Patients with congenital structural heart disease (CSHD) and inherited arrhythmias (IAs) are at high risk of ventricular tachyarrhythmias and sudden cardiac death. The present study was designed to evaluate the short- and long-term outcomes of patients with CSHD and IA who received a wearable cardioverter-defibrillator (WCD) for the prevention of sudden cardiac death. The study population included 162 patients with CSHD (n = 43) and IA (n = 119) who were prospectively followed up in a nationwide registry from 2005 to 2010. The mortality rates were compared using Kaplan-Meier survival analysis. The mean age of the study patients was 38 ± 27 years. The patients with CSHD had a greater frequency of left ventricular dysfunction (ejection fraction <30%) than did the patients with IA (37% vs 5%, respectively; p = 0.002). The predominant indication for WCD was pending genetic testing in the IA group and transplant listing in the CSHD group. Compliance with the WCD was similar in the 2 groups (91%). WCD shocks successfully terminated 3 ventricular tachyarrhythmias in the patients with IA during a median follow-up of 29 days of therapy (corresponding to 23 appropriate WCD shocks per 100 patient-years). No arrhythmias occurred in the patients with CSHD during a median follow-up of 27 days. No patients died while actively wearing the WCD. At 1 year of follow-up, the survival rates were significantly lower among the patients with CSHD (87%) than among the patients with IA (97%, p = 0.02). In conclusion, our data suggest that the WCD can be safely used in high-risk adult patients with IA and CSHD. Patients with IA showed a greater rate of ventricular tachyarrhythmias during therapy but significantly lower long-term mortality rates.
The implantable cardioverter-defibrillator (ICD) was shown to prolong survival in patients who experience cardiac arrest from ventricular tachyarrhythmia not due to a transient or reversible cause (secondary prevention) and in appropriately selected patients with left ventricular dysfunction (primary prevention). However, in a subset of patients, the risk of sudden cardiac death is temporary or is associated with a reversible cause. In these circumstances, the wearable cardioverter defibrillator (WCD) might provide protection against sudden cardiac death until the risk of ventricular arrhythmias subsides or a definitive indication for ICD implantation has been determined. Patients with congenital structural heart disease (CSHD) and inherited arrhythmias (IAs) might have electrical instability that predisposes to ventricular arrhythmias. In these high-risk populations, the WCD might provide an effective therapeutic option. The present study included 162 patients with CSHD and IA who were followed up after receiving WCD therapy for the prevention of sudden cardiac death and was designed 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 United States from 2005 through 2010. The patient data regarding the demographic and clinical baseline characteristics, compliance of use, and the rate of arrhythmic events detected and/or treated by the device, were collected by the device manufacturer (ZOLL Cardiac Management Solutions, Pittsburgh, Pennsylvania), who maintained a prospectively collected database of all patients issued a WCD in the United States for regulatory, reimbursement, and tracking purposes. All patients issued the WCD provided written consent to use their data for quality monitoring, healthcare operation activities, and/or research. The 1-year mortality data were obtained from the Social Security Death Index.
The technical details of the WCD have been previously described. In brief, the WCD is designed to detect and automatically treat ventricular tachycardia or ventricular fibrillation (VT/VF) without the need of medical personnel or bystander intervention. The WCD 3100 consists of a chest garment that holds 2 large posterior and 1 apical self-gelling defibrillator electrodes and 4 nonadhesive capacitive dry tantalum oxide electrodes for long-term electrocardiographic monitoring; the electrodes are mounted on an elastic belt (1.5 lb or ∼680-g tension) of the chest garment. A signal/noise detection algorithm is implemented to filter noise from skin movement to avoid unnecessary alarms or inappropriate defibrillator discharges. When VT/VF is detected, a sequence of alarms is initiated, starting with vibration against the skin, followed by 2 low- and high-volume alarms and a verbal warning that a shock might be delivered. Patients were trained to press the response buttons within 20 seconds to withhold the capacitor discharge as long as consciousness prevailed. Responding acted as a test of consciousness; if no response is detected, the device charges, extrudes gel from the defibrillation electrodes, and delivers ≤5 biphasic shocks of preprogrammable energy levels with a maximum output of 150 J. The WCD continuously records detected events and therapy delivered, indicates device on/off status, and monitors the electrode connections.
