The following are key points to remember from the American Heart Association (AHA) Science Advisory on wearable cardioverter-defibrillator (WCD) therapy:

1. Implantable cardioverter-defibrillators (ICDs) reduce mortality by 20-30% when implanted in patients who have received optimal medical therapy for 40 days (post-acute myocardial infarction [AMI] or revascularization) or 90 days in nonischemic cardiomyopathy.
2. Benefit from a primary prevention ICD is not time dependent either in nonischemic cardiomyopathy or after AMI, and a comparable risk for life-threatening arrhythmias exists at virtually all windows of time after index event or diagnosis.
3. Although early implantation of an ICD appears to decrease sudden cardiac death (SCD), the overall survival benefit from an ICD early after an MI or a new diagnosis of cardiomyopathy has not been observed. Nonetheless, there are high-risk patients who may derive survival benefit from early protection against SCD.
4. WCD offers a bridge from diagnosis to a point in time when further improvement in left ventricular ejection fraction is unlikely. Additionally, WCD may be employed in patients with transient contraindications to ICD implantation such as ongoing infection.
5. The detection algorithm used by the WCD has a sensitivity of 90-100% and a specificity of 98-99%. Inappropriate shock rates in early studies were approximately 1-2%.
6. Once an arrhythmia has met the detection criteria, the patient receives vibratory, audible, and visual alerts and is able to abort the shock if he or she remains conscious. If no patient response is recorded, a shock is delivered. WCD shock energies range between 75 and 150 J biphasic. The response time (detection to shock) takes 25-60 seconds. Shock efficacy rates are between 69% and 99%.
7. WCD has no pacing capability.
8. There are no completed randomized trials of WCD therapy. No definitive data are available on comparative efficacy versus alternative (or no) treatment.
9. In the largest observational series to date, daily use was >90% in >50% of the cohort, and the device discontinuation rate was 14%.
10. The AHA Advisory Panel makes the following recommendations:
    • WCDs may be appropriate as bridging therapy in situations associated with increased risk of death in which ICDs have been shown to reduce SCD, but not overall survival such as within 40 days of MI (Class IIb; Level of Evidence C).
    • Use of wearable defibrillators is reasonable when there is a clear indication for an implanted/permanent device accompanied by a transient contraindication or interruption in ICD care such as infection (Class IIa; Level of Evidence C).
    • Use of WCDs may be reasonable when there is concern about a heightened risk of SCD that may resolve over time or treatment of left ventricular dysfunction, for example, in ischemic heart disease with recent revascularization, newly diagnosed nonischemic dilated cardiomyopathy in a patient starting guideline-directed medical therapy, or secondary cardiomyopathy (tachycardia mediated, thyroid mediated, etc.) in which the underlying cause is potentially treatable (Class IIb; Level of Evidence C).
    • Use of WCDs is reasonable as a bridge to more definitive therapy such as cardiac transplantation (Class IIa; Level of Evidence C).
    • WCDs should not be used when nonarrhythmic risk is expected to significantly exceed arrhythmic risk, particularly in patients who are not expected to survive >6 months (Class III; Level of Evidence C).

Keywords: Acute Coronary Syndrome, Arrhythmias, Cardiac, Cardiomyopathies, Cardiomyopathy, Dilated, Death, Sudden, Cardiac, Defibrillators, Defibrillators, Implantable, Heart Failure, Heart Transplantation, Myocardial Infarction, Myocardial Ischemia, Primary Prevention, Stroke Volume, Tachycardia, Ventricular Dysfunction, Left

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