Author + information
- Received December 15, 2009
- Revision received March 10, 2010
- Accepted April 13, 2010
- Published online July 13, 2010.
- Mina K. Chung, MD*,* (, )
- Steven J. Szymkiewicz, MD†,
- Mingyuan Shao, MS*,
- Edwin Zishiri, MD*,
- Mark J. Niebauer, MD, PhD*,
- Bruce D. Lindsay, MD* and
- Patrick J. Tchou, MD*
- ↵*Reprint requests and correspondence:
Dr. Mina K. Chung, Department of Cardiovascular Medicine, Cleveland Clinic, 9500 Euclid Avenue, Desk J2-2, Cleveland, Ohio 44195
Objectives The purpose of this study was to determine patient compliance and effectiveness of antiarrhythmic treatment by the wearable cardioverter-defibrillator (WCD).
Background Effectiveness of the WCD for prevention of sudden death is dependent on event type, patient compliance, and appropriate management of ventricular tachycardia/ventricular fibrillation (VT/VF).
Methods Compliance and events were recorded in a nationwide registry of post-market release WCDs. Survival, using the Social Security Death Index, was compared with survival in implantable cardioverter-defibrillator (ICD) patients.
Results Of 3,569 patients wearing the WCD (age 59.3 ± 14.7 years, duration 52.6 ± 69.9 days), daily use was 19.9 ± 4.7 h (>90% of the day) in 52% of patients. More days of use correlated with higher daily use (p < 0.001). Eighty sustained VT/VF events occurred in 59 patients (1.7%). First-shock success was 76 of 76 (100%) for unconscious VT/VF and 79 of 80 (99%) for all VT/VF. Eight patients died after successful conversion of unconscious VT/VF (89.5% survival of VT/VF events). Asystole occurred in 23 (17 died), pulseless electrical activity in 2, and respiratory arrest in 1 (3 died), representing 24.5% of sudden cardiac arrests. During WCD use, 3,541 of 3,569 patients (99.2%) survived overall. Survival occurred in 72 of 80 (90%) VT/VF events and 78 of 106 (73.6%) for all events. Long-term mortality was not significantly different from first ICD implant patients but highest among patients with traditional ICD indications.
Conclusions Compliance was satisfactory with 90% wear time in >50% of patients and low sudden death mortality during use. Survival was comparable to that of ICD patients. However, asystole was an important cause of mortality in sudden cardiac arrest events.
Several studies have demonstrated implantable cardioverter-defibrillator (ICD) devices to be effective in primary and secondary sudden cardiac death (SCD) prevention in high-risk populations (1–5). These studies led to expanding indications for ICD use.
However, despite identification of risk factors indicating a high risk of SCD, ICD implantation is commonly deferred in a variety of clinical situations. Several primary prevention studies of SCD excluded patients early after acute myocardial infarction (MI) or coronary revascularization (4,5), leading to exclusion of such patients from early prophylactic ICD implantation. Moreover, early ICD implantation 6 to 40 days after acute MI with left ventricular ejection (LVEF) ≤35% has not been shown to improve early overall survival, despite a reduction in arrhythmic deaths, because patients receiving ICD shocks are at high risk of nonarrhythmic deaths during this early period (6). In Medicare patients with LVEF ≤35% and New York Heart Association functional class II or III heart failure, ICD implantation is not indicated for nonischemic dilated cardiomyopathy within 3 months of diagnosis and for ischemic cardiomyopathy within 40 days of acute MI or 3 months of revascularization. Nevertheless, SCD risk may be highest early after diagnosis or MI, as the VALIANT (Valsartan in Acute Myocardial Infarction) study demonstrated by reporting that SCD risk appears highest in the first 30 days after MI in patients with left ventricular dysfunction or heart failure (7). ICD implantation may also need to be deferred in patients with surgical contraindications, ventricular thrombi, treatable comorbidities, vascular obstructions, infections, or awaiting clearance of infection for reimplantation after extraction.
Once discharged from the hospital, these patients generally rely on emergency medical services for resuscitation should they have a sudden cardiac arrest (SCA). Additional protection has been proposed through means that include bridging with an automatic external defibrillator, antiarrhythmic drugs, or a wearable cardioverter-defibrillator (WCD). However, the automatic external defibrillator is limited by requiring a bystander to apply the defibrillator, and antiarrhythmic drugs, including amiodarone, may not be better than placebo in the prevention of SCD (1,2).
