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

**Study description**

**72**

Dillon et al. 2105 WCD patients in a

retrospective

arrhythmia

Ellenbogen

from 234 consecutive episodes of VT/VF in 173 inhospital patients who had a WCD

for primary prevention, VA, or other reasons, including device explant; 40% had a history

of myocardial

Quast et al. 79 WCD patients Salehi et al. 127 patients with CM

Seven patients (5.5%) had nine

Not reported

> sustained VT episodes, 100%

successful conversion

and

use

Singh et al. 639 WCD patients ICM

None for NICM patients

Three NICM patients (1.2%)

Mean duration 61 days (25–102)

Mean daily wear 22 h/day

0.7% of ICM

Six ICM patients (2.2%), of whom

five survived the shock and four

survived to hospital discharge

Uncontrolled

Beiert et al. 114 patients

6.1% (no NICM patients were

64 patients (56.6%) were signaled

Median duration 52.0 days (range

One patient in this study died of

asystole

25–90)

Daily wear time 23.1 h/day

(19.0–23.8)

inappropriately

 for a shock,

shocked)

One patient had an appropriate ineffective shock and was externally

defibrillated

 but

almost all due to artifacts. All

shocks were aborted by the

ICM (31.6%)

NICM (45.6%)

Congenital heart disease (5.3%)

 studies

and NICM

self-reported

 excessive alcohol

 Two patients (2.6%) for annual rate

One patient (1.3%) for annual rate

Median duration 73 days (50.0–

In 52.2% ejection fraction improved

enough that ICD implant was not

necessary

109.8)

Median daily wear time 23.3 h/day

(22.6–23.7)

Median duration 51 days

11 patients (8.6%) died during the

100 days of follow-up, but no deaths

were caused by WCD shock failure

or undersense

Median wear time 18.0 h/day

of 6.7%

of 13.6%

 infarction

 history of

 in-hospital

 et al. population came

100% had an appropriate 68% occurred during weekdays, and

55% of events happened in the

daytime

 shock

Not reported

 detection

 analysis of

**Appropriate**

1.58 appropriate

 shocks per 100

patient-months

54 total appropriate

 shocks

 **therapy**

**Inappropriate**

0.99

inappropriate

patient-months

34 total

most due to interference

inappropriate

 shocks,

 (47.1%)

 shocks per 100

Data for 1 year were analyzed Median duration of use was 36 days

(3–365)

Median wear time 21.3 h/day (0–

23.9)

Median follow-up 6 days while

Most VA occurred in

units, the ICU, and the ED

24-h survival following therapy

delivery was >90%

unmonitored

patients were in the hospital

 **therapy**

**Wear time**

**Comments**

Most frequent reason for wearing

the WCD was myocardial infarction, but study included

*Sudden Cardiac Death*

several indications Sudden Death (VEST) study (n = 2302) [15]. All patients had had a recent myocardial infarction and a left ventricular ejection fraction ≤35%; some but not all patients had undergone revascularization. Patients were randomized into two arms: guideline-directed medical treatment (control) or a WCD. In the first 90 days after myocardial infarction, the WCD did not result in a lower rate of arrhythmic death, but total mortality was lower in the WCD group (3.1% vs. 4.9%, p = 0.04, uncorrected) [15]. Despite the fact that the VEST study did not result in a lower rate of arrhythmic death for WCD patients, there are important aspects of this study that deserve deeper scrutiny. Unwitnessed arrhythmic death is difficult to ascertain, and five of the nine VEST subjects deemed to have died due to an arrhythmia were wearing the WCD at the time, and the WCD showed no evidence of a tachyarrhythmia. Since arrhythmic death is rare, even a small number of misinterpretations in a study like this may skew results. Moreover, the study was designed assuming patients would wear the WCD at least 70% of the time, and compliance dropped as the study progressed. Since fewer patients wearing the WCD died, it has been argued that there was not a single active treatment group in the study (WCD group) but rather two: patients randomized to the WCD group broken down into those who wore the WCD and those who did not [16]. Of the patients in the WCD arm of the study who died, 75% were not wearing the WCD at the time [15].

