Wearable Cardioverter-Defibrillator Use in Takotsubo Cardiomyopathy – More Data Needed or a New Indication?

DOI: 10.19102/icrm.2014.050803

Editor-in-Chief

Wearable cardioverter-defibrillators (WCDs) are a relatively novel modality for patients who are at significant risk for ventricular tachycardia (VT) or ventricular fibrillation (VF), but are not immediate candidates for implantable cardiac defibrillator (ICD) placement. LifeVest manufactured by ZOLL (Pittsburgh, PA) and approved by the FDA in 2002 remains the only commercially available wearable defibrillator to date.¹

It appears to be a successful modality for treating ventricular arrhythmias with a first-shock success rate of 99% in a recently published largest WCD registry of 3569 patients.² The WCD also appears to be safe with low rates of inappropriate shocks, and in many large registries, 70% or more of the patients were shown to wear the WCDs >80% of the time.^2,3 The specific patient populations who would benefit the most from this strategy are not well defined although WCDs have been successfully applied in a variety of patient populations including patients with history of sudden cardiac arrest from ventricular arrhythmias,^4,5 patients with inheritable arrhythmias or congenital heart disease,⁶ patients with non-ischemic cardiomyopathies or post myocardial infarction (MI) patients at high risk for sudden cardiac death (SCD).^7,8 The manuscript by Thakur et al in this current issue of the journal looks into a relatively underrepresented patient population, patients with Takotsubo cardiomyopathy (TCM), who were prescribed WCDs.

Takotsubo cardiomyopathy (TCM) is a non-ischemic, reversible cardiomyopathy that is thought to be cathecholamine mediated, and is associated with tachy and brady-arrhythmias along with repolarization abnormalities. Although the most commonly reported cause of death in these patients is ‘non-cardiac’, these patients have not been routinely followed up by event monitors to detect the incidence of life threatening arrhythmias. There is evidence that this is a subgroup of patients that are susceptible to arrhythmias and SCD and in a recent review of TCM literature, sustained VT/VF prevalence was 3.4% with limited data on the duration of cardiac monitoring used to identify transient arrhythmias.⁹

Given the need to further define the arrhythmia risk in this patient population the study presented here is both timely and appropriate. The authors have wisely used the nationwide registry of WCDs to obtain clinical data on WCD use in Takotsubo cardiomyopathy patients. Working within the limitations of a registry study useful data can be obtained, particularly in a patient population with a low incidence of disease and where any large randomized prospective studies are unlikely to take place. A number of observations can be made based on the data presented.

This is a relatively young patient population with not many comorbidities, unlike other common indications for WCDs such as post-MI patients. It is clearly important to address potentially lifesaving measures such as the WCD in such a patient population.

Of the 102 patients with Takotsubo cardiomyopathy included in this study, 9% of these patients were prescribed WCDs for secondary prevention, already proven to have significant life threatening arrhythmias during their inpatient stay. A total of 2 patients had appropriate and effective shocks for treatment of VT or VF, of which one was prescribed a WCD for secondary prevention after a VF episode in the hospital. Given the design of this study, it is not possible to determine if the patients who were benefiting from WCD in the follow up period are largely represented by the patients who were prescribed WCDs as secondary prevention. Patient compliance in this study appears very high and in line with other major WCD registries. A single patient who had an inappropriate shock was noted to not hold the button long enough; demonstrating how crucial patient education is to increase safety and to decrease inappropriate shocks by WCDs. The reason for death was unknown in 6 of the 7 patients who died in the follow up period while they were not wearing WCDs, therefore the incidence of arrhythmias and most notably VT/VF could be underrepresented.

The limitations of this study are correctly outlined by the authors including the possible discrepancies in the diagnosis of TCM, the difficulty to obtain clinical details, and the cause of death with mortality data being available from social security death index and the fact that VT/VF that did not result in death are not included in the follow up data. Data from registries are difficult to interpret, yet in this particular population with a relatively uncommon treatment modality, this study opens a door to larger studies evaluating arrhythmias, prevention and treatment in patients with TCM. Thakur et al have highlighted the need for prospective studies of WCDs and patients with Takotsubo cardiomyopathy, to avoid the possible selection bias of the TCM patients who were ’chosen’ to be prescribed WCDs and to further delineate the survival benefit of this treatment modality in this subgroup of patients.

With these results in mind, the duration patients with TCM should be advised to wear the WCD is unclear, as 5 patients died after discontinuing WCD, although of unclear cause. Given the underlying etiology of TCM, EF improvement alone may or may not be ‘enough’ for discontinuation of therapy. Besides defibrillation, the WCDs also act as event recorders, that may guide us further in characterizing further what kind of arrhythmias these patients display and help further characterize the bradyarrhythmias in addition to detecting and treating life-threatening tachyarrhythmias. It is important to note that WCDs do not have pacing capabilities, and would not be able to prevent prolonged pauses or asystolic arrests as noted in 2 patients with TCM in this study.

Lastly as indications for the WCD expand and a potentially broad range of medical providers prescribe WCDs it is important to emphasize that physicians experienced in managing arrhythmias should be involved early on in the decision process of the WCD use. This can ensure both appropriate patient selection and optimal patient follow up as we all learn more arrhythmia substrate and risk in expanding patient populations.

Ulrika Birgersdotter-Green, MD, FACC, FHRS
Professor of Medicine, Division of Cardiology
Ubgreen@mail.ucsd.edu
Director of Pacemaker and ICD Services
UC San Diego Health Sciences
San Diego, CA

Tina Baykaner, MD, MPH
Fellow, Division of Cardiology
TBaykaner@ucsd.edu
UC San Diego Health Sciences
San Diego, CA

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