The WCD is an external device capable of automatic ventricular tachycardia (VT)/ventricular fibrillation (VF) detection and defibrillation. It has been shown to improve SCA survival over reliance on emergency medical services (8), but the efficacy of the WCD in the prevention of arrhythmic SCD would seem to be highly dependent on patient compliance as well as appropriate detection and treatment of VT/VF. We sought to determine the efficacy of the WCD in the detection and treatment of VT/VF, to assess compliance of patients in wearing the device, and to compare the long-term survival of patients who wore the WCD compared with a population of patients who underwent ICD implantation.
All patients issued a WCD after market release in the U.S. are entered into a database maintained by the manufacturer (ZOLL Cardiac Management Solutions, Pittsburgh, Pennsylvania) for regulatory, reimbursement, and tracking purposes. The database contains indications, baseline demographics (age and sex), compliance, and events. All patients signed consent to use their data for quality monitoring, health care operation activities, and/or research. Patients in the U.S. who wore the WCD from August 2002 through December 2006 were included in this study. Survival of these patients was compared with that of a population of patients who underwent first ICD implantation at the Cleveland Clinic. Mortality outcomes of WCD patients with Social Security numbers were determined from the Social Security Death Index (SSDI) and de-identified survival data compared with SSDI-determined survival data in an ICD population studied under a retrospective medical records review protocol approved by the Cleveland Clinic Institutional Review Board.
The WCD is composed of 4 dry, nonadhesive capacitive electrodes for monitoring 2 surface electrocardiogram leads, 3 nonadhesive defibrillation electrodes incorporated into a chest strap assembly, and a 1.7-lbs defibrillator unit carried on a waist belt. The monitoring electrodes are positioned circumferentially around the chest and held in place by about 1.5 lbs of tension from an elastic belt. The defibrillation electrodes are positioned for apex-posterior defibrillation. If an arrhythmia is detected, an escalating alarm sequence starts, including a vibration against the skin, audible tones, and a voice cautioning bystanders of an impending shock. Patients are trained to hold a pair of response buttons during these alarms. Responding acts as a test of consciousness; if no response occurs, the device charges, extrudes gel from the defibrillation electrodes, and delivers up to 5 biphasic shocks of pre-programmable energy levels with maximum output of 150 J. The WCD records time/date stamps for device on/off switching, monitor connection to the electrodes, and electrode-to-skin contact.
For this study, 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. Days were determined as any day with at least some WCD use. During the compliance calculation, 1 day was subtracted from the total number of days to compensate for the expected partial use on the first and last days.
Electrocardiogram and defibrillation electrode contact was determined by microampere AC signals similar to conventional monitoring systems. The device also recorded electrocardiogram data for rhythms greater than a pre-programmed rate threshold that did not match a baseline template and defined such arrhythmias as ventricular arrhythmias. A buffer in the monitoring software captured 30 s of electrocardiogram signal before the determination of VT/VF. Treatment event outcomes were determined through phone contact with patients or medical personnel. In addition to recording potential VT/VF, asystole recordings occurred when the ventricular rate dropped below 20 beats/min (minimum detected QRS height 100 μV). The buffer incorporated into the monitoring software stored 5 min of an electrocardiogram before the asystole determination.
For the purposes of this study, all potentially lethal arrhythmias (sustained VT/VF or asystole) occurring within 24 h were considered a single SCA event. In addition to reviewing electrocardiogram records stored by the WCD, patient call reports were reviewed for reports of deaths while wearing a WCD. All such reports were explored to further isolate the cause of death, if possible. A ZOLL physician determined WCD shocks to be appropriate if they occurred on sustained VT/VF and inappropriate if not. Inappropriate shocks were further analyzed for inappropriate detection cause from electrocardiogram recordings and lack of response button use from patient call reports. Two-lead electrocardiograms from all shocks and baseline tracings were reviewed by 2 authors (S.J.S., E.Z.) and differences adjudicated by consensus with the first author (M.K.C.).
Although the WCD did not have pacing capability in this version, it recorded asystole events and broadcast “device disabled, call ambulance” to enlist bystander help once asystole was detected.
