Wearable Cardioverter-Defibrillator as a Bridge to Implantable Cardioverter-Defibrillator Treatment
Sudden cardiac death is the most common cause of death in patients with coronary artery disease and cardiomyopathy, accounting for approximately 300,000 deaths per year. Ventricular tachyarrhythmias (ventricular tachycardia and ventricular fibrillation) are the most common underlying etiology of sudden cardiac death. The treatment of choice for these arrhythmias is rapid countershock. Unfortunately, the majority of patients that suffer out-of-hospital sudden cardiac death do not have rapid access to countershock and survival from out-of-hospital cardiac arrest is exceedingly low.
Automatic implantable cardioverter-defibrillators (ICDs) have been proven effective in reducing mortality for patients with malignant ventricular arrhythmias. They have also proven effective in patients at high risk for arrhythmias, such as patients with a prior myocardial infarction and reduced ejection fraction. While there are standardized indications for ICD use, there are some situations where the risk of sudden cardiac death may be high, but the patient is unable or unwilling to receive a permanent ICD. An example of this is the patient with a temporary contraindication to ICD implantation, such as a systemic infection, who otherwise meets criteria for an ICD. For these patients, the wearable cardioverter-defibrillator (WCD) can be considered as a substitute for an ICD and is the most attractive alternative until the patient can receive an ICD.
In other situations, guidelines recommend a waiting period prior to the decision to implant an ICD, for example in patients immediately following myocardial infarction (MI). The optimal timing of ICD placement following an acute MI is not entirely clear. Following an acute MI, estimation of the left-ventricular ejection fraction (LVEF) is not reliable and may improve over the initial few weeks following MI. For this reason, the current standard of practice is to wait for at least 1 month following MI to allow accurate estimation of LVEF and reliable determination of whether an ICD is indicated. However, the risk for sudden cardiac death following an MI is highest in the initial month following MI. Due to the high expected rate of sudden cardiac death in the first 30 days post-MI, and the lack of indications for a permanent ICD at this time point, there is a potential for alternative treatments to prevent sudden cardiac death in this patient population.
A similar situation is present in the case of newly diagnosed nonischemic dilated cardiomyopathy. A specific etiology for nonischemic dilated cardiomyopathy is not always apparent on initial workup. Potential etiologies include some self-limited causes such as viral myocarditis, which may partially or completely resolve. As a result, a substantial percentage of patients with newly diagnosed nonischemic dilated cardiomyopathy will show an improvement in LVEF over the subsequent few months. For this reason, current guidelines recommend waiting 90 days after the diagnosis of nonischemic, dilated cardiomyopathy, before considering whether indications for an ICD are met.
WCDs consist of an electrode belt containing 4 EKG electrodes that continuously monitor cardiac rhythm. A holster is attached to the belt and holds the battery pack and alarm module. The belt is attached to a vest that contains defibrillator pads for delivering an external shock.
The WCD has similarities and differences to both ICDs and automated external defibrillators (AEDs). The WCD differs from an ICD in that it is noninvasive. However, the fact that it is noninvasive also requires patient compliance with wearing and properly connecting the device. It differs from an external defibrillator in several ways. First, it is an automatic resuscitative device and does not require additional personnel for use. Also, it can detect a ventricular arrhythmia prior to patient collapse and deliver a countershock more rapidly than can be achieved with an AED. The most obvious disadvantage of an AED is the delay in defibrillation. Expert guidelines recommend defibrillation within 2 minutes of a cardiac arrest, a threshold that may be difficult to achieve with a home AED operated by nonmedical professionals.
The overall objective of this Assessment is to determine whether the wearable cardiac defibrillator improves outcomes when used as a bridge to permanent ICD placement. The WCD as a “bridge” refers to use in patients who are at high risk of sudden cardiac death, but who do not yet meet the criteria for a permanent ICD because current ICD guidelines recommend a waiting period prior to the decision for an ICD.
Electronic search of MEDLINE® (via PubMed) was performed using the keywords “WCD,” “wearable defibrillator,” and “external defibrillator.” These terms were cross-referenced with “sudden cardiac death,” “sudden cardiac arrest,” “SCD,” and “SCA.” Search was performed from January 1995 to present. Electronic search was supplemented with a hand search of relevant bibliographies and use of the “related articles” function in MEDLINE®.
