Abrupt loss of heart function. Sudden cardiac arrest is often fatal. The victim of sudden cardiac death may or may not have diagnosed heart disease, but the most common cause of sudden cardiac death is coronary heart disease. According to the American Heart Association, sudden cardiac death occurs more than 680 times a day in the United States.
The heart has four chambers: two atria at the top and two ventricles at the bottom, which contract to pump blood through the heart. The contractions of the chambers must be precisely coordinated for the heart to pump blood effectively.
Cardiac arrest is typically caused by certain cardiac arrhythmias (heart rhythm abnormalities). These include, in particular, ventricular tachycardia (abnormally rapid heart rhythm of the ventricles) and ventricular fibrillation (chaotic rhythm or “flutter” of the ventricles), as well as, less commonly, bradycardia (abnormally slow heart rhythm). The term “massive heart attack” is sometimes used to describe cardiac arrest, but this is an error. Cardiac arrest is not the same as a heart attack. A heart attack (also known as a myocardial infarction or MI) involves destruction of heart tissue from loss of blood supply and does not necessarily cause the heart to stop pumping blood. People can go into cardiac arrest during a heart attack, but these terms do not mean the same thing.
In many cases a victim of cardiac arrest can be resuscitated if the proper treatment, known as defibrillation, is administered within a few minutes. Defibrillation is the process of delivering an electric shock to the heart to restore a normal heartbeat. Traditionally, defibrillation has been done in hospital emergency rooms. Recently, however, devices called automated external defibrillators (AEDs), which can be used by minimally trained nonmedical personnel, have become more widely available. Though there are no reliable nationwide statistics available, studies have suggested that people survive cardiac arrest more often in cities where, for example, police cruisers carry AEDs.