Wearable Defibrillator in Congenital Structural Heart Disease andInherited Arrhythmias
Mohan Rao, MDa, Ilan Goldenberg, MDa,*, Arthur J. Moss, MDa, Helmut Klein, MDa,David T. Huang, MDa, Nicole R. Bianco, PhDb, Steven J. Szymkiewicz, MDb,
Wojciech Zareba, MDa, Andrew Brenyo, MDa, Jonathan Buber, MDc, and Alon Barsheshet, MDa
The implantable cardioverter-defibrillator (ICD) wasshown to prolong survival in patients who experience car-diac arrest from ventricular tachyarrhythmia not due to atransient or reversible cause (secondary prevention)1–3 andn appropriately selected patients with left ventricular dys-unction (primary prevention).4–7 However, in a subset of
patients, the risk of sudden cardiac death is temporary or isassociated with a reversible cause. In these circumstances,the wearable cardioverter defibrillator (WCD) might pro-vide protection against sudden cardiac death until the risk ofventricular arrhythmias subsides or a definitive indicationfor ICD implantation has been determined.8,9 Patients withcongenital structural heart disease (CSHD) and inheritedarrhythmias (IAs) might have electrical instability that pre-disposes to ventricular arrhythmias.10–12 In these high-risk
aCardiology Division, University of Rochester Medical Center, Roch-ester, New York; bZOLL Cardiac Management Solutions, Pittsburgh,
ennsylvania; and cHeart Institute, Sheba Medical Center, Tel Hashomer,Israel. Manuscript received May 11, 2011; manuscript received and ac-cepted July 12, 2011.
This study was supported by funding from ZOLL Cardiac ManagementSolutions (Pittsburgh, Pennsylvania).
The data were obtained from a ZOLL database, but no additionalsupport from ZOLL was obtained for this study.
populations, the WCD might provide an effective therapeu-tic option. The present study included 162 patients withCSHD and IA who were followed up after receiving WCDtherapy for the prevention of sudden cardiac death and wasdesigned to evaluate the compliance of use, arrhythmic risk,and long-term outcome after treatment with the WCD.
Methods
The present study population included 162 adult patients(�18 years old) with diagnosed or suspected CSHD (n �43) or IA (n � 119) who were issued a WCD in the UnitedStates from 2005 through 2010. The patient data regardingthe demographic and clinical baseline characteristics, com-pliance of use, and the rate of arrhythmic events detectedand/or treated by the device, were collected by the devicemanufacturer (ZOLL Cardiac Management Solutions,Pittsburgh, Pennsylvania), who maintained a prospec-tively collected database of all patients issued a WCD inthe United States for regulatory, reimbursement, andtracking purposes. All patients issued the WCD providedwritten consent to use their data for quality monitoring,healthcare operation activities, and/or research. The1-year mortality data were obtained from the Social Se-curity Death Index.
The technical details of the WCD have been previously
described.8 In brief, the WCD is designed to detect and
1633Congenital Heart Disease/Multicenter Experience With Wearable Defibrillator
automatically treat ventricular tachycardia or ventricularfibrillation (VT/VF) without the need of medical personnelor bystander intervention. The WCD 3100 consists of achest garment that holds 2 large posterior and 1 apicalself-gelling defibrillator electrodes and 4 nonadhesive ca-pacitive dry tantalum oxide electrodes for long-term elec-trocardiographic monitoring; the electrodes are mounted onan elastic belt (1.5 lb or �680-g tension) of the chest
Table 1Patient characteristics
Variable
Age (years)WomenReason patient did not receive implantable cardioverter defibrillator*
Implantable cardioverter defibrillator explanted for infection/malfunctionBridge to heart transplantOngoing cardiac evaluationPregnancy/peripartumPlanned surgery/treatment of other medical problemsother
Ejection fraction category (%)*�5040–4930–39�30
Ejection fraction (%)*Family history of cardiac diseasePregnant/peripartumIllicit drug use
* Data on the reason patients did not get ICD were available for 120 patie
able 2ompliance and treatment by disease category
Variable
Average hours worn per dayTotal days wornReason wearable cardioverter-defibrillator use ended
Patients treated with shocksInappropriatelyAppropriately
Number of wearable cardioverter-defibrillator shocks†
InappropriateAppropriateTotal follow-up time (days)
Deaths during wearable cardioverter-defibrillator useDeaths during 1-year follow-up (after wearable cardioverter-defibrillator uTotal deaths‡
Data are presented as % or median (interquartile range).* Statistical significance was not assessed because of small numbers.† Number of events listed for descriptive purposes.‡ Mortality data during 1-year follow-up after WCD use were availableNA � not applicable.
