Science of emergency medical dispatch.

Out-of-hospital cardiac arrest (OOH-CA) claims the lives of almost 300 000 Americans each year,1 a loss of life equivalent to that caused by a September 11 World Trade Center attack on the United States every 3 days! Despite advances in public education on recognition of cardiac arrest, early notification of emergency medical services (EMS) 9-1-1 centers, lay bystander cardiopulmonary resuscitation, automated external defibrillator use, and improvements in EMS service delivery, fewer than 8% of adult OOH-CA victims survive to hospital discharge.1