Compliance to treatment with the WCD was defined as any time during a day that a WCD user had the device on, the belt connected, and ≥1 electrocardiographic lead contacting the skin. The days of use were determined as any day with ≥15 minutes of WCD use . Electrocardiographic and defibrillation electrode contact were determined by microampere AC signals similar to conventional monitoring systems. The device also recorded electrocardiographic data for rhythms greater than a preprogrammed rate threshold that did not match a baseline template and defined such arrhythmias as ventricular arrhythmias. A ZOLL physician determined the WCD shocks to be appropriate if they occurred on sustained VT/VF and inappropriate if not. Inappropriate shocks were further analyzed for the cause of inappropriate detection from the electrocardiographic recordings and a lack of response button use from the patient call reports. Two-lead electrocardiograms from all shocks and baseline tracings from patients enrolled in the present study were also reviewed by 3 of us (M.R., A.B., I.G.).
The data are reported as the percentages or median (interquartile range). The characteristics of the study patients and WCD firing were compared using the nonparametric Wilcoxon rank-sum test for continuous variables, and the chi-square or Fisher exact test, as appropriate, for categorical variables. The probability of all-cause mortality by disease category was graphically displayed according to the Kaplan-Meier method, with a comparison of cumulative events using the log-rank test. The SAS statistical software package, version 9.2 (SAS Institute, Cary, North Carolina) was used for the analyses. Two-sided p <0.05 was considered to declare statistical significance.
Results
A total of 162 patients were included in the present study, 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 noncompaction and 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, including atrial and ventricular septal defects, transposition of great vessels, truncusus arteriosis, and patent ductus arteriosis (29%). The IA group comprised patients with suspected or diagnosed long QT syndrome (54%), Brugada syndrome (33%), arrhythmogenic right ventricular dysplasia (8%), and patients with an undefined etiology of IA (5%). The patient baseline characteristics are listed in Table 1 . The mean age of the study patients was 38 ± 27 years. The proportion of women was similar in the 2 groups. The patients with CSHD had a lower ejection fraction than the IA group (37 ± 19 versus 57 ± 10, p = 0.001).
| Variable | CSHD (n = 43) | IAs (n = 119) | p Value |
|---|---|---|---|
| Age (years) | 36.6 ± 11.8 | 38.2 ± 13.1 | 0.48 |
| Women | 53% | 55% | 0.82 |
| Reason patient did not receive implantable cardioverter defibrillator ⁎ | 0.001 | ||
| Implantable cardioverter defibrillator explanted for infection/malfunction | 28% | 30% | |
| Bridge to heart transplant | 35% | 2% | |
| Ongoing cardiac evaluation | 17% | 47% | |
| Pregnancy/peripartum | 0% | 9% | |
| Planned surgery/treatment of other medical problems | 17% | 5% | |
| other | 10% | 9% | |
| Ejection fraction category (%) ⁎ | 0.002 | ||
| ≥50 | 42 | 84 | |
| 40–49 | 8 | 8 | |
| 30–39 | 15 | 3 | |
| <30 | 37 | 5 | |
| Ejection fraction (%) ⁎ | 37 ± 19 | 57 ± 10 | 0.001 |
| Family history of cardiac disease | 11% | 90% | 0.04 |
| Pregnant/peripartum | 5% | 18% | 0.04 |
| Illicit drug use | 0% | 20% | 0.001 |
⁎ Data on the reason patients did not get ICD were available for 120 patients and ejection fraction (by echocardiography) data were available for 64 patients.
Patient compliance and WCD use data are listed in Table 2 . The compliance rate for daily use with the WCD was 91% in both groups. The 2 most common reasons for discontinuing WCD use in the CSHD and IA groups were ICD implantation (32% and 42%, respectively) and completion of the WCD treatment period as planned (21% and 14%, respectively).