Full-length studies in the peer-reviewed literature were selected for inclusion that were: 1) case series, cohort studies, or controlled trials that evaluate whether the WCD can successfully detect and treat lethal ventricular arrhythmias; or 2) randomized, controlled trials that evaluated early versus delayed use of a defibrillator (ICD or WCD) for patients at high risk for sudden cardiac death who are in a waiting period to receive an ICD; and, a) included at least 25 patients per treatment group, and b) reported on at least one relevant health outcome.
A total of 5 studies met the inclusion criteria for this Assessment. Two of the 5 were uncontrolled studies that evaluated the ability of the WCD to detect and abort ventricular arrhythmias. The other 3 were randomized, controlled trials of early ICD implantation for patients at high risk for ventricular arrhythmias, 2 evaluating the early post-MI period, and the third evaluating patients following coronary artery bypass graft (CABG) surgery.
The uncontrolled studies on WCD were evaluated in order to determine whether the device functions as intended. The first study included 15 patients who were survivors of sudden cardiac arrest and who were scheduled to receive an implantable ICD. During the procedure to implant a permanent ICD, or to test of a previously inserted ICD, patients wore the WCD while the clinicians attempted to induce ventricular arrhythmias. Of the 15 patients, 10 developed ventricular tachycardia or ventricular fibrillation. The WCD correctly detected the arrhythmia in 9 of 10 cases and successfully terminated the arrhythmia in all 9 cases that were detected.
The WEARIT/BIROAD study was a prospective cohort study that evaluated the WCD in patients at high risk for sudden cardiac death, but who did not meet criteria for an ICD or who could not receive an ICD for several months. A total of 289 patients were enrolled and followed for a mean of 3.1 months. During this time, there were 8 documented episodes of arrhythmia requiring shock in 6 separate patients. Six of the 8 episodes were successfully resuscitated by the WCD. By group sequential analysis, the estimate of percent successful resuscitations was 69%. There was 99% confidence that the true rate of success was greater than 25% and 90% confidence that the true rate was greater than 44%. In the 2 cases of unsuccessful defibrillation, the authors reported that the WCD was placed incorrectly, with the therapy electrodes reversed and not directed to the skin.
Three randomized, controlled trials were identified that met the inclusion criteria, 2 that specifically examined whether early implantation of an ICD post-MI was beneficial and one that examined high-risk post-CABG patients. The first of these was the DINAMIT study, which enrolled 674 patients who were 6 to 40 days post-MI with an ejection fraction of less than 35%. There was no difference between the ICD and control groups in total mortality (7.5%/year vs. 6.9%/year, respectively, p=0.66) at a mean follow-up of 30 +/- 13 months. The ICD group did have a lower rate of arrhythmogenic death compared to controls (1.5%/year vs. 3.5%/year, respectively, p=0.009). However, the ICD group had a higher rate of nonarrhythmogenic death (6.1%/year vs. 3.5%/year, respectively, p=0.02), resulting in no net decrease in overall mortality.
The IRIS trial was similar in design to the DINAMIT trial. This study included 998 patients who were 5 to 31 days post-MI and had at least one other high risk factor, either nonsustained ventricular tachycardia or a resting pulse greater than 90. Patients were followed for a mean of 37 months. Results of the IRIS trial were similar to DINAMIT, with no difference in overall mortality between the ICD and control groups (26.1% vs. 25.8%, respectively, p=0.76). The ICD group had a decreased rate of sudden cardiac death (6.1% vs. 13.2%, respectively, p=0.049), which was offset by a higher rate of nonsudden cardiac death (15.3% vs. 8.6%, respectively, p=0.001). This study also reported noncardiac death, which was similar for the ICD and control groups (4.7% vs. 4.0%, respectively, p=0.51).
