Wearable Cardioverter Defibrillators: A Safety Net for Patients with ACS

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 cardiopulmonary resuscitation 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 (WCDs) 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 a 3.6% risk after 48 hours.

Patients with CABG or PCI awaiting ICD placement can also use WCDs. Patients with nonischemic 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 longterm survival benefit and the predictors of LVEF recovery.