Wearable Cardioverter Defibrillators: A Safety Net for ACS Patients

JULY 17, 2016
Jeannette Y. Wick, RPh, MBA, FASCP
Sudden cardiac arrest occurs 424,000 times outside of the hospital annually. Almost half (45.4%) of out-of-hospital arrests are unwitnessed, 37% are witnessed by bystanders, and 9% are witnessed by emergency medical services (EMS). 
Every minute of delay in initiating CPR reduces survival by between 7% and 10%. The survival rate of EMS-treated sudden cardiac arrests is 8.4%. 
The FDA recently approved wearable cardioverter defibrillators (WCD) for patients at high risk for sudden cardiac arrest who also lack established indications (or possess a contraindication) for an implanted cardioverter defibrillator (ICD). High-risk patients wear WCDs to ensure prompt cardioversion if sudden cardiac arrest occurs.
Now, an article published ahead-of-print in Current Cardiology Reports summarizes the WCD’s place in therapy and advantages over automatic external defibrillators in patients at high risk for sudden cardiac arrest.
Current guidelines recommend a 40-day waiting period until ICD placement after an acute myocardial infarction (MI) and 90 days after a coronary artery bypass graft (CABG) or percutaneous coronary intervention (PCI). 
WCDs prevent sudden cardiac arrest in patients with reduced left ventricular ejection fraction (LVEF) after a recent MI while waiting for an ICD. These patients have a 2.1% risk of ventricular arrhythmias within 48 hours and 3.6% risk after 48 hours.
Patients with CABG or PCI awaiting ICD placement also use WCDs. Patients with non-ischemic dilated cardiomyopathy undergoing medical therapy optimization, inherited pro-arrhythmic conditions (eg, long QT syndrome or hypertrophic cardiomyopathy), or drug-induced QT syndrome may benefit from WCDs, as well. 
Unlike automatic external defibrillators, WCDs activate without bystander help. Conscious WCD patients can delay or avert a shock with the use of a button. However, the devices may rarely activate inadvertently in patients with a supraventricular tachycardia and/or electrical noise related to poor electrode-skin contact.
Multiple studies have shown WCDs to be effective against out-of-hospital sudden cardiac arrest due to sustained ventricular tachycardia secondary to an array of indications. Nevertheless, the current authors called for more studies on long-term survival benefit and the predictors of LVEF recovery.

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