garment. A signal/noise detection algorithm is implemen-
ted to filter noise from skin movement to avoid unneces-sary alarms or inappropriate defibrillator discharges. WhenVT/VF is detected, a sequence of alarms is initiated, startingwith vibration against the skin, followed by 2 low- andhigh-volume alarms and a verbal warning that a shockmight be delivered. Patients were trained to press the re-sponse buttons within 20 seconds to withhold the capacitordischarge as long as consciousness prevailed. Responding
acted as a test of consciousness; if no response is detected,
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1634 The American Journal of Cardiology (www.ajconline.org)
the device charges, extrudes gel from the defibrillation elec-trodes, and delivers �5 biphasic shocks of preprogram-mable energy levels with a maximum output of 150 J. TheWCD continuously records detected events and therapydelivered, indicates device on/off status, and monitors theelectrode connections.
Compliance to treatment with the WCD was defined asany time during a day that a WCD user had the device on,the belt connected, and �1 electrocardiographic lead con-tacting the skin.9 The days of use were determined as anyay with �15 minutes of WCD use. Electrocardiographicnd defibrillation electrode contact were determined by mi-
Figure 1. Type of shock delivered by WCD in both groups. Event ratesinappropriate shocks in each group by total follow-up time of each group
Table 3Characteristics of patients who received wearable cardioverter defibrillato
Pt.No.
Gender Age(years)
DiseaseSuspected
Reason ICD notImplanted
DaysWorn W
1 Female 51 LQTS Ongoing cardiactesting
25
2 Female 63 LQTS ICD explanted 2
3 Female 27 LQTS Pregnancy 12
4 Female 36 Brugadasyndrome
Unknown 12
5 Male 30 ARVD Ongoing cardiactesting
17
6 Female 42 LQTS ICD explanted 3
ARVD � arrhythmogenic right ventricular dysplasia; LQTS � long Q
roampere AC signals similar to conventional monitoring r
ystems. The device also recorded electrocardiographicata for rhythms greater than a preprogrammed ratehreshold that did not match a baseline template andefined such arrhythmias as ventricular arrhythmias. AOLL physician determined the WCD shocks to be ap-ropriate if they occurred on sustained VT/VF and inap-ropriate if not. Inappropriate shocks were further ana-yzed for the cause of inappropriate detection from thelectrocardiographic recordings and a lack of responseutton use from the patient call reports. Two-lead elec-rocardiograms from all shocks and baseline tracingsrom patients enrolled in the present study were also
nd CSHD groups calculated by dividing total number of appropriate andultiplying by 100.
s
yEnd UseReason
Treatment ElectrographicFindings
Died DuringWCD Use
ICD Inappropriateshock, 1
Noise No
ICD Inappropriateshock, 1
Noise No
ICD Appropriateshocks, 2
Torsades (2episodes)
No
ICD Inappropriateshock, 1
Artifact No
Unknown Appropriateshock, 1
Ventricularfibrillation
Yes (peritonitis)
Unknown Inappropriateshocks, 4
Noise (4 episodes) No
ome; Pt. No. � patient number.
in IA a
r shock
Hoursorn/Da
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6
21
21
21
18
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1635Congenital Heart Disease/Multicenter Experience With Wearable Defibrillator
The data are reported as the percentages or median (in-terquartile range). The characteristics of the study patientsand WCD firing were compared using the nonparametricWilcoxon rank-sum test for continuous variables, and thechi-square or Fisher exact test, as appropriate, for categor-ical variables. The probability of all-cause mortality bydisease category was graphically displayed according to theKaplan-Meier method, with a comparison of cumulativeevents using the log-rank test. The SAS statistical softwarepackage, version 9.2 (SAS Institute, Cary, North Carolina)was used for the analyses. Two-sided p �0.05 was consid-ered to declare statistical significance.
