**5. Patient populations**

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

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

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 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

wearing the WCD at the time [15].

*Sudden Cardiac Death*

the end of WCD treatment, only 42% got an ICD.

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

implanted with an ICD [19].

**74**

month) [17].