Indications for WCD use
Indications for WCD were based on Medicare Durable Medical Equipment Regional Carrier local coverage policies for use. Because no coverage policy was in effect before January 2005, categories were added for patients who did not fit into the coverage policies. Indications included the following:
1. ICD explantation with delayed reimplantation (e.g., extended antibiotic therapy for infections)
2. Delays in ICD implantation (e.g., comorbidities) after a VF or sustained VT event
3. Delays in ICD implantation for genetic arrhythmogenic syndromes or congenital heart disease
4. Before ICD evaluation after MI with LVEF ≤35%
5. Before ICD evaluation after revascularization with LVEF ≤35% and past MI
6. Before ICD evaluation after diagnosis with nonischemic cardiomyopathy and LVEF ≤35%
7. Unspecified cardiomyopathy with LVEF ≤35%
8. MI with an LVEF >35% or unspecified
9. Other temporary or fluctuating SCD risk conditions (e.g., waiting for cardiac transplant)
If >1 category was specified, patients were grouped according to the following hierarchy: ICD explant > VF or sustained VT event > genetic or congenital SCA risk > nonischemic cardiomyopathy with low LVEF > coronary artery bypass graft (CABG) with low LVEF and previous MI > MI with low LVEF > MI with high or unknown LVEF > unknown low LVEF > other.
Survival outcomes were also analyzed by WCD indications, grouped by whether patients met traditional or nontraditional ICD indications. Traditional ICD indications included patients who underwent ICD explantation, had VT/VF while awaiting ICD implantation, genetic predisposition to SCD, or LVEF ≤35% with unspecified cardiomyopathy. Nontraditional ICD indications included recent MI, post-CABG, recent nonischemic cardiomyopathy, and miscellaneous or unknown indications.
Patients undergoing a first ICD implantation at the Cleveland Clinic between August 1996 and May 2004 were identified from a prospectively collected database in the Cleveland Clinic Electrophysiology Laboratory. Mortality was determined by the SSDI.
Data are reported as mean ± SD unless otherwise stated. Data were compared using Student ttests for continuous variables and chi-square tests for discrete variables. Kaplan-Meier survival analysis was performed for the WCD and ICD groups. Cox proportional hazards modeling was performed for adjusted survival analyses. Data were considered statistically significant at a 2-sided p value <0.05. All analyses were conducted using SAS version 9.1.3 (SAS Institute, Cary, North Carolina).
A total of 3,569 patients wore the WCD for at least 1 day. Baseline demographics were available for 2,731 patients (Table 1).Mean age was 59.3 ± 14.7 years (range 12 to 93 years, n = 2,723). Indications were unknown in 838 (23%) due to missing links between clinical and reimbursement datasets, primarily during early commercial use. Use totaled 143,643 patient-days. Mean duration of use was 52.6 ± 69.9 days (range 1 to 1,590 days) (Fig. 1A).
Daily use for each patient (available in 2,208 patients) was calculated by dividing the total hours worn by the number of days worn minus 1, to adjust for partial use on the first and last days worn. Median daily use was 21.7 h (91% of time available). Mean daily use was 19.9 ± 4.7 h, range 0.4 to 25.9 h (>24 h possible due to the methodology used to adjust for partial days at the beginning and end of use, although internal clocking errors cannot be completely excluded). Daily use was >90% in 52% of patients and >80% in 71% of patients. Of 2,169 patients with recorded data, 307 (14.2%) stopped wearing the WCD prematurely because of comfort issues or adverse reactions, primarily the size and weight of the monitor.
Longer duration of monitoring correlated with higher compliance rates (Fig. 1B). Patients using the device >60 days (n = 599) averaged 20.8 ± 3.7 h per day, significantly more than all other groups except those using it between 45 and 60 days (p < 0.05). Patients using it <15 days (n = 160) averaged 17.2 ± 5.9 h, significantly less than all other groups (p < 0.001).