Results
A total of 162 patients were included in the presentstudy, of whom 43 (27%) had CSHD and 119 (73%) had IA.The CSHD group included patients with tetralogy of Fallot(37%), ventricular malformations such as noncompactionand a single ventricle (13%), multiple congenital anomalies,including a combination of �2 cardiac chamber hypoplasia,septal defects, obstructive lesions, or cyanotic defects(21%), and other solitary congenital anomalies, includingatrial and ventricular septal defects, transposition of greatvessels, truncusus arteriosis, and patent ductus arteriosis(29%). The IA group comprised patients with suspected ordiagnosed long QT syndrome (54%), Brugada syndrome(33%), arrhythmogenic right ventricular dysplasia (8%), andpatients with an undefined etiology of IA (5%). The patientbaseline characteristics are listed in Table 1. The mean age ofthe study patients was 38 � 27 years. The proportion ofwomen was similar in the 2 groups. The patients with CSHDad a lower ejection fraction than the IA group (37 � 19ersus 57 � 10, p � 0.001).
Patient compliance and WCD use data are listed in Table. The compliance rate for daily use with the WCD was1% in both groups. The 2 most common reasons for dis-ontinuing WCD use in the CSHD and IA groups were ICDmplantation (32% and 42%, respectively) and completionf the WCD treatment period as planned (21% and 14%,espectively).
All patients who experienced VT/VF while wearing theCD received shock therapy from the device that appro-
riately terminated all ventricular tachyarrhythmic epi-odes, with no arrhythmic deaths occurring during WCDse. A total of 6 patients in the IA group received a shockhile wearing the WCD, but no arrhythmias were detected
nd no device therapies occurred among patients in theSHD group. The rates of appropriate and inappropriate
hocks (adjusted for follow-up time) are shown in Figure 1.n the IA group, 2 patients received a total 3 appropriatehocks for VT/VF (corresponding to an event rate of 27ppropriate shocks per 100 patient-years) and 4 patientseceived 7 inappropriate shocks because of electrocardio-raphic noise and artifacts (corresponding to an event ratef 63 inappropriate shocks per 100 patient-years). The de-ails of the patients who received appropriate and inappro-riate shocks are listed in Table 3. One patient with sus-ected long QT syndrome experienced torsades de points on
occasions and received a shock for each episode that fi
uccessfully terminated the arrhythmia (Figure 2); this pa-ient eventually received an ICD. One patient with sus-ected arrhythmogenic right ventricular dysplasia experi-nced polymorphic VT that degenerated into ventricular
Figure 2. Electrocardiogram of shocks delivered by WCD showing (A)uccessful termination of polymorphic ventricular tachycardia by WCDn patient with suspected long QT syndrome (LQTS); and (B) inappro-riate shock delivered by WCD because of baseline noise in patientith suspected Brugada syndrome. Red parts of electrocardiogram
ECG) indicate WCD charging and immediate recording after shockischarge.
brillation and was successfully treated with 1 shock. This
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1636 The American Journal of Cardiology (www.ajconline.org)
patient died 6 days later from intra-abdominal viscous rup-ture and peritonitis during WCD use. Four patients in the IAgroup received a total of 7 inappropriate shocks because ofnoise detected as VT/VF while wearing the WCD. Figure 2shows an example of an electrocardiographic recording ofbaseline artifact of noise that the WCD detected as aVT/VF event, after which an inappropriate shock wasdelivered. Kaplan-Meier survival curves demonstrated asignificantly lower survival rate at 1 year of follow-upamong the patients with CSHD (87%) compared to thosewith IA (97%, p � 0.02; Figure 3). The details of the 7
Figure 3. Kaplan-Meier cumulative proba
able 4haracteristics of patients who died during 1 year of follow-up
Pt. No. Age(years)
Gender DiseaseCategory
ReasIm
ied during wearablecardioverter-defibrillatorprescription
1 46 Male IA Chemoth
2 47 Female CSHD Bridge to
3 34 Male CSHD NA4 30 Male IA Cardiac a
testingied after wearable
cardioverter-defibrillatorprescription
1 35 Male CSHD Abnormaanatom
2 45 Male CSHD Bridge to3 59 Female CSHD Chemoth
NA � no information available or not applicable.
patients who died during the 1-year follow-up are listed
in Table 4. Four patients died during the period in whichthe WCD was prescribed, 2 patients in the IA group and2 in the CSHD group. In the IA group, 1 patient withsuspected long QT syndrome died while undergoing che-motherapy for B cell lymphoma. The second death duringWCD prescription in the IA group was due to peritonitisthat developed owing to a ruptured colon that resultedfrom bowel obstruction. This patient had experienced aprevious episode of VT/VF that was successfully termi-nated by the WCD (Figure 2). Both patients in the IAgroup were not wearing the WCD at the time of death. In
f survival at 1 year by disease category.
