Todd*

the WCD delivers therapy, it should be replaced.

**Figure 2.** *The wear time: report on the WCD.*

Patients are given a transmitter which can transmit data from the WCD directly to the clinic via a secure server. Remote transmissions do not require any patient intervention. Like cardiac implantable electronic devices, the WCD can be programmed to send out alerts when specific triggering events occur. The remote monitoring system records the number of hours per day that the patient wears the WCD, and the patient can activate the device to record an electrogram in the event of symptoms. While the WCD will attempt to make a daily remote transmission, if this is not possible, data transmission should occur at least once a week, and monthly in-clinic visits are recommended for WCD patients [5]. Reports from the WCD are shown in **Figures 2** and **3**.