The third randomized, controlled trial (CABG PATCH) evaluated high-risk post-CABG patients, selected by a low LVEF and abnormalities on signal-averaged EKG. The trial followed patients for a mean of 32 months and reported on overall mortality. Results of this trial indicated no difference in overall mortality between the ICD and control groups (HR 1.07; 95% CI: 0.81–1.42). There were no other mortality outcomes reported. There was a higher rate of infections in the ICD group, both deep sternal infections (2.7 vs. 0.4%, p<0.05) and superficial wound infections (12.3 vs. 5.9%, p<0.05). The cumulative incidence of inappropriate shocks was 50% at 1 year and 57% at 2 years.
Author’s Conclusions and Comments
There is a lack of high-quality evidence on the efficacy of the WCD in preventing sudden cardiac death for high-risk individuals. There are no controlled trials that specifically evaluate the efficacy of the WCD in comparison to alternatives for patients at high risk of sudden cardiac death. The available evidence consists of uncontrolled trials that evaluate the success of the WCD in detecting and aborting arrhythmias, and randomized, controlled trials of early ICD use post-MI and post-CABG.
Can a WCD successfully detect and abort lethal ventricular arrhythmias?
Only two uncontrolled studies were identified that directly tested the efficacy of the WCD. Despite the small amount of evidence, the evidence is sufficient to conclude that the WCD can successfully identify and terminate malignant ventricular arrhythmias. It is known that sensor leads correctly placed on the skin can successfully detect and characterize arrhythmias. It is also established that a successful countershock can be delivered externally. The use of external defibrillators is extensive, ranging from in-hospital use to public placement and use at home. The novelty of this device is in the way that it is packaged and utilized.
Second, the small amount of evidence supports that the device successfully terminates arrhythmias. In both of the uncontrolled studies, there was a relatively high rate of success for the device. In the small electrophysiology lab study, there was a 90% success rate under highly controlled conditions, where noncompliance and improper placement of the device were not issues. In the WEARIT/BIROAD study, an estimate of 69% success rate appeared to be limited primarily by the improper placement of the device. These results suggest that the feasibility and potential efficacy of the WCD in detecting and terminating arrhythmias, but they also indicate that the WCD is likely to be inferior to an ICD. This is almost certainly due to suboptimal compliance and difficulty with wearing the device correctly.* Therefore, this data corroborates the assumption that WCD should not be used as a replacement for an ICD in patients who are able to get an ICD, but only considered in those situations where the patient does not meet criteria for a permanent ICD.
Does treatment with a defibrillator (ICD or WCD) improve overall survival in patients who are at high risk for sudden cardiac death immediately following acute MI, or in other high risk patients, when used as a bridge to permanent ICD placement?
The 2 randomized, controlled trials that evaluated immediate post-MI patients do not support the hypothesis that early ICD implantation post-MI improves overall survival. In fact, both trials taken together offer fairly compelling evidence that immediate ICD placement post-MI does not improve mortality compared with delayed placement.
The results of both are consistent in demonstrating a reduction in sudden cardiac death with a corresponding increase in nonsudden cardiac death, resulting in no net difference in overall survival. This implies that the device is working as intending in aborting sudden cardiac arrest. However, it appears that these deaths are converted to nonsudden death rather than resulting in long-term survival, perhaps because the patients who experience sudden cardiac have primarily endstage disease and little hope of long-term survival.
The main limitation to these trials in extrapolating this data to the specific Assessment question is that the time frame of the trials does not correspond precisely to the period of time for which the WCD is intended. The ICD was implanted within 30 or 40 days in these trials, but follow-up continued for 2 to 3 years and results analyzed over this entire time period. This is considerably longer than the 1- to 2-month period that might be expected for the WCD.
The third randomized, controlled trial investigated a different population, i.e., high-risk post-CABG patients, but came to the same conclusion on overall mortality. There was no improvement in mortality and no trends toward improvement. This trial also reported a higher infection rate for the ICD group and a high incidence of inappropriate shocks. Thus, similar to the evidence on post-MI patients, the hypothesis that early ICD implantation as a bridge to permanent ICD improves mortality is not supported.
There was no other clinical trial evidence on the use of defibrillators for other bridging purposes. Therefore, it is not possible to address any of the other potential expanded indications for the WCD.
The indirect evidence is suggestive of no benefit to early WCD use. A clinical trial that randomizes patients to WCD or placebo and follows patients for only the initial time period prior to either permanent ICD implantation or to clinical improvement would help to definitively answer the question.