| Variable | CSHD (n = 43) | IAs (n = 119) | p Value |
|---|---|---|---|
| Average hours worn per day | 19 (12–21) | 19 (10–22) | 0.65 |
| Total days worn | 27 (10–55) | 29 (7–68) | 0.71 |
| Reason wearable cardioverter-defibrillator use ended | 0.22 | ||
| Planned finish | 21% | 14% | |
| Received implantable cardioverter defibrillator | 32% | 42% | |
| Ejection fraction improved | 3% | 13% | |
| Noncompliant | 9% | 9% | |
| Died | 6% | 2% | |
| Unknown | 29% | 20% | |
| Patients treated with shocks | NA ⁎ | ||
| Inappropriately | 0% | 3% | |
| Appropriately | 0% | 2% | |
| Number of wearable cardioverter-defibrillator shocks † | NA ⁎ | ||
| Inappropriate | 0 | 7 | |
| Appropriate | 0 | 3 | |
| Total follow-up time (days) | 5,463 | 4,047 | |
| Deaths during wearable cardioverter-defibrillator use | 5% | 2% | 0.28 |
| Deaths during 1-year follow-up (after wearable cardioverter-defibrillator use) | 8% | 1% | 0.03 |
| Total deaths ‡ | 13% | 3% | 0.02 |
⁎ 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 available for 145 patients.
All patients who experienced VT/VF while wearing the WCD received shock therapy from the device that appropriately terminated all ventricular tachyarrhythmic episodes, with no arrhythmic deaths occurring during WCD use. A total of 6 patients in the IA group received a shock while wearing the WCD, but no arrhythmias were detected and no device therapies occurred among patients in the CSHD group. The rates of appropriate and inappropriate shocks (adjusted for follow-up time) are shown in Figure 1 . In the IA group, 2 patients received a total 3 appropriate shocks for VT/VF (corresponding to an event rate of 27 appropriate shocks per 100 patient-years) and 4 patients received 7 inappropriate shocks because of electrocardiographic noise and artifacts (corresponding to an event rate of 63 inappropriate shocks per 100 patient-years). The details of the patients who received appropriate and inappropriate shocks are listed in Table 3 . One patient with suspected long QT syndrome experienced torsades de points on 2 occasions and received a shock for each episode that successfully terminated the arrhythmia ( Figure 2 ); this patient eventually received an ICD. One patient with suspected arrhythmogenic right ventricular dysplasia experienced polymorphic VT that degenerated into ventricular fibrillation and was successfully treated with 1 shock. This patient died 6 days later from intra-abdominal viscous rupture and peritonitis during WCD use. Four patients in the IA group received a total of 7 inappropriate shocks because of noise detected as VT/VF while wearing the WCD. Figure 2 shows an example of an electrocardiographic recording of baseline artifact of noise that the WCD detected as a VT/VF event, after which an inappropriate shock was delivered. Kaplan-Meier survival curves demonstrated a significantly lower survival rate at 1 year of follow-up among the patients with CSHD (87%) compared to those with IA (97%, p = 0.02; Figure 3 ). The details of the 7 patients who died during the 1-year follow-up are listed in Table 4 . Four patients died during the period in which the WCD was prescribed, 2 patients in the IA group and 2 in the CSHD group. In the IA group, 1 patient with suspected long QT syndrome died while undergoing chemotherapy for B cell lymphoma. The second death during WCD prescription in the IA group was due to peritonitis that developed owing to a ruptured colon that resulted from bowel obstruction. This patient had experienced a previous episode of VT/VF that was successfully terminated by the WCD ( Figure 2 ). Both patients in the IA group were not wearing the WCD at the time of death. In the CSHD group, 2 patients died during the period in which the WCD was prescribed and 4 after device use. Similar to the IA group, none of the patients died while wearing the device.
| Pt. No. | Gender | Age (years) | Disease Suspected | Reason ICD not Implanted | Days Worn | Hours Worn/Day | End Use Reason | Treatment | Electrographic Findings | Died During WCD Use |
|---|---|---|---|---|---|---|---|---|---|---|
| 1 | Female | 51 | LQTS | Ongoing cardiac testing | 25 | 6 | ICD | Inappropriate shock, 1 | Noise | No |
| 2 | Female | 63 | LQTS | ICD explanted | 2 | 6 | ICD | Inappropriate shock, 1 | Noise | No |
| 3 | Female | 27 | LQTS | Pregnancy | 12 | 21 | ICD | Appropriate shocks, 2 | Torsades (2 episodes) | No |
| 4 | Female | 36 | Brugada syndrome | Unknown | 12 | 21 | ICD | Inappropriate shock, 1 | Artifact | No |
| 5 | Male | 30 | ARVD | Ongoing cardiac testing | 17 | 21 | Unknown | Appropriate shock, 1 | Ventricular fibrillation | Yes (peritonitis) |
| 6 | Female | 42 | LQTS | ICD explanted | 3 | 18 | Unknown | Inappropriate shocks, 4 | Noise (4 episodes) | No |
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