**7. Appropriate and inappropriate therapy**

The WCD has been shown to deliver appropriate high-energy therapy to convert dangerous ventricular tachyarrhythmias. In a postmarket registry of 3569 WCD patients (mean duration wear was 52.6 69.9 days), first shock success occurred in 99% of cases (79/80) for all episodes of conscious VT/VF and in 100% of cases (n = 76) of unconscious VT/VF [33]. Because the WCD is an external device, it is far more exposed to sources of electromagnetic interference (noise) than implanted devices, which may result in oversensing, inappropriate arrhythmia detection, and inappropriate therapy delivery. Patients are signaled about 30 s prior to therapy delivery and may abort the shock by pressing two buttons [39, 40]. For this reason, the rate of inappropriate therapy delivery with the WCD is relatively low, occurring in approximately 0.4–3.0% of patients [6, 18, 33, 43]. See **Table 1**.

The WCD delivers rescue shock therapy only and has no pacing capability. Asystole, a recognized risk factor for dangerous ventricular tachyarrhythmias, may occur in patients with compromised cardiovascular function, such as low ejection fraction. While an ICD can detect and offer pacing support during an asystole

episode, the WCD cannot pace such patients, and there is a risk that an untreated asystole may be fatal [66].

In another study of 123 patients considered WCD candidates, at baseline 21% showed signs of clinically depressive symptoms, and 52% had anxiety. Six weeks after WCD therapy commenced, rates of depression and anxiety dropped to 7 and 25%, respectively [32]. It is not clear if patients recovered their emotional equilibrium as a result of WCD therapy or as a matter of course as they got used to their

When a patient has more than one electronic cardiac device, the potential of device-device interaction exists. The literature reports one case of a fatal devicedevice interaction between a permanent pacemaker and a WCD [70]. In this case, the patient received unipolar dual-chamber pacing, but when he developed VF, no therapy was delivered as the device inappropriately detected the large unipolar

A study sponsored by Zoll examined pacing in 60 patients testing the AAI, VVI, and DDD modes in both unipolar and bipolar device configurations to

determine if the WCD would detect the pacing spikes; patients were signaled before shock delivery and could use the patient response buttons to avert the therapy delivery. Only unipolar DDD pacing was detected by the WCD's algorithm and only in 10% of patients (6/60). This study suggests that pacing may occur

concomitantly with WCD use if unipolar configurations are avoided [2]. If unipolar pacing must be used in a particular patient, then the WCD is contraindicated. Another study of the concomitant use of the WCD and a pacemaker showed that double-counting and waveform alterations might also occur in certain bipolar pacing modes and in single-chamber as well as dual-chamber pacing [44]. Caution is urged in using the WCD in patients with pacing support from an

The WCD is "rented" to patients for a monthly fee, and reimbursement provisions vary by country. Since costs can be substantial, there is a need to better stratify patients into those who truly need a WCD for arrhythmic rescue and those who might be unlikely to benefit from it [41]. Cost-effectiveness models show that the number needed to treat to save 1 life with a WCD falls in the range of 70–110 patients over a median of 53–57 days [26]. There are situations in which the WCD poses a decided cost advantage. For example, cardiomyopathy patients who might otherwise be considered a candidate for permanent primary prevention ICD implantation may benefit from using the WCD during a recovery period; data

shows that 60% of such patients will recover to the point that an ICD

the hospital or discharge him or her to a skilled nursing facility for weeks during antimicrobial therapy and recovery. The patient is at risk for SCD

in the population and the patient had to wait at least 2 weeks before ICD

implantation is not necessary [18, 33, 41]. Thus, the costs for the temporary use of the WCD may be offset by the decision not to implant an ICD. In patients whose ICD must be removed for infection, it is sometimes necessary to keep the patient in

throughout this time. A cost-effectiveness analysis found that the WCD was costeffective in this situation in that it allowed the patient to be discharged home; the analysis is based on the assumption that there was a 2-week 5.6% risk of SCD

new identities as cardiac patients.

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

**8.4 Device-device compatibility**

pacing spikes as cardiac signals [70].

implanted pacemaker system.

**9. Costs**

replacement [71].

**81**
