Implantable cardioverter defibrillators are small battery-powered electrical impulse generators implanted in patients at risk of sudden cardiac death. Ventricular fibrillation is an abnormal heart rhythm that makes the heart quiver so it can't pump blood.
The implantable defibrillators detect potentially fatal abnormal heart rhythms and try to stop them with electric shocks. Generally, only people with a high risk of sudden cardiac death -- mostly those at high risk of abnormal heartbeats and survivors of a previous cardiac arrest -- receive the devices.
The researchers used data from the Amsterdam Resuscitation Studies registry of cardiac resuscitations by emergency medical services in the greater Amsterdam area from 1995 to 1997, and all EMS cardiac arrest interventions in the area from 2005 to 2008.
"At least 1-in-20 implantable cardioverter defibrillators carriers can expect a life-saving shock from their device each year," Dr. Rudolph W. Koster, an associate professor of cardiology at the Academic Medical Center in Amsterdam who was the study's senior author, said in a statement.
The percentage of patients with ventricular fibrillation cardiac arrest fell from 63 percent in 1995 to 1997 to 47 percent in 2005 to 2008, the study said.
The study, published in the journal Circulation, also found an estimated 339 shocks successfully stopped 194 instances of life-threatening abnormal heart rhythms in 166 people.