Updated Research on the Wearable Cardioverter-Defibrillator Vest: Interview with Mina K. Chung, MD

Interview by Jodie Elrod
Interview by Jodie Elrod
New research in the Journal of the American College of Cardiology showed that survival rates with a wearable cardioverter-defibrillator (WCD) vest were comparable to that of an implantable cardioverter defibrillator (ICD).[1] In this interview we learn more about the study from lead author Mina K. Chung, MD from the Cleveland Clinic. What was the purpose of this study? What prompted this study? The reason we wanted to look at this was to see if the WCD really worked. Unlike implantable ICDs that don't require patient input to function, the WCD requires a patient to actually wear the vest for it to work. We were also interested in looking at how effective it was for terminating arrhythmias, and whether it could be as effective as an implantable ICD, since we use it for patients we consider at potential high risk for sudden death. How many patients participated in the study? Which type of wearable cardioverter-defibrillator was utilized? A total of 3,569 patients were included in the registry. The WCD used in the study was the LifeVest (ZOLL Lifecor, Pittsburgh, PA). Tell us about the nationwide registry of post-market release WCDs. All patients issued a WCD after market release in the U.S. are entered into a database maintained by ZOLL Cardiac Management Solutions for regulatory, reimbursement, and tracking purposes. The database contains indications, baseline demographics (age and gender), compliance, and events.[1] All patients signed consent to use their data for quality monitoring, health care operation activities, and/or research.[1] Describe the patients' willingness to wear the device and percentage of patient compliance. How often did patients wear the WCD on average? In terms of compliance, one reassuring finding of the study was that we showed that the WCD was worn with good compliance by most patients. Patients did wear the vest. Daily use was >90% in over half of patients. Mean daily use was about 20 hours. Compliance was defined as the time during a day that a WCD user had the device on, the belt connected, and at least one electrocardiogram lead contacting the skin.[1] Tell us about the results. The WCD proved to be quite effective in terminating life-threatening cardiac arrest due to ventricular tachycardia or fibrillation, with first shock success in 99% of these events and an overall survival of 99.2% over the duration of its use. Survival was similar to that of patients with implantable defibrillators. We did also see that not all cardiac arrests were due to arrhythmias that could be saved by a shock. Asystole (no heart rhythm) or pulseless electrical activity accounted for a quarter of sudden cardiac arrests and had very high mortality rates. The current WCD does not have pacing capabilities, but future forms will likely incorporate the ability to pace and treat life-threatening slow heart rates as well. The study also yielded some interesting data on event rates in various groups of patients. Event rates and mortality were the highest in patients with traditional ICD indications, rationalizing use of the WCD as an acceptable temporary alternative or bridge to long-term ICD implantation. The study also showed events occurring in patients who had recent heart attacks and lower left ventricular ejection fractions. Though these patients have been reported to have a high incidence of sudden death early after their heart attacks, studies haven't shown a benefit to early ICD implantation. Currently there is coverage for a WCD in this setting, and as there does seem to be benefit in this group with WCD use, the WCD could be used as a bridge to long-term ICD implantation in this group. How many sudden cardiac arrest events occurred in patients during this time? During the time that the WCD was worn, 80 sustained VT/VF events occurred in 59 patients (1.7% of the total number of patients).[1] How many inappropriate shocks were reported with WCD use? Inappropriate shocks (not occurring on sustained VT or VF) occurred in 67 of 3,569 (1.9%) patients during 4,788 months of use (1.4% per month).[1] Inappropriate shocks are a combination of sustained inappropriate detections by the WCD and failure to use the response buttons by the patient.[1] Reasons for inappropriate detection were (multiple reasons possible during a detection): electrocardiographic signal loss, 4.4%; multicounting on normal cardiac signal, 4.4%; signal artifact, 67.6%; supraventricular tachycardia, 26.5%; and nonsustained VT, 5.9%.[1] Patient-reported reasons for failure to use the response buttons were (1 reason recorded per episode): inconsistent or unconcerned (32.4%), physically or mentally unable to respond (11.8%), sleeping (26.5%), did not remember why (10.3%), did not remember training (10.3%), mental or physical obstacle at the time (4.4%), and did not hear alarms (4.4%).[1] How were survival rates comparable to that of an implantable ICD? Why is this significant? Survival was similar to that of ICD patients, and highest in patients with traditional ICD indications, rationalizing the use of the WCD as an acceptable temporary alternative or a bridge to long-term ICD implantation.[1] What factors ensure effectiveness of the WCD for the prevention of sudden death? Compliance is important. Because sudden death mortality occurred in patients who were not wearing the WCD or who had bystander interference, electrocardiogram signal disruption, or unipolar pacing artifacts, patient instruction regarding proper use of and compliance with the WCD is vital to ensuring the efficacy of the WCD in preventing SCD.[1] Also, asystole or pulseless electrical activity accounted for 24.5% of SCA events with high associated mortality rates, rationalizing the need to incorporate pacing therapies into future WCD systems.[1] Will further research be done? Yes. We will be exploring the efficacy of the WCD in the patient population in the "bridge" time after MI or revascularization. There are also plans to incorporate pacing into future WCD systems.