Arrhythmia events, treatment efficacy, and mortality during WCD use
The WCD was designed to treat sustained VT/VF and to record sustained VT/VF and asystole. Thus, most SCA events were expected to have an associated electrocardiogram record. Events are shown in Figure 2and Table 2.There were 3 reports of deaths while a WCD was worn that did not have an associated WCD electrocardiogram recording. Two were from pulseless electrical activity confirmed by hospital telemetry recordings, and 1 was due to a respiratory arrest, documented by a physician present at the event (a prison medical ward), although telemetry recordings were not documented to determine the presence or absence of an arrhythmia. The number of patients who died not wearing the WCD was not recorded in the database but determined using the SSDI. 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). Four patients reported being conscious during the shock. First-shock success was 76 of 76 (100%) among unconscious patients and 79 of 80 (99%) for all patients. The single failure to halt VT/VF on the first attempt occurred when a conscious patient with sustained VT allowed himself to be shocked after 10 min of using the WCD response buttons to delay the shock. He was later shocked while conscious during his ambulance ride to the hospital (2 shocks, 100 and 200 J) and in the emergency department (2 shocks, 50 and 200 J). All shocks were ineffective, although pharmacologic therapy restored a normal rhythm within hours. This patient was using a WCD after ICD explantation due to device infection; the original indication for ICD implantation is unknown. Eight patients died after successful conversion of unconscious VT/VF; survival occurred in 89.5% of events. Four patients died due to recurrent arrhythmias after initially recovering consciousness and the arrival of professional medical care (1 ambulance death, 1 emergency department death, 2 telemetry deaths). One patient's spouse prevented a second WCD shock for a recurrent ventricular tachyarrhythmia minutes after a first successful shock. Two patients with recurrent arrhythmias were prevented or delayed from getting a second shock due to electrocardiogram signal disruption believed secondary to falling and wedging their bodies in an unfavorable position for proper electrode contact. The last patient had a unipolar pacemaker that paced during an episode of VF, and the large pacing artifact prevented WCD arrhythmia detection from proceeding to shock (14).
There were 23 asystole events recorded (17 deaths) and 3 pulseless electrical activity or respiratory arrests (3 deaths) while wearing the WCD, all confirmed by medical personnel present at the time. These non-VT/VF events accounted for 26 of 106 (24.5%) SCAs. One patient who was treated for VT/VF several times died 4 days after the last treatment with asystole as the presenting arrhythmia. Two treatments for VT/VF shocked the rhythm into asystole (no cardiac signal for at least 15 s), but both survived with return of rhythm. 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). Inappropriate shocks are a combination of sustained inappropriate detections by the WCD and failure to use the response buttons by the patient. 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%. 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%).
Overall acute survival
Overall acute survival during the time of WCD use was 99.2% (3,541 of 3,569 patients) with 0.78% sudden death mortality over a mean usage time of 53 days. Survival was 72 of 80 (90%) for ventricular tachyarrhythmia events and 78 of 106 (73.6%) for all events, including non-VT/VF events.
Survival and events in WCD patients by device indication
Events in individual traditional and nontraditional ICD indications are shown in Table 2. Among patients with traditional ICD indications, the WCD recorded events in the groups with ICD explanted and a history of VT/VF while awaiting ICD implantation. No shocked events occurred in the genetic predisposition to SCD and LVEF ≤35% cardiomyopathy groups, although 2 SCA events and deaths occurred in the LVEF ≤35% cardiomyopathy group. Shocked events occurred in all nontraditional ICD indications groups, except the recent MI with LVEF >35% group.
Survival by traditional compared with nontraditional ICD indications was analyzed based on SSDI mortality data (n = 2,147). Long-term (3-year) and short-term (3-month) mortality was significantly worse in the group with traditional ICD indications (Fig. 3).Short-term Kaplan-Meier curves for individual indications are shown in Figure 4,and long-term mortality estimates for the composite traditional ICD indications group and individual nontraditional indications groups are shown in Table 3.The highest mortality was observed in 3 of the 4 traditional ICD indications groups: cardiomyopathy with LVEF ≤35%, ICD explanted awaiting reimplantation, and VT/VF awaiting ICD implantation. Similar long-term mortality was observed in patients surviving a recent MI with LVEF >35%, a nontraditional ICD indication. Other nontraditional ICD indication groups demonstrated lower mortality compared with traditional ICD indication groups. These nontraditional groups included LVEF ≤35% with recent MI, post-CABG, and recent nonischemic cardiomyopathy.
