Wearable cardioverter defibrillators are used by people who may be at higher risk for sudden cardiac arrest, including those with weakened heart function, awaiting cardiac transplant or with a condition that prevents or delays them from receiving an implanted defibrillator. Researchers gathered heart rhythm records and calls about shocks from a registry of 14,475 patients with wearable defibrillators listed from 2007 through 2009. Of those, 185 (about 1 percent) received an appropriate shock and 91.6 percent survived one or more episodes of ventricular fibrillation or ventricular tachycardia, the most common abnormal rhythms during cardiac arrest. Wearable defibrillators delivered 223 inappropriate shocks to 213 people who weren’t experiencing ventricular fibrillation or ventricular tachycardia. However, no one died as a result. Researchers attribute the inappropriate shocks to signal noise, rapid non-VT rhythms, and rhythm
Only about 7 percent of people in the United States who have sudden cardiac arrest outside the hospital survive to hospital discharge, and only about 21 percent who have them in the hospital survive to discharge. “This study confirms the effectiveness of very early defibrillation as therapy for sudden cardiac arrest in high-risk patients when delivered by a wearable defibrillator,” Mosesso said. “These defibrillators provide patients the critical advantage of not having to wait for a bystander or emergency responder to recognize the cardiac arrest and use an automated external defibrillator or manual defibrillator — both of which can lead to delays in treatment and markedly worse survival rates.”