Most of these deaths occur with little or no warning, from a syndrome called sudden cardiac arrest. The most common cause of sudden cardiac arrest is a disturbance in the heart rhythm called ventricular fibrillation. Ventricular fibrillation is dangerous because it cuts off blood supply to the brain and other vital organs. The ventricles are the chambers that pump blood out of the heart and into the blood vessels. This blood supplies oxygen and nutrients to organs, cells, and other structures. If these structures do not receive enough blood, they start to shut down, or fail. If blood flow is not restored immediately, permanent brain damage or death is the result.
Ventricular fibrillation often can be treated successfully by applying an electric shock to the chest with a procedure called defibrillation. In coronary care units, most people who experience ventricular fibrillation survive, because defibrillation is performed almost immediately.
The situation is just the opposite when cardiac arrest occurs outside a hospital setting. Unless defibrillation can be performed within the first few minutes after the onset of ventricular fibrillation, the chances for reviving the person (resuscitation) are very poor. For every minute that lapses with a person remaining in ventricular fibrillation, and defibrillation is not provided, the chances of resuscitation drop by almost 10 percent. After 10 minutes, the chances of resuscitating a victim of cardiac arrest are near zero.
Cardiopulmonary resuscitation, usually known as CPR, provides temporary artificial breathing and circulation. It can deliver a limited amount of blood and oxygen to the brain until a defibrillator becomes available. However, defibrillation is the only effective way to resuscitate a victim of ventricular fibrillation.