not DaysWorn
HoursWorn/Day
Cause of DeathDuring WCD Use
Survival AfterWCD Use
Completed (days)
27 21 Noncompliant atdeath
NA
62 13 Noncompliant atdeath
NA
5 6 NA NAetic 17 21 Intra-abdominal
viscous ruptureNA
entricle 21 9 NA 221
19 23 NA 26757 21 NA 21
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1637Congenital Heart Disease/Multicenter Experience With Wearable Defibrillator
which the WCD was prescribed and 4 after device use.Similar to the IA group, none of the patients died whilewearing the device.
Discussion
The present study is the first to examine the utility of theWCD in preventing sudden cardiac death in high-risk pa-tients with CSHD and IA. Our data suggest that compliancefor WCD use is good in these high-risk populations; theWCD can be safely used in this population without evi-dence of mortality while wearing the device, but inappro-priate shocks do occur; and patients with IA had a greaterrate of ventricular tachyarrhythmias during WCD therapybut exhibited significantly lower long-term mortality ratesthan the patients with CSHD.
The WCD has previously been shown to be effective insuccessfully treating VT/VF in high-risk patients.8,9,13–15
The Wearable defibrillator Investigative Trial (WEARIT)and Bridge to ICD in Patients at Risk of Arrhythmic Death(BIROAD) studies have shown that the WCD is effective intreating ventricular tachyarrhythmias among patients withsevere left ventricular dysfunction after recent myocardialinfarction or coronary artery bypass surgery, who are oth-erwise not clear candidates for ICD placement (because ofmyocardial infarction �40 days earlier or coronary revas-cularization within the previous 90 days).15 Recently,
hung et al9 examined the outcomes of WCD use in thenited States from a nationwide registry of 3,569 patients whoore the WCD. That study reported a satisfactory compliance
ate of 90% with WCD daily use and a survival rate of 90%mong patients who experienced VT/VF events during WCDse. In that report, however, only 12 patients (0.4%) had aenetic predisposition for sudden cardiac death, in whom novents were recorded while wearing the WCD.
In the present study, we focused on the use and efficacyf WCD for the treatment and prevention of arrhythmiceath in high-risk patients with CSHD and IA. We report anverall compliance rate of 91% for WCD daily use, similaro the compliance rate reported previously by Chung et al.9
Our study demonstrated a greater 1-year mortality rateamong patients with CSHD compared to those with IA,possibly because the patients in the former group weresicker, with a lower left ventricular ejection fraction, andwere more likely to wear the WCD as a bridge to hearttransplantation. In contrast, patients with CSHD did notexperience any VT/VF events or receive any appropriate orinappropriate shocks while wearing the WCD. However, thepatients with IA had a greater rate of VT/VF for which theyreceived appropriate shocks (27 appropriate shocks per 100patient-years) during WCD use. The study by Chung et al9
had shown a somewhat lower rate of appropriate shockswith the WCD (20 appropriate WCD shocks per 100 pa-tient-years), suggesting a greater arrhythmic risk amongthose with IA while wearing the WCD than among patientswith acquired heart disease (who constituted most of thepopulation in the previous report) and that more attentionshould be paid in clinical practice to the prescription of theWCD in high-risk patients with IA. We have also observeda relatively high rate of inappropriate shocks among those
with IA (63 per 100 patient-years). Previous data indicate
that the most common cause of inappropriate shock therapywith the WCD is signal artifact,9 similar to the data from theresent study. This type of inappropriate shocks by theCD can be prevented by a patient (if conscious) by press-
ng the response button after a device alarm. Thus, it isossible that some of these events might have resulted fromisunderstanding the instructions given by healthcare pro-
essionals to the study patients before WCD use.Because the present study was based on registry data,
ifferences in disease assessment, the evaluation of specificarameters, and the documentation patterns might have in-uenced the study results. Mortality data at 1 year of fol-
ow-up after WCD use were available for 145 patients, datan the reason patients did not receive an ICD were availableor 120 patients, and data on the ejection fraction werevailable for only 64 patients. In addition, we did not collectata on the mode of death after WCD use. The present studyas underpowered to evaluate the mortality risk associatedith the CSHD or IA subgroup categorized by the ejection
raction. Despite these limitations, the present study in-luded the largest reported cohort of patients with IA orSHD using a WCD.
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