How Soon is Too Soon for Wearable Cardioverter-Defibrillators Post-MI?

Patients with depressed LV function are put at a significant risk of sudden cardiac death (SCD) after experiencing an MI; despite this risk early post-MI, current device guidelines and insurance coverage requirements recommend that patients wait 40 days or 3 months before receiving an implantable cardioverter-defibrillator (ICD), depending on whether they underwent revascularization. Wearable cardioverter-defibrillators (WCD) are intended for high-risk patients who are not candidates for ICD implantation; however, there is little evidence or randomized trials evaluating the efficacy of WCDs in these settings.

In a recent JACC article, Andrew Epstein, MD, and colleagues assessed the characteristics of and outcomes for patients who were prescribed a WCD to treat potentially fatal ventricular arrhythmias during that mandated waiting period. During the 6 years of data collection, 8,453 unique patients matched study criteria. Median time from the index MI to WCD therapy was 16 days—well below the recommended wait time. Three-quarters of patients received treatment in the first month, and 96% within the first 3 months of use. Notably, risk of ventricular tachycardia/fibrillation (VT/VF) was highest in the first month of WCD use.

A small portion of patients (1.6%) received 309 appropriate shocks after a mean of 22 days; 252 of these events successfully terminated VT/VF, nine led to asystole, and 41 were unsuccessful. Shock success resulting in survival was 84% in nonrevascularized and 95% in revascularized patients.

Overall, during the recommended waiting period, the WCD successfully treated VT/VF and SCD in 1.4% of patients. However, the authors wrote, “It is important to note that access to rapid defibrillation does not necessarily ensure SCD survival, since 0.4% of the patients in the present study died from bradycardia or asystole.” The fact that 1.4% of patients may be successfully treated in the first 3 months post-MI, with a resuscitation survival rate of 91%, implies that a select group of patients may benefit from defibrillation during the first 30 days following hospital discharge. After this period, Epstein et al. suggest, survivors may then be candidates for an ICD.

“The current state of affairs leaves a significant population of patients immediately post-MI who may be at risk of arrhythmia-mediated SCD in a ‘gap of vulnerability,’” Paul C. Zei, MD, PhD, wrote in an accompanying editorial. For this “small but definite sub-population” of post-MI patients, Dr. Zei continued, the WCD was appeared to be an effective treatment.

Aside from providing a treatment option for this sub-population of post-MI patients, Dr. Zei continued, the WCD presents other benefits that are more difficult to assess, including: acting as an event recorder, high compliance, and potential benefits over the other primary alternative noninvasive intervention (the automated external defibrillator.

However, Dr. Zei concluded, the study by Epstein et al. does not quite answer the question of how to best risk-stratify post-MI, low-EF patients in the early days post-MI. “A fraction of patients will suffer SCD during [the mandated waiting period]. Does the relatively low incidence of risk within this time frame warrant prescribing a WCD for every patient with low EF post-MI?” he questioned. “Should the WCD be prescribed for a fixed duration? If not, what are the criteria for determining when it is safe to stop wearing the WCD? Despite these unanswered questions, this study provides a bit more enlightenment on this challenging subject.”

Epstein AE, Abraham WT, Bianco N, et al. J Am Coll Cardiol. 2013;62:2000-7.
Zei P. J Am Coll Cardiol. 2013;62:2008-9.

Keywords: Incidence, Tachycardia, Ventricular, Resuscitation, Insurance Coverage, Survival Rate, Ventricular Fibrillation, Bradycardia, Death, Sudden, Cardiac, Defibrillators, Implantable

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