Survival in WCD versus ICD groups
Patient characteristics of WCD and ICD groups are shown in Table 4.Mean age was higher in patients with ICDs compared with those with WCDs. Kaplan-Meier survival curves for the WCD and ICD groups (Fig. 5),including 3-year and 3-month survival curves, show no significant survival differences between the groups, including on Cox proportional hazards analyses adjusting for age and sex (p = 0.707). Estimated mortality rates in the WCD and ICD groups (Table 3) were not significantly different.
This study reports the U.S. outcomes with the WCD. Indicated for temporary or changing SCA risk, the WCD may be useful in situations in which ICD implantation is warranted but deferred. Use has been limited by perceptions that patient compliance is low. The data reported here show compliance of at least 90% for the majority of users. Survival was comparable to that of a population of patients with ICDs.
In this study, 14.2% stopped wearing the WCD because of comfort issues or adverse reactions. In a previous published investigational study of the WCD, 68 of 289 patients (24.5%) stopped wearing an earlier version of the WCD. Although patients who stopped using the WCD prematurely complained mostly of the size and weight of the monitor/defibrillator unit, improved compliance may have been seen because the WCD used in this study was 40% smaller in size and weight. In a recent study of aspirin, angiotensin-converting enzyme inhibitor, and beta-blocker use after MI, 15% of patients stopped using all 3 medications within 30 days of hospital discharge, despite the known survival benefits of these medications (9). The rate of WCD discontinuation appears similar.
The shock efficacy results reported here are comparable to those reported in investigational studies of the WCD (8,10). In electrophysiology laboratory testing of the WCD, 100% of 20 shocks given for VF were terminated by a single shock of either 70 or 100 J (10). In 289 patients who wore the WCD, 6 of 8 (75%) defibrillation attempts were successful (8). The 2 unsuccessful defibrillations occurred in patients who had incorrectly reversed the defibrillating electrodes, such that shocks were not directed to the skin. A high first-shock conversion rate was observed in this study by the WCD, indicating efficacy in conversion of VT/VF that appears comparable to that of ICDs. First-shock efficacy has been reported to be 80% to 90% with ICDs (11), which deliver therapies rapidly but can also deliver shocks to conscious patients and/or in potentially hemodynamically stable or nonsustained VT/VF episodes. Only 10% of appropriately treated patients reported syncope during the AVID (Antiarrhythmics Versus Implantable Defibrillators) trial. In fact, up to 40% of VF-detected arrhythmias terminate during charging but before shock delivery (12). In contrast, WCD shocks are delivered to unresponsive patients who have had at least 30 s of VT/VF and who have failed to respond to the alarms by pressing the response buttons. Despite the programmed longer time to shock, shock efficacy appears to be similar to that of shocks reported with ICDs.
During pre-market release studies, 12 deaths occurred, including 6 sudden deaths. Of these, 5 occurred in patients not wearing the device and 1 in a patient who reversed a defibrillation electrode (the current version sounds an alarm when any of the defibrillation electrodes are not touching the skin properly) (8,10). Thus, despite use of the WCD, SCD can occur. However, as reported here, some SCDs may have occurred due to bystander interference, electrocardiogram signal disruption, or unipolar permanent pacing inhibiting arrhythmia detection by the WCD. The latter instance emphasizes the relative contraindication to use of the WCD with unipolar pacing, as is the case with ICDs (13). Future device improvements, such as the already implemented detection of electrode contact and improved warnings to bystanders, may help to reduce but is unlikely to completely eliminate these issues. These results highlight the importance of patient education in use of the WCD, as well as in the critical need to promote compliance in using the WCD for the prevention of SCD.
Proper instruction on use of the WCD is also important to the avoidance of inappropriate shocks. The incidence of inappropriate shocks was relatively low and comparable to that of ICDs. Inappropriate or unnecessary shocks occurred in 6 of 289 of patients (2.1%) during 901 months of use (0.7% per month) in a previously reported study (8). In the current study, inappropriate shocks occurred in 1.9% of patients at a rate of 1.4% per month. In contrast, studies of ICDs found that 0.6% to 1.5% of inappropriate shocks occur per month over the first 6 months of use (14). The ability to prevent shocks by holding the response buttons in WCD patients may have contributed to keeping a lower inappropriate shock incidence as the sustained inappropriate detection rate was 5 times the inappropriate shock rate. It is interesting to speculate from these results that this type of shock-prevention feature might be useful for selected low-risk arrhythmia treatment strategies in patients with ICDs.
