Wearable defibrillator use in heart failure (WIF): results of a prospective registry

Sudden cardiac death (SCD) is believed to account for 40 to 70% of the mortality associated with congestive heart failure (HF), with progressive pump failure causing the majority of the remaining fatalities [1, 2]. Current figures estimate that 20% of HF patients will die within one year of diagnosis [3], which represents an improvement over prior decades [4]. Thus, the sudden death rate in the first year of diagnosis is about 10%, mostly resulting from terminal ventricular arrhythmias. Further complicating the situation, some medications used in the treatment of HF (ie, inotropes and diuretics) can also contribute to ventricular tachycardia (VT) in patients [5]. Implantable cardioverter-defibrillators (ICDs) are effective in preventing SCD in HF due to ischemic and non-ischemic cardiomyopathy when cardiac function, as measured by ejection fraction (EF), is ≤ 35% [6–9]. HF patients on heart transplant lists have also been shown to benefit from ICDs [10–12]. However, ICDs may not be the most cost-effective [13], or the best method of reducing the incidence of sudden death in all HF patients, particularly in patients having a short (or uncertain) duration of risk or those with drug refractory NYHA class IV HF [14]. According to AHA/ACC/HRS guidelines for ICDs, newly diagnosed nonischemic dilated cardiomyopathy (NIDCM) patients should be medically optimized, a process that may take months, before implantation [15]. Conversely, wearable cardioverter defibrillators (WCD) such as the LifeVest® device (manufacturer: ZOLL, Pittsburgh, PA) can be used immediately to protect against SCD until long-term risk of sudden death is established or cardiac function improves.

The WCD (LifeVest®, ZOLL, Pittsburgh, PA) was FDA-approved in 2001 as an outpatient device after a clinical trial involving 285 out-of-hospital patients [16]. WCDs are intended for use in adult patients that have an increased risk of SCD if an ICD is not warranted. Since approval, more than 60,000 patients have used the LifeVest® on an outpatient basis for a wide variety of conditions. Like ICDs, WCDs are designed to detect and treat ventricular tachyarrhythmias without the need for bystander intervention. Unlike ICDs, they are completely external to the body and do not require surgical intervention. Thus, they are ideal for shorter-term applications where the risk of SCA is changing or uncertain. WCD use in the HF population is limited [16, 17]. In order to gain further clinical experience with WCD use in this population, ZOLL sponsored the WIF (Wearable defibrillator use In heart Failure) registry. The primary purpose of the WIF registry was to determine the incidence of SCA in this population, the cause of SCA (bradyarrhythmias or tachyarrhythmias), and the efficacy of early defibrillation given by the WCD. Three patient groups were followed; patients listed for heart transplantation, patients with dilated cardiomyopathy (DCM) and patients using inotropes known to cause ventricular tachyarrhythmias.

The intent of the WIF registry was to observe the use of the WCD in a population of HF patients over a 90 day period. The enrolled group represented a mix of dilated cardiomyopathy patients (Tables 1 and 2), with the majority of patients having an idiopathic (39%) or ischemic (36%) etiology of HF. Twelve patients (14.6%) were listed for cardiac transplantation, and four (4.9%) were on inotropes. As one may expect from the small sample size that resulted from lower than anticipated enrollment, there were no SCA events in the 82 patients who completed the study. Current WCD event statistics suggest an event rate for new cardiomyopathy patients wearing the WCD to be approximately 0.00013 VT/VF events per patient per day [18]. Therefore, the chance of not having an event was approximately 42%. Regardless, the WCD bridged the DCM patients until long-term therapy decisions could be made. There were also no adverse events or unnecessary shocks by the WCD during the study. Daily compliance with the WCD was a median of 21.8 hrs, which met our goal of at least 85% median daily wear time. This compliance is very similar to that of the current general commercial population (median=21.7 hr/day) [18]. Seventy percent of patients wore the device for average ≥ 80% of the day. Although assessing and comparing compliance is difficult, compliance with the WCD is similar to compliance with medications in HF populations [19].

Interestingly, 34 (41.5%) patients were considered much improved at the end of the study and no longer needed the WCD, mostly due to an improved EF (EF ≥ 35%). This may have been due to the high rate of beta-blocker use, or possibly because some patients had reversible causes of disease. However, 33% of the 12 transplant-listed patients also showed improvement. To our knowledge, few recent peer-reviewed studies have analyzed improvement in ventricular function 60–90 days post-diagnosis or acute decompensation of DCM [20, 21]. The IMAC trial, which studied intravenous immune globulin in recent onset DCM, also saw mean LVEF increase significantly in patients from 25% to 41% over a 6 month period regardless of treatment [22]. It should also be emphasized that improvement in LV function should not be taken as a “cure” and medications should be continued or monitored closely, as relapses may occur [21]. Although we do not know the cause of death, two patients who were discontinued from the WCD due to EF improvement (EF=43% and 50%) died (56 and 229 days) after removing the WCD. There was an overall 7.3% mortality rate over 288±176 days after being fit with the WCD. Unfortunately, this time period was beyond the scope of the study and the reasons for death are unknown. The mortality rate is similar to that seen in the SCD-HeFT and DEFINITE (non-ischemic) trials [7, 9].

The benefits of prophylactic ICD implantation remains contentious in DCM patients [14]. Although ICDs have been shown to be beneficial in this group of patients [7, 8], it is not without risk, and the event rate remains low (especially for those without prior MI) [23]. For this reason, risk stratification of these patients remains extremely important. A recent study showed a yearly increase in out-of-hospital mortality rates in Medicare HF patients, possibly due to shortened hospital stays [24]. It may be beneficial to the patient (and society) to give the patient enough time to potentially stabilize on medication and recover LV function, while still keeping them protected and out of the hospital. It may also be beneficial to avoid ICD placement in the transplant-listed patient, if their wait is not expected to be extremely long. These goals can be accomplished with the WCD.

In conclusion, the WCD monitored HF patients until further assessment of risk. The leading reasons for end of WCD use were improvement in left ventricular ejection fraction (LVEF) or ICD implantation if there was no significant improvement in LVSF. Due to the smaller than anticipated sample size, there were no SCD events in the 82 patients who completed the study (≤90 days). The overall 7.3% mortality rate over 288±176 days after being fit with the WCD is similar to that seen in other trials.

This research was sponsored by ZOLL Cardiac Management Solutions, Pittsburgh, PA.