Based on the available evidence, the Blue Cross and Blue Shield Association Medical Advisory Panel made the following judgments about whether use of wearable cardioverter-defibrillators (WCD) in patients who are at high risk for sudden cardiac death, but who do not meet the criteria for a permanent implantable cardioverter-defibrillator meets the Blue Cross and Blue Shield Association Technology Evaluation Center (TEC) criteria.
1. The technology must have final approval from the appropriate governmental regulatory bodies.
There is one WCD that has received approval by the U.S. Food and Drug Administration (FDA). The LifeCore WCD 2000 System® received premarket application (PMA) approval from the FDA in December 2001 for “adult patients who are at risk for cardiac arrest and are either not candidates for or refuse an implantable defibrillator.” However, these guidelines do not define the population they refer to as “at risk for cardiac arrest.” This is potentially a broad patient group, with a wide range of expected risk, and there is not a standardized threshold for the degree of risk that is considered to be high.
2. The scientific evidence must permit conclusions concerning the effect of the technology on health outcomes.
The evidence is not sufficient to conclude that the WCD improves outcomes when used as a bridge to permanent ICD implantation. There is no direct evidence in controlled trials to evaluate the efficacy of the WCD in comparison to usual treatment or alternatives. The available evidence consists of two small, uncontrolled trials evaluating the success of the WCD in detecting and aborting arrhythmias, and several randomized, controlled trials evaluating early ICD implantation for immediate post-MI and post-CABG patients at high risk for sudden cardiac death.
The small amount of evidence on whether the WCD can successfully detect and abort arrhythmias does support the contention that it works as intended when worn properly. However, the evidence on early use of any defibrillator compared to waiting until the patient meets the time frame specified in guidelines suggests that there is not a benefit to early defibrillator use. This is indirect evidence as the device used in these trials is an implantable ICD. However, since the implantable ICD is likely to be superior to the WCD, the lack of benefit for an ICD can be extrapolated fairly well to the benefits expected with the WCD.
These trials are also not definitive in ruling out a small benefit for the WCD in the immediate post-MI period. The available trials follow patients for 2 to 3 years and report no mortality benefit over this entire time frame. It is possible that these trials are underpowered to show a small benefit in mortality for an earlier and more narrowly defined time range. A clinical trial that specifically evaluates the time period that WCD is intended to be used would be required to make this conclusion.
3. The technology must improve the net health outcome; and
4. The technology must be as beneficial as any established alternatives.
The available evidence is insufficient to determine whether WCDs improve the net health outcome or are as beneficial as any established alternatives in patients who are at high risk for sudden cardiac death, but who do not meet the criteria for a permanent ICD.
5. The improvement must be attainable outside the investigational settings.
It has not yet been demonstrated whether use of WCD in patients who are at high risk for sudden cardiac death, but who do not meet the criteria for a permanent ICD improves health outcomes in the investigational setting. Therefore, it cannot be demonstrated whether improvement is attainable outside the investigational settings.
Based on the above, use of wearable cardioverter-defibrillators in patients who are at high risk for sudden cardiac death, but who do not meet the criteria for a permanent implantable cardioverter-defibrillator does not meet the TEC criteria.
*As this Assessment was in press, a nationwide WCD registry report (Chung et al. 2010) was published in the Journal of the American College of Cardiology; the results of this report do not change the conclusions of the Assessment. However, the information on compliance corroborates the conclusion of the Assessment that device compliance is probably the biggest limitation to its effectiveness. Among more than 3,500 patients enrolled in the registry, the authors report that full compliance with treatment, defined as wearing the WCD for at least 90% of the day, was achieved in only 52% of patients. A total of 71% of patients wore the device for at least 80% of the day. The device was discontinued by 14.2% of patients, primarily due to discomfort and/or inconvenience.
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; BIROAD; CABG-PATCH; cardiac arrest; cardiomyopathy; defibrillation device; ICD; IRIS; Lifecor; nonischemic; pacemaker; prophylactic; SCA; SCD; sudden cardiac death; sudden death; tachyarrhythmia; wearable; WEARIT;