There are few reported data on actual arrhythmic causes of SCD. This study documented that asystole or pulseless electrical activity accounted for 24.5% of SCA events with high associated mortality rates. These data indicate the need to incorporate pacing therapies into future WCD systems, although it is unclear whether pacing would prevent deaths in these patients.
In the analysis of events and mortality by traditional and nontraditional ICD indications, patients with traditional ICD indications had the highest long-term mortality, reinforcing these groups as higher risk populations. Among nontraditional indications groups, however, the groups with LVEF ≤35% and recent cardiovascular events, including recent MI, CABG, and a new cardiomyopathy diagnosis, had lower long-term mortality, perhaps reinforcing the appropriate deferral of ICD implantation after acute cardiac events and the use of the WCD while awaiting potential improvement in cardiac function. Paradoxically, the recent MI group with LVEF >35% demonstrated similar mortality to that of groups with traditional ICD indications. It is possible that there were other high-risk indicators that may have prompted WCD prescription, although shocked events did not occur in this group. Accordingly, these individuals may have died of nonarrhythmic causes and may not have benefited from the WCD.
The long-term survival data comparing WCD and ICD survival are reassuring that WCD therapy may be comparable to ICD therapy, rationalizing the use of the WCD as an acceptable temporary alternative or a bridge to long-term ICD implantation. Short-term (3-month) survival estimates were also performed, as the mean WCD use duration was 53 days, and were not significantly different from those of ICD patients.
With limitations inherent to a device that is external and interactive, it is evident that should an ICD be indicated, implantation of an ICD would be clearly preferable and perhaps significantly more efficacious than the WCD because patient compliance is irrelevant to ICD therapy and asystolic events could be treated. Should ICD implantation need to be deferred, however, a WCD may be elected, and this study demonstrated comparable survival in WCD and ICD patients. However, intensive patient and family education may be required to reinforce the importance of compliance in achieving effective prevention of SCD with this therapy.
Because of the nature of the registry, availability of demographic and daily use information was not complete and thus could lead to potential bias in these data. Similarly, the comparability of WCD with ICD patients in terms of demographics and disease comorbidities cannot be assessed.
The WCD was worn with >90% compliance by most patients. Sudden death mortality was 0.78% over a mean usage time of 53 days. Survival occurred in 73.6% of events and in 90% of VT/VF events. Survival was comparable 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. However, 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. 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.
The data were obtained from a ZOLL database, but no additional support from ZOLL was obtained for this study. Statistical analysis was performed independently by Cleveland Clinic statisticians. All members of the Section of Cardiac Electrophysiology and Pacing at the Cleveland Clinic participate in industry-sponsored research with Medtronic, Inc., Boston Scientific, St. Jude Medical, and Biotronik(manufacturers of ICDs), as disclosed here. Dr. Chung participates in industry-sponsored research with Medtronic, Boston Scientific, St. Jude Medical, and Biotronikand receives research support from the National Institutes of Health(NIH R01 HL090620). Dr. Szymkiewicz is Vice President of Medical Affairs, employee of ZOLL Cardiac Management Solutions, manufacturer of the Wearable Cardioverter Defibrillator vest. Dr. Niebauer participates in industry-sponsored research with Medtronic, Boston Scientific, St. Jude Medical, Biotronik, and ZOLL; has received honoraria from ZOLL; and is a member of the Data Safety Managing Board for Medtronic, Inc.Dr. Lindsay participates in industry-sponsored research with Medtronic, Boston Scientific, St. Jude Medical, and Biotronik. Dr. Tchou participates in industry-sponsored research with Medtronic, Boston Scientific, St. Jude Medical, and Biotronik.
- Abbreviations and Acronyms
- coronary artery bypass graft
- implantable cardioverter-defibrillator
- left ventricular ejection fraction
- myocardial infarction
- sudden cardiac arrest
- sudden cardiac death
- Social Security Death Index
- ventricular fibrillation
- ventricular tachycardia
- wearable cardioverter-defibrillator
- Received December 15, 2009.
- Revision received March 10, 2010.
- Accepted April 13, 2010.
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