**5. Patient populations**

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

**5.1 Transient contraindication for an ICD**

One of the main reasons for WCD use is ICD system infection, which poses a clinical challenge in that the best course of action is to extract the device and lead(s), submit the patient to a course of antibiotic therapy, and then replace the ICD system with a new device [7, 9, 45]. The rate of infections associated with cardiac implantable electronic systems continues to increase, even at high-volume centers [46]. Antimicrobial therapy may last 10–14 days or longer, depending on the nature of the infection and the patient's response. During this time, the patient is without an ICD. Leaving the ICD in place while treating an infection is associated with a high mortality rate (31–66%) [47, 48], but removing the device also increases the patient's mortality rate, albeit from 8–27% [49–51]. Thus, the clinician faces three challenges: if the device is replaced too early, the patient risks re-infection; if the patient is deprived of the device too long, there is a risk for potentially life-threatening arrhythmias; and placing the patient under close monitoring in the hospital or a long-term care facility is cost prohibitive and deleterious to the patient's quality of life. In such cases, the use

In a study of 97 ICD patients whose devices had to be explanted for infection, patients were prescribed a WCD for the mean antimicrobial treatment course of 21 days. As they recovered from infection, two patients experienced a total of four VT episodes, all of which could be successfully treated [52]. In a retrospective analysis of 8058 patients who received a WCD from 2002 to 2014 when an infected ICD was removed, 4% experienced ventricular tachyarrhythmias, and the rate of arrhythmic episodes was greatest in the first 3 weeks after device explantation (0.9, 0.7, and 0.7%, respectively), and the risk for ventricular tachyarrhythmias after device removal was 4% during the first 2 months and 10% at 1 year [25].

of a WCD can be a valuable interim solution for arrhythmic rescue.

**5.2 Bridge to cardiac transplantation/left ventricular assist device**

treated by the WCD because it lacks a pacing capability [23].

90 days. This includes patients with cardiomyopathy.

**5.4 NYHA Class IV heart failure**

**75**

**5.3 Low ejection fraction in reimbursement-mandated waiting period**

In the USA and other parts of the world, patients with an ejection fraction ≤35% may be required by reimbursement authorities and guidelines to wait out a specific period of time before an ICD may be implanted; these time periods range from 30 to

This group of patients meets the requirements for Class IV heart failure but is not otherwise indicated or qualified to receive an ICD. Some of these patients may

Heart transplantation or the use of a left ventricular assist device is the only potentially long-term therapeutic option for some patients, but during the waiting period, patients are at high risk for dangerous arrhythmias and may have other comorbid conditions as well. In a study of 121 patients prescribed with the WCD while waiting to receive a donor heart (mean 127 days), 7 patients (5.8%) were shocked appropriately, and all survived [23]. Two inappropriate therapy deliveries occurred deemed to be caused by rapid ventricular response to atrial fibrillation. In this study, two patients died of asystole during the waiting period; asystole is not

Early after the WCD was first cleared to market, an observational study called the Wearable Defibrillator Investigative Trial (WEARIT) enrolled 177 ambulatory patients who had New York Heart Association (NYHA) functional Class III or IV heart failure and an ejection fraction <30%. It was subsequently combined with a similar observational study, the Bridge to ICD in patients at risk of sudden arrhythmic death (BIROAD), which enrolled patients who had an AMI and needed bridge therapy for up to 3 months (n = 112). In 901 patient-months, the mean duration of wear was 3.1 months. Among the WEARIT patients, there were two appropriate and successful therapy deliveries in the same patient several days apart, and there were four appropriate, successful therapies delivered in two of the BIROAD patients. Two unsuccessful therapy deliveries occurred, both of which involved the improper wear of the WCD. Altogether, 12 patients died over the course of the study, none of whom were wearing the WCD at the time. Over the 901 patientmonths, there were 6 inappropriate therapy deliveries in 6 patients (0.7% per month) [17].

The WEARIT-II Registry enrolled 2000 patients, of whom 805 were diagnosed with ischemic cardiomyopathy, 927 with nonischemic cardiomyopathy, and 268 with congenital heart disease [18]. During the study, 41 patients experienced a total of 120 episodes of VT, of whom 54% received an appropriate shock. Inappropriate shocks occurred in 0.5% of patients. Many of the patients in WEARIT-II had improved their ejection fraction over the course of time they wore the WCD, and at the end of WCD treatment, only 42% got an ICD.

The Study of Wearable Cardioverter Defibrillator in Advanced Heart-Failure Patients (SWIFT) was a nonrandomized prospective study at two centers evaluating the use of the WCD in 75 patients hospitalized with advanced heart failure symptoms and LV dysfunction. Patients wore the WCD for 3 months after hospital discharge. Two-thirds of the patients (66%) had nonischemic cardiomyopathy. Eight arrhythmic events occurred in five patients, all successfully terminated by the WCD. No inappropriate therapies were delivered, and no patients died in the course of the study. When the study concluded, 28% were implanted with an ICD [19].

A summary of these trials appears in **Table 1**.
